Crystal clear: Cu₂ZnSnS₄ (CZTS) is a promising light-absorbing material for solar cells. A facile noninjection route to preparing monodisperse nanocrystalline CZTS that exhibits a wurtzite-derived crystal structure is reported (see figure), and insights into the mechanism of its formation are given. In addition, a simple approach to phase-selective synthesis of CZTS by varying the organic surfactants used in the synthesis is demonstrated.

The influence of ethereal solvents (diethyl ether (Et₂O), tetrahydrofuran (THF) or dimethoxyethane (DME)) on the formation of organolithiated compounds has been studied on the 1,2-C₂B₁₀H₁₂ platform. This platform is very attractive because it contains two C_cH adjacent units ready to be lithiated. On would expect that the closeness of both C_cH units would induce a higher resistance of the second C_cH unit being lithiated following the first lithiation. However, this is not the case, which makes 1,2-C₂B₁₀H₁₂ attractive to get a better understanding of the ethereal solvent influence on the lithiation process. The formation of carboranyl disubstituted species has been attributed to the existence of an equilibrium in which the carboranyl monolithiated species disproportionates into dilithium carborane and pristine carborane. The way Li⁺ binds to C_c in the carboranyl fragment and how the solvent stabilizes such a binding is paramount to drive the reaction to the generation of mono- and disubstituted carboranes. In fact, the proportion of mono- and disubstituted species is a consequence of the formation of contact ion pairs and, to a lesser extent, of separated ion pairs in ethereal solvents. All ethereal solvents generate contact ion pairs in which a large degree of covalent C_cLi(solvent) bonding can be assumed, according to experimental and theoretical data. Furthermore, Et₂O tends to produce carboranyllitium ion pairs with a higher degree of contact ion pairs than THF or DME. It has been determined that for a high-yield preparation of monosubstituted 1-R-1,2-C₂B₁₀H₁₁, in C_cR (R=C, S or P) coupling reactions, the reagent type defines which is the most appropriate ethereal solvent. In reactions in which a halide is generated, as with ClPPh₂ or BrCH₂CHCH₂, Et₂O appears to produce the highest degree of monosubstitution. In other situations, such as with S₈, or when no halide is generated, THF or DME facilitate the largest degree of monosubstitution. It has been shown that upon the self reaction of Li[1,2-C₂B₁₀H₁₁] to produce [LiC₄B₂₀H₂₂]⁻ the nucleophilicity of the carboranyllithium can even be further enhanced, beyond the ethereal solvent, by synergism with halide salts. The mediation of Li⁺ in producing isomerizations on allyl substituents has also been demonstrated, as Et₂O does not tend to induce isomerization, whereas THF or DME produces the propenyl isomer. The results presented here most probably can be extended to other molecular types to interpret the Li⁺ mediation in CC or other CX coupling reactions.

Ethereal solvents are not spectators on organolithium compounds! The influence of ethereal solvents (Et₂O, THF, and dimethoxyethane) on the disproportionation of Li[1,2-C₂B₁₀H₁₁] into Li₂[1,2-C₂B₁₀H₁₀] and 1,2-C₂B₁₀H₁₂, leading to mono- or disubstituted derivatives, originates in the formation of contact ion pairs (see figure). The degree of covalent C_c-Li(solvated) bond in the contact ion pair is strongly influenced by the reagent type.

The reaction of new dinuclear gold(I) organometallic complexes containing mesityl ligands and bridging bidentate phosphanes [Au₂(mes)₂(μ-LL)] (LL=dppe: 1,2-bis(diphenylphosphano)ethane 1 a, and water-soluble dppy: 1,2-bis(di-3-pyridylphosphano)ethane 1 b) with Ag⁺ and Cu⁺ lead to the formation of a family of heterometallic clusters with mesityl bridging ligands of the general formula [Au₂M(μ-mes)₂(μ-LL)][A] (M=Ag, A=ClO₄⁻, LL=dppe 2 a, dppy 2 b; M=Ag, A=SO₃CF₃⁻, LL=dppe 3 a, dppy 3 b; M=Cu, A=PF₆⁻, LL=dppe 4 a, dppy 4 b). The new compounds were characterized by different spectroscopic techniques and mass spectrometry The crystal structures of [Au₂(mes)₂(μ-dppy)] (1 b) and [Au₂Ag(μ-mes)₂(μ-dppe)][SO₃CF₃] (3 a) were determined by a single-crystal X-ray diffraction study. 3 a in solid state is not a cyclic trinuclear Au₂Ag derivative but it gives an open polymeric structure instead, with the {Au₂(μ-dppe)} fragments “linked” by {Ag(μ-mes)₂} units. The very short distances of 2.7559(6) Å (AuAg) and 2.9229(8) Å (AuAu) are indicative of gold–silver (metallophilic) and aurophilic interactions. A systematic study of their luminescence properties revealed that all compounds are brightly luminescent in solid state, at room temperature (RT) and at 77 K, or in frozen DMSO solutions with lifetimes in the microsecond range and probably due to the self-aggregation of [Au₂M(μ-mes)₂(μ-LL)]⁺ units (M=Ag or Cu; LL=dppe or dppy) into an extended chain structure, through AuAu and/or AuM metallophilic interactions, as that observed for 3 a. In solid state the heterometallic Au₂M complexes with dppe (2 a–4 a) show a shift of emission maxima (from ca. 430 to the range of 520-540 nm) as compared to the parent dinuclear organometallic product 1 a while the complexes with dppy (2 b–4 b) display a more moderate shift (505 for 1 b to a max of 563 nm for 4 b). More importantly, compound [Au₂Ag(μ-mes)₂(μ-dppy)]ClO₄ (2 b) resulted luminescent in diluted DMSO solution at room temperature. Previously reported compound [Au₂Cl₂(μ-LL)] (LL dppy 5 b) was also studied for comparative purposes. The antimicrobial activity of 1–5 and Ag[A] (A=ClO₄⁻, SO₃CF₃⁻) against Gram-positive and Gram-negative bacteria and yeast was evaluated. Most tested compounds displayed moderate to high antibacterial activity while heteronuclear Au₂M derivatives with dppe (2 a–4 a) were the more active (minimum inhibitory concentration 10 to 1 μg mL⁻¹). Compounds containing silver were ten times more active to Gram-negative bacteria than the parent dinuclear compound 1 a or silver salts. Au₂Ag compounds with dppy (2 b, 3 b) were also potent against fungi.

Two trumps one! A synergistic antimicrobial effect between gold and silver is found in novel polynuclear {Au₂Ag}_n heterometallic compounds. The luminescence of these and related tri Au₂Cu and dinuclear Au₂ organometallic derivatives has been studied and correlated with crystallographic data and metallophilic interactions. Most complexes display antibacterial activity with Au₂Ag being highly active against Gram-positive and Gram-negative bacteria (see scheme).

A temperature-sensitive polymer/carbon nanotube interface with switchable bioelectrocatalytic capability was fabricated by self-assembly of poly(N-isopropylacrylamide)-grafted multiwalled carbon nanotubes (MWNT-g-PNIPAm) onto the PNIPAm-modified substrate. Electron microscopy and electrochemical measurements revealed that these fairly thick (>6 μm) and highly porous nanocomposite films exhibited high conductivity and electrocatalytic activity. The morphological transitions in both the tethered PNIPAm chains on a substrate and those polymers wrapping around the MWNT surface resulted in the opening, closing, or tuning of its permeability, and simultaneously an electron-transfer process took place through the channels formed in the nanostructure in response to temperature change. By combining the good electron-transfer and electrochemical catalysis capabilities, the large surface area, and good biocompatibility of MWNTs with the responsive features of PNIPAm, reversible temperature-controlled bioelectrocatalysis of 1,4-dihydro-β-nicotinamide adenine dinucleotide with improved sensitivity has been demonstrated by cyclic voltammetry and electrochemical impedance spectroscopy measurements. The mechanism behind this approach was studied by Raman spectroscopy, in situ attenuated total reflection FTIR spectroscopy, and contact angle measurements. The results also suggested that the synergetic or cooperative interactions of PNIPAm with MWNTs gave rise not only to an increase in surface wettability, but also to the enhancement of the interfacial thermoresponsive behavior. This bioelectrocatalytic “smart” system has potential applications in the design of biosensors and biofuel cells with externally controlled activity. Furthermore, this concept might be proposed for biomimetics, interfacial engineering, bioelectronic devices, and so forth.

Smart catalysis! A temperature-sensitive polymer/carbon nanotube composite film with high conductivity and electrocatalytic activity was fabricated on a gold surface (see figure). The modulation of bioelectrocatalysis and electron transfer of biomolecules were achieved on the film.

Novel phenylazole ligands were applied successfully in the synthesis of cyclometalated iridium(III) complexes of the general formula [Ir(phenylazole)₂(bpy)]PF₆ (bpy=2,2′-bipyridine). All complexes were fully characterized by NMR, IR, and MS spectroscopic studies as well as by cyclic voltammetry. Three crystal structures obtained by X-ray analysis complemented the spectroscopic investigations. The excited-state lifetimes of the iridium complexes were determined and showed to be in the range of several hundred ns to multiple µs. All obtained iridium complexes were active as photosensitizers in catalytic hydrogen evolution from water in the presence of triethylamine as a sacrificial reducing agent. Applying an in situ formed iron-based water reduction catalyst derived from [HNEt₃]⁺[HFe₃(CO)₁₁]⁻ and tris[3,5-tris-(trifluoromethyl)-phenyl]phosphine as the ligand, [Ir(2-phenylbenz-oxazole)₂-(bpy)]PF₆ proved to be the most efficient complex giving a quantum yield of 16 % at 440 nm light irradiation.

Six new iridium complexes of the general formula [Ir(phenylazole)₂(bpy)]PF₆ (bpy=2,2′-bipyridine) were tested as photosensitizers in hydrogen evolution from water. The complex with 2-phenyl benzoxazole as a cyclometalating ligand (PS4) showed the best performance with a quantum yield of 16 % (see figure).

A novel core structure among bacterial lipopolysaccharides (LPS) that belong to the genus Halomonas has been characterized. H. stevensii is a moderately halophilic microorganism, as are the majority of the Halomonadaceae. It brought to light the pathogenic potential of this genus. On account of their role in immune system elicitation, elucidation of LPS structure is the mandatory starting point for a deeper understanding of the interaction mechanisms between host and pathogen. In this paper we report the structure of the complete saccharidic portion of the LPS from H. stevensii. In contrast to the finding that the O-antigen is usually covalently linked to the outer core oligosaccharide, we could demonstrate that the O-polysaccharide of H. stevensii is linked to the inner core of an LPS. By means of high-performance anion-exchange chromatography with pulsed amperometric detection we were able to isolate the core decasaccharide as well as a tridecasaccharide constituted by the core region plus one O-repeating unit after alkaline degradation of the LPS. The structure was elucidated by one- and two-dimensional NMR spectroscopy, ESI Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometry, and chemical analysis.

Bacterial inspection: In this paper, the complete saccharidic structure of the lipopolysaccharide (LPS) that belongs to the human pathogen Halomonas stevensii bacterium is reported. The tridecasaccharide that contained the core region plus one O-chain repeating unit was obtained and characterized (see scheme).

The preparation of optically pure quaternary piperidines, both fluorinated and non-fluorinated, has been achieved from a chiral imino lactone derived from (R)-phenylglycinol. In the case of the fluorinated derivatives, the addition of (trifluoromethyl)trimethylsilane (TMSCF₃) followed by iodoamination and migration of the CF₃ group allowed access to four derivatives of α-(trifluoromethyl)pipecolic acid. A theoretical study of the CF₃-group rearrangement has been carried out to help establish the reaction mechanism of this uncommon transformation. Moreover, a route to trifluoromethyl-substituted iminosugars was also developed through the diastereoselective dihydroxylation of suitable synthetic intermediates. Conversely, alkylation of the starting substrate and subsequent cross-metathesis and aza-Michael reactions led to α-alkyl derivatives of the target compounds.

Making it sweet: A series of 2,2,6-trisubstituted piperidines containing a trifluoromethyl or alkyl group at the α position are prepared from a chiral imino lactone by employing two different synthetic strategies. The final products constitute quaternary derivatives of pipecolic acid, and fluorinated analogues of iminosugars can also be conveniently accessed (see scheme; TASF=tris(dimethylamino)sulfonium difluorotrimethylsilicate, TMSCF₃=(trifluoromethyl)trimethylsilane).

The proposed role of anthocyanins in protecting plants against excess solar radiation is consistent with the occurrence of ultrafast (5–25 ps) excited-state proton transfer as the major de-excitation pathway of these molecules. However, because natural anthocyanins absorb mainly in the visible region of the spectra, with only a narrow absorption band in the UV-B region, this highly efficient deactivation mechanism would essentially only protect the plant from visible light. On the other hand, ground-state charge-transfer complexes of anthocyanins with naturally occurring electron-donor co-pigments, such as hydroxylated flavones, flavonoids, and hydroxycinnamic or benzoic acids, do exhibit high UV-B absorptivities that complement that of the anthocyanins. In this work, we report a comparative study of the photophysics of the naturally occurring anthocyanin cyanin, intermolecular cyanin–coumaric acid complexes, and an acylated anthocyanin, that is, cyanin with a pendant coumaric ester co-pigment. Both inter- and intramolecular anthocyanin–co-pigment complexes are shown to have ultrafast energy dissipation pathways comparable to those of model flavylium cation–co-pigment complexes. However, from the standpoint of photoprotection, the results indicate that the covalent attachment of co-pigment molecules to the anthocyanin represents a much more efficient strategy by providing the plant with significant UV-B absorption capacity and at the same time coupling this absorption to efficient energy dissipation pathways (ultrafast internal conversion of the complexed form and fast energy transfer from the excited co-pigment to the anthocyanin followed by adiabatic proton transfer) that avoid net photochemical damage.

Photoprotection in plants: The acylation of anthocyanins provides UV protection against photochemical damage by fast energy transfer (ET) from the excited co-pigment (Coum) to the anthocyanin (Cy) followed by ultrafast adiabatic proton transfer (PT) to water or internal conversion (IC) of the complex (see figure).

A two-electron oxidation of the Cu^II (9) and Zn^II (12) complexes of tetraphenyltetrabenzoporphyrin (TPTBP) results in the formation of stable antiaromatic [(TPTBP)Cu^II(H₂O)]²⁺⋅2 [SbF₆]⁻ (10) and [(TPTBP)Zn^II(H₂O)₂]²⁺⋅2 [SbF₆]⁻ (13) with 16π electrons on the inner ligand perimeter. X-ray structures of the parent TPTBP complexes, the dications, and singly oxidized species [(TPTBP)Cu^II]^⋅+[SbF₆]⁻ (11) reveal that the use of TPTBP rather than a porphyrin ligand reduces the degree of nonplanarity in the 16π-electron species relative to the parent 18π complex. Significant high-field shifts of the ¹H NMR signals of the outer ring protons and large positive values in calculations of nucleus-independent chemical shifts on the central cavity of the porphyrin ring provide unambiguous evidence for the antiaromatic character of the 16π Zn^II species. A combination of magnetic circular dichroism spectroscopic studies and TD-DFT calculations on both the Zn^II and Cu^II species demonstrates that the main electronic bands of the dicationic species can be readily assigned by using Michl’s 4N perimeter model. Femtosecond transient absorption studies clearly demonstrated that the number of π electrons on the inner ligand perimeter and the configuration of the central metal ion play a critical role in the excited-state relaxation dynamics. Redox potentials for conversion between the 16π, 17π, and 18π systems were measured by cyclic voltammetry in dichloromethane and benzonitrile, and UV/Vis spectra of each oxidation/reduction product were monitored by thin-layer spectroelectrochemistry.

Sweet 16: Copper(II) and zinc(II) benzofused porphyrin complexes with 16π-electron cores were prepared through two-electron oxidation of tetraphenyltetrabenzoporphyrin complexes with AgSbF₆ (see scheme). Structural characterization and a variety of spectroscopic studies were carried out to analyze the electronic structure and study key trends in the antiaromatic properties of these novel 16π-electron porphyrin species.

A series of stable organosuperbases, N-alkyl- and N-aryl-1,3-dialkyl-4,5-dimethylimidazol-2-ylidene amines, were efficiently synthesized from N,N′-dialkylthioureas and 3-hydroxy-2-butanone and their basicities were measured in acetonitrile. The derivatives with tert-alkyl groups on the imino nitrogen were found to be more basic than the tBuP₁(pyrr) phosphazene base in acetonitrile. The origin of the high basicity of these compounds is discussed. In acetonitrile and in the gas phase, the basicity of the alkylimino derivatives depends on the size of the substituent at the imino group, which influences the degree of aromatization of the imidazole ring, as measured by ¹³C NMR chemical shifts or by the calculated ΔNICS(1) aromaticity parameters, as well as on solvation effects. If a wider range of imino-substituents, including electron-acceptor substituents, is treated in the analysis then the influence of aromatization is less predominant and the gas-phase basicity becomes more dependent on the field-inductive effect, polarizability, and resonance effects of the substituent.

Bases coming on strong: A series of stable organosuperbases, N-alkyl- and N-aryl-1,3-dialkyl-4,5-dimethylimidazol-2-ylidene amines, were efficiently synthesized and their basicities were measured in acetonitrile, some of which are stronger bases than the tBuP₁(pyrr) phosphazene base and tetramethylguanidine in acetonitrile (see figure). The basicity depends on, among other factors, the size of the substituent at the imino group, which influences the degree of aromatization of the imidazole ring.

The “escape-by-crafty-scheme” strategy is an efficient approach to prepare metal-oxide nanomaterials with desirable morphology and crystal planes inherited from coordination-polymer nanoparticle precursors, which can be designed and finely tuned by soft chemical assembly of metal ions and organic ligands at the molecular level (see scheme; ptcda=perylene-3,4,9,10-tetracarboxylic dianhydride).

Go with the (segmented) flow: A gas–liquid microfluidic reactor system has been developed to study Pd-catalyzed carbonylation reactions over a range of flow regimes and reaction conditions (see picture). The segmented gas–liquid flow regime, in comparison to annular flow, enables reactions to be studied over longer reaction times and without the buildup of unwanted Pd particles.

Open chain Cbz-L-aa¹-L-Pro-Bt (Bt=benzotriazole) sequences were converted into either the corresponding trans- or cis-fused 2,5-diketopiperazines (DKPs) depending on the reaction conditions. Thermodynamic tandem cyclization/epimerization afforded selectively the corresponding trans-DKPs (69–75 %). Complementarily, tandem deprotection/cyclization led to the cis-DKPs (65–72 %). A representative set of proline-containing cis- and trans-DKPs has been prepared. A mechanistic investigation, based on chiral HPLC, kinetics, and computational studies enabled a rationalization of the results.

Stereoflexible route to DKPs: A convenient, versatile, and flexible benzotriazole-mediated methodology for the synthesis of proline-containing hetero 2,5-diketopiperazines (DKPs) is reported. Depending on the reaction conditions, either cis- or trans-configured DKPs were obtained starting from the same inexpensive l,l-dipeptidoyl benzotriazole key intermediate (see scheme). Kinetics, chiral HPLC, and computational studies forged a background for mechanistic rationalization.

The facile one-pot reaction of the stable N-heterocyclic silylene LSi: 1 (L(ArN)C(CH₂) CHC(Me)(NAr), Ar=2,6-iPr₂C₆H₃) with Me₂Zn, Me₃Al, H₃Al-NMe₃, and MeLi has been investigated. The silicon(II) atom in 1 is capable of insertion into the corresponding MC and AlH bonds under very mild reaction conditions. Thus, Me₂Zn furnishes the bis(silyl) zinc complex LSi(Me)ZnSi(Me)L 2 as the sole product, irrespective of the molar ratio of the starting materials applied. Moreover, the reactions of 1 with Me₃Al, H₃Al-NMe₃, and MeLi lead directly to the 1,1-addition products LSi(Me)(Al(thf)Me₂) 3, LSi(H)(AlH₂(NMe₃)) 4, and LSi(Me)Li(thf)₃5, respectively. All new compounds 2–5 were fully characterized by multinuclear NMR spectroscopy, mass spectrometry, elemental analyses, and single-crystal X-ray diffraction analyses.

Click to silylene: The new multifunctional silyl metal complexes 2–5 have been synthesized in high yield through facile reaction of N-heterocyclic silylene 1 with Me₂Zn, Me₃Al, H₃Al-NMe₃, and MeLi, respectively. Unexpectedly, 1 reacts with Me₂Zn in the molar ratio of 2:1 to form the disilyl zinc compound 2, whereas other metalation reagents with MC and MH bonds furnish solely the respective 1:1 adducts (see scheme). All compounds were fully characterized, including single-crystal X-ray diffraction analyses.

Palladium phosphanesulfonate [R₂P(C₆H₄-o-SO₃)PdMeL] catalysts permit the copolymerization of an exceptional large number of functional olefins with ethylene. However, these catalysts usually have reduced activity. We here have conducted a systematic study on the influence of the phosphane substituent, R, on activity and molecular weight. Phosphanes with strong σ-donating character are shown to lead to the most active catalysts. Thus, the catalyst based on phosphane bis-tert-butyl-phosphanyl-benzenesulfonic acid (R=tBu) exhibits unprecedented high activity, rapidly polymerizing ethylene at room temperature to yield a linear polymer of high molecular weight (M_w=116 000 g mol⁻¹). The influence of the R group on the catalyst ability to incorporate methyl acrylate is also investigated.

Strong donors desirable: The influence of the phosphine substituent on the activity and molecular weight of palladium phosphinesulfonate [R₂P(C₆H₄-o-SO₃)PdMeL] catalysts is investigated (see scheme). Phosphines with strong σ-donating character are shown to give more active catalysts, leading to the discovery of two catalysts, bis-tert-butyl-phosphanyl-benzenesulfonicacid (R=tBu) and [RR′P(C₆H₄-o-SO₃)PdMeL] (L=lutidine, R=tBu, R′=Ph), with unprecedented high activity.

The synthesis and photophysical properties of several porphyrin (P)–phthalocyanine (Pc) conjugates (P–Pc; 1–3) are described, in which the phthalocyanines are directly linked to the β-pyrrolic position of a meso-tetraphenylporphyrin. Photoinduced energy- and electron-transfer processes were studied through the preparation of H₂P–ZnPc, ZnP–ZnPc, and PdP–ZnPc conjugates, and their assembly through metal coordination with two different pyridylfulleropyrrolidines (4 and 5). The resulting electron-donor–acceptor hybrids, which were formed by axial coordination of compounds 4 and 5 with the corresponding phthalocyanines, mimicked the fundamental processes of photosynthesis; that is, light harvesting, the transduction of excited-state energy, and unidirectional electron transfer. In particular, photophysical studies confirmed that intramolecular energy-transfer resulted from the S₂ excited state as well as from the S₁ excited state of the porphyrins to the energetically lower-lying phthalocyanines, followed by an intramolecular charge-transfer to yield P–Pc^.+⋅C₆₀^.−. This unique sequence of processes opens the way for solar-energy-conversion processes.

Alright PET? Photoinduced energy- and electron-transfer processes were studied in several porphyrin (P)/phthalocyanine (Pc)/fullerene (C₆₀) hybrids in which the phthalocyanines were directly linked to the β-pyrrolic positions of the porphyrins and assembled through metal coordination with different pyridylfullerenes (see figure).

Ionic liquids (ILs) have attracted intensive attention in academia and industry due to their unique properties and potential applications. Nowadays, much interest is focused on finding out what is the main force that determines the properties of ionic liquids. Intuitively like NaCl, in high-temperature molten salt (HTMS) the electrostatic Coulomb force is regarded as the dominant factor that determines the behaviors of ILs. However, a large amount of evidence indicates that such a molten-salt-based simplified explanation is not consistent with the corresponding experimental results. Besides the Coulomb force, the hydrogen bond is another important noncovalent interaction in the IL and is closely related to some important properties and applications, as suggested in some new research results. Therefore in this review, we present results concerning the hydrogen bond in ILs, from the perspective of experiment and calculation, to shed light on its effects and roles. The deep insights into structure, in particular the hydrogen bonds, can provide us with a rational design for the new ILs to fulfill the demands in some complicated chemical processes.

To hydrogen bond or not? Hydrogen bonds exist in many different ionic liquids (ILs) and become a key factor to elucidate the ILs. Many properties and applications of ILs are closely related to hydrogen bonds. The integrated review on hydrogen bonds in the ILs will be helpful to design the new TSILs.

A homogeneous and disordered assembly of densely packed nanocrystals 2–3 nm in size was synthesized at room temperature in an aqueous solution without the assistance of any organic molecules. The assembled nanocrystals of titanium oxides, such as anatase titanium dioxide, sodium titanate, and a solid solution with rutile tin dioxide, formed macroscopic transparent objects 2–5 mm in size. In general, it is not easy to obtain homogeneous and disordered assembly of nanocrystals without assistance of any organic molecules for the inhibition of inhomogeneous and disordered aggregation. In the present work, the formation of the hydrated layer on the surface of nanocrystals facilitated the homogeneous and disordered assembly. The crystal phases and the compositions of the nanocrystals were controlled by the tuning of the synthetic conditions, such as the initial pH and metal source concentration. Based on the formation processes and mechanisms, this approach for the coupled synthesis and assembly can be applied to a variety of nanomaterials for preparation of homogeneous but disordered assembly.

A homogeneous and disordered assembly of densely packed titanium oxides nanocrystals 2–3 nm in size is formed by means of aqueous-solution processes at room temperature. The assembled nanocrystals form macroscopic transparent objects 2–5 mm in size. Formation of the hydrated layer on the surface of nanocrystals facilitates the generation of macroscopic objects through the inhibition of inhomogeneous and disordered aggregates.

Pyrene-fused tetraazaporphyrins were synthesized from pyrene-4,5-dicarbonitrile precursors using a recently reported procedure as the key step for the asymmetric substitution of pyrene. Metal-free, zinc- and lead-centered pyrenocyanines were obtained and their optical properties as well as their molecular assembly in the solution and bulk phases and at the liquid/solid interface were studied. The characteristic Q-band appears broadened, most likely owing to distortion of the molecule introduced by the steric demand of the angularly extended aromatic residue. The angular annulation does not bathochromically shift the Q-band as far as would have been expected for the linear case. Peripheral substitution with linear and branched alkoxy chains affords solubility of the compounds in organic solvents. The influence of the distinct steric demand of the substituents on aggregation was investigated for metal-centered pyrenocyanines by using temperature-dependent ¹H NMR and UV/Vis spectroscopy. The self-assembly at the liquid/solid interface was studied using scanning tunneling microscopy. The alkoxy substituents facilitate the anchoring of these slightly non-planar molecules on the surface of graphite. Pyrenocyanine molecules form well-ordered 2D arrays in which the molecules are arranged in rows. The angular annulation of the pyrenocyanine residue leads to characteristic adsorption behavior at the liquid/solid interface, in which the molecules adsorb in two different adsorption geometries. The alkoxy side-chains give rise to a discotic columnar superstructure and induce distinct thermotropic behavior. Dependent on the steric demand of the branched chains and the central metal atom, the molecules are rotated with respect to each other to form helical organization.

Pile or pattern? Self-assembled pyrene-fused tetraazaporphyrines have been analyzed by 2D WAXS and STM. 2D WAXS reveals π-stacked helical columns within extruded fibers, and STM shows well-ordered monolayers with multiple adsorption geometries.

The objective of this work was the synthesis of serum albumin targeted, Gd^III-based magnetic resonance imaging (MRI) contrast agents exhibiting a strong pH-dependent relaxivity. Two new complexes (Gd-glu and Gd-bbu) were synthesized based on the DO3A macrocycle modified with three carboxyalkyl substituents α to the three ring nitrogen atoms, and a biphenylsulfonamide arm. The sulfonamide nitrogen coordinates the Gd in a pH-dependent fashion, resulting in a decrease in the hydration state, q, as pH is increased and a resultant decrease in relaxivity (r₁). In the absence of human serum albumin (HSA), r₁ increases from 2.0 to 6.0 mM⁻¹ s⁻¹ for Gd-glu and from 2.4 to 9.0 mM⁻¹ s⁻¹ for Gd-bbu from pH 5 to 8.5 at 37 °C, 0.47 T, respectively. These complexes (0.2 mM) are bound (>98.9 %) to HSA (0.69 mM) over the pH range 5–8.5. Binding to albumin increases the rotational correlation time and results in higher relaxivity. The r₁ increased 120 % (pH 5) and 550 % (pH 8.5) for Gd-glu and 42 % (pH 5) and 260 % (pH 8.5) for Gd-bbu. The increases in r₁ at pH 5 were unexpectedly low for a putative slow tumbling q=2 complex. The Gd-bbu system was investigated further. At pH 5, it binds in a stepwise fashion to HSA with dissociation constants K_d1=0.65, K_d2=18, K_d3=1360 μM. The relaxivity at each binding site was constant. Luminescence lifetime titration experiments with the Eu^III analogue revealed that the inner-sphere water ligands are displaced when the complex binds to HSA resulting in lower than expected r₁ at pH 5. Variable pH and temperature nuclear magnetic relaxation dispersion (NMRD) studies showed that the increased r₁ of the albumin-bound q=0 complexes is due to the presence of a nearby water molecule with a long residency time (1–2 ns). The distance between this water molecule and the Gd ion changes with pH resulting in albumin-bound pH-dependent relaxivity.

Whither the water? The Gd^III MRI contrast agent shown has a pH-dependent relaxivity due to a change in inner-sphere hydration (q=2 to q=0) upon sulfonamide coordination. The biphenyl moiety imparts strong affinity for serum albumin, and protein binding was expected to increase pH-dependent relaxivity further. However, the inner-sphere waters are displaced when the complex binds albumin at low pH, and the pH-dependent relaxivity effect is muted.

New hetero-oligophenylene derivative (2) was synthesized which exhibits aggregation-induced emission enhancement (AIEE) in H₂O/THF (80:20). The aggregates serve as a biological probe for three different proteins, that is bovine serum albumin (BSA), cytochrome c, and lysozyme, and DNA in contrasting modes. Further, among 29 metal ions tested, the contrasting fluorescence behavior of aggregates of 2 is observed with only Pb²⁺ and Pd²⁺ ions. Multiple output logic circuits based upon the fluorescence behavior between BSA and cytochrome c and between Pb²⁺ and Pd²⁺ ions are constructed.

Propeller-shaped hetero-oligophenylene derivative 2, which exhibits aggregation-induced emission enhancement in H₂O/THF (80:20) was synthesized. The aggregates serve as a biological probe for three different proteins (bovine serum albumin (BSA), cytochrome c, and lysozyme), DNA, and two metal ions (Pb²⁺ and Pd²⁺) in contrasting modes. The fluorescence behavior between BSA and cytochrome c and between Pb²⁺ and Pd²⁺ ions mimics the performance of combinatorial logic circuits.

The selected-control preparation of uniform core–shell and yolk–shell architectures, which combine the multiple functions of a superparamagnetic iron oxide (SPIO) core and europium-doped yttrium oxide (Y₂O₃:Eu) shell in a single material with tunable fluorescence and magnetic properties, has been successfully achieved by controlling the heat-treatment conditions. Furthermore, the shell thickness and interior cavity of SPIO@Y₂O₃:Eu core–shell and yolk–shell nanostructures can be precisely tuned. Importantly, as-prepared SPIO@Y₂O₃:Eu yolk–shell nanocapsules (NCs) modified with amino groups as cancer-cell fluorescence imaging agents are also demonstrated. To the best of our knowledge, this is the first report on the selected-control fabrication of uniform SPIO@Y₂O₃:Eu core–shell nanoparticles and yolk–shell NCs. The combined magnetic manipulation and optical monitoring of magnetic–fluorescent SPIO@Y₂O₃:Eu yolk–shell NCs will open up many exciting opportunities in dual imaging for targeted delivery and thermal therapy.

In their shells: Uniform core–shell and yolk–shell architectures (see figure), which combine the functions of a superparamagnetic iron oxide (SPIO) core and europium-doped yttrium oxide (Y₂O₃:Eu) shell in a single material with tunable fluorescence and magnetic properties, are prepared. The shell thickness and interior cavity of SPIO@Y₂O₃:Eu nanostructures can also be tuned. Yolk–shell nanocapsules modified with amino groups serve as cancer-cell fluorescence imaging agents.

The induced aggregation of achiral building blocks by a chiral species to form chiral aggregates with memorized chirality has been observed for a number of systems. However, chiral memory in isolated aggregates of achiral building blocks remains rare. One possible reason for this discrepancy could be that not much is understood in terms of designing these chiral aggregates. Herein, we report a strategy for creating such isolable chiral aggregates from achiral building blocks that retain chiral memory after the facile physical removal of the chiral templates. This strategy was used for the isolation of chiral homoaggregates of neutral achiral π-conjugated carboxylic acids in pure aqueous solution. Under what we have termed an “interaction–substitution” mechanism, we generated chiral homoaggregates of a variety of π-conjugated carboxylic acids by using carboxymethyl cellulose (CMC) as a mediator in acidic aqueous solutions. These aggregates were subsequently isolated from the CMC templates whilst retaining their memorized supramolecular chirality. Circular dichroism (CD) spectra of the aggregates formed in the acidic CMC solution exhibited bisignated exciton-coupled signals of various signs and intensities that were maintained in the isolated pure homoaggregates of the achiral π-conjugated carboxylic acids. The memory of the supramolecular chirality in the isolated aggregates was ascribed to the substitution of COOH/COOH hydrogen-bonding interaction between the carboxylic acid groups within the aggregates for the hydrogen-bonding interactions between the COOH groups of the building blocks and the chiral templates. We expect that this “interaction–substitution” procedure will open up a new route to isolable pure chiral aggregates from achiral species.

Together forever: A method for the synthesis of isolable chiral aggregates of achiral building blocks was developed and used for the isolation of the chiral homoaggregates of neutral achiral π-conjugated carboxylic acids in pure aqueous solutions.

Merging three in one by a three-component organocatalytic asymmetric reaction of imines, α-bromoesters, or ketone with α,β-unsaturated aldehydes provides optically active pyrrolo-isoquinolines—an important class of molecules in life science. The reaction proceeds with excellent enantioselectivity and a number of transformations of the products obtained demonstrated the potential of the new reaction.

As part of our ongoing studies to provide an experimental basis for the improved understanding of organocatalytic reaction mechanisms we present a study on the influence of amine bases on enamine intermediate stabilization in proline catalysis. The (partial) deprotonation of the proline acid function is displayed by characteristic shifts of certain proton resonances and is also manifested by an increase of the amount of enamine intermediate upon reaching a critical pK_aH. Strong bases, such as 1,8-diazabicyclo[5.4.0]-undec-7-ene (DBU), allow for outstanding enamine stabilization in various solvents and, hence, permit the detection of enamine species that have been inaccessible until now (illustrated by the observation of minor amounts of Z enamines). The in situ NMR detection of a prolinate–DBUH⁺ ion pair supports the well-documented reversal of enantioselectivity of proline-catalyzed aminations in the presence of amine bases by disabling the bifunctional activity and switching to a “simple” stereocontrol effect (as known from the Jørgensen/Hayashi-type diarylprolinol ethers). In addition, the possibility of attractive ionic interactions between both the iminium ion and prolinate enamines available in the presence of strong amine bases suggests promotion of the Mannich pathway in aldol reactions to mainly form condensation products.

Deprotonate me if you can: Deprotonation of the proline acid function is manifested by an increase in the amount of enamine intermediates upon reaching a critical pK_aH. The in situ NMR spectroscopic detection of a prolinate–DBUH⁺ ion pair supports the reversal of enantioselectivity of proline-catalyzed aminations by disabling the bifunctional activity of proline (see figure).

Phtalimidomethyl iodide and substituted maleimidomethyl iodide were used as radical precursors in dialkylzinc-mediated radical addition to diethyl fumarate. The reactions led stereoselectively to functionalized pyrrolizidines. The radical mechanism was supported by spin-trapping experiments and rationalized by theoretical calculations. Radical additions, on the one hand, and carbozincation followed by transmetalation with copper(I), on the other, were shown to be complementary methods to achieve the formal aminomethylation of activated unsaturated compounds.

Radical attack: Phtalimidomethyl iodide and diiodomaleimidomethyl iodide were used as radical precursors in the dialkylzinc-mediated radical addition to diethyl fumarate (see scheme). The reactions led stereoselectively to functionalized pyrrolizidines. Radical additions and carbozincation followed by transmetalation with copper(I) were shown to be complementary methods to achieve the formal aminomethylation of Michael acceptors.

Simple model systems based on the 2,11-dithia[3,3]-metaparacyclophane skeleton were synthesized to study the effects of substituents on the intramolecular aromatic–aromatic interactions between benzene rings. X-ray crystallography established that, in their more stable conformations, these metaparacyclophanes featured partially overlapping aromatic rings (interplanar distances of about 3.5 Å), with the planes of the aromatic systems arranged in a slightly tilted disposition (interplanar angles in the range 5–19°). Calculations showed that these derivatives underwent topomerization by flipping of the meta-substituted ring over the para-substituted one, a process in which the two rings adopted a continuum of edge-to-face dispositions, including an orthogonal one, which were less stable than the starting face-to-face arrangement. The energy barriers to the isomerization process were experimentally determined by variable-temperature NMR spectroscopy, by using an internal temperature standard to assess even minor differences in energy (relative experimental error: (±0.1 kJ mol⁻¹). The variation in the barriers as a function of the different substituents on the interacting ring was small and apparently unrelated to the effect of the substituents on the polarity of the π-systems. An explanation based on the charge-penetration effect seemed more-suitable to rationalize the observed trends in the barriers.

Off the subs bench: 2,11-Dithia[3,3]-metaparacyclophanes were designed and synthesized to study the effect of substituents on the intramolecular aromatic–aromatic interactions between benzene rings. The energy barriers to topomerization were determined by variable-temperature NMR spectroscopy. The variation of the barriers as a function of the substitution on the interacting ring was not related to their effect on the polarity of the π-systems.

Bifunctional molecules that combine independent push–pull fluorophores and azo photochromes have been synthesized to create fluorescent structures upon light-induced migration in neat thin films. Their photochromic and emissive properties have been systematically investigated and interpreted in light of those of the corresponding model compounds. Fluorescence lifetimes and photoisomerization and fluorescence quantum yields have been determined in toluene solution. Kinetic analyses of the femtosecond transient absorption spectra reveal that the fluorophores evolve in a few picoseconds into a distorted intramolecular charge-transfer excited state, strongly stabilized in energy. Radiative relaxation to the ground state occurred competitively with the energy-transfer process to the azo moiety. Introduction of a 10 Å-long rigid and nonconjugated bridge between the photoactive units efficiently inhibits the energy transfer while it imparts enhanced free volume, which favors photoactivated molecular migration in the solid state.

Dual photoinduced action: The introduction of a rigid triptycenyl-like spacer between a photochromic azo unit and a fluorescent unit allow both moieties to keep their photophysical integrity ruled by picosecond dynamics in the excited state (see figure). This leads to fluorescent patterns in thin films that are subjected to interferential illumination.

The asymmetric alkylation of Schiff bases under basic conditions in a ball mill was performed. The starting Schiff bases of glycine were prepared beforehand by milling protected glycine hydrochloride and benzophenone imine, in the absence of solvent. The Schiff base was then reacted with a halogenated derivative in a ball mill in the presence of KOH. By adding a chiral ammonium salt derived from cinchonidine, the reaction proceeded asymmetrically under phase-transfer catalysis conditions, giving excellent yields and enantiomeric excesses up to 75 %. Because an equimolar amount of starting material was used, purification was greatly simplified.

Grinding on one side! Ball milling under solvent-free conditions is presented herein for the synthesis of glycine Schiff bases and their subsequent asymmetric alkylation to prepare chiral natural and unnatural amino acids (see scheme). The use of a cinchona-derived catalyst provided good enantiomeric excesses up to 75 %.

Rh^Iin two minds: A Rh^I-catalyzed tandem heterocyclization/[3+2] cycloaddition reaction was developed that provides rapid, efficient, and stereoselective access to highly substituted cyclopenta[c]furans from readily available 2-(1-alkynyl)-2-alken-1-ones and alkynes (see scheme). The cationic Rh^I acts as both a Lewis acid and a conventional transition-metal catalyst, providing the first example of a Rh^I species acting as a Lewis acid.

Tube versus sphere: Two differently shaped fullerenes, nanotubular D_3d(3)-C₉₆ and the somewhat flat sided C₂(181)-C₉₆ are the largest, pristine, empty-cage fullerenes to be identified structurally by X-ray crystallography to date.

F⁻detection: Two new polydentate conjugate molecules (1 and 2) as colorimetric receptors for detecting F⁻ have been synthesized and found to have high fluorescent selectivity for detecting F⁻. In particular, receptor 2 has a more rigid structure without conformational flexibity that can be used as a ratiometric receptor of F⁻.

When targeting the quadrupolar p-dianisyltetraphenyl-carbo-benzene by reductive treatment of a hexaoxy-[6]pericyclyne precursor 3 with SnCl₂/HCl, a strict control of the conditions allowed for the isolation of three C₁₈-macrocyclic products: the targeted aromatic carbo-benzene 1, a sub-reduced non-aromatic carbo-cyclohexadiene 4 A, and an over-reduced aromatic dihydro-carbo-benzene 5 A. Each of them was fully characterized by its absorption and NMR spectra, which were interpreted by comparison with calculated spectra from static structures optimized at the DFT level. According to the nucleus-independent chemical shift (NICS) value (NICS≈−13 ppm), the macrocyclic aromaticity of 5 A is indicated to be equivalent to that of 1. This is confirmed by the strong NMR spectroscopic deshielding of the ortho-CH protons of the aryl substituents, but also by the strong shielding of the internal proton of the endocyclic trans-CHCH double bond that results from the hydrogenation of one of the CC bonds of 3. Both the aromatics 1 and 5 A exhibit a high crystallinity, revealed by SEM and TEM images, which allowed for a structural determination by using an X-ray microsource. A good agreement with calculated molecular structures was found, and columnar assemblies of the C₁₈ macrocycles were evidenced in the crystal packing. The non-aromatic carbo-cyclohexadiene 4 A is shown to be an intermediate in the formation of 1 from 3. It exhibits a remarkable dichromism in solution, which is related to the occurrence of two intense bands in the visible region of its UV/Vis spectrum. These properties could be attributed to the dibutatrienylacetylene (DBA) unit that occurs in the three chromophores, but which is not involved in a macrocyclic π-delocalization in 4 A only. A versatile redox behavior of the carbo-chromophores is evidenced by cyclic voltammetry and was analyzed by calculation of the ionization potential, electron affinity, and frontier molecular orbitals.

Carbo loading: A carbo-cyclohexadiene and a dihydro-carbo-benzene were isolated as subreduced and over-reduced products of a quadrupolar carbo-benzene targeted by reduction of a hexaoxy-[6]pericyclyne (see scheme). Their manifold properties were analyzed by a constructive interplay between experimental measurements and theoretical calculations.

Template-assisted formation of multicomponent Pd₆ coordination prisms and formation of their self-templated triply interlocked Pd₁₂ analogues in the absence of an external template have been established in a single step through PdN/PdO coordination. Treatment of cis-[Pd(en)(NO₃)₂] with K₃tma and linear pillar 4,4′-bpy (en=ethylenediamine, H₃tma=benzene-1,3,5-tricarboxylic acid, 4,4′-bpy=4,4′-bipyridine) gave intercalated coordination cage [{Pd(en)}₆(bpy)₃(tma)₂]₂[NO₃]₁₂ (1) exclusively, whereas the same reaction in the presence of H₃tma as an aromatic guest gave a H₃tma-encapsulating non-interlocked discrete Pd₆ molecular prism [{Pd(en)}₆(bpy)₃(tma)₂(H₃tma)₂][NO₃]₆ (2). Though the same reaction using cis-[Pd(NO₃)₂(pn)] (pn=propane-1,2-diamine) instead of cis-[Pd(en)(NO₃)₂] gave triply interlocked coordination cage [{Pd(pn)}₆(bpy)₃(tma)₂]₂[NO₃]₁₂ (3) along with non-interlocked Pd₆ analogue [{Pd(pn)}₆(bpy)₃(tma)₂](NO₃)₆ (3′), and the presence of H₃tma as a guest gave H₃tma-encapsulating molecular prism [{Pd(pn)}₆(bpy)₃(tma)₂(H₃tma)₂][NO₃]₆ (4) exclusively. In solution, the amount of 3′ decreases as the temperature is decreased, and in the solid state 3 is the sole product. Notably, an analogous reaction using the relatively short pillar pz (pz=pyrazine) instead of 4,4′-bpy gave triply interlocked coordination cage [{Pd(pn)}₆(pz)₃(tma)₂]₂[NO₃]₁₂ (5) as the single product. Interestingly, the same reaction using slightly more bulky cis-[Pd(NO₃)₂(tmen)] (tmen=N,N,N′,N′-tetramethylethylene diamine) instead of cis-[Pd(NO₃)₂(pn)] gave non-interlocked [{Pd(tmen)}₆(pz)₃(tma)₂][NO₃]₆ (6) exclusively. Complexes 1, 3, and 5 represent the first examples of template-free triply interlocked molecular prisms obtained through multicomponent self-assembly. Formation of the complexes was supported by IR and multinuclear NMR (¹H and ¹³C) spectroscopy. Formation of guest-encapsulating complexes (2 and 4) was confirmed by 2D DOSY and ROESY NMR spectroscopic analyses, whereas for complexes 1, 3, 5, and 6 single-crystal X-ray diffraction techniques unambiguously confirmed their formation. The gross geometries of H₃tma-encapsulating complexes 2 and 4 were obtained by universal force field (UFF) simulations.

Under lock and key? Template-induced formation of multicomponent Pd₆ coordination prisms and their self-templated triply interlocked Pd₁₂ analogues in the absence of guest molecules has been achieved (see scheme). The role of the bulky blocking amine on the formation of template-free triply interlocked prisms has been established.

Self-assembly of melem C₆N₇(NH₂)₃ in hot aqueous solution leads to the formation of hydrogen-bonded, hexagonal rosettes of melem units surrounding infinite channels with a diameter of 8.9 Å. The channels are filled with strongly disordered water molecules, which are bound to the melem network through hydrogen bonds. Single-crystals of melem hydrate C₆N₇(NH₂)₃⋅xH₂O (x≈2.3) were obtained by hydrothermal treatment of melem at 200 °C and the crystal structure (R 3¯c, a=2879.0(4), c=664.01(13) pm, V=4766.4(13)×10⁶ pm³, Z=18) was elucidated by single-crystal X-ray diffraction. With respect to the structural similarity to the well-known adduct between melamine and cyanuric acid, the composition of the obtained product was further analyzed by solid-state NMR spectroscopy. Hydrolysis of melem to cyameluric acid during syntheses at elevated temperatures could thus be ruled out. DTA/TG studies revealed that, during heating of melem hydrate, water molecules can be removed from the channels of the structure to a large extent. The solvent-free framework is stable up to 430 °C without transforming into the denser structure of anhydrous melem. Dehydrated melem hydrate was further characterized by solid-state NMR spectroscopy, powder X-ray diffraction, and sorption measurements to investigate structural changes induced by the removal of water from the channels. During dehydration, the hexagonal, layered arrangement of melem units is maintained whereas the formation of additional hydrogen bonds between melem entities requires the stacking mode of hexagonal layers to be altered. It is assumed that layers are shifted perpendicular to the direction of the channels, thereby making them inaccessible for guest molecules.

Thes-heptazine compound melem C₆N₇(NH₂)₃ assembles into a hydrogen-bonded hexagonal framework in hot aqueous solution (see figure). The structure exhibits infinite channels with diameter of 8.9 Å that are filled with crystal water. TG/DTA measurements, solid-state NMR spectroscopy, powder X-ray diffraction, and sorption measurements have been employed to investigate the thermal behavior of the material, the possibility of hydrolysis, and structural changes induced by dehydration.

Highly pure monosheets of graphene dispersible in water without the help of stabilizers have been prepared by photocatalytic reduction of graphene oxide using UV light and TiO₂. More than 90 % of the highly conductive graphene was recovered in a pure form in solution, which showed no sign of aggregation even after one month (see figure).

Let there be light: A heterogeneous photocatalytic system based on easily recyclable TiO₂ or ZnO allows cross dehydrogenative coupling reactions of tertiary amines. The newly developed protocols have successfully been applied to various CC and CP bond forming reactions to provide nitro amines as well as amino ketones, nitriles and phosphonates.

The hydrofullerene C₅₀H₁₀ is synthesized by low-pressure benzene–oxygen diffusion combustion. The structure of C₅₀H₁₀ is identified through NMR, mass spectrometry, and IR and Raman spectroscopy as a D_5h symmetric closed-cage molecule with five pairs of fused pentagons stabilized by ten hydrogen atoms. UV/Vis and fluorescence spectrometric analyses disclose its optical properties as comparable with those of its chloride cousin (C₅₀Cl₁₀). Cyclic and square-wave voltammograms reveal that the first reduction potential of C₅₀H₁₀ is more negative than that of C₅₀Cl₁₀ as well as C₆₀, with implications for the utilization of C₅₀H₁₀ as a promising electron acceptor for photovoltaic applications.

Hydrofullerene electron acceptor: The small hydrofullerene C₅₀H₁₀ with D_5h symmetry was synthesized by low-pressure benzene–oxygen diffusion combustion, and identified by NMR, mass spectrometry, and IR and Raman spectroscopy. In comparison with its chlorofullerene cousin, C₅₀H₁₀ shows similar optical properties and potentially useful electrochemical properties (see figure).

A series of rhenium(I) diimine complexes cis,trans-[Re(dmb)(CO)₂(PR¹R²R³)(PR⁴R⁵R⁶)]⁺ (dmb=4,4′-dimethyl-2,2′-bipyridine, Rⁿ=phenyl or alkyl), each of which bears two phosphine ligands with various numbers of phenyl groups, has been synthesized by using the photochemical ligand-substitution reaction. Detailed studies of the structural features, not only in the crystal but also in solution, indicate that the number of phenyl groups is a crucial factor in controlling the rotational conformation of the phosphine ligands, which in turn determines the extent of the π–π interaction between the aromatic diimine ligand and the phenyl group(s). The π–π interaction strongly affected both electrochemical and photophysical properties: 1) the oxidation power of the Re complex became stronger, 2) the lifetime of the excited state became longer, and 3) the Stokes shift between the ¹MLCT absorption band and emission from the corresponding ³MLCT excited state became smaller. In particular, the diphenyl and triphenyl phosphine had much greater influence on the properties than the monophenyl phosphine ligand. Dual emission was observed from the different rotational conformers of the complexes with an intermediate number of phenyl groups in the phosphine ligands.

A group effort: Several rhenium(I) diimine complexes that bear two phosphine ligands with various numbers of phenyl groups exhibited dual emission modulated by the π–π interaction between the aromatic diimine ligand and the phenyl group(s) (see figure). The number of phenyl groups is crucial in controlling the rotational conformation of the phosphine ligands.

Polynuclear single-molecule magnets (SMMs) were diluted in a diamagnetic crystal lattice to afford arrays of independent and iso-oriented magnetic units. Crystalline solid solutions of an Fe₄ SMM and its Ga₄ analogue were prepared with no metal scrambling for Fe₄ molar fractions x down to 0.01. According to high-frequency EPR and magnetic measurements, the guest SMM species have the same total spin (S=5), anisotropy, and high-temperature spin dynamics found in the pure Fe₄ phase. However, suppression of intermolecular magnetic interactions affects magnetic relaxation at low temperature (40 mK), where quantum tunneling (QT) of the magnetization dominates. When a magnetic field is applied along the easy magnetic axis, both pure and diluted (x=0.01) phases display pronounced steps at evenly spaced field values in their hysteresis loops due to resonant QT. The pure Fe₄ phase exhibits additional steps which are firmly ascribed to two-molecule QT transitions. Studies on the field-dependent relaxation rate showed that the zero-field resonance sharpens by a factor of five and shifts from about 8 mT to exactly zero field on dilution, in agreement with the calculated variation of dipolar interactions. The tunneling efficiency also changes significantly as a function of Fe₄ concentration: the zero-field resonance is significantly enhanced on dilution, while tunneling at ±0.45 T becomes less efficient. These changes were rationalized on the basis of a dipolar shuffling mechanism and transverse dipolar fields, whose effect was analyzed by using a multispin model. Our findings directly prove the impact of intermolecular magnetic couplings on SMM behavior and disclose the magnetic response of truly isolated giant spins in a diamagnetic crystalline environment.

Single-molecule magnets (SMMs) as dopants: Crystals of a diamagnetic Ga₄ complex have been doped with the Fe₄ analogue to afford arrays of independent and iso-oriented SMMs. Suppression of intermolecular communication has a strong influence on magnetic relaxation in the low-temperature regime, leading to the disappearance of two-molecule quantum tunneling effects and to profound reshaping of hysteresis loops (see figure; Hdpm=dipivaloylmethane).

A supramolecular system that can activate an enzyme through photo-isomerization was constructed by using a liposomal membrane scaffold. The design of the system was inspired by natural signal transduction systems, in which enzymes amplify external signals to control signal transduction pathways. The liposomal membrane, which provided a scaffold for the system, was prepared by self-assembly of a photoresponsive receptor and a cationic synthetic lipid. NADH-dependent L-lactate dehydrogenase, the signal amplifier, was immobilized on the liposomal surface by electrostatic interactions. Recognition of photonic signals by the membrane-bound receptor induced photo-isomerization, which significantly altered the receptor’s metal-binding affinity. The response to the photonic signal was transmitted to the enzyme by Cu²⁺ ions. The enzyme amplified the chemical information through a catalytic reaction to generate the intended output signal.

trans-formers: A supramolecular system that is capable of activating an enzyme through photoisomerization was constructed on a liposomal membrane. Quantitative evaluation of the present system by using CD and UV spectroscopy showed that enzyme activity was effectively regulated by the specific recognition of the photonic signal by the receptor and its response (see Scheme).

The use of dendritic structures for the grafting of core–shell γ-Fe₂O₃/polymer 300 nm superparamagnetic nanoparticles (MNPs) has been performed with four metallodendrons that were functionalized with diphosphinopalladium complexes. The catalytic performance of these nanocatalysts was optimized for the Suzuki CC cross-coupling reaction. These results demonstrated the importance of optimizing the catalytic efficiency of grafted MNPs by optimizing the dendritic structures and the nature of the peripheral phosphine ligands. All of these nanocatalysts showed remarkable reactivity towards bromoarenes and they were recovered and efficiently reused by magnetic separation with almost no loss of reactivity, even after 25 cycles.

To the very core: Core–shell γ-Fe₂O₃/polymer superparamagnetic nanoparticles (MNPs, see figure) were grafted by four metallodendrons functionalized with diphosphinopalladium complexes. These nanocatalysts were optimized for the Suzuki CC cross-coupling reaction.

Dynamics and inertia: The rotation of the CF₃ top in α,α,α-trifluorotoluene becomes considerably hindered by a V₃ barrier in α,α,α-trifluoro-p-tolualdehyde. Situated in a local V₆ environment, the V₃ barrier is caused by the aldehyde group and communicated through the aromatic π system. Quite dramatically, the ground state inertial defect jumps from −1.271 to −89.961 uŲ, thus reflecting the electronically induced rigidity (see figure).

The presence of residual metal-catalyst impurities in carbon nanotubes is responsible for their toxicity. It is important to differentiate between the total amount of impurities and the redox-active (bioavailable) amount of such impurities because only the bioavailable impurities exhibit toxic effects. Herein, we report a simple and specific method for quantifying the amount of redox-active Ni present in various commercial samples of CNTs. It is based on the electrochemical oxidation of Ni(OH)₂ that is formed in alkaline solutions when Ni impurities are opened to the surrounding environment. Metallic Ni impurities play an extremely active role in toxicological assays as well as in undesired catalytic processes, and thus a method to rapidly quantify the amount of redox-active Ni is of great importance.

In the nickel of time: Ni impurities within commercially available CNT samples can become extremely active in alkaline media, with well-defined and specific electrochemical behavior. A simple, highly specific method was used to quantify the redox-active Ni by exploiting the well-known electrochemistry of Ni(OH)₂. This method was able to detect the portion of redox-active Ni in a CNT sample of total Ni content of only 0.7 wt %.

The reactions of [Cp(PPh₃)₂RuCl] (Cp=cyclopentadienyl) with phenyl propargylic alcohol 1 a, with a 3-thiophene group, are explored. The carbene complex 2 a, obtained exclusively from this reaction at low temperature, contains the naphthothiophene group, which is formed through a new cyclization process between the thiophene group and the inner carbon of the triple bond. Details of this process have been revealed by conducting the reaction at room temperature, affording the allenylidene complex 3 a as a side product. Complex 3 a is not converted into 2 a, indicating that the cyclization takes place while the triple bond is π coordinated to the metal center. Complex 2 a reacts with oxygen in the presence of NEt₃ at room temperature to afford, in high yield, naphthothiophene aldehyde 4 a, ONEt₃, OPPh₃, and [Cp(PPh₃)₂RuCl]. Molecular O₂ is likely activated by coordination to the metal center when one of the phosphane ligands dissociates. Then, NEt₃ promotes the oxygenation process by reacting with the coordinated O₂ to afford ONEt₃ and possibly an unobserved oxo-carbene complex. Coupling of the oxo and carbene ligands then yields 4 a and [Cp(PPh₃)₂RuCl] in CHCl₃. In a solvent system containing MeOH, the oxygenation reaction affords a mixture of 4 a and naphthothiophene ester 5 a–1. The reactions of [Cp(dppf)RuCl] (dppf=1,1′-bis(diphenylphosphino)ferrocene) with 1 a, also afford the carbene complex 2 a′, 4 a, and 5 a, which have been characterized by X-ray diffraction analyses. For the phenyl propargylic alcohol 1 b, with a 2-thiophene substituent, different naphthothiophene aldehyde and ester compounds are also obtained in high yields through a similar cyclization process followed by oxygenation under mild conditions.

In the reaction of [Cp(PPh₃)₂RuCl] with 1 a, containing a 3-thiophene, 2 a with a naphthothiophene was obtained through a new cyclization reaction (see scheme). Complex 2 a reacts with oxygen in the presence of NEt₃ to afford 4 a. Complex 2 a′ from the reaction of 1 a with [Cp(dppf)RuCl] (Cp=cyclopentadienyl, dppf=,1′-bis(diphenyl-phosphino)ferrocene) was characterized by X-ray diffraction analysis.

Herein, we present a full account of our efforts to couple the northern and the southern building blocks, the synthesis of which were described in the preceding paper, along with the modifications required to ultimately lead to a successful synthesis of laulimalide. Key highlights include an exceptionally efficient and atom-economical intramolecular ruthenium-catalyzed alkene–alkyne coupling to build the macrocycle, followed by a highly stereoselective 1,3-allylic isomerization promoted by a rhenium complex. Interestingly, the designed synthetic route also allowed us to prepare an analogue of the natural product that possesses significant cytotoxic activity. We also report a second generation route that provides a more concise synthesis of the natural product.

All in one piece: Efforts to couple the northern and southern building blocks, synthesized in the preceding paper, along with modifications required to lead to a successful synthesis of laulimalide are discussed. Interestingly, the designed synthetic route also allowed the preparation of an analogue of the natural product that possesses significant cytotoxic activity (see scheme). A more concise, second-generation route to the natural product is also described.

The first stage in the development of a synthetic route for the total synthesis of laulimalide (1) is described. Our retrosynthetic analysis envisioned a novel macrocyclization route to the natural product by using a Ru-catalyzed alkene–alkyne coupling. This would be preceded by an esterification of the C19 hydroxyl group, joining together two equally sized synthons, the northern fragment 7 and the southern fragment 8. Our first generation approach to the northern fragment entailed a key sequential Ru/Pd coupling sequence to assemble the dihydropyran. The key reactions proceeded smoothly, but the inability to achieve a key olefin migration led to the development of an alternative route based on an asymmetric dinuclear Zn-catalyzed aldol reaction of a hydroxyl acylpyrrole. This key reaction led to the desired diol adduct 66 with excellent syn/anti selectivity (10:1), and allowed for the successful completion of the northern fragment 7. The key step for the synthesis of the southern fragment was a chemoselective Rh-catalyzed cycloisomerization reaction to form the dihydropyran ring from a diyne precursor. This reaction proved to be selective for the formation of a six-membered ring, over a seven. The use of an electron-deficient bidentate phosphine allowed for the reaction to proceed with a reduced catalyst loading.

Making the pieces: The synthesis of two equal-sized fragments of laulimalide is described (see scheme). A key Rh-catalyzed cycloisomerization reaction allowed for an efficient synthesis of the endocyclic dihydropyran and a stereoselective acylpyrrole Zn-aldol reaction allowed for the formation of the syn-diol.

We report here on the selective synthesis of fullerene pentakisadducts 3 with an incomplete octahedral addition pattern by means of mixed [5:1]hexakisadducts 1 that involve an isoxazoline moiety as a protection group. The isoxazoline addend can be cleanly cleaved by irradiation with light. By using this protection–deprotection strategy, a variety of fullerene pentakisadducts 3 were synthesized in 29–44 % overall yield without the need of HPLC purification. This novel photolytic deprotection of 1 can be explained by an initial electron transfer that leads to a biradical, which can easily eliminate the isoxazoline added. The very efficient and straightforward syntheses of the bisfullerene 4 and the globular hexakisadduct 7, each of which involves mixed octahedral addition patterns, clearly demonstrate the advantage of fullerene pentakisadducts 3 as suitable precursors for the construction of highly functional and complex [5:1]hexakisadduct architectures. Complete structural characterization of all new compounds was carried out by MALDI mass spectrometry, UV/Vis, FTIR, ¹H NMR and ¹³C NMR spectroscopy, as well as X-ray diffraction.

Five going on six: Fullerene pentakisadducts (see figure) are versatile precursors for the synthesis of mixed [5:1]hexakisadducts. The completion of the octahedral addition pattern proceeds with quantitative regioselectivity. Fullerene pentakisadducts can easily be prepared by photolytic cleavage of an isoxazoline protective group.

The natural product deoxyschizandrin has been shown to have a wide range of biological activities. In recent years the therapeutic potential of this compound against cancers has attracted significant interest. Herein we describe a concise de novo total synthesis of deoxyschizandrin based around a double organocuprate oxidation strategy. In addition, we present the results of biological studies exploring the ability of deoxyschizandrin and synthetic precursors lacking the medium ring biaryl unit to inhibit the proliferation of a human cancer cell line. These studies led to the identification of a structurally novel agent with in vitro anticancer activity.

A concise total synthesis of the natural product deoxyschizandrin, based around a double organocuprate oxidation strategy, is reported. In addition, the results of biological studies exploring the ability of deoxyschizandrin and synthetic precursors lacking the medium ring biaryl unit to inhibit the proliferation of a human cancer cell line are presented.

Magnetic personality: The incorporation of a bulky auxiliary ligand in β-diketone-based dysprosium(III) single-ion magnets (SIMs) remarkably increases the anisotropic barriers, representing a promising route toward the design of higher anisotropic barrier SIMs (see scheme).

Morphology-controlled Pt dendritic aggregates supported on W₁₈O₄₉ nanowires were fabricated by the simple colloidal method. The synthesized nanocatalysts exhibit strong catalytic activity toward methanol oxidation and high CO tolerance because of the highly branched structure of the dendritic Pt nanostructures and assistant catalytic activity of the tungsten oxide nanowires (see figure).

Quick X-ray absorption spectroscopy (XAS) provides quantitative information about the composition of supported metal phases during catalyst activation. Decomposition of SiO₂-supported cobalt nitrate in diluted NO leads to the rapid formation of cobalt(II) hydroxynitrates below 100 °C. Their decomposition starts progressively between 110 and 170 °C to give cobalt oxide nuclei, which contribute to the enhancement of the metal oxide dispersion (see figure).

Five metal–organic frameworks (MOFs) formed by [WS₄Cu_x]^x−2 secondary building units (SBUs) and multi-pyridyl ligands are presented. The [WS₄Cu_x]^x−2 SBUs function as network vertexes showing various geometries and connectivities. Compound 1 contains one-dimensional channels formed in fourfold interpenetrating diamondoid networks with a hexanuclear [WS₄Cu₅]³⁺ unit as SBU, which shows square-pyramidal geometry and acts as a tetrahedral node. Compound 2 contains brick-wall-like layer also with a hexanuclear [WS₄Cu₅]³⁺ unit as SBU. The [WS₄Cu₅]³⁺ unit in 2 is a new type of [WS₄Cu_x]^x−2 cluster unit in which the five Cu⁺ ions are in one plane with the W atom, forming a planar unit. Compound 3 shows a nanotubular structure with a pentanuclear [WS₄Cu₄]²⁺ unit as SBU, which is saddle-shaped and acts as a tetrahedral node. Compound 4 contains large cages formed between two interpenetrated (10,3)-a networks also with a pentanuclear [WS₄Cu₄]²⁺ unit acting as a triangular node. The [WS₄Cu₄]²⁺ unit in 4 is isomeric to that in 3 and first observed in a MOF. Compound 5 contains zigzag chains with a tetrahedral [WS₄Cu₃]⁺ unit as SBU, which acts as a V-shaped connector. The influence of synthesis conditions including temperature, ligand, anions of Cu^I salts, and the ratio of [NH₄]₂WS₄ to Cu^I salt on the formation of these [WS₄Cu_x]^x−2-based MOFs were also studied. Porous MOF 3 is stable upon removal and exchange of the solvent guests, and when accommodating different solvent molecules, it exhibits specific colors depending on the polarity of incorporated solvent, that is, it shows a rare solvatochromic effect and has interesting prospects in sensing applications.

Versatile SBUs: [WS₄Cu_x]^x−2 units show different geometries and connectivities when used as secondary building units (SBUs) for constructing metal–organic frameworks (MOFs; see figure). Temperature and ligand are more important parameters for the synthesis of new [WS₄Cu_x]^x−2-based MOFs than the ratio of [NH₄]₂WS₄ to Cu^I salt.

We report the synthesis of the first organo-POM with thermoresponsive properties. Our concept will provide chemists with a new tool to design POMs whose solubility is reversibly controllable through an external stimulus. POM–polymer TBA₇[POM]-poly(N,N-diethylacrylamide) (POM–PDEAAm), was prepared by grafting PDEAAm-NH₂ (obtained by RAFT polymerization) onto the activated Dawson acyl-POM, α₂-[P₂W₁₇O₆₁SnCH₂CH₂C(O)]⁶⁻. Extensive MS analysis was used to monitor the chain-functionalization steps and to confirm the formation of the hybrid. Aqueous solutions of the (NH₄)₇[POM–PDEAAm] exhibited a LCST of 38 °C. Thus, the solubility/aggregation of the hybrid was reversibly controlled by changing the temperature. Above 38 °C, the solution became cloudy, and cleared again upon cooling. Dynamic light scattering (DLS) revealed the formation of small aggregates in the range 100 nm. We assumed that the charged POM head units prevented the formation of the larger-scattering aggregates that are usually observed for PDEAAm, and promoted the formation of micelle-like structures. The conjugate exhibited a temperature transition, which was different from that of the polymer and depended on the counterions associated with the POM. This result demonstrates the potential for merging organic (in this case, polymer) and inorganic structures to afford materials that exhibit new properties.

POM and circumstance: An organo-POM with reversibly thermocontrollable solubility was synthesized by grafting PDEAAm-NH₂ onto the activated Dawson acyl-POM. Aqueous solutions of the NH₄⁺ salt exhibited an LCST of 38 °C, above which small aggregates were formed (see figure).

Gold nanoparticles loaded onto Keggin-type insoluble polyoxometalates (Cs_xH_3−xPW₁₂O₄₀) showed superior catalytic performances for the direct conversion of cellobiose into gluconic acid in water in the presence of O₂. The selectivity of Au/Cs_xH_3−xPW₁₂O₄₀ for gluconic acid was significantly higher than those of Au catalysts loaded onto typical metal oxides (e.g., SiO₂, Al₂O₃, and TiO₂), carbon nanotubes, and zeolites (H-ZSM-5 and HY). The acidity of polyoxometalates and the mean-size of the Au nanoparticles were the key factors in the catalytic conversion of cellobiose into gluconic acid. The stronger acidity of polyoxometalates not only favored the conversion of cellobiose but also resulted in higher selectivity of gluconic acid by facilitating desorption and inhibiting its further degradation. On the other hand, the smaller Au nanoparticles accelerated the oxidation of glucose (an intermediate) into gluconic acid, thereby leading to increases both in the conversion of cellobiose and in the selectivity of gluconic acid. The Au/Cs_xH_3−xPW₁₂O₄₀ system also catalyzed the conversion of cellulose into gluconic acid with good efficiency, but it could not be used repeatedly owing to the leaching of a H⁺-rich hydrophilic moiety over long-term hydrothermal reactions. We have demonstrated that the combination of H₃PW₁₂O₄₀ and Au/Cs_3.0PW₁₂O₄₀ afforded excellent yields of gluconic acid (about 85 %, 418 K, 11 h), and the deactivation of the recovered H₃PW₁₂O₄₀–Au/Cs_3.0PW₁₂O₄₀ catalyst was not serious during repeated use.

Crazy glu: Cellulose was oxidized into gluconic acid by combining polyoxometalate (POM)-supported Au nanoparticles (NPs) and acidic POMs. Au-NP size and POM acidity are the determining factors in the selective oxidation of glucose and cellobiose.

The photochemistry of iron azido complexes is quite challenging and poorly understood. For example, the photochemical decomposition of [Fe^IIIN₃(cyclam-ac)]PF₆ ([1]PF₆), where cyclam-ac represents the 1,4,8,11-tetraazacyclotetradecane-1-acetate ligand, has been shown to be wavelength-dependent, leading either to the rare high-valent iron(V) nitrido complex [Fe^VN(cyclam-ac)]PF₆ ([3]PF₆) after cleavage of the azide N_αN_β bond, or to a photoreduced Fe^II species after FeN_azide bond homolysis. The mechanistic details of this intriguing reactivity have never been studied in detail. Here, the photochemistry of 1 in acetonitrile solution at room temperature has been investigated using step-scan and rapid-scan time-resolved Fourier transform infrared (FTIR) spectroscopy following a 266 nm, 10 ns pulsed laser excitation. Using carbon monoxide as a quencher for the primary iron-containing photochemical product, it is shown that 266 nm excitation of 1 results exclusively in the cleavage of the FeN_azide bond, as was suspected from earlier steady-state irradiation studies. In argon-purged solutions of [1]PF₆, the solvent-stabilized complex cation [Fe^II(CH₃CN)(cyclam-ac)]⁺ (2 red) together with the azide radical (N₃^.) is formed with a relative yield of 80 %, as evidenced by the appearance of their characteristic vibrational resonances. Strikingly, step-scan experiments with a higher time resolution reveal the formation of azide anions (N₃⁻) during the first 500 ns after photolysis, with a yield of 20 %. These azide ions can subsequently react thermally with 2 red to form [Fe^IIN₃(cyclam-ac)] (1 red) as a secondary product of the photochemical decomposition of 1. Molecular oxygen was further used to quench 1 red and 2 red to form what seems to be the elusive complex [Fe(O₂)(cyclam-ac)]⁺ (6).

Time-resolved spectroscopy: Time-resolved rapid-scan and step-scan spectroscopy in the mid-infrared spectral region is used to explore the photochemistry of an iron(III) azido complex, and to generate what seems to be a stable nonheme iron-superoxo complex (see figure).

The first direct intermolecular regiospecific and highly enantioselective α-allylic alkylation of linear aldehydes by a combination of achiral bench-stable Pd⁰ complexes and simple chiral amines as co-catalysts is disclosed. The co-catalytic asymmetric chemoselective and regiospecific α-allylic alkylation reaction is linked in tandem with in situ reduction to give the corresponding 2-alkyl alcohols with high enantiomeric ratios (up to 98:2 e.r.; e.r.=enantiomeric ratio). It is also an expeditious entry to valuable 2-alkyl substituted hemiacetals, 2-alkyl-butane-1,4-diols, and amines. The concise co-catalytic asymmetric total syntheses of biologically active natural products (e.g., Arundic acid) are disclosed.

Go organic! Direct intermolecular regiospecific and highly enantioselective α-allylic alkylation of linear aldehydes by a combination of achiral bench-stable Pd⁰ complexes and simple chiral amines as co-catalysts is disclosed (see scheme).

The enantioselective propargylic alkylation of propargylic alcohols with β-ketoesters in the presence of a thiolate-bridged diruthenium complex and a copper complex as co-catalyst affords the corresponding propargylic alkylated products in excellent yields as a mixture of two diastereoisomers with high enantioselectivity (up to 95 % enantiomeric excess (ee)). The findings reported herein not only open up a new type of enantioselective propargylic substitution reaction, but also a new aspect of cooperative catalytic reactions using distinct transition metals to realize a useful transformation that cannot be achieved by a single catalyst.

Homogeneous catalysis: Highly enantioselective propargylic alkylations of propargylic alcohols with β-ketoesters in the presence of a thiolate-bridged diruthenium complex and a copper complex are presented (see scheme). This methodology based on a cooperative catalytic system using distinct transition metals realizes a useful transformation that cannot be achieved by a single catalyst.

Synthesis of anisole: Aryl and heteroaryl halides undergo selective CO cross-coupling reactions with methanol in the presence of a Pd(OAc)₂/L3 catalyst system. The corresponding ethers were obtained under mild conditions in good yields. The catalytic methodology was also used for the synthesis of labeled deuterated anisoles in good yields (see scheme).

Chiral oxazolines: A synthetic method to prepare optically active oxazolines through a copper-catalyzed asymmetric desymmetrization of 1,3-diols has been successfully developed. This reaction system tolerated a diverse range of substrates to give the desired oxazoline derivatives in good to excellent yields with high enantioselectivities (see scheme).

An organoimido-substituted monovacant hexamolybdate containing additional multidentate ligands and its phenylphosphonate derivative were both synthesized directly from an aromatic amine by using an N,N-dicyclohexylcarbodiimide (DCC) protocol. The inherent chirality of these compounds and their hydrophobic shells are pictured.

Two new nanovehicles that have extended aromatic platforms as the cargo zones have been obtained. Two strategies were considered for the formation of the perylene core from two naphthalene precursors. The first was based on a Scholl-type reaction involving an oxidant, and the second used a brominated derivative to perform a homocoupling reaction. The first strategy failed under diverse coupling conditions in the presence of several strong oxidants. Nevertheless, the use of CoF₃ in trifluoroacetic acid triggered a dimerization reaction between two ester groups of one molecule and the naphthalene unit of another, thereby surprisingly yielding a ten-membered carbon macrocycle. The second strategy encountered a lack of reactivity of the substrate under several homocoupling conditions. The dimerization was not easily performed but Ullmann-type conditions ultimately gave the expected product. The low yield and low solubility of the product encouraged us to modify our initial design. The synthesis of a new chassis that incorporated additional tert-butyl groups improved the solubility of the molecules and also prevented overcyclization of the aromatic platform by blocking these positions. Some p-phenylene spacers were also intercalated between the iodine and perylene centers to increase the reactivity of the halide towards coupling reactions. Two new chassis were obtained by Scholl-type oxidative coupling using FeCl₃ as the oxidant. The introduction of four triptycene wheels allowed the formation of the two corresponding nanovehicles.

Deux nouveaux nanovéhicules ont été obtenus avec une plateforme polyaromatique pouvant servir de zone de chargement. Deux stratégies de synthèse ont été considérées pour la formation du noyau pérylène à partir de deux précurseurs naphtaléniques. La première a fait intervenir une réaction de type Scholl mettant en jeu un oxydant, tandis que la seconde a mis en œuvre un dérivé bromé afin de réaliser un homocouplage. La première stratégie a échoué malgré de nombreuses conditions de couplage testées. Néanmoins, les conditions utilisant CoF₃ dans l′acide trifluoroacétique ont abouti à une dimérisation entre deux fonctions esters d′une molécule et le noyau naphtalène d′une seconde, conduisant à la formation d′un macrocycle à 10 chaînons. La seconde stratégie a également souffert d′un manque de réactivité du substrat lors de l′homocouplage. La dimérisation n′a pu s’effectuer facilement, mais les conditions de type Ullmann ont finalement permis d′aboutir au composé souhaité. Le faible rendement combiné à la faible solubilité du produit de cette réaction nous ont conduits à corriger le design initial. La synthèse d′un nouveau châssis a été entreprise en incorporant des groupements tert-butyles supplémentaires, afin d′améliorer la solubilité des molécules mais aussi pour éviter de surcycliser le châssis polyaromatique en bloquant ces positions. Des espaceurs p-phénylène ont également été intercalés entre l′atome d′iode et le noyau pérylène pour améliorer la réactivité de l′halogénure vis-à-vis des réactions de couplage. Deux nouveaux châssis ont ainsi été obtenus par couplage oxydant de type Scholl en utilisant FeCl₃ comme oxydant. L′introduction de quatre roues triptycènes a permis d′obtenir les deux nanovéhicules correspondants.

En route! Two new molecular nanovehicles with a large dedicated cargo zone have been synthesized according to a modular strategy based on sequential double Knoevenagel and Diels–Alder reactions.

Dichloro[bis{1-(dicyclohexylphosphanyl)piperidine}]palladium [(P{(NC₅H₁₀)(C₆H₁₁)₂})₂PdCl₂] (1) is a highly active and generally applicable CC cross-coupling catalyst. Apart from its high catalytic activity in Suzuki, Heck, and Negishi reactions, compound 1 also efficiently converted various electronically activated, nonactivated, and deactivated aryl bromides, which may contain fluoride atoms, trifluoromethane groups, nitriles, acetals, ketones, aldehydes, ethers, esters, amides, as well as heterocyclic aryl bromides, such as pyridines and their derivatives, or thiophenes into their respective aromatic nitriles with K₄[Fe(CN)₆] as a cyanating agent within 24 h in NMP at 140 °C in the presence of only 0.05 mol % catalyst. Catalyst-deactivation processes showed that excess cyanide efficiently affected the molecular mechanisms as well as inhibited the catalysis when nanoparticles were involved, owing to the formation of inactive cyanide complexes, such as [Pd(CN)₄]²⁻, [(CN)₃Pd(H)]²⁻, and [(CN)₃Pd(Ar)]²⁻. Thus, the choice of cyanating agent is crucial for the success of the reaction because there is a sharp balance between the rate of cyanide production, efficient product formation, and catalyst poisoning. For example, whereas no product formation was obtained when cyanation reactions were examined with Zn(CN)₂ as the cyanating agent, aromatic nitriles were smoothly formed when hexacyanoferrate(II) was used instead. The reason for this striking difference in reactivity was due to the higher stability of hexacyanoferrate(II), which led to a lower rate of cyanide production, and hence, prevented catalyst-deactivation processes. This pathway was confirmed by the colorimetric detection of cyanides: whereas the conversion of β-solvato-α-cyanocobyrinic acid heptamethyl ester into dicyanocobyrinic acid heptamethyl ester indicated that the cyanide production of Zn(CN)₂ proceeded at 25 °C in NMP, reaction temperatures of >100 °C were required for cyanide production with K₄[Fe(CN)₆]. Mechanistic investigations demonstrate that palladium nanoparticles were the catalytically active form of compound 1.

A balancing act: Compound 1 (see scheme) is a highly active cyanation catalyst. Furthermore, a sharp balance between the rates of cyanide generation, efficient product formation, and catalyst deactivation owing to excess cyanide was observed in deactivation processes.

The first systematic series of single-crystal diffraction structures of azo lake pigments is presented (Lithol Red with cations=Mg^II, Ca^II, Sr^II, Ba^II, Na^I and Cd^II) and includes the only known structures of non-Ca examples of these pigments. It is shown that these commercially and culturally important species show structural behaviour that can be predicted from a database of structures of related sulfonated azo dyes, a database that was specifically constructed for this purpose. Examples of the successful structural predictions from the prior understanding of the model compounds are that 1) the Mg salt is a solvent-separated ion pair, whereas the heavier alkaline-earth elements Ca, Sr and Ba form contact ion pairs, namely, low-dimensional coordination complexes; 2) all of the Lithol Red anions exist as the hydrazone tautomer and have planar geometries; and 3) the commonly observed packing mode of alternating inorganic layers and organic bilayers is as expected for an ortho-sulfonated azo species with a planar anion geometry. However, the literature database of dye structures has no predictive use for organic solvate structures, such as that of the observed Na Lithol Red DMF solvate. Interestingly, the Cd salt is isostructural with the Mg salt and not with the Ca salt. It is also observed that linked eight-membered [MOSO]₂ rings are the basic coordination motif for all of the known structures of Ca, Sr and Ba salts of sulfonated azo pigments in which competing carboxylate groups are absent.

The fine art of coordination polymers: The first series of structures of an azo lake pigment is presented, namely, Mg, Ca, Sr, Ba, Cd and Na salts of the printers’ and artists’ material Lithol Red. These structures (see figure) show remarkable similarities to previously studied structures of model dyestuffs and hence the structures of the dyes can be used to predict the likely structure of sulfonated azo pigments.

1-Hydroxy-1,2-benziodoxol-3(1H)-one (IBA) is an efficient terminal oxidant for gold-catalysed, three-component oxyarylation reactions. The use of this iodine(III) reagent expands the scope of oxyarylation to include styrenes and gem-disubstituted olefins, substrates that are incompatible with the previously reported Selectfluor-based methodology. Diverse arylsilane coupling partners can be employed, and in benzotrifluoride, homocoupling is substantially reduced. In addition, the IBA-derived co-products can be recovered and recycled.

The I’s have it: The unprecedented use of an iodine(III) reagent as the terminal oxidant for gold-catalysed oxyarylation allows the substrate scope to be significantly expanded: in addition to monosubstituted olefins, styrenes and gem-disubstituted olefins are well tolerated (see scheme). With benzotrifluoride as solvent, unproductive homodimerisation of the arylsilane coupling partner is effectively suppressed.

Triphenylamine (TPA)-based conjugated hyperbranched poly(aryleneethynylene)s (PAEs), hb-P1/2, hb-P1/3, and hb-P1/4, were synthesized with high molecular weights and good solubilities through Sonogashira coupling reactions. These PAEs exhibited outstanding thermal stabilities and different emission behaviors. Tetraphenylethene (TPE)-containing hb-P1/2 fluoresced faintly in THF, although its light emission was enhanced by aggregate formation in aqueous media or in thin films, thereby exhibiting an aggregation-induced emission-enhancement (AIEE) effect. Whereas 1,1,2,3,4,5-hexaphenylsilole (HPS)-bearing hb-P1/3 showed no significant change in emission intensity with increasing water content in aqueous media, hb-P1/4, which consisted of TPA–fluorenone donor–acceptor groups, presented almost identical absorptions, but both positive and negative solvatochromic emissions in various solvents. A superquenching effect was observed in the picric-acid-detection process by using nanosuspensions of hb-P1/2. All of the polymers possessed good film formability. UV irradiation of the thin films induced simultaneous photobleaching and cross-linking, thus making them applicable in the fabrication of 2D and 3D patterns. Furthermore, the polymer films also showed high refractive indices, which were tunable upon exposure to UV light.

Branching out: Soluble, conjugated hyperbranched poly(aryleneethynylene)s (hb-PAEs) exhibit outstanding thermal stabilities and intriguing photophysical properties, such as aggregation-induced emission enhancement. These hb-PAEs also enjoy excellent film formability, photopatternability, and tunable high refractive indices, which render them promising candidates in optoelectronic applications.

Two bicyclic hexapeptides, allo-RA-V (4) and neo-RA-V (5), and one cyclic hexapeptide, O-seco-RA-V (6), were isolated from the roots of Rubia cordifolia L. Their gross structures were elucidated on the basis of spectroscopic analysis and X-ray crystallography of compound 5. The absolute stereochemistry of compounds 4 and 5 were established by their total syntheses, and the absolute stereochemistry of compound 6 by chemical correlation with deoxybouvardin (3). Comparison of the 3D structures of highly active RA-VII (1) with less-active compounds 4 and 5 suggests that the orientation of the Tyr-5 and/or Tyr-6 phenyl rings plays a significant role in their biological activity. The isolation of peptides 4–6, along with compound 3, and the comparison of their structures seem to indicate that peptide 6 may be the common precursor to bicyclic peptides 3–5 in the plant.

Allo allo: Two cycloisodityrosine-modified congeners of deoxybouvardin (RA-V) have been isolated from the roots of Rubia cordifolia. Comparison of their structures with that of RA-VII revealed that the orientation of one or both of the Tyr-5 and Tyr-6 phenyl rings plays an essential role in expressing the cytotoxic activity.

A ditopic ion-pair receptor (1), which has tunable cation- and anion-binding sites, has been synthesized and characterized. Spectroscopic analyses provide support for the conclusion that receptor 1 binds fluoride and chloride anions strongly and forms stable 1:1 complexes ([1⋅F]⁻ and [1⋅Cl]⁻) with appropriately chosen salts of these anions in acetonitrile. When the anion complexes of 1 were treated with alkali metal ions (Li⁺, Na⁺, K⁺, Cs⁺, as their perchlorate salts), ion-dependent interactions were observed that were found to depend on both the choice of added cation and the initially complexed anion. In the case of [1⋅F]⁻, no appreciable interaction with the K⁺ ion was seen. On the other hand, when this complex was treated with Li⁺ or Na⁺ ions, decomplexation of the bound fluoride anion was observed. In contrast to what was seen with Li⁺, Na⁺, K⁺, treating [1⋅F]⁻ with Cs⁺ ions gave rise to a stable, host-separated ion-pair complex, [F⋅1⋅Cs], which contains the Cs⁺ ion bound in the cup-like portion of the calix[4]pyrrole. Different complexation behavior was seen in the case of the chloride complex, [1⋅Cl]⁻. Here, no appreciable interaction was observed with Na⁺ or K⁺. In contrast, treating with Li⁺ produces a tight ion-pair complex, [1⋅Li⋅Cl], in which the cation is bound to the crown moiety. In analogy to what was seen for [1⋅F]⁻, treatment of [1⋅Cl]⁻ with Cs⁺ ions gives rise to a host-separated ion-pair complex, [Cl⋅1⋅Cs], in which the cation is bound to the cup of the calix[4]pyrrole. As inferred from liposomal model membrane transport studies, system 1 can act as an effective carrier for several chloride anion salts of Group 1 cations, operating through both symport (chloride+cation co-transport) and antiport (nitrate-for-chloride exchange) mechanisms. This transport behavior stands in contrast to what is seen for simple octamethylcalix[4]pyrrole, which acts as an effective carrier for cesium chloride but does not operates through a nitrate-for-chloride anion exchange mechanism.

Getting all the eggs in one basket: A new calix[4]pyrrole derivative with a directly appended crown-6 strap interacts in a disparate manner with various alkali cation salts under a variety of conditions, including those associated with transport.

Two ansa-half-sandwich rare-earth-metal (REM) dialkyl complexes supported by an ethylene-bridged fluorenyl (Flu)-N-heterocyclic carbene (NHC) ligand, [M{C₂H₄(η⁵-Flu-κ¹-NHC)}(CH₂SiMe₃)₂] (M=Y, 1; Lu, 2), and a chiral ansa-sandwich samarocene incorporating a C₂ ligand, [Sm(η⁵-C₁₂H₈)₂(thf)₂] (3), have been investigated for the coordination–addition polymerization of renewable methylene butyrolactones, α-methylene-γ-butyrolactone (MBL) and γ-methyl-α-methylene-γ-butyrolactone (_γMMBL). Both ansa-half-sandwich complexes 1 and 2 exhibit exceptional activity for the polymerization of _γMMBL at room temperature in dimethylformamide (DMF); with a 0.25 mol % catalyst loading, quantitative monomer conversion can be achieved under 1 min, giving a high turn-over frequency (TOF) of 24 000 h⁻¹. This TOF value represents a rate enhancement, by a factor of 8, 22, or 2400, over the polymerizations by unbridged samarocene [Sm(Cp*)₂(thf)₂] (Cp*=η⁵-pentamethylcyclopentadienyl), by bridged ansa-samarocene 3 with C₂ ligation, or by the corresponding REM trialkyls without the ansa-Flu-NHC ligation, respectively. Complexes 1 and 2 are also highly active for the polymerization of β-methyl-α-methylene-γ-butyrolactone (_βMMBL), realizing the first example of the metal-mediated coordination polymerization of this monomer and its copolymerization with _γMMBL. More remarkably, the resulting P_βMMBL homopolymer is highly stereoregular (91 % mm) and exhibits a high T_g of 290 °C. In sharp contrast, catalysts 1 and 2 have poor activity and efficiency in the polymerization of the parent MBL or the acyclic analog methyl methacrylate. Polymerization and kinetic studies using the most active catalyst (1) of the series have uncovered characteristics of its _γMMBL polymerization and yielded a unimolecular propagation mechanism. A surprising chain-initiation pathway for the polymerization in DMF by 1 has been revealed, and catalytic polymerization in the presence of an organoacid has also been examined.

Stereoreguar polymers: ansa-Half-sandwich rare-earth-metal catalysts supported by the N-heterocyclic-carbene-functionalized fluorenyl ligand exhibit exceptional activity in the coordination polymerization of renewable methylene methylbutyrolactones at room temperature (see scheme). In the case of the β-methyl derivative, both high activity and stereoselectivity are achieved at room temperature, producing the corresponding polymer with high stereoregularity as well as excellent resistance to heat and common solvents.

We report CH/π hydrogen-bond-driven self-assembly in π-conjugated skeletons based on oligophenylenevinylenes (OPVs) and trace the origin of interactions at the molecular level by using single-crystal structures. OPVs were designed with appropriate pendants in the aromatic core and varied by hydrocarbon or fluorocarbon tails along the molecular axis. The roles of aromatic π-stack, van der Waals forces, fluorophobic effect and CH/π interactions were investigated on the theromotropic liquid crystallinity of OPV molecules. Single-crystal structures of hydrocarbon OPVs provided direct evidence for the existence of CH/π interactions between the π-ring (H-bond acceptor) and alkyl CH (H-bond donor). The four important crystallographic parameters, d_c−x=3.79 Å, θ=21.49°, φ=150.25° and d_Hp−x=0.73 Å, matched in accordance with typical CH/π interactions. The CH/π interactions facilitate the close-packing of mesogens in x–y planes, which were further protruded along the c axis producing a lamellar structure. In the absence of CH/π interactions, van der Waals interactions drove the assembly towards a Schlieren nematic texture. Fluorocarbon OPVs exhibited smectic liquid-crystalline textures that further underwent Smectic A (SmA) to Smectic C (SmC) phase transitions with shrinkage up to 11 %. The orientation and translational ordering of mesogens in the liquid-crystalline (LC) phases induced H- and J-type molecular arrangements in fluorocarbon and hydrocarbon OPVs, respectively. Upon photoexcitation, the H- and J-type molecular arrangements were found to emit a blue or yellowish/green colour. Time-resolved fluorescence decay measurements confirmed longer lifetimes for H-type smectic OPVs relative to that of loosely packed one-dimensional nematic hydrocarbon-tailed OPVs.

Weak-force-driven self-assembly: CH/π hydrogen-bonding-driven diverse molecular self-assembly in π-conjugated molecules is reported (see figure). The self-organization of π-conjugated mesogens in three-dimensional crystal lattices is proved to be vital for tuning the thermotropic liquid-crystalline phases and their emission colour.

Al³⁺detection: Mononucleotide-modified metal nanoparticles (mnMNPs) can be used as a colorimetric probe for selective and sensitive detection of Al³⁺ (see figure). The aggregation of mnMNPs is selectively and sensitively induced by Al³⁺, which allowed the rapid colorimetric analysis of Al³⁺ without any prior sample preparation and specific instruments. This method can also be used for monitoring Al³⁺ changes on the living cellular surfaces under physiological conditions.

Concerted efforts: A high-potential biocathode based on co-immobilization of glucose oxidase (GOx) and horseradish peroxidase (HRP) onto carbon nanotube/carbon microfiber modified graphite rod electrode (CNT/CMF/GR) is described (see figure). The GOx/HRP biocathode shows a remarkable biocatalytic activity in the presence of glucose and oxygen.

KIE events: Hydroxylations of fatty acids by cytochrome P450 119 Compound I display no intermolecular kinetic isotope effect (KIE) in buffer and increase in rate with increasing chain length (see graph). With glycerol, the rate of reaction of lauric acid increases, and the KIE is revealed. The mechanism involves reversible formation of an unreactive complex of fatty acid with Compound I and its isomerization to a reactive one.

Ionic liquid crystals are mesogenic compounds that consist of cations and anions, usually rod-like cations and spherical anions. Herein we report a new method for the synthesis of ionic liquid crystals by using cations and anions of the same molecular shape with oppositely charged head groups. Thus, 4-alkoxyphenylpentamethylguanidinium 4-alkoxyphenylsulfonate ion pairs have been synthesised. 4-Alkoxyphenylpentamethylguanidinium iodides were also prepared to determine the influence of congruently shaped anions, in comparison with their spherical counterparts, on mesophase behaviour, which was investigated by differential scanning calorimetry (DSC), polarising optical microscopy (POM) and X-ray diffraction (XRD). All the liquid crystalline salts exhibit smectic A mesophases with strongly interdigitated bilayer structures. The guanidinium sulfonate ion pairs show mesomorphic properties from shorter alkyl chain lengths (≥C₉) and lower melting points (≈10 K), whereas the corresponding guanidinium iodides are liquid crystalline for longer alkyl chain lengths (≥C₁₄). For chains with ≥C₁₈, however, the mesophase range decreases for the sulfonate ion pairs, but not for the iodide salts.

Tuning mesophase stability: Guanidinium sulfonate ion pairs with congruently shaped anions and cations with short alkyl chains R (see scheme) have favourable mesogenic properties with respect to mesophase stability in comparison with their guanidinium counterparts with spherical iodide anions.

The most common mode of bacterial resistance to aminoglycoside antibiotics is the enzyme-catalysed chemical modification of the drug. Over the last two decades, significant efforts in medicinal chemistry have been focused on the design of non- inactivable antibiotics. Unfortunately, this strategy has met with limited success on account of the remarkably wide substrate specificity of aminoglycoside-modifying enzymes. To understand the mechanisms behind substrate promiscuity, we have performed a comprehensive experimental and theoretical analysis of the molecular-recognition processes that lead to antibiotic inactivation by Staphylococcus aureus nucleotidyltransferase 4′(ANT(4′)), a clinically relevant protein. According to our results, the ability of this enzyme to inactivate structurally diverse polycationic molecules relies on three specific features of the catalytic region. First, the dominant role of electrostatics in aminoglycoside recognition, in combination with the significant extension of the enzyme anionic regions, confers to the protein/antibiotic complex a highly dynamic character. The motion deduced for the bound antibiotic seem to be essential for the enzyme action and probably provide a mechanism to explore alternative drug inactivation modes. Second, the nucleotide recognition is exclusively mediated by the inorganic fragment. In fact, even inorganic triphosphate can be employed as a substrate. Third, ANT(4′) seems to be equipped with a duplicated basic catalyst that is able to promote drug inactivation through different reactive geometries. This particular combination of features explains the enzyme versatility and renders the design of non-inactivable derivatives a challenging task.

Under lock and key: A comprehensive analysis of substrate recognition by the aminoglycoside-modifying enzyme ANT(4′) has been performed. Our results highlight the dynamic character of the different drug complexes and provide insights into the subtle strategies employed by these proteins to achieve substrate promiscuity (see figure).

The presence of a disulfide bridge in liver bile acid binding protein (L-BABP/S-S) allows for site-selective binding of two bile acids, glycochenodeoxycholic (GCDA) and glycocholic acid (GCA), differing only in the presence of a hydroxyl group. The protein form devoid of the disulfide bridge (L-BABP) binds both bile salts without discriminating ability. We investigate the determinants of the molecular recognition process in the formation of the heterotypic L-BABP/S-S complex with GCA and GCDA located in the superficial and inner protein sites, respectively. The comparison of the NMR spectroscopy structure of heterotypic holo L-BABP/S-S, the first reported for this protein family, with that of the homotypic L-BABP complex demonstrates that the introduction of a S–S link between adjacent strands changes the conformation of three key residues, which function as hot-spot mediators of molecular discrimination. The favoured χ₁ rotameric states (t, g⁺ and g⁻ for E99, Q100 and E109 residues, respectively) allow the onset of an extended intramolecular hydrogen-bond network and the consequent stabilisation of the side-chain orientation of a buried histidine, which is capable of anchoring a specific ligand.

Site selectivity: NMR spectroscopy-derived structural data have been used to unravel the determinants of site-selective binding of liver bile acid binding protein. The presence of a disulfide bridge determines the χ₁ rotameric states of a few key residues (see figure), which function as hot-spot mediators of molecular discrimination.

Carbon nanomaterials (CNMs), such as exfoliated graphene (EG), long-chain functionalized EG, single-walled carbon nanotubes (SWNTs), and fullerene (C₆₀), have been investigated for their interaction with two structurally different gelators based on all-trans tri-p-phenylenevinylene bis-aldoxime (1) and n-lauroyl-L-alanine (2) both in solution and in supramolecular organogels. Gelation occurs in toluene through hydrogen bonding and van der Waals interactions for 1 and 2 in addition to π–π stacking specifically in the case of 1. These nanocomposites provide a thorough understanding in terms of molecular-level interactions of dimensionally different CNMs with structurally different gelators. The presence of densely wrapped CNMs encapsulated fibrous network in the resulting composites is evident from various spectroscopic and microscopic studies, indicating the presence of supramolecular interactions. Concentration- and temperature-dependent UV/Vis and fluorescence spectra show that CNMs promote aggregation of the gelator molecules, leading to hypochromism and quenching of the fluorescence intensity. Thermotropic mesophases of 1 are altered by the inclusion of a small amount of CNMs. The gel–CNM composites show increased electrical conductivity compared with that of the native organogel. Rheological studies of the composites demonstrate the formation of rigid and viscoelastic solidlike assembly due to reinforced aggregation of the gelators on CNMs. Synergistic behavior is observed in case of the composite gel of 1, containing a mixture of EG and SWNT, when compared with other mixtures of CNMs in all combinations with EG. This affords new nanocomposites with interesting optical, thermal, electrical, and mechanical properties.

Gelled together: Graphene and other nanocarbons were doped with two structurally different organogelators based on π ‒stacking and van der Waals interactions which determined their self-assembly behaviour (see figure) and brought about changes in the macroscopic behavior.

Sulfoxides are frequently used in organic synthesis as chiral auxiliaries and reagents to mediate a wide variety of chemical transformations. For example, diphenyl sulfoxide and triflic anhydride can be used to activate a wide range of glycosyl donors including hemiacetals, glycals and thioglycosides. In this way, an alcohol, enol or sulfide is converted into a good leaving group for subsequent reaction with an acceptor alcohol. However, reaction of diphenyl sulfoxide and triflic anhydride with oxathiane-based thioglycosides, and other oxathianes, leads to a different process in which the thioglycoside is oxidised to a sulfoxide. This unexpected oxidation reaction is very stereoselective and proceeds under anhydrous conditions in which the diphenyl sulfoxide acts both as oxidant and as the source of the oxygen atom. Isotopic labelling experiments support a reaction mechanism that involves the formation of oxodisulfonium (S-O-S) dication intermediates. These intermediates undergo oxygen-exchange reactions with other sulfoxides and also allow interconversion of axial and equatorial sulfoxides in oxathiane rings. The reversibility of the oxygen-exchange reaction suggests that the stereochemical outcome of the oxidation reaction may be under thermodynamic control, which potentially presents a novel strategy for the stereoselective synthesis of sulfoxides.

Sending out an SOS: The diphenyl sulfoxide/triflic anhydride combination is widely used as an activating agent for glycosylation reactions. However, oxathiane glycosyl donors are instead oxidised to sulfoxides in a stereoselective and reversible reaction. NMR spectroscopy and isotopic labelling experiments reveal the presence of oxodisulfonium (S-O-S) dication intermediates that can undergo oxygen exchange with other sulfoxides (see scheme).

Ferric–hydroperoxo complexes have been identified as intermediates in the catalytic cycle of biological oxidants, but their role as key oxidants is still a matter of debate. Among the numerous synthetic low-spin Fe^III(OOH) complexes characterized to date, [(L₅²)Fe(OOH)]²⁺ is the only one that has been isolated in the solid state at low temperature, which has provided a unique opportunity for inspecting its oxidizing properties under single-turnover conditions. In this report we show that [(L₅²)Fe(OOH)]²⁺ decays in the presence of aromatic substrates, such as anisole and benzene in acetonitrile, with first-order kinetics. In addition, the phenol products are formed from the aromatic substrates with similar first-order rate constants. Combining the kinetic data obtained at different temperatures and under different single-turnover experimental conditions with experiments performed under catalytic conditions by using the substrate [1,3,5-D₃]benzene, which showed normal kinetic isotope effects (KIE>1) and a notable hydride shift (NIH shift), has allowed us to clarify the role played by Fe^III(OOH) in aromatic oxidation. Several lines of experimental evidence in support of the previously postulated mechanism for the formation of two caged Fe^IV(O) and OH^. species from the Fe^III(OOH) complex have been obtained for the first time. After homolytic OO cleavage, a caged pair of oxidants [Fe^IVO+HO^.] is generated that act in unison to hydroxylate the aromatic ring: HO^. attacks the ring to give a hydroxycyclohexadienyl radical, which is further oxidized by Fe^IVO to give a cationic intermediate that gives rise to a NIH shift upon ketonization before the final re-aromatization step. Spin-trapping experiments in the presence of 5,5-dimethyl-1-pyrroline N-oxide and GC-MS analyses of the intermediate products further support the proposed mechanism.

Oxidation by Fe^III(OOH): Investigations on a genuine non-haem Fe^III(OOH) intermediate (see figure) in the presence of either aromatic substrates or the probe substrate [1,3,5-D₃]benzene has clarified the role played by Fe^III(OOH) in aromatic oxidations. Evidence for the formation of two caged Fe^IV(O) and OH^. species from Fe^III(OOH) has been obtained for the first time. These oxidants act in unison to give phenol products with normal kinetic isotope effects and notable hydride shifts.

Evidence for the existence of nitrile selenides, potential 1,3-dipolarophiles in cycloaddition reactions, has been provided by direct spectroscopic methods. The parent nitrile selenide, selenofulminic acid (HCNSe), and its methyl and cyano derivatives have been photolytically generated in an inert solid argon matrix from 1,2,5-selenadiazoles by 280, 254, and 313 nm UV irradiation, respectively, and studied by ultraviolet spectroscopy and mid-infrared spectroscopy. Ground-state geometries have been obtained from quantum-chemical calculations at the CCSD(T)/aug-cc-pVTZ level. Nitrile selenides are predicted to be linear with a relatively weak NSe bond.

Nitrile selenides (XCNSe, X=H, CH₃, CN) were photochemically generated in a low-temperature solid argon matrix and studied by UV and IR spectroscopies and quantum chemical calculations.

A unique class of oligothiophene-based organogelator bearing two crown ethers at both ends was synthesized. This compound could gelatinize several organic solvents, forming one-dimensional fibrous aggregates. From the observation of circular dichroism, it was confirmed that the helical handedness of the fibrous assembly is controllable by the chirality of 1,2bisammonium guests, thus suggesting that one guest molecule bridges two gelator molecules through the crown–ammonium interaction. Interestingly, we have found that such chirality is created by thermal gelation, whereas it disappears by thixotropic gelation. The new finding implies that the present organogel system is applicable as a reversible switching memory device, featuring memory creation by a heat mode and memory erasing by a mechanical mode.

Chiral memory switching: A unique class of functional organogelator based on crown ether appended oligothiophene was created, the chirality of which was influenced by the interaction with chiral ammonium guests. Stimuli-induced circular dichroism with controlled handedness of aggregates was observed. The reversibility of thixotropic/thermal behaviors can be applied to chirality switching memory devices (see scheme).

We demonstrate that the electronic structure of mesoporous silicon is affected by adsorption of nitro-based explosive molecules in a compound-selective manner. This selective response is demonstrated by probing the adsorption of two nitro-based molecular explosives (trinitrotoluene and cyclotrimethylenetrinitramine) and a nonexplosive nitro-based aromatic molecule (nitrotoluene) on mesoporous silicon using soft X-ray spectroscopy. The Si atoms strongly interact with adsorbed molecules to form SiO and SiN bonds, as evident from the large shifts in emission energy present in the Si L_2,3 X-ray emission spectroscopy (XES) measurements. Furthermore, we find that the energy gap (band gap) of mesoporous silicon changes depending on the adsorbant, as estimated from the Si L_2,3 XES and 2p X-ray absorption spectroscopy (XAS) measurements. Our ab initio molecular dynamics calculations of model compounds suggest that these changes are due to spontaneous breaking of the nitro groups upon contacting surface Si atoms. This compound-selective change in electronic structure may provide a powerful tool for the detection and identification of trace quantities of airborne explosive molecules.

Compound-selective changes in the electronic structure of mesoporous silicon have been observed upon adsorption of nitro-based explosive molecules. This selective response is demonstrated by probing the adsorption of two nitro-based molecular explosives (trinitrotoluene and cyclotrimethylenetrinitramine) and a nonexplosive nitro-based aromatic molecule (nitrotoluene) on mesoporous silicon by using soft X-ray spectroscopy (see figure).

The large tendency of catechol rings to adsorb on surfaces has been studied by STM experiments with molecular resolution combined with molecular-dynamics simulations. The strong adhesion is due to interactions with the surface and solvent effects. Moreover, the thermodynamic control over the differential adsorption of 1 and the nonanoic solvent molecules has been used to induce a new temperature-induced switchable interconversion. Two different phases that differ in their crystal packing and the presence of solvent molecules coexist upon an increase or decrease in the temperature. These results open new insight into the behavior of catechol molecules on surfaces and 2D molecular suprastructures.

Recognized strong adhesion and organization of catechols on surfaces has been used as a means to study the main parameters that control molecular self-assembly processes on surfaces, namely, the energetics (molecule/molecule, molecule/surface interactions) and thermodynamics (solvent effects) (see figure). This knowledge is used to establish temperature-induced switchable 2D supramolecular structures

Closed-shell contacts between two copper(I) ions are expected to be repulsive. However, such contacts are quite frequent and are well documented. Crystallographic characterization of such contacts in unsupported and bridged multinuclear copper(I) complexes has repeatedly invited debates on the existence of cuprophilicity. Recent developments in the application of Bader’s theory of atoms-in-molecules (AIM) to systems in which weak hydrogen bonds are involved suggests that the copper(I)–copper(I) contacts would benefit from a similar analysis. Thus the nature of electron-density distributions in copper(I) dimers that are unsupported, and those that are bridged, have been examined. A comparison of complexes that are dimers of symmetrical monomers and those that are dimers of two copper(I) monomers with different coordination spheres has also been made. AIM analysis shows that a bond critical point (BCP) between two Cu atoms is present in most cases. The nature of the BCP in terms of the electron density, ρ, and its Laplacian is quite similar to the nature of critical points observed in hydrogen bonds in the same systems. The ρ is inversely correlated to CuCu distance. It is higher in asymmetrical systems than what is observed in corresponding symmetrical systems. By examining the ratio of the local electron potential-energy density (V_c) to the kinetic energy density (G_c), |V_c|/G_c at the critical point suggests that these interactions are not perfectly ionic but have some shared nature. Thus an analysis of critical points by using AIM theory points to the presence of an attractive metallophilic interaction similar to other well-documented weak interactions like hydrogen bonding.

Mission critical: Bond critical points (BCP) in dimeric copper(I) complexes have been analyzed. The electron density and Laplacian in the BCPs are similar to those of the BCP in hydrogen bonds. The critical points show some shared character and are not completely ionic in nature (see figure). Electron density at the BCP is higher in asymmetrical dimers than in comparable symmetrical dimers.

Annular aggregation: Atomic force microscopy and the recently developed microsecond force spectroscopy are used to identify a new annular structure of human Islet amyloid polypeptide on negatively charged tantalum oxide, a substrate that has the same surface charge as cell membranes (see figure). Finally, an accumulation model is proposed to explain how annular aggregation is initiated and developed.

Synthetic solvent systems for the fine-tuned preparation of CdS nanocrystallites, active in visible-light photocatalytic hydrogen production, were studied. To control crystallite size and spectral properties, the CdS crystals were synthesised by using different solvent systems, containing a series of tetrabutylammonium amino carboxylate ionic liquids as the crystal-growth control agents. Six samples of CdS, all with similar physical and spectral properties, exhibited greatly varying photocatalytic activity, with the most active sample outperforming the least active one by almost 60 %. To rationalise this effect, the intermolecular interactions of the synthesis solvent system with the growing CdS nanocrystallites were characterised by using the Reichart betaine dye and the polarity scale. A correlation was observed between the values of the solvent system and the photocatalytic activity of the CdS nanocrystallite, suggesting that the hydrogen-bond-donating ability and/or dipolarity/polarisability interactions of the solvent system led to the preferential formation of active surfaces/surface sites on the CdS crystals.

Bipolar behaviour: The rate of hydrogen production photocatalysed by CdS was found to be dependent on the solvent system employed for the synthesis of the CdS nanocrystallites (see scheme). By using a solvatochromic approach, a correlation was found between the polarity of the synthesis solvent system and the photocatalytic activity of the CdS.

Efficient and mild: The selective monoallylation of 1,2-diols was successfully developed with Pd/Sn bimetallic catalysis in good to excellent yields. This process was carried out with high substrate tolerance under mild conditions (see scheme). The catalyst system achieved the quite high chemoselectivity even in the presence of a 1:1 mixture of the 1,2-diol and mono-ol.

Palladium is a key catalyst invaluable to many industrial processes and fine-chemical synthesis. Although recent progress has allowed the synthesis of Pd nanoparticles with various shapes by using different techniques, the facile synthesis of Pd nanocrystals and turning them into a highly active, selective, and stable catalyst systems still remain challenging. Herein, we report the highly selective one-pot synthesis of monodisperse Pd cluster nanowires in aqueous solution; these consist of interconnected nanoparticles and may serve as highly active catalysts because of the enrichment of high index facets on the surface, including {443}, {331}, and {221} steps. For the first time, carbon nanotube and γ-Al₂O₃ immobilized Pd cluster nanowires showed highly enhanced catalytic performance in the liquid-phase selective hydrogenation of cinnamaldehyde and gas-phase hydrogenation of 1,3butadiene relative to immobilized Pd icosahedra and nanocubes, as well as commercial Pd catalysts.

Power in the cluster: Monodisperse Pd cluster nanowires, which consist of interconnected nanoparticles (see figure), have been synthesized in aqueous solution and may serve as highly active catalysts due to the enrichment of high index facets on the surface. Carbon nanotube and γ-Al₂O₃ immobilized Pd cluster nanowires showed enhanced catalytic performance in hydrogenations reactions.

A series of rare-earth-metal–hydrocarbyl complexes bearing N-type functionalized cyclopentadienyl (Cp) and fluorenyl (Flu) ligands were facilely synthesized. Treatment of [Y(CH₂SiMe₃)₃(thf)₂] with equimolar amount of the electron-donating aminophenyl-Cp ligand C₅Me₄H-C₆H₄-o-NMe₂ afforded the corresponding binuclear monoalkyl complex [({C₅Me₄-C₆H₄-o-NMe(μ-CH₂)}Y{CH₂SiMe₃})₂] (1 a) via alkyl abstraction and CH activation of the NMe₂ group. The lutetium bis(allyl) complex [(C₅Me₄-C₆H₄-o-NMe₂)Lu(η³-C₃H₅)₂] (2 b), which contained an electron-donating aminophenyl-Cp ligand, was isolated from the sequential metathesis reactions of LuCl₃ with (C₅Me₄-C₆H₄-o-NMe₂)Li (1 equiv) and C₃H₅MgCl (2 equiv). Following a similar procedure, the yttrium- and scandium–bis(allyl) complexes, [(C₅Me₄-C₅H₄N)Ln(η³-C₃H₅)₂] (Ln=Y (3 a), Sc (3 b)), which also contained electron-withdrawing pyridyl-Cp ligands, were also obtained selectively. Deprotonation of the bulky pyridyl-Flu ligand (C₁₃H₉-C₅H₄N) by [Ln(CH₂SiMe₃)₃(thf)₂] generated the rare-earth-metal–dialkyl complexes, [(η³-C₁₃H₈-C₅H₄N)Ln(CH₂SiMe₃)₂(thf)] (Ln=Y (4 a), Sc (4 b), Lu (4 c)), in which an unusual asymmetric η³-allyl bonding mode of Flu moiety was observed. Switching to the bidentate yttrium–trisalkyl complex [Y(CH₂C₆H₄-o-NMe₂)₃], the same reaction conditions afforded the corresponding yttrium bis(aminobenzyl) complex [(η³-C₁₃H₈-C₅H₄N)Y(CH₂C₆H₄-o-NMe₂)₂] (5). Complexes 1–5 were fully characterized by ¹H and ¹³C NMR and X-ray spectroscopy, and by elemental analysis. In the presence of both [Ph₃C][B(C₆F₅)₄] and AliBu₃, the electron-donating aminophenyl-Cp-based complexes 1 and 2 did not sho