Chemistry - A European Journal

Intensely fluorescent azobenzene derivatives, featuring an intramolecular N–B interaction that was confirmed by X-ray crystallographic analyses, emit intense green, yellow and orange fluorescence. Their application to fluorescent vital stain visualization of living tissues was investigated by microinjection into Xenopus embryos, suggesting they are nontoxic towards the embryos. For more details see the Full Paper on page 5026 ff.

Self-discrimination ofS- and R-valine-derived bis(2-hydroxyphenyl)diamides in an ensemble of eight structurally related molecules showcase their specific aggregation through the hydrogen-bonding network of the bis(2-hydroxyphenyl)diamide framework. For more details, see the Full Paper by M. Shibasaki, N. Kumagai et al. on page 5036 ff.

Edible chemicals? A rapidly expanding area of chemical research is the use of plant biomass for the industrial production of useful organic compounds, for which there is high demand. Among the most challenging targets are simple halocarbons, alkenes, and arenes. This article highlights those targets that have been accessed recently by using biomass-derived materials as the source.

Pore genius: A nanoporous composite of graphite felt and polyaniline was developed and used as the anode of a microbial fuel cell, resulting in an order of magnitude increase in power output. The hierarchical conductive anode is a promising strategy for constructing highly efficient microbial fuel cells (see figure).

Good to excellent enantioselectivities (up to 99 % ee) of trans-cyclopropane derivatives were achieved in the cyclopropanation of alkenes with tert-butyl α-diazoacetate by using 0.5 mol % of a mononuclear chiral ruthenium aqua complex containing the chiral bis(oxazolinyl)phenyl ligand, which was obtained via CH activation by RuCl₃⋅3 H₂O in the presence of Mg and cyclooctadiene (cod). Intramolecular cyclopropanation reactions using the new Ru complex also proceed with high yields and excellent enantioselectivities.

Suzuki–Miyaura coupling: We disclose a new strategy for phenol activation in the first Suzuki–Miyaura coupling of phenol derivatives activated by forming aryl bis(2-oxo-3-oxazolidinyl)phosphines as a highly efficient and broadly applicable methodology for the diverse synthesis of biaryls and heterobiaryls (see scheme). The use of readily available, stable NiCl₂/dppp as the catalyst system also provides an important advance.

An efficient route toward functionalised cyclic ethers: Computational mechanistic analysis indicates an operative LnO σ-bond insertion mechanism with a turnover-limiting cyclisation for the intramolecular hydroalkoxylation of allenyl alcohols (see scheme).

Core in cage: By using a DFT-based basin-hopping method, we found putative global minima for three gold sulfide nanoclusters, observed in mass spectrometry, that all show a symmetric core-in-cage structure: a metallic Au core inside a cage with S as vertices and Au at the edges (see figure). This core-in-cage structure is distinct from bulk gold sulfide. This work fills the knowledge gap regarding the structure of gold sulfide nanoclusters of ≈1 nm.

A perfect fit! The cavity of a chiral binuclear Ni^II complex recognises enantiomers of amino alcohols by recognising three different groups around the chiral carbon through non-covalent interactions (see scheme). The recognised enantiomer is recoverable from the cavity by metathesis with KNO₃. Optical rotation of the isolated amino alcohol shows the enantiomer separation (ee) is 87 % in the first step and 100 % after metathesis.

Overruled! The self-assembly of a novel group of fused donor–acceptor molecules (1) comprising hexaazatriphenylene and tetrathiafulvalene branches was studied by STM at the liquid/solid interface. A 2D assembled chiral porous network with C₃ symmetry was found, which is dictated by strong interactions of the extended π-conjugated cores of the fused units with the HOPG substrate overruling the directional forces of alkyl chains.

Lithium sensing made easy: A turn-on fluorescence sensor for Li⁺ can be generated by dissolving readily accessible starting materials in a buffered aqueous solution. The sensor allows the detection of Li⁺ in the sub-millimolar concentration range.

Phosphotyrosine sensing: By using the luminescence from binuclear complexes of Tb^III, phosphorylated Tyr residues in peptides (see picture) were selectively detected in neutral aqueous solutions. These binuclear complexes were successfully used for real-time monitoring of enzymatic phosphorylation of a peptide by a tyrosine kinase.

What intense fluorescence! Several 2-borylazobenzenes have been synthesized. They emit intense green, yellow, and orange fluorescence (see picture). The 4′-siloxy derivative shows the highest fluorescence quantum yield ever reported for an azobenzene.

Self-help: Specific self-discrimination of valine-derived bis(2-hydroxyphenyl)diamides (S)- and (R)-1 a in an ensemble of eight structurally related molecules showcases the specific aggregation through the hydrogen-bonding network of the bis(2-hydroxyphenyl)diamide framework.

Update your memory! A hybrid organosilyl/-germyl Keggin polyoxotungstate was covalently grafted to an n-type silicon wafer (see figure) and the electrochemical behavior of the thus modified electrode was investigated.

Getting it together: In a noncoordinating solvent, spontaneous assembly occurs to form a tetrameric array from meso–meso-linked diporphyrins, and a dodecameric porphyrin square from L-shaped meso–meso-linked triporphyrins (see graphic). Efficient excited-energy transfer (EET) between the meso–meso-linked Zn^II–porphyrin units was revealed.

Weak, but strong enough: Weak CH hydrogen-bond donors are strong enough to control the position of anions on top of electron-deficient aromatic systems, which leads to the observation of asymmetric (η¹–η³) and symmetric (η⁶) anion–π complexes (see picture).

A reversible movement (5.672 Å) of a lattice DMF molecule from the channel of a 3D porous coordination polymer to the Mn^II center to substitute the bound aqua ligand has been observed in a single-crystal to single-crystal fashion (see figure). Depending upon bulkiness of guest molecules, either full or partial substitution takes place at the Mn^II center and the 3D channel.

It's a trap! By using deprotonated forms of Kemp's triacid as anionic building blocks that provide a system of carboxylate groups converging toward a tetrahedral or octahedral void in a crystalline environment, four or eight proximal guanidinium ions have been entrapped within it, respectively (see figure).

Electrons favor cytosines: Dinucleoside phosphate deoxycytidylyl-3′,5′-deoxyguanosine and deoxyguanylyl-3′,5′-deoxycytidine systems are investigated, and the exploration of electron attachment to these ssDNA subunits (see figure) brings us closer to reliably predicting the electron affinities of ssDNA. The results suggest that forming base-centered radical anions in ssDNA might be a pathway to either NC glycosidic bond rupture or CO σ bond breakage.

Mechanically induced chemistry: The mechanically induced reduction of a disulfide bond consists of the motion of electron pairs and a series of proton transfers. Car–Parrinello molecular dynamics simulations (see figure) reveal the elementary reaction steps of such a condensed-phase reaction.

Bichromophore photochemistry: A comparative femtosecond transient absorption study on the dichromophoric phototrigger 3′,5′-dimethoxybenzoin diethyl phosphate (DMBDP) and two reference compounds shows the governing role of inter-chromophore electronic interactions in determining the photophysics and photodeprotection pathway of DMBDP in acetonitrile (see figure; DMBF=dimethoxybenzofuran). This reveals a novel concerted deprotection–cyclization mechanism.

A versatile core: Heteroheptacenes containing thiophene and/or pyrrole rings (see picture) are shown to have structural, optical, and electrochemical properties that vary considerably depending upon the substitution of the alkyl and heterole components.

Explore your chemical senses! Water-soluble imidazolium-based squaraines have been successfully employed as fluorescent bioimaging reagents by controlling their aggregation tendencies in aqueous media (see figure). This type of squaraine can further serve as an Fe²⁺-selective sensor based on the reaction between squaraine and a hydroxyl radical.

Cool structures: The Li argyrodites Li₇PS₆ and Li₇PSe₆ and their solid solutions undergo temperature-dependent phase transitions. The respective high- (HT) and low-temperature (LT) modifications were analysed by means of X-ray and MAS-NMR methods. Special emphasis was put on the site preferences of the S/Se distribution in the solid solutions and the disorder/order of Li atoms in the HT and LT modifications.

Tandem double intramolecular hydroalkoxylation/cyclization processes for dialkynyl dialcohol substrates mediated by homoleptic [Ln{N(SiMe₃)₂}₃] lanthanide amido precatalysts exhibit a broad reaction scope in substrate type, including both alkyl and aryl primary and secondary terminal dialkynyl dialcohols and internal dialkynyl dialcohols (see scheme).

From allene to indene: Catalyzed by BF₃⋅OEt₂, the reactions of vinylidenecyclopropanes with bis(p-alkoxyphenyl)methanols lead to indene derivatives as diastereomeric rotamers by a novel cationic 1,4-aryl migration (see scheme). Mechanistic insights could be gained by means of DFT calculations.

Favoring medium-sized rings: Rh^I-catalyzed carbonylative [2+2+1] cycloadditions and cycloisomerizations of 1,n-bis(sulfonylallene)s (n=4–6) easily afford bicyclo[n.3.0]alkadienones and monocyclic compounds containing two vicinal exo-methylene moieties, respectively (see scheme; m=0–2). These reactions are characterized by [1,3]- or [1,5]-H shifts and are suitable for medium-sized ring construction.

Fine threading: A novel ultrathin β-SiC nanowire structure (see figure) has been prepared through a 1,10-phenanthroline-assisted molecule template route. Stable and strong green light emission at 500 nm and superior field emission with a low turn-on field and large current density are observed.

Simplicity does not mean inefficiency! The Pd(OAc)₂-catalyzed Heck reaction of aryl diazonium salts with 2-arylacrylates led to cis-stilbenes with good to excellent stereoselectivity. This sustainable protocol features low palladium loading in methanol at room temperature under ligand- and base-free conditions. The stereoselectivity experimentally observed for the synthesis of cis-stilbenes has been rationalized by DFT calculations.

Totally adsorbing! Detailed experimental neutron diffraction studies combined with computational investigations reveal where and how methane is adsorbed in MOFs with exceptionally high methane uptake. In addition to the open metal coordination sites, accessible small cages/channels in these MOFs are found to play a big role in storing methane (see figure).

Good storage: Cobalt ion-based coordination polymer nanowires (see figure) were synthesized by using nitrilotriacetic acid (NA) as a chelating agent by a one-step hydrothermal approach, which can be converted into porous Co₃O₄ nanowires with good lithium storage properties.