Angewandte Chemie International Edition

The recognition of tumors is possible through the dynamic formation of cyclic boronate esters between the diol moiety of the overexpressed marker sialic acid and a phenylboronic acid (pba) targeting vector. In their Communication on page 1161 ff., K. Djanashvili et al. demonstrate an MRI signal intensity enhancement at the tumor site as a result of the accumulation and prolonged retention of a Gd^III-dota-en-pba targeting contrast agent after its intravenous injection into a melanoma mouse xenograft.

Spin transitions in nanosized materials can be detected using a highly sensitive hybrid sensor, which combines anisotropic magnetoresistive and planar Hall effects. In their Communication on page 1185 ff., F. Terki, C. G. Kim, A. Bousseksou, and co-workers describe a prototype of the sensor and discuss its use for nanoscale magnetic measurements around room temperature. The picture shows an artistic view of the sensor, on which nanoparticles of a ferrous spin-crossover complex have been deposited.

The lifetime of quantum dots has been controlled by varying the geometrical configuration of quantum-dot–gold nanoparticle (AuNP) conjugates on DNA origami templates. In their Communication on page 1193 ff., J. A. Liddle et al. describe a strategy to manipulate quantum-dot lifetimes. Making measurements with a 3D single-molecule tracking system, which enables the DNA construct to be kept in its native state in solution, the size, number, and spacing of the AuNPs are found to be the critical factors.

3d transition-metal-ion coordination is crucial in many chemical processes and in the understanding of their reaction mechanisms. In their Communication on page 1170 ff. M. M. van Schooneveld, F. M. F. de Groot et al. show for cobalt(II) carboxylates that synchrotron-based 2p3d resonant X-ray emission spectroscopy (RXES) allows for a far more judicious determination of the metal-ion coordination environment than benchmark ultraviolet/visible (UV/Vis) and 2p X-ray absorption (XAS) spectroscopy do.

“My favorite author is Lao Tzu. What I look for first in a publication is the ‘flash’ that makes me think ‘a-ha’ …” This and more about Chao-Jun Li can be found on page 1082.

John Wiley & Sons, Hoboken, 2012. 336 pp., softcover, € 69.90.—ISBN 978-1118119969

For commercial viability new technologies for the sustainable generation of energy should be simple and efficient. Photoelectrodes made of boron arsenide are the latest advance: they can be synthesized easily directly from the elements and convert sunlight into electric current.

It's not magic! The effects observed in microwave-irradiated chemical transformations can in most cases be rationalized by purely bulk thermal phenomena associated with rapid heating to elevated temperatures. As discussed in this Essay, the existence of so-called nonthermal or specific microwave effects is highly doubtful.

Biomass is an abundant source of chemically diverse macromolecules. Much current effort is focused on the breakdown of these molecules into fuels or platform molecules. However, there is growing interest in using biopolymers directly to create nanostructured materials. It is highlighted how biopolymers are providing new directions in the synthesis of nanostructured materials.

Cholesterol (left-hand structure) is an essential component of lipid rafts, in which the biosynthesis of neurotoxic β-amyloid occurs. By blocking the synthesis of cholesterol, statins (right-hand structure: lovastatin) are able to decrease the amyloid load in the central nervous system and lower the risk of dementia and Alzheimer's disease. This behavior is strongly supported by the pleiotropic effects of statins on isoprenylation and neuroinflammation.

A chemically patterned surface was formed by controlled evaporative self-assembly of concentric polymer stripes, followed by the removal of weakly deposited polymer, giving ultrathin polymer stripes with a width gradient on the Si substrate (see picture). A thin film of diblock copolymer hierarchically self-assembled on the ultrathin polymer stripes, giving arrays of nanocylinders perpendicular to the surface of the film.

High-resolution photoluminescence spectroscopy employing Eu³⁺ as the structural probe unambiguously revealed a universal breakdown of crystallographic site symmetry in lanthanide-doped disordered crystals. The spectroscopic site symmetries of Eu³⁺ descend from crystallographic O_h to C_s (or C₂) in α-NaYF₄, and from crystallographic C_3h to C_s in β-NaYF₄, which were further verified by crystal-field level fitting.

Hole trapping: The hole transfer and trapping in a G-quadruplex has been investigated using laser flash photolysis and pulse radiolysis. The results show that the charge separation in the G-quadruplex takes place efficiently between riboflavin and G-bases because of the excellent hole-trapping ability of planar G-quartets.

The copper(II) ion coordination mode of Cu^II-Aβ(1–16) at physiological pH was characterized by 34 GHz pulsed ENDOR spectroscopy. ¹H/²H ENDOR and ¹⁴N ENDOR demonstrate the NH₂ terminus of aspartic acid is an equatorial ligand of Cu^II, and ¹⁷O ENDOR together with ¹H ENDOR suggest that water is an axial ligand (see picture; Cu pink, O red, N blue).

Branching out: The substrate specificity profiles for a range of ketosynthase (KS) domains from trans-AT PKSs are reported. Evidence is provided that a sterically demanding amino acid residue adjacent to the active-site Cys residue confers specificity towards non-β-methyl-branched substrates (see scheme).

Multimodal: Gold nanorods are coated with silica/polymer mutilayers, doped with surface-enhance Raman scattering (SERS) and fluorescence agents as well as photosensitizers. The structural and optical properties are tunable and stable in solutions and in living bodies. A real-time and specific in vivo SERS and fluorescence detection method using this structure is applied for tumor detection and subsequent photodynamic therapy (PDT).

Not always equal: When a mother cell that contains Au nanocages divides, the nanoparticles are unequally distributed between the two daughter cells. This unequal distribution of nanoparticles as well as their clearance from the cells (see picture) is quantitatively analyzed both in vitro and in vivo using two-photon microscopy and photoacoustic microscopy, respectively.

Dye-loaded periodic mesoporous organosilica particles functionalized with bioactive molecules were used for the generation of a nanocomposite alginate hydrogel. The affinity of cells was up to four times higher with the embedded particles than with simple alginate hydrogel, caused by both the nanometer-scale particle itself and its bioactive functionalization.

By design: The novel MRI reporter Gd^III-dota-en-pba (see picture) selectively binds to sialic acid residues, which are overexpressed on tumors. This imaging reporter accumulates in a murine melanoma B16-F10 mice xenograft and from the MRI signal intensity it is possible to quantify the sialic acid concentration that is directly associated with tumor malignancy.

Know when to fold 'em: Combination of a pH-triggered oligonucleotide conformational switch with fluorescent nanocrystals gives a sensitive pH nanosensor (see scheme). Analyte-dependent conformational changes control the distance between the nanocrystal energy donor (green) and a FRET acceptor (red), which results in a reporter for pH values in individual endosomes of living cells.

d–d excitations in detail: High-resolution 2p3d resonant X-ray emission spectroscopy (RXES) allows the observation of more as well as more intense d–d excitations than UV/Vis spectroscopy does as demonstrated on cobalt(II) carboxylates. Together with ligand field multiplet (LFM) calculations this allows their detailed electronic structure description, while 2p X-ray absorption spectroscopy (XAS) cannot discriminate these transition metal compounds.

Shine on: A new rational design strategy for near-infrared-emitting firefly luciferins that are available in vivo has been developed using intramolecular bioluminescence resonance energy transfer (BRET). The emission wavelength could be freely tuned by the choice of BRET acceptor, and NIR bioluminescence could be detected in living cells and mice without the need for luciferase manipulation.

A different light: The yellow electrochromic copolymer, propylenedioxythiophene phenylene P(ProDOT-Ph) is patterned by the micromolding in capillaries (MIMIC) process to fabricate line gratings. Under illumination by white light, colors are generated by diffraction and can be changed by applying an external voltage (see picture). The diffracted color is blue shifted by electrochemical doping, a process that is completely reversible.

Building a better SQUID: A prototype for a SQUID-like magnetometry device for the indirect detection of room-temperature switching in spin-crossover nanoparticles has been developed and used in the study of [Fe(hptrz)₃](OTs)₂ (hptrz=4-heptyl-1,2,4-triazole, OTs=p-toluenesulfonyl) nanoparticles, as a proof of concept for this novel micromagnetometry approach. The method provides significant benefits over conventional SQUID and nano-SQUID techniques.

DNA multiplication tables: A combinatorial mechanism for DNA strand displacement shares the same structure as matrix multiplication (see scheme). This system can be used to perform linear operations on DNA concentrations, such as the calculation of a weighted sum.

Single-molecule GPS: The average photon count rate and lifetime of a quantum dot (Qdot) have been controlled by varying the geometrical configuration of Qdot–gold nanoparticle (AuNP) conjugates on DNA origami. With a 3D real-time single-molecule tracking system, which allows the DNA templates to be kept in their native state in solution, the influence of AuNPs on the Qdot lifetime is determined (see picture).

Throw the switch: A new strategy for regulating spin crossover (SCO) properties by the control of an active guest molecule is proposed. As a proof of concept, maleic anhydride was incorporated into a microporous {Fe(pyrazine)[Pt(CN)₄]} framework material and chemically switched to maleic acid, thus modifying the SCO properties (see picture).

Efficient multiple-electron redox reactions are performed by galactoase oxidase, cysteine dioxygenase, sulfite reductase, and cytochrome c nitrite reductase. A post-translationally modified tyrosine–cysteine cross-link (Tyr-Cys) in their active sites is essential for their functions.

Staying alive: The major limitation of in-cell NMR spectroscopy methods is the occurrence of cell death during the NMR measurement. To overcome this problem, a bioreactor was utilized that can perfuse the cells in the NMR tube, thereby maintaining the conditions for more than 5 h. By using the bioreactor, the binding site of an externally introduced protein for an endogenous molecule in HeLa S3 cells was identified.

Three-way split: A postsynthetic click reaction has resulted in the conjugation of three bipyridine ligands at the core of a DNA three-way junction structure (see picture). Melting curve analyses revealed that Ni^II ions significantly stabilize the junction structure through the formation of a [Ni(bpy)₃]²⁺ complex which cross-links three strands. The metal complex shows a diastereomeric preference, thus indicating a chirality transfer from the DNA.

Single molecules: Large enhancements of single-molecule fluorescence up to 1100 times by using synthesized gold nanorods are reported (see picture). This high enhancement is achieved by selecting a dye with its adsorption and emission close to the surface plasmon resonance of the gold nanorods.

In a spin: The use of deuterated surface passivation agents is shown to restore dynamic nuclear polarization (DNP) surface-enhanced NMR signals that are reduced in substrates containing methyl groups, while still protecting sensitive sites on the surface (see picture). Furthermore, apolar groups such as [D₉]-trimethylsiloxy (TMS) repel radicals (yellow) away from the surface, thus diminishing detrimental paramagnetic effects induced by radical proximity.

Kinetic energy barriers that have entirely different origins are the reasons for the impedance of the catalytic N₂O/CO redox cycle mediated by both [YAlO₂]^+. and [Y₂O₂]^+. clusters (see scheme). While oxidation with N₂O is the bottleneck for [YAlO₂]^+., oxidation of [Y₂O₂]^+. with N₂O is possible, but reduction of [Y₂O₃]^+. by CO is prevented. This arises because of “doping” effects which can control local charges and spin distributions.

From the deep: The title actinomycete yielded three new abyssomicins J–L. The dimeric thioether J (see scheme) represents a unique example of a masked Michael acceptor with anti-TB properties. Mechanistic insights into the biosynthesis, biomimetic synthesis, stability, and biological mechanism of action of abyssomicins aid our understanding of, and prospects for the development of Michael-acceptor-based drugs.

A two-dimensional morphology characterizes the nanoflakes that are obtained in the bottom-up synthesis of a single-crystalline coordination polymer, Ni(H₂O)₂[Ni(CN)₄]⋅x H₂O. The 10 nm-thick nanoflakes are well-dispersed in solution and have a very high accessible surface area (240 m² g⁻¹). Thermal treatment leads to nanoporous NiO with retention of the original flake morphology.

Branching out: A simple and inexpensive cobalt/triarylphosphine catalyst promotes aldimine-directed hydroarylation of styrene with high branched regioselectivity to afford 1,1-diarylethane derivatives in good yields under mild reaction conditions. The ortho-formyl group in the hydroarylation products is amenable to dehydrative cyclization, to give fused polycyclic aromatic hydrocarbons, as well as decarbonylative removal.

Weak coordination is powerful! A Pd^II-catalyzed olefination of ortho-CH bonds of arenes directed by weakly coordinating ethers is developed by using monoprotected amino acid (MPAA) ligands. This finding provides a method for chemically modifying ethers, which are abundant in natural products and drug molecules. HFIP=hexafluoroisopropanol.

Hitting water with nanotrees: A three-dimensional branched heterojunction array for water oxidation based on cobalt-doped α-Fe₂O₃ nanorod cores and MgFe₂O₄ shells has been synthesized. Such an architecture not only has a large surface area and excellent light absorption properties, and shows fast charge transport, but also exhibits a very high photoelectrochemical activity for water oxidation and a high stability.

Organic–organic composite membranes are prepared by in situ crystallization of cage molecules in a polymer of intrinsic microporosity. This allows a direct one-step route to mixed-matrix membranes, starting with a homogeneous molecular solution. Extremely high gas permeabilities are achieved, even after ageing for more than a year, coupled with good selectivity for applications such as CO₂ recovery.

Alpha, beta, gamma: Allyl dienol carbonates (1) served as substrates for the title reaction to afford the furanones 2 in both high yields and high enantioselectivities. These furanones were eventually converted into valuable building blocks including γ-tertiary and γ-quaternary furanones (3) as well as β-quaternary butyrolactones (4). This method was used as a key step in the total synthesis of (−)-nephrosteranic acid and (−)-roccellaric acid.

Bimetallic: Upon irradiation with light in the phototherapeutic window, the bimetallic complex [(bpy)₂Os(dpp)RhCl₂(phen)]³⁺ binds to and cleaves DNA through an oxygen-independent mechanism. PCR is used as a model for in vitro DNA replication. The results show that the metal complex does not interfere with DNA amplification in the dark without O₂, but completely inhibits DNA amplification in samples exposed to red light. Taq=polymerase, PS=photosensitizer.

Cut to the chase: Direct formation of an enehydrazine, an intermediate in the classic Fischer indole synthesis, solves the regioselectivity problem associated with indolization. This approach not only achieves selective synthesis of indoles through proper selection of the vinyl halide, but also leads to quick construction of desoxyeseroline and esermethole, as well as the key structural motif in the Akuammiline alkaloid vincorine.

Hold the water: The hemicellulose fraction of lignocellulose can be converted into furfural in high yields (80 %) using solid acid catalysts (H-mordenite) in a monophasic system with γ-valerolactone (GVL) as the solvent. Furfural degradation reactions are decreased significantly when the water concentration in GVL is minimized, thus resulting in high furfural yields.

Equal and opposite: A chiral surfactant molecule was used to induce high enantioselectivity in the transformation from the achiral phase of mercury sulfide, probably through binding of the surfactant thiolate groups to Hg ions in the forming crystal. The generation of truly chiral inorganic nanocrystals of tailored size and shape should be useful for many applications, such as enantioselective catalysis and sensing.

Direct and selective: Supported gold–palladium nanoparticles are active for the oxidation of methane, giving a high selectivity for the formation of methyl hydroperoxide and methanol, using hydrogen peroxide as the oxidant (see picture). The optimal methanol selectivity is achieved by performing the reaction in the presence of hydrogen peroxide that has been generated in situ from hydrogen and oxygen.

Any old iron? Iron catalysts based on the widely available diphosphine ligand bis(diphenylphosphino)ethane have not previously fared particularly well in iron-catalyzed cross-coupling processes. However, this turns out not to be due to any inherently poor performance associated with the ligand, but rather the need to form a bis-chelate complex, either before or during the formation of an active Fe^I species.

Super bowl: Fragments of C₇₀ or higher fullerenes were easily prepared from 1,8-bis(arylethynyl)naphthalenes. The curved structures were identified by X-ray crystallography. These rigid bowl-shaped molecules have a deep bowl depth (approximately 2.30 Å) and their bowl inversions proceed via an S-shaped transition structure with a very high inversion barrier (approximately 80 kcal mol⁻¹).

Low-frequency vibrational modes of peroxo-bridged high-spin biferric complexes have been observed using nuclear resonance vibrational spectroscopy (NRVS; see picture, PVDOS=partial vibrational density-of-states) and assigned using DFT calculations. Correlations between the spectral features and the structure of peroxo-bridged cores form a basis for structural elucidation of enzyme–peroxo intermediates.

Tolerant: By using Pd(OAc)₂/PCy₃ as a catalyst, both electron-rich aromatic heterocycles and electron-deficient fluorobenzenes undergo the dehydrogenative cross-coupling with (hetero)aryl ethyl ketones in good yields. A broad range of functional groups is tolerated, thus providing a general method for the facile syntheses of chalcones or heterocyclic chalcone analogues. Furthermore, dialkyl ketones can also participate in this transformation.

Take a detour: An alternative pathway to synthesize isovaleryl coenzyme A (CoA) has recently been suggested in myxobacteria, which is highly active when leucine is limited. Each enzymatic step of this unprecedented route has now been characterized and a novel 3-methylglutaconyl CoA decarboxylase identified that has apparently evolved from CoA transferases.

Hooking up: Subunit γ of an F-ATPase with 11 point mutations was ligated chemically from six peptides and then reconstituted with further subunits of the (αβ)₃γ catalytic core complex. The biologically active protein with 286 residues currently represents the longest nonredundant polypeptide chain synthesized by chemical means. The yields of the five consecutive ligations, especially the last three, dropped the total yield to only 0.005 %.

High-spin hydrides: A new class of stable paramagnetic polyhydride complexes [M{Ru(μ-H)₃(PTol₃)₃}₂] (M=Cr–Ni) with an unprecedented trinuclear arrangement has been synthesized. The high-spin central 3d metal ion is sandwiched between six hydride ligands in a distorted octahedral fashion.

A guiding light is sufficient to switch back and forth between the flexible and the stretched, rigid form of a self-assembled coordination cage based on two square-planar-coordinated Pd^II ions and four ligands with a photochromic dithienylethene (DTE) backbone. The light-driven interconversion is clean and reversible and allows to control the encapsulation and release of the guest [B₁₂F₁₂]²⁻.

Only I and N: Hypervalent iodine(III) reagents with two reactive IN single bonds have been isolated for the first time. Their solid-state and solution structures provide evidence for enhanced electrophilicity at iodine and nucleophilic character of the imine. As a result, improved reactivity in amination reactions and unprecedented nitrogen-transfer reactions under metal-free conditions are realized.

Mobile: The title reaction affords diastereomerically pure 3,4-disubstituted pyrrolidin-2-ones, which are important structural motifs in natural products, in good to high yields. Mechanistic investigations suggest the transformation proceeds through a tandem 1,3-acyloxy migration and a subsequent 1,5-acyloxy migration. DCE=1,2-dichloroethane, IPr=1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene.