Angewandte Chemie International Edition

The innate stability of the extraordinarily reactive and enantioselective reagent [{(R)-(−)-DTBM-segphos}CuH] (whose structure is shown in the cover picture) is revealed in the Communication by Lipshutz and Frieman on page 6345 ff. Although there have been many advances in ligand-accelerated catalysis of hydrosilylations, these reactions invariably require the preparation of the catalyst prior to use owing to their limited shelf-life. This new reagent represents the first asymmetric “CuH in a Bottle”.

A direct hit! The asymmetric 1,3-dipolar cycloaddition of azomethine ylides (from imines A; EWG=electron-withdrawing group) and electrophilic alkenes B using chiral metal complexes in substoichiometric amounts provides a direct stereoselective synthesis of pyrrolidine or proline derivatives. The successful ligand/metal cation couples are rationalized on the basis of recently published results.

A question of potential! Clean reduction by dissolving base metals can be effected by employing redox catalysts of appropriate oxidation potential. The traditional use of aromatic hydrocarbons as redox catalysts has now been expanded by application of Me₃Fe^IILi and related ate complexes. The scheme shows, for example, the catalytic cycle for the reductive cleavage of phenylsulfonamides with magnesium.

Engineering on the nanometer scale: Nanoscale control over surface properties is of paramount importance in bottom-up approaches to nanofabrication, which will revolutionize nanoelectronics and biotechnology in the near future. Self-assembled monolayers can form an ideal platform for nanofabrication on silicon oxide (see picture). Their formation, derivatization, and patterning are discussed.

The first representative of the tridehydrobenzenes that could be spectroscopically characterized and isolated in cryogenic matrices is 1,2,3-tridehydrobenzene. Comparison of the measured IR spectrum with high-level ab initio calculations allows the assignment of a ²A₁ ground state to this unusual radical.

Joining the jet set: High-resolution, pure rotational spectra are obtained from a supersonic jet of TeSe prepared by laser ablation. The spectra give access to the internuclear potential, electronic structure (see picture), and details of the chemical bond of the first intermetallic ³Σ compound observed by microwave spectroscopy.

Fighting Anthrax by recognizing its coat: The spores of Bacillus anthracis bear unique oligosaccharides on their surface for interaction with a host. These specific oligosaccharides may prove useful in the development of vaccines against this major biowarfare threat. The total synthesis of such a vaccine candidate (see picture, Pent=4-pentenyl) is reported.

A split decision: Efficient heterolytic hydrogen splitting is achieved with novel tetracoordinate rhodium(I) amides. This reaction is reversible, and DFT calculations imply that the cleavage is a one-step process with a relatively low activation barrier. Ketones and imines are hydrogenated by the amide complexes without the need for further additives.

The filled/filled repulsion model can be used to explain qualitatively the trends in the acidity of the coordinated NH groups, the redox potentials of the amides, and the UV/Vis absorptions in different aggregates between a counter cation, [M(solv)_n]⁺, and the first stable diamido rhodate(1−) anion (see structure and space-filling model), which was synthesized by using the tetradentate diamino diolefin ligand (S,S)-trop₂dpen.

Outstanding in the electric field: Bundles of helical peptides undergo stochastic switching in response to the applied bias polarity as observed by STM. This behavior results from a conformational change between the α-helical (left) and 3₁₀-helical (right) states and affects the overall helix length. The interaction of the helical dipole moment with the applied electric field determines the preferred conformation of the peptides.

Building bridges: α-Conotoxins (C1–C3, C2–C4 disulfide pairing) adopt a globular conformation, whereas χ/λ-conotoxins (C1–C4, C2–C3 disulfide pairing) fold into a ribbon conformation. Amidation of the peptide C terminus has been shown to influence the folding (see picture) and hence the biological activity of conotoxins.

Heme recognizes genes: As a step towards the electronic control of reading DNA code at a molecular level, heme and DNA recognition can be linked through protein folding (see picture). Through the conversion of an engineered DNA-binding cytochrome into a heterodimer, the sequence-specific DNA recognition can be controlled by heme recognition and the oxidation state of the iron center.

New binding sites: Calcium(II) binding to the dimeric protein S100A13 triggers key conformational changes, thus creating two symmetrical copper(II)-binding sites between the helices of the monomers (see picture). These solvent-exposed binding sites are unique among the S100 proteins.

Bottled for freshness: [{(R)-DTBM-segphos}CuH] (see formula; DTBM=3,5-di-tert-butyl-4-methoxy) generated in situ represents the first reported copper hydride reagent that can be stored and used over time without loss of activity in several types of asymmetric hydrosilylation reactions.

Structural perfection up to the fifth generation of a polyphenylene dendrimer has been achieved by inserting p-terphenyl spacers into the arms of each branching unit (see picture). The stiff, monodisperse macromolecules with diameters up to 22 nm were synthesized in a stepwise manner, during which the topology of the branching units was controlled. Dendrimers containing up to 1368 phenyl rings with high porosity were generated.

The arrangement of the spins of adjacent helical cobalt–oxygen chains that form the backbone of the framework (see figure) of a microporous coordination polymer lead to metamagnetic behavior. When the polymer is heated, the metal center loses a coordinated water molecule and alters its coordination geometry from octahedral to square-pyramidal, although the framework remains stable.

Tasty tubes: Multiwalled carbon nanotubes functionalized with fluorescein isothiocyanate and amphotericin B (AmB) have been shown to be rapidly internalized by mammalian cells (see picture) without the toxic effects typically displayed upon treatment with AmB. Furthermore, the modified drug exhibits a higher antifungal activity than native AmB.

Bridging the gap: Heterogenized Shibasaki's binol/La catalyst is synthesized by a self-supporting strategy through the reactions of multitopic ligands with La(OiPr)₃ (see picture). The catalyst shows high activity and enantioselectivity, and can be reused in the asymmetric epoxidation of α,β-unsaturated ketones.

Natural not always best: Novel N-aryl urea and thiourea derivatives of dihydrocinchona alkaloids serve as efficient catalysts for the asymmetric addition of dimethyl malonate to a range of nitroalkenes. Catalytic activity and selectivity depend strongly on the relative configuration at C8/C9. Catalysts with “non-natural” inverted configuration at C9 display excellent activity and enantioselectivity at loadings as low as 0.5 mol %.

From amber to red: The water-soluble polythiophene derivative 1 forms a supramolecular complex with ATP (adenosine triphosphate) through electrostatic and hydrophobic cooperative interactions which results in a color change of the aqueous solution from yellow to pink-red (see photo; AMP/ADP=adenosine mono-/diphosphate). Besides naked-eye detection of ATP, the detection limit may be extended to 10⁻⁸ M by using fluorometry.

Pattern formation: Analysis with an array of differential receptors such as 1 rather than specific receptors leads to patterns for various proteins and glycoproteins that can be examined by principal component analysis. This allows for the direct recognition of large substrates for which the creation of synthetic specific receptors would be very difficult.

The heavy cyclopropene analogues 1H-siladigermirene R₄SiGe₂ (1 a) and 1H-trigermirene R₄Ge₃ (1 b) have been obtained, and the X-ray crystal structure of 1 a shows that it forms an isosceles triangle with a highly trans-bent endocyclic GeGe bond (bending angle 51.0(2)°). The interaction of 1 a and 1 b with CH₂Cl₂ unexpectedly affords the unusual four-membered-ring compounds 2 a and 2 b as a result of ring expansion (see scheme: E=Si, Ge; R=SiMetBu₂).

Hydrolytic enzymes: The marine planctomycete Rhodopirellula baltica DSM 10527 displays high stereo- and enantioselective alkyl sulfatase activity towards (±)-sec-alkyl sulfates with retention of configuration through cleavage of their SO bond (see scheme; pathway B), whereas inversion of configuration is observed upon cleavage of the CO bond (pathway A).

My stars! Star polymers that contain otherwise incompatible acid or base catalysts, such as para-toluenesulfonic acid or 4-(dialkylamino)pyridines moieties, at their sterically restricted cores (see scheme) are readily prepared. Homogeneous catalysis using these star polymers can perform reaction cascades in the same pot and is demonstrated with an acid-catalyzed deprotection and the nucleophilic amine-catalyzed Baylis–Hillman reaction.

Happy couples: A new hybrid technique, capillary electrophoresis combined with online detection through electrothermal atomic absorption spectroscopy, allows the study of metal speciation and metal–biomolecule interactions, important aspects of metallomics. Advantages include complete sample introduction, nanoliter sample and reagent consumption, real-time detection, high sensitivity, and low cost.

Conductive polypyrrole (Ppy) nanowires (see picture) can be grown from single adsorbed synthetic polyelectrolyte molecules by oxidative polycondensation of pyrrole. The location and length of the Ppy nanowires are defined by the location and length of the adsorbed single-molecule templates. The diameter of the Ppy nanowires varies from a few to hundreds of nanometers and can be adjusted by varying the reaction conditions.

A flexible host: The use of pyridyl-substituted cyclotriveratrylene ligands coupled with geometrically accommodating silver centers has resulted in the isolation and structural characterization of a compact [M₂L₂] molecular capsule and an [M₄L₄] tetrahedral prism (see structure). The former incarcerates two coordinated CH₃CN molecules while the latter has an unusual star-burst shape and also acts as host for CH₃CN molecules.

Overall charge unchanged: Disulfide bonds in gaseous polypeptide cations can be cleaved efficiently by ultraviolet photodissociation (UVPD) at 157 nm (see scheme). Unlike electron-capture dissociation, UVPD cleaves SS bonds without overall charge reduction in the product ions. This cleavage is suggested to be a result of electronic excitation caused by the absorption of photons of 7.9 eV.

Blueprints for an inhibitor: The de novo molecular design program SPROUT was used in conjunction with the X-ray crystal structures of the bacterial enzymes DdlB and VanA to produce a novel enzyme-selective inhibitor template. Following short and efficient synthesis and in keeping with the design predictions, the resulting inhibitor showed useful levels of enzyme-selective inhibition.

Interconversion of organonitrogen oxides: Nitrosyl, nitrosoalkane, and hydroxylamido(1−) ligands are interconverted on an organoruthenium platform (see structure and scheme). These stepwise and sequential reactions provide insights into the mechanism of the biological nitrite–ammonia interconversion, a major process in the inorganic nitrogen cycle in which nitric oxide, nitroxyl, and hydroxylamine have been invoked as intermediates.

The tail end: The Rh-catalyzed selective functionalization of commercial linear low-density polyethylene (LLDPE) with boron reagents is demonstrated. Subsequent oxidation and transformations of the boron-containing polymer yields materials that contain a variety of polar functionalities, such as hydroxy, amino, and formyl groups, at the termini of the side chains (see scheme).

Sun sensitivity: A charge-transfer sensitizer with an ion-complexing moiety formed by oxyethylene side groups (see picture) is used in a solid-state dye-sensitized solar cell. Lithium coordination to the dye backbone produces under realistic conditions photovoltages of nearly 900 mV and efficiencies of 3.8 %.

Four-gone confusion! An assembly of four N-confused porphyrinatosilver(III) subunits (see structure; N blue, Ag olive-colored, C silver/red) placed on the perimeter of a cyclic structure that comprises two silver(I) ions is effectively formed from a bis(N-confused porphyrin) free base and a silver(I) salt.