Angewandte Chemie International Edition

A fast and easy DOSY screening of ligands that affords high enantioselectivities in catalysis allows the aggregation trends of their transition-metal complexes to be predicted. In their Communication on page 2794 ff., R. Gschwind and co-workers present the first aggregation study of selected phosphoramidites and their complexes. This method is useful for catalyst optimization as no knowledge of the complex structure is necessary and the temperature range applicable to the desired catalytic reaction can be quickly determined.

Atoms at work!MoS₂–based nanocatalysts are used for the hydrodesulfurization processes in oil refineries. In their Communication on page 2708 ff., S. Helveg and co-workers demonstrate how the nanocatalysts can be imaged with single-atom sensitivity by using recent advances in high-resolution transmission electron microscopy and that the atomic arrangement of the nanocatalysts can be visualized. Picture courtesy of P. Møller and S. Nygaard, Haldor Topsøe A/S.

John Wiley & Sons, Hoboken 2009. 3824 pp., hardcover € 489.00.—ISBN 978-0471704508

Smart catalysts for new materials: A syndiospecific yttrium catalyst that operates by a chain-end-control mechanism enabled the highly alternating ring-opening polymerization of a mixture of two different enantiomerically pure 4-substituted β-propiolactones of opposite absolute configuration (see scheme). This strategy offers access to original sequentially controlled poly(β-hydroxyalkanoate)s.

Specific stimuli can be used to trigger the release of cargo encapsulated in polymer carriers in applications ranging from drug delivery to catalysis. Current approaches can be categorized in two classes: application of an external stimulus, such as light, and exploitation of environmental changes, such as chemical and enzymatic degradation (see picture).

Sulfone groups play a significant role in asymmetric organocatalysis, which has become a powerful tool for the synthesis of optically active compounds. Sulfones have become important substrates in organocatalysis because of their ability to generate both nucleophilic and electrophilic reaction partners, and because they serve as a precursor to many functional groups (see scheme; E=electrophile).

A marked profile: Various methods have been developed in the field of proteomics and metabolomics in recent years to understand the action and function of proteins and small metabolites in organisms. These methods enable the identification of the targets of natural products in complex proteomes, the characterization of protein activity, and the determination of the function of specific metabolites.

Noble decoration: DNA origami nanostructures (purple) were utilized as spatially addressable templates to organize noble-metal nanoparticles of silver (yellow balls) and gold (red ball) into well-defined discrete architectures (see examples of nanostructure designs and TEM images of the assembled structures).

Pickpocket: Perylene can be detected by inorganic–organic nanomaterials comprising ZnO nanorods (gray cylinder) and perylene diimide derivatives (red rectangle). Intercalation of perylene (yellow rectangle) in a molecular pocket at the inorganic–organic interface results in fluorescence quenching of the three components with a detection limit as low as 10⁻¹² M.

Close up: The atomic arrangement of industrial-style MoS₂ nanocatalysts can be scrutinized by using single-atom-sensitive electron microscopy (see picture). This technique, which provides an excellent agreement between simulation and experiment, allows element detection in compound materials and permits the type and the concentration of the catalytically important edge sites to be estimated.

The best of three worlds: Gold nanorods coated with poly(styrene-alt-maleic acid) (see picture; pink), the photosensitizer indocyanine green (black), and antibodies (green “Y”) serve not only as photodynamic therapy and hyperthermia agents to destroy malignant cells, but they also act as optical contrast agents to simultaneously to monitor cells by imaging in the near-IR region.

Anyone for pi? The vinylborane PhHCCH-B(C₆F₅)₂ reacts with zero-valent Group 10 transition-metal precursors to form η³-vinylborane complexes. The platinum tri-tert-butylphosphine complex exhibits an η³-borataallyl-like coordination mode whereas the nickel bis(triphenylphosphine) complex tends towards alkyl/borataalkene coordination.

Not bad at all: A simple biological circuit composed of two integrated molecular switches was developed for the detection and amplification of a specific nucleic acid in a biological extract. The nucleic acid is recognized by a molecular beacon, then a DNA polymerase and nicking endonuclease are used to rapidly amplify the signal for sensitive detection of the nucleic acid.

More than skin-deep: Synthetic skin-permeable antigens are constructed by conjugation of the cell-penetrating low-molecular-weight protamine (LMWP) peptide to protein antigens through cleavable disulfide bonds. Such artificial antigens can penetrate the stratum corneum barrier (see picture), thereby sensitizing the skin immune system to elicit robust immune responses.

Michael and Mannich cooperate: A rapid and reliable approach to highly functionalized chiral isoindolindone and azetidine derivatives, possessing multiple contiguous stereogenic centers, has been achieved (see scheme).

Without affecting the overall 3D structure, amide-to-ester backbone substitution (or ester scan) exerts a pronounced influence on the conformational equilibrium of the RGD cyclopeptide cilengitide and its derivatives (see figure; RGD=Arg-Gly-Asp). The appropriate substitution, which stabilized the receptor-complementary conformations, improved the biological activity of this integrin antagonist.

A healthy glow: Fluorogenic peptide nucleic acids (PNAs) functionalized with indoline derivatives are used to specifically sense G-quadruplex formation. Upon hybridization of both PNAs to the single-stranded flanking arms of quadruplex DNA (see scheme), the synthesis of a trimethine cyanine dye is templated. Dye formation can be detected by the appearance of a characteristic fluorescence signal.

Three is not a crowd: A method for the construction of imidazopyridine, imidazoquinoline, and imidazoisoquinoline frameworks has been developed. The synthetic utility of this method was demonstrated in a highly efficient one-pot synthesis of the drugs alpidem and zolpidem (see scheme).

Triple play: The title reaction of 1 with simple aldehydes gives 3,5,7-trisilyloxy aldehydes in high yields and diastereoselectivities with extremely low catalyst loading (see scheme). Iodobenzene facilitates the third aldol reaction by apparently acting as a Lewis base towards the silyl catalyst. Tf=trifluoromethanesulfonyl.

On your bi(cycle)ke! A series of 1,4-dimethyl bicyclic [2.2.2] diene ligands with tunable substitution at the bridge positions was accessed using a lipase resolution and a high yielding six step sequence (see scheme). The bridgehead methyl groups improve efficiency allowing less aryl boronic acid to be used in the title reaction.

Defying conventional wisdom: Ionic liquids (ILs) with long, unsaturated alkyl appendages (see top structure) defy established trends that link long ion-bound alkyl groups to higher melting points. The new ILs are also less viscous than a saturated standard (see bottom structure) at the same temperature. These features parallel those that underpin homeoviscous adaptation in certain organisms and are indirectly supportive of a fluid-mosaic-like nanoscale character.

Do the Maca-Rhena: Although there are many known stable metallabenzenes that contain a late transition metal, there are no examples of the direct observation of metallabenzenes that contain an early or middle transition metal. The isolation and structural characterization of air-stable rhenabenzenes 1 and 2 (see scheme) are reported.

Click it in: Forth and fifth generation dendrimers (see structure), bearing 30 and 62 azobenzene chromophore moieties, respectively, are conveniently prepared in satisfactory yields through a combination of divergent and convergent approaches by using the powerful Sharpless “click” reaction.

Côte d'Azole: The title reaction demonstrates the use of diverse oxazoles 2 as suitable substrates in cross-coupling reactions with azole-5-carboxylic acids 1 under palladium catalysis in the presence of copper carbonate. The reaction is successful for the synthesis of a range of bis(azole)s, and has been applied to the convergent synthesis of challenging poly azoles (dcpe=bis(dicyclohexylphosphino)ethane, DMSO=dimethyl sulfoxide, M.S.=molecular sieves).

Towards perfect asymmetric catalysis: When binol-derived N-spiro quaternary ammonium salts were used as phase-transfer catalysts in the conjugate addition of nitroalkanes to chalcones and its analogues, an intriguing reversal of enantioselectivity was observed. Novel chiral catalysts have been designed and synthesized (see structure).

Wiry frame: Manganese-doped cadmium selenide (Mn-CdSe) colloidal nanowires (see picture) exhibit ferromagnetism and good conductivity without any changed to their optical properties. The nanowires are synthesized by a novel solution–liquid–solid approach that offers a low-cost route towards magnetically active quantum wires with excellent potential applications in electronics, photonics, and spintronics.

Branching out: A new ruthenium(IV) complex (1), containing a P,O-chelating ligand, is an efficient precatalyst for regioselective allylations starting from various allylic alcohol derivatives.

Hyper-reactive: A highly reactive, fully fluorinated hypervalent iodine reagent (see formula) mediates new transformations (e.g. the one-pot conversion of sulfides to sulfoximines) and serves as a stoichiometric oxidant in well-established reactions (e.g. C–C bond cleavage and the conversion of alcohols into aldehydes).

Thermal decarboxylation of 1-phenylpyrazolium-3-carboxylates from the mesomeric betaine class of substances leads to pyrazole-N-heterocyclic carbenes, which immediately rearrange to multiply substituted 4-aminoquinolines (see scheme). These species are of interest for the synthesis of heterocycles and pharmacologically active compounds.

DOSY awakening: The aggregation trends of phosphoramidite transition-metal complexes, which can catalyze highly enantioselective reactions, can be predicted by a DOSY NMR screening of the free ligands (see picture). This method is valuable for catalyst optimization as no structural knowledge of the complexes is required.