Angewandte Chemie International Edition

Alternatives to the structure of Hittorf phosphorus were predicted a few years ago, and these have now been confirmed experimentally as phosphorus nanorods. A. Pfitzner, H. Eckert, and co-workers report on page 4228 ff. that these new allotropic forms of phosphorus can be isolated from the adduct compounds (CuI)₈P₁₂ and (CuI)₃P₁₂ by extraction with an aqueous cyanide solution. The nanorods have been characterized by high-resolution TEM and ³¹P magic-angle spinning NMR spectroscopy.

A catalytic option: Tertiary amines are converted into the corresponding α-amino nitriles in the presence of hydrated ruthenium trichloride (5 mol %), sodium cyanide (1.2 equiv), and molecular oxygen (see scheme). This is a valuable alternative to the Strecker synthesis of α-amino nitriles and can be used to prepare N-aryl glycine derivatives and unsymmetrical 1,2-diamines.

Dots in cells: Recent advances in the use of functionalized semiconductor quantum dots in bioimaging, from cancer studies to blood-flow monitoring, are described. The image shows a mouse fibroplast labeled with two different sizes (and therefore two different colors) of CdSe/ZnS quantum dots.

A spectrum of unusual features: N₂O reduction is accomplished in biology by an active site consisting of a μ₄-sulfide-bridged tetranuclear copper cluster (the Cu_Z center), which has many unusual spectroscopic features. Recent studies have led to electronic-structure descriptions of resting Cu_Z, its catalytically relevant form, and elucidated the role of Cu_Z in N₂O activation and reduction (see scheme).

A rational improvement of rhodium/iridium-catalyzed olefin oxygenation by dioxygen or hydrogen peroxide requires more detailed insight into underlying mechanisms and ligand effects (see scheme). In this Review, results from model studies are related to known catalytic systems, and differences between rhodium/iridium- and palladium-catalyzed olefin oxidation are discussed.

Make mine a triple: The tetraphenyl phosphonium salts of [(CF₃)₃BCX]⁻ (X=P, As) are stable even well above room temperature. The synthesis of these first phospha- and arsaethynyl complexes of boron from (CF₃)₃BCO is carried out in two steps (see scheme). The complex [(CF₃)₃BCAs]⁻ is the first stable anionic arsaalkyne.

Classical feeding experiments indicate involvement of nonribosomal peptide, polyketide, and isoprenoid biosynthesis in the formation of the myxobacterial antibiotic leupyrrin (1). The resulting structural elements are modified further (e.g. by a semipinacol-like rearrangement and oxidative formation of a methylene bridge) to yield the unique leupyrrin framework.

Platinum dumbbells: The reaction of platinum nitrate with concentrated sulfuric acid at 350 °C leads to the deep red oxide–sulfate (NH₄)Pt₃O₂(SO₄)₃, in which six [Pt₂]⁶⁺ dumbbells are linked by oxide ions and sulfate groups to the novel cluster anion [Pt₁₂O₈(SO₄)₁₂]⁴⁻ (see picture). The structure of the core of this anion matches exactly the recent prediction for dodecanuclear complexes built from six metal dumbbells.

An enzymatic amplification cycle is used in a novel detection scheme for scanning electrochemical microscopy (SECM). An immobilized enzyme system comprising galactosidase and PQQ-dependent glucose dehydrogenase was imaged by SECM with high sensitivity and high lateral resolution. PQQ=pyrroloquinolinequinone.

A novel concept for triggering conformational transitions, and thus changes in structure and function, in peptides with a switching element S provides intriguing perspectives for studying molecular processes (see scheme) that play a key role, for example, in early events of Alzheimer's disease.

A motion breaking with tradition: The cis–trans isomerization of nonpolar conjugated π systems does not proceed simply by the 180° twist of a CC bond (“one-bond flip”, OBF), but by the rotation of a central CH group out of the plane (“hula twist”, HT). The hula-twist motion does not require any external constraint but is driven by an internal force: the slope on the way through a conical intersection.

Divide and conquer: A novel approach was used to separate solvent effects from the intrinsic interactions involved in the association of biological complexes (see figure). The enthalpy of solvent reorganization for the formation of an intermolecular hydrogen bond in a biomolecular complex was determined by comparing the solution and gas-phase stabilities of structurally related complexes.

Robo copper: A mechanically robust corrugated sheet, 1 DOP-Cu, is composed of mats of individual chain-bundles joined by π–π interactive forces (see structure). Upon electrochemical charge injection into 1 DOP-Cu, the variations of the cell parameters of the Li-inserted phase were observed by X-ray diffraction. The mechanical deformation of the whole sheet is produced by a Cu^II/Cu^I redox process.

Pressing a rubber stamp inked with carboxylic acids onto an amine-terminated surface leads to the formation of amide bonds at room temperature (see scheme). Oligopeptides were created on the surface in this way from a monolayer. This rapid and uncatalyzed formation of amide bonds is attributed to the nanoscale confinement of the molecules between the stamp and the preorganized monolayer substrate. PDMS=poly(dimethylsiloxane).

A masked combination chemotherapy which relies on the embedding of a number of active components, in a latent form, within a single endoperoxidic chemical entity is the aim of the research presented. The approach is illustrated by means of purposely designed bicyclic endoperoxide prodrug prototypes 1 and subsequently validated through the study of model compounds 2 (Ar=Ph, p-FC₆H₄, p-ClC₆H₄).

Out of the blue: A reversible temperature-dependent change in the absorption characteristics of spin-coated terephthalic acid/diacetylene polymers is observed. The polymer is prepared by topochemical photopolymerization of the diacetylene side chains of the stacked terephthalic acid units (see picture). The absorption bands of the polymeric product move reversibly from 640 nm (blue form of the polymer) to 580 nm (red form) during heating–cooling cycles.

First among unequals: Equal CC bond lengths, as found in benzene, are not necessary for aromaticity. [18]Annulene is the next Hückel monocycle where D_6h symmetry is possible topologically (see picture). However, this widely accepted structure of [18]annulene is not correct. The ¹H NMR chemical shifts and energy computations show that [18]annulene prefers CC bond-length alternation and C₂ symmetry.

The five crucial steps in the first total synthesis of (+)-scyphostatin from D-arabinose involve (see picture): a) stereoselective aldol coupling to form a quaternary stereocenter, b) ring-closing metathesis (RCM) to construct the cyclohexene ring, c) Negishi coupling for the preparation of the fatty acid side chain, d) amide formation to connect the cyclohexene and fatty acid segments, e) stereospecific epoxide-ring formation.

Opportunities with silver: A dinuclear silver(I) compound was found to efficiently catalyze the intramolecular amidation of saturated CH bonds of carbamates and sulfamates (see scheme). This highly regioselective, stereospecific reaction offers a practical method for the construction of cyclic nitrogen-containing organic molecules.

Higher capacity rechargeable batteries can be constructed by using mesoscale nickel hydroxide tubes as the positive-electrode material. The tubes were prepared by deposition of nickel ions and aqueous ammonia in an anodic alumina membrane as the template. The picture shows a high-resolution TEM image of the tubes.

The folding/unfolding of a protein structure has been studied through measuring the donor–donor energy migration between two fluorescent probes (F) coupled selectively to the N termini of the homodimeric DsbC protein (see picture). The fluorometric strategy provides a convenient and reliable method to investigate conformational changes in dimeric proteins.

A phosphinoyl radical leaving group in the β position is a key feature of a new Ti^III-mediated domino radical cyclization/β elimination reaction of vinylic phosphine oxides, which affords alkylidenepyrrolidines in good yields (see scheme).

A common bicyclic intermediate was used in an efficient strategy towards lepadins B, D, E, and H shown. These alkaloids are members of a family of natural products with diverse biological activity. The described total syntheses of lepadins D, E, and H enabled the full elucidation of their configuration.

An attractive alternative to the currently existing methods for the metal-catalyzed oxidation of sulfides to sulfoxides is asymmetric iron-catalyzed oxidation with hydrogen peroxide as the terminal oxidant (see scheme). In the presence of a benzoic acid derivative, this simple process provides sulfoxides with up to 96 % ee in moderate to good yields (up to 78 %).

Extracting the P: Two novel amorphous allotropes of elemental phosphorus that consist of polymeric chains (see example depicted) were obtained in a pure form by extraction from their copper iodide adducts with an aqueous solution of potassium cyanide. ³¹P NMR spectra and high-resolution TEM images suggest that the structure of these phosphorus nanorods is unchanged after extraction.

Exclusive coupling: High turnover numbers were attained in the dehydrogenative coupling reaction between C(sp²) and C(sp³) atoms. A zirconium catalyst mediates the coupling reactions of heterocyclic arenes and lactams exclusively at the carbon atom adjacent to the nitrogen atom of the latter under an oxygen atmosphere (see scheme).