Angewandte Chemie International Edition

Microstructured reactors such as the SuperFocus Interdigital micromixer offer an alternative to conventional large-scale techniques. Flow patterns with reduced layer thicknesses lead to enlarged reactive surfaces that result in short mixing times, and thus high-throughput reactions can be achieved. In their review on page 406 ff. K. Jähnisch, V. Hessel, et al. examine the potential of this new and powerful technology.

The direct route. Low-temperature experiments and calculations on the ring expansion of (1-methylcyclobutyl)fluorocarbene, which involves considerable movement of the heavy nuclei, indicate that tunneling through the barrier is more favorable than the classical route over the “mountain pass” (see picture).

Increased stability of oxidation catalysts results from the self-assembly of the catalysts under near-turnover conditions from oxidatively resistant precursors. The described polyoxometalate epoxidation catalyst uses a green oxidant (H₂O₂), solvent, and separation conditions and is fast, selective, and safe. This self-assembling system is an important step towards truly green catalysis (see scheme).

Good things come in small packages: The reduced dimensions of microstructured reactors offer many advantages in chemistry, particularly with respect to enhanced conversion, selectivity, and safety. This Review presents a discussion of the process parameters and the design of such reactors, which are crucial to their development and optimization.

Iron muscles into mussels: Marine mussels adhere to rocks with a protein-based glue. An iron complex is the key curing agent in this adhesive, and the iron center is coordinated by three DOPA residues (see picture). These studies present the first identified case in which a transition-metal center is integral to forming a noncrystalline biological material.

Blocking the path to cancer: Application of efficient strategy for a phenotype-based screening of compound libraries to a library of sulindac-derived compounds (see scheme) yielded new inhibitors of the tumor-relevant Ras signal transduction pathway with high fidelity (as shown by microscopy). The results underline the advantage of using biologically prevalidated compound classes in chemical biology research.

Tracking down the target: The biological targets of eight new Ras-pathway inhibitors were investigated. Several of the compounds were shown to inhibit the RasGTP–Raf interaction (see example shown) and NMR data strongly suggest that this inhibition is the result of direct interaction between the inhibitors and the Ras protein. An inhibitor with a target probably downstream of MAP kinase was also found.

Charge control as a tool for assembly: Dense layers of individual, charged nanocrystals are formed at the aqueous/organic interface upon a slight reduction of the surface charge. The layers are remarkably robust, they creep up the glass (see picture). This method should be widely applicable to a broad range of charged colloids and will lead to the production of new materials.

Contrary to popular belief, the redox chemistry of Cr–catecholato complexes [Cr^III(cat)₃]³⁻ has been shown by X-ray absorption spectroscopic data to be predominantly metal-based and not ligand-based. The observed increase in the energies of the edge and pre-edge features of the spectra (see picture) and the decrease in the CrO bond lengths on oxidation are consistent with the formation of [Cr^IV(cat)₃]²⁻ and [Cr^V(cat)₃]⁻, both with a strong electron delocalization between the metal ion and the ligands.

A templating method is used to create conductive polymers that have a helical superstructure. The driving force is an electrostatic interaction between the negative charge in a synthetic lipid and the cationic charge generated in the polymers during oxidative electrochemical polymerization of ethylenedioxythiophene (EDOT) and a pyrrole (see picture; CV=cyclic voltammetry).

Computer modeling methods predict that the natural zeolite laumontite will undergo pressure-induced hydration. Specifically, the water-poor analogue “leonhardite” transforms to the fully hydrated laumontite structure (see picture), a transformation with significant geochemical impact. The models and methodologies employed are also capable of replicating the observed dehydration behavior of laumontite.

Imprismed metals: Hydrothermal crystallization of Fe and Co oxalates from extremely concentrated KBr solutions yield a coordination network where the paramagnetic metal ions are in rare coordination geometries (see structure). Both materials show a strong 1D magnetic character and for the Fe^II derivative no long-range order is seen above 2 K, making it a candidate for a Spin 2 quasi-1D quantum antiferromagnet.

Odd compounds: The study of bimetallic complexes spanned by linear carbon chains was mainly restricted to even-numbered chains. The fluorodesilylation of silylated propargylidynes now provides a range of C₃-spanned heterobimetallic complexes based on Ru and either Mo or W (e.g. see picture).

A real step-saver! In a one-step procedure for the synthesis of bicyclic amidines, the azido group is used directly as the nucleophile in the ring-forming reaction. Many functionalized and chiral bicyclic amidines were synthesized in good yield under mild reaction conditions.

Ionic liquids obtain firm support: Polymer-supported imidazolium salts are shown to be highly efficient catalysts for fluorination and other nucleophilic substitution reactions. The polystyrene-based ionic materials catalyze fluorination reactions (such as that shown in the scheme; X=BF₄, OTf) in very high yield, and can be reused for many such reactions.

Exceedingly large, planar porphyrin systems composed of 49 non-hydrogen nuclei in highly delocalized π systems display exceptionally low-energy transitions in UV/Vis/NIR spectroscopy and in cyclic voltammetry. The spectra shown are for cis palladium complex depicted and the corresponding trans isomer

A versatile organometallic intermediate, an alkenyloxazoline–titanium complex, has been developed that enables one-pot multicomponent diastereoselective and asymmetric coupling processes to be achieved in a remarkably efficient manner (see scheme).

Activity-based enzyme acylation: Although small peptides are specifically cyclized by nonribosomal peptide cyclases (thioesterases, TEs) in nature, artificial N-acetylcysteamine thioester (SNAC) mimics have often failed to act as substrates for these enzymes in vitro. However, new reactive peptidyl aromatic thioesters solve this problem by selective acylation of the enzyme active site (see scheme).

An integrated approach for detecting proteins that is low-cost, portable, battery-operated, and works under field conditions such as direct sunlight has been developed. The “POCKET immunoassay” uses commercially available components, and exhibits an analytical performance approaching that of established bench-top techniques. It may be appropriate for the diagnosis of infectious diseases, such as HIV/AIDS, in developing countries (see picture).

Stable, deep-blue neutral radicals [(Me₃SiN)P(μ₃-NtBu)₃{μ₃-Li(thf)}₃X] (X=Br, I) with distorted cubic structures are obtained by the oxidation of [{Li₃[P(NtBu)₃(NSiMe₃)]}₂] with halogens in THF (see picture). The cubes comprise the radical dianion [P(NtBu)₃(NSiMe₃)]^.2−_, two Li⁺ ions, and a molecule of LiX. Solvation in very dilute THF solution releases (thf)₃LiX and generates the cyclic radical monoanion [(Me₃SiN)(tBuN)P(μ-NtBu)₂Li(thf)₂]^.−.

Oligopeptides with heterogeneous backbones, i.e., oligopeptides containing more than one monomer type, may be a fruitful source of new foldamers. This conclusion was suggested by studies on oligomers comprising L-α-amino acid and cyclic β-amino acid residues in a sequentially alternating pattern, which are shown to display helical secondary structure in solution.

With as few as seven residues, acyclic α/β-peptides, which consist of alternating units of (L)-alanine and of cis-β-aminocyclopropanecarboxylic acids (cis-β-ACCs, see structure), form stable 3₁₃-helix turns in solution. The configuration of the cis-β-ACCs was found to be crucial for the helical structure of this new class of foldamers.

High yields and enantioselectivities are obtained in a dynamic kinetic asymmetric transformation in which the CO bond of alcohols, silyl ethers, and acetals are substituted by a CC bond. For example, the racemic indanyl silyl ether 1 is converted into (S)-2 in the presence of the chiral Lewis acidic Ti^IV complex 3.

Interfaces of supported metal nanoparticles, in particular the metal–support interface, are still very difficult to characterize. Since magnetic properties are strongly correlated to structural properties, ferromagnetic resonance spectroscopy can be used (see picture). The high sensitivity of the method is demonstrated for processes at both the particle–gas and the particle–support interface.

Self-assembled monolayers of both aliphatic and aromatic thiols can be produced with no apparent contact-angle hysteresis by a modified “template-stripping” method. Organothiol solutions serve as splitting reagents for the removal of the mica from the gold surface. These new ultrasmooth SAM surfaces (see the AFM image) provide new information on interfacial properties including wetting and adhesion.