Volume 3 Issue 5, May 2011

Energetic adsorption of molecules on surfaces is known to either trigger local chemical reactions or initiate the recoil of adsorbates away from the surface. Now, another possible outcome has been observed — the long-range 'cart-wheeling' of energetic molecules across a surface.

Enzymes that selectively oxidize unactivated C–H bonds are capable of constructing complex molecules with high efficiency. A new member of this enzyme family is RedG, a Reiske-type oxygenase that catalyses chemically challenging cyclizations in the biosynthesis of prodiginine natural products.

There is a long history of gas-phase studies of bimolecular reactions, but the presence of surrounding molecules complicates analogous studies in solution. Now, advances in ultrafast laser technology have enabled the detailed study of vibrational energy release in a reaction in solution.

Heterogeneous catalyst systems comprising metals supported on oxides are widespread. Evidence now suggests that it is the interfacial regions that are most catalytically active, and this has been exploited to create a tandem nanocatalyst system.

Keeping the organic and inorganic precursors in separate, immiscible solutions guides the growth of metal-organic frameworks into uniform thin layers that are shaped just like the liquid-liquid interface.

Crystalline networks containing empty cavities can host a variety of molecules but also promote reactions between guests. Through robust crystallinity and a pseudo-solution state (dynamic movements) within their pores, these crystalline molecular flasks enable the direct observation of species — including unstable intermediates — during a reaction by in situ X-ray diffraction.

The creation of ‘smart surfaces’ that can act as switches or memory devices will rely on systems with bistable states that can be interconverted externally. Now, a low-voltage and robust surface-confined switch that transduces an electrical input into an optical and magnetic output is described.

The reaction of enols and enolates with electrophiles is used extensively in synthesis. Here, protein engineering — substituting amino acid residues in an enzyme active site — is used to produce biocatalysts for the control of enolate chemistry. The adapted enzymes enable stereoselective C–C bond formation yielding N-heterocycles in high diastereomeric excess by the reaction of trisubstituted-enolates.

The development of high-performance ‘smart’ catalysts will rely on the rational design of nanoscale metal–metal oxide interfaces. A tandem catalyst that has both CeO₂-Pt and Pt-SiO₂ interfaces is now reported, and is capable of catalysing sequential reactions to convert methanol into ethylene.

Organolithiums are the prototypical nucleophilic reagent, but the direct use of them as nucleophiles in catalytic asymmetric synthesis has been problematic. Long sought after, conditions have now been identified that allow the highly enantioselective catalytic formation of C–C bonds by a direct S_N2′ reaction of organolithiums with allylic halides.

The intrinsically hybrid nature of metal–organic frameworks (MOFs) — microporous crystalline solids composed of metal ions and organic ligands — has been exploited to grow thin MOF films at the aqueous–organic interface of a biphasic reaction mixture. These materials exhibit selective permeability and can also be obtained as hollow capsules that have potential as microreactors.

Enzyme-mediated oxidative cyclizations in nature are a powerful demonstration of the utility of selective C–H activation. Here, Rieske oxygenase-like enzymes RedG and McpG are shown to mediate regio- and stereodivergent carbocyclization of undecylprodigiosin to streptorubin B and metacycloprodigiosin, respectively. Understanding these remarkably selective C–H activations could inspire the design of biomimetic catalysts with similar capabilities.

Crystal growth in nature is controlled by biomolecules to produce precisely engineered crystal shapes. Now, facet-specific peptide sequences that have been rationally selected through a biomimetic evolution process are used as regulating agents for predictable synthesis of platinum nanocrystals with selectively exposed crystal surfaces.

The recoil of adsorbates away from and towards surfaces is well-known. Here, long-range recoil in the plane of the surface, which leads to reaction at a distance, is described. Surface reactions are shown to propel their physisorbed ethylenic products across the rough surface of Si(100) by up to 200 Å before re-attachment.

Macromolecules with antimicrobial properties are promising materials for combating multi-drug-resistant microbes. Now, it has been shown that amphiphilic cationic polycarbonates that are biodegradable can self-assemble into micellar nanoparticles that can kill gram-positive bacteria, MRSA and fungi efficiently, even at low concentrations. Moreover, no significant toxicity is observed during in vivo studies in mice.

Although it is mainly known for its toxicity, beryllium possesses an array of properties that makes it attractive for a variety of non-industrial purposes. Ralph Puchta discusses why it is not always best avoided.