Articles in 2009

Many lab-on-a-chip applications use microarrays for the high-throughput screening of a range of materials, including biomolecules such as DNA and proteins, as well as living cells. To address some of the limitations of traditional printed microarrays, researchers have now developed robust hydrogel-based systems with thiol-ene chemistry that enables different covalent attachment strategies to be implemented in an orthogonal fashion.

Although molecular motors that ‘walk’ along tracks are common in biological systems, the only artificial analogues reported so far have been made from DNA. It has now been shown, however, that a synthetic small molecule with two ‘feet’ can take steps along a molecular track, and that the direction of movement can be biased under certain conditions.

The construction and operation of interlocked molecular machines often rely on the mutual recognition of different building blocks through a range of non-covalent interactions. Researchers have now shown that the versatility of bipyridinium systems can be increased by taking advantage of the complexes formed between their radical cations; with this approach they have been able to make electrochemically switchable bi- and tristable rotaxanes.

Chemists have very few tools at their disposal for controlling synthetic processes under physiological conditions. Now, a monomer has been prepared that oligomerizes in living cells under the control of various triggers (pH change, disulfide reduction and enzymatic cleavage), showing promise for imaging or therapeutic applications.

Two abundant feedstocks, dinitrogen and carbon monoxide, have the strongest bonds in chemistry, so breaking them is a significant challenge. An organometallic hafnium compound has now been shown to induce nitrogen cleavage on addition of carbon monoxide, with simultaneous assembly of new nitrogen–carbon and carbon–carbon bonds.

Many synthetic processes rely on the ability to selectively couple oxygenated molecules. Here a study of low-temperature selective cross-coupling of aldehydes with methanol on a gold surface is presented. The results allow the construction of a mechanistic model for such coupling reactions that will be applicable under a wide range of reaction conditions.

Combining the benefits of homogeneous and heterogeneous processes may lead to important advances in catalysis. This has now been achieved using selectively oxidized and supported electrophilic platinum nanoparticles that catalyse a range of π-bond activation reactions previously only catalysed homogeneously.

Both hydrogen and xenon form unusual phases at very high pressures. Researchers have now observed that an unexpectedly stable compound forms when a hydrogen-rich mixture of the two gases is subjected to pressures in the gigapascal range. Xenon dimers and other unusual bonding states are revealed in this compound, which is stable to megabar pressures.

When making nanoparticles it is often desirable to produce samples in which there is little variation in the size of the structures that are formed. Hollow self-assembled metal–organic cages have now been shown to be effective templates for the preparation of monodisperse silica nanoparticles, and may also prove useful for the controlled synthesis of nanoparticles from other materials.

An organic polymer scaffold has now been developed that can capture and release functionalized inorganic nanoparticles by the threading and de-threading of pseudorotaxane linkages. The capture–release cycles are reversible and programmable both chemically and electrochemically. In mixtures of different nanoparticles, the scaffold can capture one type selectively — thus acting as a selective nanoparticle ‘sponge’.

A cooperative reaction is reported whereby the halogenation of one silicon atom on a surface is shown to induce, invariably, halogenation of a neighbouring silicon. This is a first step towards using surface-propagated cooperative reactions to create molecular-scale patterns on surfaces.

Small alkanes are typically isomerized on tungstated-alumina solid-acid catalysts, but the origin of the activity has been unclear. Now, high-resolution imaging has revealed subnanometre Zr-WO_x clusters to be the active sites.

Copper-containing proteins can be classified into types 1 and 2, depending on their functional or spectroscopic properties. Now, a protein that fits neither type has been built using a scaffold made from the protein Pseudomonas aeruginosa azurin.

Complete chiral symmetry breaking of an amino acid derivative is achieved by circularly polarized light irradiation of a solution of the racemate in contact with racemic crystals, followed by abrasive grinding. The chirality of the amino acid derivative in the resultant crystals is fully determined by the rotation sense of the irradiation.

Small peptide-derived catalysts are shown to be effective in the enantioselective sulfonylation of polyols. The observation that, using closely related catalysts, enantiotopic alcohols can be phosphorylated or sulfonylated, raises questions about the details of catalyst–substrate recognition and, from a biomimetic standpoint, the role of histidine residues in enzyme active sites.

The development of molecules that target protein–protein interactions is one of the main goals of contemporary medicinal chemistry. Computational alanine scanning and molecular dynamics now leads to the identification of two peptide sequences that are important in microtubule assembly, and shows that the in silico activity can be translated into in vitro activity.

The properties of surfaces can be tailored by coating them with a thin film of molecules, for example by forming self-assembled monolayers. Now, researchers have shown how dynamic covalent chemistry can be used to reversibly pattern different compounds on to a surface with a high degree of spatial control to produce molecular gradients.

The ability to study structural changes of DNA in live cells is of considerable interest. Here, a dinuclear ruthenium (II) complex that acts as a multifunctional stain for DNA and its use in both luminescence and transmission electron microscopy studies is described.

Plastic solar cells contain a blend of conjugated polymer and fullerene electron-acceptor material that phase separates, resulting in the formation of heterojunctions. Improving the performance of these devices requires an understanding of the blend morphology. Now researchers show how a microwave-assisted synthesis method can be used to create structurally diverse copolymers enabling the investigation of their structure–function relationship.

Materials built from metal centres and organic ligands have traditionally attracted attention for their channels’ host–guest properties. Now, controlling the occupancy of the channels by guest molecules has resulted in a framework that conducts protons under anhydrous conditions and acts as a gas-tight membrane, offering a promising approach to fuel-cell electrolytes.