Articles in 2010

Discrete metal–organic polyhedra are usually prepared from metal ions and organic linkers by a direct self-assembly approach in solution. Now, using the polyhedra themselves as starting materials, it has been shown that a wider variety of structures can be obtained through the partial or complete substitution of their linkers.

Monodentate ligands with complementary hydrogen bonding units can self-assemble to form pseudo-bidentate ligands. Here, a combinatorial approach to the synthesis and analysis of reactions using these ligands allows the rapid identification of the most suitable ligand pair for highly selective rhodium-catalysed asymmetric hydrogenation.

The phosphoric acid fuel cell is limited by its slow rate of oxygen reduction at the cathode, but now an approach to the rational design of improved catalysts for this process has been developed. Molecular patterning of platinum surfaces with cyanide adsorbates is used to block the adsorption of spectator anions without hindering oxygen reduction, thus improving catalytic activity.

A detailed understanding of solute–solvent interactions is crucial to appreciating the important role aqueous ions play in various biological and catalytic processes. Now soft X-ray spectroscopy reveals new features in aqueous ion spectra that are due to solute–solvent interaction and electron transfer.

Catalytically oxidizing water to produce oxygen is so challenging that even the enzyme that performs the task in nature must be regenerated every 30 mins. Now, stable oxygen-evolving anodes have been made by tethering a polyoxometalate catalyst to a conducting bed of carbon nanotubes.

Aqueous lithium-ion batteries have great potential as stationary power sources, but they have had problems with poor stability. A significant improvement in their cycling stability has been achieved by eliminating oxygen, adjusting the electrolyte pH values, and using a carbon-coated electrode material.

Kinetic resolution — which relies on the difference in reaction rates of isomers — is most often used in the context of separation of stereoisomers. Here, a self-assembling container molecule is used to protect certain guest molecules from the bulk reaction medium and effect a resolution of constitutional isomers.

The structure of many natural products can often only be confirmed by comparison with a synthetic sample. Here, scanning probe microscopy techniques allow the ultimate discrimination between structures suggested by the standard range of analytical techniques, proving the power of single-molecule imaging for molecular structure determination.

Magnesium hydride is a potential hydrogen-storage material, but its use is hampered by its high stability and slow hydrogen sorption processes. Dimeric magnesium compounds can act as models for these materials, and it is now shown that they can be easily and reversibly hydrogenated across the magnesium–magnesium bond.

The structural diversity of natural products offers great potential for the identification of new drugs. Here, the gene cluster responsible for the production of a meroterpenoid, pyripyropene, has been identified, and reconstitution of the biosynthetic sequence involved allows the production of analogous synthetic structures with potentially new bioactivity.

The cortistatins have attracted a lot of attention in the synthetic community because of their interesting biological activity. Here, four of the cortistatin family are prepared from a common precursor. This efficient synthesis will assist in an investigation of structure–activity relationships and understanding of the biosynthetic route to these compounds.

The wealth of solution-chemistry properties of a well-known M₆L₄ coordination cage can be transferred into the solid state by networking the cage into a highly porous crystalline structure. The material behaves as a ‘fullerene sponge’, absorbing up to 35 wt% of C₆₀ or C₇₀ into the crystal, with a preference for C₇₀ when exposed to mixtures of the two.

A series of chiral metal–organic frameworks with channels of tunable size have been modified through post-synthetic functionalization to bear catalytic centres along their pore walls. The resulting materials catalyse a carbon–carbon-bond-forming reaction, and the enantioselectivity of the transformation can be altered by changing the size of the channels.

Tetrathiafulvalene (TTF)-based [3]catenanes are shown to display multiple stable redox states dominated by TTF···TTF radical dimer interactions occurring within the cavity of what is essentially a ‘molecular flask’. These stabilizing interactions are found to be the basis of a novel recognition motif that can be employed to drive molecular switching under redox control.

Interlocked molecules commonly include one (or more) monocyclic component — examples comprising bicyclic or tricyclic structures are much more rare and usually involve metal–ligand coordination or additional templates. Now, the dynamic self-assembly of twenty organic molecules in a one-pot synthesis has been shown to produce tetrahedral covalent cages, which interpenetrate during the process to form triply interlocked dimers.

In nature, enzymes can orchestrate the combination of several different catalytic species, but mimicking this with synthetic catalysts is often problematic due to undesirable interactions between the catalysts. Here, an N-heterocyclic carbene and a Lewis acid cooperate to catalyse the efficient formation of γ-lactams.

Whereas synthetic DNA nanostructures are widely studied, the use of RNA as a structural building block is much less common. Now, it has been shown that tRNA molecules can be designed to assemble into a rigid and thermally stable square antiprism structure that may prove useful for delivery applications inside cells.

Steps are known to be important sites on the surface of heterogeneous catalysts. Now it is shown that the density of steps on a palladium surface can alter its stability, and thus reactivity, and is key to understanding the oscillatory behaviour of the CO oxidation reaction at atmospheric pressure.

The interactions of metal ions with metaloxo species are crucial in many important biological processes, such as the oxygen-evolving complex (OEC) in photosystem II, but their exact function remains elusive. Now, the binding of metal ions to a non-haem oxoiron complex has been studied and the observed changes to its electron-transfer properties provide insights into the active site of the OEC.

The chemistry of the U≡N species is little known, even though solid uranium nitride has been proposed for use as a nuclear fuel. Now, photolysis of a uranium azide complex has been shown to release N₂ and generate a transient U≡N fragment that can activate C–H bonds.