Volume 2 Issue 9, September 2010

It might come as a disappointment to some chemists, but just as there are uncertainties in physics and mathematics, there are some chemistry questions we may never know the answer to either, suggests Fredric M. Menger.

The first thing that comes to mind about uranium is certainly not its similarity to iron. Chemists have now shown that the two have a lot in common.

The aggregation of proteins into fibrils plays a crucial role in neurological conditions such as Parkinson's disease. Further insight into fibril formation has now been gained that reveals the effect of hydrophobic surfaces, including air.

Interlocking molecules in solution usually requires recognition motifs that direct the assembly of the building blocks. Triply interlocked catenanes have now been constructed just relying on the interpenetration of structures typical of the solid state and slow reversible covalent bond formation.

A highly basic gold catalyst has been shown to mediate the reaction of aromatic C–H bonds with carbon dioxide. The reaction provides a potential method of fixing atmospheric carbon dioxide and producing valuable chemical products.

The oxygen-evolving centre in the protein complex photosystem II involves Ca²⁺ within a high-valent oxomanganese cluster, but the role of Ca²⁺ has yet to be clarified. Interestingly, the electron-transfer behaviour of a non-haem oxoiron(IV) complex has now been found to be significantly altered by Lewis acid metal-ion binding to the oxo atom.

Aerosol particles are crucially important to the chemistry of the atmosphere, influencing both climate and air quality. This Review discusses progress in understanding the radical-initiated heterogeneous oxidation of atmospheric aerosols, focusing on the reaction mechanisms and kinetics, and also their effects on the physico-chemical properties of particles.

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.

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.

A Lewis-acid-catalysed 1,3-dipolar cycloaddition provides rapid access to a variety of substituted spirooxindoles. Initial cellular evaluations supports the view that compound collections based on natural-product-inspired scaffolds constructed with complex stereochemistry, and decorated with assorted substituents, will be a rich source of compounds with diverse bioactivity.

Although intermetallic compounds and alloys feature metal atoms bonded solely to other metal atoms, this motif is unusual in molecular compounds. Now, three compounds with lanthanide metals surrounded by transition metal atoms have been made. Although reactive, they mimic intermetallic bonding and form a conceptual link from coordination compounds.

The assembly and evaluation of molecular structures on surfaces has been boosted by advances in single-molecule techniques. The development of such methods are continued here, showing that double-stranded DNA, bound to the tip of an atomic force microscope, can be deposited on the surface of a gold electrode using an electrical trigger.

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.

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.

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.

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.

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.

Xenon difluoride is one of the most stable noble-gas fluoride compounds with a simple linear molecular structure. It has now been shown to undergo several phase transitions at high pressures to give extended solids and even a metallic phase containing XeF₈ polyhedra.

As a rare and precious metal that is also resistant to wear and tarnish, platinum is known to be particularly well-suited to jewellery. Vivian Yam reflects on how, beyond its prestigious image, platinum has also found its way into a variety of fields ranging from the petrochemical to the pharmaceutical industry.