Articles in 2014

The conversion of water to oxygen is an essential process for both natural and artificial photosynthesis. Important intermediates in the stepwise mechanism of water oxidation on the surface of cobalt oxide have now been spectroscopically identified, providing key insights for the development of higher-efficiency catalysts made from Earth-abundant materials.

The chemistry of group 13 metals (M) is dominated by +1 and +3 oxidation states, so MX₂ species are typically metal–metal-bonded dimers, M(II)₂X₄ or mixed-valence species M(I)M(III)X₄. Now, monomeric M(II)(boryl)₂ radicals have been prepared for gallium, indium and thallium. The compounds — structurally characterized by X-ray crystallography — are stable up to 130 °C and exhibit dominant metal-centred radical character.

Compartmentalization of complex chemical networks is an essential step towards the creation of cell-scale molecular systems. The encapsulation of a synthetic biochemical oscillating reaction system into cell-sized emulsion droplets is now demonstrated; a large variability in its oscillatory dynamics is observed, which is attributed to partitioning effects.

Ion mobility–mass spectrometry has enabled the study of conformation and dynamics of membrane proteins in the gas phase. Here, the enhanced flexibility of macromolecular ATPase was investigated by comparing arrival time distributions of distinct species and relating them to different solution conditions, leading to the proposal of a nucleotide-triggered regulatory mechanism.

When molecules collide with atoms or other molecules their quantum mechanical character can lead to the diffraction of matter waves. Making use of advances in molecular beam technology, such diffraction oscillations have now been observed with unprecedented sharpness and angular resolution in the benchmark NO + He, Ne, or Ar systems.

An artificial reaction centre has been designed that contains a benzimidazole–phenol model of the Tyr–His relay in photosystem II. It has been seen to mimic both the short internal hydrogen bond of the natural relay, and — using electron paramagnetic resonance —the relaxation behaviour that accompanies proton-coupled electron transfer in photosystem II.

Helices are found at every level of natural systems, where their dynamic potential is exploited to achieve a variety of functions. Here, liquid-crystalline molecular switches embedded in a polymer are used to prepare biomimetic spring-like materials that can convert molecular motion into macroscopic work.

In cold chemistry, quantum phenomena in reactants' translational motion lead to the temporary trapping of reactants in a collisional complex. It is now shown that this metastable complex is responsible for a dramatic quantum kinetic isotope effect as observed in Penning ionization reactions at low temperatures.

Light-driven proton pumps are used in biology to create a proton gradient that can be subsequently converted into chemical energy. Here, an artificial light-harvesting system based on a membrane doped with a spiropyran is described. Irradiation with UV light generates a proton flux across the membrane and results in the generation of an electrical current.

A dye that both maximizes electrolyte compatibility and improves light-harvesting properties has been designed for dye-sensitized solar cells. In cells based on the cobalt(II)/(III) redox mediator, use of the dye resulted in a power-conversion efficiency of 13%, revealing the great potential of porphyrin dyes for future solar cell applications.

Self-organization that occurs far from thermodynamic equilibrium is ubiquitous in nature but has remained challenging to control in synthetic supramolecular systems. A complex system has now been devised that displays such behaviour. Porphyrin derivative monomers undergo living supramolecular polymerization, a reaction underpinned by the interplay of two supramolecular polymerization pathways.

Enzymatic catalysis relies on stereoelectronic complementarity between the enzyme's active site and the substrate's transition state. A simple model system illustrating this tenet has now been devised. The bowl-to-bowl inversion of corannulene, catalysed inside the cavity of a synthetic receptor by an induced-fit mechanism, arises from ground-state destabilization combined with transition-state stabilization.

Copolymers of ethylene and polar monomers are produced industrially using free radical polymerization that leads to broad molecular weight distributions of products with ill-defined structures. Now, an organo–cobalt complex is shown to control the radical copolymerization of ethylene with polar monomers under mild experimental conditions, and allows access to block-like copolymers with targeted compositions and monomer distributions.

The extraction of uranium from seawater is limited by the high concentrations of carbonate and competing metal ions. Now, a highly selective uranyl-binding protein with femtomolar affinity has been developed. This protein can extract up to 60% uranium from synthetic seawater when immobilized on bacterial cell surfaces or amylose resin.

Non-noble-metal-based MoS₂ nanostructures are hydrogen evolution catalysts whose active sites are known to be located at the edges. Supported thiomolybdate [Mo₃S₁₃]²⁻ nanoclusters have now been prepared that exhibit a structural motif similar to that of MoS₂ edges. The nanoclusters, synthesized by a scalable route, demonstrate a high turnover frequency.

Selective C–H functionalization reactions often rely on the directing effects of chelating groups embedded within the substrate. Here, an alkene hydrosilylation is used to install a pyridine-containing auxiliary that subsequently directs C–H functionalization at the homoallylic position. Oxidation of the silacycle product results in a formal 1,4-dioxygenation of an alkene.

A terpene-forming carbocation reaction is described for which a single transition-state structure leads to the formation of many isomeric products via pathways that feature multiple sequential bifurcations. Dynamic effects are shown to contribute to the selectivity of the reaction, with consequences for how enzymes control the biosynthesis of complex natural products.

It has been suggested that bioactive natural products are an attractive starting point for the construction of screening libraries. Here, four families of biologically active alkaloids are used as the basis for the construction of 686 new compounds suitable for screening. The libraries thus prepared have characteristics comparable to representative natural products and are highly rule-of-five compliant.

The reaction F + H₂ → HF + H is the only source of interstellar HF, but studying it at relevant cold temperatures has proved problematic. Now, the rates of this reaction have been measured at various temperatures down to 11 K and their remarkable agreement with state-of-the-art quantum mechanical calculations has been shown. (Background © Image Asset Management/Alamy)

The observation of long-lived coherent oscillations in the nonlinear spectra of photosynthetic proteins has raised significant discussion on the role of quantum effects in biology. Using a model system, the signatures of inter-exciton coherence have been isolated, which has allowed the influence of vibronic coupling to be studied in unprecedented detail.