Volume 3 Issue 7, July 2011

The search for efficient oxygen reduction catalysts made from perovskite oxides rather than expensive precious metals is hindered by the sheer range of these oxides — where should the search begin? Developing design rules that can identify the best candidates is the first step towards a more targeted strategy.

The discoveries of ruthenium– and iron–nitrido complexes that can be transformed to release ammonia could be important steps towards realizing the catalytic reduction of nitrogen under mild reaction conditions.

The mechanism of NO and O₂ production through the photolysis of the nitrate radical has long proved elusive. Now, theoretical studies help to explain previous experiments, suggesting that two distinct pathways are responsible that both involve 'roaming dynamics' on the 'dark' excited electronic state.

A catalyst has been developed that enables poly(propylene carbonate) chains to be made in which the configuration of the repeat units changes gradually from exclusively S at one end of the chain to exclusively R at the other. The improved physical properties of this 'stereogradient' polymer may help its adoption as an environmentally friendly material.

Do unusual geometries always come from the force exerted by a protein, a solid-state lattice or bulky ligands? In a new iron(II) complex, simple ligands stabilize a square-planar high-spin complex through finesse rather than force.

Peptide macrocycles have a number of important applications. Among other things, the reduced conformational freedom of the cyclic structure enables strong binding to the extended contact regions of protein–protein complexes. Here, emerging methods directed towards the synthesis of these valuable molecules are reviewed.

Nitrenium salts have been known for more than 100 years. Despite being isoelectronic and isostructural to the ubiquitous N-heterocyclic carbene ligands and other main-group analogues, their coordination to metals has remained elusive. Here, the first examples of nitrenium ions as ligands for transition metals are described, along with investigations of their electronic properties.

One of the hurdles facing the development of effective catalysts to produce ammonia from nitrogen is the stability of the metal nitrides that form during the reaction. Now, the hydrogenolysis of nitride ligands with hydrogen is reported and attributed to PNP pincer ligand cooperativity.

Single-molecule magnets hold great promise for device miniaturization but the blocking temperatures at which they perform must first reach practical values. Now, the electronically diffuse N₂³⁻ radical bridge has been shown to endow two di-lanthanide complexes with good magnetic properties — a di-gadolinium complex displays a strong magnetic coupling and its di-dysprosium analogue a high blocking temperature.

Loline is a small alkaloid with a deceptively simple-looking structure. Here, a remarkably short synthesis is reported, the key step of which is a transannular aminobromination. The synthesis provides access to loline and to several other members of the loline family in sufficient yield to support a programme investigating the complex biological interactions of these compounds.

With the cost of noble metal oxygen-reduction catalysts rendering some fuel cells and batteries prohibitively expensive, the search for effective and cheaper catalysts is underway and would be speeded up by ‘design principles’. Now, the catalytic activity of oxide materials has been correlated to σ*-orbital occupation and the extent of metal–oxygen covalency.

Small nanoparticles with controlled morphologies can be prepared for catalysis applications by colloidal methods using stabilizing ligands. A solvent-extraction method has now been described that removes the ligands without affecting the morphology of the nanoparticles, or their catalytic activity over a range of reactions.

Oligosaccharides displayed at cell surfaces have important biological functions — such as controlling the entry of viruses — but a full understanding of this behaviour requires the synthesis of such compounds, which remains challenging. Here, two synthetic octasaccharides were shown to have remarkably similar inhibition of herpes simplex virus type 1 infection of cell cultures to the natural oligosaccharide identified in enzymatic studies.

In extended networks, light-induced magnetic ordering through spin change typically involves a charge-transfer mechanism, and thus a valence change of the magnetic metal centres. Now, such long-range ordering has been achieved in a three-dimensional metal–organic framework through the low-spin to high-spin transition of iron(II) centres, leading to a pronounced spontaneous magnetization.

Russell Boyd ponders on how selenium — despite close similarities with its neighbours of the chalcogen family, sulfur and tellurium — continues to reveal chemical and biological activities of its own.