Volume 4 Issue 7, July 2012

Supramolecular ligands are promising tools for interacting with proteins, but how exactly they bind together has so far been difficult to characterize. An unambiguous picture of the interaction between a synthetic ligand and the surface of cyctochrome c has now been obtained in solution and in the solid state.

The tunicamycins, secondary metabolites of various Streptomyces species, are invaluable tools in glycobiology. It has now been shown that their biosynthesis involves an unusual exo-glycal intermediate produced by previously unknown short-chain dehydrogenase/reductase activity.

The mechanism of the S_N2 reaction is fundamental to understanding and controlling the stereochemistry of organic reactions, but surrounding solvent molecules may complicate the textbook picture. Micro-solvation studies have now explored the stereochemical consequences of the presence of one or two solvent molecules.

To improve the efficiency of molecular motors, a better understanding of the dynamics of their functional motions is required. Now, ultrafast fluorescence spectroscopy has been used to monitor the excited-state evolution of a light-driven molecular motor.

The successful synthesis of acyclic silylenes that are isolable at ambient temperature offers striking new opportunities to use stable silylenes for the activation of important small molecules such as dihydrogen and alkanes — hitherto almost completely the domain of transition metals.

A calixarene–protein host–guest complex has been characterized in detail by using a combination of NMR spectroscopy and X-ray crystallography. The water-soluble sulfonato-calix[4]arene binds to cytochrome c at various lysine residues to yield a dynamic complex. This interaction may serve to facilitate crystallization by mediating protein–protein contacts.

How do solvent molecules influence the dynamics of a chemical reaction? Crossed-beam molecular imaging experiments reveal how different reaction mechanisms can be either suppressed or enhanced by the presence of one water molecule. The study finds that steric effects are responsible for the observed dynamics.

Construction of the remarkable 11-carbon frame of the antibiotic tunicamycin is shown to use cyclic enol ethers (exo-glycals) — the first time such intermediates have been seen in biology. Exo-glycal synthase TunA uses an elegantly subtle mechanism to control regioselectivity and with exo-glycal epimerase TunF sets a logical chemical stage for downstream radical C–C coupling.

The light-driven power stroke of a unidirectional molecular motor is studied using ultrafast fluorescence spectroscopy. The evolution on the excited-state energy surface is observed on the 100 fs timescale and is accompanied by damped coherent molecular motion. The implications of these observations for the operation of the molecular motors are discussed.

Coupling reactions of nitrogen atoms represent elementary steps to many important, heterogeneously catalysed reactions, such as the Haber–Bosch process or selective catalytic reduction of NO_x to N₂. Here, the synthesis and characterization of closed- and open-shell, square-planar iridium nitrido complexes is described, indicating considerable nitridyl radical character for the open shell complex.

Bisadamantyl 1,2-dioxetane is a luminescent mechanophore that, when incorporated into polymer chains or networks, emits visible light when its 4-membered ring is opened by sonication in solution or by deformation of a bulk sample. This phenomenon mimics biological mechanoluminescence and highlights the potential to study the failure of polymeric materials with high spatial and temporal resolution.

Mild, controllable homocatenation of many elements is a considerable challenge, usually due to their low homonuclear σ-bond enthalpy. This is particularly difficult for boron, despite its high homonuclear σ -bond enthalpy. The controllable metal-templated catenation of four boron atoms is now demonstrated — a step towards oligomers of monovalent boron and polyboranes.

Quantifying polymer reaction kinetics requires the non-Markovian dynamics of monomer motion to be taken into account. This difficulty is overcome by explicitly determining the typical reactive conformations of the polymer, which are found to be more extended than equilibrium conformations, leading to reaction times significantly shorter than predicted by existing Markovian theories.

Crystals of hexacene prepared from a monoketone precursor are found to be stable up to 300 °C in the dark, but readily decompose when exposed to light. An organic-field transistor made with a single crystal of hexacene was found to have superior properties to one made from pentacene under analogous conditions.

Lithium–air batteries have the possibility of having a very high energy density, but their use has been hampered by a limited number of charge–discharge cycles and a low current-rate capability. Now, exploiting a suitable, stable electrolyte allows an advanced lithium–air battery to operate with many cycles at various capacity and rate values.

Richard Wilson relates how the rare, highly radioactive, highly toxic element protactinium puzzled chemists for a long time, and was discovered and named twice from two different isotopes before finding its place in fundamental research.