Volume 7 Issue 8, August 2015

Hybrid organic–inorganic lead halide perovskites have recently emerged as ground-breaking photovoltaic materials. A recent confocal fluorescence microscopy study now raises hopes that perovskite solar cells can reach efficiencies beyond the recent record of 20%.

A pair of artificial DNA bases have now been shown to adopt an edge-to-edge geometry in DNA which is similar that found in Watson–Crick base pairing. Aptamers containing these bases have also been shown to bind more strongly to a target than those developed using only the four naturally occurring bases.

How complex is it to synthesize a given molecular target? Can this be answered by a computer? Now, a model of synthetic complexity that factors in methodology developments has resulted in a complexity index that evolves alongside them.

Molecules can transfer charge between electron donors and acceptors, and can also transport charge when connected between metallic electrodes. These processes are assumed to show generally similar trends, however, a significant departure from this has now been observed in a series of biphenyl bridges.

Based initially on the outcome of certain reactions but later backed up by spectroscopic evidence, chemists have proposed — for more than a century — the existence of arynes as extremely reactive intermediates in chemical transformations. Now, with the help of atomic force microscopy, it is finally possible to generate and directly visualize this elusive intermediate.

Fe(II) complexes display transitions between spin states that can be triggered externally. Now the light-induced ΔS = 2 transition upon excitation of the metal-to-ligand charge-transfer states of Fe(II)-polypyridine complexes has been investigated at high time-resolution in the visible and the ultraviolet range. It has been shown to occur in less than 50 fs — that is, on a sub-vibrational timescale.

Rigid star-shaped azobenzene tetramers form a porous molecular crystal when the azobenzene moieties are in the trans configuration, and a non-porous amorphous material on their isomerization to the cis configuration. These two forms are reversibly interconverted in the solid state by light irradiation, thus enabling the photoswitching of optical and gas-capture properties.

The facile, spontaneous dimerization of a simple alkenylbutenolide monomer is relevant to the biosynthesis of racemic paracaseolide A. As supported by computation, a fully (C₂-)symmetric, bis-pericyclic Diels–Alder cycloaddition transition state structure is invoked to account for the atypical exo-selectivity and room-temperature reactivity.

Controlling the self-assembly of nanoparticles using light has been demonstrated in many systems where the particle surfaces are functionalized with photoswitchable ligands. Now, it has been shown that the light-controlled self-assembly of non-photoresponsive nanoparticles can be achieved in a quantitative and reversible fashion by placing them in a photoresponsive medium.

The reactivity of a monooxygenase (P450 PikC) has been modified through protein and substrate engineering, and applied to the oxidation of unactivated methylene C–H bonds. The protein engineering was guided by using molecular dynamics and quantum mechanical calculations to develop a predictive model for substrate scope, site selectivity and stereoselectivity of the C–H hydroxylation.

Often reactions can be described by classical mechanics; however, this is prohibited in cases in which quantum phenomena emerge. Now angular distributions measured for the H + D₂ reaction have been seen to display characteristic oscillation patterns in backward scattering — theory shows that they are caused by quantum interferences between classical mechanisms similar to those found in the double-slit experiment.

The total chemical synthesis of large proteins requires the development of methodology that rapidly couples unprotected peptide fragments. Here a highly strained four-membered-ring amino acid is described that enables such couplings by the formation of serine residues.

A method for high-throughput analysis of whole-cell biocatalysts for industrial biotechnology has been developed. The process relies on a combination of specifically tailored bacterial sensor cells that are incubated with biocatalyst variants within nanolitre-sized compartments. The product is secreted by the whole-cell biocatalysts and taken up by the sensor cells, which initiates a sequence of reactions that finish with the synthesis of green fluorescent protein.

Pekka Pyykkö discusses the history and characteristics of gadolinium.