Volume 5 Issue 12, December 2013

Using chemical reactions and diffusion to control pattern formation requires the careful design of reaction networks and a balance of kinetics that is difficult to achieve. Now, it has been shown that DNA-based reaction networks provide a robust method for transforming patterns.

An RNA replicase ribozyme has long been sought by chemists interested in the origin of life. Now, a selection strategy employing a low-temperature water–ice mixture as the medium has led to discovery of a ribozyme that can catalyse polymerization of an RNA chain greater than its own length.

London dispersion forces have been cited as an important factor in protein folding, drug–receptor interactions, and catalyst selectivities. However, careful analysis of a model system finds that the dispersion interactions are only minor contributors to the formation of complexes in solution.

Mastering how to completely control the exact monomer sequence of synthetic polymers is the ultimate key for establishing true biomimetic macromolecular chemistry. A versatile one-pot approach for the synthesis of well-defined multiblock copolymers with short block lengths offers another approach on the road towards this lofty goal.

Single-molecule and -particle fluorescence microscopy — traditionally applied to biophysical studies — has recently been used to gain insight into chemical systems. Still at its nascent stage, this approach presents great opportunities for the chemistry community through the observation of chemical reactions and their mechanisms as typically depicted in textbooks: molecule by molecule.

The programmable nature of chemical reactions enables the creation of complex networks; however, it can be difficult to redesign the underlying reactions. Here, systematic and quantitative control over the diffusivity and reactivity of DNA molecules yields highly programmable chemical reaction networks that execute macroscale pattern transformation algorithms, such as edge detection.

Attractive van der Waals dispersion forces have been implicated in mechanisms as diverse as gecko adhesion and anaesthesia. Now, it has been found using synthetic molecular balances that dispersion forces between alkyl chains are an order of magnitude weaker in solution than they are in the gas phase.

Molecular self-replication through ribozyme-catalysed RNA synthesis could shed light on the origins of life. Here, a polymerase ribozyme capable of synthesizing an RNA sequence longer than itself is described, based on a cold-adapted ribozyme variant evolved in ice. This process demonstrates the potential for the emergence of novel ribozyme phenotypes in altered reaction environments.

Singlet exciton fission produces two triplet excited states from one excited singlet through interchromophoric coupling, which is thought to require local order. Now, a triplet yield of 200% and diffusion-limited triplet formation are reported in solutions of TIPS pentacene. Kinetic studies revealed an excimer intermediate and enabled suggestions of design principles for the promotion of singlet fission.

The coupling of carbon monoxide molecules is an attractive prospect for organic synthesis, but only a few metal complexes are known to do this. A compound containing a boron–boron triple bond has now been shown to induce the coupling of four CO molecules, through an intermediate with a single CO.

A stable tetranuclear boron dication with a rhomboid B₄ skeleton has been formed by B–B coupling between two diborane cations. In the course of this unusual reaction — which is not feasible for the isolobal ethyl cation analogues — two electron-precise B–B bonds are converted into two B–B–B three-centre bonds.

Polymers that exhibit a mechanical response to external stimuli are technologically important. Here, a polymer is described that shows a very large negative thermal expansion on heating or irradiation with near-infrared light. This property is stable over hundreds of cycles and is shown to be driven by a conformational change of an s-dibenzocyclooctadiene unit within the polymer structure.

The ability to self-heal is an important survival feature in nature, with in-built systems working to correct faults and extend the lifetimes of organisms. Now, self-healing chemistry has been applied to overcome the short cycling lifetime of high-capacity rechargeable lithium-ion batteries with silicon-microparticle anodes that suffer from mechanical fractures.

Despite their appearance in a number of bioactive natural products, the synthesis of 5-membered carbocycles has received much less attention than synthesis of their 6-membered counterparts. Here, a Michael-aldol-β-lactonization cascade is used to forge two C-C bonds, one C-O bond, two rings and up to three contiguous stereocentres and deliver complex cyclopentanes with high levels of relative and absolute stereocontrol.

Bacteria use signalling networks to control population behaviour. Here it is shown that polymers that promote clustering of bacteria can influence bacterial signalling and induce unexpected responses in quorum-sensing-controlled phenotypes. These responses can be better modulated by controlling the affinity of the polymer to both bacteria and signalling molecules.

Joel D. Blum considers the two faces of mercury. It has many unique and useful properties in chemistry — yet it comes with a dark and dangerous side.