Volume 5 Issue 9, September 2013

A nanographene compound incorporating five- and seven-membered rings is found to have a highly distorted non-planar structure and serves as a model system for studying the effect of defects in graphene sheets.

Selective reaction of one alcohol among many in complex molecules can be achieved by the use of a catalyst that forms a single covalent bond to a nearby functional group.

A crystalline polymer serves both as the seed and as one component of a diblock copolymer for the growth of unusual multi-armed micelles.

Chemical reactions with activation barriers generally slow to a halt in the extreme cold of dense interstellar clouds. Low-temperature experiments on the reaction of OH with methanol have now shown that below 200 K there is a major acceleration in the rate that can only be explained by enhanced quantum mechanical tunnelling through the barrier.

Selective conversion of C–H bonds into C–N bonds to form N-heterocycles would streamline the synthesis of these important structural motifs. Now, an iron(II) catalyst has been developed that can transform alkyl azides into cyclic secondary amines by controlling the iron imido intermediate to react only with the nearby aliphatic C–H bond.

A grossly warped nanographene, C₈₀H₃₀, that incorporates five 7-membered rings and one 5-membered ring embedded in a hexagonal lattice has been synthesized, isolated and fully characterized. Experiments revealing how the properties of such a large graphene subunit are affected by multiple odd-membered-ring defects are also reported.

In interstellar clouds, reactions that have an activation barrier have previously been considered too slow to be significant because of the low temperatures experienced. However, large enhancements in the rate coefficient for the reaction of OH with methanol have now been observed at temperatures below 100 K. A mechanism involving tunnelling has been proposed.

The combination of organocatalytic and photoredox cycles has attracted much attention for its ability to solve long-standing problems in asymmetric catalysis. Here, it is shown that easily available chiral organic catalysts can guide both the stereoselectivity-defining events and, through the transient formation of photon-absorbing chiral electron donor–acceptor complexes, the photoactivation of the substrates.

Materials typically break down in response to the repeated mechanical forces that they experience during use. Now, it has been shown that a mechanochemically active polymer can respond to shear forces by forming more bonds than are broken, leading to improved mechanical properties under conditions that would otherwise be destructive.

Structural analysis of the enzyme transketolase at sub-ångström resolution shows the existence of physically distorted covalent intermediates with elongated scissile substrate bonds. These observations highlight the ability of enzymes to enhance the reactivity of reaction intermediates leading to a more efficient process.

A counter-intuitive strategy that combines a chiral Lewis base catalyst with an achiral Lewis base co-catalyst results in an exceptionally large increase in the facility of catalytic enantioselective silylation of polyols. The catalytic ensemble drives such reactions to completion within a few hours, rather than the usual two–five days, without loss of enantioselectivity.

The catalytic activity of gold nanoparticles is known to be dependent on size, but less is known about the activity of even smaller gold clusters. It is now shown that clusters with 5 to 10 atoms supported on multiwalled carbon nanotubes are as active as enzymes for the oxidation of thiophenol to disulfide with O₂.

A molecular probe has been designed that distinguishes double-stranded DNA with single base-pair specificity. In this approach, two destabilizing bubbles, in which the base pairs are mismatched, are generated for each point mutation in the target DNA.

The manipulation of complex molecules offers an avenue for developing new therapeutics and biological probes. Here, a catalyst is described that forms a covalent bond to the substrate before selectively functionalizing a proximal functional group. Cis-1,2-diols are targeted allowing for the derivatization of the axial hydroxyls of monosaccharides in the presence of unprotected equatorial hydroxyls.

Hydrophobe/water interfaces are crucial for many chemical processes, but to be fully understood, a better appreciation of the behaviour of non-hydrogen-bonded OH groups of water is required. It is now shown that such ‘dangling’ OH structures are entropically stabilized and form cooperatively, that is, the probability of their formation depends nonlinearly on hydrophobic surface area.

Brett F. Thornton and Shawn C. Burdette look back at the discovery — and the many different names — of element 86.