Volume 5 Issue 10, October 2013

Millimetre-sized single crystals of covalent organic frameworks have been constructed by taking advantage of a reversible dimerization reaction of nitroso groups.

Covalently bonding groups to the walls of carbon nanotubes has been previously observed to quench their photoluminescence. Now, it has been shown that, if you get the chemistry just right, their photoluminescence can in fact be significantly brightened by introducing defects through functionalization.

Preparing powerful reactive intermediates such as enolates and homoenolates for C–C bond formation used to require strong bases and stoichiometric reagents. They can now be catalytically generated from α-functionalized aldehydes or even from saturated esters under mild conditions using N-heterocyclic carbene catalysts.

Although caesium is well known in its oxidation state +I, many chemists have speculated about a possible higher state. Such a species has not yet been prepared, but based on quantum-chemical calculations CsF_n compounds have now been predicted to be stable.

The application of catalytic methods to main group substrates has recently allowed access to a wide range of catenated structures based on elements across the p-block. These breakthroughs have already impacted areas such as hydrogen storage and transfer, functional inorganic polymers, and ceramic thin films.

Modular construction using connectable molecular subunits is a powerful strategy for making new carbon-based materials. So far, large crystals have been produced only from subunits linked by weak interactions. Covalently bonded analogues have now been prepared by reversible self-addition polymerization of suitable monomers and structurally characterized by single-crystal X-ray diffraction.

Direct β-carbon activation of saturated carbonyl compounds represents a significant fundamental challenge in organic chemistry. Here, the catalytic activation of saturated ester β-sp³ carbon as nucleophile via N-heterocyclic carbene organocatalysis is reported. The catalytically generated nucleophilic β-carbon undergoes enantioselective reactions with various electrophiles.

The controlled functionalization of single-walled carbon nanotubes has been shown to brighten their photoluminescence up to 28 times, which challenges our current understanding of how chemical defects affect low-dimensional carbon materials. This significantly improved photon conversion efficiency promises to advance a broad range of optoelectronic and imaging applications based on carbon nanotubes.

Caesium has so far not been found in oxidation states higher than +1, but quantum chemical calculations have now shown that, under high pressures, 5p inner shell electrons of caesium can participate in — and become the main components of — bonds. Caesium is predicted to form stable CsF_n molecules that resemble isoelectronic XeF_n.

Biological receptors communicate information through ligand-induced conformational changes. A synthetic receptor with a boron-containing binding site that can selectively and reversibly complex a ligand (such as a purine nucleoside) is shown to function in a similar fashion. The resulting conformational change is relayed through the receptor, communicating structural information about the ligand to a spectroscopic reporter more than 2 nm away.

Diversity oriented synthesis (DOS) aims to build structurally diverse compound libraries — potentially useful in drug discovery — from a small number of starting materials. Here, the build/couple/pair algorithm — commonly used in DOS — is extended to incorporate variations in the coupling step as well as in the starting materials. This produces a compound library with exceptionally high diversity in fewer than five steps from a common precursor.

The site-specific incorporation of dendritic DNA amphiphiles into a DNA cage controls whether the resultant structures show intermolecular self-assembly or intramolecular assembly. Intramolecular assembly creates a hydrophobic core within the cage that is capable of encapsulating small molecules. These molecules can be released on addition of specific DNA strands.

A base-stabilized silicon analogue of a reactive carbon species (vinyl carbene) is reported that features a silicon–silicon double bond and a silylene functionality, coordinated by an N-heterocyclic carbene. Ultraviolet–visible light and nuclear magnetic resonance spectroscopy in solution confirms that disilenyl silylene exists in equilibrium with the corresponding cyclotrisilene and free N-heterocyclic carbene.

An asymmetric pentalene-containing C₁(51383)-C₈₄ fullerene cage is found in two different metal carbide metallofullerenes. This particular cage can, in simple steps, rearrange into many well-known fullerene cages that are more stable and more symmetric, suggesting it is likely that metallofullerenes are generated by a ‘top-down’ formation mechanism.

The trioxacarcins are polyoxygenated natural products that potently inhibit the growth of cultured human cancer cells. Here, the syntheses of trioxacarcin A, DC-45-A1 and structural analogues are described — the majority of which were found to be active in antiproliferative assays. A convergent, component-based route comprising sequential stereoselective glycosylation reactions allows assembly of these analogues in 11 steps or fewer.

Somobrata Acharya explores the history, properties and uses of lead — an ancient metal that is still very relevant to today's technologies, but should be used with caution.