Research articles

Polytheonamide B is a large non-ribosomal peptide with very high bioactivity. The synthesis described here includes the first preparation of several non-proteinogenic amino acids and a general coupling strategy for large non-natural peptides. The synthesis is a key step necessary to understand and utilize the bioactivity of this and similar compounds.

The uptake of ammonia by a covalent–organic framework (COF) containing a high density of Lewis-acidic boron sites has been found to be significantly greater than that exhibited by other state-of-the-art porous materials. The ammonia can be removed by heating under vacuum and the structural integrity of the COF is maintained during adsorption/desorption cycles.

The synthesis of interlocked compounds such as catenanes and rotaxanes has undergone much development in recent years, but molecular knots are still relatively hard to make. It has now been shown that a linear bipyridine oligomer can fold around a single zinc-ion template to form a complex that can be cyclized to give a molecular trefoil knot.

A methodology for describing local electronic transmission through bridging molecules between metallic electrodes is presented. Its application to simple alkane, phenyl and cross-conjugated systems highlights an unexpected number of cases whereby ‘through space’, rather than ‘through bond’ terms dominate and that interference effects coincide with the reversal of ring currents.

The movement of oxygen ions through materials is important in electrolytes and separation membranes, but is rare at lower temperatures. Two different low-temperature diffusion pathways are revealed during the reduction process of CaFeO_2.5 to CaFeO₂. The two pathways are significantly different, resulting in anisotropy.

Chlorine-activation reactions on polar stratospheric cloud (PSC) particles are crucial to ozone depletion in the winter/spring polar stratosphere and their rates depend on the phase state of the PSC particle surface. Now experiments show that, on particle formation, a phase separation into pure ice with a residual solution coating takes place.

The ability to rapidly functionalize polymers is vital for application development. Here, a method for the introduction of masked ketenes into monomers for both ring-opening metathesis and radical-type polymerizations is described. These ketenes — a group previously underexploited in polymer chemistry — allow both crosslinking and post-polymerization functionalization of the polymers.

The selective construction of multiple adjacent stereocentres is an important challenge for synthetic organic methodology, and only a handful of catalytic methods exist that can forge adjacent quaternary and tertiary stereocentres. Here, a palladium-catalysed multiple-bond-forming cascade leads to the construction of such systems in high yield, diastereomeric ratio and enantiomeric excess.

A method for observing the photodynamics of single molecules, without having to immobilize them to a surface or confine them within vesicles, has been used to study the important photosynthetic antenna protein, allophycocyanin. Light-induced conformational changes and a complex relationship between fluorescence intensity and lifetime have been observed.

A combined theoretical and experimental approach has been used to investigate the structure and bonding of an all-boron cluster (B₁₉⁻). Calculations suggest that the minimum energy structure is a near-planar one — in which a pentagonal B₆ unit is encircled by a larger B₁₃ ring — possessing two concentric aromatic π systems.

A perforated framework material of gallium antimony sulfide is able to selectively extract caesium ions from solution. After this capture, the holes close and prevent the ions leaching back out. This dynamic response could be used to remove caesium from nuclear waste.

Silicon, like carbon, favours a four-coordinate geometry and this underpins the frameworks of the wide range of inorganic and organosilicon compounds, from silicate minerals to polysilanes. Although some pentavalent silicon compounds have already been reported, this work presents the first example where two five-coordinate silicon atoms are bonded to each other.

Ready access to sugars in which the various hydroxyl groups are differentially protected will be of benefit in the production of vaccines, antibiotics and drugs. Here, a chemoenzymatic method that provides a direct route to such protected sugars is described.

Highly diastereoselective Negishi cross-coupling reactions between 2-, 3- and 4-substituted cycloalkylzinc reagents and aryl iodides are described. In all cases, the thermodynamically most stable diastereomers of the cross-coupling products were obtained. NMR spectroscopy and density functional theory calculations were performed in order to rationalize the observed stereoselectivities.

The incorporation of non-natural base pairs into double-stranded DNA, especially those mediated by metal–ligand interactions, offers new opportunities for synthetic DNA materials. The structural implications of such modifications will help guide developments in this area, and a solution structure of a B-type DNA duplex containing consecutive metal-mediated base pairs has now been elucidated.

Well-resolved images of small molecules and their motions can be obtained with high-resolution transmission electron microscopy. It has now been shown that this technique can also be used to visualize individual chemical reactions involving the dimerization of fullerenes and metallo-fullerenes trapped inside carbon nanotubes by monitoring how the positions of their atoms change over time.

The bulk properties of materials that lack long-range order have been widely studied, but their local structures remain difficult to elucidate. Now, using scanning tunnelling microscopy, researchers have been able to look more closely at the structural motifs of robust, two-dimensional glassy networks assembled through metal–ligand interactions.

Precise calculations of molecular properties from first-principles set great problems for large systems because their conventional computational cost increases exponentially with size. Quantum computing offers an alternative, and here the H₂ potential energy curve is calculated using the latest photonic quantum computer technology.