Articles in 2018

The accessibility of materials’ porous domains is typically explored through bulk, and often non-visual, measurements. Now, an integrated fluorescence microscopy approach has established a direct visual relationship between pore architecture (which depends on pore sizes and interconnectivity), molecular transport, and in turn catalytic performance in industrial-grade catalyst particles.

Catalytic activation of non-polar unstrained C−C bonds remains challenging. Now, the C(aryl)−C(aryl) bonds in 2,2′-biphenols can be cleaved using phosphinites as a recyclable directing group through a rhodium-based spirocyclic intermediate. In particular, the biaryl linkage found in softwood lignin could be cleaved using this method.

Limitations associated with the primary amination of aryl C–H bonds include the poor control of regioselectivity with electron-rich substrates and the challenging nature of the reaction in the case of electron-deficient arenes. Now, site-directed C–C bond primary amination of simple alkylarenes and benzyl alcohols provides a route for the direct and efficient preparation of anilines.

Establishing a fundamental understanding of the electronic structure of actinides remains a challenging task for both experiment and theory. Now, it is shown that for the uranium dimer, relativity and electron correlation affects not only the nature of the electronic ground state, but also lowers the bond multiplicity in comparison to previous studies.

A series of in vitro and in vivo studies has now shown that 5fC is linked to increased nucleosome occupancy and stability. Moreover, there is evidence that Schiff base formation between histones and 5fC impacts RNA polymerase II transcription activity in mouse embryonic stem cells.

So far, monosubstituted carbenes have only been spectroscopically characterized at very low temperatures. Now, it has been shown that a bulky, chemically inert, amino substituent is enough to tame the intrinsic tendency of carbenes towards dimerization, enabling their isolation at room temperature.

Steric effects in a fundamental energy-transfer reaction at collision energies from over 1,000 K down to 20 mK have now been studied. At high energies a pronounced dependence of the reactivity on the reactant orientation is observed, but this effect is not present at the lowest energies because of dynamic reorientation.

A chemical proteomic strategy has now been developed for profiling pyridoxal-phosphate dependent enzymes (PLP-DEs) in cells. Pyridoxal-based probes are phosphorylated in situ and bind to cellular PLP-DEs as cofactor mimics. The method accessed 73% of the Staphylococcus aureus PLP-dependent proteome and annotated uncharacterized proteins as novel PLP-DEs.

A direct conversion of carboxylic acids to alpha-olefins without the need for a stoichiometric additive has now been reported. The transformation is enabled by a dual cobalt/iridium proton-reduction–photoredox catalyst system, and can proceed on abundant fatty acids as well as on complex carboxylic acids.

Inhibiting the interaction between amyloid-β (Aβ) and a neuronal cell surface receptor, LilrB2, could offer a potential route for treating Alzheimer’s disease. Now, binding sites between Aβ and LilrB2 have been discovered and computational selection has identified inhibitors that block this binding site. Cell-penetrating inhibitors were found to block the Aβ–LilrB2 interaction and limit Aβ-induced cytotoxicity.

Binding interactions, whether between a biological receptor and ligand or between a synthetic host and guest, are frequently stronger for larger molecules than for smaller ones. This is commonly believed to arise from increased dispersion interactions, but it has now been shown that cavitation energies—always required to dissolve molecules in solution—can be more important.

The inherent synthetic tuneability of organic materials makes them attractive in photocatalysis, but they tend to have low quantum efficiencies for water splitting. A crystalline covalent organic framework featuring a benzo-bis(benzothiophene sulfone) moiety has now been shown to exhibit high activity for photochemical hydrogen evolution from water.

Catalytic superoxide dismutase mimics typically involve manganese centres. Now, a complex based on redox-inactive zinc(ii) and a redox-active quinol ligand is found to catalytically degrade superoxide. The reaction, proposed to occur through oxidation of the ligand to a quinoxyl radical, is hastened rather than inhibited by the presence of phosphate.

A paradoxical case of a well-defined diradicaloid that has an unusually large singlet–triplet energy gap (ΔE_S-T) imparted by the thiophene sulfur atom is reported. Quantum chemistry, organic synthesis, molecular spectroscopies, X-ray crystal analysis and high-temperature magnetic measurements help account for the dichotomy between the large diradical character and large ΔE_ST.

MoS₂ single layers spontaneously undergo a slow oxygen substitution reaction under ambient conditions giving rise to solid-solution-type 2D molybdenum oxy-sulfide crystals. The oxygen substitution sites of the 2D MoS_2−xO_x crystals act as efficient single-atom catalytic centres for the hydrogen evolution reaction.

Chemically depolymerizing biomass polysaccharides to simple sugars is often controlled by the balance between depolymerization and degradation kinetics, which has limited the concentration of solutions that can be obtained and overall yields. The reversible stabilization of carbohydrates by acetal formation pushes back these limits and creates stabilized sugars that have advantageous properties for further upgrading.

New natural-product-inspired molecules are often limited by their only partial coverage of biologically relevant chemical space. Combining fragments of natural products has now been shown to yield pseudo natural products, which — while still being inspired by natural products — populate previously unexplored areas of chemical space and have novel biological activities.

The simplest sugar—glycolaldehyde—has recently been detected in space and now a mechanistic rationale for its formation is presented, which includes its onward reaction to the next higher aldose, glyceraldehyde. The key species in the chemistry at play is the formaldehyde isomer hydroxymethylene, which reacts with the carbonyl component in an essentially barrierless carbonyl–ene-type reaction.

Layered coordination polymers are attractive for the preparation of advanced 2D materials but they are typically non-magnetic insulators. Now such a layered network, CrCl₂(pyrazine)₂, has been prepared that comprises a paramagnetic metal ion and a redox-active ligand. The material exhibits both magnetism — with a ferrimagnetic ground state — and high electrical conductivity.

A composite knot with nine crossings of the same handedness has been prepared from a hexameric circular helicate in 41% yield in a two-step synthesis. An isomeric cyclic [3]catenane topologically constrained to always have at least three twists within the links is also formed. Both topologies have a high degree of writhe, analogous to that of supercoiled DNA.