Articles in 2018

Covalent organic frameworks (COFs), whose heterogeneous backbones can be easily tuned at the molecular level, are promising photocatalysts for artificial photosynthesis. Sulfone-rich crystalline, wettable COFs have now been shown to exhibit high photocatalytic hydrogen evolution rates with platinum nanoparticles as co-catalysts.

Stuart Cantrill explains why looking to the heavens for element 61 — named after the Titan who stole fire from the gods — could extend the periodic table.

Superoxide dismutase mimics can help regulate the levels of O₂^•− in the body, but typically rely on redox-active metals that are toxic in their free form. Now, a complex featuring a redox-active quinol moiety complexed to a redox-inactive zinc centre has been shown to catalyse O₂^•− dismutation.

Magnetic or electric fields have long been used to align or orient atomic or molecular species in a molecular beam. Now, experiments in a merged beam apparatus show that an external magnetic field can be used to favour one particular reaction path.

Heteromultivalency, which involves the simultaneous interactions of more than one type of ligand with more than one type of receptor, is common in biological systems but challenging to engineer artificially. Now, a heteromultivalent platform prepared by co-assembling cyclodextrin and calixarene amphiphiles has shown self-adaptive peptide binding with high affinity. The platform was used to sequester amyloid β-peptides, reducing amyloid cytotoxicity.

Solid acid heterogeneous catalysts are widely used in industrial chemical processes, but understanding the exact molecular structures responsible for catalytic activity has proved difficult. Now, the structure of the strong Brønsted acid site for a sulfated zirconium-based metal–organic framework has been shown to consist of a specific arrangement of adsorbed water and sulfate moieties on the zirconium clusters.

Typical methods for the enantioselective α-functionalizations of ketones join ketone enolate nucleophiles with carbon or heteroatom electrophiles. We report an umpolung strategy to achieve this transformation with masked ketone electrophiles and a wide range of conventional heteroatom and carbon nucleophiles catalysed by a metallacyclic iridium catalyst in high yield and enantioselectivity.

The use of Li or Na as electrodes in Li-Na alloy–O₂ batteries creates formidable challenges for both safety and stability because of their oxidative corrosion and the growth of dendrites and cracks on their surface. Now, an aprotic bimetal Li-Na alloy–O₂ battery with high cycling stability has been developed using a Li-Na eutectic alloy anode and an electrolyte additive.

Nitrogen fixation—the direct conversion of dinitrogen into ammonia or other nitrogen-containing products—is notoriously difficult to promote under mild conditions. Now, the reactivity of a multimetallic diuranium(iii) complex recently found capable of reducing and functionalizing N₂ has been explored, replacing its nitride bridge with an oxo bridge, which resulted in a markedly different reactivity.

Synthetic receptors can be used to help understand biological systems, but rarely compete in terms of affinity or selectivity. Now, a glucose-binding compound has been prepared that, despite its symmetry and simplicity, can match all but the strongest glucose-binding proteins. The high binding affinity and outstanding selectivity of this receptor may translate into biomedical applications.

N-heterocyclic carbenes (NHCs) are valuable surface anchors, but their use has remained limited to either spherical or planar nanomaterials. Now, they have been grafted onto gold nanorods through a bidentate ligand featuring a thiolate and a NHC–gold complex. The resulting nanorods are robust towards a wide range of harsh conditions and show promise for photothermal therapy.

The preparation of conjugates between proteins and small molecules is often challenging and requires several synthetic steps to functionalize each component for conjugation. Now, a conjugation methodology that leverages an electrophilic Se–S bond of selenocysteine to create bioconjugates between polypeptides and complex small molecules has been described.

The structural features and catalytic performances of catalyst particles have now been correlated using a fluorescence microscopy approach, by tracking nanoprobes as well as fluorescent reaction products. Such mapping enables exploration of structure–function relationships, which is essential for the design of better catalysts.

A 27 kDa photosensitizer protein (PSP) has now been developed and used to design a miniature photocatalytic CO₂-reducing enzyme. Visible light drives the PSP efficiently to the long-lived triplet excited state (PSP*), and then to a super-reducing radical (PSP^•), which is strong enough to reduce many CO₂-reducing catalysts. The 3D structure of PSP^• at 1.8 Å resolution was determined by X-ray crystallography.

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.