Volume 15 Issue 2, February 2023

Amilra Prasanna (AP) de Silva talks to Nature Chemistry about his path in chemistry, from photochemistry to sodium sensors to logic gates, through connections between people and between two places that share more than it may seem, Sri Lanka and Northern Ireland.

Interlocking macrocyclic carbon nanomaterials is an exciting way to tune their molecular properties, but all-conjugated catenanes and rotaxanes are extremely challenging to make. Now, fully π-conjugated [2]- and [3]catenanes as well as a [3]rotaxane have been prepared through an ‘active metal template’ approach.

Post-translational modification of proteins is widely used for studying biological processes; however, competing reactions can provide numerous challenges. Now, a visible-light photocatalytic diselenide contraction enables the highly chemoselective functionalization of selenopeptides and proteins under mild conditions.

The selective removal of one oxygen atom from sulfones, without over-reduction to sulfide, is a challenging task. Now, through organocatalysis and incorporation of a cyano group into the sulfone, an asymmetric deoxygenation strategy has been developed, providing an efficient method for the synthesis of chiral sulfinyl compounds.

2+2-cycloaddition reactions have long been considered key transformations in the biosynthesis of cyclobutane-containing natural products, but enzymes for these reactions have not yet been identified. Now, a 2+2 cyclase has been discovered, characterized and bioengineered to catalyse cycloadditions with different selectivity.

An active-template approach has been used to prepare π-conjugated interlocked nanocarbons derived from [n]cycloparaphenylenes. A metal ion bound within the central cavity of a precursor macrocycle first catalyses cross-coupling reactions and then the resulting mechanically interlocked intermediates are further transformed into π-conjugated species—[2] and [3]catenanes as well as a conjugated [3]rotaxane.

Cycloaddition reactions are among the most useful reactions in chemical synthesis, but biosynthetic enzymes with 2 + 2 cyclase activity have yet to be observed. Now it is shown that a β-barrel-fold protein catalyses competitive 2 + 2 and 4 + 2 cycloaddition reactions. This protein can be engineered to preferentially produce the exo-2 + 2, exo-4 + 2 or endo-4 + 2 product.

The direct conversion of sulfones to chiral sulfinyl compounds is one of the major challenges in the fields of asymmetric synthesis and organosulfur chemistry. Now, through incorporation of a cyano group into the sulfone, an organocatalytic asymmetric deoxygenation strategy has been developed that enables the synthesis of chiral sulfinyl compounds.

The transition state, a transient species where bond transformation occurs, fundamentally controls reaction dynamics. This important species can be probed through the photodetachment of an anionic precursor, as has now been shown in the F + NH₃ reaction. A combination of theory and experiment reveals resonances that span the transition state.

Heavy analogues of carbynes of the type R–\({{{\dot{\mathrm E:}}}}\), where E is a group 14 element, are difficult to isolate in the condensed phase due to their high reactivity. Now, a germylyne radical supported by a sterically hindered hydrindacene ligand has been prepared and structurally characterized. Theoretical calculations show that the spin density mainly resides at the germanium centre.

Expanding the biocatalysis toolbox for C–N bond formation is of great value. Now, a biocatalytic amination strategy using a new-to-nature mechanism involving nitrogen-centred radicals has been developed. The transformations are enabled by synergistic photoenzymatic catalysis, providing intra- and intermolecular hydroamination products with high yields and levels of enantioselectivity.

Photoelectrochemical cells are hampered by electron–hole recombination. Now, supramolecular machinery has enabled the docking of macrocyclic electron-accepting redox mediators to a dye through pseudorotaxane formation. Upon electron transfer from the dye, the anionic redox-mediator rings are launched away from the surface, reducing charge recombination, establishing charge separation and improving the efficiency of the solar cells in which they feature.

The facile release of corrosive HCl gas and plasticizers from poly(vinyl chloride) (PVC) makes it a challenging material to recycle. Now, it has been shown that PVC waste can be directly used as a halogen source to synthesize chloroarenes. This paired electro(de)chlorination is mediated by a phthalate plasticizer already contained in PVC waste.

Gold nanoparticles typically exhibit hard-sphere-like assembly behaviour, but now the size, morphology and symmetry of crystals of Au₂₅ nanoparticles have been tuned. The presence of excess tetraethylammonium cations has been shown to promote the one-dimensional assembly of the nanoparticles, which in turn form rod-like crystals, by stabilizing dynamically detached ligands from adjacent particles into interparticle linkers through CH⋯π and ion-pairing interactions.

Modulation of surface properties and functions can be achieved through covalent and non-covalent molecular binding, but the lack of responsiveness and requirement for specific binding groups makes spatiotemporal control challenging. Now, it has been shown that adaptive insertion of a hydrophobic anchor into a poly(ethylene glycol) host is an effective non-covalent binding strategy for programmable surface functionalization.

Polyketide natural products often contain common repeat motifs that are synthesized using iterative processes. Now a masked 1,3-diol motif, generated by a two-step process based on boronic ester homologation, has enabled the efficient iterative synthesis of polyacetates, including bahamaolide A. In addition to oxidation, the 1,3-polyboronic esters were shown to undergo various stereospecific transformations.

Identifying and quantifying the biodistribution of synthetic polymeric nanoparticles in biological milieu is crucial for biomedical applications. Now, it has been shown that encoded polymeric amphiphiles with discrete molar masses undergo sequence- and length-dependent self-assembly into precise digital micelles that can be used in direct sequence reading and ex vivo label-free quantification assays.

Kinetic isotope effect studies can provide valuable insights into the complex mechanisms of the oxygen reduction reaction; however, inaccessibility to ultra-high-purity D₂O has made this difficult. Now, a methodology to prepare ultra-pure D₂O has been developed and inverse kinetic isotope effects have subsequently been measured for the oxygen reduction reaction on platinum single-crystal surfaces, providing mechanistic insights.

Geminal disubstitution of cyclic monomers is known to improve the chemical recyclability of their polymers, but usually at the expense of performance properties. Now, geminal disubstitution of a six-membered lactone has been shown to synergistically enable chemical recyclability back to the monomer and enhance the materials performance of the resulting polyesters, with properties that rival or exceed those of polyethylene.

The nitrogen reduction reaction is an extremely valuable but energy-intensive process. Now, a coordination polymer based on a [Zn–N₂–Zn] unit has been shown to promote the formation of ammonia under ambient conditions by a photocatalytic reaction. The N₂ moieties within the framework are reduced, creating unsaturated [Zn²⁺···Zn⁺] intermediates that are able to capture external N₂ and sustain the cycle.

Methane hydrate clogs pipelines, is difficult to extract profitably, and exists in quantities sufficient to screw up Earth’s climate. Brett Thornton and Christian Stranne consider this confounding cage compound.