Articles in 2017

Colloidal particles of metal–organic frameworks (ZIF-8 and UiO-66) with different polyhedral shapes can self-assemble into well-ordered, porous three-dimensional superstructures. These superstructures function as photonic crystals, with a photonic band gap that depends on the size of the MOF particles and shifts upon the sorption of guests within their pores.

Oxidation chemistry is critical to introducing molecular complexity during chemical synthesis. Development of sustainable oxidation chemistry demands strategies to harness O₂ as a terminal oxidant. Access to hypervalent iodine compounds — a class of broadly useful chemical oxidants — from O₂ increases the scope of aerobic oxidation chemistry that can be achieved.

Although organocopper compounds are well known in organic chemistry, only recently has a set of catalytic reactions emerged that involve intermediates containing a copper-substituted stereogenic carbon centre. Now, a mechanistic study demonstrates that a better understanding of this distinction offers ways to address significant limitations in scope and enantioselectivity, explaining why unexpected variations in selectivity can occur.

The use of activating and directing groups can dramatically alter the course of a reaction. Now, it has been shown that an azo group can effectively perform as both in chiral phosphoric-acid catalysed formal nucleophilic aromatic substitution of azobenzene derivatives with indoles, affording axially chiral arylindoles with excellent enantioselectivities.

Steroids are arguably the most well studied and successful class of natural-product-inspired pharmaceuticals, yet step-economical and enantiospecific de novo synthesis remains challenging. Now, it is shown that the combination of metallacycle-mediated annulative cross-coupling and vinyl cyclopropane rearrangement chemistry can be used to deliver a variety of partially aromatic synthetic steroids in a concise, flexible and enantiospecific fashion.

Determining the structure­–activity relationships for complex structures can be quite challenging, but it is often the method by which many natural products are optimized for use as drugs. Now, the combination of a fluoroaryl borane catalyst, a phosphine additive and a silane reducing agent enables the late-stage selective modification of complex bioactive natural products in order to provide rapid access to a wide array of structures, and therefore functions.

Rationally designed arrays of hydrogen bonds between aromatic oligoamide segments have now been shown to generate abiotic helix-turn-helix and unexpected dimeric and trimeric helix bundle motifs. These structures show kinetic and thermodynamic stability, and cooperative folding in nonpolar solvents.

The biosynthesis of secondary metabolites such as stephacidin A and its congeners continues to intrigue both biochemists and synthetic chemists. Now, a laboratory chemical synthesis of these natural products has been achieved based on a bioinspired synthetic strategy, which may provide key insights into the possible biosynthesis of these captivating molecules.

Providing detailed structural descriptions of the ultrafast photochemical events that occur in light-sensitive proteins is key to their understanding. Now, excited-state structures in the reversibly switchable fluorescent protein rsEGFP2 have been solved by time-resolved crystallography using an X-ray laser. These structures enabled the design of a mutant with improved photoswitching quantum yields.

A 335 base-pair gene encoding the green fluorescent protein iLOV and an epigenetically modified variant have now been assembled by click-DNA ligation of ten functionalized oligonucleotides. The resulting fully synthetic gene contained eight triazoles at the sites of chemical ligation, yet the synthetic gene was shown to be fully biocompatible in Escherichia coli.

Singlet fission — the conversion of one singlet exciton into two triplet excitons, could improve the efficiency of photovoltaic devices — but its mechanism is still to be fully understood. Now, in films of TIPS-tetracene, it has been shown that the formation of the triplet pair state, which has been proposed to mediate singlet fission, is ultrafast and vibronically coherent in this endothermic fission system.

Two important properties in an activated chemical reaction are the barrier height and its geometrical dependence. Now, a method has been developed to directly map the angle-dependent barrier to reaction from polarized scattering data for the Cl + CHD₃ reaction. The method should be applicable to many other direct reactions with a colinear barrier.

Crystals are typically thought to be brittle and fragile materials, but needles of copper(II) acetylacetonate have now been shown to be flexible enough to be reversibly tied into a knot. Mechanistic investigations using synchrotron X-ray diffraction determined that the elastic bending occurs through rotation of the molecules within the crystal lattice.

Two coordination cages have been devised that undergo covalent modification during a cascade of two orthogonal Diels–Alder reactions. This results in increased lipophilicity for the second cage, enabling its phase transfer and separation from the first. The trigger, relay and inhibition features of this cascade system mimic key aspects of natural post-translational modification cascades.

Despite advances in peptide synthesis techniques, explicit control over the quaternary structure of synthetic peptides has remained elusive. Now, the dynamic covalent chemistry of hydrazide- and aldehyde-containing peptides has now been shown to enable the formation of unique quaternary structures with topological diversity. Using this method, oligomers were assembled into complex structures showing dramatic enhancements of antimicrobial effectiveness versus Staphylococcus Aureus.

The first demonstration of a protein designed entirely from first principles that binds a small-molecule cofactor in a precisely predetermined orientation has now been described. The design method utilizes a remote protein core that both anchors and predisposes a flexible binding site for the desired cofactor-binding geometry.

Chemically termolecular reactions — arising from the collision of ephemeral collision complexes with other chemically reactive species — have been neglected in current gas-phase chemical mechanisms of combustion and planetary atmospheres. First-principles calculations reveal that such chemically termolecular reactions constitute major pathways affecting macroscopic observables.

Intercalation — a cornerstone of materials science with wide-ranging applications — has now been demonstrated in a superatomic crystal. A redox-active tetracyanoethylene guest was inserted into the lattice of a material consisting of alternate layers of {Co₆Te₈} clusters and C₆₀ fullerenes, leading to a single-crystal-to-single-crystal transformation that significantly modulates the material's optical and electrical transport properties.

Polyoxygenated aliphatic chains with multiple hydroxyl groups are common in a wide array of compounds, often with potent biological activity. Now, a new ruthenium catalyst enables selective dehydrogenation of a single hydroxyl group in a broad scope of complex polyols. This site-selective modification facilitates the rapid incorporation of nitrogen-based functional groups into diverse natural products.

Interest in surface-mediated chemistry has led to the design of small molecule models for surfaces, which provide mechanistic insight and have practical applications. Now, the cooperative behaviour of five nickel centres has been shown to provide reactivity reminiscent of highly active metal surface sites, leading to carbon-atom abstraction from alkenes under ambient conditions.