Articles in 2015

Pyrroles are a common substructure in pharmaceuticals, materials and natural products. Now a multicomponent, titanium-catalysed synthesis of polysubstituted pyrroles — a nitrenoid analogue of the Pauson–Khand reaction — is reported. Stoichiometric and kinetic studies suggest that the reaction proceeds through an unusual Ti^II/Ti^IV redox cycle.

The functionalization of primary amines by C–H activation is often hindered by their strong metal-coordinating properties. Now, a steric tethering approach — which temporarily converts amino alcohols into hindered secondary amines — has been developed. The approach allows these amino alcohols to be transformed into structurally complex and diverse products using palladium-catalysed aliphatic C–H activation.

Although millions of zeolite structures have been predicted, only about 200 have been prepared over the past six decades. An assembly–disassembly–organization–reassembly process has now enabled the synthesis of two zeolites previously thought to be unfeasible, which have high framework energy and rare structural features such as odd-membered rings.

Singlet fission, a spin-allowed conversion of a spin-singlet state into a pair of spin-triplet excitons, may be useful for the development of next-generation photovoltaics. Ultrafast coherence measurements now show that vibrational motions play a critical role in fission as they facilitate the mixing of triplet-pair states with singlet excitons.

Uncertainty associated with solution-based electron-transfer studies of DNA–metal-complex systems has now been overcome by combining X-ray and time-resolved infrared data obtained for ruthenium polypyridyl–DNA crystals. Using these methods both the geometry of the reaction site and the kinetics of the reversible photo-induced one-electron oxidation of guanine have been determined.

α-Substituted-β-hydroxy ketones are valuable intermediates, but their preparation by alkylation of enolates is difficult with hindered electrophiles. Now, a direct method for preparing α-substituted-β-hydroxy ketones — including those having α-quaternary centres — by addition of Grignard reagents to epoxyhydrazones has been developed, enabling the stereocontrolled incorporation of a wide range of carbon based substituents.

Oxynitrides are garnering interest because of their variety of novel properties, but their synthesis has typically involved highly reducing conditions that put significant constraints on their composition, structure and properties. Now, the lability of H⁻ in perovskite oxyhydride BaTiO_3−xH_x has enabled H^–/N^3– exchange at a lower temperature, yielding a ferroelectric oxynitride BaTiO_3−xN_2x/3.

The stability of charged fullerenes is not as well understood as that of their neutral counterparts, with, for example, more frequent violations of the isolated-pentagon and pentagon-adjacency penalty rules. Now, a simple model based on the concepts of cage connectivity and frontier π orbitals predicts the relative stability of cationic and anionic fullerene isomers.

Cross-couplings between boronic acids and halides are a mainstay of synthetic organic chemistry but enantioselective ${\text{C}}_{s{p}^2}-{\text{C}}_{s{p}^3}$ couplings are rare, and simply retaining the stereochemistry of the starting material is problematic. Now, it is shown that racemic allylic halides can converted to single enantiomer products by a rhodium(I)-catalysed asymmetric allylic arylation using arylboronic acids

Avoiding equal probability for clockwise and anticlockwise rotation is essential for the function of molecular motors, and both biological and synthetic systems take advantage of chirality to control the rotary direction. Now it has been shown, by integrating two rotor moieties in a symmetric meso motor design, that light-driven unidirectional rotary motion can be achieved in an achiral system.

O-linked N-acetyl-glucosamine (O-GlcNAc) has been identified as an endogenous modification of α-synuclein; however, its effect on the properties of the protein is unclear. Now, recombinant protein and synthetic peptides have been combined to produce both unmodified and site-specifically O-GlcNAc-modified α-synuclein. The O-GlcNAc modification at threonine 72 was shown to inhibit the aggregation and associated toxicity of α-synuclein.

Using iron instead of the scarce ruthenium in light-harvesting complexes is challenging because iron complexes generally have short-lived excited states. Now an iron complex has been developed that has a long-lived excited state, which can lead to photo-induced electron injection into nanoporous TiO₂ with a yield of 92%.

A manganese catalyst is reported that aminates C–H bonds via a mechanism that lies between that of reactive noble metals (concerted) and chemoselective base metals (stepwise). Rather than exhibiting intermediate reactivity and selectivity, [Mn(^tBuPc)] is an outlier, and aminates all C(sp³)–H bonds, including 1°, while remaining tolerant of oxidizable π-functionality.

The rotational state of a molecule is not generally considered to play a role in how fast it reacts; however, when the temperature is low quantum effects become more important. Now, it is shown that at low temperatures rotationally excited H₂ molecules react with He faster than non-rotating ground-state molecules — a process mediated by stronger long-range attraction.

Amphiphilic-peptide-driven opening of elastin-like protein molecules triggers the self-assembly of a multilayered membrane. This dynamic system can undergo morphogenesis into hierarchically ordered tubular structures that can be used to create complex scaffolds for tissue engineering.

The self-assembly of short amphiphilic α-helicomimetic foldamers bearing proteinaceous side-chains can be controlled by manipulating the side-chain sequence. This enables the foldamers to be programmed to form either discrete helical bundles containing isolated cavities, or pH-responsive water-filled channels with controllable pore diameters.

Covalent organic frameworks (COFs) feature periodic layers and ordered pores that make them promising for applications in catalysis, but they typically suffer from poor stability. Now, adding methoxy groups to its pore walls has been shown to strengthen a COF's interlayer interactions, resulting in a stable, crystalline, porous material that can be further converted into chiral organocatalysts.

Impure glycerol is obtained as a significant by-product of biodiesel production. Now it is shown that this crude glycerol can be reacted with water over very simple basic or redox oxide catalysts to produce methanol in high yields, together with other useful chemicals, in a one-step low pressure process.

Multicomponent supramolecular hydrogels have been prepared using a self-sorting mixture of two different gelators—one of which is photosensitive. Irradiation of the gels through a mask leads to the photosensitive network being selectively removed by a light-triggered gel-to-sol transition in a process that can be used to produce patterned gels with spatially controlled properties.

Labelling biomolecules to improve the sensitivity of analysis can perturb their interactions. Now, microfluidic and chemical tools have been used to allow simple, sensitive detection of a labelled system to reveal the behaviour of the native and physiologically relevant unlabelled system. The system was used to characterize the solution-phase behaviour of a clinically relevant protein–protein interaction.