Articles in 2015

Incorporation of a π-clamp—a four-residue sequence (Phe-Cys-Pro-Phe)—into a protein enables the site-specific modification of the π-clamp cysteine side-chain. The π-clamp can be genetically encoded and does not require protecting-groups or catalysts to provide selective conjugation.

The selective conversion of abundant and inexpensive alkane feedstocks into value-added speciality chemicals is a significant and challenging goal, and methods for catalytically converting alkanes into useful linear alkylsilanes are unknown, to date. Now, a strategy combining alkane dehydrogenation with regioselective olefin isomerization–hydrosilylation to produce linear alkylsilanes is described.

Factory assembly lines often feature robots that pick up, reposition and connect components in a programmed manner. Now, it has been shown that a molecular machine is able to pick up a cargo, reposition it, set it down and release it at a site approximately 2 nm away from the starting position.

Intracellular bodies called liquid organelles are rich in nucleic acids and proteins, and are thought to occur by liquid–liquid phase coexistence. Now, enzymatic control over the phosphorylation state of a simple cationic peptide, thereby altering its electrostatic interaction with RNA, has been shown to drive formation and dissolution of droplets that mimic these intracellular liquid bodies.

The encapsulation and stabilization of an oxygen tolerant [NiFe]-hydrogenase, sequestered within the bacteriophage P22 capsid, has now been achieved through a directed self-assembly process. Probing the catalytic activity and infrared spectroscopic signatures of the bio-inspired assembly shows that the capsid provides stability and protection to the hydrogenase cargo.

Little is known about how the identity of a leaving group affects the dynamics of a bimolecular nucleophilic substitution reaction. A study of the reaction of F⁻ with CH₃Cl, and comparison to its reaction with CH₃I, now reveals key insights into such effects, with reactant orientation considered a key factor in understanding the behaviour observed.

Doping mesoporous materials is an attractive way to tune their properties, but typically disrupts the host materials’ structures. Ultrasmall graphitic pencil nanodots have now been prepared, doped with heteroatoms, and inserted in a well-dispersed manner within the ordered structure of mesoporous materials including TiO₂, carbon and silica, by a co-assembly approach.

A synthetic receptor has been designed to form pseudorotaxanes and polypseudorotaxanes with oligo/polysaccharides in water. Target substrates have all-equatorial substitution patterns, and include cellulose, cellodextrins and the cationic polysaccharide chitosan. The results suggest an approach to dissolving these polysaccharides under mild conditions and could prove useful for processing these abundant renewable resources.

Glycosyl cations are universally accepted as key intermediates in the mechanism of glycosylation—the reaction that covalently links carbohydrates to other molecules—but their high reactivity makes them difficult to characterize. Using HF/SbF₅ superacid, two glucosyl cations have been generated and stabilized, then characterized by NMR spectroscopy aided by computation and their conformation elucidated.

Bio-derived γ-butyrolactone (γ-BL) is commonly referred to as ‘non-polymerizable’ due to its low strain energy. Now it has been shown that ring-opening polymerization of γ-BL can in fact proceed to high conversions under ambient pressure with a suitable catalyst, producing high-molecular-weight polymers with controlled topologies and complete recyclability.

The self-assembly of building blocks is an enticing route towards functional materials, yet understanding and controlling the mechanisms at play has remained challenging. Now the different morphologies and emission colours of the aggregates of a platinum(II) compound has enabled its assembly pathways into different structures to be controlled and visualized in real time.

The structural order of supramolecular assemblies typically depends on the enantiomeric purity of their building blocks. Now, a perylene bisimide (PBI) derivative has been described that assembles into a single-handed supramolecular helix, which in turn packs into domains with an identical crystalline order irrespective of the PBI's chirality. A cogwheel mechanism is proposed.

Gels formed by metal–ligand coordination typically consist of single metal ions linked together by polymer chains. Now, metal–organic cages have been used as junctions instead. A gel was prepared that features a large number of polymer chains at each junction, including loops that further serve to functionalize the material.

The isomerization of the retinal chromophore of rhodopsin is the photochemical process that initiates the sense of vision. Now, heterodyne-detected transient grating spectroscopy has been used to resolve coherent vibrational dynamics during this process, helping to identify strictly local vibrational motions as the origin of the coherent surface crossing, which occurs on a sub-50-fs timescale.

Purely organic molecules with complex interlocked architectures have proved difficult to prepare in water. Now, a three-dimensional organic [2]catenane has been obtained in a weakly acidic aqueous solution, through an almost quantitative self-assembly process relying on dynamic hydrazone linkages. The catenane is kinetically stable in neutral and weakly basic environments.

Copper is a transition metal ion essential for the regulation of cellular oxidative stress and ATP production. Now, the inhibition of copper-trafficking proteins by a small molecule has been shown to significantly reduce proliferation of cancer cells. The results indicate that copper-trafficking proteins could represent new anti-tumour therapeutic targets.

Tridecafullerenes with 120 peripheral carbohydrate groups have been made in one step from hexakis-adducts of [60]fullerene by using azide–alkyne click chemistry. This synthetic approach offers control over the size and multivalency of these ‘sugar superballs', which are shown to be potent inhibitors of cell infection by an artificial Ebola virus, with IC₅₀ values in the sub-nanomolar range.

Amides have historically been considered stable and unreactive functional groups because of resonance stabilization. Here, it is demonstrated that Boc-activated amides can be employed in Suzuki–Miyaura couplings using non-precious-metal catalysis. The overall reaction is complementary to the widely employed Weinreb ketone synthesis.

[Fe]-hydrogenase has an iron-guanylylpyridinol cofactor and catalyses the reversible hydrogenation of a methenyl-tetrahydromethanopterin. Now, [Fe]-hydrogenase has been reconstituted using synthetic cofactor mimics. The enzyme containing a mimic with a 2-hydroxy-pyridine group was active, whereas one containing a 2-methoxy-pyridine group was inactive. This result, together with DFT computations, supports a catalytic mechanism involving the deprotonated pyridinol hydroxy group as a proton acceptor.

Synthetic anion transporters that replace the activity of defective anion channels have been proposed as treatments for cystic fibrosis; however, it remains uncertain whether such molecules are fundamentally toxic. A series of bis- and tris-(thio)ureas capable of transporting anions have now been tested in cells expressing halide-sensitive yellow fluorescent protein. One bis-urea compound proved especially effective while showing almost no toxicity.