Articles in 2017

Hexacoordinate silicon is seen often in molecular compounds, but very rarely in crystalline silicate materials. Now, reversible Si–O chemistry has been used to assemble octahedral dianionic SiO₆ building units and anthracene derivatives into crystalline microporous silicate organic frameworks that share characteristics of both covalent organic frameworks and inorganic zeolites.

A DNA-based reaction network has now been developed that creates a French flag pattern with immobile and sharp borders from a shallow initial concentration gradient. The output pattern can be used to control the macroscopic organization of DNA-decorated particles thereby inducing a French flag pattern of colloidal aggregation.

Reports of superconductivity in K_xPicene spurred interest in alkali-intercalated polyaromatic hydrocarbon (PAH) compounds, but their compositions and structures have remained unclear. Now crystalline K₂Pentacene and K₂Picene — neither of which are superconducting — have been prepared by mild synthesis. Structural analysis shows that the cation sites arise within the molecular layers from reorientation of the PAHs within a herringbone packing.

The field of high-valent uranium chemistry has been dominated by the linear uranyl moiety [UO₂]²⁺ and its imido analogues. A family of tetrakis(imido)uranate dianions has now been developed that displays four uranium–nitrogen multiple bonds. Their geometry is dictated by cation coordination and steric factors rather than electronic ones.

Cooperative electronic properties that arise purely from carbon π-electrons can lead to unconventional superconductivity and quantum magnetism. New packing architectures have now been established in two caesium-intercalated polyaromatic hydrocarbons, CsPhenanthrene and Cs₂Phenanthrene, both strongly correlated multi-orbital Mott insulators. The frustrated magnetic topology in CsPhenanthrene also renders it a spin-½ quantum spin liquid candidate.

The assembly–disassembly–organization–reassembly (ADOR) process has recently enabled the synthesis of unusual — and sometimes previously inaccessible — inorganic materials. Further insight into its complex mechanism has now been gained that explains the unexpected formation and structure of such a zeolite.

Cross coupling under transition-metal-free conditions is an attractive and economic alternative to traditional transition-metal-catalysed methods. Metal-free coupling of azaallyls has now been demonstrated with vinyl bromide electrophiles, delivering allylic amines in excellent yields. Moreover, mechanistic evidence supports dual reaction pathways triggered by azaallyl anions and radicals.

Polypropionates can be grown — one carbon atom at a time — using the iterative homologation of boronic esters. This assembly line strategy was enabled through the use of enantioenriched lithiated α-chlorosilanes as masked carbinol units. Polypropionates were obtained in a fully stereocontrolled manner, including the stereochemically challenging anti–anti isomers.

Berkelium is the only transplutonium element predicted to be able to exhibit both +III and +IV oxidation states in solution. Bk(IV) has now been stabilized through chelation with a siderophore derivative. The resulting neutral coordination compound was characterized and compared with the negatively charged species obtained by chelation of neighbouring trivalent actinides.

An interconverting system of three distinct stereoisomers of a cuboctahedral Co^II-based cage is able to regulate the binding affinities of large anionic guests. Through cooperative templation with fullerene guests, the cage converts into a desymmetrized cage that in turn exhibits positive cooperativity in binding of an icosahedral anion; this interaction is anti-cooperative in the fullerene-free parent.

A chiral molecule on a metal surface can set up a prochiral molecule for an enantioselective reaction step by forming a hydrogen-bonded complex that imposes a specific adsorption geometry. Time-lapsed scanning tunnelling microscopy and density functional theory studies reveal that such complexes can sometimes switch between states of opposing prochirality.

The self-propagation of misfolded conformations of tau occurs in neurodegenerative diseases, including Alzheimer's disease. The microtubule-binding region, tau_244-372, reproduces much of the aggregation behaviour of tau in cells and animal models. Now, it has been shown that a 31-residue peptide from tau's R3 domain forms a cross-β conformation that efficiently seeds aggregation of tau_244-372 in cells.

Dissociative reactions in the solid state are prone to sample damage. Now, improved sample handling and measurement conditions enable the study of the dissociative reaction of a model triatomic system in the solid state on ultrafast timescales, revealing the significant impact of lattice coordination on the reaction pathway.

Abiotic hydrogel polymer nanoparticles with affinity for a key vascular endothelial growth factor (VEGF₁₆₅) have now been developed. This high-protein affinity was engineered by carefully controlling the amount and the substitution pattern of sulfated N-acetylglucosamines and the inclusion of a hydrophobic group in the monomer.

The manner in which carboxylates bind to the surface of nanoparticles has been an important question in materials science. Now, multinuclear magnetic resonance experiments — alongside DFT calculations, XPS and TEM measurements — have elucidated the three-dimensional ligand structures of gold nanoparticles capped with various ratios of carboxylate-containing ligands, and enabled the determination of the most probable binding modes.

Tyrosine sulfation strongly enhances the inhibition of thrombin by the tick-derived anticoagulants madanin-1 and chimadanin. Protein chemical synthesis and structural studies have revealed a mode of inhibition that is unprecedented among cysteine-free anticoagulant proteins. This inhibition occurs through the recognition of the highly basic exosite II of thrombin.

Chiral iminium ions generated from an amine catalyst and enals are key organocatalytic intermediates in thermal asymmetric processes. Now, visible-light excitation of these iminium ions can turn these compounds into strong oxidants to enable enantioselective photochemical β-alkylations of enals with silanes, which are unachievable via conventional ground state pathways.

Although DNA nanotechnology has found many applications in developing functional structures, there has never been an independent device contained within a 3D crystal. Now, a self-assembled three-state device that can change the colour of its crystal by diffusion of DNA-ligated dyes has been reported, representing the potential to develop programmable nanomechanical devices.

Main-chain polymetallocenes are typically static in nature due to strong metal–ligand bonding. Now, it has been shown that such polymers based on nickelocene are dynamic due to weaker nickel–cyclopentadienyl interactions, and at low concentration or at elevated temperature, depolymerization to the moderately strained monomer occurs.

Breathing metal–organic frameworks (MOFs) are functional materials whose molecular-scale pores can reversibly open and close. In contrast to typical defined structural transitions, continuous breathing has now been observed for a diamondoid MOF. Removal of two different solvents leads to two desolvated MOF polymorphs with dramatically different porosities and gas uptake properties, including CO₂/CH₄ selectivities. Partial desolvation introduces pressure-gated CO₂ adsorption.