Volume 9 Issue 9, September 2017

Suzanne Bart from Purdue University talks to Nature Chemistry about her investigations into the chemistry of actinides, and why she finds them both challenging and rewarding.

Merging the advantages of homogeneous and heterogeneous catalysts is a useful strategy for creating improved catalytic systems. Now, a concept has been developed that uses single Pd atoms — supported within liquid alloy droplets — that emerge from the droplet subsurface and interior to react with molecules approaching from the gas phase.

Mathematically modelling metal–ligand bonding in late transition-metal complexes has been an important tool in catalyst development — although lacking for early transition metals such as Cr and Ti. Now, a simple method for measuring ligand donor properties promises to elevate high-valent early transition metal catalysis to the same level.

Catalysis involving high-valent metals is an important facet of modern chemistry, but tools for catalyst development in this field have lagged behind those for low-valent systems. Now, an experimental system that can accurately model and predict reactivity has been developed to aid high-valent catalyst design.

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.

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.

Unlike in the d block, intervalence charge transfer is rare in the 5f block owing to localized valence electrons and poor overlap between metal and ligand orbitals. Delocalization of 5f electrons has now been observed in a Pu(III)/Pu(IV)–pyridinedicarboxylate solid-state compound. It occurs through metal-to-ligand charge transfer with both plutonium centres.

Creating systems that merge some of the advantages of both heterogeneous and molecular catalysis is a useful approach to developing improved catalysts. Following this strategy, a liquid mixture of gallium and palladium supported on porous glass has now been shown to form an active catalyst for alkane dehydrogenation that is resistant to coke formation and is thus highly stable.

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.

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.

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.

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.

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.

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.

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.

Chlorodifluoromethane (ClCF₂H), an inexpensive and abundant industrial raw material, represents an ideal and straightforward reagent for introducing the difluoromethyl group. However, efficient approaches for activation of the typically inert ClCF₂H are limited. Now, ClCF₂H is employed via a difluorocarbene pathway for palladium-catalysed difluoromethylation of arylboronic acids with broad substrate scope.

The first new element produced after the Second World War has led a rather peaceful life since entering the period table — until it became the target of those producing superheavy elements, as Andreas Trabesinger describes.