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Covalency in actinide–ligand bonding is poorly understood compared to that in other parts of the periodic table due to the lack of experimental data. Here, pulsed electron paramagnetic resonance methods are used to directly measure the electron spin densities at coordinated ligands in molecular thorium and uranium complexes.
Although the synthetic chemistry of carbon dioxide has generally been limited to two-electron pathways, single-electron mechanisms would open avenues to new reactivity. Now, the coupling of carbon dioxide and amines to produce α-amino acids can be achieved by an organic photoredox catalyst in continuous flow.
Higher-order cycloadditions — cycloadditions involving more than six π electrons — provide easy access to complex molecules containing heterocyclic or carbocyclic scaffolds. Now, it has been shown that aminocatalytic activation of 2-cycloalkenones affords mixtures of dienamines that can undergo [6 + 4] cycloadditions with heptafulvenes through a cross dienamine, or [8 + 2] cycloadditions through a linear dienamine.
Unlike in biomolecular systems, synthetic self-assembly is largely spontaneous, thus limiting the complexity and functionality of the materials one can create. Now, self-assembly under out-of-equilibrium conditions is demonstrated for a metastable supramolecular system. Differentiation of nanoparticles into nanofibres and nanosheets — with electronically distinct states — is achieved through kinetic control, illustrating pathway-dependent material properties.
The operational simplicity of modifying the surfaces of thiol-capped gold nanoparticles has been a hallmark of their success in materials chemistry, despite having limited control over the surface composition. Now, SNAr chemistry on activated perfluoroaromatics has been shown to mimic this simplicity and allow for the synthesis of atomically precise nanomolecules.
Using self-assembly to generate hydrogen-bonded organic networks is an underexplored method when preparing functional framework materials. Now, taking cue from DNA, bio-inspired G-quadruplexes are used as both intrinsic electron donors and hydrogen-bonding linkers to assemble rylene diimide acceptors. The resulting rectangular grids form layered crystalline frameworks, in which photoexcitation produces long-lived mobile charge carriers.
The transmission of chemical information across lipid bilayer membranes is crucial in biological systems. Now, an artificial chemical system able to both transduce and amplify chemical signals across a membrane has been developed. The system works by exploiting the controlled translocation of a synthetic molecule that is embedded within a vesicle membrane.
The use of earth-abundant metals in catalysis is a prerequisite for the development of sustainable synthetic chemical processes for the future. Now, biomass-derived chemicals can be used in an efficient iron-catalysed reaction to make complex spirocycles. The resulting products contain two asymmetric centres that are furnished in high stereoselectivity.
Effective regulation over the motion of self-propelled micro- and nanomotors is a challenging proposition. Now, self-assembled stomatocyte nanomotors with thermoresponsive polymer brushes have been designed that sense changes in local temperature and regulate the accessibility of the hydrogen peroxide fuel — thereby adjusting the speed and behaviour of nanomotor itself.
Parallel kinetic resolution (PKR) of N-heterocycles via asymmetric acylation has been achieved using quasienantiomers of polymer supported hydroxamic acid reagents. Flow techniques provide physical separation of the reagents, establishing a practical implementation of PKR. The enantioenriched amide products can be readily deprotected to reveal the desired amine without detectable epimerization.
Singlet fission — the splitting of a singlet exciton into two triplets — is a process that could be exploited to improve the power conversion efficiency of solar cells. Spectroscopic data now suggest that coherent and incoherent mechanisms for singlet fission in crystalline hexacene coexist and occur on different timescales.
Nature has evolved a variety of different mechanisms to generate chemical diversity; however, the reactions responsible for generating such diverse chemical libraries are often not clear. Now, the mechanisms employed by entomopathogenic bacteria for the biosynthesis of a large family of bioactive peptides have been identified. These include substrate promiscuity, enzyme cross-talk and enzyme stoichiometry.
A computational method to design cyclic protein homo-oligomers has been developed. Using this approach, a series of idealized repeat proteins incorporating designed interfaces that direct their assembly into complexes possessing cyclic symmetry were fabricated. 15 out of 96 oligomers that were characterized experimentally were shown to be consistent with the computational model.
Methods utilizing renewable feedstocks are critical to accessing molecules of industrial importance in light of the present ecological and economic climate. Here, it is shown that umpolung reactivity of carbonyl compounds can be used for nucleophilic additions to yield a diverse array of valuable alcohols as an alternative to using stoichiometric organometallic reagents.
Polytheonamides are giant peptide toxins produced by the uncultivated sponge bacterium Entotheonella factor. The biosynthesis of polytheonamides involves up to 50 post-translational modifications. Now, heterologous expression in Escherichia coli and Rhizobium hosts have shown that a minimalistic, iterative enzyme set introduces this exceptional molecular complexity via epimerizations, C-/N-methylations, hydroxylations, dehydration and proteolytic maturation.
The direct transfer of primary amino and hydroxyl groups to arylmetals in a scalable and environmentally friendly fashion remains a formidable synthetic challenge. Here, it is demonstrated that bench-stable N–H and N–alkyl oxaziridines can be used as efficient multifunctional reagents, without deprotonation, for the direct primary amination and hydroxylation of (hetero)arylmetals.
Aggregation usually prevents dissolution of graphene in water. Now, hydroxide ion adsorption has been shown to allow the stabilization of true single-layer graphene in water — with no surfactant required — so long as the liquid is degassed beforehand. The resulting aqueous dispersions can contain high concentrations of exfoliated graphene that are stable for several months.
Homogeneous crystal nucleation has now been observed by transmission electron microscopy in real time on a molecular scale. Countercation-dependent observations of polyoxometalate proto-crystal formation confirm existence of a higher energy classical molecular attachment mechanism, as well as a lower energy two-step mechanism via an intermediate dense phase.
Flat, prochiral molecules form chiral adsorbates on achiral surfaces, but such assemblies are globally racemic. Now, it is shown that this mirror symmetry can be broken through stereocontrolled on-surface synthesis. Enantiopure helicene molecules can be transformed into flat, enantiofacially adsorbed products through a cascade of reactions on Ag(111) monitored by high-resolution scanning probe microscopy.
Isolating nanoscale species in liquids permits their scalable manipulation, enabling numerous fundamental and applied processes. Thus, achieving true dissolution of 2D materials is particularly desirable. Now, ionic salts of a range of important layered materials have been shown to spontaneously dissolve, yielding solutions of charged, monodisperse, undamaged and easy-to-manipulate 2D nanosheets.
