Articles in 2012

The site-selective initiation and propagation of an atom-transfer radical polymerization reaction forms an addressable crosslinked polymer constrained within the interior cavity of a virus-like particle derived from the bacteriophage P22. This protein–polymer hybrid is useful as a new vehicle for high-density delivery of small-molecule cargos.

The self-sorting of molecular building blocks should allow 2D surface patterns to be transcribed into 3D functional materials. Here, a non-empirical approach to the templated synthesis of supramolecular architectures on surfaces is reported, starting with a theoretical model and followed by comprehensive experimental validation, including direct evidence for functional relevance of the produced materials.

Metal–organic frameworks featuring unsaturated metal sites have emerged as promising materials for CO₂ capture, but the host–guest interactions at play have remained poorly understood. An approach based on quantum chemical calculations has now been devised to generate force fields that accurately describe a MOF's metal sites and predict its gas uptake abilities.

Better understanding of the mechanisms of singlet fission may facilitate its implementation in solar cells, improving their efficiency. Although singlet fission in tetracene is endothermic, it is now observed not to be thermally activated; rather a quantum coherent process allows access to the higher-energy multi-exciton state, which then forms two triplet excitons through an entropic driving force.

Understanding the nature of complex zeolite particles, used as catalysts in industrial reactors, is vital for their further development. Now, an integrated approach to visualizing granules of a hierarchical MFI-type zeolite, on length scales from nanometres to millimetres, is reported.

The chemical modification of graphene is important for its use in many applications. Now it is shown that the reactivity of graphene towards covalent modification varies widely depending on its underlying support substrate, and that the substrate can be patterned to induce spatial control of chemical reactions in graphene.

A coordination cage has been prepared that self-assembles through second-order templation. Peripheral perchlorate or hexafluorophosphate template anions direct the formation of a hollow prism whose central pocket was able to bind a small anionic guest such as halide or azide, in a manner reminiscent to signal transduction in biological systems.

Selective carbohydrate binding is a difficult task, usually accomplished by proteins (lectins) or complex synthetic analogues. It has now been achieved by a remarkably simple compound, accessible in just five steps from commercially available materials. This new receptor is highly selective for all-equatorial carbohydrates, and may be used to sense glucose through changes in anthracene fluorescence.

Metal cations play an important role in biological proton relays by modulating the pK_a values of surrounding amino acids. This effect has now been used to induce the isomerization of two hydrazone switches using a single input. It is found that a combination of electrostatic repulsion and conformational changes are required for the proton relay to take place.

Reactions with unstable and highly reactive zwitterionic intermediates generated in transition-metal-catalysed processes provide new opportunities for molecular constructions. Here imines, activated by chiral organocatalysts, have been employed to trap the zwitterionic intermediates to give polyfunctionalized indole and oxindole derivatives in a single step with excellent diastereoselectivity and enantioselectivity.

In heterogeneous catalytic processes the Arrhenius parameters are often found to be interrelated (compensation phenomenon). Using state-of-the-art experiments and density functional theory, the origin of compensation is studied. A similar dependence on the rate-limiting surface-coverage term is found for both apparent activation energy and prefactor terms, which can be translated into surface configurational entropy contributions.

Chemical glycosylations are perhaps the most important reactions in glycoscience, but the mechanisms are not well understood. Here, quantum chemical calculations combined with natural-abundance NMR measurements of ¹³C kinetic isotope effects reveal both associative and dissociative mechanisms at the extremes of a continuum that depends on the relative stereochemistry of the substrate and the anomeric configuration of the product.

Selective modifications of structurally complex molecules bearing multiple reactive functional groups often require cumbersome multistep synthetic efforts. Here, aptameric protective groups based on short RNA sequences are described — they bind to neamine antibiotics, simultaneously protecting several functionalities and enabling regio- and chemoselective functionalizations.

Simplified bryostatin analogues are shown to potently induce latent HIV expression in vitro. These analogues display comparable or better potency when compared with bryostatin. Moreover, they are up to 1,000-fold more potent in inducing latent HIV expression than prostratin, the current lead preclinical candidate.

Simple uranium complexes, UX₃, are shown to disproportionate in the presence of a reducing agent under mild conditions, cooperatively binding and reducing arenes. This enables arene C–H bond activation and borylation, and the trapping of reactive substituted arenes in inverse sandwich complexes.

Organometallic reagents are widely used as nucleophiles in asymmetric catalysis. Here, alkylmetal species generated in situ by hydrometallation of alkenes are used in enantioselective copper-catalysed C–C bond formation. The process is formally an asymmetric reductive coupling of an alkene to an enone, and tolerates many functional groups.

The pressure- and temperature-dependent changes of various hydrogen bonds within ubiquitin have been determined at very high resolution using NMR H-bond scalar couplings. The measured perturbations show a correlation with the sequence separation between donor and acceptor residues, and indicate that certain topologically crucial H-bonds are specifically stabilized.

A bench-stable, aryl sulfonyl triazene is described that can be appended to alcohols or amines and used as a directing group to effect remote desaturation of unactivated aliphatics to produce olefins. The reaction is mild, operationally simple, requires no added metals and produces unsaturated tosylates or tosylamides available for further functionalization.

The collective excited states (excitons) in supramolecular light-harvesting systems depend intimately on their structure and it is crucial to understand how these states interact. Now it is shown that simple redox chemistry can be used to address this fundamental question by simplifying the complex excitonic interactions in such multichromophoric systems.

Marinomycin A is a member of a new class of bis-salicylate-containing polyene macrodiolide, with potent antibiotic activity against methicillin-resistant Staphylococcus aureus (MRSA) and vancomycin-resistant Enterococcus faecium (VREF). Here, a triply convergent synthesis of this agent is described that uses the salicylate moiety as a novel molecular switch for the chemoselective construction of the macrodiolide.