Articles in 2012

Polymer mechanochemistry can trigger a wide range of often unanticipated reactivity, but the focus of these systems typically falls on the structure of the mechanophore rather than the intervening polymer backbone. Now, it has been shown that a poly(norbornene) backbone has a substantial impact on a mechanochemical ring-opening reaction, despite having only a minor effect on the force-free reaction.

A hydrindanone-based approach to yohimbinoid natural products has been developed. A judicious choice of reaction conditions — inspired by prior work by the Stork group — allows effective control of the stereochemistry at C3 of the yohimbinoid skeleton. This approach has resulted in the first total syntheses of the C3 epimeric natural products venenatine and alstovenine.

The oxidation of methane to create useful feedstocks is hampered by over-oxidation when using O₂. Now a process using gaseous sulfur as a ‘soft’ oxidant for selective conversion to ethylene over metal sulfide catalysts has been developed. Simulations show that both methane activation and ethylene selectivity is linearly correlated with catalyst metal-sulfur bond strength.

A form of π backbonding is observed in a π-diborene complex of platinum, and confirmed by calculations. This interaction partially fills a bonding π orbital on the diborene ligand, strengthening the B–B bond. That π backbonding can strengthen bonds overturns ingrained notions that π backbonding is exclusively a bond-weakening phenomenon.

A 24 π-electron antiaromatic hexaphyrin derivative (rosarin) with a near-planar geometry enforced by bridging phenylene groups has been shown to undergo a proton-coupled electron transfer reduction when treated with certain protic acids. The reduction proceeds in a stepwise fashion to give first a 25 π-electron non-aromatic system and then a 26 π-electron aromatic ring.

Natural products populate areas of chemical space not occupied by average synthetic molecules. Here, an analysis of more than 180,000 natural product structures results in a library of 2,000 natural-product-derived fragments, which resemble the properties of the natural products themselves and give access to novel inhibitor chemotypes.

Milling and grinding, long used to alter the chemical and physical properties of materials, have recently garnered interest as alternatives to traditional solution-based syntheses — but these reactions remain difficult to monitor. High-energy synchrotron X-ray radiation has now enabled the in situ observation, in real time, of solid-state transformations occurring during the mechanochemical syntheses of metal–organic frameworks.

The in situ trapping of pyridynes is an efficient method for the generation of a variety of substituted pyridines but, until now, the method has been hampered by a lack of regiocontrol. Here, proximal halide and sulfamate substituents are shown to perturb pyridyne distortion and thus govern regioselectivities in pyridyne reactions.

An artificial transfer hydrogenase, based on the incorporation of a biotinylated iridium-piano-stool complex in streptavidin, is shown to be fully compatible with a range of biocatalysts. The location of the active metal centre inside the protein scaffold efficiently prevents mutual inactivation processes and enables the concurrent interplay with oxidative enzymes.

The infrared spectra of gas-phase protonated water clusters and protonated liquid water have been calculated from molecular simulations using a ‘clusters-in-liquid’ approach, which is restricted to a selected set of charged atoms. The infrared absorption due to the central proton in the H₂O···H⁺···OH₂ moiety is found near 1,740 cm⁻¹.

The lithium–O₂ battery can theoretically provide energy densities that greatly exceed that of Li-ion, but it requires more efficient catalysts (or ‘promoters’) than carbon for oxygen reduction and evolution. Here, we report a tailor-made mesoporous metallic oxide that results in high reversible capacities and operates over many cycles.

Oxatriquinane is a remarkably stable alkyl oxonium ion, despite the fact that its carbon–oxygen bond lengths are 1.54 Å. The robust nature of this fused tricyclic molecule enabled the addition of increasing steric bulk to the system, culminating in a tri-tert-butyloxatriquinane with a record 1.62 Å C–O bond distance.

The discovery and synthesis of inorganic clusters can be both time consuming and limited by a lack of reproducibility. An automated flow process coupled with multiple batch crystallization has now been successfully used to rapidly screen and scale-up the syntheses of inorganic clusters, including polyoxometalates and manganese-based single-molecule magnets.

Xenon is an inert element at ambient conditions but may become reactive under pressure. It has now been predicted that pressure stabilizes increasing oxidation states of Xe atoms (from Xe⁰ to Xe²⁺ to Xe⁴⁺ to Xe⁶⁺), and thus a series of compounds — XeO, XeO₂ and XeO₃ — become thermodynamically stable at megabar pressures.

The selective dissociation and formation of different functional groups in a single organic molecule may prove useful for making nanoscale devices and offer new opportunities for studying changes in electronic structure. It has now been shown that bond-selective chemistry can be induced and visualized at the submolecular level in a complex thiol-based molecule using a scanning tunnelling microscope.

Supramolecular gels whose properties can be tuned through non-covalent interactions — typically metal coordination or hydrogen bonding — are attracting attention in various fields. Researchers have now shown that halogen bonding is also strong enough to be relied on; it interferes with competitive, gel-inhibitory hydrogen bonding to induce co-gelation between two urea-based components.

A {U₁₂Mn₆} wheel-shaped cluster that has been assembled through cation–cation interactions exhibits single-molecule-magnet behaviour. Single-molecule magnets are promising for magnetic storage devices at the nanoscale, and the observation of magnetic bistability with an open hysteresis loop and high relaxation barrier in this 5f–3d complex suggests that uranium-based compounds could be useful components.

Site-selective functionalizations of complex small molecules can generate targeted derivatives with exceptional step-efficiency, but general strategies for maximizing selectivity in this context are rare. Investigations with the ion-channel-forming natural product amphotericin B have revealed that site-selectivity can be tuned by simply modifying the electronic nature of the reagents.

Hydroxyl radicals (OH) are important in many chemical systems, including combustion and atmospheric reactions, however experimentally measuring their velocities in specific internal quantum states has proved difficult. Now differential cross-sections for inelastic scattering of fully state-specified OH with He and Ar have been observed for the first time using velocity-map imaging in a crossed-molecular-beam arrangement.

The precise pairing of cysteine residues in proteins is routinely achieved in nature. However, the comparable pairing within polypeptides is a long-standing challenge for the preparation of multicyclic species. Here, a straightforward approach to direct the inter-/intramolecular pairing of cysteine residues within peptides using a minimal CXC motif is presented.