Articles in 2014

Studies of the Earth's atmosphere have shown that more than 90% of xenon is depleted — the so-called missing Xe paradox. Now a theoretical study shows that Xe and Fe/Ni can form inter-metallic compounds of XeFe₃ and XeNi₃ under conditions found in the Earth's inner core, and could provide a solution to the puzzle.

A hybrid protocell model is described in which a fatty acid membrane spontaneously assembles on the surface of coacervate microdroplets with molecularly crowded interiors. The membrane-enclosed protocells exhibit uptake and exclusion properties that differ from the uncoated droplets. The internal structure can be disassembled at high ionic strength without loss of membrane integrity. This model may help to reconcile alternative mechanisms of prebiotic compartmentalization.

A series of quadruplet decoding tRNAs has been developed to form an optimized orthogonal translation system. These tRNAs enable efficient, site-specific incorporation of multiple unnatural amino acids into a protein, with a substantial increase in yield over previous methods. The amino acids are then used to site-specifically label a protein with a pair of fluorophores, enabling studies of the protein's dynamics.

The biosynthesis of lipid mediators has not previously been identified in mitochondria. Here, polyunsaturated cardiolipins are shown to be oxidized in the mitochondria by cytochrome c. Subsequent hydrolysis of these oxygenated species generates a variety of oxygenated fatty acids as well as non-oxygenated and oxygenated lyso-cardiolipins. These reactions represent a new biosynthetic pathway for the production of lipid mediators.

Cascade reactions allow step-economical generation of molecular complexity. Now, a butatriene equivalent, TMSCH₂C ≡ CCH₂OH, is used to couple two powerful and convergent cycloadditions — the homologous Diels–Alder ([5 + 2]) and the Diels–Alder ([4 + 2]) reactions –– through a vinylogous Peterson elimination, en route to a series of kinase inhibitors inspired by staurosporine.

Reversible chirality switching and memory is demonstrated in a helical polyacetylene. Both the helicity of the polymer backbone and the axial chirality of the side chains contribute to the memory effect. When used to produce a chiral stationary phase for a chromatographic enantiomer resolution it was possible to switch the elution order under identical chromatographic conditions.

Solar thermal fuels have recently attracted an increasing amount of attention as a potential method for solar energy capture, conversion, storage and utilization. Azobenzene-functionalized single-walled carbon nanotubes demonstrate the proof-of-principle for increasing kinetic stability and energy densities by templating photoswitchable molecules on nanostructures to achieve highly (con)strained configurations.

Self-powered micropumps that are turned on by the presence of their respective substrates are formed from surface-immobilized, ATP-independent enzymes. Coupling substrate-sensing with transport enables the design of devices that deliver cargo in response to specific stimuli. Demonstrated here is the release of insulin at a rate proportional to ambient glucose concentration.

Cytosine base modifications 5-methylcytosine (5mC), 5-hydroxymethylcytosine (5hmC) and 5-formylcytosine (5fC) are present in mammalian DNA. Reduced bisulfite sequencing is now developed for quantitatively sequencing 5fC at single-base resolution. This method is then applied with oxidative bisulfite sequencing to gain a map of 5mC, 5hmC and 5fC in mouse embryonic stem cells.

Actinides generally form ionic compounds, however, when electron-rich ligands with large hyperpolarizabilities are used, partially covalent bonds can also form. Now a rare californium borate is shown to exhibit significant differences from other f-elements in its structure and bonding. Quantum mechanical calculations support Cf and ligand orbital interactions, also indicating partial covalent bonding.

Thiol-based self-assembled monolayers have a huge variety of potential applications but are hampered by oxidative and thermal instability. Now, N-heterocyclic carbenes are shown to form densely packed layers on Au(111) that are considerably more stable than thiol films, resisting hot organic solvents, acid, base, oxidant and oxidative electrohemical etching.

Criegee intermediates play an important role in atmospheric chemistry but their direct study has proved difficult. Transient infrared absorption spectroscopy has now been used to probe the decay kinetics of the Criegee intermediate CH₂OO directly, revealing that its self-reaction is extremely rapid. This may have important consequences for the interpretation of previous laboratory experiments.

FeFe hydrogenases, the enzymes that oxidize or produce H₂, are inactivated under oxidizing conditions. Here, it is shown that this inactivation results from H₂ binding to coordination positions that are normally blocked by intrinsic CO ligands. This flexibility of the active site prevents irreversible oxidative damage.

Amyloid fibril formation is often catalysed by mature fibrils or other aggregates on the fibrillization pathway; however, fibrils cannot normally catalyse other chemical reactions. Here, small seven-residue peptides designed from first principles are shown to form amyloid fibrils that can efficiently catalyse ester hydrolysis.

Restoring a protein's function in response to specific stimuli can enable a signalling pathway to be activated and the effect monitored over time. Here, a chemical rescue strategy for restoring protein function inside live cells is described, in which palladium catalysts are used to deprotect a propargylcarbamate group of a lysine analogue.

Strained hydrocarbons are more than molecular curiosities — they often have promising materials properties, and even just making them offers challenges that push the limits of synthetic methods. Now, a short, efficient and room-temperature synthesis of [5]cycloparaphenylene, a carbon nanohoop with 119 kcal per mol of strain energy, is reported.

Radical polymerization of a metastable lactone intermediate — formed from carbon dioxide and butadiene using a palladium catalyst — produces a high-CO₂-content (29 wt%) polymer. This approach circumvents the thermodynamic and kinetic barriers typically associated with direct copolymerization of carbon dioxide and olefins, and can also be applied to one-pot co- and terpolymerization of carbon dioxide and 1,3-butadienes.

A Ni-Ga catalyst that reduces CO₂ to methanol at ambient pressure has been discovered through a descriptor-based computational analysis, and has been shown experimentally to be particularly active and selective. This represents a first step towards the development of small-scale low-pressure processes for CO₂ reduction to methanol from distributed hydrogen production.

The availability of facile cross-coupling protocols is sometimes blamed for the high occurrence of ‘flat’ aromatic molecules in drug-screening collections. Here, reagents are described that make possible the one-step transformation of aldehydes into medium-ring saturated N-heterocycles. The methodology has exceptional substrate scope and functional group tolerance and provides a route to heterocycles not easily prepared by other methods.

A family of dipeptide-based metal–organic frameworks has been shown to respond to the presence of guests in a cooperative manner controlled by one amino acid residue. When the linker features a serine residue, guest removal enables the formation of hydrogen bonds between the residue's side-chains, causing a conformational change that closes the MOF's porous domain.