Volume 6 Issue 5, May 2014

Biological solar energy conversion requires the coordinated and rapid movement of protons and electrons through complex proteins, called reaction centres. Now, an artificial and structurally simple reaction centre has been synthesized that mimics an important, photosynthetic charge relay.

Anfinsen's principle tells us that the folded structure of a protein is determined solely by its sequence. Now, it has been shown that the rate at which a polypeptide chain is synthesized in the cell can affect which of two alternative folded structures it adopts.

Labelling of proteins with pairs of fluorophores enables their conformations to be studied; however, complete incorporation of labels in multiple, pre-defined locations is very difficult. Now, a combination of double unnatural amino acid mutagenesis and selective chemical modification offers a general method to achieve this.

Force-induced covalent bond changes in mechanophore-linked polymers typically require large, irreversible material deformation, limiting successive activation cycles. Now, repeated force-induced reactions have been achieved by incorporating flex-activated mechanophores into elastomeric networks.

The synthesis of [5]CPP, the smallest and by far the most strained member of the family of macrocycles known as cycloparaphenylenes, has been reported in quick succession by two different research groups. But how long will the new record holder retain its title?

Nanoscopic templates functionalized with light-reactive chromophores could ultimately be used to store solar energy and later release it as heat. Now, it has been shown that packing the chromophores together increases both storage capacity and lifetime.

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.

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.

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.

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.

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.

An artificial reaction centre has been designed that contains a benzimidazole–phenol model of the Tyr–His relay in photosystem II. It has been seen to mimic both the short internal hydrogen bond of the natural relay, and — using electron paramagnetic resonance —the relaxation behaviour that accompanies proton-coupled electron transfer in photosystem II.

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.

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.

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.

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.

Eric Ansoborlo considers the disproportionate potency of polonium compared with its relative scarcity on Earth.