Articles in 2013

Pentalyne — a bicyclic anti-aromatic molecule that contains a strained five-membered ring — is a challenging synthetic target. Incorporation of an osmium centre has been shown to stabilize such features and enable the preparation of two osmapentalyne derivatives. Despite featuring the smallest angles observed so far at a carbyne moiety, these molecules benefit from Möbius aromaticity and reduced ring strain.

Previously unobserved types of reactive species formed on the core ionization of liquid water have been identified using a combination of liquid microjet photoemission spectroscopy and ab initio calculations. The charge-separated di-cationic species are formed within a few femtoseconds, through proton-transfer-mediated processes followed by autoionization.

Using ab initio simulations external mechanical forces are shown to trigger structural changes to disulfide bridges that result in conformations that are less susceptible to nucleophilic attack. This finding is crucial for the interpretation of recent force microscopy experiments, and could be important for understanding protein regulation.

Macrocycles are key compounds in supramolecular chemistry, yet their efficient preparation is an ever present challenge. Now, it has been shown that a C₅-symmetric macrocycle, termed ‘cyanostar’, can be formed in high yields on multigram scales in one pot. Cyanostars form unusually strong sandwich complexes with large and weakly coordinating anions and can template the formation of a dialkylphosphate [3]rotaxane.

For researchers to rapidly adopt new synthetic methodology, they need to gauge whether the reaction will work for their substrate — a point not easily conveyed by traditional screens of reaction scope. Here, a simple method is described to assess the likely scope and limitations of a chemical reaction beyond the idealized conditions initially reported.

A general and selective palladium-catalysed cross-coupling of aryl- and alkenyl-bromides with a wide range of alkyl-, aryl- and heteroaryl-lithium reagents is reported. The process proceeds quickly at room temperature, and avoids the notorious lithium–halogen exchange and homocoupling side-reactions commonly associated with these extremely reactive organometallic compounds.

Methods for stabilizing enzymatic activity in the gastrointestinal tract are rarely investigated because of the difficulty in protecting proteins from an environment that promotes their digestion. Now, functionally diverse polymers have been conjugated to therapeutic enzymes, which lead to a substantial enhancement of their in vivo activity in the gastrointestinal tract.

Many-electron quantum modelling of the metal clusters in metalloenzymes is a long-standing ambition for theoreticians. Here, using the density matrix renormalization group, the many-electron wavefunctions of the Mn₄CaO₅ cluster of photosystem II are computed, providing new insights into the electronic structure and reactivity at the level of many-particle quantum mechanics and entanglement.

A tubular assembly based on barrel-shaped chaperonin protein mutants, held together through coordination to magnesium ions, has been devised that carries and delivers guests into cells. The hydrolysis of ATP — present in much higher concentration inside the cell than outside — induces a conformational change in chaperonin that in turn triggers the guest release.

The average single-nanocrystal spectral linewidth within an ensemble of nanocrystal emitters in solution can be directly and quantitatively measured using photon-correlation Fourier spectroscopy (S-PCFS). Variations in single-nanocrystal linewidths between batches are found to be significant and synthetically tunable, introducing new avenues for the optimization of nanocrystals for optical applications.

The disassembly of a parent zeolite and its reassembly into two zeolites with targeted topologies is described. This process demonstrates that it is possible to target specific ring sizes in a zeolite by replacing one size of unit in the structure with alternative units of a different size.

A scanning tunnelling microscope has been used to image multistep chemical reactions at a solid/liquid interface with single-molecule resolution. On reacting Mn(III) porphyrins with either O₂ or a single oxygen donor, at least four distinct reaction intermediates and products were detected and their interconversion could be observed in real space and real time.

Carbon nanotubes (CNTs) are typically produced as a mixture of tubes with different diameters and sidewall structures — parameters that determine the optical and electronic properties of these materials. Now, it has been shown that discrete carbon nanorings can be used as templates to control the bottom-up growth of CNTs with a narrow distribution of diameters.

The influence of protein motions on the chemical step of enzyme reactions is a contentious issue. Now, by constructing free-energy surfaces using an explicit solvent coordinate, it is shown that, although some structural flexibility is required, protein motions can be described as equilibrium fluctuations.

Removing Mg²⁺ from RNA and replacing it with Fe²⁺ confers on some RNAs the ability to catalyse single-electron transfer. Here, it is hypothesized that Fe²⁺ was an RNA cofactor on the early Earth, when iron was benign and abundant, and was replaced by Mg²⁺ during a period known as the great oxidation, brought on by photosynthesis.

Natural products are enduring leads for exploring cell biology, yet structure–activity relationship studies and 'arming' of these small molecules for subsequent cellular probe synthesis remains a challenge. Here, a strategy for derivatization of natural products by C–H amination, aziridination and unusual N-aminations is described. Selective derivatization of eupalmarin acetate led to identification of this natural product's target.

Darwinian evolution involves competition between members of a population. Here, the synthesis of a hydrophobic dipeptide catalysed by a second dipeptide in a model protocell — a vesicle — is described. The reaction product partitions to the vesicle membrane, which grows by accumulating fatty acids derived from neighbouring vesicles. Thus, an encapsulated catalyst drives competition between the model protocells.

A general method for the stereoretentive Pd-catalysed cross-coupling of secondary alkyl azastannatranes and aryl electrophiles is described. This work constitutes the first example of a stereoretentive cross-coupling reaction using an unactivated, isolable, optically active organometallic nucleophile.

Recharging Li–O₂ batteries requires oxidation of the discharge product solid Li₂O₂. Now a redox-mediating molecule is shown to assist this process by transferring electron–holes between solid Li₂O₂ and the positive electrode in a non-aqueous Li–O₂ cell. This allows the cell to be charged at rates that are otherwise impossible.

Pyrolysis of defined nitrogen-ligated cobalt acetate complexes onto a commercial carbon support transforms the complexes into heterogeneous Co₃O₄ materials. These reusable non-noble-metal catalysts are highly selective for the industrially important hydrogenation of structurally diverse and functionalized nitroarenes to anilines.