Volume 2 Issue 6, June 2010

Controlling the movements of molecular systems through external stimuli is crucial for the construction of nanoscale mechanical machines. A spring-like compound has now been prepared — a double helicate that retains its handedness under ion-triggered extension and contraction.

Can two identical reactors with the same concentrations, under identical physical conditions, have reaction rates that differ by a factor of a thousand? A study now shows that, although not true in uncrowded environments, a reactant's starting point makes a large difference to reaction kinetics in identically crowded systems, such as cellular nuclei.

Despite knowing that the active centres of many metalloprotein enzymes are iron porphyrin 'haem' complexes, chemists find them difficult to imitate. Now, the assembly of haem-like centres into a crystalline, stable, nanoporous array shows promise for biomimetic catalysis.

The composition of dynamic small-molecule libraries can be biased by the addition of a target compound — such as a protein — that binds selectively to one of the components in the mixture. The chemistry of the library must, however, be compatible with the target and it has now been shown that aniline-catalysed exchange of acylhydrazones fits the bill.

Mechanical linking of small cage structures leads to a type of metal–organic framework with an architecture topologically distinct from those constructed so far.

Ultrasound can be used to control molecular processes as delicate as rotation around a single carbon–carbon bond.

A new concept termed 'robust dynamics' is presented as the intellectual centerpiece to the union between metal–organic frameworks (MOFs) and mechanically interlocking molecules. Robust dynamics allows highly flexible entities, which are bound covalently to MOF backbones, to carry out repeated movements without affecting the integrity of the overall structure.

Helical molecules in biological systems commonly undergo extension, contraction and unidirectional twisting motions, but such twisting — promising for the construction of molecular machines — has rarely been achieved in synthetic systems. Now, a chiral double helix has been prepared whose spring-like motion is accompanied by an anisotropic twist under the control of sodium ions.

Although fullerenes have been synthesized from graphite for a long time, the exact mechanism is relatively unknown. Now, in situ microscopy and quantum chemical modelling have directly followed the formation of fullerenes from a single graphitic sheet — graphene.

The rational design of catalytic materials requires synthetic control over their reactive properties. Now, the activity of dealloyed Pt–Cu bimetallic nanoparticles, which catalyse the oxygen reduction reaction, can be tuned through control of the geometric strain at their surface.

There has been much interest in the assembly and properties of metal–organic frameworks. Here, a new type is described in which an infinite three-dimensional polycatenane is assembled from a discrete octahedral nanocage through the interlocking of all its six vertices.

Weakly polar XH/π interactions are thought to be capable of influencing both the structure and function of proteins, but such interactions are usually identified from three-dimensional structural models. Now, using NMR spectroscopy and isotopic labelling, it has been shown that individual methyl/π interactions can be detected directly in proteins by measuring weak scalar couplings between the nuclei involved.

The time taken for a reactant to reach a target is best represented theoretically by a distribution of times. This distribution has now been calculated analytically and shows quantitatively that in the case of uncrowded environments, a reactant's starting point — in relation to the target — does not influence the search time. It does, however, have an effect in the case of crowded systems — leading to ‘geometry-controlled kinetics’.

The ability to selectively transform the C–H bonds of simple alkanes to useful functional groups such as alcohols is a key step in the move away from petrochemical feedstocks. Now, it has been shown that the oxidation of alkanes can be catalysed by a bulky polyoxometalate species using hydrogen peroxide as a stoichiometric oxidant.

The decomposition of ammonia is an important process if ammonia is to be used as a hydrogen storage medium. The most active catalyst for this is ruthenium, but its expense has provoked the search for alternatives. Now, using theory to guide the investigation, researchers have identified a bimetallic nickel–platinum surface as an active catalyst for this process.

The composition of a dynamic combinatorial library can be altered by adding a target molecule that either stabilizes (or destabilizes) one or more of its members. The range of reversible chemical reactions compatible with biological targets such as proteins is somewhat limited, but now it has been shown that aniline-catalysed acylhydrazone formation is effective in this context.

Glass is widely used as an electrical insulator in electrodes, but in spite of its high resistance, 100-nm-thick layers of glass have now been shown to be sufficiently conductive for electrochemical measurements. Obtaining redox couples through glass-covered nanoelectrodes suggests that the pH response of the glass is due to the formation of a hydrogel layer in acidic solution.

Efficient conduction of protons on a micrometre scale is critical for the development of fuel cell membranes — a key component of clean energy sources. Now, self-assembling amphiphilic polymers have been shown to provide a nanoscale organization of proton-conducting functionalities that dramatically increases anhydrous proton conductivity.

Jean-Marie Tarascon ponders on the value of lithium, an element known for about 200 years, whose importance is now fast increasing in view of the promises it holds for energy storage and electric cars.