CHEMICALS WORLD

Light significantly accelerates hydrogen generation from formic acid, according to a report by German scientists. Combining the process with a small fuel cell could create a power source suitable for replacing batteries in laptops and other mobile devices, they claim.

American chemists have developed an 'electronic glue' to link nanocrystals together - allowing groups of the crystals to be highly conductive. Since nanocrystals have unique optical and electrical properties, this research could provide some exciting new materials for use in light-emitting devices or solar cells.

Nanocrystals are crystalline nanoparticles of metals ranging from cadmium to silicon, and can be grown with precisely controlled size and shape. But despite their exciting range of optical properties, they have found few applications so far.

'The problem is getting the crystals to 'talk' to one another,' says Maksym Kovalenko, lead author on the project at the University of Chicago, US, 'And this problem arises from the way the crystals are made.'

Organic ligands are used to control and stabilise nanocrystals during their synthesis, Kovalenko explains, which results in the crystals being sandwiched between layers of insulating material. Although individual nanocrystals are semiconducting and have found niche applications - such as in making quantum dots or acting as fluorescent biological markers - electrical charge is restricted from passing through larger groups.

Instead of using organic ligands, Kovalenko's team discovered that some metal chalcogenide complexes can work the same way but do not shield the crystals from the transfer of electrical charge. In one example, the team used a ligand exchange process to switch the organic ligands on gold nanocrystals for a tin sulphide complex of Sn₂S₆^4-.

The mixture was then heated gently, which left a tight honeycombed structure of gold nanoparticles surrounded by charge-heavy ligands - creating a highly conductive solid material. Other crystals and complexes are also under investigation by the team, who are confident that this technique can be applied to many other systems.

Researchers in the US have adapted a DNA amplification technique to develop a simpler way to rapidly screen chemical reactions. The process should improve reaction screening methods known as 'chemical speed-dating' - where hundreds of different substrates are mixed together but only a few interact strongly.

These reaction screens are a great way to quickly probe chemical space to discover new reactions, and this new technique builds on the polymerase chain reaction (PCR) to eliminate some awkward processing steps, boost efficiency and accuracy.

The speed-dating process works by attaching hundreds of different substrates to short, single strands of DNA. When warmed to 60°C, the strands are too short to pair up naturally - but where two substrates have reacted, their DNA tails pair up, forming a short piece of DNA that resembles a hairpin.

Traditionally, one of the substrates typically needs to be mounted on a bead to isolate and identify the compounds that have reacted, which can be a time-consuming practice. Now, David Liu's team at Harvard University, US, have simplified the method by modifying the polymerase chain reaction (used to copy single strands of DNA millions of times) to selectively replicate only the DNA strands where a reaction has occurred.

Materials displaying 'self-erasing' colour images have been created by chemists in the US, who have studied how certain nanoparticles can assemble and disassemble themselves under different wavelengths of light.

The materials, which are printed with ultraviolet (UV) light and erased with visible light, could one day be used for self-expiring bus tickets or for carrying secret messages.

'Self-erasing papers are important for time-sensitive materials and secure communications,' said study leader Bartosz Grzybowski of Northwestern University in Evanston, Illinois. 'On the fundamental level, what we describe is also a very different way of looking at the concept of information storage. We're not using traditional coloured inks per se, but rather we "generate" or "elicit" colours only when particles in the film self-assemble.