Scientists are imitating natural methods of making chemical reactions happen, writes Kirstin Goldring.
The chemical industry is moving towards more environmentally friendly practices. Researchers in Ireland are part of this effort which focuses on the development of "greener" chemical processes.
"There is general recognition of the need for the development of more efficient and environmentally friendly chemical technologies," says Dr Stephen Connon of the school of chemistry at Trinity College, Dublin.
Dr Connon's group is interested in substances called catalysts, which make chemical reactions go faster but are not changed themselves at the end of the reaction. Catalysts are often used in the production of important industrial chemicals.
"Catalysts are of vital importance in the chemical industry, they allow reactions which are inherently very slow, or do not occur at all, to proceed at convenient speeds," says Dr Connon. "Catalysis is a central enabling technology in the pursuit of 'greener' processes that allow reactions to proceed faster and/or at lower temperatures than analogous uncatalysed reactions."
Over the last 50 years, the development of highly effective catalysts has revolutionised the way chemists make molecules. However some of these are based on the use of compounds containing metals that can in some cases have drawbacks.
'WHILE MANY METAL-BASEDsystems are benign, some catalytically useful metal-based compounds are toxic, others can be highly sensitive to air and water, which complicates their use on large scale, while some are based on expensive metals, for example palladium and platinum, which are currently more expensive than gold," he says.
Researchers are interested in catalysts which do not use metals. In order to achieve this chemists are turning to nature for inspiration, says Dr Connon. "All life, from you and I to the smallest bacterium, is completely dependent on thousands of enzymes, nature's catalysts, to accelerate chemical reactions vital for survival, which do not usually occur at speeds compatible with life. Enzymes are generally large, complex protein molecules that have been evolving for a long time, some for millions, if not billions of years, and are therefore highly specialised and efficient. More importantly, many enzymes are metal-free."
ENZYMES ARE GENERALLYtoo large to be conveniently prepared using conventional chemical methods. However, smaller molecules can be designed along biological principles which are not as effective as enzymes yet which still can accelerate reactions. Only in the past 10 years has the research community really begun to realise the potential of these small, relatively simple catalysts, he believes.
Dr Connon's group has been involved in the design of such "organocatalysts" since 2003. "Organocatalysts are usually prepared from cheap natural materials such as amino acids, carbohydrates or plant-derived compounds which are stable and easily modified, meaning that the catalyst properties can be quickly fine-tuned to suit a given reaction they are to catalyse."
Dr Seamus McCooey, a recently graduated PhD student from the group, focused on designing organocatalysts, which like enzymes, but unlike most traditional catalysts, can make two rather than one substance in a reaction more reactive.
"By making small modifications to an inexpensive compound obtained from cinchona tree species, we obtained a metal-free catalyst which could temporarily modify the properties of both components of a chemical reaction simultaneously," says Dr Connon. "Products which are very useful synthetic 'building-blocks' for pharmaceutically and biologically important molecules can be constructed."
Recycling of the catalyst at the end of the reaction, a traditionally costly and difficult process, has been the focus for PhD student Ciaran O'Dálaigh. In collaboration with Professor Yurii Gun'ko and Dr Serena Corr also at Trinity, he has been involved in attaching magnetic nanoparticles to organocatalysts.
"After the reaction the magnetic catalyst is very easily removed by exposing the vessel to an external magnet and then pouring off the liquid containing the products, leaving the catalysts behind to be used again as many as 30 times," says Dr Connon, whose catalysis work is funded by Science Foundation Ireland (SFI) and the Irish Council for Science, Engineering and Technology (IRCSET).