Some of the most challenging problems in science concern the behaviour of the most commonplace compound on the planet’s surface - water. But some of the mysteries are now being unravelled by the latest analysis and imaging techniques in an unfolding story that was presented at a recent conference organised by the European Science Foundation (ESF) focusing on interaction between water and other compounds at the molecular level.
Some of the greatest puzzles involve the interaction between molecules of water and other compounds as they come into proximity. These problems are not purely academic, because they have vital implications for understanding many important processes and biochemical reactions within organisms, some of them implicated in human disease. The molecular properties of water also have great importance for materials science, nanotechnology, and the semiconductor industry.
The underlying problem is that at the molecular level the behaviour of water and particularly interactions with other substances is extremely complex, and correspondingly difficult to explain in a few words. Before some of the exotic effects can be exploited, they must be thoroughly understood, and this in turn depends upon being able to observe the processes in some way. A major focus of the ESF conference was on new techniques for revealing information about the behaviour of water at the molecular scale in different circumstances, according to the conference’s chair Marie-Clare Bellissent-Funel. “Various techniques were used to reveal information of water at solid, soft, vapour, protein, membrane, and other interfaces,” she said.
High resolution x-ray diffraction is an important technique for analysing water molecules at interfaces, observing the way high-energy x-ray beams are scattered at the points of interaction. The location and orientation of individual water molecules can be detected that way, and already a lot has been learned about the crucial role played by them in critical biochemical reactions, including those involving docking or interactions between proteins. Water molecules also play a crucial role in ushering key components of biology such as metal ions into cells through permeable membranes, and details of further progress understanding the processes involved were presented at the conference. “The understanding of such events could find application in development of medication and design of nanofluidic devices,” said Bellissent-Funel.
Such events can only be properly understood by analysing not just the static structure at a point in time, but the dynamic changes over time, and emerging techniques for this were also discussed at the ESF conference, as Bellissent-Funel pointed out. This is difficult to do at present purely by observation, but progress has been made by combining experiments with computer based simulations.
Such simulations incorporate a description of the unusual geometry of the water molecule, which is the source of all the strange and important properties of water. The molecule comprises an oxygen atom with two hydrogen atoms hanging off like Mickey Mouse ears. This gives the molecule an uneven distribution of electric charge, enabling it readily to form weak but significant hydrogen bonds with molecules of both water and other compounds.
Computer models are also being used to simulate behaviour of solutions, in which hydrogen bonds between molecules of water and the solute (substance being dissolved) prevent the latter conglomerating and therefore precipitating out. This is a function of water’s “interaction potential”, which means the ability or tendency of water molecules to form hydrogen bonds with other molecules. The ability to simulate the behaviour of interactions between water and solute molecules, rather than just between water molecules, represents an important development, said Bellissent-Funel.
The overall complexity of water interface physics was reflected at the ESF conference by the breadth and depth of the presentations, and also by the fact that key speakers were drawn from all over the world, including the US and Japan. But Bellissent-Funel emphasised that Europe had growing strengths and has been successful in recruiting new talent into this dynamic, challenging, and hugely promising field, even attracting some from outside the continent. “It was clear from the short contributions and posters that there is an impressive set of young researchers in this general area, and also that some of them come originally from outside Europe,” said Bellissent-Funel. A key point is that these researchers by necessity span a range of disciplines across the whole scientific spectrum, reflecting the fundamental importance of water science.
The conference, “Water Interfaces in Physics, Chemistry and Biology, A Multidisciplinary Approach”, was held at Universitätszentrum Obergurgl at Ötz Valley, near Innsbruck, Austria in December 2007.
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