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Water, water, everywhere - CMD19/CMMP with The Physics Congress 2002

March 26, 2002

Over half our planet is covered in water, and life cannot exist without it. But despite how common and important it is, surprisingly little is known about the structure of water, especially when it is next to other materials. A detailed understanding of how water behaves would not only reveal how biomolecules assemble or function - and possibly enable new treatments for illnesses and diseases to be developed - but would show how many artificial substances and structures, from paint and clay to hard disk drives and nanomachines, are affected by moisture.

At the Condensed Matter conference on Wednesday 10 April, part of the Institute of Physics Congress in Brighton, Chandra Ramanujan from physicist Professor John Pethica`s research group at the University of Oxford will describe how recent experiments using a high power microscope appear to be showing the arrangement of water molecules as they touch a surface. At the same meeting Dr Jan Swenson, a physicist from Chalmers University of Technology in Sweden, will review his experiments which are starting to reveal how water behaves when it is in a confined space - such as in a biological cell.

Professor Pethica`s team built a new type of atomic force microscope (AFM) for their studies. An AFM works in a similar way to a record player. It has a lever with a hard tip, just like a stylus, that passes over the surface under study. Whereas the movements of a record player`s stylus represent the music that is stored as a wavy groove on the surface of the record, the needle of an AFM is pulled up and down by the molecules on the surface beneath it. This movement then reveals the structure and arrangement of these molecules.

Similar apparatus has been used in the past to reveal the structure of liquids with larger molecules than water, but because of their tiny size, seeing how water molecules arrange themselves near surfaces has proved somewhat tricky. However having recently produced the clearest results to date, the Oxford team thinks it may finally have detected this arrangement.

"The importance of this is that if you could measure the structure of water by this mechanical means over a variety of different surfaces - including biologically active surfaces ? you would know something about how the water was affecting the interactions near those surfaces," explains Professor Pethica.

This could be particularly relevant for proteins that have both hydrophobic (water hating) and hydrophilic (water loving) parts. It is thought to be the interactions of these different parts of proteins with water that makes them the shape they are. If it became possible to work out how to alter the shape of a protein, and determine how this change in shape affects the job the protein does in the body, scientists could potentially diagnose and treat certain illnesses and diseases.

To understand biological processes more fully, it will also be vital to learn how confined water behaves. "Confined water is a requirement for all life," says Dr Swenson. "It is confined water which interacts with biomolecules and is responsible for how they work," he explains.

One particular area of interest for Swenson`s team is the behaviour of `supercooled` water in confined conditions. Normally when liquids are cooled below their freezing point they become solids. Supercooled liquids however remain liquid even when they are below their freezing point.

"Water can be supercooled below 0°C in nature, for example in trees," says Swenson. "In many of these systems it is important that the water remains in the supercooled state since the formation of ice can destroy many natural materials," he continues.

So far his experiments ? using dried strawberries and red onion to confine the water ? have shown that the chemical bonds between water molecules become stronger in the supercooled regime. However, their strength depends on what shape the cavity confining them has, and how they interact with the cavity walls.

Institute of Physics