Biological and other soft matter

The session was divided into two parts, separated by the partial solar eclipse. The first part was devoted to discussion of pressure effects on polymers. K. Mortensen (Riso, Denmark) discussed neutron diffraction studies on polymer and copolymer blends, systems sufficiently understood theoretically that specific predictions of the effects of pressure can be made and tested. H. King (Exxon R. & E., USA) summarized the historically important role of pressure in understanding the structure of crystalline and amorphous polyolefins, major commodity materials produced in huge volumes. King also discussed recent experiments on water-soluble polymers which shed light on the roles of the van der Waals and hydrogen bonding energies in determining the pressure behavior. Talks on the effects of pressure on biological materials followed the eclipse. R. Templer (Imperial College, UK) described x-ray studies on the effects of pressure on lyotropic liquid crystals made of biomembrane lipids. These are some of the most pressure sensitive condensed matter systems known and exhibit large changes in phase structure with changes of only a few hundred atmospheres of pressure. The final three talks were devoted to pressure effects on proteins. G. Hummer (Los Alamos National Lab., USA) described theoretical work aimed at understanding why proteins unfold when pressure is applied. The central theme is that the unfolding results from the increased proclivity of water molecules to intercalate into the protein, as opposed to the more conventional wisdom that pressure promotes a proclivity for the polypeptide strands to disperse into the bulk water. Thus, water under pressure acts as a kind of plasticising agent. An important prediction of the work is that the radius of gyration of a pressure-denatured protein would be smaller than that of a thermally denatured protein. C. Royer (Centre de Biochimie Structurale, Montpellier, France) reviewed the substantial progress now being made in experimental studies of the folding and unfolding process - both its nature and its kinetics - and showed that radius of gyration measurements of pressure-unfolded staphylococcal nuclease support Hummer's predictions. P. Urayama (Cornell University, USA) noted that there is little understanding of the structural basis of the many effects of pressure on proteins because there have been so few crystallographic studies of proteins under pressure. He described a technique that allows high-resolution crystallography to be performed on proteins which have been frozen into a highpressure state. Short poster oral presentations were given by W.C.K. Poon (Edinburgh U., UK) on agarose gelation and R. Winter (Dortmund U., Germany) on lipid high-pressure phase behavior. The microsymposium served to illustrate both the richness of effects of modest pressures on biological and other soft condensed matter and the need to understand the structural basis of these effects.

Roland Winter and Sol M. Gruner, Chairs