MOLECULAR FORCES

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During the past months, Evan Evans and the PI have solved the long-standing problem of relating the mechanical motion of neighboring membranes or linear macromolecules to the long-range forces acting between them. Specifically, we have derived formulae giving the undulations in a multilamellar lattice in terms of the hydration, electrostatic and van der Waals forces between layers. We have identified the additional contributions of these undulations to the total interactions between layers. We have succeeded in explaining a long-standing anomaly in the decay of electrostatic forces between phospholipid bilayer membranes. This apparently abstract achievement is a first and difficult step in learning to relate forces to molecular motion, a central problem in molecular assembly. Our strategy has now lead us to design several experiments to measure molecular motion from x-ray scattering. With R.P. Rand and S.M. Gruner, the PI has been measuring the stability of lipid assemblies, most notably of phospholipids in the inverted hexagonal phase. These studies are aimed at illuminating the possible intermediate states of lipids during fusion processes and at identifying the energetic factors in membrane pore formation. E. Barouch and the PI are examining a set of methematical solutions of the electrostatic double layer problem in various geometries. The object of this examination is to test a popular method, the Derjaguin approximation, used to interpret measurements of forces between surfaces.