MOLECULAR-DYNAMICS STUDIES OF SIMPLE MEMBRANE WATER INTERFACES - STRUCTURE AND FUNCTIONS IN THE BEGINNINGS OF CELLULAR LIFE

Molecular dynamics computer simulations of the structure and functions of a simple membrane are performed in order to examine whether membra nes provide an environment capable of promoting protobiological evolut ion. Our model membrane is composed of glycerol 1-monooleate. It is fo und that the bilayer surface fluctuates in time and space, occasionall y creating thinning defects in the membrane. These defects are essenti al for passive transport of simple ions across membranes because they reduce the Born barrier to this process by approximately 40%. Negative ions are transferred across the bilayer more readily than positive io ns due to favorable interactions with the electric field at the membra ne-water interface. Passive transport of neutral molecules is, in gene ral, more complex than predicted by the solubility-diffusion model. In particular, molecules which exhibit sufficient hydrophilicity and lip ophilicity concentrate near membrane surfaces and experience ''interfa cial resistance'' to transport. The membrane-water interface forms an environment suitable for heterogeneous catalysis. Several possible mec hanisms leading to an increase of reaction rates at the interface are discussed. We conclude that vesicles have many properties that make th em very good candidates for earliest protocells. Some potentially frui tful directions of experimental and theoretical research on this subje ct are proposed.