MONTE-CARLO STUDIES OF AN IDEALIZED MODEL OF A LIPID WATER-SYSTEM

Employing Monte Carlo dynamics, the equilibrium and dynamic properties of lipid-water systems are studied in the context of a diamond lattice realization. The model faithfully describes the lipid molecule geometry and reproduces the essential physical properties of real membranes. These include the phase transitions from quasi-crystalline phase <-- --> liquid bilayer <-- --> nonbilayer, quasi-hexagonal phase <-- --> dissolved liquid solution. Furthermore, the structure, ordering, and dynamics of the model liquid bilayer are in good accord with experiment, and the values of segmental ordering parameters are close to those obtained from NMR data. Due to the diamond lattice representation and a very efficient simulation algorithm, the intermediate distance scale dynamic features of the water-lipid system could be examined; these include lateral diffusion in the bilayer, the formation of a nonbilayer phase, the transbilayer diffusion of the lipid molecule, and the diffusion of a lipid molecule in the water phase. The present model can be also used to generate initial configurations for more detailed molecular (or Brownian) dynamics studies of lipid-water systems.