Stretching effects on the permeability of water molecules across a lipid bilayer.
Using a coarse grained molecular dynamics model of a solvent-surfactant system, we study the effects of stretching on the permeability of water across a lipid bilayer. The density profile, free energy profile, diffusion profile, and tail ordering parameter were computed for a set of stretched membranes maintained at constant area. We computed the water permeability across each membrane using the inhomogeneous solubility-diffusion model first proposed by Marrink and Berendsen [J. Phys. Chem. 98, 4155 (1994)]. We find that even though the resistance to permeation profile shows a great deal of qualitative change as the membranes are stretched, the overall permeability remains nearly constant within the relevant range of stretching. This is explained by the fact that the main barrier to permeation, located in the densest section of the tails, is insensitive to increased area per lipid, as a result of competing effects. Expansion leads to thinning and a higher density in the tail region, the latter leading to an increase in the free energy barrier. However, this is compensated by the reduction in the transverse distance to cross and a larger diffusion coefficient due to increased disordering in the chains.
Gauthier
Alain
A
Ottawa-Carleton Institute for Physics, University of Ottawa Campus, 150 Louis Pasteur, Ottawa, Ontario K1N-6N5, Canada.
Joós
Béla
B
D000465:Algorithms; D003198:Computer Simulation; D004058:Diffusion; D008051:Lipid Bilayers / Q000737:chemistry*; D008560:Membrane Fluidity; D008954:Models, Biological; D008968:Molecular Conformation; D010539:Permeability; D012995:Solubility; D012997:Solvents / Q000737:chemistry*; D013499:Surface Properties; D013501:Surface-Active Agents / Q000737:chemistry*; D013816:Thermodynamics; D014867:Water / Q000737:chemistry*
D008051:Lipid Bilayers; D012997:Solvents; D013501:Surface-Active Agents; D014867:Water