[A study of water autodiffusion in model biological membranes, oriented lipid bilayers]

The autodiffusion of water in a multibilayer structure formed by dipalmitoyl phosphatidylcholine and oriented on glass plates was studied by the method of NMR with magnetic field pulse gradient. It was shown that water molecules occur in several states differing in the degree of interaction with lipid molecules. A spectrum of the coefficients of water autodiffusion in a direction transversal to bilayers was found. The use of samples with different distances between the plates and an analysis of the dependence of the mode of diffuse decay of spin echo on diffusion time and the orientation of the sample, as well as measurements at temperatures above and below the gel-liquid crystal phase transition in cholesterol-containing samples enabled one to discriminate the diffuse decay component responsible for the transbilayer movement of water. The coefficient of bilayer permeability was estimated using the Tanner model. It was shown that the formation of mechanical defects ("cracks") in plane oriented bilayers is the most probable reason for the presence of the water component with the relatively high coefficient of diffusion.