[A study of the physico-chemical properties of lecithin membranes using hydrophobic and hydrophilic spin probes]

Some physico-chemical properties of lecithin lyposomes and the effects of pH, temperature and ionic strength changes are studied by ESR using hydrophobic and hydrophylic nitroxyl radicals as spin probes. The structure differences between outer and inner layers of bilayer liposomes are observed using auxiliary water soluble paramagnetic complex and attributed tentatively to the different curvature signs of both layers. Lower estimates of transversal diffusion rates of both probes throught the membrane are obtained using exchange broadening technique and water soluble reducing agent. The limiting step in this diffusion is revealed, caused by the transport of a charged group of the diffusing molecule through the hydrophobic membrane space.