An ESR study of the hydration steps of lecithin multilayers

A spin-labeled stearic acid and other spin-labeled molecules have been used for an ESR study of the hydration process of the egg lecithin lamellar phase for water concentrations, CW greater than 10%. Two hydration steps are found for CW approximately 20% and CW congruent to 30%, in good agreement with results of the literature. To explain discontinuities in the behavior of three spin-labeled molecules at CW congruent to 20%, a conformational change of the phosphatidylcholine polar head and a phase transition in the polar interface are proposed.