Mobility of water bound to biological membranes: A proton NMR relaxation study

Water proton nuclear magnetic resonance relaxation measurements have been obtained for aqueous suspensions of red cell membranes. These data support a model in which water molecules are exchanging rapidly between a bound phase with restricted motions and a free phase with dynamic properties similar to liquid water. From this model and these data, estimates are obtained for the relaxation time for bound phase water. Possible relaxation mechanisms for bound phase water are discussed and some support is found for an intermolecular interaction modulated by translational motions characterized by a diffusion constant of 10^?9 cm²/s.