[Study of the aqueous phase transition in a collagen--water system by the calorimetric and NMR methods]

Heat capacity and line width of proton magnetic resonance of collagen were studied by means of low-temperature calorimatry and high resolution NMR spectroscopy at different values of moisture in the temperature range of ice-water phase transition. Peculiarities of water phase transition in the presence of biopolymers were revealed. It was shown that a definite part of H2O in the "hydration layers" of the macromolecules (0.35 g of H2O/g of protein) is not transformed into ice even at a temperature decrease up to 4 K. The NMR data show that the total mobility of the bound water molecules remains high enough up to the water concentration at which the inner hydration layer of the macromolecule is formed. After the formation of hydrogen-bound water chains in the hydrate layers of collagen the mobility of the bound water molecules decreases.