An important characteristic of hydration water is that it remains unfrozen or mobile (on the NMR time scale) at temperatures much lower than the freezing point of free solvent. This phenomenon proved to be very valuable for investigating the state of water in systems such as muscle, collagen, tissues, membranes; as well as for studying the changes in macromolecular-water interactions induced by external factors (gamma-irradiation), and the changes in water structure which result during natural, biological and physical processes such as growth and division of cells, muscle strain, cancerous growth. The proton NMR spectra obtained from hydration water in frozen samples furnish unprecedented information concerning the macromolecular-water interactions and the state of water in biological systems.

There is a vast scope for the application of the NMR studies of hydration water to explore and study in detail the effects produced by certain toxins, drugs, carcinogens and radiations: to investigate the sensitivity and specificty of different organs to these and other related perturbing factors.

There is increasing evidence showing that cross-relaxation between the protons of water molecules and of the macromolecular chain contributes to the relaxation rates of water protons. Eventually, it may become necessary to revise and reconsider the interpretation of certain previously published results in the light of cross-relaxation.

Water constitutes the major component of all living systems, for example it represents about 70-80% of the total cell constituent. There is conclusive evidence showing that water does not simply serve as an inert medium, but it participates at the molecular level in basic biological interactions and in fundamental biological processes. In fact, the hydration water molecules constitute an integral part of any macromolecular or cellular system under consideration. The importance of water in maintaining the structural integrity of proteins is well-established. Nevertheless, investigators in different domains have not fully recognized the important and crucial role that hydration water molecules may play in various biophysical and radiobiological processes. While postulating ingenious theories and mechanisms to explain such processes, many authors have either totally neglected the participation of water or considered it simply in terms of the overall medium effects. Hopefully, the NMR studies of water carried out very extensively in different laboratories would largely contribute to unravel the vital functional and structural roles played by water at the molecular level in many biolgoical interactions and biophysical processes.