Studies of Hydration by Broad-Line Pulsed NMR

Water molecules are distributed among a great variety of materials: organic and inorganic crystals, gels and sols of natural products with mineralogical, botanical, and zoological origins, as well as industrial products. The water molecules in living cells and their constituents are essential, not only as a solvent or a supporting medium, but also as an indispensable component. One of the effective methods of characterizing such water molecules is a proton magnetic resonance measurement. Kuntz et al. [l] once observed that frozen protein and nucleic acid solutions at −35°C show relatively narrow (100 milligauss) proton magnetic resonance signals. They showed that this signaI is assignable to water of hydration. Thus, at this temperature (−35°C), the regular solvent water is frozen, and practically all the protons in the macromolecules are immobilized, so that only the water of hydration is sufficiently mobile in the given system to reduce the dipolar broadening and to give a signal. On the basis of this finding, they determined the amounts of hydration (mobile water molecules) for a number of polypeptides, proteins, nucleic acids, and ribosome [1–3].