Modification of 4 MHz NMR water proton relaxation times in highly diluted aqueous solutions

The NMR properties of water in the vicinity of molecules in solution differ from those of water in the pure state. Water molecules interact with the solute via hydrogen bonds and/or electrostatic forces related to their high dipolar momentum. At room temperature, the correlation times t of rotational and translational movements, of the order of 10-11 to 10-12 s in pure water may increase to 10-8 or even 10-6 in the hydration layer of macromolecules (Packer, 1977; Fung, 1977; Mathur-DeVre, 1979), giving rise to a drastic reduction in Tl and T2 water proton NMR relaxation times from 2–3 s to a few hundred milliseconds. Similarly, lowering the temperature of pure water promotes hydrogen bonding and affects relaxation in the same way as the introduction of a solute, leading to water correlation times as high as 10–5 s in ice (Glasel, 1972). Due to the wide 10-5-10-11 s range in correlation times observed in biological or non biological systems, NMR relaxation in the 1–100 MHz domain is one of the potent techniques capable of demonstrating modifications in the mobility and degree of organization of water molecules in solutions or tissues, although it is not very precise in determining the absolute structure. NMR medical imaging is a clear strong successful application of this principle.