Mobility of water in biological systems studied by ¹⁷O NMR via multiple-quantum filtered relaxation analysis

Multiple-quantum filtering NMR sequences were used to study the multiexponential relaxation behaviour of H₂¹⁷O in the presence of macromolecules. By this means, the fraction and the correlation time of water in slow motion, or 'bound' water, were determined, in addition to the relaxation time of bulk water in the extreme narrowing limit. Experiments were carried out on aqueous solutions of bovine serum albumin, hen egg white lysozyme and intact human red blood cells in which intracellular water properties were studied. The small fraction of bound water of less than 1% seems to correspond to 'strongly bound' water, whereas the behaviour of bulk water was different from that of pure water and may be due to weak (or transient) interactions with macromolecules. The experiments and the data analysis gave reproducible results which support the idea that diverse samples could be studied in this way in order to help understand their water properties.