Water binding of Polysaccharides-NMR and ESR studies

In this paper proton and deuteron NMR relaxation data of water in various physiologically important polysaccharides are presented as a function of the water content. The relaxation times are analyzed by assuming a fast exchange of water molecules between an unbound and a bound water fraction. From this model it can be estimated that less than two water molecules are bound per sugar ring. The water relaxation behavior varies considerably for the different polysaccharide solutions probably caused by the different polymer mobilities which are reduced by decreasing water contents. Microviscosities studied by ESR spectroscopy show that the bulk war,er mobility is only slightly affected by the water content. Mean rotational correlation times of the water molecules determined from deuteron relaxation increases from 3 ps in pure water to about 1 ns for 30 wt % water in dextran solution. The NMR relaxation times of the samples prepared by the osmotic stress technique are affected only slightly by varying Na+ content. Hence, electrostatics plays only a minor role for the water binding properties of aqueous polysaccharide solutions.