Counterion binding and hydration of hyaluronate and chondroitin in solution: An 17O, 23Na,and 25Mg nuclear-magnetic-relaxation study

Nuclear magnetic relaxation rates of H₂¹⁷O, ²³Na⁺, and ²⁵Mg²⁺ have been measured in aqueous hyaluronate solutions. The dependence on solution pH of the relaxation rates has been investigated, as well as the competition behavior of Na⁺ with Ca²⁺ and Mg²⁺. H₂¹⁷O and ²³Na⁺ relaxation rates in chondroitin and hyaluronate solutions have been compared in the interval, 2 ? pH ? 12.5. The ion binding of hyaluronate can be fully accounted for by Coulomb interactions, with no need to involve chemical specificity. The hydration is only slighly pH dependent, and is comparable in magnitude to hydration of synthetic polyelectrolytes and monosaccharides. Ion-binding and hydration properties of hyaluronate and chondroitin are quite similar, except at elevated pH. At alkaline pH, an increase in charge density with pH is seen in hyaluronate and, to a much lesser degree, in chondroitin, possibly due to the titration of hydroxy groups. H₂¹⁷O data indicate an alkali-induced transition in both glycosaminoglycans.