Hydration of sodium hyaluronate, NMR study of an oriented sample

A sample of highly oriented Na-hyaluronate was prepared with a wet--spinning method and equilibrated to 75% relative humidity. Its proton NMR spectrum was recorded as a function of the angle theta between the hyaluronate helix axis and the external magnetic field. It appeared as a singlet with an angle-dependent line width expressed by delta v o + A(1-3cos2 theta)2. This reveals a residual intramolecular dipolar interaction of anisotropically rotating water molecules. The merging of the expected doublet into a single line is assumed to be caused by proton exchange between water molecules. The result indicates a hydration similar to that of many other fibrous biopolymers at comparable relative humidities.