C-13-NMR studies of hyaluronan: Conformational sensitivity to varied environment

Hyaluronan(HA) samples ranging in size from small oligosaccharides to high molecular weight polymer have been studied by C-13-NMR spectroscopy. In neutral aqueous solutions, the chemical shifts of carbons directly involved in the beta-1,3 glucuronidic linkage are found to be sensitive to (1) residue Linkage position in short chains, (2) oligomer degree of polymerization, (3) solvent ionic strength, and (4) monovalent us divalent counterions. The carbons of the beta-1,4-glucosaminidic linkage show less sensitivity to the above conditions. Thus conformational versatility for HA in aqueous solution is correlated with a chemical shift change primarily in carbons of the beta-1,3 linkage. We have also compared the C-13 spectrum of HA in neutral aqueous salt solutions to spectra observed in dimethyl sulfoxide (DMSO) solution (ordered 2- or 4-fold HA form) or the solid state (Na+ counterion, tetragonal 4-fold helical HA form). The solid state spectrum is similar to that found in DMSO but differs substantially from the aqueous solution spectrum. The differences are attributed to (1) rotation of the acetamido group, with concomitant change in hydrogen bonding and average conformation at the beta-1,4 linkage, and (2) loss of hydrogen bonds in aqueous solution and consequent change in average conformation at the beta-1,3 linkage.