Secondary structure in glycosaminoglycuronans: N.M.R. spectra in dimethyl sulphoxide of disaccharides related to hyaluronic acid and chondroitin sulphate.
1H-N.m.r.spectra for solutions in dimethyl sulphoxide-d6 of disaccharides related to hyaluronate and chondroitin sulphate are compared with those of their methylated derivatives. All resonances, including those of HO and HN groups, have been assigned. The temperature and concentration dependences suggest that HO-4 of the hexosamine residue in hyalobiouronate (but not that in chondrosinate) is hydrogen-bonded to O-5 of the uronic acid residue. The resonance of HO-2 of the uronate residue of chondrosinate also shows anomalies that may arise from intra-residue hydrogen-bonding. These findings confirm the existence of some features previously suggested to be present in glycosaminoglycuronan polymers. The resonance of HO-4 of the uronate residue in the disaccharides and in sodium (methyl alpha-D-glucopyranosid)uronate behaves as though there was a hydrogen bond between the carboxylate group and HO-4.