PROTON AND C-13 NMR-STUDIES ON XANTHAN DERIVATIVES

High-resolution NMR spectra of a number of xanthan derivatives have been obtained. Enzymic hydrolysis with cellulases was used to produce xanthan fragments as small as the pentasaccharide repeat unit. Spectral resolution improved as the molecular weight of the samples was decreased. Changes in the chemical shift of some anomeric proton and carbon resonances indicated that substantial conformational transitions had taken place on depolymerisation. Partial and complete removal of pyruvyl and acetyl substituents, plus proton-carbon-13 correlation NMR spectroscopy and homonuclear Hartmann-Hahn spectroscopy, were used to assist in the assignment of a number of resonances. Comparison of spectra from samples run at ambient (27-degrees-C) and high temperature (90-degrees-C) revealed chemical shift changes, particularly of anomeric resonances, which were probably a consequence of conformational transitions induced about the glycosidic linkages by heating or cooling.