ESR STUDY OF THE CONFORMATIONAL TRANSITION OF SPIN-LABELED XANTHAN GUM IN AQUEOUS-SOLUTION

The order to disorder transition of xanthan molecules in aqueous solut ions has been studied using e.s.r. spectroscopy. Nitroxide spin-label was covalently attached to carboxyl groups on the xanthan side chains. The e.s.r. spectra obtained for aqueous spin-labelled xanthan solutio ns at varying ionic strengths contained both isotropic and anisotropic components at room temperature. The anisotropic component was attribu ted to the association of the side chains with the xanthan cellulosic backbone and was found to be present in greater proportions al increas ing ionic strength. The spectra gradually changed with rising temperat ure and the proportion of anisotropic component decreased. This spectr al change reflected the disruption of the side chain association with the backbone during the conformational change. Hysteresis effects were observed following sequential heating and cooling cycles suggesting t hat chain aggregation occurred.