Effects of temperature and glycerol on the de-organisation of hsian-tsao (Mesona procumbens Hemsl) polysaccharide solution by electron spin resonance spectroscopy

Abstract

The effect of different glycerol concentration on the molecular transition on heating of hsian-tsao polysaccharide solution was investigated by electron spin resonance (ESR), using nitroxide radicals (4-amino TEMPO) as labels that covalently attached to the carboxyl groups of uronic acid of the hsian-tsao polysaccharide chains. As indicated by the increased rotational correlation time ðtcÞ and broadening ESR resonance signals due to anisotropic effects, the mobility of the polymer chains became more restricted with reducing temperature and increasing glycerol concentration (0–80%). A change in anisotropic ratio (p value) likely reflecting the molecular dissociation and conformational disordering of the polysaccharide was observed during heating at 40–50 8C, and being more remarkable as glycerol concentration increased. The increment in glycerol concentration resulted in a two-fold increase in activation energy of the conformational transition (from 17.93 to 35.15 kJ/mol).