Binding of hexadecyltrimethylammonium bromide to starch polysaccharides. Part II. Calorimetric study

Isothermal titration calorimetry was used to study the interaction between hexadecyltrimethylammonium bromide, CTAB, and three starch polysaccharides, amylose from potato, amylopectin from potato and amylopectin from barley. The enthalpy change for consecutive additions of CTAB to starch polysaccharide solutions were measured at 27°C. The starch-CTAB interaction enthalpies, ΔHr, were calculated by subtracting the enthalpy of micelle dissociation and dilution from the observed heat and relating the interaction enthalpy to the amount of interacting CTAB. The interaction was studied at three polysaccharide concentrations, 0.1, 0.25 and 0.5% w/w. The exothermic interaction enthalpy was constant and quite large in the main part of the concentration range studied for all three-starch polysaccharides. Amylose had an interaction enthalpy of −55 kJ/mol CTAB while the amylopectin samples had an interaction enthalpy of −40 kJ/mol CTAB. Amylopectin and amylose seemed to have a similar interaction with CTAB, the small differences were probably due to the differences in structure between the polysaccharides.