An investigation by light scattering of the state of aggregation of amylose in aqueous solutions

Aqueous alkali has been assumed to be a good solvent for amylose, and has been used as a medium for physicochemical studies on this polymer. It is shown that there is a slow but substantial reduction in the turbidity of normal KOH solutions of amylose, even in the almost total absence of oxygen. More significantly there is a corresponding, but much more rapid, drop in turbidity in neutral solutions (pH 6.5–7.0). At pH 4.0 the turbidities are, in general, constant for up to at least 30 days. The results are interpreted on the basis of aggregates, which evidently must be of a very special type and are termed “native” aggregates. It is suggested that these may consist of amylose in essentially the helical configuration. The properties of these aggregates are in strong contrast to those of the retrograded aggregates. In the form of the first type of aggregate the amylose will not retrograde, at room temperature, without undergoing first a drop in turbidity suggesting that the transition from the “native” to the retrograded aggregate passes through the molecular state. The native aggregates are stabilized toward both disaggregation and retrogradation by pretreatment with iodine. Disaggregation is accompanied by a drop in relative viscosity. Some of the implications of these unexpected observations are pointed out.