Amylose-Iodine Complex. II. Molecular Weight Estimates

Ultracentrifugation measurements made by the Archibald method on solutions of amylose-iodine-iodide (AI) complexes, containing 0.003% amylose of weight average molecular weight 4.0 X 10(5) at 3.6 X 10(-3) M KI, yield an apparent molecular weight at the meniscus of 8 X 10(5) when measurements are extrapolated to 1200 rpm. Sedimentation equilibrium measurements at 1200 rpm yield apparent molecular weight at the meniscus of 6 X 10(5) and at the cell bottom of 2.4 X 10(6). Heterogeneity and aggreagation are major features of AI complex solution behavior. Apparent molecular weights increase as a function of increasing potassium iodide concentration and with time. This behavior directly correlates with AI complex sedimentation coefficient behavior previously reported. Molecular weight estimates are of the same order for AI complex solutions saturated and 65-70% saturated with respect to the iodine-binding capacity of amylose. Qualitative estimates of net macroion charge effects upon apparent molecular weights are presented.