Amylose-Iodine Complex. I. Sedimentation Behavior

Sedimentation measurements are reported on solutions of blue amylose-iodine complexes in the range of 0.001 to 0.007% amylose. Amylose fractions B and F2, of weight average molecular weight average molecular weight 4.0 X 10(5) and 3.4 X 10(4), respectively, were used in this study. Iodine complexes of these fractions formed polydisperse solutions of limited solubility and stability. Sedimentation coefficients increased as a function of potassium iodide concentration. Values for fraction B complexes varied from (16.3 +/- 1.0) X 10(-13) at 1.2 X 10(-3) M KI to (57.2 +/- 7.5) X 10(-13) at 8.3 X 10(-3) M KI; values for fraction F2 complexes varied from (10.0 +/- 1.2) X 10(-13) at 1.2 X 10(-13) M KI to (24.8 +/- 3.9) X 10(-13) at 9.5 X 10(-3) M KI. At constant potassium iodide concentration, sedimentation coefficients, within our experimental error of 10 to 15% standard deviation, are independent of amylose concentration. Time dependence of sedimentation coefficient values was observed for solutions either saturated or unsaturated with respect to the iodine-binding capacity of amylose. For iodine-saturated complex solutions, sedimentation coefficients extrapolated to zero potassium iodide concentration were two to three times greater than for the parent amylose. Measurements are evaluated in terms of possible polyelectrolytic charge effects and aggregation. Under conditions used in these experiments, aggregation of amylose-iodide complexes appears to be the mechanism responsible for the large increase in sedimentation coefficients.