The interaction of carboxymethylamylose and diethylaminoethylamylose with iodine

Spectrophotometric titrations of slightly substituted carboxymethylamylose (CM‐Amy) and diethylaminoethylamylose (DEAE‐Amy) with iodine in the presence of iodide (I 2 /I − ) were carried out as a function of iodide concentration, temperature, and polymeric charge. Binding isotherms for the polymer‐I 2 /I − complex are reported in terms of an apparent binding constant ( K a ) plotted versus degree of saturation of the complex (θ). The dependence of K a upon polymeric charge is interpreted as evidence for the negatively charged character of the bound species. The cooperative nature of the binding process is evident in the positive slope of K a vs (θ). Whereas the apparent binding constants and binding cooperativities for the derivatives are smaller than for the amylose‐I 2 /I − complex, the binding enthalpies deduced from the temperature dependence of K a at θ = 0.5 appear to be the same for amylose and CM‐Amy. A viscometric titration of fully charged CM‐Amy with I 2 /I − , conducted at dialysis equilibrium between the CM‐Amy‐I 2 /I − solution and the polymer‐free solvent phase, disclosed a maximum in the plot of intrinsic viscosity ([η]) vs θ. The increase in [η] at small θ was interpreted as a reflection of polyelectrolyte expansion provoked by absorption of the negatively charged bound species; the subsequent decline in [η] is attributed to stabilization by I 2 /I − of compact helical sequences or to the formation at higher θ of intermolecular aggregates.