Amylose-Iodine Complex. IV. The Complex in Dimethyl Sulfoxide-Water Mixtures

Abstract

Abstract The temperature at which the blue color due to the formation of amylose-iodine complex fades completely has been determined with a system of amylose and iodine dissolved in dimethyl sulfoxide-water mixtures. This temperature rises with the increase in the concentration of iodine in mixtures, and also with the increasing concentration of water in the mixed solvents. The spectrophotometric results show that the nature of the amylose-iodine complex in a dimethyl sulfoxide-water mixture is similar to that of one in water, and that the triiodide ion or a chemical species similar to the ion, i.e., the polyiodide ion, contributes to the formation of the complex. The viscometric studies show that the amylose molecule takes a deformed helix conformation prior to the formation of the blue iodine complex and that this conformational prerequisite to the complex formation is fulfilled when the water concentration in a dimethyl sulfoxide-water mixture exceeds a critical value. These results stated above may indicate that the triiodide (polyiodide) ion plays the part of “stabilizer” for the fixation of iodine molecules within the helically-wound chain of the amylose molecule when the amylose exists primarily as a deformed helix in solution.