On the blue color of triiodide ions in starch and starch fractions. III. Resonance Raman spectra of bluing species in amylose

In order to clarify the characteristics of the basic units responsible for the blue coloring of iodine/iodide in amylose, we made a resonance Raman spectroscopic study at several KI concentrations using excitation by Ar⁺, He-Ne, and Kr⁺ lasers and amyloses with the degrees of polymerization (DP) of 30, 100, 300, and 1000. Similar Raman spectra were observed, regardless of the KI and I₂ concentrations, DP, and excitation wavelengths. Four Raman lines appearing at 159, 111, 55, and 27 cm^?1 were obviously fundamental tones, with a degree of depolarization ρ of ca. 1/3 for every spectrum. However, the internal ratios of the intensities of the 159, 55, and 27 cm^?1 lines to that of the 111-cm^?1 line decreased with increasing KI concentration. Based on the value of ρ, the assignment of the fundamental lines was made by taking a schematic model of the true motions as a projection in separately analyzing the modes of stretching and bending vibrations for a pseudolinear polyiodide chain, which we found to be perturbed by the external forces of the amylose lattice. In accordance with the variation of the force constants from the assignment of the spectra associated with the change in the composition of the bound species, it was concluded that the basic unit changed from I to I through I with decreasing KI concentration.