On the complexation of α-cyclodextrin in iodide and iodide-iodine aqueous solutions

Ultrasonic attenuation spectra, measured between 400 kHz and 2 GHz, of α-cyclodextrin/potassium iodide/water mixtures have been reconsidered and have been compared to recent attenuation coefficient data obtained from a single frequency method. At variance with the latter data the analysis of broadband spectra reveals two relaxation terms within the frequency range of measurement. The high frequency term with relaxation time between 1.4 and 3 ns is assigned to the rotational isomerization of the excocyclic hydroxymethyl group of the cycloamylose. With the α-cyclodextrin solution the low frequency relaxation with relaxation time 21 ns is assumed to be due to fluctuations of the glucosidic bond torsion angles. With the potassium iodide containing solutions the low frequency relaxation with relaxation times between 6 and 9 ns reflects the formation of cyclodextrin-iodide inclusion complexes.