Ultrasonic investigations of inclusion complexation of α-cyclodextrin by iodide ions in pseudo-binary aqueous system

The paper reports study of the complexation processes in aqueous solutions of α-cyclodextrin and iodide ions. The speed and absorption of ultrasonic waves have been measured by the resonance method on a Resoscan™ System apparatus. Density and capacity of the system have been also measured. All measurements have been performed at the constant temperature T = 298.15 K. On the basis of these data, thermodynamical parameters - such as molar volume, molar adiabatic compressibility and their excess functions, have been calculated. To be able to express the concentration of the ternary solution in mole fraction, the initial solutions of the water/α-CD ratio of 550/1 (∼ 0.1 mol/l) and of the water/KI (or water/(KI + 0,77 I2)) at the same ratio, have been prepared. The composition of molecular complexes formed in the solution has been determined on the basis of the correlation between the extremes of the excess functions and ultrasonic absorption for different compositions of the mixtures. The results obtained have suggested formation of inclusion complexes between α-cyclodextrin and iodide ions of the specific stoichiometric compositions: (α-CD)2 I3−I2, (α-CD) I3−I2 and (α-CD)2 I−.