Molecular recognition kinetics of beta-cyclodextrin for several alcohols by ultrasonic relaxation method

Ultrasonic absorption coefficients in aqueous solutions of 2-propanol, 2-bu tanol, and 2-methyl-1-propanol (guest) in concentrations less than 0.40 mol dm(-3) with beta -cyclodextrin (host) in the range below 0.011 mol dm(-3) were measured in the frequency range 0.8-95 MHz at 25 degreesC. A single De bye-type relaxational absorption was found only when both solutes coexisted . From the concentration dependences of the relaxation frequency and the am plitude of the relaxation, the cause of the observed relaxation was attribu ted to a perturbation of a chemical equilibrium associated with a dynamic i nteraction between beta -cyclodextrin and the alcohols. The rate and thermo dynamic parameters for the dynamic interaction were determined, and the res ults were compared with those for other alcoholic systems with beta -cyclod extrin, which were reported previously. The isomeric effect of the guests o n the dynamic interaction with beta -cyclodextrin was considered and it is deduced from the experimental results that the hydrophobicity of the guests is very sensitive for recognition by the host. Also, an anchor mechanism w as proposed for the complexation between the host and guest.