Thermodynamic and spectroscopic studies of alanine and phenylalanine in aqueous β-cyclodextrin solutions

Ultrasonic speed, u and density, rho have been measured for DL-alanine (Ala) and L-phenylalanine (Phe) in aqueous beta-cyclodextrin (beta-CD) at 298.15, 303.15, 308.15, and 313.15 K. The complexation of Ala and Phe with beta-CD has been studied by means of UV-vis and thermodynamic (ultrasonic speed and density) studies. Using the measured ultrasonic speed and density data the apparent molar compressibility (kappa(S, phi)), apparent molar volume (V-phi), limiting apparent molar compressibility (kappa(0)(S, phi)), limiting apparent molar volume (V-phi(0)), their constants (S-K and S-v), and hydration number (n(H)) have been obtained. The positive values of transfer properties at infinite dilution for Ala and Phe in beta-CD is the outcome of the balance between released water molecules from beta-CD cavity and hydrophobic groups of Ala and Phe that enter into the macrocycle beta-CD cavity. The experimental results have also been discussed on the basis of UV-vis absorbance. The results indicate the formation of a more stable host-guest complex between Phe-beta-CD than between Ala-beta-CD. (C) 2013 King Saud University. Production and hosting by Elsevier B.V.