Interaction of L-tryptophan with α-cyclodextrin: Studies with calorimetry and proton nuclear magnetic resonance spectroscopy

Abstract

The interaction of L-tryptophan with α-cyclodextrin was investigated in a 0.1 M phosphate buffer at pH 7.4 with a LKB 2277 microcalorimeter, using flow mixed mode at 25°C. The thermodynamic parameters for inclusion complex formation obtained are as follows; ΔG0 = − 7.03 kJ/mol (K = 17.0), ΔH0 = − 9.50 kJ/mol, ΔS0 = − 8.3 J/mol K. The driving force for inclusion complex formation was considered to be mainly van der Waals–London dispersion force, and the contribution of hydrogen bonding was secondary in importance. Also, from the measurements of the proton nuclear magnetic resonance spectra and the model building with Corey–Pauling–Koltum atomic models, the probable structures of the complex, together with conformational change of L-tryptophan by complexation, were determined. © 2001 Wiley-Liss, Inc. and the American Pharmaceutical Association J Pharm Sci 90:134–140, 2001