INTERACTION OF 2-NAPHTHALENESULFONATE WITH BETA-CYCLODEXTRIN - STUDIES WITH CALORIMETRY AND PROTON NUCLEAR-MAGNETIC-RESONANCE SPECTROSCOPY

The interaction of 2-naphthalenesulfonate (2-NS) with beta-cyclodextri n (beta-CD) was investigated in a 0.1 M phosphate buffer at pH 7.4 usi ng an LKB 2277 microcalorimeter and a flow-mixed mode at 25 degrees C. The thermodynamic parameters for inclusion complex formation obtained were as follows: Delta G degrees=-14.7 kJ/mol (K=381 M-1), Delta H de grees= -26.4 kJ/mol, Delta S degrees= -39.1 J/mol K. The formation con stant K was determined as 428 M-1 at the same temperature from the cha nge in chemical shift of the proton nuclear magnetic resonance spectra (H-1-NMR) in 0.1 M phosphate buffered deuterium oxide solution at pD 7.4. The main driving force for inclusion complex formation was consid ered to be the van der Waals-London dispersion force. From measurement s of the H-1-NMR and model building with Corey-Pauling-Koltun atomic m odels, the probable structure of the complex was determined to be: the naphthalene ring of 2-NS is included deeply at the head of 6-H and 7- H of 2-NS in the cavity of beta-CD from the secondary hydroxyl group s ide, the sulfonate group being outside the cavity.