INTERACTION OF 6-P-TOLUIDINYLNAPHTHALENE-2-SULFONATE WITH BETA-CYCLODEXTRIN

The interaction of 6-p-toluidinylnaphthalene-2-sulfonate (TNS) with be ta-cyclodextrin was investigated in 0.1 M phosphate buffer at pH 7.4 b y fluorescence spectroscopy. Using the fluorescence enhancement of TNS in the presence of beta-cyclodextrin, the thermodynamic parameters fo r the formation of two kinds of the inclusion complex (molar ratio of beta-cyclodextrin to TNS = 1:1 and 2:1) were determined as follows: De lta G degrees(1) (1:1 complex) = -20.0 kJ mol(-1) at 25 degrees C, Del ta H degrees(1) = -19.6 kJ mol(-1), Delta S degrees(1) = -1.7 J mol(-1 ) K-1, Delta G degrees(2) (2:1 complex) at 25 degrees C = -6.14 kJ mol (-1), Delta H degrees(2) = -2.80 kJ mol(-1), Delta S degrees(2) = 16.7 J mol(-1) K-1. From the thermodynamic parameters, the main driving fo rce for the 1:1 inclusion complex formation was considered to be the v an der Waals-London dispersion force, while the contribution of the hy drophobic interaction was small. Also, the hydrogen bonding was sugges ted to contribute to the inclusion complex formation. The main driving force for the 2:1 inclusion complex formation was the hydrophobic int eraction. Also, from the measurements of proton nuclear magnetic reson ance spectra and studies with Corey-Pauling-Koltun atomic models, the probable structure was determined and discussed in connection with the thermodynamic parameters.