[Study on the inclusion behavior of p-sulphonatocalix[4]arene with acridine by spectrofluorometric titrations]

p-sulphonatocalix[4] arene (1) was prepared according to the literature, and spectrofluorometric titrations were performed to investigate the inclusion behavior of (1) and acridine in citrate buffer solution (pH 5.92, 0.1 mol x L(-1)) at different temperatures. It was found that in definite concentration range, the emission peak of acridine exhibited a slight red shift and th fluorescence intensity decreased when (1) was added. They form stable host-guest complex, and the stoichiometry of the inclusion complex is 1 : 1. The stability constants of the inclusion complex at 15.0 degrees C, 20.0, 25.0 and 30.0 degrees C were determined as 3.08 x 10(5), 4.45 x 10(4), 2.58 x 10(4) and 8.90 x 10(3), respectively. The thermodynamic parameters of inclusion process, deltaG, deltaH and deltaS, were determined. The experimental results indicated that the inclusion process was an exothermic and enthalpy-driven process. It was found that the stability constants descended when temperature rose. The most probable pattern of the inclusion complex between (1) and acridine was proposed as: acridine partially goes into the cavity of (1), and the protonated N atom and the negatively charged sulphonyl group bond firmly owing to strong electrostatic interaction. With the main contribution of electrostatic interaction and the assistance of Van de Waals and hydrophobic interaction, the host and the guest molecules form 1 : 1 supramolecular complex.