| Abstract
| - The complex stability constants (Ka) and thermodynamic parameters (ΔG°, ΔH°, and TΔS°) for 1:1complexation of water-soluble calix[4]arene, thiacalix[4]arene, and calix[5]arene sulfonates with pyridineand their methylated derivatives have been determined by means of isothermal titration calorimetry atpH 2.0 and 7.2 at 298.15 K, and their binding modes have been investigated by NMR spectroscopy. Theresults obtained show that sulfonatocalixarenes afford stronger binding ability toward pyridine guests atpH 2.0, attributable to the positive electrostatic interactions and the more extensive desolvation effects,but present higher molecular selectivity at pH 7.2 owing to the strengthened C−H···π interactions. ThepH-responsible binding ability and molecular selectivity are discussed from the viewpoint of electrostatic,π-stacking, van der Waals interactions and size-fit relationship between host and guest. A close comparisonfurther demonstrates that the C−H···π interactions and van der Waals interactions play a more importantrole than π···π interactions in the present inclusion complexation.
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