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Supramolecular interaction of procaine with p-sulfonated calix[6]arene

Hai-Long Liu, Yan Zhao, Li-Ming Du2, Tao-Tao Pang, Ying-Chao Yang

The inclusion interaction between procaine (PC) and p-sulfonated calix[6]arene (SC6A) was investigated via fluorescence and 1H NMR spectroscopy. The effects of pH, temperature, ionic strength, and SC6Aconcentrationwere examined in detail. In a Britton–Robinson solution with a pH of 7.5, the fluorescence of PC significantly quenched upon the addition of SC6A, which revealed the formation of inclusion complexes between PC and SC6A. The stoichiometric ratio of 1:1 was obtained via the continuous variation method. The inclusion constant of PC–SC6A complexes was 1.29 × 104 L/mol, which was obtained via the nonlinear curve fitting method. The 1H NMRspectra verified that the aliphatic chain of PCmay be partially penetrated into the hydrophobic cavity of SC6A. This finding was confirmed by density functional theory calculations.