Study on the intermolecular complexation behavior between p-sulfonatocalix[4]arene with l-tyrosine

The formation of the complexation behavior of host molecules water-soluble p-sulfonatocalix[4]arene (p-SCX4) with l-tyrosine (l-Tyr) guest molecule has been studied by spectrophotometric including fluorescence and nuclear magnetic resonance (NMR) spectroscopy. Experimental conditions including concentration of p-SCX4 and medium acidity were investigated in detail. The results showed that p-SCX4 forms 1:1 complexes with l-Tyr in water. Their stability constant determined by spectrofluorometric titration is 15761 L mol. Moreover, to obtain information about the binding mechanism of the interaction, 1H NMR studies were carried out showing that the water-soluble p-SCX4 was found to be able to complex the aromatic l-Tyr, and the part of benzene ring of amino acid penetrated into the hydrophobic cavity of calix[4]arene and charged aliphatic chain of l-Tyr stick out of the cavity. In addition, the thermodynamic parameters for the complexation of p-SCX4 with l-Tyr were determined through Van’t Hoff analysis. The obtained data further confirmed the binding mode of p-SCX4 with l-Tyr. The related mechanism is proposed to explain the complexation processes.