Recognition of aromatic amino acids and proteins with p-sulfonatocalix[4]arene - a luminescence and theoretical approach

Abstract

The host–guest interaction of p-sulfonatocalix[4]arene (p-SC4) with aromatic amino acids (AAs) and two proteins has been studied using UV–Vis absorption, fluorescence, and theoretical methods. Spectral studies supported by binding constant and calculated binding energy (BE) values show that p-SC4 binds more strongly with tyrosine compared with other AAs. The application of Bader's theory of atoms in molecule shows the involvement of various types of noncovalent interactions in the formation of the host–guest complexes. Both tyrosine and histidine have strong electrostatic interaction with the sulfonato group and other two AAs have dominant π−π interaction with the aromatic rings of calixarene. In addition, the role of C−H···O, C−H···π and lone pair···π (lp···π) interactions in the stabilization of p-SC4-AA complexes has also been realized from the atoms in molecule analysis. The electron density at the bond critical points varies with the calculated BEs and trend in BEs is in good agreement with the experimental binding constant values. The work has been extended to the binding of p-SC4 with proteins, bovine serum albumin and ovalbumin. Ovalbumin exhibits stronger binding with p-SC4 than bovine serum albumin.