Spectrophotometric and thermodynamic studies of the interactions of 4-carboxyl-2,6-dinitrophenylazohydroxynaphthalenes with bovine serum albumin

Abstract

The intermolecular interaction occurring between bovine serum albumin and 4-carboxyl-2,6-dinitrophenylazohydroxynaphthalene in aqueous media has been studied spectrophotometrically at different temperatures including body temperature. Evidence for the formation of new molecular complexes was established by hypsochromic and hypochromic shifts of the spectra of dye-BSA complexes compared to the spectra of unbound dyes. One congener (AZ-02) gave a minor peak characteristic of charge-transfer complexation. The binding constants of the four monoazo dyes were investigated and found to vary according to the dye structure and temperature of investigation. AZ-01 and -04 combined with BSA at approximately 1:1 mol ratio while the other two congeners with additional proton donors gave greater than this mole ratio. Thermodynamic considerations established that the dyes utilized the various forms of binding modes; hydrogen bonding, hydrophobic bonding, van der Waals and AZ-03 was particularly involved in electrostatic interactions giving positive entropy change for a small enthalpy change. The observed properties were correlated with the genotoxicity potentials of the monoazo dyes. The results obtained should prove beneficial in designing other molecules in this category of chemical class.