Abstract
The modes of interaction of four congeneric monoazo dyes, 4-carboxyl-2,6-dinitrophenylazohydroxynaphthalenes with calf thymus double strand DNA in aqueous medium have been investigated spectrophotometrically. Characteristic spectral changes observed at two temperatures (293 and 310K) were assigned to either change in absorption intensity or change in wavelengths. The changes bear a direct relationship with the structures of the dyes. All the dyes gave good binding constants with DNA. Using Job's method of continuous variation, varying stoichiometric ratios were established between the dyes and DNA. Thermodynamic considerations enabled the delineation of the binding modes to be hydrogen bonding (AZ-01 and -03), electrostatic interactions (AZ-03) and hydrophobic bonding (AZ-04). Correlation of the formation constant with Massieu–Planck's constant established the hydrophobic interaction between DNA and AZ-04. The observed binding modes were related to the earlier genotoxicity assessments of the dyes.The results obtained should prove beneficial in designing other congeners in this phenylazohydroxynaphthalene chemical class.
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