Synthesis, characterization and interaction studies of 2,7-naphthalenediol,2-[(4-Bromophenyl)]azo, with calf thymus deoxyribonucleic acid (ct-DNA)

In this study, at first, an azo dye, 2,7-naphthalenediol,2-[(4-Bromophenyl)azo (BPAND) as a ligand has been synthesized by addition of p-Bromoaniline to the modified montomorillonite K10 clay. This ligand was characterized using 1H-NMR, UV-Vis and IR spectroscopies. Subsequently, its interaction with calf thymus deoxyribonucleicacid,ct-DNA was investigated in 5 mM phosphate buffer solution, pH=7 using UV-Vis absorption, thermal denaturation and viscosity measurement. From spectrophotometric titration experiments, the binding constant of BPAND with ct-DNA was found to be (2.89±0.2)×10^7 M^-1 at 25°C. In order to determine changes in thermodynamic properties such as binding constant, Gibbs free energy, binding enthalpy and binding entropy, this experiment was done at various temperatures. The enthalpy and entropy changes were -2.852±0.634 kJ/mol and -814.065 ±2.52 J/mol.K, respectively.Thermal denaturation experiments show the increasing of melting temperature of ct- DNA (about 0.06°C less than 0.6) due to binding of BPAND ligand. From these results, the mechanism and the stoichiometry of binding were determined. The results revealed that this interaction is exothermic (negative enthalpy change) along with negative entropy change. Therefore, the driving force in these interactions is enthalpy and the process is enthalpy-driven and suggests that the main driving force for the ct-DNA-BPAND complex formation is being Van der Waals or hydrogen binding.