An insight into the interaction of phenanthridine dyes with polyriboadenylic acid: Spectroscopic and thermodynamic approach

We have investigated the interaction of two phenanthridine ligands namely ethidium bromide and propidium iodide with single and double stranded polyriboadenylic acid using various spectroscopic techniques. Both of them were found to bind with the single stranded polymer, while no interaction was observed with the double stranded one. Thermodynamic studies revealed that in both the cases the binding were characterized by negative enthalpy and negative entropy changes. Ionic strength dependence studies revealed a lesser electrolytic contribution to the total Gibbs free energy change in both the cases compared to the non-electrolytic contribution. Our results may be of potential use in the design of specific phenanthridine derivatives and understanding the structure activity relationship for improved therapeutic applications.