In vitro thermodynamic and spectroscopic investigation on the interaction of tramadol hydrochloride with bovine serum albumin measured by fluorescence quenching method

To interpret the pharmacokinetics and pharmacodynamics properties of a drug molecule, plasma protein binding plays a substantial factor. The present study has been done to investigate the interaction of Tramadol hydrochloride (TRD) with bovine serum albumin (BSA) under physiological condition (pH 7.40) using UV absorption and fluorescence spectrophotometry at different temperatures (298K and 308K). Spectral methods are the most robust techniques for scrutinising the reactivity of chemical agents and biological systems since it permits nonintrusive measurements of the sample molecule in low concentration under identical physiological conditions. Quenching of BSA was also observed in presence of TRD by the fluorescence method. Quenching constants were determined at different temperatures (298K and 308K) using the Stern-Volmer equation. The thermodynamic parameters namely, enthalpy change (∆H), entropy change (∆S), and Gibb’s free energy change (∆G) were analysed based on Van’t Hoff equation. It was found that with the increase of temperature, the value of Stern-Volmer constant increases in case of TRD. From this quenching mechanism, it was found that quenching of BSA-TRD system is static. Based on the thermodynamic parameters, hydrophobic interaction and hydrogen bonding were found to be involved in the formulation of complexes in BSA-TRD system. As Gibb’s free energy change was negative, the interaction was a spontaneous process for the BSA-TRD system at both temperatures (298K and 308K). Binding constants (K) and the number of binding sites (n) were determined at different temperatures (298K and 308K). Based on the findings from the experiment regarding the interaction of BSA-TRD, the drug-protein binding mole ratio is 1:1 at temperatures 298K and 308K. The binding process is reversible and spontaneous.