Binding of diclofenac sodium with bovine serum albumin at different temperatures, pH and ionic strengths.

The study was designed to examine the binding of diclofenac sodium with bovine serum albumin (BSA) at different temperatures (20°, 30° and 40°C), pH (6.4,7.4 and 8.4) and ionic strengths (μ = 0.1, 0.2 and 0.3) by means of equilibrium dialysis method. The concentration of diclofenac sodium was maintained at wider range from 15 to 900 μmole/l and BSA concentration was maintained at 61.5 μmole/l. The data obtained were interpreted by nonlinear regression method using Graphpad prism software. The analysis showed that the interaction between diclofenac sodium with BSA results in two-site saturable binding. A decrease in association constant was observed with increasing temperature. The average standard free energy change (ΔG°) value was -7.07 (site I) and -4.2 (site II) Kcal/mol. The standard enthalpy change (ΔH°) and the standard entropy change (ΔS°) were-7.8 Kcal/mole, -2.35 cal/mole (site I) and -7.4 Kcal/mole, -10.5 cal/mole (site II), respectively. The negative enthalpy change suggested the binding between diclofenac sodium and the binding sites of BSA were spontaneous and exothermic. The negative value of ΔH° and ΔS° indicated hydrogen bonding and van der Waal's force was the major mechanism for diclofenac sodium and BSA interaction. Increase in pH and ionic strength also caused decrease in association constant of diclofenac sodium and BSA binding.