Binding of diclofenac sodium with bovine serum albumin at different temperatures, <i style="">p</i>H and ionic strengths

Abstract

The study was designed to examine the binding of diclofenac sodium with bovine serum albumin (BSA) at different temperatures (20°, 30° and 40°C),<i style="">p</i>H (6.4,7.4 and 8.4) and ionic strengths (<img src='/image/spc_char/micro.gif'> = 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 <img src='/image/spc_char/micro.gif'>mole/l and BSA concentration was maintained at 61.5 <img src='/image/spc_char/micro.gif'>mole/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 <i style="">p</i>H and ionic strength also caused decrease in association constant of diclofenac sodium and BSA binding.