Thermodynamic Analysis for Cationic Surfactants Binding to Bovine Serum Albumin

In the present study, the binding isotherms for interaction of a homologous series of n-alkyltrimethyl ammonium bromides with bovine serum albumin (BSA) have been analyzed on basis of intrinsic thermodynamic quantities. In this regards, the intrinsic Gibbs free energy of binding, AGb(i,)„ has been estimated at various surfactant concentrations and its trend of variation for both binding sets have been interpreted on basis of cooperativity and hydrophobicity of process. Subsequently, the contribution of electrostatic and hydrophobic interactions in AG,, have been estimated using a published method which has been previously introduced by us for analysis of jack bean urease-cationic surfactant system. The results represent the favoring predominate role of hydrophobic interactions and inhibiting rule of electrostatic interaction in binding affinity of both sets. The predominate role of hydrophobic interactions in the second binding set can be related to entropy statistical effect, which arises from numerous number of binding sites in this set but it may be referred to large amount of positive charge density and accessible hydrophobic surface area of BSA in first binding set.