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 the basis of intrinsic thermodynamic quantities. In this regard, the intrinsic Gibbs free energy of binding,  [image omitted], has been estimated at various surfactant concentrations and its trend of variation for both binding sets have been interpreted on the basis of cooperativity and hydrophobicity of the process. Subsequently, the contribution of electrostatic and hydrophobic interactions in  [image omitted], 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 favouring predominate role of hydrophobic interactions and minor 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 a large amount of positive charge density and accessible hydrophobic surface area of BSA in first binding set.