INTERACTION OF BILE-SALTS WITH HEXADECYLTRIMETHYLAMMONIUM BROMIDE AND SODIUM DODECYL-SULFATE

The results of the interaction of cetyltrimethylammonium bromide (CTAB) and sodium dodecyl sulfate (SDS) with sodium cholate (NaC), sodium deoxycholate (NaDC), sodium dehydrocholate (NaDHC), sodium chenodeoxycholate (NaCDC), sodium taurodeoxycholate (NaTDC), sodium taurochenodeoxycholate (NaTCDC), and equimolar mixtures of NaC, NaDC, NaCDC, NaDHC, NaTDC, NaTCDC, and sodium lithocholate (NaLC) determined by conductance, surface tension, and calorimetric methods have been presented. A 1:1 interacted species between CTAB and the bile salt has been found to form in solution at concentrations below the critical micelle concentration (cmc) of the components. While in the pure state individual components exhibit a single cmc, their binary combinations (where CTAB is a component) have evidenced formation of two widely varied cmc's. Both conductimetric and surface tension methods have corroborated the formation of the lower or the first cmc, whereas conductimetric and calorimetric methods have evidenced the formation of the higher or the second cmc. The results have been analyzed and used for the evaluation of counter-ion binding and thermodynamics of micellization and interfacial adsorption of the detergent molecules. Although the micellization enthalpies (DELTA-H-degrees m) of pure components are measurable, the CTAB-bile salt combinations have shown negligible DELTA-H-degrees m, supporting entropy-driven mixed-micelle formation. The extents of interaction among the mixed components have been estimated from Rubing's theory. The trends of interaction of the bile salts with CTAB and SDS have been found to be dependent on the cmc values and the composition.