Thermodynamics of sodium dodecyl sulphate (SDS) micellization in the presence of some biologically relevant pH buffers

Three complementary experimental techniques: isothermal titration calorimetry, differential scanning calorimetry and conductometric titration, have successfully been applied to describe the process of sodium dodecyl sulphate (SDS) micellization in the presence of pH buffering substances, namely 2-(N-morpholino)ethanesulfonic acid, piperazine-N,N’-bis(2-ethanesulfonic acid), 4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid and 3-(N-morpholino)propanesulfonic acid, commonly used in biological experiments as well as in calorimetric studies. The measurements were taken in aqueous solutions (pH 6.5), at 298.15 K. The influence of the buffer components as well as the composition of the system under study on the critical micelle concentration, the molar standard enthalpy for micelle formation (ΔmicH0) and the molar heat capacity that corresponds to the thermal midpoint (Tm) of micelle transition has been discussed. It has been shown that the dependence of SDS stability on the kind of buffer may be helpful for the precise interpretation of the molecular recognition processes.