Critical micelle concentration (CMC) of SDS micelles at different pH, and added salt concentrations

Abstract

Detergents are amphipathic molecules that consisting of hydrophobic tail and a hydrophilic head group. They can self aggregate to form micelles at a threshold concentration called the critical micelle concentration (CMC). Therefore, at above CMC, the detergent micelles are used as a solvent for hydrophobic peptides/proteins. In addition, the micelles are used as a mimic for membrane or lipid-binding proteins in the structural studies. It has been known that the size of the micelles changes with detergent and added salt concentrations. In NMR spectroscopic studied the size of the molecule/complex is a major factor to be considered. Therefore, the determination of CMC of a detergent is very useful for proper sample preparation in NMR. The micelle formation of detergents is associated with the changes of conductance of the solution. Therefore, we used a conductance measurement method to determine the CMC of sodium-dodecylsulphate (SDS) In this research, the effects of salt concentration, type of salt, pH of the medium, and the presence of amino acids, on CMC of SDS have been determined. We found that there is a considerable effect on CMC due to added salt concentrations, a rapid decrease in CMC is observed with increasing salt concentrations. In addition, the strong electrolytic solutions like NaCl are much more effective on the CMC of detergent micelles than the salts like sodium acetate. Further, we noticed that the effect of pH of the medium on CMC is negligible in the considered pH range.