Chaotropic solvents increase the critical micellar concentrations of detergents

Monomer detergent concentrations of Triton X-100, Chaps (3-[(3-cholamidopropyl)-dimethylammonio]-1-propanesulfonate), and sodium dodecyl sulfate in guanidine hydrochloride, formamide, and urea solutions were measured by an ultrafiltration procedure. This simple and rapid procedure effectively separated the monomer forms of these detergents from their respective micelle forms. Critical micellar concentrations of these detergents in water measured by this procedure agreed well with previously reported values. Both ionic and nonionic chaotropic agents, e.g., guanidine hydrochloride, formamide, and urea, are demonstrated to significantly shift the equilibrium between the monomer and the micellar form of various detergents toward the direction of monomer in a concentration-dependent manner. Thus, monomer/micelle ratio of detergents in solution can be manipulated over a wide range by the concomitant use of chaotropic solvents. This has direct applications in experiments involving destruction of biomembranes and solubilization of hydrophobic molecules in aqueous solutions.