Critical micelle concentration (CMC)

Schematic of a phospholipid micelle

Critical micelle concentration (CMC) is defined as the concentration of detergents above which micelles are spontaneously formed. The CMC is important in biology because at concentrations above it the detergents form complexes with lipophilic proteins. Below this borderline, detergents merely partition into membranes without solubilising membrane proteins.

Detergent	CMC (%w/v)	CMC (mM)	MW	Type
BRIJ 35	0.11	0.09	1200	non-ionic
NP-40	0.017	0.3	~650	non-ionic
Saponin	~0.1		mixture	non-ionic
Triton X-100	0.021	0.3	~650	non-ionic
Tween 20	0.073	0.059	~1228	non-ionic
SDS	0.23	7-10	288.5	ionic
CHAPS	0.49	6-10	615	zwitterionic

Note: The molecular weights for some detergents are average values. Triton X-100, for example, can range between 600 and over 650 MW depending on synthesis. The exact molecular weight influences the CMC.

Note: Saponin is a class of amphiphilic, natural metabolites with detergent properties often extracted from plants. CMC may vary.

Sources

• new, abbreviated Detergent guide, Calbiochem
• Commonly used detergents, Frost lecture, UFL
• Urum et al 2004, incl. data on saponin

See also

• Wikipedia: Critical micelle concentration
• old (2001) Calbiochem Detergent brochure