What is the critical micelle concentration (CMC)?
Amphipathic detergents in aqueous solution exhibit concentration-dependent self-assembly thermodynamically governed by hydrophobic effect. Monomers exist freely at low concentration with hydrophobic tails partially exposed to water energetically unfavorable. Upon reaching threshold called critical micelle concentration CMC, tail sequestration drives spontaneous formation of spherical or ellipsoidal aggregates called micelles where hydrophobic tails cluster inward forming oily core while hydrophilic heads face water outward, minimizing free energy. CMC is characteristic for each detergent influenced by tail length, head group, ionic strength, temperature and pH. Below CMC detergents exist mainly as monomers insufficient to solubilize membranes; above CMC monomer concentration remains roughly constant and additional detergent forms micelles capable of solubilizing lipids and membrane proteins. Measurements via surface tension, dye solubilization or fluorescence track CMC. It does not denote protein denaturation point, detergent inactivation pH or phosphorylation requirement, purely physical chemistry parameter defining aggregate formation essential for membrane biology and purification strategies. Such detailed mechanistic insight is frequently examined in competitive tests including NEET, CUET, CSIR-NET and GATE where transporter classification, energetics and disease linkage are integrated into problem-solving questions.
Ref: Garavito & Ferguson-Miller, J Biol Chem 2001, Detergent micellization; le Maire et al., 2000.