Interaction of DNA with Cationic Micelles: Effects of Micelle Surface Charge Density, Micelle Shape, and Ionic Strength on Complexation and DNA Collapse

Complexation between DNA and cationic/nonionic micelles of dodecyldimethylamine oxide (DMDAO) at various ionic strengths ( I ) was studied by monitoring turbidity or dynamic light scattering as a function of pH at various ionic strengths ( I ). Complexation takes place at a critical degree of micelle protonation (β c ) and is therefore primarily controlled by the ratio of cationic:nonionic surfactant, not by the ratio of surfactant:DNA. β c corresponds to a critical micelle surface charge density (σ c ), which increases nearly linearly with I . The dependence of β c on I displays a discontinuity when the DMDAO micelle shape changes from spherical to rodlike. The proximity of the complexation boundary to the coil/coil−globule coexistence boundary reported from fluorescence microscopy 1 indicates that the DNA−micelle complexation observed by scattering also corresponds to micelle-induced collapse of DNA.