Cationic Gemini Surfactant-Plasmid Deoxyribonucleic Acid Condensates as a Single Amphiphilic Entity.

A critical aggregate concentration for the surfactant-DNA "complex" or "condensate" consisting of the 16-3-16 gemini surfactant and circular plasmid DNA was determined using surface tensiometry, dynamic light scattering, and conductometry. This surfactant-DNA complex acts as an amphiphile itself, for example, decreasing the surface tension of water until a critical concentration is reached. The evidence presented here introduces a new way of considering these surfactant-DNA condensates, not simply as aggregates in solution but as surface-active agents in their own right. At concentrations below the critical aggregate concentration, there is some dissociation of surfactant molecules from the condensate, creating a more "loose" or "relaxed" complex; however, at and above the critical aggregate concentration, the surfactant-DNA system forms smaller and more uniformly distributed condensates once again. This behavior is analogous to demicellization/micellization that occurs in typical surfactant systems.