The DNA sequence (TTAGGG)<sub>4</sub> forms a highly folded quadruplex structure with a high negative charge density due to the close proximities of the phosphate groups in the folded structure. At concentrations above the <i>cmc</i> (critical micelle concentration), dicationic Gemini surfactants self-assemble into large micelles with high positive charge densities due to the close proximities of the ammonium groups in the tightly packed micelle. Since DNA secondary structures are stabilized by mono and divalent cations, we were interested in the interaction of a dicationic Gemini surfactant with DNA. In this study, solutions of DNA and a 12-4-12 Gemini surfactant were prepared in buffer with different DNA/surfactant ratios. At surfactant concentrations greater than 0.375 mM, a precipitate formed and no DNA was found in the supernatant; in samples prepared with lower concentrations of surfactant, precipitates formed but residual DNA was found in the supernatants. In those samples where the DNA was not totally precipitated, the DNA assumed a quadruplex conformation which was stabilized relative to the quadruplex in buffer alone. A complex equilibrium between surfactant (S), micelle (M), quadruplex (Q) and aggregate (A) for this system is proposed to account for these observations. Finally, a method will be described to recover the DNA from the precipitate.

Aggragation of Gemini surfactant based micelles by a DNA quadruplex

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