An investigation into the mixing interactions of cationic gemini surfactant/pDNA complexes with various poloxamers: effects of cationic gemini surfactant tail structures on mixed micellar behaviour.

The mixing interactions of a 16-3-16/pDNA complex (a 10 : 1 charge ratio of N+ : P-) with seven Pluronics (P105, L101, F77, F68, P65, L64, and L62) and a 16-3-phy/pDNA complex (a 10 : 1 N+ : P- charge ratio) with five Pluronics (L62, F127, L44, F87, and P105) are investigated using surface tension measurements and are interpreted using Clint's, Rubingh's, and Maeda's mixed micelle models. These gemini/pDNA/Pluronic systems have potential for applications as transfection vectors. Prior work from our group, using the same mixed micellar models to investigate six 16-3-16/pDNA/Pluronic (F87, P84, L121, F127, P103, and L44) systems, showed that greater synergism in these systems was correlated with greater transfection in COS-7 cells. Here, we re-evaluate the suitability of the mixed surfactant models for describing these systems. The results show that the interaction parameters for these systems depend significantly on the gemini surfactant identity. This effect is attributed to increased steric hindrance from the bulky phytanyl tail of 16-3-phy. Ethidium bromide fluorescence measurements for the 16-3-phy/pDNA/Pluronic mixed systems show that the length of the Pluronic PPO block affects the ability of the gemini/pDNA complexes to form condensed complexes with the pDNA. Overall, the gemini surfactant structure significantly affects interaction parameter values but does not affect DNA condensation in these systems. This suggests that the previously observed correlation between synergism and transfection is likely 16-3-16/pDNA/Pluronic system specific and not generalizable to other gemini/pDNA/Pluronic systems.