Dr. V.A. Raghunathan: Tuning the structure of DNA-cationic surfactant complexes with cosurfactants and counterions

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     Tuning the structure of DNA-cationic surfactant complexes  with cosurfactants and counterions

     Dr. V.A. Raghunathan, Raman Research Institute, Bangalore, India  

We have studied the structure of complexes formed by DNA with cationic surfactants that self-assemble into cylindrical micelles. An intercalated close-packed hexagonal structure of these complexes is found, where each micelle is surrounded by 6 DNA. Tuning the morphology and flexibility of the surfactant aggregates by adding a cosurfactant is found to induce lamellar and inverted hexagonal structures of these complexes. Further, the competition between the surfactant counterion and DNA polyion to bind to the micelles is found to result in novel close-packed structures of the two cylindrical macroions. One of the structures has a square lattice, whereas the other corresponds to the intercalated hexagonal structure with a superlattice of DNA vacancies. The transformation between the different structures results from the expulsion of DNA from the complex due to the gradual charging of the micelles on increasing the counterion concentration in the solution.