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The interaction of DNA with cationic gemini surfactant trimethylene-1,3-bis(dodecyl dimethyl-ammonium bromide)(12-3-12)and anionic surfactant sodium dodecyl sulfate(SDS)mixed system has been investigated by measuring the fluorescence,zeta potential,UV-Vis spectrum,and circular dichroism.In the absence of SDS,owing to the electrostatic and hydrophobic interactions,12-3-12 forms micelle-like structure on the DNA chain before the micellization in bulk phase.For the mixed system of 12-3-12 and SDS,the negative charges on SDS can compete against DNA to bind with cationic 12-3-12 because of the stronger interaction between oppositely charged surfac- tants,and thus,the catanionic mixed micelles are formed before the formation of DNA/12-3-12 complexes.Thereafter,the positive charges on the mixed micelles bind with DNA,and thus,the change of the zeta potential from negative to positive is distinctly different from the system without SDS.Meanwhile,the existence of SDS post- pones the exclusion of ethidium bromide(EB)from DNA/EB complexes.The conformation of DNA undergoes a change from native B-form to chiralψ-phase as binding with 12-3-12 process.Upon adding SDS to the DNA/12-3-12 complex solution,however,DNA is released to the bulk and theψ-phase returns to B-form again.
The interaction of DNA with cationic gemini surfactant trimethylene-1,3-bis (dodecyl dimethyl-ammonium bromide) (12-3-12) and anionic surfactant sodium dodecyl sulfate (SDS) mixed system has been investigated by measuring the fluorescence, zeta potential , UV-Vis spectrum, and circular dichroism. The absence of SDS, due to the electrostatic and hydrophobic interactions, 12-3-12 forms micelle-like structure on the DNA chain before the micellization in bulk phase. For the mixed system of 12-3-12 and SDS, the negative charges on SDS can compete against DNA to bind with cationic 12-3-12 because of stronger interaction between oppositely charged surfac- tants, and thus, the catanionic mixed micelles are formed before the formation of DNA / 12-3-12 complexes. After, the positive charges on the mixed micelles bind with DNA, and thus, the change of the zeta potential from negative to positive is distinctly different from the system without SDS .Meanwhile, the existence of SDS post- pones the exclusion o f ethidium bromide (EB) from DNA / EB complexes. The conformation of DNA undergoes a change from native B-form to chiralψ-phase as binding with 12-3-12 process. complex solution, however, DNA is released to the bulk and theψ-phase returns to B-form again.