Xiaofang Zhao

East China University of Science and Technology, Shanghai, Shanghai Shi, China

Are you Xiaofang Zhao?

Claim your profile

Publications (4)8.91 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: 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 surfactants, 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 postpones the exclusion of ethidium bromide (EB) from DNA/EB complexes. The conformation of DNA undergoes a change from native B-form to chiral ψ-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 the ψ-phase returns to B-form again.
    Chinese Journal of Chemical Engineering 12/2008; · 0.92 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: The interaction between DNA and cationic gemini surfactant trimethylene-1, 3-bis (dodecyldimethylammonium bromide) (12-3-12) has been investigated by the measurements of fluorescence, surface tension, UV spectrum and circular dichroism (CD). Micelle-like structure of 12-3-12 induced by DNA appears at critical aggregation concentration (CAC), which is much lower than critical micelle concentration (CMC) of 12-3-12 in DNA-free solution. CAC is independent of DNA concentration, but the CMC of the mixed solutions of DNA and 12-3-12(CMCmix) increases with the increasing of DNA concentration. The surface tensions of the mixed system are higher than that of the pure surfactant solution, much different from the so-called synergistic lowering of the surface tension for other polymer-surfactant systems. Phase separation occurs after the neutralization point and the precipitate redissolves with superfluous 12-3-12. Cationic surfactant 12-3-12 can exclude ethidium bromide (EB) from the DNA/EB complex, and this process does not depend on the DNA concentration but on the charge ratio of 12-3-12 to DNA. The binding constant of EB to DNA decreases sharply at the charge ratio from 0.5 to 1.0. Circular dichroism (CD) spectra show that DNA undergoes a conformational transition from native B-form to chiral ψ-phase with increasing of 12-3-12.
    Biophysical chemistry 10/2008; · 2.28 Impact Factor
  • Xiaofang Zhao, Yazhuo Shang, Honglai Liu, Ying Hu
    [Show abstract] [Hide abstract]
    ABSTRACT: Interactions between DNA and the cationic gemini surfactant trimethylene-1,3-bis(dodecyldimethylammonium bromide) (12-3-12) in aqueous solution have been investigated by UV-vis transmittance, zeta potential, and fluorescence emission spectrum. Complexes of DNA and gemini surfactant are observed in which the negative charges of DNA are neutralized by cationic surfactants effectively. The DNA-induced micelle-like structure of the surfactant due to the electrostatic and hydrophobic interactions is determined by the fluorescence spectrum of pyrene. It is found that the critical aggregation concentration (CAC) for DNA/12-3-12 complexes depends little on the addition of sodium bromide (NaBr) because of the counterbalance salt effect. However, at high surfactant concentration, NaBr facilitates the formation of larger DNA/surfactant aggregates. Displacement of ethidium bromide (EB) by surfactant evidently illustrates the strong cooperative binding between surfactant and DNA. In contrast to that in the absence of surfactant, the added NaBr at high surfactant concentration influences not only the binding of surfactant with DNA, but also the stability of DNA/EB complex.
    Journal of Colloid and Interface Science 11/2007; 314(2):478-83. · 3.55 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Decondensation of DNA molecules, previously compacted by cationic gemini surfactant 12-3-12 · 2Br, has been successfully achieved by introducing triblock copolymer (PEO)20–(PPO)70–(PEO)20 (P123). P123 can interact with 12-3-12 · 2Br to form supramolecular assemblies through hydrophobic interactions, while not interacting with DNA. When introducing 12-3-12 · 2Br into P123/DNA system, the presence of P123 will inhibit the formation of DNA/12-3-12 · 2Br complexes due to the stronger interaction between P123 and 12-3-12 · 2Br. For previously formed DNA/12-3-12 · 2Br complexes, the addition of P123 can lead to the release of DNA from the complex, which should be attributed to the complexation of P123 with free 12-3-12 · 2Br surfactants in bulk phase followed by the breakup of the thermodynamic equilibrium between surfactant aggregates associated with DNA and free surfactants in bulk phase. CD experiments reveal that 12-3-12 · 2Br can change the conformation of DNA from typical B-form to ψ-phase by formation of DNA/12-3-12 · 2Br complexes. However, the release of the surfactant from the complex induced by P123 turns DNA conformation from ψ-phase back to B-form.
    Colloid and Polymer Science · 2.16 Impact Factor