Polyanionic DNA interacts with cationic amphiphiles to form electrostatic complexes exhibiting rich self-assembledstructures. This type of complex has been considered as a nonviral carrier in gene therapy and as a template fornanostructure construction. Here we report a thermally-induced phase transition of the complexes of DNA with themixtures of a cationic surfactant, dodecyltrimethyl bromide (DTAB), and a neutral lipid, dioleoylphosphatidylethanolamine (DOPE), in fully hydrated state. An order-order transition between a multilamellar (
![](/isubscribe/journals/langd5/22/i18/eqn/la060862ze10001.gif)
) phase and aninverted hexagonal (
![](/isubscribe/journals/langd5/22/i18/eqn/la060862ze10002.gif)
) phase was found to occur with the transition temperature adjustable by the DTAB-to-DNAbase pair molar ratio (
x) and DOPE-to-DTAB molar ratio (
m). The stability of the
![](/isubscribe/journals/langd5/22/i18/eqn/la060862ze10003.gif)
phase was enhanced at lower
m and
x, as the
![](/isubscribe/journals/langd5/22/i18/eqn/la060862ze10004.gif)
-to-
![](/isubscribe/journals/langd5/22/i18/eqn/la060862ze10005.gif)
transition temperature increased with the decreases of these two parameters. The suppressionof
![](/isubscribe/journals/langd5/22/i18/eqn/la060862ze10006.gif)
-to-
![](/isubscribe/journals/langd5/22/i18/eqn/la060862ze10007.gif)
transition at lower
x was attributed to the lower entropic gain from the counterion release due to thepresence of uncomplexed DNA in the bulk solution.