ABSTRACT

DNA is an amphiphilic polymer that contains hydrophobic bases and carbohydrates and phosphate groups, which are hydrophilic. The bases promote an association between DNA molecules, whereas the hydrophilic parts oppose self-assembly. The double helix of DNA is its most important selfassembly structure. Mixtures of DNA and cationic surfactants show a strong associative behavior. In solution, DNA molecules present an extended conformation (coil), whereas at high concentrations of surfactant, the DNA molecules undergo compaction. This transition can be followed by uorescence microscopy (FM). Complexes between DNA and cationic surfactants have attracted an increased interest lately due to the possibility of using these systems for gene transfection [1]. The nature of both the DNA and the surfactant [2-4] has been found to inuence the phase separation limits and also the structure of the DNA-surfactant complexes. Surfactants are not the only class of molecules interacting strongly with DNA. For instance, the binding of positively charged proteins, as well as poly-l-lysine and poly-l-arginine, multivalent ions and multivalent polyamines, such as spermidine or spermine are known to condense large DNA coils [5,6], resulting in (associative) phase separation in sufciently concentrated solutions.