| DNA condensation in vitro has been of interest for many years as a model of naturally occurring DNA packaging (e.g. chromatin, sperm head and virus capsid packing). More recently, DNA condensation has been of interest in optimizing artificial gene delivery, as the lack of efficient methods is a limiting obstacle to human gene therapy. More specifically, a variety of gene carriers have been developed to facilitate the release of DNA from the carrier in order to increase nucleus uptake efficiency and subsequent gene expression. The research presented in this dissertation provides a means to control DNA compaction and expansion with light illumination using the interaction of a photoresponsive cationic surfactant, azoTAB, with DNA. The surfactant undergoes a reversible photoisomerization upon exposure to visible trans isomer, more hydrophobic) or UV (cis isomer, more hydrophilic) light. As a result, surfactant binding to DNA and the resulting DNA condensation can be tuned with light. Through the use of a new experimental setup, fluorescence microscopy was employed to visualize reversible, light-controlled coil-to-globule transitions of single DNA molecules, free in solution. The setup also allowed for the evaluation of the kinetics of both compaction and expansion processes and, thus, provides a new, non-intrusive method, to study DNA. Comparison of the interaction with DNA of several photoresponsive surfactants who differ from one another by their hydrophobic character showed that both electrostatic and hydrophobic forces are important in the compaction process. Moreover, the use of several dyes as probes allowed to propose a mode of binding between surfactant molecules and DNA, and hypothesized on forces involved at the onset of compaction. Finally, the combination of a cationic photoresponsive azoTAB surfactant with an anionic surfactant SDBS is shown to form vesicles. The interaction between catanionic vesicles and DNA, and the action of light on the complex are investigated. |
