Studies of inorganic and organic interactions with supported and free standing phospholipid monolayers and bilayers.

The application of self-assembled monolayers on Hg in biosensor technology dictates the need to develop a thorough understanding of the system by using it to develop the structure-activity relations of biologically active compounds and upgrading the system to stable bilayer configurations on Hg. In this thesis four aspects of the properties of phospholipid layers on Hg in electric fields have been investigated as follows:
(1) Effects of electrolyte ions on the potential-induced phase transitions exhibited by 1,2-dioleoyl phosphatidylcholine (DOPC) monolayer on hanging mercury drop electrode (HMDE) and mercury film electrode (MFE) are examined using alternating current voltammetry (ACV) and chronoamperometry. Results show that the underlying mechanism of phase transitions is affected by the concentration and sizes of electrolyte ions affecting the structure of electrical double layer at the lipid electrolyte and Hg electrolyte interface.
(2) Fluorescence spectroscopic and electrochemical impedance techniques have been applied to study the interaction of substituted biphenyls with DOPC vesicles and Hg supported monolayers. The extent and type of interaction of substituted biphenyls with membrane models depends on the position and electron withdrawing/donating properties of substituents.
(3) Electrochemical impedance used to study the interactions of small di- and tri-peptides of prebiotic relevance with DOPC monolayers on Hg shows that dispersion and electrostatic forces are responsible for interactions between DOPC monolayer and relatively apolar, and polar charged peptides respectively. In addition, an increase in their chain length causes an increase in DOPC/peptide interactions.
(4) DOPC bilayers can be supported on HMDE and their lipid density varied by controlling the electrode area using RCV. The bilayer configurations are found less permeable than monolayers to aqueous Zn2+ at potentials positive to -1.2 V using chronoamperometry. Impedance studies have highlighted the ion movements into the DOPC bilayer as dielectric relaxation. Furthermore, silica nanoparticles have also been found to interact with bilayer configurations using RCV.