Electrooptical relaxation spectrometry of membrane electroporation in lipid vesicles

The classical interpretation of the experimental electric turbidity and absorbance dichroisms has been extended to account for chemical contributions to the dichroitic signal caused by changes in the immediate neighborhood of the scattering centers or chromophores. In diluted suspensions of lipid bilayer vesicles (Lecithin (20%), concentration 1 mM) of radius a=90 nm, doped with diphenylhexatrienyl-phosphatidylcholine (β-DPH pPC, 5 μM), the chemical modes refer to the entrance of water into the head-group region of the lipids in the bilayer and into those membrane parts constituting the electropores. We propose here, an extended analytical approach to correctly analyze turbidity and absorbance relaxation data on membrane electroporation (ME) and electro-elongation of lipid vesicles. It is shown that the combination of turbidity and absorbance data provides a tool to quantify molecular order and rapid motion of optical probes within the vesicle bilayer in terms of order parameters.