Madrid, Elena (2012)
Ph.D. thesis, University of Birmingham.
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Electrochemistry and polarization modulation infrared reflection absorption spectroscopy (PM-IRRAS) measurements were used to characterize the structure and organization of a mimetic biological membrane supported at a Au(111) electrode surface to determine the influence of molecule structure on ensemble properties.
Creation and deposition of mimetic membranes was carried out by combining Langmuir-Blodgett / Langmuir-Schaefer (LBLS) techniques. The LB-LS methodology allows the building of symmetric bilayers and more realistic systems based on a mixture of phospholipids that can be asymmetrically distributed across the bilayer.
The phospholipids that have been studied in this work are DMPC, DMPE and DMPS. They differ from each other in the headgroup. However, they are all symmetric lipids with two saturated acyl chains of 14 carbon atoms.
The electrochemical techniques have characterized the permeability of the film and have detected phase transitions of the lipids at the electrode. PM-IRRAS has provided information regarding the phase state, orientation of phospholipid acyl chains and degree of hydrogen bonding of the headgroup and glycerol region as the applied field was varied.
Results have shown that DMPE bilayers contain less solvent content than DMPC and DMPS bilayers. DMPE molecules packed more tightly due to the hydrogen bonding network between the phosphate and the ammonium group of the neighbouring DMPE molecules which hinder the bilayer from hydration. The hydrocarbon chain orientation was less tilted from the surface normal than that of DMPC but very similar to DMPS at adsorption potentials. During desorption, DMPS has increased hydration of the carbonyl groups and the acyl chains tilted, increasing the compactness between them. The headgroups of DMPS remain hydrated, which increases the capacity of the bilayer.
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