Angular light scattering from phospholipid vesicles and the effect of magnetic fields
Angular light scattering from phospholipid vesicles and the effect of magnetic fields
Phospholipid bilayers represent true two-dimensional assemblies that can be well characterized physically. They exhibit a remarkable range of phases and phase transitions. They are composed of weakly diamagnetic anisotropic molecules which show magnetic birefringence. The main objective of the work reported in this thesis was to study the behavioural and structural changes of phospholipid bilayers in different phases and the effect of magnetic fields on them. Two types of liposomes have been used, multilamellar vesicles (MLV's) and the simpler structured giant unilamellar vesicles (GUV's). Two phospholipids and their mixture were used in preparing MLV's and GUV's namely Dipalmitoyl phosphatidyl-choline (DPPC) and Dimyristoyl phosphatidyl-choline (DMPC). The phase transition temperatures of DPPC-MLV's were detected by means of changes in turbidity of MLV suspensions which were found to be in agreement with the reported results. The phase transition temperatures of DPPC, DMPC and DPPC/DMPC mixtures were measured for GUV's using 90o light scattering. In the vicinity of the phase transition temperature (Tm) of these lipids an anomalous increase in scattered light was observed. The effect of a magnetic field on both types of liposomes was studied by turbidity and 90o light scattering and gave consistent results. The turbidity and scattered light intensity were found to decrease upon application of the field, the effect being greater above Tm. The depolarization ratio was found to decrease upon application of the field which suggested the formation of a more ordered state in the bilayer structure and an increase in the packing density of the molecules. A super-diamagnetic cluster model was suggested to account for the decrease in the scattered light intensity upon application of the magnetic field. Initial studies are reported of the application of the Fisher Cluster model to the changes in the bilayer at the main transition temperature (Tm). The analysis of the angular light scattering data predicts an increase in the diameter of GUV's by about 20% which is in reasonable agreement with the microscopically observed increase in the surface of such liposomes, while the derived optical anisotropy values were larger than those predicted for small unilamellar vesicles (SUV's). (D71903/87)
University of Southampton
Monem, Ahmed Soltan Mohamed Abd
1986
Monem, Ahmed Soltan Mohamed Abd
Monem, Ahmed Soltan Mohamed Abd
(1986)
Angular light scattering from phospholipid vesicles and the effect of magnetic fields.
University of Southampton, Doctoral Thesis.
Record type:
Thesis
(Doctoral)
Abstract
Phospholipid bilayers represent true two-dimensional assemblies that can be well characterized physically. They exhibit a remarkable range of phases and phase transitions. They are composed of weakly diamagnetic anisotropic molecules which show magnetic birefringence. The main objective of the work reported in this thesis was to study the behavioural and structural changes of phospholipid bilayers in different phases and the effect of magnetic fields on them. Two types of liposomes have been used, multilamellar vesicles (MLV's) and the simpler structured giant unilamellar vesicles (GUV's). Two phospholipids and their mixture were used in preparing MLV's and GUV's namely Dipalmitoyl phosphatidyl-choline (DPPC) and Dimyristoyl phosphatidyl-choline (DMPC). The phase transition temperatures of DPPC-MLV's were detected by means of changes in turbidity of MLV suspensions which were found to be in agreement with the reported results. The phase transition temperatures of DPPC, DMPC and DPPC/DMPC mixtures were measured for GUV's using 90o light scattering. In the vicinity of the phase transition temperature (Tm) of these lipids an anomalous increase in scattered light was observed. The effect of a magnetic field on both types of liposomes was studied by turbidity and 90o light scattering and gave consistent results. The turbidity and scattered light intensity were found to decrease upon application of the field, the effect being greater above Tm. The depolarization ratio was found to decrease upon application of the field which suggested the formation of a more ordered state in the bilayer structure and an increase in the packing density of the molecules. A super-diamagnetic cluster model was suggested to account for the decrease in the scattered light intensity upon application of the magnetic field. Initial studies are reported of the application of the Fisher Cluster model to the changes in the bilayer at the main transition temperature (Tm). The analysis of the angular light scattering data predicts an increase in the diameter of GUV's by about 20% which is in reasonable agreement with the microscopically observed increase in the surface of such liposomes, while the derived optical anisotropy values were larger than those predicted for small unilamellar vesicles (SUV's). (D71903/87)
This record has no associated files available for download.
More information
Published date: 1986
Identifiers
Local EPrints ID: 460756
URI: http://eprints.soton.ac.uk/id/eprint/460756
PURE UUID: 855791f3-4b3b-4095-8432-877e498674bc
Catalogue record
Date deposited: 04 Jul 2022 18:29
Last modified: 04 Jul 2022 18:29
Export record
Contributors
Author:
Ahmed Soltan Mohamed Abd Monem
Download statistics
Downloads from ePrints over the past year. Other digital versions may also be available to download e.g. from the publisher's website.
View more statistics