Phase transitions and magnetic field effects in model biomembranes
Phase transitions and magnetic field effects in model biomembranes
Phospholipid molecules which form the basic matrix of biological membranes are weakly diamagnetically anisotropic; they also undergo a so-called gel to liquid crystalline phase transition at a particular temperature Tc at which all types of order decrease. The main objective of the work reported in this thesis was to utilize the free energy balance at the lipid phase transition to study the effects of magnetic fields on simple model membrane systems. Two types of model membrane system have been used; planar lipid bilayers (black lipid membranes or BLMs) and multilamellar liposomes (MLVs). With BLMs, attempts at cooling a membrane through its phase transition have met with limited success. However, an outcome of the ELM work has been the construction of a novel compact BLM cell with good temperature control whilst the associated transmission optics (phase gradient by contrast modulation) enables solvent and bubble movements in the Plateau-Gibbs border to be studied. Turbidity as a function of temperature measurements on MLVs are a powerful means of detecting lipid bilayer phase transitions. Such measurements have been used to construct phase diagrams for DMPC-DPPC and DMPC-DSPC mixtures and to study charge induced "pretransitions" in DPPC-DPPE mixtures. By encapsulating a pH indicator dye (phenol red) within MLVs, dye leakage studies in the phase transition region for DPPC and DMPC-DPPC mixtures have been performed. A permeability anomaly exists for DPPC liposomes at Tc (42°C) whilst dye leakage for DMPC-DPPC liposomes begins at the "pretransition" which is several degrees below the first appearance of liquid crystalline phase. An intriguing strongly temperature dependent magnetic field effect has been observed and characterized by changes in turbidity in the pretransition and main transition temperature region for all types of multilamellar liposomes used. This effect is largest in the liquid crystalline phase, being greater for binary than for single component liposomes, and is maximal around the equimolar DMPC-DPPC mixture region.
University of Southampton
1982
Braganza, Lellis Francis
(1982)
Phase transitions and magnetic field effects in model biomembranes.
University of Southampton, Doctoral Thesis.
Record type:
Thesis
(Doctoral)
Abstract
Phospholipid molecules which form the basic matrix of biological membranes are weakly diamagnetically anisotropic; they also undergo a so-called gel to liquid crystalline phase transition at a particular temperature Tc at which all types of order decrease. The main objective of the work reported in this thesis was to utilize the free energy balance at the lipid phase transition to study the effects of magnetic fields on simple model membrane systems. Two types of model membrane system have been used; planar lipid bilayers (black lipid membranes or BLMs) and multilamellar liposomes (MLVs). With BLMs, attempts at cooling a membrane through its phase transition have met with limited success. However, an outcome of the ELM work has been the construction of a novel compact BLM cell with good temperature control whilst the associated transmission optics (phase gradient by contrast modulation) enables solvent and bubble movements in the Plateau-Gibbs border to be studied. Turbidity as a function of temperature measurements on MLVs are a powerful means of detecting lipid bilayer phase transitions. Such measurements have been used to construct phase diagrams for DMPC-DPPC and DMPC-DSPC mixtures and to study charge induced "pretransitions" in DPPC-DPPE mixtures. By encapsulating a pH indicator dye (phenol red) within MLVs, dye leakage studies in the phase transition region for DPPC and DMPC-DPPC mixtures have been performed. A permeability anomaly exists for DPPC liposomes at Tc (42°C) whilst dye leakage for DMPC-DPPC liposomes begins at the "pretransition" which is several degrees below the first appearance of liquid crystalline phase. An intriguing strongly temperature dependent magnetic field effect has been observed and characterized by changes in turbidity in the pretransition and main transition temperature region for all types of multilamellar liposomes used. This effect is largest in the liquid crystalline phase, being greater for binary than for single component liposomes, and is maximal around the equimolar DMPC-DPPC mixture region.
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Published date: 1982
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Local EPrints ID: 460608
URI: http://eprints.soton.ac.uk/id/eprint/460608
PURE UUID: 15058f7b-dc35-4fa7-928d-9605d1f076c7
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Date deposited: 04 Jul 2022 18:25
Last modified: 04 Jul 2022 18:25
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Author:
Lellis Francis Braganza
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