The polymorphism of headgroup methylated phosphatidylethanolamines
The polymorphism of headgroup methylated phosphatidylethanolamines
A combination of calorimetry, X-ray diffraction and density measurements have been used to perform detailed investigations into the lyotropic properties of the C16 chain length dialkyl dihexadecylphosphatidylethanolamine (DHPE) and its headgroup methylated derivatives in water. The first binary phase diagrams of such systems are presented. In addition, the detailed temperature and composition dependencies is of the dimensions of the gel (Lβ or L_beta'), fluid bilayer (L_α), and inverted hexagonal (HII) phases for each system have been determined. Methylation lowers the gel→fluid bilayer transition temperature, but progressively increases the lamellar→non-lamellar transition temperature. The structure of the non-lamellar phase is also affected by the degree of headgroup methylation; for DHPE the non-lamellar phase is HII, monomethyl-DHPE exhibits complex non-equilibrium phase behaviour with additional diffraction lines observed with the inverted hexagonal phase, cubic phases appear between Lα and H_II for dimethyl-DHPE, but for the trimethylated DHPC non-lamellar phases are largely suppressed. A striking observation is that although methylation greatly increases the limiting hydration of the gel and fluid bilayer phases with the addition of a single methyl group being most marked, the limiting hydration of the H_II is nearly unchanged. The investigation is then extended by studying the interactions present within these systems. In chapter 4 the osmotic pressure technique is used to induce stress into these systems. The results indicate that increasing methylation of the headgroup increases its ability to order the intervening water layer. Chapter 5 presents studies of various phospholipids in the non-aqueous solvent, ethylammonium nitrate, with the interesting observation that the formation of cubic phases is now induced for DHPE. In addition, the first observation of liquid crystal formation in a non-hydrogen bonded solvent, 3-methyl sydnone is reported. Taken together, the results allow a detailed description of the effects of temperature, hydration, methylation and osmotic pressure on the polymorphic phase behaviour, structure of the mesophases and the balance of forces present for these phospholipid systems.
University of Southampton
1989
Hogan, Jacqueline Louise
(1989)
The polymorphism of headgroup methylated phosphatidylethanolamines.
University of Southampton, Doctoral Thesis.
Record type:
Thesis
(Doctoral)
Abstract
A combination of calorimetry, X-ray diffraction and density measurements have been used to perform detailed investigations into the lyotropic properties of the C16 chain length dialkyl dihexadecylphosphatidylethanolamine (DHPE) and its headgroup methylated derivatives in water. The first binary phase diagrams of such systems are presented. In addition, the detailed temperature and composition dependencies is of the dimensions of the gel (Lβ or L_beta'), fluid bilayer (L_α), and inverted hexagonal (HII) phases for each system have been determined. Methylation lowers the gel→fluid bilayer transition temperature, but progressively increases the lamellar→non-lamellar transition temperature. The structure of the non-lamellar phase is also affected by the degree of headgroup methylation; for DHPE the non-lamellar phase is HII, monomethyl-DHPE exhibits complex non-equilibrium phase behaviour with additional diffraction lines observed with the inverted hexagonal phase, cubic phases appear between Lα and H_II for dimethyl-DHPE, but for the trimethylated DHPC non-lamellar phases are largely suppressed. A striking observation is that although methylation greatly increases the limiting hydration of the gel and fluid bilayer phases with the addition of a single methyl group being most marked, the limiting hydration of the H_II is nearly unchanged. The investigation is then extended by studying the interactions present within these systems. In chapter 4 the osmotic pressure technique is used to induce stress into these systems. The results indicate that increasing methylation of the headgroup increases its ability to order the intervening water layer. Chapter 5 presents studies of various phospholipids in the non-aqueous solvent, ethylammonium nitrate, with the interesting observation that the formation of cubic phases is now induced for DHPE. In addition, the first observation of liquid crystal formation in a non-hydrogen bonded solvent, 3-methyl sydnone is reported. Taken together, the results allow a detailed description of the effects of temperature, hydration, methylation and osmotic pressure on the polymorphic phase behaviour, structure of the mesophases and the balance of forces present for these phospholipid systems.
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Published date: 1989
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Local EPrints ID: 461063
URI: http://eprints.soton.ac.uk/id/eprint/461063
PURE UUID: 60a57df2-6a02-4278-b434-63f718cf20cd
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Date deposited: 04 Jul 2022 18:34
Last modified: 04 Jul 2022 18:34
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Author:
Jacqueline Louise Hogan
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