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DOPC-DOPE composition dependent Lα-HII thermotropic phase transition: SAXD study
M Klacsová1, A Bóta2, P Balgavý1
1Department of Physical Chemistry of Drugs, Faculty of Pharmacy, Comenius University in Bratislava, Odbojárov 10, 832 32 Bratislava, Slovakia.
Chemistry and Physics of Lipids
|May 16, 2016
Summary
Heating mixed dioleoylphosphatidylcholine-dioleoylphosphatidylethanolamine (DOPC-DOPE) lipids reveals fluid lamellar, inverse hexagonal, and inverse cubic phases. Lipid composition significantly influences phase transitions and structural parameters.
Area of Science:
- Lipid bilayer polymorphism
- Soft matter physics
- Materials science
Background:
- Understanding lipid phase behavior is crucial for biological membranes and drug delivery systems.
- Dioleoylphosphatidylcholine (DOPC) and dioleoylphosphatidylethanolamine (DOPE) are common membrane lipids with distinct headgroups.
- Mixed lipid systems exhibit complex phase diagrams influenced by composition and temperature.
Purpose of the Study:
- To investigate the structural polymorphism of mixed DOPC-DOPE lipid systems.
- To determine the phase transition temperatures and lattice parameters under varying conditions.
- To elucidate the influence of lipid composition on lyotropic phase formation.
Main Methods:
- Small-angle X-ray diffraction (SAXD) was employed to analyze lipid structures.
- Experiments were conducted across a temperature range of 5-80°C.
- Varying mole fractions of DOPC and DOPE were systematically studied.
Main Results:
- A phase sequence of fluid lamellar (Lα), inverse hexagonal (HII), and inverse cubic (QII) phases was observed at XDOPE ≥ 0.65.
- A superposition of two bicontinuous cubic QII phases (Pn3m and Ia3d space groups) was identified.
- Phase transition temperatures and lattice spacings decreased with increasing DOPE content.
Conclusions:
- Lipid composition critically controls the lyotropic phase behavior of DOPC-DOPE mixtures.
- Structural rearrangements occur during the Lα to HII phase transition.
- The transition mechanism varies with changing lipid composition.
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