Polymorphic phase behavior of unsaturated lysophosphatidylethanolamines: a 31P NMR and X-ray diffraction study

Area of Science:

• Lipid Polymorphism
• Biophysical Chemistry
• Materials Science

Background:

• Glycerophosphoethanolamines (PE) are key components of biological membranes.
• Understanding their phase behavior is crucial for applications in drug delivery and biomaterials.
• Polymorphic phase transitions influence the structural organization and functional properties of lipid dispersions.

Purpose of the Study:

• To investigate the polymorphic phase behavior of specific PE lipids (1-oleoyl-, 1-linoleoyl-, and 1-linolenoyl-sn-3-glycerophosphoethanolamine).
• To determine the influence of temperature and pH on the structural organization of these PE dispersions.
• To assess the potential of PE lipids in forming functional vesicles for encapsulation and membrane potential studies.

Main Methods:

• 31P Nuclear Magnetic Resonance (NMR) spectroscopy.
• Small-angle and wide-angle X-ray diffraction (XRD).
• Freeze-fracture electron microscopy.
• Encapsulation studies with [3H]inulin.
• Membrane potential measurements.

Main Results:

• 1-oleoyl-sn-3-glycerophosphoethanolamine (1-C18:1c-PE) forms lamellar phases at low temperatures (pH 7).
• Above 20°C, X-ray diffraction shows no long-range order, while NMR indicates lamellar structure up to 90°C for 1-C18:1c-PE.
• At pH 8.2, 1-C18:1c-PE forms multilamellar vesicles; Large Unilamellar Vesicles (LUVETs) can be formed at pH 7, capable of trapping [3H]inulin and supporting a K+ diffusion potential.
• At pH 8.5 and above, 1-C18:1c-PE forms fluid micellar dispersions.
• LUVETs from 1-C18:1c-PE at pH 9 fail to trap [3H]inulin or support a membrane potential.

Conclusions:

• The polymorphic phase behavior of PE lipids is highly sensitive to temperature and pH.
• pH plays a critical role in dictating the formation of lamellar, micellar, or vesicular structures.
• Functional LUVETs can be prepared from 1-C18:1c-PE under specific pH conditions, highlighting their potential in controlled release applications.