Lateral diffusion study of excimer-forming lipids in lamellar to inverted hexagonal phase transition of unsaturated phosphatidylethanolamine
✍ Scribed by Sun-Yung Chen; Kwan Hon Cheng; D. Mark Ortalano
- Publisher
- Elsevier Science
- Year
- 1990
- Tongue
- English
- Weight
- 621 KB
- Volume
- 53
- Category
- Article
- ISSN
- 0009-3084
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✦ Synopsis
Using multi-frequency cross-correlation fluorometry, the monomer fluorescence lifetime of l-palmitoyl-2-[10-(1-pyrenyl)decanoyl)phosphatidylcholine (Py-PC) was employed to determine the lateral diffusion constant (DT) of dioleoylphosphatidylethanolamine (DOPE) in both the lamellar (L) and the inverted hexagonal (Hn) phases. The values of D r increased with temperature in both phases. However, the rate of increase of D T declined abruptly at ,~ 10--13°C (L-H n transition temperature), as indicated by the existence of an inflection point in the log (DT/T) vs. I/T plot. This observation suggests that the translational motion of lipids in the H H phase is lower than that in the L phase upon temperature extrapolation. Lipid perturbants, cholesterol and diacylglycerol, were found to destabilize the L phase of DOPE. This was demonstrated by a downshift of the inflection point in the log(DT/7) vs. I/T plot in the presence of the perturhants. Both cholesterol and 1,2-dioleoyl-snglycerol (diolein) decreased the lateral diffusion constant in both phases. Diolein promoted the I-I u phase more effectively than did the cholesterol. This is explained by an intrinsic wedge-shape geometry of diolein which strongly favors the formation of inverted cylindrical packing of the lipids.