Fluid phase structure of EPC and DMPC bilayers

• Published in: Chemistry and physics of lipids Vol. 95; no. 1; pp. 83 - 94
• Main Authors: Petrache, Horia I., Tristram-Nagle, Stephanie, Nagle, John F.
• Format: Journal Article
• Language: English
• Published: Ireland Elsevier Ireland Ltd 01-09-1998
• Subjects: Area per lipid; Dimyristoylphosphatidylcholine - chemistry; Fluctuations, Synchrotron X-ray diffraction; Lipid bilayers; Lipid Bilayers - chemistry; Membranes, Artificial; Osmolar Concentration; Osmotic pressure; Phosphatidylcholines - chemistry; Synchrotrons; Temperature; X-Ray Diffraction; Area per lipid; Fluctuations, Synchrotron X-ray diffraction; Osmotic pressure; Lipid bilayers
• ISSN: 0009-3084; 1873-2941
• DOI: 10.1016/S0009-3084(98)00068-1

X-ray diffraction data taken at high instrumental resolution were obtained for EPC and DMPC under various osmotic pressures, primarily at
T=30°C. The headgroup thickness
D
HH was obtained from relative electron density profiles. By using volumetric results and by comparing to gel phase DPPC we obtain areas
A
EPC
F
=69.4±1.1 Å
2 and
A
DMPC
F
=59.7±0.2 Å
2. The analysis also gives estimates for the areal compressibility
K
A
. The
A
F
results lead to other structural results regarding membrane thickness and associated waters. Using the recently determined absolute electrons density profile of DPPC, the
A
F
results also lead to absolute electron density profiles and absolute continuous transforms ∣
F(
q)∣ for EPC and DMPC. Limited measurements of temperature dependence show directly that fluctuations increase with increasing temperature and that a small decrease in bending modulus
K
c
accounts for the increased water spacing reported by Simon et al. (1995) Biophys. J. 69, 1473–1483.