Structure of polymerizable lipid bilayers VII: lateral organization of diacetylenic phosphatidylcholines with short proximal acyl chains.
As an extension of recent results (Rhodes, Xu and Bittman (1992) Biochim. Biophys. Acta 1128, 93; Hui, Xu and Bittman (1992) Langmuir 8, 2724) with a C18 diacetylenic phosphatidylcholine, bilayers of 1,2-bis(pentacosa-4,6-diynoyl)-sn-glycero-3-phosphocholine (C25) were investigated using X-ray diffraction on multibilayers and electron diffraction on Langmuir-Blodgett deposited bilayers. Monolayers of this lipid form solid (gel phase) domains at pi > 14 mN/m. Electron diffraction data indicated that the chain spacing in these domains is 4.25 A and that the chains are tilted at angle of approximately 35 degrees relative to the bilayer plane. Wide angle data from X-ray diffraction experiments indicated a similar spacing and chain tilt. Small angle data showed that the lamellar repeat was 70 A at high humidity and < or = 60 A at low humidity. The bilayer electron density profiles indicated a bilayer structure with no interdigitation. High angle reflections indicate that the principal acyl chain repeat is preserved as a function of hydration but some rearrangement occurs for other reflections. The approximately 10 A reflection corresponding to the headgroup spacing previously observed with C18-diacetylenic phosphatidylcholine bilayers was not observed. The results are interpreted in terms of a packing model and possible limitations or constraints to the polymerization process.
Rhodes
D G
DG
Pharmaceutics Division, College of Pharmacy, University of Texas at Austin 78712-1074.
Hui
S W
SW
Xu
Y H
YH
Byun
H S
HS
Singh
M
M
Bittman
R
R
D000114:Acetylene / Q000031:analogs & derivatives* / Q000737:chemistry; D002152:Calorimetry, Differential Scanning; D002855:Chromatography, Thin Layer; D008051:Lipid Bilayers / Q000737:chemistry*; D010713:Phosphatidylcholines / Q000737:chemistry*; D000078789:Polyacetylene Polymer; D011108:Polymers / Q000737:chemistry*; D053279:Polyynes; D014961:X-Ray Diffraction
D008051:Lipid Bilayers; D010713:Phosphatidylcholines; D000078789:Polyacetylene Polymer; D011108:Polymers; D053279:Polyynes; C082361:polydiacetylene; D000114:Acetylene