title: How does acyl chain length affect thermotropic phase behavior of saturated diacylphosphatidylcholine-cholesterol binary bilayers?
abstract: Thermotropic phase behavior of diacylphosphatidylcholine (CnPC)-cholesterol binary bilayers (n=14-16) was examined by fluorescence spectroscopy using 6-propionyl-2-(dimethylamino)naphthalene (Prodan) and differential scanning calorimetry. The former technique can detect structural changes of the bilayer in response to the changes in polarity around Prodan molecules partitioned in a relatively hydrophilic region of the bilayer, while the latter is sensitive to the conformational changes of the acyl chains. On the basis of the data from both techniques, we propose possible temperature T-cholesterol composition Xch phase diagrams for these binary bilayers. A notable feature of our phase diagrams, including our previous results for diheptadecanoylphosphatidylcholine (C17PC) and distearoylphosphatidylcholine (C18PC), is that there is a peritectic-like point around Xch=0.15, which can be interpreted as indicating the formation of a 1:6-complex of cholesterol and CnPCs within the binary bilayer irrespective of the acyl chain length. We could give a reasonable explanation for such complex formation using the modified superlattice view. Our results also showed that the Xch value of the abolition of the main transition is almost constant for n=14-17 (ca. 0.33), while it increases to ca. 0.50 for n=18. By contrast, a biphasic n-dependence of Xch was observed for the abolition of the pretransition, suggesting that there are at least two antagonistic n-dependent factors. We speculate that this could be explained by the enhancement of the van der Waals interaction with increases in n and the weakening of the repulsion between the neighboring headgroups with decreases in n.
authors.affiliation: Department of Life System, Institute of Technology and Science, The University of Tokushima, 2-1 Minamijosanjima-cho, Tokushima 770-8506, Japan.
authors.forename: Nobutake
authors.initials: N
authors.lastname: Tamai
authors.forename: Takuya
authors.initials: T
authors.lastname: Izumikawa
authors.forename: Suguru
authors.initials: S
authors.lastname: Fukui
authors.forename: Maiko
authors.initials: M
authors.lastname: Uemura
authors.forename: Masaki
authors.initials: M
authors.lastname: Goto
authors.forename: Hitoshi
authors.initials: H
authors.lastname: Matsuki
authors.forename: Shoji
authors.initials: S
authors.lastname: Kaneshina
mesh_terms: D002152:Calorimetry, Differential Scanning; D002784:Cholesterol / Q000737:chemistry*; D008051:Lipid Bilayers; D010713:Phosphatidylcholines / Q000737:chemistry*; D013050:Spectrometry, Fluorescence
chemical_list: D008051:Lipid Bilayers; D010713:Phosphatidylcholines; D002784:Cholesterol
keywords: Cholesterol; Diacylphosphatidylcholine; Lateral phase separation; Peritectic point; Phase diagram; Superlattice