title: Gauging the effect of impurities on lipid bilayer phase transition temperature.
abstract: We report on the gel-to-fluid phase transition behavior of unilamellar vesicles formed with 1,2-dimyristoyl-sn-phosphatidylcholine (14:0 DMPC). We have interrogated the gel-to-fluid transition temperature of these bilayer structures using the chromophore perylene incorporated in their nonpolar region. We observe a discontinuous change in the reorientation time of perylene sequestered within the bilayer at the known melting transition temperature of 14:0 DMPC, 24 degrees C. The perylene reorientation data reveal a local viscosity of 14.5 +/- 2.5 cP in the gel phase, and 8.5 +/- 1.5 cP in the fluid phase. We have also incorporated small amounts of 1,2-dimyristoleoyl-sn-glycero-3-phosphocholine (14:1 DMPC) into these unilamellar vesicles and find that the melting transition temperature for these bilayers varies in a regular manner with the amount of 14:1 DMPC present. These data demonstrate that very little "contaminant" is required to cause a substantial change in the gel-to-fluid transition temperature, even though these contaminants do not alter the viscosity of the bilayer sensed by perylene, either above or below the melting transition.
authors.affiliation: Department of Chemistry, Michigan State University, East Lansing, Michigan 48824-1322, USA.
authors.forename: Monique M
authors.initials: MM
authors.lastname: Koan
authors.forename: G J
authors.initials: GJ
authors.lastname: Blanchard
mesh_terms: D002863:Chromogenic Compounds / Q000737:chemistry; D004134:Dimyristoylphosphatidylcholine / Q000737:chemistry* / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D008051:Lipid Bilayers / Q000737:chemistry*; D046529:Microscopy, Electron, Transmission; D008954:Models, Biological; D010569:Perylene / Q000737:chemistry; D044367:Phase Transition / Q000187:drug effects*; D013696:Temperature; D014783:Viscosity
chemical_list: D002863:Chromogenic Compounds; D008051:Lipid Bilayers; D010569:Perylene; D004134:Dimyristoylphosphatidylcholine