Thermotropic phase behavior of model membranes composed of phosphatidylcholines containing cis-monounsaturated acyl chain homologs of oleic acid: differential scanning calorimetric and phosphorus-31 NMR spectroscopic studies

Abstract

The thermotropic phase behavior of dioleoylphosphatidylcholine and six of its longer chain homologues was studied by differential scanning calorimetry and 31P nuclear magnetic resonance (NMR) spectroscopy. Aqueous dispersions of these compounds all exhibit a single endotherm upon heating but upon cooling exhibit at least two exotherms, both of which occur at temperatures lower than those of their heating endotherm. The single transition observed upon heating was shown by 31P NMR spectroscopy to be a net conversion from a condensed, subgel-like phase (Lc phase) to the liquid-crystalline state. Aqueous ethylene glycol dispersions of these compounds also exhibit single endotherms upon heating and cooling exotherms centered at temperatures lower than those of their corresponding heating endotherm. However, the behavior of the aqueous ethylene glycol dispersions differs with respect to their transition temperatures and enthalpies as well as the extent of "undercooling" observed, and there is some evidence of discontinuities in the cooling behavior of the odd- and even-numbered members of the homologous series. Like the aqueous dispersions, 31P NMR spectroscopy also shows that the calorimetric events observed in aqueous ethylene glycol involve net interconversions between an Lc-like phase and the liquid-crystalline state. However, the Lc phase formed in aqueous ethylene glycol dispersions exhibits a considerably broader powder pattern than that observed in water. This, together with the fact that the transition enthalpies of the aqueous ethylene glycol dispersions are considerably higher than those of the aqueous dispersions, indicates that these lipids form more ordered Lc phases in aqueous ethylene glycol.(ABSTRACT TRUNCATED AT 250 WORDS)

Hydration-optimized oriented phospholipid bilayer samples for solid-state NMR structural studies of membrane proteins

“…1a, for comparison. This motionally averaged powder pattern is characteristic of phospholipids in liquid crystalline bilayers [10][11][12], as expected for DOPC well above its chain melting transition temperature of −18 °C [13,14]. In this spectrum, the 45 ppm chemical shift anisotropy reflects an average orientation of the phosphocholine headgroups nearly parallel to the bilayer surface [15].…”

Microtubes self-assembled from a cholesterol-modified nucleoside

“…The temperature dependence of the tube diameter has been reported before for tubular structures formed from 12-hydroxystearic acid. 13 In contrast to that system, however, the transition from larger to smaller diameters of the 1 : DOPC tubes is not reversed upon decreasing the temperature. It should also be noted that the main gel-to-liquid transition of DOPC takes place at temperatures well below 0 °C; 13 therefore, the mechanism of tube formation cannot be related to the phase transition of the phospholipid , as is the case for diacetylenic phosphocholines and several other tube-forming lipids.…”

Effect of a Local Anesthetic Lidocaine Hydrochloride on the Bilayer Structure of Phospholipids

“…DOPC bilayer membrane has been most thoroughly studied as a typical unsaturated lipid bilayer membrane, which exists as a liquid crystalline state because of extremely low temperature of phase transition 34,35) . SAXS and Prodan fluorescence patterns for DOPC vesicle suspensions are very similar to those for EPC vesicles as is seen from and .…”