Thermotropic mesomorphism in aqueous dispersions of 1-palmitoyl-2-oleoyl- and 1,2-dilauroyl-phosphatidylglycerols in the presence of excess Na+ or Ca2+.
1-Palmitoyl-2-oleoyl-sn-glycero-3-phospho-rac-glycerol (POPG) and 1,2-dilauroyl-sn-glycero-3-phospho-rac-glycerol (DLPG) have been made by the conversion of the appropriate lecithins in the presence of crude phospholipase D and excess glycerol. Aqueous dispersions of the lipids have been examined by differential scanning calorimetry and 31P-nuclear magnetic resonance spectroscopy. When dispersed in excess Na+ at pH 7, POPG and DLPG underwent gel to liquid-crystalline phase transitions at -2.0 +/- 1.3 and -3.7 +/- 1.9 degrees C, respectively. The enthalpy of transition for POPG in excess Na+ was 6.2 +/- 0.3 kcal X mol-1 (1 cal = 4.1868 J), but the value for DLPG in Na+ was variable. In the presence of excess Ca2+ at pH 7, both phospholipids displayed complex thermotropic mesomorphism. For DLPG in the presence of excess Ca2+, thermal events did not occur at the same temperatures as did those for POPG in excess Ca2+. The complexity of the observed behaviour may have arisen because of the formation of intermediate forms which slowly interconverted to more stable forms.
D002118:Calcium / Q000494:pharmacology*; D002152:Calorimetry, Differential Scanning; D006358:Hot Temperature; D009682:Magnetic Resonance Spectroscopy; D008859:Microscopy, Polarization; D010715:Phosphatidylglycerols; D012964:Sodium / Q000494:pharmacology*
D010715:Phosphatidylglycerols; D012964:Sodium; D002118:Calcium