Phase transition properties of 1,2- and 1,3-diacylphosphatidylethanolamines with modified head groups (original) (raw)

The phase transition properties of dilute aqueous suspensions of "nonhydrated" (Le., lipid suspensions which had not been heated above room temperature or above the main phase transition temperature of the fully hydrated lipid, whichever was lower) and hydrated 1,2(a)-and 1,3(@)-dipalmitoylphosphatidylethanolamines with modified head groups have been determined by high-sensitivity differential scanning calorimetry at a scan rate of 0.1 K m i d. In both the 1,2 and 1,3 series, the head-group modifications Abbreviations: DSC, differential scanning calorimetry; T,, temperature of maximal excess apparent specific heat (Cmax); AT1,,, transition width in degrees centigrade at AHd, calorimetric enthalpy; AHVH, van't Hoff enthalpy; AHdT, total calorimetric enthalpy evaluated by integration of the curve of C vs. T (excess apparent specific heat vs. temperature); N, number of molecules in a cooperative unit (N = AHvH/AHEsi); TLC, thin-layer chromatography; TNH, temperature at