Abstract
The temperatures and enthalpies of the phase transitions of suspensions of di-al-kylphosphatidylcholines in buffered water solutions, prepared and stored under a variety of experimental conditions, were determined in a differential scanning calorimeter (DSC) to evaluate their potential as standard reference materials for the calibration of DSCs. The di-alkylphosphatidylcholine suspensions were 10 mass% 1,2-ditetradecanoyl- sn-glycero-3-phosphocholine (DMPC), and 1,2-dihexadecanoyl- sn-glycero-3-phosphocholine in aqueous buffered solutions at pH 7.0. A subtransition at 8.5° C with an enthalpy of 15.5 kJ mol −1 was observed in the DMPC suspensions after storage of the sample at −5.5° C for 2 days. The profile shape and the temperature and enthalpy values of the subtransition, the pretransition, and the ice peaks of the suspensions depended on the preparation and storage conditions of the samples. A relative standard deviation of 10% was obtained for the enthalpy values of the main transition and a standard deviation of 0.05° C for the main transition temperature. Transition temperatures and enthalpies were also determined for suspensions of 1,2-dioc-tadecanoyl- sn-glycero-3-phosphocholine, 1,2-dieicosanoyl-, sn-glycero-3-phosphocholine, and 1,2-di-9- cis-octadecenoyl- sn-glycero-3-phosphocholine in buffered water solutions.
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