A differential scanning calorimetry study of the thermal behavior of water-dipalmitoylphosphatidylcholine mixtures at subzero temperatures: effects of water content, surface charge, and cholesterol.
The thermal behavior of partly and fully hydrated dipalmitoylphosphatidylcholine (DPPC) alone and mixed with dipalmitoylphosphatidylglycerol (DPPG) or cholesterol (chol) was studied at subzero temperatures with differential scanning calorimetry (DSC). The melting characteristics of the frozen water provided information on the fraction of nonfreezing and freezing (subzero melting) hydration water and excess or bulk water (melting at 0 degrees C). Incorporation of DPPG or cholesterol into the DPPC structure increased the subzero temperature interval compared with pure DPPC. The maximum number of molecules of hydration water (nonfreezing and freezing) was similar for DPPC and DPPC/cholesterol systems: approximately 20 mol water/mol of phospholipid; under the selected conditions, no maximum for DPPC/DPPG could be assessed. Combinations of DPPC/cholesterol-water showed a complex thermogram with both endothermic and exothermic responses.
Department of Pharmaceutics, Subfaculty of Pharmacy, University of Utrecht, The Netherlands.
J C
JC
Offringa
R
R
Plekkenpol
D J
DJ
Crommelin
D015060:1,2-Dipalmitoylphosphatidylcholine / Q000032:analysis*; D002152:Calorimetry, Differential Scanning; D002784:Cholesterol / Q000032:analysis; D003080:Cold Temperature; D010715:Phosphatidylglycerols / Q000032:analysis; D013499:Surface Properties; D014867:Water / Q000032:analysis*
D010715:Phosphatidylglycerols; D014867:Water; D015060:1,2-Dipalmitoylphosphatidylcholine; D002784:Cholesterol; C030345:1,2-dipalmitoylphosphatidylglycerol