Relationships between miscibility behavior and chemical structure of phospholipids in pseudobinary systems |
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Authors: | H -D Dörfler |
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Institution: | Technische Universit?t Dresden, Institut für Physikalische Chemie und Elektrochemie, D-01069 Dresden, Germany, DE
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Abstract: | The influence of chain length differences of cephalines and the influence of the head group methylation on the miscibility
behavior of N-methylated phosphatidylethanolamine (PE) mixtures in aqueous dispersions were tested. Nine different phase diagrams
were studied by means of differential scanning calorimetry. The phase diagrams of the five pseudobinary cephaline/cephaline/water
systems (fatty acid chain length: C
n
, n = 12–18) showed that in the high temperature Lα phase all the homologous cephalines were completely miscible. In the low-temperature phase a distinct succession of the phase
diagram types was observed according to increasing chain length differences of the PEs: complete miscibilty (C12/C14; C14/C16), peritectic mixing behavior (C12/C16; C14/C18), eutectic mixing behavior (C12/C18). Furthermore four phase diagrams of pseudobinary phospholipid systems consisting of N-methylated PEs with different numbers
of methyl groups and a constant length of fatty acid chains were investigated and compared. These four phase diagrams showed
phase separations in the low-temperatures phase (gel phase). The width and the concentration range of the miscibility gaps
changed systematically with increasing degree of methylation of the head group of the mixing components and are connected
with different possibilities of PEs to form hydrogen bridges between the mixture components.
Received: 26 August 1999/Accepted: 30 August 1999 |
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Keywords: | Phase diagrams Pseudobinary systems Miscibility Calorimetry Phospholipids |
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