Differential scanning calorimetric study of the thermotropic phase behavior of a polymerizable, tubule-forming lipid
A comparative study of the polymorphism exhibited by the polymerizable, tubule-forming phospholipid 1,2-bis(10,12-tricosadiynoyl)- sn-glycero-3-phosphocholine (DC 23PC) and its saturated analog 1,2-ditricosanoyl-sn-glycero-3-phosphocholine (DTPC) in aqueous suspension is reported. Differential scann...
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Veröffentlicht in: | Chemistry and physics of lipids 1988-10, Vol.48 (3), p.215-230 |
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Format: | Artikel |
Sprache: | eng |
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Zusammenfassung: | A comparative study of the polymorphism exhibited by the polymerizable, tubule-forming phospholipid 1,2-bis(10,12-tricosadiynoyl)-
sn-glycero-3-phosphocholine (DC
23PC) and its saturated analog 1,2-ditricosanoyl-sn-glycero-3-phosphocholine (DTPC) in aqueous suspension is reported. Differential scanning calorimetry (DSC), as well as freeze-fracture electron microscopy and Raman spectroscopy, have been used to study the influence on phase behavior of rigid diacetylene groups in the fatty acyl chains of a phosphatidylcholine. DTPC large multilamellar vesicle (MLV) and small unilamellar vesicle (SUV) suspensions were found to retain liposome morphology after chain cristallization had occured. In marked contrast, diacetylenic DC
23PC suspensions do not maintain liposomal morphology in converting to the low temperature phase. Large MLVs of DC
23PC with outer diameters in excess of 1μm convert to a gel phase with cylindrical or tubular morphology at 38°C, just a few degrees below the lipid's chain melting temperature (
T
M(H), i.e. temperature of an endothermic event observed during a heating scan) of 43.1°C. Unlike the large MLVs, small MLVs or SUVs of DC
23PC, with diameters of 0.4± 0.3
μm and 0.04 ± 0.02
μm, respectively, exhibit metastability in the liquid-crystalline state for several tens of degrees below the chain melting temperature prior to converting to a gel phase which, by electron microscopy, manifests itself as extended multilamellar sheets. Raman data collected at
T
M(H) — 40°C demonstrate that the gel state formed by DC
23PC is very highly ordered relative to that of DTPC, suggesting that special chain packing requirements are responsible for the novel phase behavior of DC
23PC. |
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ISSN: | 0009-3084 1873-2941 |
DOI: | 10.1016/0009-3084(88)90092-8 |