| Popis: |
The structural and thermal properties of aqueous dispersions of the totally synthetic cerebrosides, d-erythro-N-palmitoyl galactosyl- and glucosyl-C18-sphingosine (C16:0-GalCer and C16:0-GluCer, respectively) have been studied using differential scanning calorimetry (DSC) and X-ray diffraction. Over the temperature range 0–100°C, both C16:0-GalCer and C16:0-GluCer show complex thermal transitions characteristic of polymorphic behavior of exclusively bilayer phases. On heating, hydrated C16:0-GalCer undergoes an exothermic bilayer–bilayer transition at 59°C to produce a stable bilayer crystal form. X-ray diffraction at 70°C reveals a bilayer structure with an ordered hydrocarbon chain-packing arrangement. This ordered bilayer phase undergoes an endothermic chain-melting transition at 85°C to the bilayer liquid crystalline state. Similar behavior is exhibited by hydrated C16:0-GluCer which undergoes the exothermic transition at 49°C and a chain-melting transition at 87°C. The exothermic transitions observed on heating hydrated C16:0-GalCer and C16:0-GluCer are irreversible and dependent upon previous chain melting, prior cooling rate, and time of incubation at low temperatures. Thus, the structure and properties of totally synthetic C16:0-GalCer and C16:0-GluCer with identical sphingosine (C18:1) and fatty acid (C16:0) chains are quite similar, suggesting that the precise isomeric structure of the linked sugar plays only a minor role in regulating the properties of hydrated cerebrosides. Further, these studies indicate that the complex thermal behavior and bilayer phase formation exhibited by these single-suga cerebrosides are intrinsic properties and not due to the heterogeneity of the sphingosine base found in natural and partially synthetic cerebrosides.—Saxena, K., R. I. Duclos, P. Zimmermann, R. R. Schmidt, and G. G. Shipley. Structure and properties of totally synthetic galactoand gluco-cerebrosides. J. Lipid Res. 1999. 40: 839–849. |
