Structure and properties of totally synthetic galacto- and gluco-cerebrosides.
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 degrees 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 degrees C to produce a stable bilayer crystal form. X-ray diffraction at 70 degrees C reveals a bilayer structure with an ordered hydrocarbon chain-packing arrangement. This ordered bilayer phase undergoes an endothermic chain-melting transition at 85 degrees C to the bilayer liquid crystalline state. Similar behavior is exhibited by hydrated C16:0-GluCer which undergoes the exothermic transition at 49 degrees C and a chain-melting transition at 87 degrees 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-sugar cerebrosides are intrinsic properties and not due to the heterogeneity of the sphingosine base found in natural and partially synthetic cerebrosides.
Saxena
K
K
Department of Biophysics and Biochemistry, Center for Advanced Biomedical Research, Boston University School of Medicine, 80 East Concord Street, Boston, MA 02118-2394, USA.
Duclos
R I
RI
Zimmermann
P
P
Schmidt
R R
RR
Shipley
G G
GG
D002152:Calorimetry, Differential Scanning; D005699:Galactosylceramides / Q000737:chemistry*; D005963:Glucosylceramides / Q000737:chemistry*; D008051:Lipid Bilayers / Q000737:chemistry; D015394:Molecular Structure; D013816:Thermodynamics; D014867:Water; D014961:X-Ray Diffraction
D005699:Galactosylceramides; D005963:Glucosylceramides; D008051:Lipid Bilayers; C120051:N-palmitoylglucosylsphingosine; D014867:Water; C032840:N-palmitoylgalactosylsphingosine