title: Polymorphic phases of galactocerebrosides: spectroscopic evidence of lamellar crystalline structures.
abstract: Fourier transform infrared spectroscopy was applied to study the structural and thermal properties of bovine brain galactocerebroside (GalCer) containing amide linked non-hydroxylated or alpha-hydroxy fatty acids (NFA- and HFA-GalCer, respectively). Over the temperature range 0-90 degrees C, both GalCer displayed complex thermal transitions, characteristic of polymorphic phase behavior. Upon heating, aqueous dispersions of NFA- and HFA-GalCer exhibited high order-disorder transition temperatures near 80 and 72 degrees C, respectively. En route to the chain melting transition, the patterns of the amide I band of NFA-GalCer were indicative of two different lamellar crystalline phases, whereas those of HFA-GalCer were suggestive of lamellar gel and crystalline bilayers. Cooling from the liquid-crystalline phase resulted in the formation of another crystalline phase of NFA-GalCer and a gel phase of HFA-GalCer, with a phase transition near 62 and 66 degrees C, respectively. Prolonged incubation of GalCer bilayers at 38 degrees C revealed conversions among lamellar crystalline phases (NFA-GalCer) or between lamellar gel and crystalline bilayer structures (HFA-GalCer). Spectral changes indicated that the temperature and/or time induced formation of the lamellar crystalline structures of NFA- and HFA-GalCer was accompanied by partial dehydration and by rearrangements of the hydrogen bonding network and bilayer packing mode of GalCer.
authors.affiliation: Hormones, Growth, and Development Research Group, Loeb Health Research Institute, Ottawa, ON, Canada.
authors.forename: M
authors.initials: M
authors.lastname: Bou Khalil
authors.forename: D
authors.initials: D
authors.lastname: Carrier
authors.forename: P T
authors.initials: PT
authors.lastname: Wong
authors.forename: N
authors.initials: N
authors.lastname: Tanphaichitr
mesh_terms: D000818:Animals; D001923:Brain Chemistry; D002417:Cattle; D003460:Crystallization; D005227:Fatty Acids / Q000737:chemistry; D005699:Galactosylceramides / Q000737:chemistry*; D006358:Hot Temperature; D006860:Hydrogen Bonding; D006880:Hydroxy Acids / Q000737:chemistry; D006900:Hydroxylation; D008051:Lipid Bilayers / Q000737:chemistry*; D017550:Spectroscopy, Fourier Transform Infrared; D013329:Structure-Activity Relationship; D013816:Thermodynamics
chemical_list: D005227:Fatty Acids; D005699:Galactosylceramides; D006880:Hydroxy Acids; D008051:Lipid Bilayers