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Chemische Prozesse und Phasenübergänge Poster: Mi., 14:00–16:30 M-P180
Phase behavior of aqueous dispersions of mixtures of ceramide, cholesterol
and protonated fatty acid
Sofia L. Souza 1 , M. José Capitan 2 , Sérgio S. Funari 3 , Jesus Alvarez 4 , Eurico
Melo 1
1 Instituto de Tecnologia Química e Biológica, Av. da República-EAN, 2784-505 Oeiras,
Portugal – 2 Instituto de estructura de la materia- CSIC. C/ Serrano 119, 28006-
Madrid, Spain – 3 Hasylab, DESY, Notkestrasse 85, D-22607 Hamburg, Germany –
4 Dpto. Física de la materia condensada Universidad Autónoma de Madrid, Canto-
blanco. 28049 Madrid, Spain
The lipid matrix of the stratum corneum (SC) of mammals is a mixture, whose main
components are ceramides (Cer), cholesterol (Chol) and saturated fatty acids (FA).
Probably because of being so unusual, and also due to the absence of applications of
alike lipid blends in the industry, the physical-chemical properties of mixtures involving
these classes of lipids have not been the object of systematic studies similar to those
existing for ubiquitous lipids, such as cholines.
Our objective in this work is the study of the thermotropic binary phase diagrams for
the system containing C16 acyl ceramide and cholesterol, Cer16/Chol, at low ionic
strength (100 mM) in excess water. Once obtained the binary phase diagram of
Cer16/Chol we investigate the effect of the presence of palmitic acid FA16, ionized
and protonated, in the thermotropism and structural properties of the mixture. The
experiments including FA were done only for the relative Cer/Chol composition found
in the SC lipid matrix (54:46 Cer16/Chol mole ratio), in this way crossing the composition
equivalent to the Cer/Chol/FA relative abundances in the SC. From DSC we
obtained the more plausible phase boundaries that were subsequently checked, and
structurally characterized, by simultaneous SAXD and WAXD as a function of temperature.
Ceramide systems are known to have metastable phases attributed to the strong interaction
between headgroups. Pure Cer16 forms a lamellar phase that, as observed with
other sphingolipids, suffers no thermal expansion until the phase transition, observed
by DSC at 90 o C. In the region from 47-65 o C the chain structure gradually changes
from ordered to relatively disordered. In the presence of Chol two new phases appear:
one that can be ascribed to pure Chol in the monohydrate or anhydrous form, and
other that may be interpreted as the result of Chol being dissolved in Cer16 lamellae.
The analysis of the data allows the deduction of the thermotropic phase diagram for
the Cer16/Chol system in excess water. From the DSC thermograms, and the SAX
and WAX diffractograms of the mixtures between 54:46 Cer16/Chol and FA16 at two
extreme pH values (corresponding to fully protonated and fully deprotonated FA16)
we also deduce the phase behavior of these mixtures as a function of the FA16 molar
fraction.