highly ordered bilayer structure of stratum corneum lipids To better understand the phase behavior of a pseudoceramide ( SCL ) observed in the intercellular space of SC ( 3 -5 ) .
(SLE), a potential skin moisturizer and/or a drug carrier, we Therefore, the molecular mechanism for the self-assembly investigated the lipid-lipid interaction between SLE and a sterolof the lipid bilayer as well as their physicochemical propcombined fatty acid (CEOS), which has a sterol ring and a carerties has attracted much attention from the viewpoint of boxyl group in a molecule. X-ray analysis showed that a hexagonal the barrier properties of SC ( 6 -13 ) .
packing (4.15 A ˚spacing) and a liquid-like packing (4.5 A ˚spacing)
The SCL lamellae are composed mainly of ceramides, coexisted within the hydrocarbon chains of the SLE/CEOS (1/1 free fatty acids, cholesterol, and cholesteryl esters. Elias sugmole) lipid mixture. The structural characteristics were very simigested that the presence of ceramides and sphingolipids is lar to those of the SLE/stearic acid/cholesterol (1/1/1 mole) system, which was in a stable lamellar a-phase. However, in the SLE/ the basis for the structural organization of SCL in bilayers stearic acid (1/1 mole) system, there was only a strong hexagonal (4, 9). Moreover, using electron micrographic techniques, reflection in the wide-angle X-ray profile. The melting enthalpy Wertz showed that ceramides could take part in the bilayer (23.9 kJ mol 01 ) and entropy (75.0 J mol 01 K 01 ) of the SLE/ formation (10). Therefore, ceramides have been considered CEOS system were also smaller than those ( DH m Å 43.9 kJ mol 01 , to play an essential role for inhibition of transepidermal DS m Å 131.6 J mol 01 K 01 ) of the SLE/stearic acid system. The water loss and skin moisturization.
X-ray data along with the DSC results suggested that the sterol
Even though ceramides constitute the major fraction of ring of CEOS molecule contributed to the enhancement of molecuhuman SCL, they exist in nature only in trace amounts.
lar motion or the decrease in the molecular packing of lipids. A
To make them commercially available for dermatological strong hydrogen bond between the carboxyl group of CEOS and application, Imokawa and co-workers synthesized a pseudothe amide group of SLE molecule was also considered to be imceramide (sphingolipid E, SLE) which has a molecular portant for the formation of the stable a-phase, as suggested by FT-IR spectroscopy. Further, in the presence of water, the three structure analogous to that of the natural non-hydroxy fatty artificial SC lipids, SLE/CEOS (1/1 mole), SLE/stearic acid/choacid ceramide of type 2 (17). The pseudoceramide was lesterol (1/1/1 mole), and SLE/stearic acid (1/1 mole), were all found to have a water-retaining property similar to that of capable of forming lamellar structures. ᭧ 1997 Academic Press the natural lipids when applied to the dry and scaly skin Key Words: stratum corneum lipids; bilayer; pseudoceramide; (18). Therefore, the synthetic ceramide has been suggested sterol-combined fatty acid; stearic acid; cholesterol; aggregation to be useful as a skin moisturizer and/or a drug carrier (19).
structure; hydrogen bonds.
It is essential for industrial applications to study the physicochemical properties of SLE, such as phase behavior, as well as its intermolecular interaction with other amphiphiles.