Two- and Three-Dimensional Physical–Chemical Characterization of CER[AP]: A Study of Stereochemistry and Chain Symmetry

Abstract

The stratum corneum represents the first skin barrier against chemical and physical damage. These unique properties are based on its peculiar lipid composition with ceramides (CERs) as the main protagonists. In this study, the structural and chemical properties of the α-OH phytosphingosine [AP] CER class have been investigated. α-OH CERs are present in the stratum corneum in their d-forms; however, in most model systems the diastereomer mixture with the synthetically produced l-form is used. The d-form is well-known to form a hydrogen bonding network that helps to reduce the permeability of the lipid matrix, while the l-form does not show any hydrogen bonding network formation. In this paper, 2D (monolayers) and 3D (aqueous dispersions) models have been used to thoroughly study the physical–chemical behaviors of CER­[AP] diastereomers taking into account how the symmetry of the chain pattern influences the behavior of the molecules. The chains of both diastereomers arrange in an oblique unit cell, but only the d-CER­[AP] forms a supramolecular lattice (subgel phase) in both model systems. Interestingly, the chain pattern does not play any role in structure formation since the hydrogen bonding network dictates the packing properties. The 1:1 mixture of the diastereomers phase separates into two domains: one is composed of practically pure d-form and the other one is composed of a mixture of the l-form with a certain amount of d-form molecules.

Comment on “Clinical significance of the water retention and barrier function‐improving capabilities of ceramide‐containing formulations: A qualitative review”

“…2S, 3R-sphingosine and 2S, 3S, 4R-phytosphingosine) together with Rα-hydroxy fatty acids have recently been studied. 5,6 For at least one marketed ceramide, AP, the α-hydroxy fatty acid component consists of the two diastereomers of which the natural R-isomer promotes tighter lipid packing and the authors conclude that it should be preferred compared with the unnatural S-isomer or the racemic version. 6 The representative structures of other types of molecules (pseudoceramides) that are used in skin-care products are shown in Figure 1b.…”

“…5,6 For at least one marketed ceramide, AP, the α-hydroxy fatty acid component consists of the two diastereomers of which the natural R-isomer promotes tighter lipid packing and the authors conclude that it should be preferred compared with the unnatural S-isomer or the racemic version. 6 The representative structures of other types of molecules (pseudoceramides) that are used in skin-care products are shown in Figure 1b. Moreover, in comparison to skin ceramides none of these contain intricate esters of long-chain omega-hydroxy fatty acids like those in acylceramides or N-acylated α-hydroxy fatty acids or multiple sphingoid-like base mimics.…”