title: Fatty Acid Chain Length Dependence of Phase Separation Kinetics in Stratum Corneum Models by IR Spectroscopy.
abstract: The main barrier to permeability in human skin resides in the stratum corneum (SC), a layered structure consisting of anucleated, flattened cells (corneocytes) embedded in a heterogeneous lamellar lipid matrix. While lipid structures and packing propensities in the SC and in SC models have been extensively investigated, only limited data are available concerning the kinetics and mechanism of formation of lamellar phases and particular lipid packing motifs. In our prior investigation, kinetic IR spectroscopy measurements probed the temporal sequence of phase separation leading to ordered structures in a three component SC model of equimolar structurally heterogeneous ceramide[NS], chain perdeuterated stearic acid, and cholesterol. In the current work, the phase separation kinetic effects of specific fatty acid chain lengths with a synthetic structurally homogeneous ceramide[NS] in similar ternary mixtures are examined. These are compared with a mixture containing ceramide[NS] with an unsaturated acid chain. The kinetic events are sensitive to the difference in chain lengths between the ceramide acid chain and the fatty acid as well as to the presence of unsaturation in the former. The observed kinetic behaviors span a wide range of phase separation times, ranging from the formation of a solid solution stable for at least 200 h, to a system in which an orthorhombic fatty acid structure is essentially completely formed within the time resolution of the experiment (15 min). The data seem to offer some features of a spinodal phase separation at relatively short times. Overall the approach offers a possible means for addressing several unanswered questions pertinent to skin pharmacology, such as the roles of a wide variety of ceramide and fatty acid species and the design of therapeutic interventions for repair of pathological conditions of the SC.
authors.affiliation: †Department of Chemistry, Newark College, Rutgers University, Newark, New Jersey 07102, United States.
authors.forename: Richard
authors.initials: R
authors.lastname: Mendelsohn
authors.affiliation: †Department of Chemistry, Newark College, Rutgers University, Newark, New Jersey 07102, United States.
authors.forename: Emann
authors.initials: E
authors.lastname: Rabie
authors.affiliation: ‡Johnson and Johnson Consumer Companies, Inc., 199 Grandview Road, Skillman, New Jersey 08558, United States.
authors.forename: Russel M
authors.initials: RM
authors.lastname: Walters
authors.affiliation: †Department of Chemistry, Newark College, Rutgers University, Newark, New Jersey 07102, United States.
authors.forename: Carol R
authors.initials: CR
authors.lastname: Flach
mesh_terms: D002518:Ceramides / Q000737:chemistry; D002784:Cholesterol / Q000737:chemistry; D004817:Epidermis / Q000737:chemistry*; D005227:Fatty Acids / Q000737:chemistry*; D006801:Humans; D007700:Kinetics; D013055:Spectrophotometry, Infrared
chemical_list: D002518:Ceramides; D005227:Fatty Acids; D002784:Cholesterol