Ceramides belong to sphingolipids, an important group of cellular and extracellular lipids. Their physiological functions range from cell signaling to participation in the formation of barriers against water evaporation. In the skin, they are essential for the permeability barrier, together with free fatty acids and cholesterol. We examined the periodical structure and permeability of lipid films composed of ceramides (Cer; namely, N-lignoceroyl 6-hydroxysphingosine, CerNH24, and N-lignoceroyl sphingosine, CerNS24), lignoceric acid (LIG; 24:0), and cholesterol (Chol). X-ray diffraction experiments showed that the CerNH24-based samples form either a short lamellar phase (SLP, d ∼ 5.4 nm) or a medium lamellar phase (MLP, d = 10.63-10.78 nm) depending on the annealing conditions. The proposed molecular arrangement of the MLP based on extended Cer molecules also agreed with the relative neutron scattering length density profiles obtained from the neutron diffraction data. The presence of MLP increased the lipid film permeability to the lipophilic model permeant (indomethacin) relative to the CerNS24-based control samples and the samples that had the same lipid composition but formed an SLP. Thus, the arrangement of lipids in various nanostructures is responsive to external conditions during sample preparation. This polymorphic behavior directly affects the barrier properties, which could also be (patho)physiologically relevant.

Faculty of Chemical Technology University of Chemistry and Technology Prague Technická 5 166 28Prague Czech Republic

Faculty of Pharmacy Comenius University Bratislava Odbojárov 10 832 32Bratislava Slovakia

Frank Laboratory of Neutron Physics Joint Institute for Nuclear Research Joliot Curie 6 141980Dubna Russia

Heinz Maier Leibnitz Zentrum Technische Universität München Lichtenbergstr 1 85748Garching Germany

Skin Barrier Research Group Charles University Faculty of Pharmacy in Hradec Králové Heyrovského 1203 500 05Hradec Králové Czech Republic

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Koch K.; Barthlott W. Plant Epicuticular Waxes: Chemistry, Form, Self-Assembly and Function. Nat. Prod. Commun. 2006, 1, 1934578X0600101123.10.1177/1934578x0600101123. DOI

McCulley J. P.; Shine W. E. The Lipid Layer: The Outer Surface of the Ocular Surface Tear Film. Biosci. Rep. 2001, 21, 407–418. 10.1023/a:1017987608937. PubMed DOI

Chen J.; Nichols K. K. Comprehensive shotgun lipidomics of human meibomian gland secretions using MS/MSall with successive switching between acquisition polarity modes. J. Lipid Res. 2018, 59, 2223–2236. 10.1194/jlr.d088138. PubMed DOI PMC

Ginzel M. D.; Blomquist G. J.. Insect Hydrocarbons: Biochemistry and Chemical Ecology. In Extracellular Composite Matrices in Arthropods; Cohen E., Moussian B., Eds.; Springer International Publishing: Cham, 2016; pp 221–252.

Méndez S.; Martí M.; Barba C.; Parra J. L.; Coderch L. Thermotropic Behavior of Ceramides and Their Isolation from Wool. Langmuir 2007, 23, 1359–1364. 10.1021/la0621315. PubMed DOI

Cwiklik L. Tear film lipid layer: A molecular level view. Biochim. Biophys. Acta 2016, 1858, 2421–2430. 10.1016/j.bbamem.2016.02.020. PubMed DOI

Elias P. M. Epidermal Lipids, Membranes, and Keratinization. Int. J. Dermatol. 1981, 20, 1–19. 10.1111/j.1365-4362.1981.tb05278.x. PubMed DOI

Wertz P. W. Stratum corneum lipids and water. Exog. Dermatol. 2004, 3, 53–56. 10.1159/000086155. DOI

Kováčik A.; Opálka L.; Šilarová M.; Roh J.; Vávrová K. Synthesis of 6-hydroxyceramide using ruthenium-catalyzed hydrosilylation–protodesilylation. Unexpected formation of a long periodicity lamellar phase in skin lipid membranes. RSC Adv. 2016, 6, 73343–73350. 10.1039/C6RA16565F. DOI

Opálka L.; Kováčik A.; Sochorová M.; Roh J.; Kuneš J.; Lenčo J.; Vávrová K. Scalable Synthesis of Human Ultralong Chain Ceramides. Org. Lett. 2015, 17, 5456–5459. 10.1021/acs.orglett.5b02816. PubMed DOI

Dahlén B.; Pascher I. Molecular arrangements in sphingolipids. Thermotropic phase behaviour of tetracosanoylphytosphingosine. Chem. Phys. Lipids 1979, 24, 119–133. 10.1016/0009-3084(79)90082-3. DOI

Futerman A. H.; Hannun Y. A. The complex life of simple sphingolipids. EMBO Rep. 2004, 5, 777–782. 10.1038/sj.embor.7400208. PubMed DOI PMC

Merrill A. H. De Novo Sphingolipid Biosynthesis: A Necessary, but Dangerous, Pathway. J. Biol. Chem. 2002, 277, 25843–25846. 10.1074/jbc.r200009200. PubMed DOI

Sandhoff R. Very long chain sphingolipids: Tissue expression, function and synthesis. FEBS Lett. 2010, 584, 1907–1913. 10.1016/j.febslet.2009.12.032. PubMed DOI

Hannun Y. A. Functions of Ceramide in Coordinating Cellular Responses to Stress. Science 1996, 274, 1855–1859. 10.1126/science.274.5294.1855. PubMed DOI

Hannun Y. A.; Obeid L. M. Principles of bioactive lipid signalling: lessons from sphingolipids. Nat. Rev. Mol. Cell Biol. 2008, 9, 139–150. 10.1038/nrm2329. PubMed DOI

Burgert A.; Schlegel J.; Bécam J.; Doose P. S.; Bieberich E.; Schubert-Unkmeir A.; Sauer M. Characterization of plasma membrane ceramides by super-resolution microscopy. Angew. Chem., Int. Ed. Engl. 2017, 56, 6131–6135. 10.1002/anie.201700570. PubMed DOI PMC

Kraft M. L. Sphingolipid Organization in the Plasma Membrane and the Mechanisms That Influence It. Front. Cell Dev. Biol. 2017, 4, 154.10.3389/fcell.2016.00154. PubMed DOI PMC

Landmann L. The epidermal permeability barrier. Comparison between in vivo and in vitro lipid structures. Eur. J. Cell Biol. 1984, 33, 258–64. PubMed

de Jager M.; Groenink W.; van der Spek J.; Janmaat C.; Gooris G.; Ponec M.; Bouwstra J. Preparation and characterization of a stratum corneum substitute for in vitro percutaneous penetration studies. Biochim. Biophys. Acta 2006, 1758, 636–644. 10.1016/j.bbamem.2006.04.001. PubMed DOI

Goldsmith L. A.; Baden H. P. Uniquely Oriented Epidermal Lipid. Nature 1970, 225, 1052–1053. 10.1038/2251052a0. PubMed DOI

Bouwstra J. A.; Gooris G. S.; Cheng K.; Weerheim A.; Bras W.; Ponec M. Phase behavior of isolated skin lipids. J. Lipid Res. 1996, 37, 999–1011. 10.1016/s0022-2275(20)42010-3. PubMed DOI

Bouwstra J. A.; Gooris G. S.; van der Spek J. A.; Bras W. Structural Investigations of Human Stratum Corneum by Small-Angle X-Ray Scattering. J. Invest. Dermatol. 1991, 97, 1005–1012. 10.1111/1523-1747.ep12492217. PubMed DOI

McIntosh T. J.; Stewart M. E.; Downing D. T. X-ray Diffraction Analysis of Isolated Skin Lipids: Reconstitution of Intercellular Lipid Domains. Biochemistry 1996, 35, 3649–3653. 10.1021/bi952762q. PubMed DOI

Iwai I.; Han H.; Hollander L. d.; Svensson S.; Öfverstedt L.-G.; Anwar J.; Brewer J.; Bloksgaard M.; Laloeuf A.; Nosek D.; Masich S.; Bagatolli L. A.; Skoglund U.; Norlén L. The Human Skin Barrier Is Organized as Stacked Bilayers of Fully Extended Ceramides with Cholesterol Molecules Associated with the Ceramide Sphingoid Moiety. J. Invest. Dermatol. 2012, 132, 2215–2225. 10.1038/jid.2012.43. PubMed DOI

Mojumdar E. H.; Gooris G. S.; Groen D.; Barlow D. J.; Lawrence M. J.; Demé B.; Bouwstra J. A. Stratum corneum lipid matrix: Location of acyl ceramide and cholesterol in the unit cell of the long periodicity phase. Biochim. Biophys. Acta 2016, 1858, 1926–1934. 10.1016/j.bbamem.2016.05.006. PubMed DOI

Swartzendruber D. C.; Wertz P. W.; Kitko D. J.; Madison K. C.; Downing D. T. Molecular models of the Intercellular Lipid Lamellae in Mammalian Stratum Corneum. J. Invest. Dermatol. 1989, 92, 251–257. 10.1111/1523-1747.ep12276794. PubMed DOI

White S. H.; Mirejovsky D.; King G. I. Structure of lamellar lipid domains and corneocyte envelopes of murine stratum corneum. An x-ray diffraction study. Biochemistry 1988, 27, 3725–3732. 10.1021/bi00410a031. PubMed DOI

Hou S. Y. E.; Mitra A. K.; White S. H.; Menon G. K.; Ghadially R.; Elias P. M. Membrane Structures in Normal and Essential Fatty Acid-Deficient Stratum Corneum: Characterization by Ruthenium Tetroxide Staining and X-Ray Diffraction. J. Invest. Dermatol. 1991, 96, 215–223. 10.1111/1523-1747.ep12461361. PubMed DOI

Bouwstra J. A.; Gooris G. S.; Vries M. A. S.; van der Spek J. A.; Bras W. Structure of human stratum corneum as a function of temperature and hydration: A wide-angle X-ray diffraction study. Int. J. Pharm. 1992, 84, 205–216. 10.1016/0378-5173(92)90158-x. DOI

Garson J. C.; Doucet J.; Lévêque J. L.; Tsoucaris G. Oriented structure in human stratum corneum revealed by X-ray diffraction. J. Invest. Dermatol. 1991, 96, 43–49. 10.1111/1523-1747.ep12514716. PubMed DOI

Bouwstra J. A.; Gooris G. S.; Dubbelaar F. E. R.; Weerheim A. M.; IJzerman A. P.; Ponec M. Role of ceramide 1 in the molecular organization of the stratum corneum lipids. J. Lipid Res. 1998, 39, 186–196. 10.1016/s0022-2275(20)34214-0. PubMed DOI

Schreiner V.; Pfeiffer G. S.; Lanzendörfer S.; Wenck G.; Diembeck H.; Gooris W.; Proksch E.; Bouwstra J. Barrier Characteristics of Different Human Skin Types Investigated with X-Ray Diffraction, Lipid Analysis, and Electron Microscopy Imaging. J. Invest. Dermatol. 2000, 114, 654–660. 10.1046/j.1523-1747.2000.00941.x. PubMed DOI

Janssens M.; van Smeden J.; Gooris G. S.; Bras W.; Portale G.; Caspers P. J.; Vreeken R. J.; Kezic S.; Lavrijsen A. P. M.; Bouwstra J. A. Lamellar Lipid Organization and Ceramide Composition in the Stratum Corneum of Patients with Atopic Eczema. J. Invest. Dermatol. 2011, 131, 2136–2138. 10.1038/jid.2011.175. PubMed DOI

Kiselev M. A.; Ryabova N. Y.; Balagurov A. M.; Dante S.; Hauss T.; Zbytovska J.; Wartewig S.; Neubert R. H. H. New insights into the structure and hydration of a stratum corneum lipid model membrane by neutron diffraction. Eur. Biophys. J. 2005, 34, 1030–1040. 10.1007/s00249-005-0488-6. PubMed DOI

Schröter A.; Kessner D.; Kiselev M. A.; Hauß T.; Dante S.; Neubert R. H. H. Basic Nanostructure of Stratum Corneum Lipid Matrices Based on Ceramides [EOS] and [AP]: A Neutron Diffraction Study. Biophys. J. 2009, 97, 1104–1114. 10.1016/j.bpj.2009.05.041. PubMed DOI PMC

Groen D.; Gooris G. S.; Barlow D. J.; Lawrence M. J.; van Mechelen J. B.; Demé B.; Bouwstra J. A. Disposition of Ceramide in Model Lipid Membranes Determined by Neutron Diffraction. Biophys. J. 2011, 100, 1481–1489. 10.1016/j.bpj.2011.02.001. PubMed DOI PMC

Mojumdar E. H.; Gooris G. S.; Barlow D. J.; Lawrence M. J.; Deme B.; Bouwstra J. A. Skin lipids: localization of ceramide and fatty acid in the unit cell of the long periodicity phase. Biophys. J. 2015, 108, 2670–2679. 10.1016/j.bpj.2015.04.030. PubMed DOI PMC

Pullmannová P.; Ermakova E.; Kováčik A.; Opálka L.; Maixner J.; Zbytovská J.; Kučerka N.; Vávrová K. Long and very long lamellar phases in model stratum corneum lipid membranes. J. Lipid Res. 2019, 60, 963–971. 10.1194/jlr.M090977. PubMed DOI PMC

Parrott D. T.; Turner J. E. Mesophase formation by ceramides and cholesterol: a model for stratum corneum lipid packing?. Biochim. Biophys. Acta 1993, 1147, 273–276. 10.1016/0005-2736(93)90013-p. PubMed DOI

de Jager M. W.; Gooris G. S.; Dolbnya I. P.; Bras W.; Ponec M.; Bouwstra J. A. The phase behaviour of skin lipid mixtures based on synthetic ceramides. Chem. Phys. Lipids 2003, 124, 123–134. 10.1016/s0009-3084(03)00050-1. PubMed DOI

Bouwstra J. A.; Honeywell-Nguyen P. L.; Gooris G. S.; Ponec M. Structure of the skin barrier and its modulation by vesicular formulations. Prog. Lipid Res. 2003, 42, 1–36. 10.1016/s0163-7827(02)00028-0. PubMed DOI

Kováčik A.; Vogel A.; Adler J.; Pullmannová P.; Vávrová K.; Huster D. Probing the role of ceramide hydroxylation in skin barrier lipid models by 2H solid-state NMR spectroscopy and X-ray powder diffraction. Biochim. Biophys. Acta, Biomembr. 2018, 1860, 1162–1170. 10.1016/j.bbamem.2018.02.003. PubMed DOI

Kováčik A.; Pullmannová P.; Pavlíková L.; Maixner J.; Vávrová K. Behavior of 1-Deoxy-, 3-Deoxy- and N -Methyl-Ceramides in Skin Barrier Lipid Models. Sci. Rep. 2020, 10, 1–12. PubMed PMC

Kováčik A.; Šilarová M.; Pullmannová P.; Maixner J.; Vávrová K. Effects of 6-Hydroxyceramides on the Thermotropic Phase Behavior and Permeability of Model Skin Lipid Membranes. Langmuir 2017, 33, 2890–2899. 10.1021/acs.langmuir.7b00184. PubMed DOI

Školová B.; Janůšová B.; Zbytovská J.; Gooris G.; Bouwstra J.; Slepička P.; Berka P.; Roh J.; Palát K.; Hrabálek A.; Vávrová K. Ceramides in the Skin Lipid Membranes: Length Matters. Langmuir 2013, 29, 15624–15633. 10.1021/la4037474. PubMed DOI

Georgii R.; Weber T.; Brandl G.; Skoulatos M.; Janoschek M.; Mühlbauer S.; Pfleiderer C.; Böni P. The multi-purpose three-axis spectrometer (TAS) MIRA at FRM II. Nucl. Instrum. Methods Phys. Res., Sect. A 2018, 881, 60–64. 10.1016/j.nima.2017.09.063. DOI

Kučerka N.; Nieh M.-P.; Pencer J.; Sachs J. N.; Katsaras J. What determines the thickness of a biological membrane. Gen. Physiol. Biophys. 2009, 28, 117–125. 10.4149/gpb_2009_02_117. PubMed DOI

Tristram-Nagle S.; Liu Y.; Legleiter J.; Nagle J. F. Structure of Gel Phase DMPC Determined by X-Ray Diffraction. Biophys. J. 2002, 83, 3324–3335. 10.1016/s0006-3495(02)75333-2. PubMed DOI PMC

Nagle J. F.; Akabori K.; Treece B. W.; Tristram-Nagle S. Determination of mosaicity in oriented stacks of lipid bilayers. Soft Matter 2016, 12, 1884–1891. 10.1039/c5sm02336j. PubMed DOI PMC

Franks N. P.; Lieb W. R. The structure of lipid bilayers and the effects of general anaesthetics: An X-ray and neutron diffraction study. J. Mol. Biol. 1979, 133, 469–500. 10.1016/0022-2836(79)90403-0. PubMed DOI

Ryabova N. Y.; Kiselev M. A.; Dante S.; Hauß T.; Balagurov A. M. Investigation of stratum corneum lipid model membranes with free fatty acid composition by neutron diffraction. Eur. Biophys. J. 2010, 39, 1167–1176. 10.1007/s00249-009-0569-z. PubMed DOI

Dante S.; Hauss T.; Dencher N. A. β-Amyloid 25 to 35 Is Intercalated in Anionic and Zwitterionic Lipid Membranes to Different Extents. Biophys. J. 2002, 83, 2610–2616. 10.1016/s0006-3495(02)75271-5. PubMed DOI PMC

Schmitt T.; Lange S.; Sonnenberger S.; Dobner B.; Demé B.; Langner A.; Neubert R. H. H. The long periodicity phase (LPP) controversy part I: The influence of a natural-like ratio of the CER[EOS] analogue [EOS]-br in a CER[NP]/[AP] based stratum corneum modelling system: A neutron diffraction study. Biochim. Biophys. Acta 2019, 1861, 306–315. 10.1016/j.bbamem.2018.06.008. PubMed DOI

Hrubovčák P.; Kondela T.; Ermakova E.; Kučerka N. Application of small-angle neutron diffraction to the localization of general anesthetics in model membranes. Eur. Biophys. J. 2019, 48, 447–455. PubMed

Kučerka N.; Hrubovčák P.; Dushanov E.; Kondela T.; Kholmurodov K. T.; Gallová J.; Balgavý P. Location of the general anesthetic n-decane in model membranes. J. Mol. Liq. 2019, 276, 624–629. 10.1016/j.molliq.2018.12.039. DOI

Samoylova N. Y.; Kiselev M. A.; Hauß T. Effect of DMSO, urea and ethanol on hydration of stratum corneum model membrane based on short-chain length ceramide [AP]. Chem. Phys. Lipids 2019, 221, 1–7. 10.1016/j.chemphyslip.2019.02.012. PubMed DOI

Kirschner D. A.; Sidman R. L. X-ray diffraction study of myelin structure in immature and mutant mice. Biochim. Biophys. Acta 1976, 448, 73–87. 10.1016/0005-2736(76)90077-8. PubMed DOI

Kučerka N.; Pencer J.; Sachs J. N.; Nagle J. F.; Katsaras J. Curvature Effect on the Structure of Phospholipid Bilayers. Langmuir 2007, 23, 1292.10.1021/la062455t. PubMed DOI PMC

Pullmannová P.; Staňková K.; Pospíšilová M.; Školová B.; Zbytovská J.; Vávrová K. Effects of sphingomyelin/ceramide ratio on the permeability and microstructure of model stratum corneum lipid membranes. Biochim. Biophys. Acta 2014, 1838, 2115–2126. 10.1016/j.bbamem.2014.05.001. PubMed DOI

Pullmannová P.; Pavlíková L.; Kováčik A.; Sochorová M.; Školová B.; Slepička P.; Maixner J.; Zbytovská J.; Vávrová K. Permeability and microstructure of model stratum corneum lipid membranes containing ceramides with long (C16) and very long (C24) acyl chains. Biophys. Chem. 2017, 224, 20–31. 10.1016/j.bpc.2017.03.004. PubMed DOI

Schmitt T.; Gupta R.; Lange S.; Sonnenberger S.; Dobner B.; Hauß T.; Rai B.; Neubert R. H. H. Impact of the ceramide subspecies on the nanostructure of stratum corneum lipids using neutron scattering and molecular dynamics simulations. Part I: impact of CER[NS]. Chem. Phys. Lipids 2018, 214, 58–68. 10.1016/j.chemphyslip.2018.05.006. PubMed DOI

McIntosh T. J.; Waldbillig R. C.; Robertson J. D. The molecular organization of asymmetric lipid bilayers and lipid-peptide complexes. Biochim. Biophys. Acta 1977, 466, 209–230. 10.1016/0005-2736(77)90220-6. PubMed DOI

Worthington C. R.; Blaurock A. E. A Structural Analysis of Nerve Myelin. Biophys. J. 1969, 9, 970–990. 10.1016/s0006-3495(69)86431-3. PubMed DOI PMC

Ranck J. L.; Zaccaï G.; Luzzati V. The structure of a lipid-water lamellar phase containing two types of lipid monolayers. An X-ray and neutron scattering study. J. Appl. Crystallogr. 1980, 13, 505–512. 10.1107/s0021889880012678. DOI

Silva T.; Claro B.; Silva B. F. B.; Vale N.; Gomes P.; Gomes M. S.; Funari S. S.; Teixeira J.; Uhríková D.; Bastos M. Unravelling a Mechanism of Action for a Cecropin A-Melittin Hybrid Antimicrobial Peptide: The Induced Formation of Multilamellar Lipid Stacks. Langmuir 2018, 34, 2158–2170. 10.1021/acs.langmuir.7b03639. PubMed DOI

Kumar K.; Chavarha M.; Loney R. W.; Weiss T. M.; Rananavare S. B.; Hall S. B. The Lγ Phase of Pulmonary Surfactant. Langmuir 2018, 34, 6601–6611. 10.1021/acs.langmuir.8b00460. PubMed DOI PMC

Abrahamsson S.; von Sydow E. Variation of unit-cell dimensions of a crystal form of long normal chain carboxylic acids. Acta Crystallogr. 1954, 7, 591–592. 10.1107/s0365110x54001910. DOI

Marsh D. Lateral order in gel, subgel and crystalline phases of lipid membranes: Wide-angle X-ray scattering. Chem. Phys. Lipids 2012, 165, 59–76. 10.1016/j.chemphyslip.2011.11.001. PubMed DOI

Pascher I.; Sundell S. Molecular arrangements in sphingolipids: crystal structure of the ceramide N-(2d,3d-dihydroxyoctadecanoyl)-phytosphingosine. Chem. Phys. Lipids 1992, 62, 79–86. 10.1016/0009-3084(92)90056-u. DOI

Dahlén B.; Pascher I. Molecular arrangements in sphingolipids. Crystal structure of N-tetracosanoylphytosphingosine. Acta Crystallogr., Sect. B: Struct. Crystallogr. Cryst. Chem. 1972, 28, 2396–2404.

Finegold L. X.Cholesterol in Membrane Models; Taylor & Francis, 1992.

Katsaras J.; Raghunathan V. A.; Dufourc E. J.; Dufourcq J. Evidence for a Two-Dimensional Molecular Lattice in Subgel Phase DPPC Bilayers. Biochemistry 1995, 34, 4684–4688. 10.1021/bi00014a023. PubMed DOI

McIntosh T. J. The effect of cholesterol on the structure of phosphatidylcholine bilayers. Biochim. Biophys. Acta 1978, 513, 43–58. 10.1016/0005-2736(78)90110-4. PubMed DOI

McIntosh T. J.; Waldbillig R. C.; Robertson J. D. Lipid bilayer ultrastructure: Electron density profiles and chain tilt angles as determined by X-ray diffraction. Biochim. Biophys. Acta 1976, 448, 15–33. 10.1016/0005-2736(76)90073-0. PubMed DOI

Khare R. S.; Worthington C. R. The structure of oriented sphingomyelin bilayers. Biochim. Biophys. Acta 1978, 514, 239–254. 10.1016/0005-2736(78)90295-x. PubMed DOI

Khare R. S.; Worthington C. R. An X-Ray Diffraction Study of Sphingomyelin-Cholesterol Interaction in Oriented Bilayers. Mol. Cryst. Liq. Cryst. 1977, 38, 195–206. 10.1080/15421407708084386. DOI

Ensikat H. J.; Boese M.; Mader W.; Barthlott W.; Koch K. Crystallinity of plant epicuticular waxes: electron and X-ray diffraction studies. Chem. Phys. Lipids 2006, 144, 45–59. 10.1016/j.chemphyslip.2006.06.016. PubMed DOI

Bouwstra J. A.; Thewalt J.; Gooris G. S.; Kitson N. A Model Membrane Approach to the Epidermal Permeability Barrier: An X-ray Diffraction Study. Biochemistry 1997, 36, 7717–7725. 10.1021/bi9628127. PubMed DOI

Worcester D. L.; Franks N. P. Structural analysis of hydrated egg lecithin and cholesterol bilayers II. Neutron diffraction. J. Mol. Biol. 1976, 100, 359–378. 10.1016/s0022-2836(76)80068-x. PubMed DOI

Ruettinger A.; Kiselev M. A.; Hauss T.; Dante S.; Balagurov A. M.; Neubert R. H. H. Fatty acid interdigitation in stratum corneum model membranes: a neutron diffraction study. Eur. Biophys. J. 2008, 37, 759–771. 10.1007/s00249-008-0258-3. PubMed DOI

Rerek M. E.; Markovic B.; Van Wyck D.; Garidel P.; Mendelsohn R.; Moore D. J. Phytosphingosine and Sphingosine Ceramide Headgroup Hydrogen Bonding: Structural Insights through Thermotropic Hydrogen/Deuterium Exchange. J. Phys. Chem. B 2001, 105, 9355–9362. 10.1021/jp0118367. DOI

Garidel P. Structural organisation and phase behaviour of a stratum corneum lipid analogue: ceramide 3A. Phys. Chem. Chem. Phys. 2006, 8, 2265.10.1039/b517540b. PubMed DOI

Garidel P.; Fölting B.; Schaller I.; Kerth A. The microstructure of the stratum corneum lipid barrier: Mid-infrared spectroscopic studies of hydrated ceramide:palmitic acid:cholesterol model systems. Biophys. Chem. 2010, 150, 144–56. 10.1016/j.bpc.2010.03.008. PubMed DOI

Banc A.; Charbonneau C.; Dahesh M.; Appavou M.-S.; Fu Z.; Morel M.-H.; Ramos L. Small angle neutron scattering contrast variation reveals heterogeneities of interactions in protein gels. Soft Matter 2016, 12, 5340–5352. 10.1039/c6sm00710d. PubMed DOI

Hill J. R.; Wertz P. W. Molecular models of the intercellular lipid lamellae from epidermal stratum corneum. Biochim. Biophys. Acta 2003, 1616, 121–126. 10.1016/s0005-2736(03)00238-4. PubMed DOI

Narangifard A.; Wennberg C. L.; den Hollander L.; Iwai I.; Han H.; Lundborg M.; Masich S.; Lindahl E.; Daneholt B.; Norlén L. Molecular Reorganization during the Formation of the Human Skin Barrier Studied In Situ. J. Invest. Dermatol. 2021, 141, 1243–1253. 10.1016/j.jid.2020.07.040. PubMed DOI

Narangifard A.; den Hollander L.; Wennberg C. L.; Lundborg M.; Lindahl E.; Iwai I.; Han H.; Masich S.; Daneholt B.; Norlén L. Human skin barrier formation takes place via a cubic to lamellar lipid phase transition as analyzed by cryo-electron microscopy and EM-simulation. Exp. Cell Res. 2018, 366, 139–151. 10.1016/j.yexcr.2018.03.010. PubMed DOI

Lundborg M.; Narangifard A.; Wennberg C. L.; Lindahl E.; Daneholt B.; Norlén L. Human skin barrier structure and function analyzed by cryo-EM and molecular dynamics simulation. J. Struct. Biol. 2018, 203, 149–161. 10.1016/j.jsb.2018.04.005. PubMed DOI

Školová B.; Hudská K.; Pullmannová P.; Kováčik A.; Palát K.; Roh J.; Fleddermann J.; Estrela-Lopis I.; Vávrová K. Different Phase Behavior and Packing of Ceramides with Long (C16) and Very Long (C24) Acyls in Model Membranes: Infrared Spectroscopy Using Deuterated Lipids. J. Phys. Chem. B 2014, 118, 10460–10470. 10.1021/jp506407r. PubMed DOI

Engberg O.; Kováčik A.; Pullmannová P.; Juhaščik M.; Opálka L.; Huster D.; Vávrová K. The Sphingosine and Acyl Chains of Ceramide [NS] Show Very Different Structure and Dynamics That Challenge Our Understanding of the Skin Barrier. Angew. Chem., Int. Ed. 2020, 59, 17383–17387. 10.1002/anie.202003375. PubMed DOI PMC

Ranck J. L.; Zaccaï G.; Luzzati V. The structure of a lipid–water lamellar phase containing two types of lipid monolayers. An X-ray and neutron scattering study. J. Appl. Crystallogr. 1980, 13, 505–512. 10.1107/s0021889880012678. DOI

Avila R. L.; Inouye H.; Baek R. C.; Yin X.; Trapp B. D.; Feltri M. L.; Wrabetz L.; Kirschner D. A. Structure and stability of internodal myelin in mouse models of hereditary neuropathy. J. Neuropathol. Exp. Neurol. 2005, 64, 976–990. 10.1097/01.jnen.0000186925.95957.dc. PubMed DOI

Beddoes C. M.; Gooris G. S.; Bouwstra J. A. Preferential arrangement of lipids in the long-periodicity phase of a stratum corneum matrix model. J. Lipid Res. 2018, 59, 2329–2338. 10.1194/jlr.m087106. PubMed DOI PMC

Antunes E.; Cavaco-Paulo A. Stratum corneum lipid matrix with unusual packing: A molecular dynamics study. Colloids Surf., B 2020, 190, 110928.10.1016/j.colsurfb.2020.110928. PubMed DOI

Norlén L. Molecular skin barrier models and some central problems for the understanding of skin barrier structure and function. Skin Pharmacol. Appl. Skin Physiol. 2003, 16, 203–211. 10.1159/000070842. PubMed DOI

The intriguing molecular dynamics of Cer[EOS] in rigid skin barrier lipid layers requires improvement of the model