Ascorbyl palmitate interaction with phospholipid monolayers: Electrostatic and rheological preponderancy |
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Authors: | Milagro Mottola Natalia Wilke Luciano Benedini Rafael Gustavo Oliveira Maria Laura Fanani |
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Affiliation: | 1. Centro de Investigaciones en Química Biológica de Córdoba (CIQUIBIC-CONICET), Departamento de Química Biológica, Facultad de Ciencias Químicas, Universidad Nacional del Córdoba, Haya de la Torre y Medina Allende, Ciudad Universitaria, X5000HUA Córdoba, Argentina;2. Instituto de Química del Sur (INQUISUR-CONICET), Departamento de Química, Universidad Nacional del Sur, 8000FTN Bahía Blanca, Argentina |
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Abstract: | Ascorbyl palmitate (ASC16) is an anionic amphiphilic molecule of pharmacological interest due to its antioxidant properties. We found that ASC16 strongly interacted with model membranes. ASC16 penetrated phospholipid monolayers, with a cutoff near the theoretical surface pressure limit. The presence of a lipid film at the interface favored ASC16 insertion compared with a bare air/water surface. The adsorption and penetration time curves showed a biphasic behavior: the first rapid peak evidenced a fast adsorption of charged ASC16 molecules to the interface that promoted a lowering of surface pH, thus partially neutralizing and compacting the film. The second rise represented an approach to the equilibrium between the ASC16 molecules in the subphase and the surface monolayer, whose kinetics depended on the ionization state of the film. Based on the Langmuir dimiristoylphosphatidylcholine + ASC16 monolayer data, we estimated an ASC16 partition coefficient to dimiristoylphosphatidylcholine monolayers of 1.5 × 105 and a ΔGp = − 6.7 kcal·mol− 1. The rheological properties of the host membrane were determinant for ASC16 penetration kinetics: a fluid membrane, as provided by cholesterol, disrupted the liquid-condensed ASC16-enriched domains and favored ASC16 penetration. Subphase pH conditions affected ASC16 aggregation in bulk: the smaller structures at acidic pHs showed a faster equilibrium with the surface film than large lamellar ones. Our results revealed that the ASC16 interaction with model membranes has a highly complex regulation. The polymorphism in the ASC16 bulk aggregation added complexity to the equilibrium between the surface and subphase form of ASC16, whose understanding may shed light on the pharmacological function of this drug. |
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Keywords: | ASC16, ascorbyl palmitate DMPC, 1,2-dimyristoyl-sn-glycero-3-phosphocholine DMPG, 1,2-dimyristoyl-sn-glycero-3-phospho-(1&prime -rac-glycerol) Chol, cholesterol LE, liquid-expanded LC, liquid-condensed CP, collapsed phase π, surface pressure ΔV, surface potential MMA, mean molecular area Cs&minus 1, compressibility modulus BAM, Brewster angle microscopy DLS, dynamic light scattering SAXS, small angle X-ray scattering |
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