title: Interactions between Phospholipids and Organic Phases: Insights into Lipoproteins and Nanoemulsions.
abstract: The adsorption of phosphatidylcholines (PCs), dissolved in squalene or squalane as an organic phase, was studied at the interface with water. Using profile analysis tensiometry, the equilibrium adsorption isotherms, minimum molecular interfacial areas, and solubility limits were derived. For squalene, differences in PC solubility and interfacial adsorption were found, depending on PC saturation. Compared to saturated PCs, unsaturated PCs showed a 3-fold-lower interfacial density but up to a 28-fold-higher critical aggregation concentration (CAC). In addition, the solubility limit of unsaturated PC in squalene and in its saturated form squalane diverged by a factor of 739. These findings provided evidence for steric repulsion or π-π interactions of π bonds in both solvent and solute or both effects acting complementarily. In squalane, low solubilities but high interfacial densities were found for all investigated PCs. Changes in fatty acid chain lengths showed that the influence of the increases in entropy and enthalpy on solubility is much smaller than solvent/solute interactions. Oxidation products of squalene lowered the interfacial tension, but increasing concentrations of PC expelled them from the interface. The CAC of saturated PC was increased by oxidation products of squalene whereas that of unsaturated PCs was not. Our findings indicate that the oxidation of triglycerides in lipoprotein cores can lead to increased solubility of saturated phospholipids covering the lipoproteins, contributing to destabilization, coalescence, and terminally the formation of atherosclerotic plaques. The consideration of solvent/solute interactions in molecular modeling may contribute to the interfacial tension and the corresponding kinetic or thermodynamic stability of lipoproteins. Measured areas per molecule prove that PCs form monolayers of different interfacial densities at the squalene/water interface but multilayers at the squalane/water interface. These findings showed that combinations of solvent or solute saturation affect the outcome for nanoemulsions forming either expanded or condensed monolayers or multilayers.
authors.affiliation: Karlsruhe Institute of Technology (KIT), Institute of Mechanical Process Engineering and Mechanics , 76131 Karlsruhe, Germany.|Abnoba GmbH, 75177 Pforzheim, Germany.
authors.forename: Ellen
authors.initials: E
authors.lastname: Hildebrandt
authors.affiliation: Abnoba GmbH, 75177 Pforzheim, Germany.
authors.forename: Alberto
authors.initials: A
authors.lastname: Dessy
authors.affiliation: Karlsruhe Institute of Technology (KIT), Institute of Mechanical Process Engineering and Mechanics , 76131 Karlsruhe, Germany.|Abnoba GmbH, 75177 Pforzheim, Germany.
authors.forename: Jan-Hendrik
authors.initials: JH
authors.lastname: Sommerling
authors.affiliation: Karlsruhe Institute of Technology (KIT), Institute of Mechanical Process Engineering and Mechanics , 76131 Karlsruhe, Germany.
authors.forename: Gisela
authors.initials: G
authors.lastname: Guthausen
authors.affiliation: Karlsruhe Institute of Technology (KIT), Institute of Mechanical Process Engineering and Mechanics , 76131 Karlsruhe, Germany.
authors.forename: Hermann
authors.initials: H
authors.lastname: Nirschl
authors.affiliation: Abnoba GmbH, 75177 Pforzheim, Germany.|Carl Gustav Carus-Institute, Association for the Promotion of Cancer Therapy , 75223 Niefern-Oeschelbronn, Germany.
authors.forename: Gero
authors.initials: G
authors.lastname: Leneweit
mesh_terms: D004655:Emulsions; D008074:Lipoproteins / Q000737:chemistry*; D010713:Phosphatidylcholines / Q000737:chemistry*; D055550:Protein Stability; D013185:Squalene / Q000737:chemistry*
chemical_list: D004655:Emulsions; D008074:Lipoproteins; D010713:Phosphatidylcholines; D013185:Squalene