title: Unit cell volume and liquid-phase immiscibility in oleate-stearate lipid mixtures.
abstract: The structural basis of immiscibility of stearic acid (SA) in two unsaturated lipids at room temperature was examined. A 5% SA mixture in octadec-9-enoic acid (OA) is cloudy; a 5% SA solution in the methyl ester of OA (MeOA) is fully miscible. At 10% SA in MeOA, a clear and immiscible phase formed. The composition of this immiscible phase however was not 10% SA, but 25% SA. Adding additional SA altered the amount of the second phase, not its stoichiometry. Molecular mechanics explains the molecular basis for the ratio of saturated and unsaturated lipids in the different phases. Packing order of lipids within a unit volume explains the discrete lipid composition ratio forming each of the observed miscible and immiscible phases. The smallest unit cell volume that explains the observed stoichiometry is a cube (not a sphere).
authors.affiliation: United States Department of Agriculture, Beltsville Agricultural Research Service, Agricultural Research Service, Beltsville, MD 20705, USA. walter.schmidt@ars.usda.gov
authors.forename: Walter F
authors.initials: WF
authors.lastname: Schmidt
authors.forename: Swati
authors.initials: S
authors.lastname: Mookherji
authors.forename: Michael A
authors.initials: MA
authors.lastname: Crawford
mesh_terms: D000480:Alkynes / Q000737:chemistry*; D005231:Fatty Acids, Unsaturated / Q000737:chemistry*; D009682:Magnetic Resonance Spectroscopy; D009829:Oleic Acids / Q000737:chemistry*; D013059:Spectrum Analysis, Raman; D013229:Stearic Acids / Q000737:chemistry*
chemical_list: D000480:Alkynes; D005231:Fatty Acids, Unsaturated; D009829:Oleic Acids; D013229:Stearic Acids; C031183:stearic acid; C066014:9-stearolic acid