title: Cooperative effects of fatty acids and n-butanol on lipid membrane phase behavior.
abstract: Biodiesel-derived crude glycerol can be fermented to produce n-butanol, which is a platform chemical for biorefining and a biofuel. One limitation to crude glycerol fermentation is the presence of long-chain fatty acids (FAs) that can partition into cellular membranes, leading to membrane fluidization and interdigitation, which can inhibit cellular function. In this work, we have examined the phase behavior of dipalmitoylphosphatidylcholine (DPPC, C16:0) membranes and the membrane partitioning of n-butanol as a function of FA degree of unsaturation (steric, oleic, and linoleic acids) using differential scanning calorimetry (DSC) and monolayer surface pressure studies. All three FAs at 15mol% (85mol% DPPC) prevented interdigitation by n-butanol based on the DSC results. n-Butanol partitioning and membrane expansion was greatest for DPPC/oleic acid membranes, where monounsaturated oleic acid (OA, C18:1) was miscible in gel and fluid phase DPPC. Saturated steric acid (SA, C18:0), which ordered the membranes and yielded a SA-rich phase during melting, led to a modest increase in n-butanol partitioning compared to DPPC alone. Di-unsaturated linoleic acid (LA, C18:2), which disordered the membranes and phase separated, had little affect on n-butanol partitioning into the DPPC-rich phases. The effects of OA and LA are attributed to the additional interfacial area provided by these FAs due to acyl tail 'kinks' at the carbon double bonds. These results show that exogenous FAs can partition into membranes, impacting n-butanol partitioning and acting cooperatively with n-butanol to alter membrane structure.
authors.affiliation: Department of Chemical Engineering, University of Rhode Island, 16 Greenhouse Rd, Kingston, RI, United States. Electronic address: gbothun@uri.edu.
authors.forename: Geoffrey D
authors.initials: GD
authors.lastname: Bothun
authors.affiliation: Department of Chemical Engineering, University of Rhode Island, 16 Greenhouse Rd, Kingston, RI, United States.
authors.forename: Lauren
authors.initials: L
authors.lastname: Boltz
authors.affiliation: Department of Chemical Engineering, University of Rhode Island, 16 Greenhouse Rd, Kingston, RI, United States.
authors.forename: Yogi
authors.initials: Y
authors.lastname: Kurniawan
authors.affiliation: Department of Chemistry, University of Alabama in Huntsville, 301 Sparkman Dr, Huntsville, AL, United States.
authors.forename: Carmen
authors.initials: C
authors.lastname: Scholz
mesh_terms: D015060:1,2-Dipalmitoylphosphatidylcholine / Q000737:chemistry*; D020001:1-Butanol / Q000737:chemistry*; D002152:Calorimetry, Differential Scanning; D007700:Kinetics; D019787:Linoleic Acid / Q000737:chemistry*; D008051:Lipid Bilayers / Q000737:chemistry*; D008567:Membranes, Artificial; D019301:Oleic Acid / Q000737:chemistry*; D013229:Stearic Acids / Q000737:chemistry*; D013816:Thermodynamics
chemical_list: D008051:Lipid Bilayers; D008567:Membranes, Artificial; D013229:Stearic Acids; D015060:1,2-Dipalmitoylphosphatidylcholine; D019301:Oleic Acid; C031183:stearic acid; D020001:1-Butanol; D019787:Linoleic Acid
keywords: Fatty acid; Lipid monolayer; Lipid phase behavior; Surface pressure