title: Effect of lamellarity and size on calorimetric phase transitions in single component phosphatidylcholine vesicles.
abstract: Nano-differential scanning calorimetry (nano-DSC) is a powerful tool in the investigation of unilamellar (small unilamellar, SUVs, or large unilamellar, LUVs) vesicles, as well as lipids on supported bilayers, since it measures the main gel-to-liquid phase transition temperature (Tm), enthalpies and entropies. In order to assign these transitions in single component systems, where Tm often occurred as a doublet, nano-DSC, dynamic light scattering and cryo-transmission electron microscopy (cryo-TEM) data were compared. The two Tms were not attributable to decoupled phase transitions between the two leaflets of the bilayer, i.e. nano-DSC measurements were not able to distinguish between the outer and inner leaflets of the vesicle bilayers. Instead, the two Tms were attributed to mixtures of oligolamellar and unilamellar vesicles, as confirmed by cryo-TEM images. Tm for the oligolamellar vesicles was assigned to the peak closest to that of the parent multilamellar vesicle (MLV) peak. The other transition was higher than that of the parent MLVs for 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC), and increased in temperature as the vesicle size decreased, while it was lower in temperature than that of the parent MLVs for 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC), and decreased as the vesicle size decreased. These subtle shifts arose due to small differences in the values of ΔH and ΔS, since Tm is determined by their ratio (ΔH/ΔS). It was not possible to completely eliminate oligolamellar structures for MLVs extruded with the 200 nm pore size filter, even after 120 passes, while these structures were eliminated for MLVs extruded through the 50 nm pore size filter.
authors.affiliation: Department of Chemistry, Temple University, Philadelphia, PA 19122, USA.
authors.forename: Jelena
authors.initials: J
authors.lastname: Drazenovic
authors.affiliation: Department of Chemistry, Temple University, Philadelphia, PA 19122, USA.
authors.forename: Hairong
authors.initials: H
authors.lastname: Wang
authors.affiliation: Department of Chemistry, Temple University, Philadelphia, PA 19122, USA.
authors.forename: Kristina
authors.initials: K
authors.lastname: Roth
authors.affiliation: Department of Chemistry, Immaculata University, Immaculata, PA 19345, USA.
authors.forename: Jiangyue
authors.initials: J
authors.lastname: Zhang
authors.affiliation: Department of Chemistry, Temple University, Philadelphia, PA 19122, USA.
authors.forename: Selver
authors.initials: S
authors.lastname: Ahmed
authors.affiliation: Department of Chemical Engineering, University of Rhode Island, Kingston, RI 02881, USA.
authors.forename: Yanjing
authors.initials: Y
authors.lastname: Chen
authors.affiliation: Department of Chemical Engineering, University of Rhode Island, Kingston, RI 02881, USA.
authors.forename: Geoffrey
authors.initials: G
authors.lastname: Bothun
authors.affiliation: Department of Chemistry, Temple University, Philadelphia, PA 19122, USA. Electronic address: slwunder@temple.edu.
authors.forename: Stephanie L
authors.initials: SL
authors.lastname: Wunder
mesh_terms: D015060:1,2-Dipalmitoylphosphatidylcholine / Q000031:analogs & derivatives* / Q000737:chemistry; D020285:Cryoelectron Microscopy; D004134:Dimyristoylphosphatidylcholine / Q000737:chemistry*; D007700:Kinetics; D008027:Light; D008051:Lipid Bilayers / Q000737:chemistry*; D008081:Liposomes / Q000737:chemistry*; D044367:Phase Transition; D010713:Phosphatidylcholines / Q000737:chemistry*; D012542:Scattering, Radiation; D013816:Thermodynamics
chemical_list: D008051:Lipid Bilayers; D008081:Liposomes; D010713:Phosphatidylcholines; D015060:1,2-Dipalmitoylphosphatidylcholine; C081581:colfosceril palmitate; D004134:Dimyristoylphosphatidylcholine
keywords: Coupled phase transition; DMPC; Gel-to-liquid phase transition temperature; Unilamellar vesicle; Vesicle curvature; Vesicle lamellarity