title: Comprehensive characterization of temperature- and pressure-induced bilayer phase transitions for saturated phosphatidylcholines containing longer chain homologs.
abstract: Complete elucidation of the phase behavior of phospholipid bilayers requires information on the subtransition from the lamellar crystal (Lc) phase to the gel phase. However, for bilayers of saturated diacylphosphatidylcholines (CnPCs), especially longer chain homologs, equilibration in the Lc phase is known to be very slow. In this study, bilayer phase transitions of three CnPCs with longer acyl chains, C19PC, C20PC and C21PC, were observed by differential scanning calorimetry under atmospheric pressure and by light-transmittance measurements under high pressure. Using lipid samples treated by thermal annealing enabled the observation of the sub-, pre- and main transitions of the C19PC and C20PC bilayers under atmospheric pressure. Only the pre- and main transitions could be observed for the C21PC bilayer due to very slow kinetics of the Lc phase formation for lipids with long acyl chains. The temperature and pressure phase diagrams constructed and phase-transitions quantities (enthalpy, entropy and volume changes) evaluated for these bilayers were compared with one another and with those of bilayers of the CnPC homologs examined in previous studies. These results allowed us (1) to clarify the temperature- and pressure-dependent phase sequence and phase stability of the CnPC (n=12-22) bilayers as a function of the hydrophobicity of the molecules, (2) to prove the presence of a shorter and a longer limit (n=13 and 21) in the acyl chain length for the pressure-induced bilayer interdigitation and (3) to reveal the chain-length dependence of the thermodynamic quantities of the subtransitions including the volume change.
authors.affiliation: Laboratory for Neutron Scattering and Imaging, Paul Scherrer Institute, CH-5232 Villigen PSI, Switzerland.
authors.forename: Masaki
authors.initials: M
authors.lastname: Goto
authors.affiliation: Department of Biological Science and Technology, Faculty of Engineering, The University of Tokushima, 2-1 Minamijosanjima-cho, Tokushima 770-8506, Japan.
authors.forename: Takuya
authors.initials: T
authors.lastname: Endo
authors.affiliation: Department of Biological Science and Technology, Faculty of Engineering, The University of Tokushima, 2-1 Minamijosanjima-cho, Tokushima 770-8506, Japan.
authors.forename: Takahiro
authors.initials: T
authors.lastname: Yano
authors.affiliation: Department of Life System, Institute of Technology and Science, The University of Tokushima, 2-1 Minamijosanjima-cho, Tokushima 770-8506, Japan.
authors.forename: Nobutake
authors.initials: N
authors.lastname: Tamai
authors.affiliation: Laboratory for Neutron Scattering and Imaging, Paul Scherrer Institute, CH-5232 Villigen PSI, Switzerland.
authors.forename: Joachim
authors.initials: J
authors.lastname: Kohlbrecher
authors.affiliation: Department of Life System, Institute of Technology and Science, The University of Tokushima, 2-1 Minamijosanjima-cho, Tokushima 770-8506, Japan. Electronic address: matsuki@bio.tokushima-u.ac.jp.
authors.forename: Hitoshi
authors.initials: H
authors.lastname: Matsuki
mesh_terms: D001274:Atmospheric Pressure; D057927:Hydrophobic and Hydrophilic Interactions; D007700:Kinetics; D008051:Lipid Bilayers / Q000737:chemistry*; D044367:Phase Transition; D010713:Phosphatidylcholines / Q000737:chemistry*; D013696:Temperature; D013816:Thermodynamics
chemical_list: D008051:Lipid Bilayers; D010713:Phosphatidylcholines
keywords: Bilayer membrane; Diacylphosphatidylcholine; Interdigitation; Phase transition; Pressure; Subgel phase