title: Electric Field Effect on Phospholipid Monolayers at an Aqueous-Organic Liquid-Liquid Interface.
abstract: The electric potential difference across cell membranes, known as the membrane potential, plays an important role in the activation of many biological processes. To investigate the effect of the membrane potential on the molecular ordering of lipids within a biomimetic membrane, a self-assembled monolayer of 1-stearoyl-2-oleoyl-sn-glycero-3-phosphocholine (SOPC) lipids at an electrified 1,2-dichloroethane/water interface is studied with X-ray reflectivity and interfacial tension. Measurements over a range of electric potential differences, -150 to +130 mV, that encompass the range of typical biomembrane potentials demonstrate a nearly constant and stable structure whose lipid interfacial density is comparable to that found in other biomimetic membrane systems. Measurements at higher positive potentials, up to 330 mV, illustrate a monotonic decrease in the lipid interfacial density and accompanying variations in the interfacial configuration of the lipid. Molecular dynamics simulations, designed to mimic the experimental conditions, show that the measured changes in lipid configuration are due primarily to the variation in area per lipid with increasing applied electric field. Rotation of the SOPC dipole moment by the torque from the applied electric field appears to be negligible, except at the highest measured potentials. The simulations confirm in atomistic detail the measured potential-dependent characteristics of SOPC monolayers. Our hybrid study sheds light on phospholipid monolayer stability under different membrane potentials, which is important for understanding membrane processes. This study also illustrates the use of X-ray surface scattering to probe the ordering of surfactant monolayers at an electrified aqueous-organic liquid-liquid interface.
authors.affiliation: †Department of Physics, University of Illinois at Chicago, Chicago, Illinois 60607, United States.
authors.forename: Hao
authors.initials: H
authors.lastname: Yu
authors.affiliation: ‡Department of Chemistry, University of Illinois at Chicago, Chicago, Illinois 60607, United States.
authors.forename: Irena
authors.initials: I
authors.lastname: Yzeiri
authors.affiliation: †Department of Physics, University of Illinois at Chicago, Chicago, Illinois 60607, United States.
authors.forename: Binyang
authors.initials: B
authors.lastname: Hou
authors.affiliation: †Department of Physics, University of Illinois at Chicago, Chicago, Illinois 60607, United States.
authors.forename: Chiu-Hao
authors.initials: CH
authors.lastname: Chen
authors.affiliation: †Department of Physics, University of Illinois at Chicago, Chicago, Illinois 60607, United States.
authors.forename: Wei
authors.initials: W
authors.lastname: Bu
authors.forename: Petr
authors.initials: P
authors.lastname: Vanysek
authors.affiliation: ∥The Center for Advanced Radiation Sources, University of Chicago, Chicago, Illinois 60637, United States.
authors.forename: Yu-Sheng
authors.initials: YS
authors.lastname: Chen
authors.affiliation: ∥The Center for Advanced Radiation Sources, University of Chicago, Chicago, Illinois 60637, United States.
authors.forename: Binhua
authors.initials: B
authors.lastname: Lin
authors.affiliation: †Department of Physics, University of Illinois at Chicago, Chicago, Illinois 60607, United States.|‡Department of Chemistry, University of Illinois at Chicago, Chicago, Illinois 60607, United States.
authors.forename: Petr
authors.initials: P
authors.lastname: Král
authors.affiliation: †Department of Physics, University of Illinois at Chicago, Chicago, Illinois 60607, United States.
authors.forename: Mark L
authors.initials: ML
authors.lastname: Schlossman
mesh_terms: D055590:Electromagnetic Phenomena; D005025:Ethylene Dichlorides / Q000737:chemistry*; D008027:Light; D008564:Membrane Potentials; D008567:Membranes, Artificial; D056004:Molecular Dynamics Simulation; D010713:Phosphatidylcholines / Q000737:chemistry*; D012399:Rotation; D012542:Scattering, Radiation; D013499:Surface Properties; D019415:Torque; D014867:Water / Q000737:chemistry*; D014965:X-Rays
chemical_list: D005025:Ethylene Dichlorides; D008567:Membranes, Artificial; D010713:Phosphatidylcholines; D014867:Water; C024565:ethylene dichloride; C027891:1-stearoyl-2-oleoyl-sn-glycero-3-phosphocholine