title: Incorporating headgroup structure into the Poisson-Boltzmann model of charged lipid membranes.
abstract: Charged lipids often possess a complex headgroup structure with several spatially separated charges and internal conformational degrees of freedom. We propose a headgroup model consisting of two rod-like segments of the same length that form a flexible joint, with three charges of arbitrary sign and valence located at the joint and the two terminal positions. One terminal charge is firmly anchored at the polar-apolar interface of the lipid layer whereas the other two benefit from the orientational degrees of freedom of the two headgroup segments. This headgroup model is incorporated into the mean-field continuum Poisson-Boltzmann formalism of the electric double layer. For sufficiently small lengths of the two rod-like segments a closed-form expression of the charging free energy is calculated. For three specific examples--a zwitterionic headgroup with conformational freedom and two headgroups that carry an excess charge--we analyze and discuss conformational properties and electrostatic free energies.
authors.affiliation: Beijing National Laboratory for Molecular Sciences, Department of Polymer Science and Engineering and Key Laboratory of Polymer Chemistry and Physics of Ministry of Education, College of Chemistry, Peking University, Beijing 100871, China.
authors.forename: Muyang
authors.initials: M
authors.lastname: Wang
authors.forename: Er-Qiang
authors.initials: EQ
authors.lastname: Chen
authors.forename: Shuang
authors.initials: S
authors.lastname: Yang
authors.forename: Sylvio
authors.initials: S
authors.lastname: May
mesh_terms: D007477:Ions / Q000737:chemistry; D008051:Lipid Bilayers / Q000737:chemistry*; D008563:Membrane Lipids / Q000737:chemistry*; D008956:Models, Chemical; D055672:Static Electricity
chemical_list: D007477:Ions; D008051:Lipid Bilayers; D008563:Membrane Lipids