title: CHARMM36 united atom chain model for lipids and surfactants.
abstract: Molecular simulations of lipids and surfactants require accurate parameters to reproduce and predict experimental properties. Previously, a united atom (UA) chain model was developed for the CHARMM27/27r lipids (Hénin, J., et al. J. Phys. Chem. B. 2008, 112, 7008-7015) but suffers from the flaw that bilayer simulations using the model require an imposed surface area ensemble, which limits its use to pure bilayer systems. A UA-chain model has been developed based on the CHARMM36 (C36) all-atom lipid parameters, termed C36-UA, and agreed well with bulk, lipid membrane, and micelle formation of a surfactant. Molecular dynamics (MD) simulations of alkanes (heptane and pentadecane) were used to test the validity of C36-UA on density, heat of vaporization, and liquid self-diffusion constants. Then, simulations using C36-UA resulted in accurate properties (surface area per lipid, X-ray and neutron form factors, and chain order parameters) of various saturated- and unsaturated-chain bilayers. When mixed with the all-atom cholesterol model and tested with a series of 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC)/cholesterol mixtures, the C36-UA model performed well. Simulations of self-assembly of a surfactant (dodecylphosphocholine, DPC) using C36-UA suggest an aggregation number of 53 ± 11 DPC molecules at 0.45 M of DPC, which agrees well with experimental estimates. Therefore, the C36-UA force field offers a useful alternative to the all-atom C36 lipid force field by requiring less computational cost while still maintaining the same level of accuracy, which may prove useful for large systems with proteins.
authors.affiliation: Department of Chemical and Biomolecular Engineering, University of Maryland , College Park, Maryland 20742, United States.
authors.forename: Sarah
authors.initials: S
authors.lastname: Lee
authors.forename: Alan
authors.initials: A
authors.lastname: Tran
authors.forename: Matthew
authors.initials: M
authors.lastname: Allsopp
authors.forename: Joseph B
authors.initials: JB
authors.lastname: Lim
authors.forename: Jérôme
authors.initials: J
authors.lastname: Hénin
authors.forename: Jeffery B
authors.initials: JB
authors.lastname: Klauda
mesh_terms: D002784:Cholesterol / Q000737:chemistry; D004134:Dimyristoylphosphatidylcholine / Q000737:chemistry; D008051:Lipid Bilayers / Q000737:chemistry; D008055:Lipids / Q000737:chemistry*; D008823:Micelles; D056004:Molecular Dynamics Simulation; D010767:Phosphorylcholine / Q000031:analogs & derivatives / Q000737:chemistry; D013501:Surface-Active Agents / Q000737:chemistry*
chemical_list: D008051:Lipid Bilayers; D008055:Lipids; D008823:Micelles; D013501:Surface-Active Agents; D010767:Phosphorylcholine; C028810:dodecylphosphocholine; D002784:Cholesterol; D004134:Dimyristoylphosphatidylcholine