@article {2009|1864,
	title = {Models for phosphatidylglycerol lipids put to a structural test},
	journal = {J. Phys. Chem. B},
	volume = {113},
	number = {19},
	year = {2009},
	pages = {6958{\textendash}6963},
	publisher = {Center for Molecular Modeling, Department of Chemistry, University of Pennsylvania, 231 South 34th Street, Philadelphia, Pennsylvania 19104-6323, USA. jhenin@cmm.chem.upenn.edu},
	abstract = {Three atomistic empirical models for phosphatidylglycerol (PG) lipids are tested against structural data in the crystal and liquid crystal states. Simulations of the anhydrous crystal of dimyristoyl-phosphatidylglycerol (DMPG) show that only the CHARMM force field describes the conformation and interactions of PG head groups accurately. The other two models do not reproduce the native network of hydrogen bonds, suggesting the presence of biases in their conformational and nonbonded interaction properties. The CHARMM model is further validated in the biologically relevant liquid crystal phase by comparing experimental small-angle X-ray scattering spectra from DMPG unilamellar vesicles with data calculated from fluid bilayer simulations. The good agreement found in this model-free comparison implies that liquid crystal PG bilayers as described by CHARMM exhibit realistic bilayer thickness and lateral packing. Last, this model is used to simulate a fluid bilayer of palmitoyl-oleoyl-phosphatidylglycerol (POPG). The resulting view of the POPG bilayer structure is at variance with that proposed previously based on simulations, in particular, with respect to lateral packing of head groups and the role of counterions.},
	keywords = {chemistry, Crystallography, Lipid Bilayers, Models, Molecular, Phosphatidylglycerols, Scattering, Small Angle, Water, X-Ray},
	doi = {10.1021/jp900645z},
	author = {J{\'e}r{\^o}me H{\'e}nin and Wataru Shinoda and Michael L Klein}
}
@article {2008|1866,
	title = {United-Atom Acyl Chains for {CHARMM} Phospholipids},
	journal = {J. Phys. Chem. B.},
	volume = {112},
	number = {23},
	year = {2008},
	pages = {7008{\textendash}7015},
	publisher = {Center for Molecular Modeling, Department of Chemistry, University of Pennsylvania, 231 S. 34th Street, Philadelphia, Pennsylvania 19104-6323, and Research Institute for Computational Sciences, National Institute of Advanced Industrial Science and Technol},
	abstract = {In all-atom simulations of lipid membranes, explicit hydrogen atoms contained in the hydrocarbon region are described by a large number of degrees of freedom, although they convey only limited physical information. We propose an implicit-hydrogen model for saturated and monounsaturated acyl chains, aimed at complementing the all-atom CHARMM27 model for phospholipid headgroups. Torsional potentials and nonbonded parameters were fitted to reproduce experimental data and free energy surfaces of all-atom model systems. Comparative simulations of fluid-phase POPC bilayers were performed using the all-hydrogen force field and the present model. The hybrid model accelerates a typical bilayer simulation by about 50\% while sacrificing a minimal amount of detail with respect to the fully atomistic description. In addition, the united-atom description is energetically compatible with all-atom CHARMM models, making it suitable for simulations of complex membrane systems.},
	doi = {10.1021/jp800687p},
	author = {J{\'e}r{\^o}me H{\'e}nin and Wataru Shinoda and Michael L Klein}
}
