@article{curtis_bahrami_weikl_hall_2015, title={Modeling nanoparticle wrapping or translocation in bilayer membranes}, volume={7}, ISSN={["2040-3372"]}, DOI={10.1039/c5nr02255j}, abstractNote={The spontaneous wrapping of nanoparticles by membranes is of increasing interest as nanoparticles become more prevalent in consumer products and hence more likely to enter the human body. We introduce a simulations-based tool that can be used to visualize the molecular level interaction between nanoparticles and bilayer membranes. By combining LIME, an intermediate resolution, implicit solvent model for phospholipids, with discontinuous molecular dynamics (DMD), we are able to simulate the wrapping or embedding of nanoparticles by 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) bilayer membranes. Simulations of hydrophilic nanoparticles with diameters from 10 Å to 250 Å show that hydrophilic nanoparticles with diameters greater than 20 Å become wrapped while the nanoparticle with a diameter of 10 Å does not. Instead this smaller particle became embedded in the bilayer surface where it can interact with the hydrophilic head groups of the lipid molecules. We also investigate the interaction between a DPPC bilayer and hydrophobic nanoparticles with diameters 10 Å to 40 Å. These nanoparticles do not undergo the wrapping process; instead they directly penetrate the membrane and embed themselves within the inner hydrophobic core of the bilayers.}, number={34}, journal={NANOSCALE}, author={Curtis, Emily M. and Bahrami, Amir H. and Weikl, Thomas R. and Hall, Carol K.}, year={2015}, pages={14505–14514} }
 @article{curtis_xiao_sofou_hall_2015, title={Phase Separation Behavior of Mixed Lipid Systems at Neutral and Low pH: Coarse-Grained Simulations with DMD/LIME}, volume={31}, ISSN={["0743-7463"]}, DOI={10.1021/la504082x}, abstractNote={We extend LIME, an intermediate resolution, implicit solvent model for phospholipids previously used in discontinuous molecular dynamics simulations of 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) bilayer formation at 325 K, to the description of the geometry and energetics of 1,2-distearoyl-sn-glycero-3-phospho-L-serine (DSPS) and 1,2-dihenarachidoyl-sn-glycero-3-phosphocholine (21PC) and mixtures thereof at both neutral and low pH at 310 K. A multiscale modeling approach is used to calculate the LIME parameters from atomistic simulation data on a mixed DPPC/DSPS system at different pH values. In the model, 17 coarse-grained sites represent DSPS and 18 coarse-grained sites represent 21PC. Each of these coarse-grained sites is classified as 1 of 9 types. LIME/DMD simulations of equimolar bilayers show the following: (1) 21PC/DSPS bilayers with and without surface area restrictions separate faster at low pH than at neutral pH, (2) 21PC/DSPS systems separate at approximately the same rate regardless of whether they are subjected to surface area restrictions, and (3) bilayers with a molar ratio of 9:1 (21PC:DSPS) phase separate to form heterogeneous domains faster at low pH than at neutral pH. Our results are consistent with experimental findings of Sofou and co-workers (Bandekar et al. Mol. Pharmaceutics, 2013, 10, 152-160; Karve et al. Biomaterials, 2010, 31, 4409-4416) that more doxorubicin is released from 21PC/DSPS liposomes at low pH than at neutral pH, presumably because greater phase separation is achieved at low pH than at neutral pH. These are the first molecular-level simulations of the phase separation in mixed lipid bilayers induced by a change in pH.}, number={3}, journal={LANGMUIR}, author={Curtis, Emily M. and Xiao, Xingqing and Sofou, Stavroula and Hall, Carol K.}, year={2015}, month={Jan}, pages={1086–1094} }
 @article{bahrami_raatz_agudo-canalejo_michel_curtis_hall_gradzielski_lipowsky_weikl_2014, title={Wrapping of nanoparticles by membranes}, volume={208}, ISSN={["1873-3727"]}, DOI={10.1016/j.cis.2014.02.012}, abstractNote={How nanoparticles interact with biomembranes is central for understanding their bioactivity. Biomembranes wrap around nanoparticles if the adhesive interaction between the nanoparticles and membranes is sufficiently strong to compensate for the cost of membrane bending. In this article, we review recent results from theory and simulations that provide new insights on the interplay of bending and adhesion energies during the wrapping of nanoparticles by membranes. These results indicate that the interplay of bending and adhesion during wrapping is strongly affected by the interaction range of the particle–membrane adhesion potential, by the shape of the nanoparticles, and by shape changes of membrane vesicles during wrapping. The interaction range of the particle–membrane adhesion potential is crucial both for the wrapping process of single nanoparticles and the cooperative wrapping of nanoparticles by membrane tubules.}, journal={ADVANCES IN COLLOID AND INTERFACE SCIENCE}, author={Bahrami, Arnir H. and Raatz, Michael and Agudo-Canalejo, Jaime and Michel, Raphael and Curtis, Emily M. and Hall, Carol K. and Gradzielski, Michael and Lipowsky, Reinhard and Weikl, Thomas R.}, year={2014}, month={Jun}, pages={214–224} }
 @article{curtis_hall_2013, title={Molecular Dynamics Simulations of DPPC Bilayers Using "LIME", a New Coarse-Grained Model}, volume={117}, ISSN={["1520-5207"]}, DOI={10.1021/jp309712b}, abstractNote={A new intermediate resolution model for phospholipids, LIME, designed for use with discontinuous molecular dynamics (DMD) simulations is presented. The implicit-solvent model was developed using a multiscale modeling approach in which the geometric and energetic parameters are obtained by collecting data from atomistic simulations of a system composed of 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) molecules and explicit water. In the model, 14 coarse-grained sites that are classified as 1 of 6 types represent DPPC. DMD simulations performed on a random solution of DPPC resulted in the formation of a defect-free bilayer in less than 4 h. The bilayer formed quantitatively reproduces the main structural properties (e.g., area per lipid, bilayer thickness, bond order parameters) that are observed experimentally. In addition, the bilayer transitions from a liquid-crystalline phase to a tilted gel phase when the temperature is reduced. Transbilayer movement of a lipid from the bottom leaflet to the top leaflet is observed when the temperature is increased.}, number={17}, journal={JOURNAL OF PHYSICAL CHEMISTRY B}, author={Curtis, Emily M. and Hall, Carol K.}, year={2013}, month={May}, pages={5019–5030} }