1
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Reinhardt A, Chew PY, Cheng B. A streamlined molecular-dynamics workflow for computing solubilities of molecular and ionic crystals. J Chem Phys 2023; 159:184110. [PMID: 37962445 DOI: 10.1063/5.0173341] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/21/2023] [Accepted: 10/20/2023] [Indexed: 11/15/2023] Open
Abstract
Computing the solubility of crystals in a solvent using atomistic simulations is notoriously challenging due to the complexities and convergence issues associated with free-energy methods, as well as the slow equilibration in direct-coexistence simulations. This paper introduces a molecular-dynamics workflow that simplifies and robustly computes the solubility of molecular or ionic crystals. This method is considerably more straightforward than the state-of-the-art, as we have streamlined and optimised each step of the process. Specifically, we calculate the chemical potential of the crystal using the gas-phase molecule as a reference state, and employ the S0 method to determine the concentration dependence of the chemical potential of the solute. We use this workflow to predict the solubilities of sodium chloride in water, urea polymorphs in water, and paracetamol polymorphs in both water and ethanol. Our findings indicate that the predicted solubility is sensitive to the chosen potential energy surface. Furthermore, we note that the harmonic approximation often fails for both molecular crystals and gas molecules at or above room temperature, and that the assumption of an ideal solution becomes less valid for highly soluble substances.
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Affiliation(s)
- Aleks Reinhardt
- Yusuf Hamied Department of Chemistry, University of Cambridge, Lensfield Road, Cambridge CB2 1EW, United Kingdom
| | - Pin Yu Chew
- Yusuf Hamied Department of Chemistry, University of Cambridge, Lensfield Road, Cambridge CB2 1EW, United Kingdom
| | - Bingqing Cheng
- Institute of Science and Technology Austria, Am Campus 1, 3400 Klosterneuburg, Austria
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2
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Schaefer D, Kohns M, Hasse H. Molecular modeling and simulation of aqueous solutions of alkali nitrates. J Chem Phys 2023; 158:134508. [PMID: 37031112 DOI: 10.1063/5.0141331] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 04/05/2023] Open
Abstract
A set of molecular models for the alkali nitrates (LiNO3, NaNO3, KNO3, RbNO3, and CsNO3) in aqueous solutions is presented and used for predicting the thermophysical properties of these solutions with molecular dynamics simulations. The set of models is obtained from a combination of a model for the nitrate anion from the literature with a set of models for the alkali cations developed in previous works of our group. The water model is SPC/E and the Lorentz–Berthelot combining rules are used for describing the unlike interactions. This combination is shown to yield fair predictions of thermophysical and structural properties of the studied aqueous solutions, namely the density, the water activity and the mean ionic activity coefficient, the self-diffusion coefficients of the ions, and radial distribution functions, which were studied at 298 K and 1 bar; except for the density of the solutions of all five nitrates and the activity properties of solutions of NaNO3, which were also studied at 333 K. For calculating the water the activity and the mean ionic activity coefficient, the OPAS ( osmotic pressure for the activity of selvents) method was applied. The new models extend an ion model family for the alkali halides developed in previous works of our group in a consistent way.
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Affiliation(s)
- Dominik Schaefer
- Laboratory of Engineering Thermodynamics (LTD), RPTU Kaiserslautern, 67663 Kaiserslautern, Germany
| | - Maximilian Kohns
- Laboratory of Engineering Thermodynamics (LTD), RPTU Kaiserslautern, 67663 Kaiserslautern, Germany
| | - Hans Hasse
- Laboratory of Engineering Thermodynamics (LTD), RPTU Kaiserslautern, 67663 Kaiserslautern, Germany
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3
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Cheng B. Computing chemical potentials of solutions from structure factors. J Chem Phys 2022; 157:121101. [DOI: 10.1063/5.0107059] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
The chemical potential of a component in a solution is defined as the free energy change as the amount of the component changes. Computing this fundamental thermodynamic property from atomistic simulations is notoriously difficult, because of the convergence issues in free energy methods and finite size effects. This paper presents the so-called S0 method, which can be used to obtain chemical potentials from static structure factors computed from equilibrium molecular dynamics simulations under the isothermal-isobaric ensemble. This new method is demonstrated on the systems of binary Lennard-Jones particles, urea--water mixtures, a NaCl aqueous solution, and a high-pressure carbon-hydrogen mixture.
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4
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Polarizable force fields for accurate molecular simulations of aqueous solutions of electrolytes, crystalline salts, and solubility: Li+, Na+, K+, Rb+, F−, Cl−, Br−, I−. J Mol Liq 2022. [DOI: 10.1016/j.molliq.2022.119659] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
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5
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Bianco V, Conde MM, Lamas CP, Noya EG, Sanz E. Phase diagram of the NaCl–water system from computer simulations. J Chem Phys 2022; 156:064505. [DOI: 10.1063/5.0083371] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022] Open
Affiliation(s)
- V. Bianco
- Departamento de Química Física (Unidad de I+D+i asociada al CSIC), Facultad de Ciencias Químicas, Universidad Complutense de Madrid, 28040 Madrid, Spain
| | - M. M. Conde
- Departamento de Ingeniería Química Industrial y Medio Ambiente, Escuela Técnica Superior de Ingenieros Industriales, Universidad Politécnica de Madrid, 28006 Madrid, Spain
| | - C. P. Lamas
- Departamento de Química Física (Unidad de I+D+i asociada al CSIC), Facultad de Ciencias Químicas, Universidad Complutense de Madrid, 28040 Madrid, Spain
- Instituto de Química Física Rocasolano, Consejo Superior de Investigaciones Científicas, CSIC, Calle Serrano 119, 28006 Madrid, Spain
| | - E. G. Noya
- Instituto de Química Física Rocasolano, Consejo Superior de Investigaciones Científicas, CSIC, Calle Serrano 119, 28006 Madrid, Spain
| | - E. Sanz
- Departamento de Química Física (Unidad de I+D+i asociada al CSIC), Facultad de Ciencias Químicas, Universidad Complutense de Madrid, 28040 Madrid, Spain
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6
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DeFever RS, Maginn EJ. Computing the Liquidus of Binary Monatomic Salt Mixtures with Direct Simulation and Alchemical Free Energy Methods. J Phys Chem A 2021; 125:8498-8513. [PMID: 34543018 DOI: 10.1021/acs.jpca.1c06107] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
We describe and validate a free-energy-based method for computing the liquidus for binary solid-liquid phase diagrams in molecular simulations of monatomic salts. The method is demonstrated by calculating the liquidus for LiCl-KCl and MgCl2-KCl salt mixtures with the polarizable ion model (PIM). The free-energy-based method is cross-validated with direct coexistence simulations. Both techniques show excellent agreement with one another. Though the predictions of the PIM disagree with experiments, we use our free-energy-based approach to decouple the contributions of liquid mixture nonidealities and pure component solid-liquid equilibrium to the phase diagram. In both mixtures, the PIM accurately reproduces the liquid phase nonidealities but fails to predict the liquidus because it does not accurately predict the pure component melting temperature of LiCl or MgCl2.
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Affiliation(s)
- Ryan S DeFever
- Department of Chemical and Biomolecular Engineering, University of Notre Dame, Notre Dame, Indiana 46556, United States
| | - Edward J Maginn
- Department of Chemical and Biomolecular Engineering, University of Notre Dame, Notre Dame, Indiana 46556, United States
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7
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Blow KE, Quigley D, Sosso GC. The seven deadly sins: When computing crystal nucleation rates, the devil is in the details. J Chem Phys 2021; 155:040901. [PMID: 34340373 DOI: 10.1063/5.0055248] [Citation(s) in RCA: 19] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022] Open
Abstract
The formation of crystals has proven to be one of the most challenging phase transformations to quantitatively model-let alone to actually understand-be it by means of the latest experimental technique or the full arsenal of enhanced sampling approaches at our disposal. One of the most crucial quantities involved with the crystallization process is the nucleation rate, a single elusive number that is supposed to quantify the average probability for a nucleus of critical size to occur within a certain volume and time span. A substantial amount of effort has been devoted to attempt a connection between the crystal nucleation rates computed by means of atomistic simulations and their experimentally measured counterparts. Sadly, this endeavor almost invariably fails to some extent, with the venerable classical nucleation theory typically blamed as the main culprit. Here, we review some of the recent advances in the field, focusing on a number of perhaps more subtle details that are sometimes overlooked when computing nucleation rates. We believe it is important for the community to be aware of the full impact of aspects, such as finite size effects and slow dynamics, that often introduce inconspicuous and yet non-negligible sources of uncertainty into our simulations. In fact, it is key to obtain robust and reproducible trends to be leveraged so as to shed new light on the kinetics of a process, that of crystal nucleation, which is involved into countless practical applications, from the formulation of pharmaceutical drugs to the manufacturing of nano-electronic devices.
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Affiliation(s)
- Katarina E Blow
- Department of Physics, University of Warwick, Coventry CV4 7AL, United Kingdom
| | - David Quigley
- Department of Physics, University of Warwick, Coventry CV4 7AL, United Kingdom
| | - Gabriele C Sosso
- Department of Chemistry, University of Warwick, Coventry CV4 7AL, United Kingdom
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8
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Fang C, Loo WS, Wang R. Salt Activity Coefficient and Chain Statistics in Poly(ethylene oxide)-Based Electrolytes. Macromolecules 2021. [DOI: 10.1021/acs.macromol.0c01850] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Affiliation(s)
- Chao Fang
- Department of Chemical and Biomolecular Engineering, University of California Berkeley, Berkeley, California 94702, United States
- Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, United States
| | - Whitney S. Loo
- Department of Chemical and Biomolecular Engineering, University of California Berkeley, Berkeley, California 94702, United States
| | - Rui Wang
- Department of Chemical and Biomolecular Engineering, University of California Berkeley, Berkeley, California 94702, United States
- Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, United States
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9
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Patel LA, Yoon TJ, Currier RP, Maerzke KA. NaCl aggregation in water at elevated temperatures and pressures: Comparison of classical force fields. J Chem Phys 2021; 154:064503. [PMID: 33588550 DOI: 10.1063/5.0030962] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022] Open
Abstract
The properties of water vary dramatically with temperature and density. This can be exploited to control its effectiveness as a solvent. Thus, supercritical water is of keen interest as solvent in many extraction processes. The low solubility of salts in lower density supercritical water has even been suggested as a means of desalination. The high temperatures and pressures required to reach supercritical conditions can present experimental challenges during collection of required physical property and phase equilibria data, especially in salt-containing systems. Molecular simulations have the potential to be a valuable tool for examining the behavior of solvated ions at these high temperatures and pressures. However, the accuracy of classical force fields under these conditions is unclear. We have, therefore, undertaken a parametric study of NaCl in water, comparing several salt and water models at 200 bar-600 bar and 450 K-750 K for a range of salt concentrations. We report a comparison of structural properties including ion aggregation, hydrogen bonding, density, and static dielectric constants. All of the force fields qualitatively reproduce the trends in the liquid phase density. An increase in ion aggregation with decreasing density holds true for all of the force fields. The propensity to aggregate is primarily determined by the salt force field rather than the water force field. This coincides with a decrease in the water static dielectric constant and reduced charge screening. While a decrease in the static dielectric constant with increasing NaCl concentration is consistent across all model combinations, the salt force fields that exhibit more ionic aggregation yield a slightly smaller dielectric decrement.
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Affiliation(s)
- Lara A Patel
- Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA
| | - Tae Jun Yoon
- Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA
| | - Robert P Currier
- Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA
| | - Katie A Maerzke
- Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA
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10
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Dynamic and Static Properties of Aqueous NaCl Solutions at 25°C as a Function of NaCl Concentration: A Molecular Dynamics Simulation Study. J CHEM-NY 2020. [DOI: 10.1155/2020/6661196] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022] Open
Abstract
We present the result of molecular dynamics (MD) simulations to calculate the molar conductivity
of NaCl in SPC/E water at 25°C as a function of NaCl concentration (c) using Ewald sums employing a velocity Verlet algorithm. It is found that the MD result for Λm with Ewald sum parameter κ = 0.10 Å−1 gives the closest one to the experimental data and that the obtained radial distribution functions
(r) with κ = 0.10 Å−1 show a dramatic change with a very deep minimum of
(r) and, as a result, sharp maxima of
(r) and
(r) at the distance 9.95 Å, which indicates a characteristic of ionic atmosphere, the basis of the Debye–Hückel theory of ionic solutions. The static and dynamic properties of NaCl (aq) solutions are analyzed in terms of radial distribution functions, hydration numbers, coordination numbers around Na+ and Cl−, residence times of water around Na+ and Cl−, water diffusion, and ion-ion electrostatic energies to explain the behavior of the molar conductivity Λm of NaCl obtained from our MD simulations.
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11
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Hantal G, Horváth RA, Kolafa J, Sega M, Jedlovszky P. Surface Affinity of Alkali and Halide Ions in Their Aqueous Solution: Insight from Intrinsic Density Analysis. J Phys Chem B 2020; 124:9884-9897. [PMID: 33084342 DOI: 10.1021/acs.jpcb.0c05547] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The surface tension of all aqueous alkali halide solutions is higher than that of pure water. According to the Gibbs adsorption equation, this indicates a net depletion of these ions in the interfacial region. However, simulations and experiments show that large, soft ions, such as I-, can accumulate at the liquid/vapor interface. The presence of a loose hydration shell is usually considered to be the reason for this behavior. In this work, we perform computer simulations to characterize the liquid-vapor interface of aqueous alkali chloride and sodium halide solutions systematically, considering all ions from Li+ to Cs+ and from F- to I-. Using computational methods for the removal of surface fluctuations, we analyze the structure of the interface at a dramatically enhanced resolution, showing that the positive excess originates in the very first molecular layer and that the next 3-4 layers account for the net negative excess. With the help of a fictitious system with charge-inverted ion pairs, we also show that it is not possible to rationalize the surface affinity of ions in solutions in terms of the properties of anions and cations separately. Moreover, the surface excess is generally dominated by the smaller of the two ions.
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Affiliation(s)
- György Hantal
- Institute of Physics and Materials Science, University of Natural Resources and Life Sciences, Peter Jordan Straße 82, A-1190 Vienna, Austria
| | - Réka A Horváth
- Department of Inorganic and Analytical Chemistry, Budapest University of Technology and Economics, Szt. Gellért tér 4, H-1111 Budapest, Hungary
| | - Jiří Kolafa
- Department of Physical Chemistry, University of Chemistry and Technology, 166 28 Prague 6, Czech Republic
| | - Marcello Sega
- Forschungszentrum Jülich GmbH, Helmholtz Institute Erlangen-Nürnberg for Renewable Energy (IEK-11), Fürther Straße 248, D-90429 Nürnberg, Germany
| | - Pál Jedlovszky
- Department of Chemistry, Eszterházy Károly University, Leányka utca 6, H-3300 Eger, Hungary
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12
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Rahbari A, Hens R, Ramdin M, Moultos OA, Dubbeldam D, Vlugt TJH. Recent advances in the continuous fractional component Monte Carlo methodology. MOLECULAR SIMULATION 2020. [DOI: 10.1080/08927022.2020.1828585] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/23/2022]
Affiliation(s)
- A. Rahbari
- Engineering Thermodynamics, Process & Energy Department, Faculty of Mechanical, Maritime and Materials Engineering, Delft University of Technology, Delft, Netherlands
| | - R. Hens
- Engineering Thermodynamics, Process & Energy Department, Faculty of Mechanical, Maritime and Materials Engineering, Delft University of Technology, Delft, Netherlands
| | - M. Ramdin
- Engineering Thermodynamics, Process & Energy Department, Faculty of Mechanical, Maritime and Materials Engineering, Delft University of Technology, Delft, Netherlands
| | - O. A. Moultos
- Engineering Thermodynamics, Process & Energy Department, Faculty of Mechanical, Maritime and Materials Engineering, Delft University of Technology, Delft, Netherlands
| | - D. Dubbeldam
- Van 't Hoff Institute for Molecular Sciences, University of Amsterdam, Amsterdam, Netherlands
| | - T. J. H. Vlugt
- Engineering Thermodynamics, Process & Energy Department, Faculty of Mechanical, Maritime and Materials Engineering, Delft University of Technology, Delft, Netherlands
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13
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Kolafa J. Pressure in Molecular Simulations with Scaled Charges. 1. Ionic Systems. J Phys Chem B 2020; 124:7379-7390. [PMID: 32790401 DOI: 10.1021/acs.jpcb.0c02641] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Charge scaling, rationalized as MDEC (molecular dynamics in electronic continuum) or ECC (electronic continuum correction), has become a widely used simple approach to how to avoid self-consistent induced dipoles yet approximately take into account the effects of electronic polarizability. It has been assumed that the continuum permittivity does not depend on density; in turn, pressure is calculated by standard formulas. In this work, we elaborate a complementary approximation of density-independent molecular polarizability and derive formulas for pressure corrections within the MDEC framework; real behavior lies between these two extremes. The pressure corrections for test ionic systems are huge and negative, leading to sizable densities in constant-pressure MDEC simulations. A comparison of MDEC results with equivalent polarizable systems gives a good pressure match for a crystal but very low MDEC pressures for ionic liquids. These results witness about the importance of a correct density dependence not only of continuum permittivity in MDEC simulations but also of polarizability in polarizable simulations.
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Affiliation(s)
- Jiří Kolafa
- Department of Physical Chemistry, University of Chemistry and Technology, Prague, Technická 5, 166 28 Praha 6, Czech Republic
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14
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Kelly BD, Smith WR. A Simple Method for Including Polarization Effects in Solvation Free Energy Calculations When Using Fixed-Charge Force Fields: Alchemically Polarized Charges. ACS OMEGA 2020; 5:17170-17181. [PMID: 32715202 PMCID: PMC7376688 DOI: 10.1021/acsomega.0c01148] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 03/16/2020] [Accepted: 06/11/2020] [Indexed: 06/11/2023]
Abstract
The incorporation of polarizability in classical force-field molecular simulations is an ongoing area of research. We focus here on its application to hydration free energy simulations of organic molecules. In contrast to computationally complex approaches involving the development of explicitly polarizable force fields, we present herein a simple methodology for incorporating polarization into such simulations using standard fixed-charge force fields, which we call the alchemically polarized charges (APolQ) method. APolQ employs a standard classical alchemical free energy change simulation to calculate the free energy difference between a fully polarized solute particle in a condensed phase and its unpolarized state in a vacuum. APolQ can in principle be applied to any microscopically homogeneous system (e.g., pure or mixed solvents). We applied APolQ to hydration free energy data for a test set of 45 neutral solute molecules in the FreeSolv database and compared results obtained using three different water models (SPC/E, TIP3P, and OPC3) and using minimal basis iterative Stockholder (MBIS) and restrained electrostatic potential (RESP) partial charge methodologies. In comparison with AM1-BCC, we found that APolQ outperforms it for the test set. Despite our method using default GAFF parameters, the MBIS partial charges yield absolute average deviations 1.5-1.9 kJ mol-1 lower than using AM1 bond charge correction (AM1-BCC). We conjecture that this method can be further improved by fitting the Lennard-Jones and torsional parameters to partial charges derived using MBIS or RESP methodologies.
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Affiliation(s)
- Braden D. Kelly
- Department
of Mathematics and Statistics, University
of Guelph, Guelph, Ontario N1G 2W1, Canada
| | - William R. Smith
- Department
of Mathematics and Statistics, University
of Guelph, Guelph, Ontario N1G 2W1, Canada
- Department
of Chemical Engineering, University of Waterloo, Waterloo, Ontario N2L 3G1, Canada
- Faculty
of Science, Ontario Tech University, Oshawa, Ontario L1H 7K4, Canada
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15
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Urano R, Shinoda W, Yoshii N, Okazaki S. Exact long-range Coulombic energy calculation for net charged systems neutralized by uniformly distributed background charge using fast multipole method and its application to efficient free energy calculation. J Chem Phys 2020; 152:244115. [DOI: 10.1063/5.0007957] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Affiliation(s)
- Ryo Urano
- Department of Materials Chemistry, Nagoya University, Nagoya 464-8603, Japan
| | - Wataru Shinoda
- Department of Materials Chemistry, Nagoya University, Nagoya 464-8603, Japan
| | - Noriyuki Yoshii
- Department of Materials Chemistry, Nagoya University, Nagoya 464-8603, Japan
- Center for Computational Science, Graduate School of Engineering, Nagoya University, Nagoya 464-8603, Japan
| | - Susumu Okazaki
- Department of Materials Chemistry, Nagoya University, Nagoya 464-8603, Japan
- Center for Computational Science, Graduate School of Engineering, Nagoya University, Nagoya 464-8603, Japan
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16
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Dočkal J, Lísal M, Moučka F. Molecular Force Field Development for Aqueous Electrolytes: 2. Polarizable Models Incorporating Crystalline Chemical Potential and Their Accurate Simulations of Halite, Hydrohalite, Aqueous Solutions of NaCl, and Solubility. J Chem Theory Comput 2020; 16:3677-3688. [DOI: 10.1021/acs.jctc.0c00161] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Jan Dočkal
- Department of Physics, Faculty of Science, J. E. Purkyně University, 400 96 Ústí n. Lab., Czech Republic
| | - Martin Lísal
- Department of Physics, Faculty of Science, J. E. Purkyně University, 400 96 Ústí n. Lab., Czech Republic
- Department of Molecular and Mesoscopic Modelling, Institute of Chemical Process Fundamentals of the CAS, v. v. i., 165 02 Prague 6-Suchdol, Czech Republic
| | - Filip Moučka
- Department of Physics, Faculty of Science, J. E. Purkyně University, 400 96 Ústí n. Lab., Czech Republic
- Department of Molecular and Mesoscopic Modelling, Institute of Chemical Process Fundamentals of the CAS, v. v. i., 165 02 Prague 6-Suchdol, Czech Republic
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17
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Saric D, Kohns M, Vrabec J. Dielectric constant and density of aqueous alkali halide solutions by molecular dynamics: A force field assessment. J Chem Phys 2020; 152:164502. [PMID: 32357782 DOI: 10.1063/1.5144991] [Citation(s) in RCA: 13] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022] Open
Abstract
The concentration dependence of the dielectric constant and the density of 11 aqueous alkali halide solutions (LiCl, NaCl, KCl, RbCl, CsCl, LiI, NaI, KI, CsI, KF, and CsF) is investigated by molecular simulation. Predictions using eight non-polarizable ion force fields combined with the TIP4P/ε water model are compared to experimental data. The influence of the water model and the temperature on the results for the NaCl brine are also addressed. The TIP4P/ε water model improves the accuracy of dielectric constant predictions compared to the SPC/E water model. The solution density is predicted well by most ion models. Almost all ion force fields qualitatively capture the decline of the dielectric constant with the increase of concentration for all solutions and with the increase of temperature for NaCl brine. However, the sampled dielectric constant is mostly in poor quantitative agreement with experimental data. These results are related to the microscopic solution structure, ion pairing, and ultimately the force field parameters. Ion force fields with excessive contact ion pairing and precipitation below the experimental solubility limit generally yield higher dielectric constant values. An adequate reproduction of the experimental solubility limit should therefore be a prerequisite for further investigations of the dielectric constant of aqueous electrolyte solutions by molecular simulation.
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Affiliation(s)
- Denis Saric
- Thermodynamics and Energy Technology, University of Paderborn, 33098 Paderborn, Germany
| | - Maximilian Kohns
- Laboratory of Engineering Thermodynamics, Technische Universität Kaiserslautern, 67633 Kaiserslautern, Germany
| | - Jadran Vrabec
- Thermodynamics and Process Engineering, Technical University Berlin, 10587 Berlin, Germany
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18
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Anwar J, Leitold C, Peters B. Solid–solid phase equilibria in the NaCl–KCl system. J Chem Phys 2020; 152:144109. [DOI: 10.1063/5.0003224] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/23/2023] Open
Affiliation(s)
- Jamshed Anwar
- Department of Chemistry, Lancaster University, Lancaster LA1 4YW, United Kingdom
| | - Christian Leitold
- Department of Chemical and Biomolecular Engineering, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, USA
| | - Baron Peters
- Department of Chemical and Biomolecular Engineering, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, USA
- Department of Chemistry and Biochemistry, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, USA
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19
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Kelly BD, Smith WR. Alchemical Hydration Free-Energy Calculations Using Molecular Dynamics with Explicit Polarization and Induced Polarity Decoupling: An On–the–Fly Polarization Approach. J Chem Theory Comput 2020; 16:1146-1161. [DOI: 10.1021/acs.jctc.9b01139] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
Affiliation(s)
- Braden D. Kelly
- Department of Mathematics and Statistics, University of Guelph, Guelph, ON N1G 2W1, Canada
| | - William R. Smith
- Department of Mathematics and Statistics, University of Guelph, Guelph, ON N1G 2W1, Canada
- Department of Chemical Engineering, University of Waterloo, Waterloo, ON N2L 3G1, Canada
- Faculty of Science, Ontario Tech University, Oshawa, ON L1H 7K4, Canada
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20
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Qiao C, Zhang J, Jiang P, Zhao S, Song X, Yu J. A molecular approach for predicting phase diagrams of ternary aqueous saline solutions. Chem Eng Sci 2020. [DOI: 10.1016/j.ces.2019.115278] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/25/2022]
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21
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Lbadaoui-Darvas M, Takahama S. Water Activity from Equilibrium Molecular Dynamics Simulations and Kirkwood-Buff Theory. J Phys Chem B 2019; 123:10757-10768. [DOI: 10.1021/acs.jpcb.9b06735] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Mária Lbadaoui-Darvas
- ENAC/IIE Swiss Federal Institute of Technology Lausanne (EPFL), CH-1015 Lausanne, Switzerland
| | - Satoshi Takahama
- ENAC/IIE Swiss Federal Institute of Technology Lausanne (EPFL), CH-1015 Lausanne, Switzerland
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22
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Boothroyd S, Anwar J. Solubility prediction for a soluble organic molecule via chemical potentials from density of states. J Chem Phys 2019; 151:184113. [PMID: 31731842 DOI: 10.1063/1.5117281] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
While the solubility of a substance is a fundamental property of widespread significance, its prediction from first principles (starting from only the knowledge of the molecular structure of the solute and solvent) remains a challenge. Recently, we proposed a robust and efficient method to predict the solubility from the density of states of a solute-solvent system using classical molecular simulation. The efficiency, and indeed the generality, of the method has now been enhanced by extending it to calculate solution chemical potentials (rather than probability distributions as done previously), from which solubility may be accessed. The method has been employed to predict the chemical potential of Form 1 of urea in both water and methanol for a range of concentrations at ambient conditions and for two charge models. The chemical potential calculations were validated by thermodynamic integration with the two sets of values being in excellent agreement. The solubility determined from the chemical potentials for urea in water ranged from 0.46 to 0.50 mol kg-1, while that for urea in methanol ranged from 0.62 to 0.85 mol kg-1, over the temperature range 298-328 K. In common with other recent studies of solubility prediction from molecular simulation, the predicted solubilities differ markedly from experimental values, reflecting limitations of current forcefields.
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Affiliation(s)
- Simon Boothroyd
- Chemical Theory and Computation, Department of Chemistry, Lancaster University, Lancaster LA1 4YB, United Kingdom
| | - Jamshed Anwar
- Chemical Theory and Computation, Department of Chemistry, Lancaster University, Lancaster LA1 4YB, United Kingdom
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23
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Zeron IM, Abascal JLF, Vega C. A force field of Li +, Na +, K +, Mg 2+, Ca 2+, Cl -, and SO 4 2- in aqueous solution based on the TIP4P/2005 water model and scaled charges for the ions. J Chem Phys 2019; 151:134504. [PMID: 31594349 DOI: 10.1063/1.5121392] [Citation(s) in RCA: 125] [Impact Index Per Article: 25.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023] Open
Abstract
In this work, a force field for several ions in water is proposed. In particular, we consider the cations Li+, Na+, K+, Mg2+, and Ca2+ and the anions Cl- and SO4 2-. These ions were selected as they appear in the composition of seawater, and they are also found in biological systems. The force field proposed (denoted as Madrid-2019) is nonpolarizable, and both water molecules and sulfate anions are rigid. For water, we use the TIP4P/2005 model. The main idea behind this work is to further explore the possibility of using scaled charges for describing ionic solutions. Monovalent and divalent ions are modeled using charges of 0.85 and 1.7, respectively (in electron units). The model allows a very accurate description of the densities of the solutions up to high concentrations. It also gives good predictions of viscosities up to 3 m concentrations. Calculated structural properties are also in reasonable agreement with the experiment. We have checked that no crystallization occurred in the simulations at concentrations similar to the solubility limit. A test for ternary mixtures shows that the force field provides excellent performance at an affordable computer cost. In summary, the use of scaled charges, which could be regarded as an effective and simple way of accounting for polarization (at least to a certain extend), improves the overall description of ionic systems in water. However, for purely ionic systems, scaled charges will not adequately describe neither the solid nor the melt.
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Affiliation(s)
- I M Zeron
- Depto. Química Física, Fac. Ciencias Químicas, Universidad Complutense de Madrid, 28040 Madrid, Spain
| | - J L F Abascal
- Depto. Química Física, Fac. Ciencias Químicas, Universidad Complutense de Madrid, 28040 Madrid, Spain
| | - C Vega
- Depto. Química Física, Fac. Ciencias Químicas, Universidad Complutense de Madrid, 28040 Madrid, Spain
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24
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Moučka F, Zamfir S, Bratko D, Luzar A. Molecular polarizability in open ensemble simulations of aqueous nanoconfinements under electric field. J Chem Phys 2019; 150:164702. [PMID: 31042910 DOI: 10.1063/1.5094170] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022] Open
Abstract
Molecular polarization at aqueous interfaces involves fast degrees of freedom that are often averaged-out in atomistic-modeling approaches. The resulting effective interactions depend on a specific environment, making explicit account of molecular polarizability particularly important in solutions with pronounced anisotropic perturbations, including solid/liquid interfaces and external fields. Our work concerns polarizability effects in nanoscale confinements under electric field, open to an unperturbed bulk environment. We model aqueous molecules and ions in hydrophobic pores using the Gaussian-charge-on-spring BK3-AH representation. This involves nontrivial methodology developments in expanded ensemble Monte Carlo simulations for open systems with long-ranged multibody interactions and necessitates further improvements for efficient modeling of polarizable ions. Structural differences between fixed-charge and polarizable models were captured in molecular dynamics simulations for a set of closed systems. Our open ensemble results with the BK3 model in neat-aqueous systems capture the ∼10% reduction of molecular dipoles within the surface layer near the hydrophobic pore walls in analogy to reported quantum mechanical calculations at water/vapor interfaces. The polarizability affects the interfacial dielectric behavior and weakens the electric-field dependence of water absorption at pragmatically relevant porosities. We observe moderate changes in thermodynamic properties and atom and charged-site spatial distributions; the Gaussian distribution of mobile charges on water and ions in the polarizable model shifts the density amplitudes and blurs the charge-layering effects associated with increased ion absorption. The use of polarizable force field indicates an enhanced response of interfacial ion distributions to applied electric field, a feature potentially important for in silico modeling of electric double layer capacitors.
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Affiliation(s)
- F Moučka
- Department of Chemistry, Virginia Commonwealth University, Richmond, Virginia 23221, USA
| | - S Zamfir
- Department of Chemistry, Virginia Commonwealth University, Richmond, Virginia 23221, USA
| | - D Bratko
- Department of Chemistry, Virginia Commonwealth University, Richmond, Virginia 23221, USA
| | - A Luzar
- Department of Chemistry, Virginia Commonwealth University, Richmond, Virginia 23221, USA
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25
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Nieto-Draghi C, Rousseau B. Thermodynamically Consistent Force Field for Coarse-Grained Modeling of Aqueous Electrolyte Solution. J Phys Chem B 2019; 123:2424-2431. [DOI: 10.1021/acs.jpcb.8b11190] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Affiliation(s)
- Carlos Nieto-Draghi
- IFP Energies nouvelles, 1-4 Avenue de Bois Préau, 92852 Rueil-Malmaison, France
| | - Bernard Rousseau
- Laboratoire de Chimie Physique, UMR 8000 CNRS, Université Paris-Sud, 91405 Orsay, France
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26
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Saravi SH, Ravichandran A, Khare R, Chen CC. Bridging two-liquid theory with molecular simulations for electrolytes: An investigation of aqueous NaCl solution. AIChE J 2019. [DOI: 10.1002/aic.16521] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
Affiliation(s)
- Sina H. Saravi
- Dept. of Chemical Engineering; Texas Tech University; Lubbock TX 79409
| | | | - Rajesh Khare
- Dept. of Chemical Engineering; Texas Tech University; Lubbock TX 79409
| | - Chau-Chyun Chen
- Dept. of Chemical Engineering; Texas Tech University; Lubbock TX 79409
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27
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Kolafa J. Free Energy of Classical Molecular Crystals by Thermodynamic Integration from a Harmonic Reference. J Chem Theory Comput 2019; 15:68-77. [PMID: 30461278 DOI: 10.1021/acs.jctc.8b00674] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
We develop an algorithm for calculating the normal modes of vibration of mechanical systems with constraints, particularly of molecules with rigid bonds and models of rigid molecules, and use it to obtain the harmonic free energy of a crystal. The anharmonic correction is then calculated by the conventional thermodynamic integration over temperature in the NVT ensemble. Attention is paid to finite-size errors, tail corrections, thermostat choice, ergodicity, and other sources of inaccuracies. The calculated free energy of ice XIV modeled by the TIP4P/2005 potential agrees with the previously reported value and is by one order more accurate.
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Affiliation(s)
- Jiří Kolafa
- Department of Physical Chemistry , University of Chemistry and Technology , Technická 5 , 166 28 Praha 6 , Czech Republic
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28
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Espinosa JR, Wand CR, Vega C, Sanz E, Frenkel D. Calculation of the water-octanol partition coefficient of cholesterol for SPC, TIP3P, and TIP4P water. J Chem Phys 2018; 149:224501. [PMID: 30553262 DOI: 10.1063/1.5054056] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
We present a numerical study of the relative solubility of cholesterol in octanol and water. Our calculations allow us to compare the accuracy of the computed values of the excess chemical potential of cholesterol for several widely used water models (SPC, TIP3P, and TIP4P). We compute the excess solvation free energies by means of a cavity-based method [L. Li et al., J. Chem. Phys. 146(21), 214110 (2017)] which allows for the calculation of the excess chemical potential of a large molecule in a dense solvent phase. For the calculation of the relative solubility ("partition coefficient," log10 P o / w ) of cholesterol between octanol and water, we use the OPLS/AA force field in combination with the SPC, TIP3P, and TIP4P water models. For all water models studied, our results reproduce the experimental observation that cholesterol is less soluble in water than in octanol. While the experimental value for the partition coefficient is log10 P o / w = 3.7, SPC, TIP3P, and TIP4P give us a value of log10 P o / w = 4.5, 4.6, and 2.9, respectively. Therefore, although the results for the studied water models in combination with the OPLS/AA force field are acceptable, further work to improve the accuracy of current force fields is needed.
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Affiliation(s)
- Jorge R Espinosa
- Departamento de Quimica Fisica, Facultad de Ciencias Quimicas, Universidad Complutense de Madrid, 28040 Madrid, Spain
| | - Charlie R Wand
- Department of Chemistry, University of Cambridge, Lensfield Road, Cambridge CB2 1EW, United Kingdom
| | - Carlos Vega
- Departamento de Quimica Fisica, Facultad de Ciencias Quimicas, Universidad Complutense de Madrid, 28040 Madrid, Spain
| | - Eduardo Sanz
- Departamento de Quimica Fisica, Facultad de Ciencias Quimicas, Universidad Complutense de Madrid, 28040 Madrid, Spain
| | - Daan Frenkel
- Department of Chemistry, University of Cambridge, Lensfield Road, Cambridge CB2 1EW, United Kingdom
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29
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Svoboda M, Moučka F, Lísal M. Saturated aqueous NaCl solution and pure water in Na-montmorillonite clay at thermodynamic conditions of hydraulic fracturing: Thermodynamics, structure and diffusion from molecular simulations. J Mol Liq 2018. [DOI: 10.1016/j.molliq.2018.08.144] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
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30
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Jiang H, Debenedetti PG, Panagiotopoulos AZ. Communication: Nucleation rates of supersaturated aqueous NaCl using a polarizable force field. J Chem Phys 2018; 149:141102. [DOI: 10.1063/1.5053652] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Affiliation(s)
- Hao Jiang
- Department of Chemical and Biological Engineering, Princeton University, Princeton, New Jersey 08544, USA
| | - Pablo G. Debenedetti
- Department of Chemical and Biological Engineering, Princeton University, Princeton, New Jersey 08544, USA
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31
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Li L, Totton T, Frenkel D. Computational methodology for solubility prediction: Application to sparingly soluble organic/inorganic materials. J Chem Phys 2018; 149:054102. [PMID: 30089373 DOI: 10.1063/1.5040366] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
The solubility of a crystalline material can be estimated from the absolute free energy of the solid and the excess solvation free energy. In the earlier work, we presented a general-purpose molecular-dynamics-based methodology enabling solubility predictions of crystalline compounds, yielding accurate estimates of the aqueous solubilities of naphthalene at various pressures and temperatures. In the present work, we investigate a number of prototypical complex materials, including phenanthrene, calcite, and aragonite over a range of temperatures and pressures. Our results provide stronger evidence for the power of the methodology for universal solubility predictions.
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Affiliation(s)
- Lunna Li
- Department of Chemistry, University of Cambridge, Cambridgeshire CB2 1EW, United Kingdom
| | - Tim Totton
- BP Exploration Operating Co. Ltd., Sunbury-on-Thames TW16 7LN, United Kingdom
| | - Daan Frenkel
- Department of Chemistry, University of Cambridge, Cambridgeshire CB2 1EW, United Kingdom
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32
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Wang HW, Vlcek L, Neuefeind JC, Page K, Irle S, Simonson JM, Stack AG. Decoding Oxyanion Aqueous Solvation Structure: A Potassium Nitrate Example at Saturation. J Phys Chem B 2018; 122:7584-7589. [PMID: 29991255 DOI: 10.1021/acs.jpcb.8b05895] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
The ability to probe the structure of a salt solution at the atomic scale is fundamentally important for our understanding of many chemical reactions and their mechanisms. The capability of neutron diffraction to "see" hydrogen (or deuterium) and other light isotopes is exceptional for resolving the structural complexity around the dissolved solutes in aqueous electrolytes. We have made measurements using oxygen isotopes on aqueous nitrate to reveal a small hydrogen-bonded water coordination number (3.9 ± 1.2) around a nitrate oxyanion. This is compared to estimates made using the existing method of nitrogen isotope substitution and those of computational simulations (>5-6 water molecules). The low water coordination number, combined with a comparison to classical molecular dynamics simulations, suggests that ion-pair formation is significant. This insight demonstrates the utility of experimental diffraction data for benchmarking atomistic computer simulations, enabling the development of more accurate intermolecular potentials.
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33
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Wand CR, Totton TS, Frenkel D. Addressing hysteresis and slow equilibration issues in cavity-based calculation of chemical potentials. J Chem Phys 2018; 149:014105. [PMID: 29981554 DOI: 10.1063/1.5036963] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
In this paper, we explore the strengths and weaknesses of a cavity-based method to calculate the excess chemical potential of a large molecular solute in a dense liquid solvent. Use of the cavity alleviates some technical problems associated with the appearance of (integrable) divergences in the integrand during alchemical particle growth. The excess chemical potential calculated using the cavity-based method should be independent of the cavity attributes. However, the performance of the method (equilibration time and the robustness) does depend on the cavity attributes. To illustrate the importance of a suitable choice of the cavity attributes, we calculate the partition coefficient of pyrene in toluene and heptane using a coarse-grained model. We find that a poor choice for the functional form of the cavity may lead to hysteresis between growth and shrinkage of the cavity. Somewhat unexpectedly, we find that, by allowing the cavity to move as a pseudo-particle within the simulation box, the decay time of fluctuations in the integrand of the thermodynamic integration can be reduced by an order of magnitude, thereby increasing the statistical accuracy of the calculation.
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Affiliation(s)
- C R Wand
- Department of Chemistry, University of Cambridge, Cambridgeshire CB2 1EW, United Kingdom
| | - T S Totton
- BP Exploration Operating Co. Ltd., Sunbury-on-Thames TW16 7LN, United Kingdom
| | - D Frenkel
- Department of Chemistry, University of Cambridge, Cambridgeshire CB2 1EW, United Kingdom
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34
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Moučka F, Kolafa J, Lísal M, Smith WR. Chemical potentials of alkaline earth metal halide aqueous electrolytes and solubility of their hydrates by molecular simulation: Application to CaCl2, antarcticite, and sinjarite. J Chem Phys 2018; 148:222832. [DOI: 10.1063/1.5024212] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023] Open
Affiliation(s)
- Filip Moučka
- Department of Molecular and Mesoscopic Modelling, Institute of Chemical Process Fundamentals of the CAS, v. v. i., 165 02 Prague 6-Suchdol, Czech Republic
- Department of Physics, Faculty of Science, J. E. Purkinje University, 400 96 Ústí nad Labem, Czech Republic
| | - Jiří Kolafa
- Department of Physical Chemistry, University of Chemistry and Technology, Prague, 166 28 Praha 6, Czech Republic
| | - Martin Lísal
- Department of Molecular and Mesoscopic Modelling, Institute of Chemical Process Fundamentals of the CAS, v. v. i., 165 02 Prague 6-Suchdol, Czech Republic
- Department of Physics, Faculty of Science, J. E. Purkinje University, 400 96 Ústí nad Labem, Czech Republic
| | - William R. Smith
- Department of Mathematics and Statistics, University of Guelph, Guelph, Ontario N1G 2W1, Canada
- Department of Chemistry, University of Guelph, Guelph, Ontario N1G 2W1, Canada
- Department of Chemical Engineering, University of Waterloo, Waterloo, Ontario N2L 3G1, Canada
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35
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Zimmermann NER, Vorselaars B, Espinosa JR, Quigley D, Smith WR, Sanz E, Vega C, Peters B. NaCl nucleation from brine in seeded simulations: Sources of uncertainty in rate estimates. J Chem Phys 2018; 148:222838. [DOI: 10.1063/1.5024009] [Citation(s) in RCA: 44] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/24/2023] Open
Affiliation(s)
- Nils. E. R. Zimmermann
- Computational Research Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA
| | - Bart Vorselaars
- School of Mathematics and Physics, University of Lincoln, Brayford Pool, Lincoln LN6 7TS, United Kingdom
| | - Jorge R. Espinosa
- Departmento de Quimica-Fisica I, Facultad de Ciencias Quimicas, Universidad Complutense de Madrid, 28040 Madrid, Spain
| | - David Quigley
- Department of Physics, University of Warwick, Gibbet Hill Road, Coventry CV4 7AL, United Kingdom
| | - William R. Smith
- Department of Mathematics and Statistics, University of Guelph, Guelph, Ontario N1G2W1, Canada
- Department of Chemistry, University of Guelph, Guelph, Ontario N1G2W1, Canada
| | - Eduardo Sanz
- Departmento de Quimica-Fisica I, Facultad de Ciencias Quimicas, Universidad Complutense de Madrid, 28040 Madrid, Spain
| | - Carlos Vega
- Departmento de Quimica-Fisica I, Facultad de Ciencias Quimicas, Universidad Complutense de Madrid, 28040 Madrid, Spain
| | - Baron Peters
- Department of Chemical Engineering, University of California, Santa Barbara, California 93106, USA
- Department of Chemistry and Biochemistry, University of California, Santa Barbara, California 93106, USA
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36
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Li L, Totton T, Frenkel D. Computational methodology for solubility prediction: Application to the sparingly soluble solutes. J Chem Phys 2018; 146:214110. [PMID: 28595415 DOI: 10.1063/1.4983754] [Citation(s) in RCA: 54] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
The solubility of a crystalline substance in the solution can be estimated from its absolute solid free energy and excess solvation free energy. Here, we present a numerical method, which enables convenient solubility estimation of general molecular crystals at arbitrary thermodynamic conditions where solid and solution can coexist. The methodology is based on standard alchemical free energy methods, such as thermodynamic integration and free energy perturbation, and consists of two parts: (1) systematic extension of the Einstein crystal method to calculate the absolute solid free energies of molecular crystals at arbitrary temperatures and pressures and (2) a flexible cavity method that can yield accurate estimates of the excess solvation free energies. As an illustration, via classical Molecular Dynamic simulations, we show that our approach can predict the solubility of OPLS-AA-based (Optimized Potentials for Liquid Simulations All Atomic) naphthalene in SPC (Simple Point Charge) water in good agreement with experimental data at various temperatures and pressures. Because the procedure is simple and general and only makes use of readily available open-source software, the methodology should provide a powerful tool for universal solubility prediction.
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Affiliation(s)
- Lunna Li
- Department of Chemistry, University of Cambridge, Cambridgeshire CB2 1EW, United Kingdom
| | - Tim Totton
- BP Exploration Operating Co. Ltd., Sunbury-on-Thames TW16 7LN, United Kingdom
| | - Daan Frenkel
- Department of Chemistry, University of Cambridge, Cambridgeshire CB2 1EW, United Kingdom
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37
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Ross GA, Rustenburg AS, Grinaway PB, Fass J, Chodera JD. Biomolecular Simulations under Realistic Macroscopic Salt Conditions. J Phys Chem B 2018; 122:5466-5486. [PMID: 29649876 PMCID: PMC6078207 DOI: 10.1021/acs.jpcb.7b11734] [Citation(s) in RCA: 59] [Impact Index Per Article: 9.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023]
Abstract
Biomolecular simulations are typically performed in an aqueous environment where the number of ions remains fixed for the duration of the simulation, generally with either a minimally neutralizing ion environment or a number of salt pairs intended to match the macroscopic salt concentration. In contrast, real biomolecules experience local ion environments where the salt concentration is dynamic and may differ from bulk. The degree of salt concentration variability and average deviation from the macroscopic concentration remains, as yet, unknown. Here, we describe the theory and implementation of a Monte Carlo osmostat that can be added to explicit solvent molecular dynamics or Monte Carlo simulations to sample from a semigrand canonical ensemble in which the number of salt pairs fluctuates dynamically during the simulation. The osmostat reproduces the correct equilibrium statistics for a simulation volume that can exchange ions with a large reservoir at a defined macroscopic salt concentration. To achieve useful Monte Carlo acceptance rates, the method makes use of nonequilibrium candidate Monte Carlo (NCMC) moves in which monovalent ions and water molecules are alchemically transmuted using short nonequilibrium trajectories, with a modified Metropolis-Hastings criterion ensuring correct equilibrium statistics for an ( Δμ, N, p, T) ensemble to achieve a ∼1046× boost in acceptance rates. We demonstrate how typical protein (DHFR and the tyrosine kinase Src) and nucleic acid (Drew-Dickerson B-DNA dodecamer) systems exhibit salt concentration distributions that significantly differ from fixed-salt bulk simulations and display fluctuations that are on the same order of magnitude as the average.
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Affiliation(s)
- Gregory A. Ross
- Computational and Systems Biology Program, Sloan Kettering Institute, Memorial Sloan Kettering Cancer Center, New York, NY 10065
- Present address: Schrödinger, New York, NY 10036
| | - Ariën S. Rustenburg
- Computational and Systems Biology Program, Sloan Kettering Institute, Memorial Sloan Kettering Cancer Center, New York, NY 10065
- Graduate Program in Physiology, Biophysics, and Systems Biology, Weill Cornell Medical College, New York, NY 10065
| | - Patrick B. Grinaway
- Computational and Systems Biology Program, Sloan Kettering Institute, Memorial Sloan Kettering Cancer Center, New York, NY 10065
- Graduate Program in Physiology, Biophysics, and Systems Biology, Weill Cornell Medical College, New York, NY 10065
| | - Josh Fass
- Computational and Systems Biology Program, Sloan Kettering Institute, Memorial Sloan Kettering Cancer Center, New York, NY 10065
- Tri-Institutional Training Program in Computational Biology and Medicine, New York, NY 10065
| | - John D. Chodera
- Computational and Systems Biology Program, Sloan Kettering Institute, Memorial Sloan Kettering Cancer Center, New York, NY 10065
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38
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Water Activity and Freezing Points in Aqueous Solutions of Manganese Nitrate: Experimental and Modeling. J SOLUTION CHEM 2018. [DOI: 10.1007/s10953-018-0753-9] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
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39
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Zhang L, Wang J, Wang H, Wang W, Li Z, Liu J, Yang X, Ji X, Luo Y, Hu C, Hou Y, He Q, Fang J, Wang J, Liu Q, Li G, Lu Q, Zhang X. Moderate and strong static magnetic fields directly affect EGFR kinase domain orientation to inhibit cancer cell proliferation. Oncotarget 2018; 7:41527-41539. [PMID: 27223425 PMCID: PMC5173076 DOI: 10.18632/oncotarget.9479] [Citation(s) in RCA: 32] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/09/2016] [Accepted: 04/27/2016] [Indexed: 01/23/2023] Open
Abstract
Static magnetic fields (SMFs) can affect cell proliferation in a cell-type and intensity-dependent way but the mechanism remains unclear. At the same time, although the diamagnetic anisotropy of proteins has been proposed decades ago, the behavior of isolated proteins in magnetic fields has not been directly observed. Here we show that SMFs can affect isolated proteins at the single molecular level in an intensity-dependent manner. We found that Epidermal Growth Factor Receptor (EGFR), a protein that is overexpressed and highly activated in multiple cancers, can be directly inhibited by SMFs. Using Liquid-phase Scanning Tunneling Microscopy (STM) to examine pure EGFR kinase domain proteins at the single molecule level in solution, we observed orientation changes of these proteins in response to SMFs. This may interrupt inter-molecular interactions between EGFR monomers, which are critical for their activation. In molecular dynamics (MD) simulations, 1-9T SMFs caused increased probability of EGFR in parallel with the magnetic field direction in an intensity-dependent manner. A superconducting ultrastrong 9T magnet reduced proliferation of CHO-EGFR cells (Chinese Hamster Ovary cells with EGFR overexpression) and EGFR-expressing cancer cell lines by ~35%, but minimally affected CHO cells. We predict that similar effects of magnetic fields can also be applied to some other proteins such as ion channels. Our paper will help clarify some dilemmas in this field and encourage further investigations in order to achieve a better understanding of the biological effects of SMFs.
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Affiliation(s)
- Lei Zhang
- High Magnetic Field Laboratory, Chinese Academy of Sciences and University of Science and Technology of China, Hefei, Anhui 230026, China
| | - Jihao Wang
- High Magnetic Field Laboratory, Chinese Academy of Sciences and University of Science and Technology of China, Hefei, Anhui 230026, China.,Hefei National Laboratory for Physical Sciences at The Microscale, University of Science and Technology of China, Hefei, Anhui 230026, China
| | - HongLei Wang
- Laboratory of Molecular Modeling and Design, State Key Laboratory of Molecular Reaction Dynamics, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian, Liaoning 116023, China
| | - Wenchao Wang
- High Magnetic Field Laboratory, Chinese Academy of Sciences and University of Science and Technology of China, Hefei, Anhui 230026, China
| | - Zhiyuan Li
- High Magnetic Field Laboratory, Chinese Academy of Sciences and University of Science and Technology of China, Hefei, Anhui 230026, China
| | - Juanjuan Liu
- High Magnetic Field Laboratory, Chinese Academy of Sciences and University of Science and Technology of China, Hefei, Anhui 230026, China
| | - Xingxing Yang
- High Magnetic Field Laboratory, Chinese Academy of Sciences and University of Science and Technology of China, Hefei, Anhui 230026, China
| | - Xinmiao Ji
- High Magnetic Field Laboratory, Chinese Academy of Sciences and University of Science and Technology of China, Hefei, Anhui 230026, China
| | - Yan Luo
- High Magnetic Field Laboratory, Chinese Academy of Sciences and University of Science and Technology of China, Hefei, Anhui 230026, China
| | - Chen Hu
- High Magnetic Field Laboratory, Chinese Academy of Sciences and University of Science and Technology of China, Hefei, Anhui 230026, China
| | - Yubin Hou
- High Magnetic Field Laboratory, Chinese Academy of Sciences and University of Science and Technology of China, Hefei, Anhui 230026, China
| | - Qianqian He
- High Magnetic Field Laboratory, Chinese Academy of Sciences and University of Science and Technology of China, Hefei, Anhui 230026, China
| | - Jun Fang
- High Magnetic Field Laboratory, Chinese Academy of Sciences and University of Science and Technology of China, Hefei, Anhui 230026, China
| | - Junfeng Wang
- High Magnetic Field Laboratory, Chinese Academy of Sciences and University of Science and Technology of China, Hefei, Anhui 230026, China
| | - Qingsong Liu
- High Magnetic Field Laboratory, Chinese Academy of Sciences and University of Science and Technology of China, Hefei, Anhui 230026, China
| | - Guohui Li
- Laboratory of Molecular Modeling and Design, State Key Laboratory of Molecular Reaction Dynamics, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian, Liaoning 116023, China
| | - Qingyou Lu
- High Magnetic Field Laboratory, Chinese Academy of Sciences and University of Science and Technology of China, Hefei, Anhui 230026, China.,Hefei National Laboratory for Physical Sciences at The Microscale, University of Science and Technology of China, Hefei, Anhui 230026, China.,Collaborative Innovation Center of Advanced Microstructure, Nanjing University, Nanjing, Jiangsu 210093, China
| | - Xin Zhang
- High Magnetic Field Laboratory, Chinese Academy of Sciences and University of Science and Technology of China, Hefei, Anhui 230026, China
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40
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Young JM, Panagiotopoulos AZ. System-Size Dependence of Electrolyte Activity Coefficients in Molecular Simulations. J Phys Chem B 2018; 122:3330-3338. [DOI: 10.1021/acs.jpcb.7b09861] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Jeffrey M. Young
- Department of Chemical and Biological Engineering, Princeton University, Princeton, New Jersey 08544, United States
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41
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Wang C, Ren P, Luo R. Ionic Solution: What Goes Right and Wrong with Continuum Solvation Modeling. J Phys Chem B 2017; 121:11169-11179. [PMID: 29164898 DOI: 10.1021/acs.jpcb.7b09616] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Solvent-mediated electrostatic interactions were well recognized to be important in the structure and function of molecular systems. Ionic interaction is an important component in electrostatic interactions, especially in highly charged molecules, such as nucleic acids. Here, we focus on the quality of the widely used Poisson-Boltzmann surface area (PBSA) continuum models in modeling ionic interactions by comparing with both explicit solvent simulations and the experiment. In this work, the molality-dependent chemical potentials for sodium chloride (NaCl) electrolyte were first simulated in the SPC/E explicit solvent. Our high-quality simulation agrees well with both the previous study and the experiment. Given the free-energy simulations in SPC/E as the benchmark, we used the same sets of snapshots collected in the SPC/E solvent model for PBSA free-energy calculations in the hope to achieve the maximum consistency between the two solvent models. Our comparative analysis shows that the molality-dependent chemical potentials of NaCl were reproduced well with both linear PB and nonlinear PB methods, although nonlinear PB agrees better with SPC/E and the experiment. Our free-energy simulations also show that the presence of salt increases the hydrophobic effect in a nonlinear fashion, in qualitative agreement with previous theoretical studies of Onsager and Samaras. However, the lack of molality-dependency in the nonelectrostatics continuum models dramatically reduces the overall quality of PBSA methods in modeling salt-dependent energetics. These analyses point to further improvements needed for more robust modeling of solvent-mediated interactions by the continuum solvation frameworks.
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Affiliation(s)
| | - Pengyu Ren
- Department of Biomedical Engineering, University of Texas , Austin, Texas 78712, United States
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42
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Ross GA, Bruce Macdonald HE, Cave-Ayland C, Cabedo Martinez AI, Essex JW. Replica-Exchange and Standard State Binding Free Energies with Grand Canonical Monte Carlo. J Chem Theory Comput 2017; 13:6373-6381. [PMID: 29091438 PMCID: PMC5729546 DOI: 10.1021/acs.jctc.7b00738] [Citation(s) in RCA: 34] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
![]()
The
ability of grand canonical Monte Carlo (GCMC) to create and
annihilate molecules in a given region greatly aids the identification
of water sites and water binding free energies in protein cavities.
However, acceptance rates without the application of biased moves
can be low, resulting in large variations in the observed water occupancies.
Here, we show that replica-exchange of the chemical potential significantly
reduces the variance of the GCMC data. This improvement comes at a
negligible increase in computational expense when simulations comprise
of runs at different chemical potentials. Replica-exchange GCMC is
also found to substantially increase the precision of water binding
free energies as calculated with grand canonical integration, which
has allowed us to address a missing standard state correction.
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Affiliation(s)
- Gregory A Ross
- Computational and Systems Biology Program, Sloan Kettering Institute, Memorial Sloan Kettering Cancer Center , New York, New York 10065, United States
| | | | | | - Ana I Cabedo Martinez
- Department of Chemistry, University of Southampton , Southampton, SO17 1BJ, United Kingdom
| | - Jonathan W Essex
- Department of Chemistry, University of Southampton , Southampton, SO17 1BJ, United Kingdom
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43
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Benavides AL, Portillo MA, Chamorro VC, Espinosa JR, Abascal JLF, Vega C. A potential model for sodium chloride solutions based on the TIP4P/2005 water model. J Chem Phys 2017; 147:104501. [DOI: 10.1063/1.5001190] [Citation(s) in RCA: 60] [Impact Index Per Article: 8.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Affiliation(s)
- A. L. Benavides
- Departamento de Ingeniería Física, División de Ciencias e Ingenierías, Universidad de Guanajuato, Loma del Bosque 103, Col. Lomas del Campestre, CP 37150 León, Mexico
| | - M. A. Portillo
- Departamento de Química Física I, Facultad de Ciencias Químicas, Universidad Complutense de Madrid, 28040 Madrid, Spain
| | - V. C. Chamorro
- Departamento de Química Física I, Facultad de Ciencias Químicas, Universidad Complutense de Madrid, 28040 Madrid, Spain
| | - J. R. Espinosa
- Departamento de Química Física I, Facultad de Ciencias Químicas, Universidad Complutense de Madrid, 28040 Madrid, Spain
| | - J. L. F. Abascal
- Departamento de Química Física I, Facultad de Ciencias Químicas, Universidad Complutense de Madrid, 28040 Madrid, Spain
| | - C. Vega
- Departamento de Química Física I, Facultad de Ciencias Químicas, Universidad Complutense de Madrid, 28040 Madrid, Spain
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44
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Mullen RG, Maginn EJ. Reaction Ensemble Monte Carlo Simulation of Xylene Isomerization in Bulk Phases and under Confinement. J Chem Theory Comput 2017; 13:4054-4062. [DOI: 10.1021/acs.jctc.7b00498] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Ryan Gotchy Mullen
- Department of Chemical and
Biomolecular Engineering, University of Notre Dame, Notre Dame, Indiana, United States
| | - Edward J. Maginn
- Department of Chemical and
Biomolecular Engineering, University of Notre Dame, Notre Dame, Indiana, United States
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45
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Noroozi J, Paluch AS. Microscopic Structure and Solubility Predictions of Multifunctional Solids in Supercritical Carbon Dioxide: A Molecular Simulation Study. J Phys Chem B 2017; 121:1660-1674. [DOI: 10.1021/acs.jpcb.6b12390] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Javad Noroozi
- Department
of Chemical and Petroleum Engineering, Sharif University of Technology, Tehran, Iran
| | - Andrew S. Paluch
- Department
of Chemical, Paper and Biomedical Engineering, Miami University, Oxford, Ohio 45056, United States
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46
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Cox CE, Phifer JR, Ferreira da Silva L, Gonçalves Nogueira G, Ley RT, O’Loughlin EJ, Pereira Barbosa AK, Rygelski BT, Paluch AS. Combining MOSCED with molecular simulation free energy calculations or electronic structure calculations to develop an efficient tool for solvent formulation and selection. J Comput Aided Mol Des 2017; 31:183-199. [DOI: 10.1007/s10822-016-0001-6] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/27/2016] [Accepted: 12/16/2016] [Indexed: 11/28/2022]
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47
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Affiliation(s)
- Mónika Valiskó
- Department of Physical Chemistry, University of Pannonia, Veszprém, Hungary
| | - Dezső Boda
- Department of Physical Chemistry, University of Pannonia, Veszprém, Hungary
- Institute of Advanced Studies Kőszeg (iASK), Kőszeg, Hungary
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48
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Moučka F, Svoboda M, Lísal M. Modelling aqueous solubility of sodium chloride in clays at thermodynamic conditions of hydraulic fracturing by molecular simulations. Phys Chem Chem Phys 2017; 19:16586-16599. [DOI: 10.1039/c7cp02121f] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023]
Abstract
To address the high salinity of flow-back water during hydraulic fracturing, we have studied the equilibrium partitioning of NaCl and water between the bulk phase and clay pores.
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Affiliation(s)
- Filip Moučka
- Laboratory of Aerosols Chemistry and Physics
- Institute of Chemical Process Fundamentals of the CAS, v. v. i
- 165 02 Prague 6-Suchdol
- Czech Republic
- Department of Physics
| | - Martin Svoboda
- Laboratory of Aerosols Chemistry and Physics
- Institute of Chemical Process Fundamentals of the CAS, v. v. i
- 165 02 Prague 6-Suchdol
- Czech Republic
- Department of Physics
| | - Martin Lísal
- Laboratory of Aerosols Chemistry and Physics
- Institute of Chemical Process Fundamentals of the CAS, v. v. i
- 165 02 Prague 6-Suchdol
- Czech Republic
- Department of Physics
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49
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Kolafa J. Solubility of NaCl in water and its melting point by molecular dynamics in the slab geometry and a new BK3-compatible force field. J Chem Phys 2016; 145:204509. [DOI: 10.1063/1.4968045] [Citation(s) in RCA: 36] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023] Open
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50
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Benavides AL, Aragones JL, Vega C. Consensus on the solubility of NaCl in water from computer simulations using the chemical potential route. J Chem Phys 2016; 144:124504. [PMID: 27036458 DOI: 10.1063/1.4943780] [Citation(s) in RCA: 83] [Impact Index Per Article: 10.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022] Open
Abstract
The solubility of NaCl in water is evaluated by using three force field models: Joung-Cheatham for NaCl dissolved in two different water models (SPC/E and TIP4P/2005) and Smith Dang NaCl model in SPC/E water. The methodology based on free-energy calculations [E. Sanz and C. Vega, J. Chem. Phys. 126, 014507 (2007)] and [J. L. Aragones et al., J. Chem. Phys. 136, 244508 (2012)] has been used, except, that all calculations for the NaCl in solution were obtained by using molecular dynamics simulations with the GROMACS package instead of homemade MC programs. We have explored new lower molalities and made longer runs to improve the accuracy of the calculations. Exploring the low molality region allowed us to obtain an analytical expression for the chemical potential of the ions in solution as a function of molality valid for a wider range of molalities, including the infinite dilute case. These new results are in better agreement with recent estimations of the solubility obtained with other methodologies. Besides, two empirical simple rules have been obtained to have a rough estimate of the solubility of a certain model, by analyzing the ionic pairs formation as a function of molality and/or by calculating the difference between the NaCl solid chemical potential and the standard chemical potential of the salt in solution.
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Affiliation(s)
- A L Benavides
- Departamento de Química Física, Facultad de Ciencias Químicas, Universidad Complutense de Madrid, 28040 Madrid, Spain
| | - J L Aragones
- Department of Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA
| | - C Vega
- Departamento de Química Física, Facultad de Ciencias Químicas, Universidad Complutense de Madrid, 28040 Madrid, Spain
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