1
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Tolokh IS, Folescu DE, Onufriev AV. Inclusion of Water Multipoles into the Implicit Solvation Framework Leads to Accuracy Gains. J Phys Chem B 2024; 128:5855-5873. [PMID: 38860842 PMCID: PMC11194828 DOI: 10.1021/acs.jpcb.4c00254] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/12/2024] [Revised: 05/28/2024] [Accepted: 05/29/2024] [Indexed: 06/12/2024]
Abstract
The current practical "workhorses" of the atomistic implicit solvation─the Poisson-Boltzmann (PB) and generalized Born (GB) models─face fundamental accuracy limitations. Here, we propose a computationally efficient implicit solvation framework, the Implicit Water Multipole GB (IWM-GB) model, that systematically incorporates the effects of multipole moments of water molecules in the first hydration shell of a solute, beyond the dipole water polarization already present at the PB/GB level. The framework explicitly accounts for coupling between polar and nonpolar contributions to the total solvation energy, which is missing from many implicit solvation models. An implementation of the framework, utilizing the GAFF force field and AM1-BCC atomic partial charges model, is parametrized and tested against the experimental hydration free energies of small molecules from the FreeSolv database. The resulting accuracy on the test set (RMSE ∼ 0.9 kcal/mol) is 12% better than that of the explicit solvation (TIP3P) treatment, which is orders of magnitude slower. We also find that the coupling between polar and nonpolar parts of the solvation free energy is essential to ensuring that several features of the IWM-GB model are physically meaningful, including the sign of the nonpolar contributions.
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Affiliation(s)
- Igor S. Tolokh
- Department
of Computer Science, Virginia Tech, Blacksburg, Virginia 24061, United States
| | - Dan E. Folescu
- Department
of Computer Science, Virginia Tech, Blacksburg, Virginia 24061, United States
- Department
of Mathematics, Virginia Tech, Blacksburg, Virginia 24061, United States
| | - Alexey V. Onufriev
- Department
of Computer Science, Virginia Tech, Blacksburg, Virginia 24061, United States
- Department
of Physics, Virginia Tech, Blacksburg, Virginia 24061, United States
- Center
for Soft Matter and Biological Physics, Virginia Tech, Blacksburg, Virginia 24061, United States
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2
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Bass L, Elder LH, Folescu DE, Forouzesh N, Tolokh IS, Karpatne A, Onufriev AV. Improving the Accuracy of Physics-Based Hydration-Free Energy Predictions by Machine Learning the Remaining Error Relative to the Experiment. J Chem Theory Comput 2024; 20:396-410. [PMID: 38149593 PMCID: PMC10950260 DOI: 10.1021/acs.jctc.3c00981] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2023]
Abstract
The accuracy of computational models of water is key to atomistic simulations of biomolecules. We propose a computationally efficient way to improve the accuracy of the prediction of hydration-free energies (HFEs) of small molecules: the remaining errors of the physics-based models relative to the experiment are predicted and mitigated by machine learning (ML) as a postprocessing step. Specifically, the trained graph convolutional neural network attempts to identify the "blind spots" in the physics-based model predictions, where the complex physics of aqueous solvation is poorly accounted for, and partially corrects for them. The strategy is explored for five classical solvent models representing various accuracy/speed trade-offs, from the fast analytical generalized Born (GB) to the popular TIP3P explicit solvent model; experimental HFEs of small neutral molecules from the FreeSolv set are used for the training and testing. For all of the models, the ML correction reduces the resulting root-mean-square error relative to the experiment for HFEs of small molecules, without significant overfitting and with negligible computational overhead. For example, on the test set, the relative accuracy improvement is 47% for the fast analytical GB, making it, after the ML correction, almost as accurate as uncorrected TIP3P. For the TIP3P model, the accuracy improvement is about 39%, bringing the ML-corrected model's accuracy below the 1 kcal/mol threshold. In general, the relative benefit of the ML corrections is smaller for more accurate physics-based models, reaching the lower limit of about 20% relative accuracy gain compared with that of the physics-based treatment alone. The proposed strategy of using ML to learn the remaining error of physics-based models offers a distinct advantage over training ML alone directly on reference HFEs: it preserves the correct overall trend, even well outside of the training set.
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Affiliation(s)
- Lewis Bass
- Department of Computer Engineering, Virginia Tech, Blacksburg, Virginia 24061, United States
| | - Luke H Elder
- Department of Computer Science, Virginia Tech, Blacksburg, Virginia 24061, United States
| | - Dan E Folescu
- Department of Computer Science, Virginia Tech, Blacksburg, Virginia 24061, United States
- Department of Mathematics, Virginia Tech, Blacksburg, Virginia 24061, United States
| | - Negin Forouzesh
- Department of Computer Science, California State University, Los Angeles, California 90032, United States
| | - Igor S Tolokh
- Department of Computer Science, Virginia Tech, Blacksburg, Virginia 24061, United States
| | - Anuj Karpatne
- Department of Computer Science, Virginia Tech, Blacksburg, Virginia 24061, United States
| | - Alexey V Onufriev
- Department of Computer Science, Virginia Tech, Blacksburg, Virginia 24061, United States
- Department of Physics, Virginia Tech, Blacksburg, Virginia 24061, United States
- Center for Soft Matter and Biological Physics, Virginia Tech, Blacksburg, Virginia 24061, United States
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3
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Kalayan J, Chakravorty A, Warwicker J, Henchman RH. Total free energy analysis of fully hydrated proteins. Proteins 2023; 91:74-90. [PMID: 35964252 PMCID: PMC10087023 DOI: 10.1002/prot.26411] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/28/2022] [Revised: 08/04/2022] [Accepted: 08/09/2022] [Indexed: 12/15/2022]
Abstract
The total free energy of a hydrated biomolecule and its corresponding decomposition of energy and entropy provides detailed information about regions of thermodynamic stability or instability. The free energies of four hydrated globular proteins with different net charges are calculated from a molecular dynamics simulation, with the energy coming from the system Hamiltonian and entropy using multiscale cell correlation. Water is found to be most stable around anionic residues, intermediate around cationic and polar residues, and least stable near hydrophobic residues, especially when more buried, with stability displaying moderate entropy-enthalpy compensation. Conversely, anionic residues in the proteins are energetically destabilized relative to singly solvated amino acids, while trends for other residues are less clear-cut. Almost all residues lose intraresidue entropy when in the protein, enthalpy changes are negative on average but may be positive or negative, and the resulting overall stability is moderate for some proteins and negligible for others. The free energy of water around single amino acids is found to closely match existing hydrophobicity scales. Regarding the effect of secondary structure, water is slightly more stable around loops, of intermediate stability around β strands and turns, and least stable around helices. An interesting asymmetry observed is that cationic residues stabilize a residue when bonded to its N-terminal side but destabilize it when on the C-terminal side, with a weaker reversed trend for anionic residues.
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Affiliation(s)
- Jas Kalayan
- Division of Pharmacy and Optometry, Faculty of Biology, Medicine and Health, University of Manchester, Manchester, UK
| | - Arghya Chakravorty
- Department of Chemistry and Biophysics, University of Michigan, Ann Arbor, Michigan, USA
| | - Jim Warwicker
- Manchester Institute of Biotechnology and School of Biological Sciences, Faculty of Biology, Medicine and Health, University of Manchester, Manchester, UK
| | - Richard H Henchman
- Sydney Medical School, Faculty of Medicine and Health, University of Sydney, Sydney, Australia
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4
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Caruso A, Zhu X, Fulton JL, Paesani F. Accurate Modeling of Bromide and Iodide Hydration with Data-Driven Many-Body Potentials. J Phys Chem B 2022; 126:8266-8278. [PMID: 36214512 DOI: 10.1021/acs.jpcb.2c04698] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
Abstract
Ion-water interactions play a central role in determining the properties of aqueous systems in a wide range of environments. However, a quantitative understanding of how the hydration properties of ions evolve from small aqueous clusters to bulk solutions and interfaces remains elusive. Here, we introduce the second generation of data-driven many-body energy (MB-nrg) potential energy functions (PEFs) representing bromide-water and iodide-water interactions. The MB-nrg PEFs use permutationally invariant polynomials to reproduce two-body and three-body energies calculated at the coupled cluster level of theory, and implicitly represent all higher-body energies using classical many-body polarization. A systematic analysis of the hydration structure of small Br-(H2O)n and I-(H2O)n clusters demonstrates that the MB-nrg PEFs predict interaction energies in quantitative agreement with "gold standard" coupled cluster reference values. Importantly, when used in molecular dynamics simulations carried out in the isothermal-isobaric ensemble for single bromide and iodide ions in liquid water, the MB-nrg PEFs predict extended X-ray absorption fine structure (EXAFS) spectra that accurately reproduce the experimental spectra, which thus allows for characterizing the hydration structure of the two ions with a high level of confidence.
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Affiliation(s)
- Alessandro Caruso
- Department of Chemistry and Biochemistry, University of California San Diego, La Jolla, California92093, United States
| | - Xuanyu Zhu
- Department of Chemistry and Biochemistry, University of California San Diego, La Jolla, California92093, United States
| | - John L Fulton
- Physical and Computational Sciences Directorate, Pacific Northwest National Laboratory, Richland, Washington99352, United States
| | - Francesco Paesani
- Department of Chemistry and Biochemistry, University of California San Diego, La Jolla, California92093, United States.,Materials Science and Engineering, University of California San Diego, La Jolla, California92093, United States.,San Diego Supercomputer Center, University of California San Diego, La Jolla, California92093, United States
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5
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Rahimi AM, Jamali S, Bardhan JP, Lustig SR. Solvation Thermodynamics of Solutes in Water and Ionic Liquids Using the Multiscale Solvation-Layer Interface Condition Continuum Model. J Chem Theory Comput 2022; 18:5539-5558. [PMID: 36001344 DOI: 10.1021/acs.jctc.2c00248] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Molecular assembly processes are generally driven by thermodynamic properties in solutions. Atomistic modeling can be very helpful in designing and understanding complex systems, except that bulk solvent is very inefficient to treat explicitly as discrete molecules. In this work, we develop and assess two multiscale solvation models for computing solvation thermodynamic properties. The new SLIC/CDC model combines continuum solvent electrostatics based on the solvent layer interface condition (SLIC) with new statistical thermodynamic models for hydrogen bonding and nonpolar modes: cavity formation, dispersion interactions, combinatorial mixing (CDC). Given the structures of 500 solutes, the SLIC/CDC model predicts Gibbs energies of solvation in water with an average accuracy better than 1 kcal/mol, when compared to experimental measurements, and better than 0.8 kcal/mol, when compared to explicit-solvent molecular dynamics simulations. The individual SLIC/CDC energy mode values agree quantitatively with those computed from explicit-solvent molecular dynamics. The previously published SLIC/SASA multiscale model combines the SLIC continuum electrostatic model with the solvent-accessible surface area (SASA) nonpolar energy mode. With our new, improved parametrization method, the SLIC/SASA model now predicts Gibbs energies of solvation with better than 1.4 kcal/mol average accuracy in aqueous systems, compared to experimental and explicit-solvent molecular dynamics, and better than 1.6 kcal/mol average accuracy in ionic liquids, compared to explicit-solvent molecular dynamics. Both models predict solvation entropies, and are the first implicit-solvation models capable of predicting solvation heat capacities.
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Affiliation(s)
- Ali Mehdizadeh Rahimi
- Department of Mechanical and Industrial Engineering, Northeastern University, 360 Huntington Ave., Boston Massachusetts 02115, United States
| | - Safa Jamali
- Department of Mechanical and Industrial Engineering, Northeastern University, 360 Huntington Ave., Boston Massachusetts 02115, United States
| | - Jaydeep P Bardhan
- Pacific Northwest National Laboratory, 902 Battelle Blvd., Richland, Washington 99354, United States
| | - Steven R Lustig
- Department of Chemical Engineering, Northeastern University, 360 Huntington Ave., Boston, Massachusetts 02115, United States
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6
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Nizomov Z, Asozoda M, Nematov D. Characteristics of Nanoparticles in Aqueous Solutions of Acetates and Sulfates of Single and Doubly Charged Cations. ARABIAN JOURNAL FOR SCIENCE AND ENGINEERING 2022. [DOI: 10.1007/s13369-022-07128-2] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
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7
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Zhu J, Xu P, Zhao E, Zhang X, Li X, Li J. The impacts of net charge on the water dispersity of nanoparticles. J Mol Liq 2022. [DOI: 10.1016/j.molliq.2021.117105] [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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8
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Zhang J, Wang F, Cao Z, Wang Q. New State-Diagram of Aqueous Solutions Unveiling Ionic Hydration, Antiplasticization, and Structural Heterogeneities in LiTFSI-H 2O. J Phys Chem B 2021; 125:13041-13048. [PMID: 34788045 DOI: 10.1021/acs.jpcb.1c08431] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Here, we report a new state-diagram for aqueous solutions based on concentration-dependent glass-transition temperatures of concentrated and ice freeze-concentrated solutions. Different from the equilibrium phase diagram, this new state-diagram can provide comprehensive information about the hydration numbers of solutes, nonequilibrium vitrification/cold-crystallization, and vitrification/devitrification processes of aqueous solutions in three distinct concentration zones separated by two critical water-content points of only functions of the hydration number. Based on this new state-diagram, we observe the comparable hydration ability of LiTFSI to LiCl and an atypical concentration-dependent cold-crystallization behavior of the LiTFSI-H2O system. These results unveil the negligible hydration ability of TFSI- in a water-rich solution, characterize the antiplasticizing effect of water induced by the strengthened Li+-TFSI--H2O interaction when only hydration water and confined water are present, and confirm the increasing fraction of water-rich domains with the decrease in water content when the cation and anion become incompletely hydrated on average. These results highlight the novel water-content-mediated interactions among the anion, cation, and H2O for LiTFSI-H2O.
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Affiliation(s)
- Jinbing Zhang
- School of Mathematics and Physics, University of Science and Technology Beijing, Beijing 100083, China.,Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China
| | - Fengping Wang
- School of Mathematics and Physics, University of Science and Technology Beijing, Beijing 100083, China
| | - Zexian Cao
- Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China.,Songshan Lake Materials Laboratory, Dongguan 523808, China
| | - Qiang Wang
- Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China
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9
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Pireddu G, Scalfi L, Rotenberg B. A molecular perspective on induced charges on a metallic surface. J Chem Phys 2021; 155:204705. [PMID: 34852473 DOI: 10.1063/5.0076127] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Understanding the response of the surface of metallic solids to external electric field sources is crucial to characterize electrode-electrolyte interfaces. Continuum electrostatics offer a simple description of the induced charge density at the electrode surface. However, such a simple description does not take into account features related to the atomic structure of the solid and to the molecular nature of the solvent and of the dissolved ions. In order to illustrate such effects and assess the ability of continuum electrostatics to describe the induced charge distribution, we investigate the behavior of a gold electrode interacting with sodium or chloride ions fixed at various positions, in a vacuum or in water, using all-atom constant-potential classical molecular dynamics simulations. Our analysis highlights important similarities between the two approaches, especially under vacuum conditions and when the ion is sufficiently far from the surface, as well as some limitations of the continuum description, namely, neglecting the charges induced by the adsorbed solvent molecules and the screening effect of the solvent when the ion is close to the surface. While the detailed features of the charge distribution are system-specific, we expect some of our generic conclusions on the induced charge density to hold for other ions, solvents, and electrode surfaces. Beyond this particular case, the present study also illustrates the relevance of such molecular simulations to serve as a reference for the design of improved implicit solvent models of electrode-electrolyte interfaces.
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Affiliation(s)
- Giovanni Pireddu
- Sorbonne Université, CNRS, Physico-chimie des Électrolytes et Nanosystèmes Interfaciaux, PHENIX, F-75005 Paris, France
| | - Laura Scalfi
- Sorbonne Université, CNRS, Physico-chimie des Électrolytes et Nanosystèmes Interfaciaux, PHENIX, F-75005 Paris, France
| | - Benjamin Rotenberg
- Sorbonne Université, CNRS, Physico-chimie des Électrolytes et Nanosystèmes Interfaciaux, PHENIX, F-75005 Paris, France
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10
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Fossat M, Zeng X, Pappu RV. Uncovering Differences in Hydration Free Energies and Structures for Model Compound Mimics of Charged Side Chains of Amino Acids. J Phys Chem B 2021; 125:4148-4161. [PMID: 33877835 PMCID: PMC8154595 DOI: 10.1021/acs.jpcb.1c01073] [Citation(s) in RCA: 36] [Impact Index Per Article: 12.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/05/2021] [Revised: 04/07/2021] [Indexed: 02/07/2023]
Abstract
Free energies of hydration are of fundamental interest for modeling and understanding conformational and phase equilibria of macromolecular solutes in aqueous phases. Of particular relevance to systems such as intrinsically disordered proteins are the free energies of hydration and hydration structures of model compounds that mimic charged side chains of Arg, Lys, Asp, and Glu. Here, we deploy a Thermodynamic Cycle-based Proton Dissociation (TCPD) approach in conjunction with data from direct measurements to obtain estimates for the free energies of hydration for model compounds that mimic the side chains of Arg+, Lys+, Asp-, and Glu-. Irrespective of the choice made for the hydration free energy of the proton, the TCPD approach reveals clear trends regarding the free energies of hydration for Arg+, Lys+, Asp-, and Glu-. These trends include asymmetries between the hydration free energies of acidic (Asp- and Glu-) and basic (Arg+ and Lys+) residues. Further, the TCPD analysis, which relies on a combination of experimental data, shows that the free energy of hydration of Arg+ is less favorable than that of Lys+. We sought a physical explanation for the TCPD-derived trends in free energies of hydration. To this end, we performed temperature-dependent calculations of free energies of hydration and analyzed hydration structures from simulations that use the polarizable Atomic Multipole Optimized Energetics for Biomolecular Applications (AMOEBA) force field and water model. At 298 K, the AMOEBA model generates estimates of free energies of hydration that are consistent with TCPD values with a free energy of hydration for the proton of ca. -259 kcal/mol. Analysis of temperature-dependent simulations leads to a structural explanation for the observed differences in free energies of hydration of ionizable residues and reveals that the heat capacity of hydration is positive for Arg+ and Lys+ and negative for Asp- and Glu-.
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Affiliation(s)
| | | | - Rohit V. Pappu
- Department of Biomedical Engineering
and Center for Science & Engineering of Living Systems, Washington University in St. Louis, St. Louis, Missouri 63130, United States
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11
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Herman KM, Heindel JP, Xantheas SS. The many-body expansion for aqueous systems revisited: III. Hofmeister ion-water interactions. Phys Chem Chem Phys 2021; 23:11196-11210. [PMID: 33899854 DOI: 10.1039/d1cp00409c] [Citation(s) in RCA: 13] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
We report a Many Body Energy (MBE) analysis of aqueous ionic clusters containing anions and cations at the two opposite ends of the Hofmeister series, viz. the kosmotropes Ca2+ and SO42- and the chaotropes NH4+ and ClO4-, with 9 water molecules to quantify how these ions alter the interaction between the water molecules in their immediate surroundings. We specifically aim at quantifying how various ions (depending on their position in the Hofmeister series) affect the interaction between the surrounding water molecules and probe whether there is a qualitatively different behavior between kosmotropic vs. chaotropic ions. The current results when compared to the ones reported earlier for water clusters [J. P. Heindel and S. S. Xantheas, J. Chem. Theor. Comput., 2020, 16, 6843-6855] as well as for alkali metal and halide ion aqueous clusters of the same size [J. P. Heindel and S. S. Xantheas, J. Chem. Theor. Comput., 2021, 17, 2200-2216], which lie in the middle of the Hofmeister series, offer a complete account of the effect an ion across the Hofmeister series from "kosmotropes" to "chaotropes" has on the interaction between the neighboring water molecules. Through this analysis, noteworthy differences between the MBE of kosmotropes and chaotropes were identified. The MBE of kosmotropes is dominated by ion-water interactions that extend beyond the 4-body term, the rank at which the MBE of pure water converges. The percentage contribution of the 2-B term to the total cluster binding energy is noticeably larger. The disruption of the hydrogen bonded network due to the dominant ion-water interactions results in weak, unfavorable water-water interactions. The MBE for chaotropes, on the other hand, was found to converge more quickly as it more closely resembles that of pure water clusters. Chaotropes exhibit weaker overall binding energies and weaker ion-water interactions in favor of water-water interactions, somewhat recovering the pattern of the 2-4 body terms exemplified by pure water clusters. A remarkable anti-correlation between the 2-B ion-water (I-W) and water-water (W-W) interactions as well as between the 3-B (I-W-W) and (I-W) interactions was found for both kosmotropic and chaotropic ions. This anti-correlation is linear for both monatomic anions and monatomic cations, suggesting the existence of underlying physical mechanisms that were previously unexplored. The consideration of two different structural arrangements (ion inside and outside of a water cluster) suggests that fully solvated (ion inside) chaotropes disrupt the hydrogen bonding network in a similar manner to partially solvated (ion outside) kosmotropes and offers useful insights into the modeling requirements of bulk vs. interfacial ion solvation. It is noteworthy that the 2-B contribution to the total Basis Set Superposition Error (BSSE) correction for both kosmotropic and chaotropic ions follows the universal erf profile vs. intermolecular distance previously reported for pure water, halide ion-water and alkali metal ion-water clusters. When scaled for the corresponding dimer energies and distances, a single profile fits the current results together with all previously reported ones for pure water and halide water clusters. This finding lends further support to schemes for accurately estimating the 2-B BSSE correction in condensed environments.
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Affiliation(s)
- Kristina M Herman
- Department of Chemistry, University of Washington, Seattle, WA 98195, USA.
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12
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de Izarra A, Choi C, Jang YH, Lansac Y. Ionic Liquid for PEDOT:PSS Treatment. Ion Binding Free Energy in Water Revealing the Importance of Anion Hydrophobicity. J Phys Chem B 2021; 125:1916-1923. [DOI: 10.1021/acs.jpcb.0c10068] [Citation(s) in RCA: 16] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Affiliation(s)
- Ambroise de Izarra
- GREMAN, CNRS UMR 7347, Université de Tours, 37200 Tours, France
- Department of Energy Science and Engineering, DGIST, Daegu 42988, Korea
| | - Changwon Choi
- Department of Energy Science and Engineering, DGIST, Daegu 42988, Korea
| | - Yun Hee Jang
- Department of Energy Science and Engineering, DGIST, Daegu 42988, Korea
| | - Yves Lansac
- GREMAN, CNRS UMR 7347, Université de Tours, 37200 Tours, France
- Department of Energy Science and Engineering, DGIST, Daegu 42988, Korea
- Laboratoire de Physique des Solides, CNRS UMR 8502, Université Paris-Saclay, 91405 Orsay, France
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13
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Kwan V, Consta S. Molecular Characterization of the Surface Excess Charge Layer in Droplets. JOURNAL OF THE AMERICAN SOCIETY FOR MASS SPECTROMETRY 2021; 32:33-45. [PMID: 32597645 DOI: 10.1021/jasms.0c00053] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/11/2023]
Abstract
The surface excess charge layer (SECL) in droplets has often been associated with distinct chemistry. We examine the effect of the nature of ions in the composition and structure of SECL by using molecular dynamics. We find that in the presence of simple ions the thickness of SECL is invariant not only with respect to droplet size but also with respect to the nature of the ions. In the presence of simple ions, this layer has a thickness of ∼1.5-1.7 nm but in the presence of macroions it may extend to ∼2.0 nm. The proportion of ions contained in SECL depends on the nature of the ions and the droplet size. For the same droplet size, I- and model H3O+ ions show considerably higher concentration than Na+ and Cl- ions. We identify the maximum ion concentration region, which, in nanodrops, may partially overlap with SECL. As the relative shape fluctuations decrease when microdrop size is approached, the overlap between SECL and maximum ion concentration region increases. We suggest the extension of the bilayer droplet structure assumed in the equilibrium partitioning model of Enke to include the maximum ion concentration region that may not coincide with SECL in nanodrops. We compute the ion concentrations in SECL, which are those that should enter the kinetic equation in the ion-evaporation mechanism, instead of the overall drop ion concentration that has been used.
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Affiliation(s)
- Victor Kwan
- Department of Chemistry, The University of Western Ontario, London, Ontario, Canada N6A 5B7
| | - Styliani Consta
- Department of Chemistry, The University of Western Ontario, London, Ontario, Canada N6A 5B7
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14
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Carvalho WSP, Lee C, Zhang Y, Czarnecki A, Serpe MJ. Probing the response of poly (N-isopropylacrylamide) microgels to solutions of various salts using etalons. J Colloid Interface Sci 2020; 585:195-204. [PMID: 33279702 DOI: 10.1016/j.jcis.2020.11.045] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/19/2020] [Revised: 10/20/2020] [Accepted: 11/10/2020] [Indexed: 12/20/2022]
Abstract
The Hofmeister series is a qualitative ordering of ions according to their ability to precipitate proteins in aqueous solution and is extremely important to consider when trying to understand materials and biomolecular structure and function. Herein, we utilized optical devices (etalons) composed of poly(N-isopropylacrylamide) (pNIPAm)-co-10% acrylic acid (AAc) or pNIPAm-based microgels to investigate how various salts in the Hofmeister series influenced the microgel hydration state. Etalons were exposed to a series of salts solutions at different concentrations and the position of the peaks in the reflectance spectra monitored using reflectance spectroscopy. As expected, pNIPAm-co-10%AAc microgel-based etalons responded to the presence of ions, although in this case the response to cations deviated from the Hofmeister series. However, when using etalons prepared with pNIPAm-based microgels, the responses followed the Hofmeister series for both cation and anions. Finally, we observed that the sensitivity of etalons prepared with pNIPAm microgels was significantly higher than the response obtained from etalons composed of pNIPAm-co-10%AAc microgels. This was explained by considering the charge on the pNIPAm-co-10%AAc microgels that influences how osmotic and Hofmeister effects impacts hydration state.
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Affiliation(s)
| | - Cayo Lee
- Department of Chemistry, University of Alberta, Edmonton, AB T6G 2G2, Canada
| | - Yingnan Zhang
- Department of Chemistry, University of Alberta, Edmonton, AB T6G 2G2, Canada
| | - Adam Czarnecki
- Department of Chemistry, University of Alberta, Edmonton, AB T6G 2G2, Canada
| | - Michael J Serpe
- Department of Chemistry, University of Alberta, Edmonton, AB T6G 2G2, Canada.
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15
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Cox SJ, Thorpe DG, Shaffer PR, Geissler PL. Assessing long-range contributions to the charge asymmetry of ion adsorption at the air-water interface. Chem Sci 2020; 11:11791-11800. [PMID: 34094413 PMCID: PMC8162909 DOI: 10.1039/d0sc01947j] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Anions generally associate more favorably with the air–water interface than cations. In addition to solute size and polarizability, the intrinsic structure of the unperturbed interface has been discussed as an important contributor to this bias. Here we assess quantitatively the role that intrinsic charge asymmetry of water's surface plays in ion adsorption, using computer simulations to compare model solutes of various size and charge. In doing so, we also evaluate the degree to which linear response theory for solvent polarization is a reasonable approach for comparing the thermodynamics of bulk and interfacial ion solvation. Consistent with previous works on bulk ion solvation, we find that the average electrostatic potential at the center of a neutral, sub-nanometer solute at the air–water interface depends sensitively on its radius, and that this potential changes quite nonlinearly as the solute's charge is introduced. The nonlinear response closely resembles that of the bulk. As a result, the net nonlinearity of ion adsorption is weaker than in bulk, but still substantial, comparable to the apparent magnitude of macroscopically nonlocal contributions from the undisturbed interface. For the simple-point-charge model of water we study, these results argue distinctly against rationalizing ion adsorption in terms of surface potentials inherent to molecular structure of the liquid's boundary. Cations and anions have different affinities for the air-water interface. The intrinsic orientation of surface molecules suggests such an asymmetry, but the bias is dominated by solvent response that is spatially local and significantly nonlinear.![]()
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Affiliation(s)
- Stephen J Cox
- Department of Chemistry, University of Cambridge Lensfield Road Cambridge CB2 1EW UK
| | - Dayton G Thorpe
- Chemical Sciences Division, Lawrence Berkeley National Laboratory Berkeley CA 94720 USA.,Department of Physics, University of California Berkeley CA 94720 USA
| | - Patrick R Shaffer
- Department of Chemistry, University of California Berkeley CA 94720 USA
| | - Phillip L Geissler
- Chemical Sciences Division, Lawrence Berkeley National Laboratory Berkeley CA 94720 USA.,Department of Chemistry, University of California Berkeley CA 94720 USA
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16
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17
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Sáenz-Tavera IDC, Rosas-García VM. Ab initio calculations and reduced density gradient analyses of the structure and energetics of hydrated calcium fluoride and calcium carbonate. Phys Chem Chem Phys 2019; 21:5744-5758. [DOI: 10.1039/c8cp06353b] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
Abstract
We studied microhydrated calcium fluoride, calcium carbonate and their ions at the MP2/6-311++G** level of theory and found that water–water non-covalent interactions destabilize the solvation shell, and are compensated by cooperative hydrogen bonds.
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Affiliation(s)
| | - Victor M. Rosas-García
- Universidad Autónoma de Nuevo León
- UANL
- Facultad de Ciencias Químicas
- Ave. Universidad S/N
- Cd. Universitaria
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18
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Chae S, Oh S, Siddiqa AJ, Choi KH, Lee WG, Jang WS, Lee JS, Kim YM, Huh J, Kim SM, Choi JY. Highly concentrated single-chain atomic crystal LiMo 3Se 3 solution using ion-exchange chromatography. Chem Commun (Camb) 2018; 54:12503-12506. [PMID: 30345436 DOI: 10.1039/c8cc06306k] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Ion-exchange chromatography can be used to effectively replace the lithium ion of LiMo3Se3 with a proton. The enlargement of the Stern layer distance caused by this ion exchange improves the dispersibility of (Mo3Se3-)∞ chains and also prevents the re-bundling and aggregation of nanowires in aqueous solutions, even at high concentrations (1 mg mL-1).
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Affiliation(s)
- Sudong Chae
- School of Advanced Materials Science & Engineering, Sungkyunkwan University, Suwon 16419, Republic of Korea
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19
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Cox SJ, Geissler PL. Interfacial ion solvation: Obtaining the thermodynamic limit from molecular simulations. J Chem Phys 2018; 148:222823. [DOI: 10.1063/1.5020563] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022] Open
Affiliation(s)
- Stephen J. Cox
- Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA
| | - Phillip L. Geissler
- Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA
- Department of Chemistry, University of California, Berkeley, California 94720, USA
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20
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Onufriev AV, Izadi S. Water models for biomolecular simulations. WILEY INTERDISCIPLINARY REVIEWS-COMPUTATIONAL MOLECULAR SCIENCE 2017. [DOI: 10.1002/wcms.1347] [Citation(s) in RCA: 94] [Impact Index Per Article: 13.4] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Affiliation(s)
- Alexey V. Onufriev
- Department of Physics; Virginia Tech; Blacksburg VA USA
- Department of Computer Science; Virginia Tech; Blacksburg VA USA
- Center for Soft Matter and Biological Physics; Virginia Tech; Blacksburg VA USA
| | - Saeed Izadi
- Early Stage Pharmaceutical Development; Genentech Inc.; South San Francisco, CA USA
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21
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22
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Situm A, Rahman MA, Allen N, Kabengi N, Al-Abadleh HA. ATR-FTIR and Flow Microcalorimetry Studies on the Initial Binding Kinetics of Arsenicals at the Organic–Hematite Interface. J Phys Chem A 2017; 121:5569-5579. [DOI: 10.1021/acs.jpca.7b03426] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- Arthur Situm
- Department
of Chemistry and Biochemistry, Wilfrid Laurier University, Waterloo, ON N2L 3C5, Canada
| | - Mohammad A. Rahman
- Department
of Chemistry and Biochemistry, Wilfrid Laurier University, Waterloo, ON N2L 3C5, Canada
| | | | | | - Hind A. Al-Abadleh
- Department
of Chemistry and Biochemistry, Wilfrid Laurier University, Waterloo, ON N2L 3C5, Canada
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23
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Molavi Tabrizi A, Goossens S, Mehdizadeh Rahimi A, Cooper CD, Knepley MG, Bardhan JP. Extending the Solvation-Layer Interface Condition Continum Electrostatic Model to a Linearized Poisson–Boltzmann Solvent. J Chem Theory Comput 2017; 13:2897-2914. [DOI: 10.1021/acs.jctc.6b00832] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Amirhossein Molavi Tabrizi
- Department
of Mechanical and Industrial Engineering, Northeastern University, Boston, Massachusetts 02115, United States
| | - Spencer Goossens
- Department
of Mechanical and Industrial Engineering, Northeastern University, Boston, Massachusetts 02115, United States
| | - Ali Mehdizadeh Rahimi
- Department
of Mechanical and Industrial Engineering, Northeastern University, Boston, Massachusetts 02115, United States
| | - Christopher D. Cooper
- Departamento
de Ingeniería Mecánica and Centro Científico
Tecnológico de Valparaíso (CCTVal), Universidad Técnica Federico Santa María, Valparaiso, Chile
| | - Matthew G. Knepley
- Department
of Computational and Applied Mathematics, Rice University, Houston, Texas 77005, United States
| | - Jaydeep P. Bardhan
- Department
of Mechanical and Industrial Engineering, Northeastern University, Boston, Massachusetts 02115, United States
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24
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Mao Y, Shao Y, Dziedzic J, Skylaris CK, Head-Gordon T, Head-Gordon M. Performance of the AMOEBA Water Model in the Vicinity of QM Solutes: A Diagnosis Using Energy Decomposition Analysis. J Chem Theory Comput 2017; 13:1963-1979. [PMID: 28430427 DOI: 10.1021/acs.jctc.7b00089] [Citation(s) in RCA: 24] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The importance of incorporating solvent polarization effects into the modeling of solvation processes has been well-recognized, and therefore a new generation of hybrid quantum mechanics/molecular mechanics (QM/MM) approaches that accounts for this effect is desirable. We present a fully self-consistent, mutually polarizable QM/MM scheme using the AMOEBA force field, in which the total energy of the system is variationally minimized with respect to both the QM electronic density and the MM induced dipoles. This QM/AMOEBA model is implemented through the Q-Chem/LibEFP code interface and then applied to the evaluation of solute-solvent interaction energies for various systems ranging from the water dimer to neutral and ionic solutes (NH3, NH4+, CN-) surrounded by increasing numbers of water molecules (up to 100). In order to analyze the resulting interaction energies, we also utilize an energy decomposition analysis (EDA) scheme which identifies contributions from permanent electrostatics, polarization, and van der Waals (vdW) interaction for the interaction between the QM solute and the solvent molecules described by AMOEBA. This facilitates a component-wise comparison against full QM calculations where the corresponding energy components are obtained via a modified version of the absolutely localized molecular orbitals (ALMO)-EDA. The results show that the present QM/AMOEBA model can yield reasonable solute-solvent interaction energies for neutral and cationic species, while further scrutiny reveals that this accuracy highly relies on the delicate balance between insufficiently favorable permanent electrostatics and softened vdW interaction. For anionic solutes where the charge penetration effect becomes more pronounced, the QM/MM interface turns out to be unbalanced. These results are consistent with and further elucidate our findings in a previous study using a slightly different QM/AMOEBA model ( Dziedzic et al. J. Chem. Phys. 2016 , 145 , 124106 ). The implications of these results for further refinement of this model are also discussed.
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Affiliation(s)
| | - Yihan Shao
- Department of Chemistry and Biochemistry, University of Oklahoma , Norman, Oklahoma 73019, United States
| | - Jacek Dziedzic
- School of Chemistry, University of Southampton , Highfield, Southampton SO17 1BJ, U.K.,Faculty of Applied Physics and Mathematics, Gdańsk University of Technology , Gdańsk 80-233, Poland
| | - Chris-Kriton Skylaris
- School of Chemistry, University of Southampton , Highfield, Southampton SO17 1BJ, U.K
| | | | - Martin Head-Gordon
- Chemical Science Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, United States
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25
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Luo W, Hirajima T, Sasaki K. Selective adsorption of inorganic anions on unwashed and washed hexadecyl pyridinium-modified montmorillonite. Sep Purif Technol 2017. [DOI: 10.1016/j.seppur.2016.12.004] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/20/2022]
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26
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Molavi Tabrizi A, Goossens S, Mehdizadeh Rahimi A, Knepley M, Bardhan JP. Predicting solvation free energies and thermodynamics in polar solvents and mixtures using a solvation-layer interface condition. J Chem Phys 2017. [DOI: 10.1063/1.4977037] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Affiliation(s)
- Amirhossein Molavi Tabrizi
- Department of Mechanical and Industrial Engineering, Northeastern University, Boston, Massachusetts 02115, USA
| | - Spencer Goossens
- Department of Mechanical and Industrial Engineering, Northeastern University, Boston, Massachusetts 02115, USA
| | - Ali Mehdizadeh Rahimi
- Department of Mechanical and Industrial Engineering, Northeastern University, Boston, Massachusetts 02115, USA
| | - Matthew Knepley
- Department of Computational and Applied Mathematics, Rice University, Houston, Texas 77005, USA
| | - Jaydeep P. Bardhan
- Department of Mechanical and Industrial Engineering, Northeastern University, Boston, Massachusetts 02115, USA
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27
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Naranjo D, Moldenhauer H, Pincuntureo M, Díaz-Franulic I. Pore size matters for potassium channel conductance. J Gen Physiol 2016; 148:277-91. [PMID: 27619418 PMCID: PMC5037345 DOI: 10.1085/jgp.201611625] [Citation(s) in RCA: 26] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/19/2016] [Accepted: 08/10/2016] [Indexed: 01/31/2023] Open
Abstract
Ion channels are membrane proteins that mediate efficient ion transport across the hydrophobic core of cell membranes, an unlikely process in their absence. K+ channels discriminate K+ over cations with similar radii with extraordinary selectivity and display a wide diversity of ion transport rates, covering differences of two orders of magnitude in unitary conductance. The pore domains of large- and small-conductance K+ channels share a general architectural design comprising a conserved narrow selectivity filter, which forms intimate interactions with permeant ions, flanked by two wider vestibules toward the internal and external openings. In large-conductance K+ channels, the inner vestibule is wide, whereas in small-conductance channels it is narrow. Here we raise the idea that the physical dimensions of the hydrophobic internal vestibule limit ion transport in K+ channels, accounting for their diversity in unitary conductance.
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Affiliation(s)
- David Naranjo
- Centro Interdisciplinario de Neurociencia de Valparaíso, Universidad de Valparaíso, Playa Ancha, Valparaíso 2360103, Chile
| | - Hans Moldenhauer
- Centro Interdisciplinario de Neurociencia de Valparaíso, Universidad de Valparaíso, Playa Ancha, Valparaíso 2360103, Chile
| | - Matías Pincuntureo
- Centro Interdisciplinario de Neurociencia de Valparaíso, Universidad de Valparaíso, Playa Ancha, Valparaíso 2360103, Chile Programa de Doctorado en Ciencias, mención Biofísica y Biología Computacional, Universidad de Valparaíso, Valparaíso 2360103, Chile
| | - Ignacio Díaz-Franulic
- Centro Interdisciplinario de Neurociencia de Valparaíso, Universidad de Valparaíso, Playa Ancha, Valparaíso 2360103, Chile Center for Bioinformatics and Integrative Biology, Universidad Andrés Bello, Santiago 8370146, Chile Fraunhofer Chile Research, Las Condes 7550296, Chile
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28
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Izadi S, Onufriev AV. Accuracy limit of rigid 3-point water models. J Chem Phys 2016; 145:074501. [PMID: 27544113 PMCID: PMC4991989 DOI: 10.1063/1.4960175] [Citation(s) in RCA: 167] [Impact Index Per Article: 20.9] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/03/2016] [Accepted: 07/19/2016] [Indexed: 11/14/2022] Open
Abstract
Classical 3-point rigid water models are most widely used due to their computational efficiency. Recently, we introduced a new approach to constructing classical rigid water models [S. Izadi et al., J. Phys. Chem. Lett. 5, 3863 (2014)], which permits a virtually exhaustive search for globally optimal model parameters in the sub-space that is most relevant to the electrostatic properties of the water molecule in liquid phase. Here we apply the approach to develop a 3-point Optimal Point Charge (OPC3) water model. OPC3 is significantly more accurate than the commonly used water models of same class (TIP3P and SPCE) in reproducing a comprehensive set of liquid bulk properties, over a wide range of temperatures. Beyond bulk properties, we show that OPC3 predicts the intrinsic charge hydration asymmetry (CHA) of water - a characteristic dependence of hydration free energy on the sign of the solute charge - in very close agreement with experiment. Two other recent 3-point rigid water models, TIP3PFB and H2ODC, each developed by its own, completely different optimization method, approach the global accuracy optimum represented by OPC3 in both the parameter space and accuracy of bulk properties. Thus, we argue that an accuracy limit of practical 3-point rigid non-polarizable models has effectively been reached; remaining accuracy issues are discussed.
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Affiliation(s)
- Saeed Izadi
- Department of Biomedical Engineering and Mechanics, Virginia Tech, Blacksburg, Virginia 24060, USA
| | - Alexey V Onufriev
- Departments of Computer Science and Physics, Center for Soft Matter and Biological Physics, Virginia Tech, Blacksburg, Virginia 24060, USA
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29
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Reif MM, Hünenberger PH. Origin of Asymmetric Solvation Effects for Ions in Water and Organic Solvents Investigated Using Molecular Dynamics Simulations: The Swain Acity-Basity Scale Revisited. J Phys Chem B 2016; 120:8485-517. [PMID: 27173101 DOI: 10.1021/acs.jpcb.6b02156] [Citation(s) in RCA: 34] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The asymmetric solvation of ions can be defined as the tendency of a solvent to preferentially solvate anions over cations or cations over anions, at identical ionic charge magnitudes and effective sizes. Taking water as a reference, these effects are quantified experimentally for many solvents by the relative acity (A) and basity (B) parameters of the Swain scale. The goal of the present study is to investigate the asymmetric solvation of ions using molecular dynamics simulations, and to connect the results to this empirical scale. To this purpose, the charging free energies of alkali and halide ions, and of their hypothetical oppositely charged counterparts, are calculated in a variety of solvents. In a first set of calculations, artificial solvent models are considered that present either a charge or a shape asymmetry at the molecular level. The solvation asymmetry, probed by the difference in charging free energy between the two oppositely charged ions, is found to encompass a term quadratic in the ion charge, related to the different solvation structures around the anion and cation, and a term linear in the ion charge, related to the solvation structure around the uncharged ion-sized cavity. For these simple solvent models, the two terms are systematically counteracting each other, and it is argued that only the quadratic term should be retained when comparing the results of simulations involving physical solvents to experimental data. In a second set of calculations, 16 physical solvents are considered. The theoretical estimates for the acity A are found to correlate very well with the Swain parameters, whereas the correlation for B is very poor. Based on this observation, the Swain scale is reformulated into a new scale involving an asymmetry parameter Σ, positive for acitic solvents and negative for basitic ones, and a polarity parameter Π. This revised scale has the same predictive power as the original scale, but it characterizes asymmetry in an absolute sense, the atomistic simulations playing the role of an extra-thermodynamic assumption, and is optimally compatible with the simulation results. Considering the 55 solvents in the Swain set, it is observed that a moderate basity (Σ between -0.9 and -0.3, related to electronic polarization) represents the baseline for most solvents, while a highly variable acity (Σ between 0.0 and 3.0, related to hydrogen-bond donor capacity modulated by inductive effects) represents a landmark of protic solvents.
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Affiliation(s)
- Maria M Reif
- Physics Department (T38), Technische Universität München , D-85748 Garching, Germany
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30
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Śmiechowski M. Anion–water interactions of weakly hydrated anions: molecular dynamics simulations of aqueous NaBF4and NaPF6. Mol Phys 2016. [DOI: 10.1080/00268976.2016.1157219] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022]
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31
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Jensen KP, Jorgensen WL. Halide, Ammonium, and Alkali Metal Ion Parameters for Modeling Aqueous Solutions. J Chem Theory Comput 2015; 2:1499-509. [PMID: 26627020 DOI: 10.1021/ct600252r] [Citation(s) in RCA: 275] [Impact Index Per Article: 30.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
A complete set of Lennard Jones parameters for the halide ions, F(-), Cl(-), Br(-), and I(-), ammonium ion, and the alkali metal ions is reported. The parameters have been optimized using Monte Carlo simulations and free energy perturbation theory with the TIP4P water model to reproduce experimental free energies of hydration and locations of the first maxima of the ion-oxygen radial distribution functions, to provide water coordination numbers consistent with experimental ranges, and to exhibit gas-phase monohydrate energies in reasonable agreement with ab initio values. Average errors for absolute and relative free energies of hydration for the ions are ca. 1 kcal/mol. For the halides, this is the first self-consistent set of parameters that has been optimized for aqueous-phase performance. The good results for relative free energies of hydration are particularly auspicious for use of the new parameters in a wide variety of liquid-phase simulations where halide and alkali cations are systematically varied.
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Affiliation(s)
- Kasper P Jensen
- Department of Chemistry, Yale University, New Haven, Connecticut 06520-8107
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32
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Waluyo I, Nordlund D, Bergmann U, Schlesinger D, Pettersson LGM, Nilsson A. A different view of structure-making and structure-breaking in alkali halide aqueous solutions through x-ray absorption spectroscopy. J Chem Phys 2015; 140:244506. [PMID: 24985653 DOI: 10.1063/1.4881600] [Citation(s) in RCA: 54] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
X-ray absorption spectroscopy measured in transmission mode was used to study the effect of alkali and halide ions on the hydrogen-bonding (H-bonding) network of water. Cl(-) and Br(-) are shown to have insignificant effect on the structure of water while I(-) locally weakens the H-bonding, as indicated by a sharp increase of the main-edge feature in the x-ray absorption spectra. All alkali cations act as structure-breakers in water, weakening the H-bonding network. The spectral changes are similar to spectra of high density ices where the 2nd shell has collapsed due to a break-down of the tetrahedral structures, although here, around the ions, the breakdown of the local tetrahedrality is rather due to non-directional H-bonding to the larger anions. In addition, results from temperature-dependent x-ray Raman scattering measurements of NaCl solution confirm the H-bond breaking effect of Na(+) and the effect on the liquid as similar to an increase in temperature.
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Affiliation(s)
- Iradwikanari Waluyo
- Stanford Synchrotron Radiation Lightsource, SLAC National Accelerator Laboratory, P.O. Box 20450, Stanford, California 94309, USA
| | - Dennis Nordlund
- Stanford Synchrotron Radiation Lightsource, SLAC National Accelerator Laboratory, P.O. Box 20450, Stanford, California 94309, USA
| | - Uwe Bergmann
- Linac Coherent Light Source, SLAC National Accelerator Laboratory, P.O. Box 20450, Stanford, California 94309, USA
| | - Daniel Schlesinger
- Department of Physics, AlbaNova University Center, Stockholm University, SE-106 91 Stockholm, Sweden
| | - Lars G M Pettersson
- Department of Physics, AlbaNova University Center, Stockholm University, SE-106 91 Stockholm, Sweden
| | - Anders Nilsson
- Stanford Synchrotron Radiation Lightsource, SLAC National Accelerator Laboratory, P.O. Box 20450, Stanford, California 94309, USA
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33
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Mukhopadhyay A, Tolokh IS, Onufriev AV. Accurate evaluation of charge asymmetry in aqueous solvation. J Phys Chem B 2015; 119:6092-100. [PMID: 25830623 DOI: 10.1021/acs.jpcb.5b00602] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Charge hydration asymmetry (CHA)-a characteristic dependence of hydration free energy on the sign of the solute charge-quantifies the asymmetric response of water to electric field at microscopic level. Accurate estimates of CHA are critical for understanding hydration effects ubiquitous in chemistry and biology. However, measuring hydration energies of charged species is fraught with significant difficulties, which lead to unacceptably large (up to 300%) variation in the available estimates of the CHA effect. We circumvent these difficulties by developing a framework which allows us to extract and accurately estimate the intrinsic propensity of water to exhibit CHA from accurate experimental hydration free energies of neutral polar molecules. Specifically, from a set of 504 small molecules we identify two pairs that are analogous, with respect to CHA, to the K(+) /F(-) pair-a classical probe for the effect. We use these "CHA-conjugate" molecule pairs to quantify the intrinsic charge-asymmetric response of water to the microscopic charge perturbations: the asymmetry of the response is strong, ∼50% of the average hydration free energy of these molecules. The ability of widely used classical water models to predict hydration energies of small molecules correlates with their ability to predict CHA.
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Affiliation(s)
- Abhishek Mukhopadhyay
- †Department of Physics and ‡Department of Computer Science, Virginia Tech, Blacksburg, Virginia 24061, United States
| | - Igor S Tolokh
- †Department of Physics and ‡Department of Computer Science, Virginia Tech, Blacksburg, Virginia 24061, United States
| | - Alexey V Onufriev
- †Department of Physics and ‡Department of Computer Science, Virginia Tech, Blacksburg, Virginia 24061, United States
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34
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Shi Y, Ren P, Schnieders M, Piquemal JP. Polarizable Force Fields for Biomolecular Modeling. REVIEWS IN COMPUTATIONAL CHEMISTRY 2015. [DOI: 10.1002/9781118889886.ch2] [Citation(s) in RCA: 30] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
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35
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Hygroscopicity of Mixed Glycerol/Mg(NO3)2/Water Droplets Affected by the Interaction between Magnesium Ions and Glycerol Molecules. J Phys Chem B 2015; 119:5558-66. [PMID: 25860879 DOI: 10.1021/acs.jpcb.5b00458] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Tropospheric aerosols are usually complex mixtures of inorganic and organic components, which can influence the hygroscopicities of each other. In this research, we applied confocal Raman technology combined with optical microscopy to investigate the relationship between the hygroscopic behavior and the molecular interactions of mixed glycerol/Mg(NO3)2/water droplets. Raman spectra provide detailed structural information about the interactions between glycerol molecules and Mg(2+) ions, as well as information about the interactions between glycerol and NO3(-) ions through electrostatic interaction and hydrogen bonding. The change of the CH2 stretching band of glycerol molecules in mixed droplets suggests that the backbone structures of glycerol mainly transform from αα to γγ in the dehumidifying process, and the additional Mg(2+) ions strongly influence the structure of glycerol molecules. Because the existence of glycerol suppresses the crystallization of Mg(NO3)2·6H2O in the dehumidifying process, Mg(NO3)2 molecules in mixed droplets form an amorphous state rather than forming crystals of Mg(NO3)2·6H2O when the relative humidity is lower than 17.8%. Moreover, in mixed droplets, the molar ratio of NO3(-) to glycerol is higher in the center than in the outer region.
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36
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Soniat M, Hartman L, Rick SW. Charge Transfer Models of Zinc and Magnesium in Water. J Chem Theory Comput 2015; 11:1658-67. [DOI: 10.1021/ct501173n] [Citation(s) in RCA: 27] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Affiliation(s)
- Marielle Soniat
- Department
of Chemistry, University of New Orleans, New Orleans, Louisiana 70148, United States
| | - Lisa Hartman
- Benjamin Franklin High School, New Orleans, Louisiana 70122, United States
| | - Steven W. Rick
- Department
of Chemistry, University of New Orleans, New Orleans, Louisiana 70148, United States
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37
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Guo X, Wang Y, Li C, Huai P, Wu G. Optimum complexation of uranyl with amidoxime in aqueous solution under different pH levels: density functional theory calculations. Mol Phys 2015. [DOI: 10.1080/00268976.2014.993732] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/24/2022]
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38
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Carvalho NF, Pliego JR. Cluster-continuum quasichemical theory calculation of the lithium ion solvation in water, acetonitrile and dimethyl sulfoxide: an absolute single-ion solvation free energy scale. Phys Chem Chem Phys 2015; 17:26745-55. [DOI: 10.1039/c5cp03798k] [Citation(s) in RCA: 45] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
A solvation free energy scale excluding the net electrostatic potential inside the solute cavity is presented.
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Affiliation(s)
- Nathalia F. Carvalho
- Departamento de Ciências Naturais
- Universidade Federal de São João del Rei
- São João del-Rei
- Brazil
| | - Josefredo R. Pliego
- Departamento de Ciências Naturais
- Universidade Federal de São João del Rei
- São João del-Rei
- Brazil
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39
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Bardhan JP, Knepley MG. Communication: modeling charge-sign asymmetric solvation free energies with nonlinear boundary conditions. J Chem Phys 2014; 141:131103. [PMID: 25296776 PMCID: PMC4193973 DOI: 10.1063/1.4897324] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/18/2014] [Accepted: 09/25/2014] [Indexed: 01/28/2023] Open
Abstract
We show that charge-sign-dependent asymmetric hydration can be modeled accurately using linear Poisson theory after replacing the standard electric-displacement boundary condition with a simple nonlinear boundary condition. Using a single multiplicative scaling factor to determine atomic radii from molecular dynamics Lennard-Jones parameters, the new model accurately reproduces MD free-energy calculations of hydration asymmetries for: (i) monatomic ions, (ii) titratable amino acids in both their protonated and unprotonated states, and (iii) the Mobley "bracelet" and "rod" test problems [D. L. Mobley, A. E. Barber II, C. J. Fennell, and K. A. Dill, "Charge asymmetries in hydration of polar solutes," J. Phys. Chem. B 112, 2405-2414 (2008)]. Remarkably, the model also justifies the use of linear response expressions for charging free energies. Our boundary-element method implementation demonstrates the ease with which other continuum-electrostatic solvers can be extended to include asymmetry.
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Affiliation(s)
- Jaydeep P Bardhan
- Department of Mechanical and Industrial Engineering, Northeastern University, Boston, Massachusetts 02115, USA
| | - Matthew G Knepley
- Computation Institute, The University of Chicago, Chicago, Illinois 60637, USA
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40
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Michel J, Henchman RH, Gerogiokas G, Southey MWY, Mazanetz MP, Law RJ. Evaluation of Host–Guest Binding Thermodynamics of Model Cavities with Grid Cell Theory. J Chem Theory Comput 2014; 10:4055-68. [DOI: 10.1021/ct500368p] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
Affiliation(s)
- Julien Michel
- EaStCHEM
School of Chemistry, Joseph Black Building, King’s Buildings, Edinburgh EH9 3JJ, United Kingdom
| | - Richard H. Henchman
- Manchester
Institute of Biotechnology, The University of Manchester, 131 Princess
Street, Manchester M1 7DN, United Kingdom
- School
of Chemistry, The University of Manchester, Oxford Road, Manchester M13 9PL, United Kingdom
| | - Georgios Gerogiokas
- EaStCHEM
School of Chemistry, Joseph Black Building, King’s Buildings, Edinburgh EH9 3JJ, United Kingdom
| | - Michelle W. Y. Southey
- Evotec (U.K.) Limited, Innovation
Drive 114 Milton Park, Abingdon, Oxfordshire, OX14 4RZ, United Kingdom
| | - Michael P. Mazanetz
- Evotec (U.K.) Limited, Innovation
Drive 114 Milton Park, Abingdon, Oxfordshire, OX14 4RZ, United Kingdom
| | - Richard J. Law
- Evotec (U.K.) Limited, Innovation
Drive 114 Milton Park, Abingdon, Oxfordshire, OX14 4RZ, United Kingdom
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41
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Phan CM, Nguyen CV, Yusa SI, Yamada NL. Synergistic adsorption of MIBC/CTAB mixture at the air/water interface and applicability of Gibbs adsorption equation. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2014; 30:5790-5796. [PMID: 24804567 DOI: 10.1021/la500721d] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/03/2023]
Abstract
The synergistic adsorption of a binary surfactant mixture was investigated by tensiometry and neutron reflectometry. The results directly contradicted the conventional Gibbs adsorption equation. The accompanied molecular simulation demonstrated a multilayer arrangement at the synergic conditions, with three distinctively oriented water layers. The positive synergism can be explained by considering the relationship between water orientation and surface tension, in a similar manner to Langmuir's proposal in 1920s. In spite of the supporting evidence, the relationship has not been quantified in literature. The molecular orientation and arrangement are not included in the current theoretical framework, which simplifies the adsorbed zone into a single monolayer. A new theoretical framework is needed to properly quantify the interfacial adsorption for the mixed surfactant systems.
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Affiliation(s)
- Chi M Phan
- Department of Chemical Engineering, Curtin University , Perth, WA 6845, Australia
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42
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Mukhopadhyay A, Aguilar BH, Tolokh IS, Onufriev AV. Introducing Charge Hydration Asymmetry into the Generalized Born Model. J Chem Theory Comput 2014; 10:1788-1794. [PMID: 24803871 PMCID: PMC3985468 DOI: 10.1021/ct4010917] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/18/2013] [Indexed: 12/15/2022]
Abstract
The effect of charge hydration asymmetry (CHA)-non-invariance of solvation free energy upon solute charge inversion-is missing from the standard linear response continuum electrostatics. The proposed charge hydration asymmetric-generalized Born (CHA-GB) approximation introduces this effect into the popular generalized Born (GB) model. The CHA is added to the GB equation via an analytical correction that quantifies the specific propensity of CHA of a given water model; the latter is determined by the charge distribution within the water model. Significant variations in CHA seen in explicit water (TIP3P, TIP4P-Ew, and TIP5P-E) free energy calculations on charge-inverted "molecular bracelets" are closely reproduced by CHA-GB, with the accuracy similar to models such as SEA and 3D-RISM that go beyond the linear response. Compared against reference explicit (TIP3P) electrostatic solvation free energies, CHA-GB shows about a 40% improvement in accuracy over the canonical GB, tested on a diverse set of 248 rigid small neutral molecules (root mean square error, rmse = 0.88 kcal/mol for CHA-GB vs 1.24 kcal/mol for GB) and 48 conformations of amino acid analogs (rmse = 0.81 kcal/mol vs 1.26 kcal/mol). CHA-GB employs a novel definition of the dielectric boundary that does not subsume the CHA effects into the intrinsic atomic radii. The strategy leads to finding a new set of intrinsic atomic radii optimized for CHA-GB; these radii show physically meaningful variation with the atom type, in contrast to the radii set optimized for GB. Compared to several popular radii sets used with the original GB model, the new radii set shows better transferability between different classes of molecules.
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Affiliation(s)
| | - Boris H. Aguilar
- Department
of Computer Science, Virginia Tech, Blacksburg, Virginia 24061, United States
| | - Igor S. Tolokh
- Department
of Computer Science, Virginia Tech, Blacksburg, Virginia 24061, United States
| | - Alexey V. Onufriev
- Department
of Physics, Virginia Tech, Blacksburg, Virginia 24061, United States
- Department
of Computer Science, Virginia Tech, Blacksburg, Virginia 24061, United States
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43
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Milosevic M, Staal KJ, Bargeman G, Schuur B, de Haan AB. Fractionation of aqueous sodium salts by liquid–liquid extraction in aqueous two phase systems. Sep Purif Technol 2014. [DOI: 10.1016/j.seppur.2014.01.058] [Citation(s) in RCA: 3] [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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44
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Reif MM, Oostenbrink C. Net charge changes in the calculation of relative ligand-binding free energies via classical atomistic molecular dynamics simulation. J Comput Chem 2014; 35:227-43. [PMID: 24249099 PMCID: PMC4237198 DOI: 10.1002/jcc.23490] [Citation(s) in RCA: 53] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/13/2013] [Accepted: 10/13/2013] [Indexed: 12/11/2022]
Abstract
The calculation of binding free energies of charged species to a target molecule is a frequently encountered problem in molecular dynamics studies of (bio-)chemical thermodynamics. Many important endogenous receptor-binding molecules, enzyme substrates, or drug molecules have a nonzero net charge. Absolute binding free energies, as well as binding free energies relative to another molecule with a different net charge will be affected by artifacts due to the used effective electrostatic interaction function and associated parameters (e.g., size of the computational box). In the present study, charging contributions to binding free energies of small oligoatomic ions to a series of model host cavities functionalized with different chemical groups are calculated with classical atomistic molecular dynamics simulation. Electrostatic interactions are treated using a lattice-summation scheme or a cutoff-truncation scheme with Barker-Watts reaction-field correction, and the simulations are conducted in boxes of different edge lengths. It is illustrated that the charging free energies of the guest molecules in water and in the host strongly depend on the applied methodology and that neglect of correction terms for the artifacts introduced by the finite size of the simulated system and the use of an effective electrostatic interaction function considerably impairs the thermodynamic interpretation of guest-host interactions. Application of correction terms for the various artifacts yields consistent results for the charging contribution to binding free energies and is thus a prerequisite for the valid interpretation or prediction of experimental data via molecular dynamics simulation. Analysis and correction of electrostatic artifacts according to the scheme proposed in the present study should therefore be considered an integral part of careful free-energy calculation studies if changes in the net charge are involved.
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Affiliation(s)
- Maria M Reif
- Institute for Molecular Modeling and Simulation, University of Natural Resources and Life Sciences ViennaMuthgasse 18, 1190, Wien, Austria
| | - Chris Oostenbrink
- Institute for Molecular Modeling and Simulation, University of Natural Resources and Life Sciences ViennaMuthgasse 18, 1190, Wien, Austria
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45
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46
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Pomogaeva A, Chipman DM. Hydrogen atom in water from ambient to high temperatures. J Phys Chem B 2013; 117:16530-41. [PMID: 24298910 DOI: 10.1021/jp4106844] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/21/2023]
Abstract
The aqueous hydrogen atom is studied with molecular dynamics simulations from ambient temperature to near the critical point. The radial distribution functions find a hydrogen atom coordination number of about 13 water molecules at 300 K to about 4 water molecules at 646 K. The radial and angular distribution functions indicate that first-shell water molecules tend to orient to maximize hydrogen bonding interactions with other water molecules. These orientational tendencies diminish with temperature. The calculated diffusion coefficient agrees very well with experimental results known near ambient temperatures. It fits a simple activation model to about 575 K, above which the diffusion becomes much faster than predicted by the fit. To temperatures of at least 500 K there is evidence for caging on a time scale of about 1 ps, but the evidence disappears at very high temperatures. Values of the aqueous hydrogen hyperfine coupling constant are obtained by averaging the results of density functional calculations on clusters extracted from the simulations. The hyperfine coupling calculations do not agree well with experiment for reasons that are not understood now, pointing to the need for further research on this problem.
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Affiliation(s)
- Anna Pomogaeva
- Radiation Laboratory, University of Notre Dame , Notre Dame, Indiana 46556-5674, United States
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47
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Vlcek L, Chialvo AA, Simonson JM. Correspondence between Cluster-Ion and Bulk Solution Thermodynamic Properties: On the Validity of the Cluster-Pair-Based Approximation. J Phys Chem A 2013; 117:11328-38. [DOI: 10.1021/jp408632e] [Citation(s) in RCA: 38] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023]
Affiliation(s)
- Lukas Vlcek
- Chemical
Sciences Division, Geochemistry & Interfacial Sciences Group, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831-6110, United States
- Joint
Institute for Computational Sciences, Oak Ridge National Laboratory, Oak
Ridge, Tennessee 37831-6173, United States
| | - Ariel A. Chialvo
- Chemical
Sciences Division, Geochemistry & Interfacial Sciences Group, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831-6110, United States
| | - J. Michael Simonson
- Chemical
& Engineering Materials Division, Oak Ridge National Laboratory, Oak
Ridge, Tennessee 37831-6475, United States
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48
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Chipman DM. Water from Ambient to Supercritical Conditions with the AMOEBA Model. J Phys Chem B 2013; 117:5148-55. [DOI: 10.1021/jp400750z] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/23/2023]
Affiliation(s)
- Daniel M. Chipman
- Radiation Laboratory, University of Notre Dame, Notre Dame, Indiana 46556-5674, United States
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49
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Ion desolvation as a mechanism for kinetic isotope fractionation in aqueous systems. Proc Natl Acad Sci U S A 2012; 109:18689-94. [PMID: 23112160 DOI: 10.1073/pnas.1208184109] [Citation(s) in RCA: 77] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Molecular dynamics simulations show that the desolvation rates of isotopes of Li(+), K(+), Rb(+), Ca(2+), Sr(2+), and Ba(2+) may have a relatively strong dependence on the metal cation mass. This inference is based on the observation that the exchange rate constant, k(wex), for water molecules in the first hydration shell follows an inverse power-law mass dependence (k(wex) ∝ m(-γ)), where the coefficient γ is 0.05 ± 0.01 on average for all cations studied. Simulated water-exchange rates increase with temperature and decrease with increasing isotopic mass for each element. The magnitude of the water-exchange rate is different for simulations run using different water models [i.e., extended simple point charge (SPC/E) vs. four-site transferrable intermolecular potential (TIP4P)]; however, the value of the mass exponent γ is the same. Reaction rate theory calculations predict mass exponents consistent with those determined via molecular dynamics simulations. The simulation-derived mass dependences imply that solids precipitating from aqueous solution under kinetically controlled conditions should be enriched in the light isotopes of the metal cations relative to the solutions, consistent with measured isotopic signatures in natural materials and laboratory experiments. Desolvation effects are large enough that they may be a primary determinant of the observed isotopic fractionation during precipitation.
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50
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Zidi ZS. On the stability of ion water clusters at atmospheric conditions: Open system Monte Carlo simulation. J Chem Phys 2012; 137:124107. [DOI: 10.1063/1.4754528] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023] Open
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