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Naleem N, Bentenitis N, Smith PE. A Kirkwood-Buff derived force field for alkaline earth halide salts. J Chem Phys 2018; 148:222828. [PMID: 29907021 DOI: 10.1063/1.5019454] [Citation(s) in RCA: 20] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022] Open
Abstract
The activity and function of many macromolecules in cellular environments are coupled with the binding of divalent ions such as calcium or magnesium. In principle, computer simulations can be used to understand the molecular level aspects of how many important macromolecules interact with ions. However, most of the force fields currently available often fail to accurately reproduce the properties of divalent ions in aqueous environments. Here we develop classical non-polarizable force fields for the aqueous alkaline earth metal halides (MX2), where M = Mg2+, Ca2+, Sr2+, Ba2+ and X = Cl-, Br-, I-, which can be used in bimolecular simulations and which are compatible with the Simple Point Charge/Extended (SPC/E) water model. The force field parameters are specifically developed to reproduce the experimental Kirkwood-Buff integrals for aqueous solutions and thereby the experimental activity derivatives, partial molar volumes, and excess coordination numbers. This ensures that a reasonable balance between ion-ion, ion-water, and water-water distributions is obtained. However, this requires a scaling of the cation to water oxygen interaction strength in order to accurately reproduce the integrals. The scaling factors developed for chloride salts are successfully transferable to the bromide and iodide salts. Use of these new models leads to reasonable diffusion constants and dielectric decrements. However, the performance of the models decreases with increasing salt concentration (>4m), and simulations of the pure crystals exhibited unstable behavior.
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Affiliation(s)
- Nawavi Naleem
- Department of Chemistry, Kansas State University, 213 CBC Building, 1212 Mid Campus Dr. North, Manhattan, Kansas 66506-0401, USA
| | - Nikolaos Bentenitis
- Department of Chemistry, Kansas State University, 213 CBC Building, 1212 Mid Campus Dr. North, Manhattan, Kansas 66506-0401, USA
| | - Paul E Smith
- Department of Chemistry, Kansas State University, 213 CBC Building, 1212 Mid Campus Dr. North, Manhattan, Kansas 66506-0401, USA
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Dharmawardhana CC, Ichiye T. Building better water models using the shape of the charge distribution of a water molecule. J Chem Phys 2018; 147:194103. [PMID: 29166096 DOI: 10.1063/1.4986070] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022] Open
Abstract
The unique properties of liquid water apparently arise from more than just the tetrahedral bond angle between the nuclei of a water molecule since simple three-site models of water are poor at mimicking these properties in computer simulations. Four- and five-site models add partial charges on dummy sites and are better at modeling these properties, which suggests that the shape of charge distribution is important. Since a multipole expansion of the electrostatic potential describes a charge distribution in an orthogonal basis set that is exact in the limit of infinite order, multipoles may be an even better way to model the charge distribution. In particular, molecular multipoles up to the octupole centered on the oxygen appear to describe the electrostatic potential from electronic structure calculations better than four- and five-site models, and molecular multipole models give better agreement with the temperature and pressure dependence of many liquid state properties of water while retaining the computational efficiency of three-site models. Here, the influence of the shape of the molecular charge distribution on liquid state properties is examined by correlating multipoles of non-polarizable water models with their liquid state properties in computer simulations. This will aid in the development of accurate water models for classical simulations as well as in determining the accuracy needed in quantum mechanical/molecular mechanical studies and ab initio molecular dynamics simulations of water. More fundamentally, this will lead to a greater understanding of how the charge distribution of a water molecule leads to the unique properties of liquid water. In particular, these studies indicate that p-orbital charge out of the molecular plane is important.
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Affiliation(s)
| | - Toshiko Ichiye
- Department of Chemistry, Georgetown University, Washington, DC 20057, USA
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3
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Tran KN, Tan ML, Ichiye T. A single-site multipole model for liquid water. J Chem Phys 2016; 145:034501. [DOI: 10.1063/1.4958621] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Affiliation(s)
- Kelly N. Tran
- Department of Chemistry, Georgetown University, Washington, DC 20057, USA
| | - Ming-Liang Tan
- Department of Chemistry, Georgetown University, Washington, DC 20057, USA
| | - Toshiko Ichiye
- Department of Chemistry, Georgetown University, Washington, DC 20057, USA
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Tan ML, Tran KN, Pickard FC, Simmonett AC, Brooks BR, Ichiye T. Molecular Multipole Potential Energy Functions for Water. J Phys Chem B 2015; 120:1833-42. [DOI: 10.1021/acs.jpcb.5b09565] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- Ming-Liang Tan
- Department
of Chemistry, Georgetown University, Washington, DC 20057, United States
- Laboratory
of Computational Biology, National Heart, Lung, and Blood Institute, National Institutes of Health, Rockville, Maryland 20892, United States
| | - Kelly N. Tran
- Department
of Chemistry, Georgetown University, Washington, DC 20057, United States
| | - Frank C. Pickard
- Laboratory
of Computational Biology, National Heart, Lung, and Blood Institute, National Institutes of Health, Rockville, Maryland 20892, United States
| | - Andrew C. Simmonett
- Laboratory
of Computational Biology, National Heart, Lung, and Blood Institute, National Institutes of Health, Rockville, Maryland 20892, United States
| | - Bernard R. Brooks
- Laboratory
of Computational Biology, National Heart, Lung, and Blood Institute, National Institutes of Health, Rockville, Maryland 20892, United States
| | - Toshiko Ichiye
- Department
of Chemistry, Georgetown University, Washington, DC 20057, United States
- Laboratory
of Computational Biology, National Heart, Lung, and Blood Institute, National Institutes of Health, Rockville, Maryland 20892, United States
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Tan ML, Miller BT, Te J, Cendagorta JR, Brooks BR, Ichiye T. Hydrophobic hydration and the anomalous partial molar volumes in ethanol-water mixtures. J Chem Phys 2015; 142:064501. [PMID: 25681917 DOI: 10.1063/1.4906750] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022] Open
Abstract
The anomalous behavior in the partial molar volumes of ethanol-water mixtures at low concentrations of ethanol is studied using molecular dynamics simulations. Previous work indicates that the striking minimum in the partial molar volume of ethanol VE as a function of ethanol mole fraction XE is determined mainly by water-water interactions. These results were based on simulations that used one water model for the solute-water interactions but two different water models for the water-water interactions. This is confirmed here by using two more water models for the water-water interactions. Furthermore, the previous work indicates that the initial decrease is caused by association of the hydration shells of the hydrocarbon tails, and the minimum occurs at the concentration where all of the hydration shells are touching each other. Thus, the characteristics of the hydration of the tail that cause the decrease and the features of the water models that reproduce this type of hydration are also examined here. The results show that a single-site multipole water model with a charge distribution that mimics the large quadrupole and the p-orbital type electron density out of the molecular plane has "brittle" hydration with hydrogen bonds that break as the tails touch, which reproduces the deep minimum. However, water models with more typical site representations with partial charges lead to flexible hydration that tends to stay intact, which produces a shallow minimum. Thus, brittle hydration may play an essential role in hydrophobic association in water.
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Affiliation(s)
- Ming-Liang Tan
- Department of Chemistry, Georgetown University, Washington, District of Columbia 20057, USA
| | - Benjamin T Miller
- Laboratory of Computational Biology, National Heart, Lung, and Blood Institute, National Institutes of Health, Rockville, Maryland 20892, USA
| | - Jerez Te
- Department of Chemistry, Georgetown University, Washington, District of Columbia 20057, USA
| | - Joseph R Cendagorta
- Department of Chemistry, Georgetown University, Washington, District of Columbia 20057, USA
| | - Bernard R Brooks
- Laboratory of Computational Biology, National Heart, Lung, and Blood Institute, National Institutes of Health, Rockville, Maryland 20892, USA
| | - Toshiko Ichiye
- Department of Chemistry, Georgetown University, Washington, District of Columbia 20057, USA
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Tan ML, Cendagorta JR, Ichiye T. The molecular charge distribution, the hydration shell, and the unique properties of liquid water. J Chem Phys 2014; 141:244504. [DOI: 10.1063/1.4904263] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Affiliation(s)
- Ming-Liang Tan
- Department of Chemistry, Georgetown University, Washington DC 20057, USA
| | | | - Toshiko Ichiye
- Department of Chemistry, Georgetown University, Washington DC 20057, USA
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