151
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Vincze J, Valiskó M, Boda D. Response to “Comment on ‘The nonmonotonic concentration dependence of the mean activity coefficient of electrolytes is a result of a balance between solvation and ion–ion correlations’” [J. Chem. Phys. 134, 157101 (2011)]. J Chem Phys 2011. [DOI: 10.1063/1.3575602] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
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152
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Understanding the role of ion interactions in soluble salt flotation with alkylammonium and alkylsulfate collectors. Adv Colloid Interface Sci 2011; 163:1-22. [PMID: 21353193 DOI: 10.1016/j.cis.2011.01.003] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/26/2010] [Revised: 01/06/2011] [Accepted: 01/10/2011] [Indexed: 11/22/2022]
Abstract
There is anecdotal evidence for the significant effects of salt ions on the flotation separation of minerals using process water of high salt content. Examples include flotation of soluble salt minerals such as potash, trona and borax in brine solutions using alkylammonium and alkylsulfate collectors such as dodecylamine hydrochloride and sodium dodecylsulfate. Although some of the effects are expected, some do not seem to be encompassed by classical theories of colloid science. Several experimental and modeling techniques for determining solution viscosity, surface tension, bubble-particle attachment time, contact angle, and molecular dynamics simulation have been used to provide further information on air-solution and solid-solution interfacial phenomena, especially with respect to the interfacial water structure due to the presence of dissolved ions. In addition atomic force microscopy, and sum frequency generation vibrational spectroscopy have been used to provide further information on surface states. These studies indicate that the ion specificity effect is the most significant factor influencing flotation in brine solutions.
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153
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Corradini D, Gallo P, Rovere M. Structure and thermodynamics of supercooled aqueous solutions: Ionic solutes compared with water in a hydrophobic environment. J Mol Liq 2011. [DOI: 10.1016/j.molliq.2010.03.017] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
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154
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Calero C, Faraudo J, Aguilella-Arzo M. Molecular dynamics simulations of concentrated aqueous electrolyte solutions. MOLECULAR SIMULATION 2011. [DOI: 10.1080/08927022.2010.525513] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
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155
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Corradini D, Rovere M, Gallo P. Structural Properties of High and Low Density Water in a Supercooled Aqueous Solution of Salt. J Phys Chem B 2011; 115:1461-8. [DOI: 10.1021/jp1101237] [Citation(s) in RCA: 41] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- D. Corradini
- Dipartimento di Fisica, Università “Roma Tre”, Via della Vasca Navale 84, I-00146 Roma, Italy
| | - M. Rovere
- Dipartimento di Fisica, Università “Roma Tre”, Via della Vasca Navale 84, I-00146 Roma, Italy
| | - P. Gallo
- Dipartimento di Fisica, Università “Roma Tre”, Via della Vasca Navale 84, I-00146 Roma, Italy
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156
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Gallo P, Corradini D, Rovere M. Ion hydration and structural properties of water in aqueous solutions at normal and supercooled conditions: a test of the structure making and breaking concept. Phys Chem Chem Phys 2011; 13:19814-22. [DOI: 10.1039/c1cp22166c] [Citation(s) in RCA: 64] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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157
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Marcus Y. Effect of ions on the structure of water: structure making and breaking. Chem Rev 2010; 109:1346-70. [PMID: 19236019 DOI: 10.1021/cr8003828] [Citation(s) in RCA: 1073] [Impact Index Per Article: 76.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
Affiliation(s)
- Yizhak Marcus
- Institute of Chemistry, The Hebrew University of Jerusalem, Jerusalem 91904, Israel
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158
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Corradini D, Gallo P, Rovere M. Molecular dynamics studies on the thermodynamics of supercooled sodium chloride aqueous solution at different concentrations. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2010; 22:284104. [PMID: 21399276 DOI: 10.1088/0953-8984/22/28/284104] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/30/2023]
Abstract
In this paper we compare recent results obtained by means of molecular dynamics computer simulations on the thermodynamics of TIP4P bulk water and on solutions of sodium chloride in TIP4P water. The concentrations studied are c = 0.67, 1.36 and 2.10 mol kg( - 1). The results are checked against change of water-salt potential and size effects. The systems are studied in a wide range of temperatures, going from ambient temperature to the supercooled region. Analysis of simulated state points, performed on the isochores and on the isotherm plane, allowed the determination of the limit of mechanical stability and of the temperature of maximum density lines. While the presence of ions in the system does not affect the limit of mechanical stability with respect to the bulk, it causes the temperature of the maximum density line to shift to lower pressure and temperature upon increasing concentration. The occurrence of minima in the trend of potential energy as a function of density and the inflections in the low temperature isotherms suggest the presence of liquid-liquid coexistence for bulk water and for the sodium chloride solutions at all concentrations studied.
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Affiliation(s)
- D Corradini
- Dipartimento di Fisica, Università Roma Tre, Via della Vasca Navale 84, I-00146 Roma, Italy
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159
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Zhang C, Raugei S, Eisenberg B, Carloni P. Molecular Dynamics in Physiological Solutions: Force Fields, Alkali Metal Ions, and Ionic Strength. J Chem Theory Comput 2010; 6:2167-75. [DOI: 10.1021/ct9006579] [Citation(s) in RCA: 49] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023]
Affiliation(s)
- Chao Zhang
- German Research School for Simulation Sciences, FZ-Juelich/RWTH Aachen University, Aachen, Germany, Pacific Northwest National Laboratory, 902 Battelle Boulevard, Richland, Washington 99352, Rush University Medical Center, 1653 W. Congress Parkway, Chicago, Illinois 60612, and SISSA, CNR-INFN-DEMOCRITOS, and Italian Institue of Technology (IIT), SISSA Unit, Trieste, Italy
| | - Simone Raugei
- German Research School for Simulation Sciences, FZ-Juelich/RWTH Aachen University, Aachen, Germany, Pacific Northwest National Laboratory, 902 Battelle Boulevard, Richland, Washington 99352, Rush University Medical Center, 1653 W. Congress Parkway, Chicago, Illinois 60612, and SISSA, CNR-INFN-DEMOCRITOS, and Italian Institue of Technology (IIT), SISSA Unit, Trieste, Italy
| | - Bob Eisenberg
- German Research School for Simulation Sciences, FZ-Juelich/RWTH Aachen University, Aachen, Germany, Pacific Northwest National Laboratory, 902 Battelle Boulevard, Richland, Washington 99352, Rush University Medical Center, 1653 W. Congress Parkway, Chicago, Illinois 60612, and SISSA, CNR-INFN-DEMOCRITOS, and Italian Institue of Technology (IIT), SISSA Unit, Trieste, Italy
| | - Paolo Carloni
- German Research School for Simulation Sciences, FZ-Juelich/RWTH Aachen University, Aachen, Germany, Pacific Northwest National Laboratory, 902 Battelle Boulevard, Richland, Washington 99352, Rush University Medical Center, 1653 W. Congress Parkway, Chicago, Illinois 60612, and SISSA, CNR-INFN-DEMOCRITOS, and Italian Institue of Technology (IIT), SISSA Unit, Trieste, Italy
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160
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Yang L, Huang K. Electric Conductivity in Electrolyte Solution under External Electromagnetic Field by Nonequilibrium Molecular Dynamics Simulation. J Phys Chem B 2010; 114:8449-52. [DOI: 10.1021/jp102593m] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
Affiliation(s)
- LiJun Yang
- College of Electronics and Information Engineering, Sichuan University, Chengdu, 610064, People’s Republic of China
| | - KaMa Huang
- College of Electronics and Information Engineering, Sichuan University, Chengdu, 610064, People’s Republic of China
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161
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Sala J, Guàrdia E, Martí J. Effects of concentration on structure, dielectric, and dynamic properties of aqueous NaCl solutions using a polarizable model. J Chem Phys 2010; 132:214505. [DOI: 10.1063/1.3429253] [Citation(s) in RCA: 45] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/12/2023] Open
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162
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163
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Joung IS, Cheatham TE. Molecular dynamics simulations of the dynamic and energetic properties of alkali and halide ions using water-model-specific ion parameters. J Phys Chem B 2009; 113:13279-90. [PMID: 19757835 PMCID: PMC2755304 DOI: 10.1021/jp902584c] [Citation(s) in RCA: 388] [Impact Index Per Article: 25.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The dynamic and energetic properties of the alkali and halide ions were calculated using molecular dynamics (MD) and free energy simulations with various different water and ion force fields including our recently developed water-model-specific ion parameters. The properties calculated were activity coefficients, diffusion coefficients, residence times of atomic pairs, association constants, and solubility. Through calculation of these properties, we can assess the validity and range of applicability of the simple pair potential models and better understand their limitations. Due to extreme computational demands, the activity coefficients were only calculated for a subset of the models. The results qualitatively agree with experiment. Calculated diffusion coefficients and residence times between cation-anion, water-cation, and water-anion showed differences depending on the choice of water and ion force field used. The calculated solubilities of the alkali-halide salts were generally lower than the true solubility of the salts. However, for both the TIP4P(EW) and SPC/E water-model-specific ion parameters, solubility was reasonably well-reproduced. Finally, the correlations among the various properties led to the following conclusions: (1) The reliability of the ion force fields is significantly affected by the specific choice of water model. (2) Ion-ion interactions are very important to accurately simulate the properties, especially solubility. (3) The SPC/E and TIP4P(EW) water-model-specific ion force fields are preferred for simulation in high salt environments compared to the other ion force fields.
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Affiliation(s)
- In Suk Joung
- Department of Bioengineering, College of Engineering, Department of Medicinal Chemistry, College of Pharmacy, and Department of Pharmaceutics and Pharmaceutical Chemistry, College of Pharmacy, University of Utah, Salt Lake City, Utah 84112, USA
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164
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Kitayama A, Yamanaka S, Kadota K, Shimosaka A, Shirakawa Y, Hidaka J. Diffusion behavior in a liquid-liquid interfacial crystallization by molecular dynamics simulations. J Chem Phys 2009; 131:174707. [DOI: 10.1063/1.3254517] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
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165
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Ibuki K, Bopp PA. Molecular dynamics simulations of aqueous LiCl solutions at room temperature through the entire concentration range. J Mol Liq 2009. [DOI: 10.1016/j.molliq.2008.08.005] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/21/2022]
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166
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Shevkunov SV. Polarization effects in Cl−(H2O) n clusters. Computer simulation. COLLOID JOURNAL 2009. [DOI: 10.1134/s1061933x0903017x] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
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167
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Raju SG, Balasubramanian S. Aqueous solution of [bmim][PF6]: ion and solvent effects on structure and dynamics. J Phys Chem B 2009; 113:4799-806. [PMID: 19338368 DOI: 10.1021/jp8111777] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
Abstract
A dilute aqueous solution of the salt 1-n-butyl,3-methylimidazolium hexafluorophosphate ([bmim][PF(6)]) has been studied using molecular dynamics simulations to investigate the effect of ions on water and vice versa. The anion is found to diffuse faster than the cation in the solution, in contrast to observations in the pure ionic liquid. Distributions of pair energies have been employed to identify ion association, and around 13% of the ions were found to exist as pairs. The mean potential energy of water molecules present in the coordination shell of an anion is less than that of water molecules coordinated to a cation. The former kind also exhibit two distinct orientational preferences with respect to the anion. The larger diffusion coefficient of the anion is related to the faster dynamics of water molecules in its hydration layer, as evidenced from the relaxation of their residence time correlation function.
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Affiliation(s)
- S G Raju
- Chemistry and Physics of Materials Unit, Jawaharlal Nehru Centre for Advanced Scientific Research, Jakkur, Bangalore 560 064, India
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168
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Daub CD, Leung K, Luzar A. Structure of Aqueous Solutions of Monosodium Glutamate. J Phys Chem B 2009; 113:7687-700. [DOI: 10.1021/jp810379m] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Christopher D. Daub
- Department of Chemistry, Virginia Commonwealth University, Richmond, Virginia 23284, and Sandia National Laboratories, MS 1415, Albuquerque, New Mexico 87185
| | - Kevin Leung
- Department of Chemistry, Virginia Commonwealth University, Richmond, Virginia 23284, and Sandia National Laboratories, MS 1415, Albuquerque, New Mexico 87185
| | - Alenka Luzar
- Department of Chemistry, Virginia Commonwealth University, Richmond, Virginia 23284, and Sandia National Laboratories, MS 1415, Albuquerque, New Mexico 87185
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169
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Corradini D, Gallo P, Rovere M. Effect of concentration on the thermodynamics of sodium chloride aqueous solutions in the supercooled regime. J Chem Phys 2009; 130:154511. [DOI: 10.1063/1.3119634] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
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170
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Yamaguchi T, Matsuoka T, Koda S. A theoretical study on the frequency-dependent electric conductivity of electrolyte solutions. II. Effect of hydrodynamic interaction. J Chem Phys 2009; 130:094506. [DOI: 10.1063/1.3085717] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/13/2023] Open
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171
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Kerisit S, Liu C. Molecular simulations of water and ion diffusion in nanosized mineral fractures. ENVIRONMENTAL SCIENCE & TECHNOLOGY 2009; 43:777-782. [PMID: 19245016 DOI: 10.1021/es8016045] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/27/2023]
Abstract
Molecular dynamics simulations were carried out to investigate the effects of confinement and of the presence of the mineral surface on the diffusion of water and electrolyte ions in nanosized mineral fractures. Feldspar was used as a representative mineral because recent studies found that it is an important mineral that hosts contaminants within its intragrain fractures at the U.S. Department of Energy Hanford site. Several properties of the mineral-water interface were varied, such as the fracture width, the ionic strength of the contacting solution, and the surface charge,to provide atomic-level insights into the diffusion of ions and contaminants within intragrain regions. In each case, the self-diffusion coefficient of water and that of the electrolyte ions were computed as a function of distance from the mineral surface. Our calculations reveal a 2.0-2.5 nm interfacial region within which the self-diffusion coefficient of water and that of the electrolyte ions decrease asthe diffusing species approach the surface. As a result of the extent of the interfacial region, water and electrolyte ions are predicted to never reach bulk-like diffusion in fractures narrower than approximately 5 nm. The average diffusion coefficient along the mineral fracture was computed as a function of fracture width and indicated that the surface effects only become negligible for fractures several tens of nanometers wide. The molecular dynamics results improve our conceptual models of ion transport in nanoscale pore regions surrounded by mineral surfaces in porous media.
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Affiliation(s)
- Sebastien Kerisit
- Chemical and Materials Sciences Division, Pacific Northwest National Laboratory, Richland, Washington 99352, USA.
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172
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Kitayama A, Yamanaka S, Kadota K, Shirakawa Y, Shimosaka A, Hidaka J. Diffusion and Cluster Formation near NaCl Solution/Organic Solvent Interface in a Crystallization Process. JOURNAL OF CHEMICAL ENGINEERING OF JAPAN 2009. [DOI: 10.1252/jcej.08we312] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Affiliation(s)
- Akira Kitayama
- Department of Chemical Engineering and Materials Science, Doshisha University
| | - Shinya Yamanaka
- Department of Chemical Engineering and Materials Science, Doshisha University
| | - Kazunori Kadota
- Department of Chemical Engineering and Materials Science, Doshisha University
| | - Yoshiyuki Shirakawa
- Department of Chemical Engineering and Materials Science, Doshisha University
| | - Atsuko Shimosaka
- Department of Chemical Engineering and Materials Science, Doshisha University
| | - Jusuke Hidaka
- Department of Chemical Engineering and Materials Science, Doshisha University
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173
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Shevkunov SV. Charge separation in water molecule clusters under thermal fluctuations: 2. Ionization-recombination equilibrium. COLLOID JOURNAL 2008. [DOI: 10.1134/s1061933x08050153] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
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174
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Corradini D, Gallo P, Rovere M. Thermodynamic behavior and structural properties of an aqueous sodium chloride solution upon supercooling. J Chem Phys 2008; 128:244508. [DOI: 10.1063/1.2939118] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
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175
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Gupta R, Chandra A. Single particle and pair dynamics in water–formic acid mixtures containing ionic and neutral solutes: Nonideality in dynamical properties. J Chem Phys 2008; 128:184506. [DOI: 10.1063/1.2913058] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022] Open
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176
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Khavrutskii IV, Dzubiella J, McCammon JA. Computing accurate potentials of mean force in electrolyte solutions with the generalized gradient-augmented harmonic Fourier beads method. J Chem Phys 2008; 128:044106. [PMID: 18247929 DOI: 10.1063/1.2825620] [Citation(s) in RCA: 59] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/20/2023] Open
Abstract
We establish the accuracy of the novel generalized gradient-augmented harmonic Fourier beads (ggaHFB) method in computing free-energy profiles or potentials of mean force (PMFs) through comparison with two independent conventional techniques. In particular, we employ umbrella sampling with one dimensional weighted histogram analysis method (WHAM) and free molecular dynamics simulation of radial distribution functions to compute the PMF for the Na(+)-Cl(-) ion-pair separation to 16 A in 1.0M NaCl solution in water. The corresponding ggaHFB free-energy profile in six dimensional Cartesian space is in excellent agreement with the conventional benchmarks. We then explore changes in the PMF in response to lowering the NaCl concentration to physiological 0.3 and 0.1M, and dilute 0.0M concentrations. Finally, to expand the scope of the ggaHFB method, we formally develop the free-energy gradient approximation in arbitrary nonlinear coordinates. This formal development underscores the importance of the logarithmic Jacobian correction to reconstruct true PMFs from umbrella sampling simulations with either WHAM or ggaHFB techniques when nonlinear coordinate restraints are used with Cartesian propagators. The ability to employ nonlinear coordinates and high accuracy of the computed free-energy profiles further advocate the use of the ggaHFB method in studies of rare events in complex systems.
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Affiliation(s)
- Ilja V Khavrutskii
- Howard Hughes Medical Institute, Center for Theoretical Biological Physics, Department of Chemistry and Biochemistry, University of California San Diego, La Jolla, California 92093-0365, USA.
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177
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McKenzie I, Dilger H, Roduner E, Scheuermann R, Zimmermann U. Solvation of a Hydrogen Isotope in Aqueous Methanol, NaCl, and KCl Solutions. J Phys Chem B 2008; 112:3070-6. [DOI: 10.1021/jp0769882] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/17/2023]
Affiliation(s)
- Iain McKenzie
- Institut für Physikalische Chemie, Universität Stuttgart, Pfaffenwaldring 55, D-70569 Stuttgart, Germany, and Laboratory for Muon Spin Spectroscopy, Paul Scherrer Institute, CH-5232 Villigen, Switzerland
| | - Herbert Dilger
- Institut für Physikalische Chemie, Universität Stuttgart, Pfaffenwaldring 55, D-70569 Stuttgart, Germany, and Laboratory for Muon Spin Spectroscopy, Paul Scherrer Institute, CH-5232 Villigen, Switzerland
| | - Emil Roduner
- Institut für Physikalische Chemie, Universität Stuttgart, Pfaffenwaldring 55, D-70569 Stuttgart, Germany, and Laboratory for Muon Spin Spectroscopy, Paul Scherrer Institute, CH-5232 Villigen, Switzerland
| | - Robert Scheuermann
- Institut für Physikalische Chemie, Universität Stuttgart, Pfaffenwaldring 55, D-70569 Stuttgart, Germany, and Laboratory for Muon Spin Spectroscopy, Paul Scherrer Institute, CH-5232 Villigen, Switzerland
| | - Ulrich Zimmermann
- Institut für Physikalische Chemie, Universität Stuttgart, Pfaffenwaldring 55, D-70569 Stuttgart, Germany, and Laboratory for Muon Spin Spectroscopy, Paul Scherrer Institute, CH-5232 Villigen, Switzerland
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178
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Liu H, Jameson CJ, Murad S. Molecular dynamics simulation of ion selectivity process in nanopores. MOLECULAR SIMULATION 2008. [DOI: 10.1080/08927020801966087] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/22/2022]
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179
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Kim JS, Yethiraj A. A Diffusive Anomaly of Water in Aqueous Sodium Chloride Solutions at Low Temperatures. J Phys Chem B 2008; 112:1729-35. [DOI: 10.1021/jp076710+] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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180
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Aziz EF, Eisebitt S, Eberhardt W, Cwiklik L, Jungwirth P. Existence of Oriented Ion−Hydroxide Clusters in Concentrated Aqueous NaCl Solution at pH 13. J Phys Chem B 2008; 112:1262-6. [DOI: 10.1021/jp075031w] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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181
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Thomas AS, Elcock AH. Molecular Dynamics Simulations of Hydrophobic Associations in Aqueous Salt Solutions Indicate a Connection between Water Hydrogen Bonding and the Hofmeister Effect. J Am Chem Soc 2007; 129:14887-98. [DOI: 10.1021/ja073097z] [Citation(s) in RCA: 135] [Impact Index Per Article: 7.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Andrew S. Thomas
- Contribution from the Department of Biochemistry, University of Iowa, Iowa City, Iowa 52242
| | - Adrian H. Elcock
- Contribution from the Department of Biochemistry, University of Iowa, Iowa City, Iowa 52242
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182
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Nigro B, Re S, Laage D, Rey R, Hynes JT. On the ultrafast infrared spectroscopy of anion hydration shell hydrogen bond dynamics. J Phys Chem A 2007; 110:11237-43. [PMID: 17004732 DOI: 10.1021/jp064846m] [Citation(s) in RCA: 62] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023]
Abstract
Molecular Dynamics simulations are used to examine the title issue for the I-/HOD/D2O solution system in connection with recent ultrafast infrared spectroscopic experiments. It is argued that the long "modulation time" associated with the spectral diffusion of the OH frequency, extracted in these experiments, should be interpreted as reflecting the escape time of an HOD from the first hydration shell of the I- ion, i.e., the residence time of an HOD in this solvation shell. Shorter time features related to the oscillation of the OH ...I- hydrogen bond and the breaking and making of this bond are also discussed.
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Affiliation(s)
- Bruno Nigro
- Département de Chimie, UMR 8640 PASTEUR, Ecole Normale Supérieure, 24 rue Lhomond, 75231 Paris, France.
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183
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Chowdhuri S, Chandra A. Dynamics of halide ion-water hydrogen bonds in aqueous solutions: dependence on ion size and temperature. J Phys Chem B 2007; 110:9674-80. [PMID: 16686518 DOI: 10.1021/jp057544d] [Citation(s) in RCA: 123] [Impact Index Per Article: 7.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
We have carried out a series of molecular dynamics simulations to investigate the dynamics of X(-)-water (X = F, Cl, Br, and I) and water-water hydrogen bonds in aqueous alkali halide solutions at room temperature and also of Cl(-)-water and water-water hydrogen bonds at seven different temperatures ranging from 238 to 318 K. The hydrogen bonds are defined by using a set of configurational criteria with respect to the anion(oxygen)-oxygen and anion(oxygen)-hydrogen distances and the anion(oxygen)-oxygen-hydrogen angle for an anion(water)-water pair. The results of the hydrogen bond dynamics are obtained for two different cutoff values for the angular criterion. In both cases, similar dynamical behavior of the hydrogen bonds is found with respect to their dependence on ion size and temperature. The fluoride ion-water hydrogen bonds are found to break at a much slower rate than water-water hydrogen bonds, while the lifetimes of chloride and bromide ion-water hydrogen bonds are found to be shorter than those of fluoride ion-water ones but still longer than water-water hydrogen bonds. The short-time dynamics of iodide ion-water hydrogen bonds is found to be slightly faster, while its long-time dynamics is found to be slightly slower than the corresponding water-water hydrogen bond dynamics. Correlations of the observed dynamics of anion(water)-water hydrogen bonds with those of rotational and translational diffusion and residence times of water molecules in ion(water) hydration shells are also discussed. With variation of temperature, the lifetimes of both Cl(-)-water and water-water hydrogen bonds are found to show Arrhenius behavior with a slightly higher activation energy for the Cl(-)-water hydrogen bonds.
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Affiliation(s)
- Snehasis Chowdhuri
- Department of Chemistry, Indian Institute of Technology, Kanpur, India 208016
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184
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Gupta R, Chandra A. Nonideality in diffusion of ionic and hydrophobic solutes and pair dynamics in water-acetone mixtures of varying composition. J Chem Phys 2007; 127:024503. [PMID: 17640133 DOI: 10.1063/1.2751192] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022] Open
Abstract
We have performed a series of molecular dynamics simulations of water-acetone mixtures containing either an ionic solute or a neutral hydrophobic solute to study the extent of nonideality in the dynamics of these solutes with variation of composition of the mixtures. The diffusion coefficients of the charged solutes, both cationic and anionic, are found to change nonmonotonically with the composition of the mixtures showing strong nonideality of their dynamics. Also, the extent of nonideality in the diffusion of these charged solutes is found to be similar to the nonideality that is observed for the diffusion and orientational relaxation of water and acetone molecules in these mixtures which show a somewhat similar changes in the solvation characteristics of charged and dipolar solutes with changes of composition of water-acetone mixtures. The diffusion of the hydrophobic solute, however, shows a monotonic increase with increase of acetone concentration showing its different solvation characteristics as compared to the charged and dipolar solutes. The links between the nonideality in diffusion and solvation structures are further confirmed through calculations of the relevant solute-solvent and solvent-solvent radial distribution functions for both ionic and hydrophobic solutes. We have also calculated various pair dynamical properties such as the relaxation of water-water and acetone-water hydrogen bonds and residence dynamics of water molecules in water and acetone hydration shells. The lifetimes of both water-water and acetone-water hydrogen bonds and also the residence times of water molecules are found to increase steadily with increase in acetone concentration. No maximum or minimum was found in the composition dependence of these pair dynamical quantities. The lifetimes of water-water hydrogen bonds are always found to be longer than that of acetone-water hydrogen bonds in these mixtures. The residence times of water molecules are also found to follow a similar trend.
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Affiliation(s)
- Rini Gupta
- Department of Chemistry, Indian Institute of Technology, Kanpur, India 208016
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185
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Raghunathan AV, Aluru NR. Self-consistent molecular dynamics formulation for electric-field-mediated electrolyte transport through nanochannels. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2007; 76:011202. [PMID: 17677433 DOI: 10.1103/physreve.76.011202] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/02/2007] [Indexed: 05/16/2023]
Abstract
A self-consistent molecular dynamics (SCMD) formulation is presented for electric-field-mediated transport of water and ions through a nanochannel connected to reservoirs or baths. The SCMD formulation is compared with a uniform field MD approach, where the applied electric field is assumed to be uniform, for 2nm and 3.5nm wide nanochannels immersed in a 0.5M KCl solution. Reservoir ionic concentrations are maintained using the dual-control-volume grand canonical molecular dynamics technique. Simulation results with varying channel height indicate that the SCMD approach calculates the electrostatic potential in the simulation domain more accurately compared to the uniform field approach, with the deviation in results increasing with the channel height. The translocation times and ionic fluxes predicted by uniform field MD can be substantially different from those predicted by the SCMD approach. Our results also indicate that during a 2ns simulation time K+ ions can permeate through a 1nm channel when the applied electric field is computed self-consistently, while the permeation is not observed when the electric field is assumed to be uniform.
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Affiliation(s)
- A V Raghunathan
- Department of Mechanical Science and Engineering, Beckman Institute for Advanced Science and Technology, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, USA
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186
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Chen AA, Pappu RV. Quantitative characterization of ion pairing and cluster formation in strong 1:1 electrolytes. J Phys Chem B 2007; 111:6469-78. [PMID: 17518490 DOI: 10.1021/jp0708547] [Citation(s) in RCA: 97] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Aqueous solutions of 1:1 strong electrolytes are considered to be the prototype for complete ionic dissociation. Nonetheless, clustering of strong 1:1 electrolytes has been widely reported in all atom molecular dynamics simulations, and their presence is indirectly implicated in a diverse range of experimental results. Is there a physical basis for nonidealities such as ion pairing and cluster formation in aqueous solutions of strong 1:1 electrolytes? We attempt to answer this question by direct comparison of results from detailed molecular dynamics simulations to experimentally observed properties of 1:1 electrolytes. We report the analysis of a series of lengthy molecular dynamics simulations of alkali-halide solutions carried out over a wide range of physiologically relevant concentrations using explicit representations of water molecules. We find evidence for pronounced nonideal behavior of ions at all concentrations in the form of ion pairs and clusters which are in rapid equilibrium with dissociated ions. The phenomenology for ion pairing seen in these simulations is congruent with the multistep scheme proposed by Eigen and Tamm based on data from ultrasonic absorption experiments. For a given electrolyte, we show that the dependence of cluster populations on concentration can be described through a single set of equilibrium constants. We assess the accuracy of calculated ion pairing constants by favorable comparison to estimates obtained by Fuoss and co-workers and based on conductometric experiments. Ion pairs and clusters form on length scales where the size of individual water molecules is as important as the hard core radius of ions. Ion pairing results as a balance between the favorable Coulomb interactions and the unfavorable partial desolvation of ions needed to form a pair.
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Affiliation(s)
- Alan A Chen
- Molecular Biophysics Program & Center for Computational Biology, Washington University School of Medicine, St. Louis, Missouri 63110, USA
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187
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Mallik BS, Chandra A. Hydrogen bond and residence dynamics of ion–water and water–water pairs in supercritical aqueous ionic solutions: Dependence on ion size and density. J Chem Phys 2006; 125:234502. [PMID: 17190562 DOI: 10.1063/1.2403867] [Citation(s) in RCA: 58] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/20/2023] Open
Abstract
We have carried out a series of molecular dynamics simulations to investigate the hydrogen bond and residence dynamics of X(-)-water (X=F, Cl, and I) and pairs in aqueous solutions at a temperature of 673 K. The calculations are done at six different water densities ranging from 1.0 to 0.15 g cm(-3). The hydrogen bonds are defined by using a set of configurational criteria with respect to the anion(oxygen)-oxygen and anion(oxygen)-hydrogen distances and the anion(oxygen)-oxygen-hydrogen angle for an anion(water)-water pair. The F(-)-water hydrogen bonds are found to have a longer lifetime than all other hydrogen bonds considered in the present study. The lifetime of Cl(-)-water hydrogen bonds is shorter than that of F(-)-water hydrogen bonds but longer than the lifetime of water-water hydrogen bonds. The lifetimes of I(-)-water and water-water hydrogen bonds are found to be very similar. Generally, the lifetimes of both anion-water and water-water hydrogen bonds are found to be significantly shorter than those found under ambient conditions. In addition to hydrogen bond lifetimes, we have also calculated the residence times and the orientational relaxation times of water molecules in ion(water) hydration shells and have discussed the correlations of these dynamical quantities with the observed dynamics of anion(water)-water hydrogen bonds as functions of the ion size and density of the supercritical solutions.
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Affiliation(s)
- Bhabani S Mallik
- Department of Chemistry, Indian Institute of Technology, Kanpur, India
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188
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Du H, Rasaiah JC, Miller JD. Structural and Dynamic Properties of Concentrated Alkali Halide Solutions: A Molecular Dynamics Simulation Study. J Phys Chem B 2006; 111:209-17. [PMID: 17201445 DOI: 10.1021/jp064659o] [Citation(s) in RCA: 81] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The physicochemical properties of alkali halide solutions have long been attributed to the collective interactions between ions and water molecules in the solution, yet the structure of water in these systems and its effect on the equilibrium and dynamic properties of these systems are not clearly understood. Here, we present a systematic view of water structure in concentrated alkali halide solutions using molecular dynamics simulations. The results of the simulations show that the size of univalent ions in the solution has a significant effect on the dynamics of ions and other transport properties such as the viscosity that are correlated with the structural properties of water in aqueous ionic solution. Small cations (e.g., Li+) form electrostatically stabilized hydrophilic hydration shells that are different from the hydration shells of large ions (e.g., Cs+) which behave more like neutral hydrophobic particles, encapsulated by hydrogen-bonded hydration cages. The properties of solutions with different types of ion solvation change in different ways as the ion concentration increases. Examples of this are the diffusion coefficients of the ions and the viscosities of solutions. In this paper we use molecular dynamics (MD) simulations to study the changes in the equilibrium and transport properties of LiCl, RbCl, and CsI solutions at concentrations from 0.22 to 3.97 M.
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Affiliation(s)
- Hao Du
- Department of Metallurgical Engineering, 135 South 1460 East, 412 William C. Browning Building, University of Utah, Salt Lake City, Utah 84112, USA
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189
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Bouazizi S, Nasr S, Jaîdane N, Bellissent-Funel MC. Local Order in Aqueous NaCl Solutions and Pure Water: X-ray Scattering and Molecular Dynamics Simulations Study. J Phys Chem B 2006; 110:23515-23. [PMID: 17107207 DOI: 10.1021/jp0641583] [Citation(s) in RCA: 78] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The microstructures of pure water and aqueous NaCl solutions over a wide range of salt concentrations (0-4 m) under ambient conditions are characterized by X-ray scattering and molecular dynamics (MD) simulations. MD simulations are performed with the rigid SPC water model as a solvent, while the ions are treated as charged Lennard-Jones particles. Simulated data show that the first peaks in the O...O and O...H pair correlation functions clearly decrease in height with increasing salt concentration. Simultaneously, the location of the second O...O peak, the signature of the so-called tetrahedral structure of water, gradually disappears. Consequently, the degree of hydrogen bonding in liquid water decreases when compared to pure fluid. MD results also show that the hydration number around the cation decreases as the salt concentration increases, which is most likely because some water molecules in the first hydration shell are occasionally substituted by chlorine. In addition, the fraction of contact ion pairs increases and that of solvent-separated ion pairs decreases. Experimental data are analyzed to deduce the structure factors and the pair correlation functions of each system. X-ray results clearly show a perturbation of the association structure of the solvent and highlight the appearance of new interactions between ions and water. A model of intermolecular arrangement via MD results is then proposed to describe the local order in each system, as deduced from X-ray scattering data.
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Affiliation(s)
- Salah Bouazizi
- Laboratoire Physico-Chimie des Matériaux, Département de Physique, Faculté des Sciences de Monastir, 5019 Monastir, Tunisia
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190
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Abstract
Molecular dynamics simulations are carried out to investigate the permeation of ions and water in a membrane consisting of single wall carbon nanotubes possessing no surface charges connecting two reservoirs. Our simulations reveal that there are changes in the first hydration shell of the ions upon confinement in tubes of 0.82 or 0.90 nm effective internal diameter. Although the first minimum in the g(r) is barely changed in the nanotube compared to in the bulk solution, the hydration number of Na(+) ion is reduced by 1.0 (from 4.5 in bulk to 3.5 in the 0.90 nm tube) and the hydration number is reduced further in the 0.82 nm tube. The changes in the hydration shell of Cl(-) ion are negligible, within statistical errors. The water molecules of the first hydration shell of both ions exchange less frequently inside the tube than in the bulk solution. We compare ion trajectories for ions in the same tube under identical reservoir conditions but with different numbers of ions in the tubes. This permits investigation of changes in structure and dynamics which arise from multiple ion occupancy in a carbon nanotube possessing no surface charges. We also investigated the effects of tube flexibility. Ions enter the tubes so as to form a train of ion pairs. We find that the radial distribution profiles of Na(+) ions broaden significantly systematically with increasing number of ion pairs in the tube. The radial distribution profiles of Cl(-) ions change only slightly with increasing number of ions in the tube. Trajectories reveal that Na(+) ions do not pass each other in 0.90 nm tubes, while Cl(-) ions pass each other, as do ions of opposite charge. An ion entering the tube causes the like-charged ions preceding it in the tube to be displaced along the tube axis and positive or negative ions will exit the tube only when one or two other ions of the same charge are present in the tube. Thus, the permeation mechanism involves multiple ions and Coulomb repulsion among the ions plays an essential role.
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Affiliation(s)
- Hongmei Liu
- Department of Chemical Engineering, University of Illinois at Chicago, Chicago, IL 60607, USA
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191
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Ghorai PK, Yashonath S. Evidence in Support of Levitation Effect as the Reason for Size Dependence of Ionic Conductivity in Water: A Molecular Dynamics Simulation. J Phys Chem B 2006; 110:12179-90. [PMID: 16800534 DOI: 10.1021/jp061511w] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/16/2023]
Abstract
We report extensive molecular dynamics simulations of (i) model ions in water at high concentrations as a function of the size and charge of the ion as well as (ii) realistic simulation of Cl- and Br- ions at low concentrations in water at room temperature. We also analyze existing experimental data in light of the results obtained here. The halide ion simulations have been carried out using the interaction potentials of Koneshan et al. (J. Phys. Chem. B 1998, 102, 4193). We compute structural and dynamical properties of ions in water and explore their variation with size and charge of the ion. We find that ions of certain intermediate sizes exhibit a maximum in self-diffusivity in agreement with previous experimental measurements and computer simulations. We analyze molecular dynamics trajectories in light of the previous understanding of the levitation effect (LE) and the recent suggestion that ionic conductivity has its origin in LE (J. Phys. Chem. B 2005, 109, 8120). We report the distribution of void and neck radii that exist amidst water. Our analysis suggests that the ion with maximum self-diffusivity is characterized by a lower activation energy and a single-exponential decay of F(s)(k,t). The behavior of these and other related quantities of the ion with maximum self-diffusivity are characteristic of the anomalous regime of the LE. The simulation results of Br- and Cl- ions in water also yield results in agreement with the predictions of LE. A plot of experimental conductivity data in the literature for alkali ions in water by Kay and Evans (J. Phys. Chem. 1966, 70, 2325) also yields a lower activation energy for the ion with maximum conductivity in excellent agreement with the LE. To the best of our knowledge, none of the existing theories predict a lower activation energy for the ion with maximum conductivity.
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Affiliation(s)
- Pradip Kr Ghorai
- Solid State and Structural Chemistry Unit, Indian Institute of Science, Bangalore-560012, India
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192
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Effect of an external electric field on liquid water using molecular dynamics simulation with a flexible potential. ACTA ACUST UNITED AC 2006. [DOI: 10.1007/s11741-006-0127-1] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/23/2022]
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193
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Thomas AS, Elcock AH. Direct Observation of Salt Effects on Molecular Interactions through Explicit-Solvent Molecular Dynamics Simulations: Differential Effects on Electrostatic and Hydrophobic Interactions and Comparisons to Poisson−Boltzmann Theory. J Am Chem Soc 2006; 128:7796-806. [PMID: 16771493 DOI: 10.1021/ja058637b] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Proteins and other biomolecules function in cellular environments that contain significant concentrations of dissolved salts and even simple salts such as NaCl can significantly affect both the kinetics and thermodynamics of macromolecular interactions. As one approach to directly observing the effects of salt on molecular associations, explicit-solvent molecular dynamics (MD) simulations have been used here to model the association of pairs of the amino acid analogues acetate and methylammonium in aqueous NaCl solutions of concentrations 0, 0.1, 0.3, 0.5, 1, and 2 M. By performing simulations of 500 ns duration for each salt concentration properly converged estimates of the free energy of interaction of the two molecules have been obtained for all intermolecular separation distances and geometries. The resulting free energy surfaces are shown to give significant new insights into the way salt modulates interactions between molecules containing both charged and hydrophobic groups and are shown to provide valuable new benchmarks for testing the description of salt effects provided by the simpler but faster Poisson-Boltzmann method. In addition, the complex many-dimensional free energy surfaces are shown to be decomposable into a number of one-dimensional effective energy functions. This decomposition (a) allows an unambiguous view of the qualitative differences between the salt dependence of electrostatic and hydrophobic interactions, (b) gives a clear rationalization for why salt exerts different effects on protein-protein association and dissociation rates, and (c) produces simplified energy functions that can be readily used in much faster Brownian dynamics simulations.
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Affiliation(s)
- Andrew S Thomas
- Department of Biochemistry, University of Iowa, Iowa City, Iowa 52242, USA
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194
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Bahadur R, Russell LM, Alavi S, Martin ST, Buseck PR. Void-induced dissolution in molecular dynamics simulations of NaCl and water. J Chem Phys 2006; 124:154713. [PMID: 16674257 DOI: 10.1063/1.2185091] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022] Open
Abstract
To gain a better understanding of the interaction of water and NaCl at the surface during dissolution, we have used molecular dynamics to simulate the interface with two equal-sized slabs of solid NaCl and liquid water in contact. The introduction of voids in the bulk of the salt, as well as steps or pits on the surface of the NaCl slab results in a qualitative change of system structure, as defined by radial distribution functions (RDFs). As an example, the characteristic Na-Na RDF for the system changes from regularly spaced narrow peaks (corresponding to an ordered crystalline structure), to a broad primary and smaller secondary peak (corresponding to a disordered structure). The change is observed at computationally short time scales of 100 ps, in contrast with a much longer time scale of 1 mus expected for complete mixing in the absence of defects. The void fraction (which combines both bulk and surface defects) required to trigger dissolution varies between 15%-20% at 300 K and 1 atm, and has distinct characteristics for the physical breakdown of the crystal lattice. The void fraction required decreases with temperature. Sensitivity studies show a strong dependence of the critical void fraction on the quantity and distribution of voids on the surface, with systems containing a balanced number of surface defects and a rough surface showing a maximum tendency to dissolve. There is a moderate dependence on temperature, with a 5% decrease in required void fraction with a 100 K increase in temperature, and a weak dependence on water potential model used, with the SPC, SPC/E, TIP4P, and RPOL models giving qualitatively identical results. The results were insensitive to the total quantity of water available for dissolution and the duration of the simulation.
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Affiliation(s)
- Ranjit Bahadur
- Scripps Institution of Oceanography, University of California-San Diego, La Jolla, California 92093-0221, USA
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195
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Mudi A, Chakravarty C. Effect of Ionic Solutes on the Hydrogen Bond Network Dynamics of Water: Power Spectral Analysis of Aqueous NaCl Solutions. J Phys Chem B 2006; 110:8422-31. [PMID: 16623528 DOI: 10.1021/jp056003l] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
To understand the modifications of the hydrogen bond network of water by ionic solutes, power spectra as well as static distributions of the potential energies of tagged solvent molecules and solute ions have been computed from molecular dynamics simulations of aqueous NaCl solutions. The key power spectral features of interest are the presence of high-frequency peaks due to localized vibrational modes, the existence of a multiple time scale or 1/falpha frequency regime characteristic of networked liquids, and the frequency of crossover from 1/falpha type behavior to white noise. Hydrophilic solutes, such as the sodium cation and the chloride anion, are shown to mirror the multiple time scale behavior of the hydrogen bond network fluctuations, unlike hydrophobic solutes which display essentially white noise spectra. While the power spectra associated with tagged H2O molecules are not very sensitive to concentration in the intermediate frequency 1/falpha regime, the crossover to white noise is shifted to lower frequencies on going from pure solvent to aqueous alkali halide solutions. This suggests that new and relatively slow time scales enter the picture, possibly associated with processes such as migration of water molecules from the hydration shell to the bulk or conversion of contact ion pairs into solvent-separated ion pairs which translate into variations in equilibrium transport properties of salt solutions with concentration. For anions, cations, and solvent molecules, the trends in the alpha exponents of the multiple time scale region and the self-diffusivities are found to be strongly correlated.
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Affiliation(s)
- Anirban Mudi
- Department of Chemistry, Indian Institute of Technology-Delhi, New Delhi 110016, India
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196
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Reorientational dynamics of water in aqueous ionic solutions at supercritical conditions: A computer simulation study. J Mol Liq 2006. [DOI: 10.1016/j.molliq.2005.11.028] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
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197
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Hwang H, Schatz GC, Ratner MA. Ion Current Calculations Based on Three Dimensional Poisson−Nernst−Planck Theory for a Cyclic Peptide Nanotube. J Phys Chem B 2006; 110:6999-7008. [PMID: 16571014 DOI: 10.1021/jp055740e] [Citation(s) in RCA: 42] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Ion current calculations based on Poisson-Nernst-Planck (PNP) theory are performed for a synthetic cyclic peptide nanotube that consists of eight or ten cyclo[(-L-Trp-D-Leu-)4] embedded in a lipid bilayer membrane to investigate the ion transport properties of the nanotube. To explore systems with arbitrary geometries, three-dimensional PNP theory is implemented using a finite difference method. The influence of dipolar lipid molecules on the ion currents is also examined by turning on or off the charges of the lipid dipoles in dipalmitoylphosphatidylcholine (DPPC). Comparisons between the calculated and experimentally measured ion currents show that the PNP approach agrees well with the measurements at low ion concentrations but overestimates the currents at higher concentrations. Concentration profiles reveal the selectivity of the peptide nanotube to cations, which is attributed to the negatively charged carbonyl oxygens inside the nanotube. The dominant cation and the minimum anion concentrations inside the cyclic peptide nanotube suggest that these cyclic peptide nanotubes can be employed as ion sensors. In the case of the polar DPPC bilayer, smaller currents are obtained in the calculation. The variation of current with polarity of the lipids implies that both polar and nonpolar lipid bilayer membranes can be utilized to regulate ion currents in the peptide nanotube and other ion channels. Strengths and limitations of the PNP theory are also discussed.
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Affiliation(s)
- Hyonseok Hwang
- Department of Chemistry, Northwestern University, 2145 Sheridan Road, Evanston, Illinois 60208-3113, USA
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198
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Guàrdia E, Laria D, Martí J. Hydrogen Bond Structure and Dynamics in Aqueous Electrolytes at Ambient and Supercritical Conditions. J Phys Chem B 2006; 110:6332-8. [PMID: 16553451 DOI: 10.1021/jp056981p] [Citation(s) in RCA: 87] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
Hydrogen bond (HB) connectivity in aqueous electrolyte solutions at ambient and supercritical conditions has been investigated by molecular dynamics techniques. Alkali metal and halides with different sizes have been considered. Modifications in the water HB architecture are more noticeable in the first ionic solvation shells and do not persist beyond the second shells. The coordination pattern is established between partners located in the first and second solvation shells. High-temperature results show dramatic reductions in the coordination number of water; at liquidlike densities the number of HBs is close to 2, while in steamlike environments water monomers are predominant. The addition of ions does not bring important modifications in the original HB structure for pure water. From the dynamical side, the lifetime of HBs shows minor modifications due to the simultaneous competing effects from a weaker HB structure combined with a slower reorientational dynamics of water induced by the Coulomb coupling with solute. At supercritical conditions, the overall dynamics of HB is roughly 1 order of magnitude faster than that at ambient conditions, regardless of the particular density considered.
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Affiliation(s)
- Elvira Guàrdia
- Departament de Física i Enginyeria Nuclear, Universitat Politècnica de Catalunya, B4-B5 Campus Nord UPC, 08034 Barcelona, Catalonia, Spain.
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199
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Chowdhuri S, Chandra A. Solute size effects on the solvation structure and diffusion of ions in liquid methanol under normal and cold conditions. J Chem Phys 2006; 124:084507. [PMID: 16512729 DOI: 10.1063/1.2172598] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022] Open
Abstract
We have performed a series of molecular dynamics simulations of alkali metal (Li+, Na+, K+, Rb+, and Cs+) and halide (F-, Cl-, Br-, and I-) ions in liquid methanol at two different temperatures to investigate the effects of ion size on the hydration structure and diffusion of ions in methanol under normal and cold conditions. Simulations are also carried out for some of the larger cations such as I+, (CH3)4N+, and (C2H5)4N+ and also neutral alkali metal atoms in methanol at both temperatures. With the increase of ion size, the diffusion coefficients of both positive and negative ions are found to show anomalous behavior. For cations, it is found that the maximum of the diffusion coefficient versus ion size curve occurs at the rather large cation of (CH3)4N+ unlike in water where the maximum occurs at the relatively smaller ion of Rb+. For halide ions, the anomalous behavior, i.e., the increase of diffusion with ion size, continues up to iodide ion and no maximum is observed. These results are in good agreement with experimental observations. The diffusion coefficients of neutral atoms are found to be greater in methanol than that in water and they decrease monotonically with solute size, whereas the diffusion coefficients of the corresponding ions are found to be smaller in methanol. Accordingly, an ion experiences a smaller Stokes friction and a higher dielectric friction in methanol than in water. These contrasting effects are believed to be responsible for the shift of the maximum of ion diffusion toward a larger ion size when compared with similar anomalous size dependence in liquid water.
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Affiliation(s)
- Snehasis Chowdhuri
- Department of Chemistry, Indian Institute of Technology, Kanpur 208016, India
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200
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Shevkunov SV. Interaction of water molecules with the electric field of an ionic-crystal surface. RUSS J ELECTROCHEM+ 2006. [DOI: 10.1134/s1023193506010022] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
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