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Basu T, Das S, Majumdar S. Elucidating the influence of electrostatic force on the re-arrangement of H-bonds of protein polymers in the presence of salts. SOFT MATTER 2024; 20:2361-2373. [PMID: 38372459 DOI: 10.1039/d3sm01440a] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/20/2024]
Abstract
Polyampholytes/proteins have an intriguing network of hydrogen bonds (H-bonds), especially their secondary structure, which plays a crucial role in determining the conformational stability of the polymer. The changes in protein secondary structure in the protein-salt system have been extensively deciphered by researchers, yet their pathways for breakage and recreation are unknown. Understanding the mechanism of protein conformational changes towards their biological activities, like protein folding, remains one of the main challenges and requires multiscale analysis of this strongly correlated system. Herein, salts have been used to reveal the re-arrangement behavior in the H-bond network of proteins under the influence of electrostatic interactions, as the strength of electrostatic forces is much stronger than that of H-bonds. At lower salt concentrations, there are negligible changes in the secondary structures as the electrostatic forces induced by the salt ions are less. Later, the existing H-bonds break and reconstruct new H-bonds at higher salt concentrations due to the influence of the stronger electrostatic interaction induced by the large number of salt ions. Molecular dynamics (MD) simulations and FTIR studies have been used rigorously to decipher the reason behind the re-arrangement of the H-bonds within gelatin (protein). The re-arrangement in the H-bond has also been observed with time from simulations and experiments. Thus, this study could provide a fresh perspective on the conformational changes of polyampholytes/proteins and will also influence the studies of protein folding-unfolding interaction in the presence of salt ions.
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Affiliation(s)
- Tithi Basu
- Department of Chemical Engineering, Indian Institute of Technology Hyderabad, Telangana, 502285, India.
| | - Sougat Das
- Department of Chemical Engineering, Indian Institute of Technology Hyderabad, Telangana, 502285, India.
| | - Saptarshi Majumdar
- Department of Chemical Engineering, Indian Institute of Technology Hyderabad, Telangana, 502285, India.
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2
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Shock CJ, Stevens MJ, Frischknecht AL, Nakamura I. Molecular dynamics simulations of the dielectric constants of salt-free and salt-doped polar solvents. J Chem Phys 2023; 159:134507. [PMID: 37795785 DOI: 10.1063/5.0165481] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/28/2023] [Accepted: 09/15/2023] [Indexed: 10/06/2023] Open
Abstract
We develop a Stockmayer fluid model that accounts for the dielectric responses of polar solvents (water, MeOH, EtOH, acetone, 1-propanol, DMSO, and DMF) and NaCl solutions. These solvent molecules are represented by Lennard-Jones (LJ) spheres with permanent dipole moments and the ions by charged LJ spheres. The simulated dielectric constants of these liquids are comparable to experimental values, including the substantial decrease in the dielectric constant of water upon the addition of NaCl. Moreover, the simulations predict an increase in the dielectric constant when considering the influence of ion translations in addition to the orientation of permanent dipoles.
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Affiliation(s)
- Cameron J Shock
- Department of Physics, Michigan Technological University, Houghton, Michigan 49931, USA
| | - Mark J Stevens
- Center for Integrated Nanotechnologies, Sandia National Laboratories, Albuquerque, New Mexico 87185, USA
| | - Amalie L Frischknecht
- Center for Integrated Nanotechnologies, Sandia National Laboratories, Albuquerque, New Mexico 87185, USA
| | - Issei Nakamura
- Department of Physics, Michigan Technological University, Houghton, Michigan 49931, USA
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3
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Zhang C, Yue S, Panagiotopoulos AZ, Klein ML, Wu X. Why Dissolving Salt in Water Decreases Its Dielectric Permittivity. PHYSICAL REVIEW LETTERS 2023; 131:076801. [PMID: 37656852 DOI: 10.1103/physrevlett.131.076801] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/26/2023] [Revised: 04/30/2023] [Accepted: 07/07/2023] [Indexed: 09/03/2023]
Abstract
The dielectric permittivity of salt water decreases on dissolving more salt. For nearly a century, this phenomenon has been explained by invoking saturation in the dielectric response of the solvent water molecules. Herein, we employ an advanced deep neural network (DNN), built using data from density functional theory, to study the dielectric permittivity of sodium chloride solutions. Notably, the decrease in the dielectric permittivity as a function of concentration, computed using the DNN approach, agrees well with experiments. Detailed analysis of the computations reveals that the dominant effect, caused by the intrusion of ionic hydration shells into the solvent hydrogen-bond network, is the disruption of dipolar correlations among water molecules. Accordingly, the observed decrease in the dielectric permittivity is mostly due to increasing suppression of the collective response of solvent waters.
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Affiliation(s)
- Chunyi Zhang
- Department of Physics, Temple University, Philadelphia, Pennsylvania 19122, USA
| | - Shuwen Yue
- Department of Chemical and Biological Engineering, Princeton University, Princeton, New Jersey 08544, USA
| | | | - Michael L Klein
- Department of Physics, Temple University, Philadelphia, Pennsylvania 19122, USA
- Institute for Computational Molecular Science, Temple University, Philadelphia, Pennsylvania 19122, USA
- Department of Chemistry, Temple University, Philadelphia, Pennsylvania 19122, USA
| | - Xifan Wu
- Department of Physics, Temple University, Philadelphia, Pennsylvania 19122, USA
- Institute for Computational Molecular Science, Temple University, Philadelphia, Pennsylvania 19122, USA
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Maji D, Biswas R. Dielectric relaxation and dielectric decrement in ionic acetamide deep eutectic solvents: Spectral decomposition and comparison with experiments. J Chem Phys 2023; 158:2888209. [PMID: 37139998 DOI: 10.1063/5.0147378] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/22/2023] [Accepted: 04/17/2023] [Indexed: 05/05/2023] Open
Abstract
Frequency-dependent dielectric relaxation in three deep eutectic solvents (DESs), (acetamide+LiClO4/NO3/Br), was investigated in the temperature range, 329 ≤ T/K ≤ 358, via molecular dynamics simulations. Subsequently, decomposition of the real and the imaginary components of the simulated dielectric spectra was carried out to separate the rotational (dipole-dipole), translational (ion-ion), and ro-translational (dipole-ion) contributions. The dipolar contribution, as expected, was found to dominate all the frequency-dependent dielectric spectra over the entire frequency regime, while the other two components together made tiny contributions only. The translational (ion-ion) and the cross ro-translational contributions appeared in the THz regime in contrast to the viscosity-dependent dipolar relaxations that dominated the MHz-GHz frequency window. Our simulations predicted, in agreement with experiments, anion-dependent decrement of the static dielectric constant (ɛs ∼ 20 to 30) for acetamide (ɛs ∼ 66) in these ionic DESs. Simulated dipole-correlations (Kirkwood g factor) indicated significant orientational frustrations. The frustrated orientational structure was found to be associated with the anion-dependent damage of the acetamide H-bond network. Single dipole reorientation time distributions suggested slowed down acetamide rotations but did not indicate presence of any "rotationally frozen" molecule. The dielectric decrement is, therefore, largely static in origin. This provides a new insight into the ion dependence of the dielectric behavior of these ionic DESs. A good agreement between the simulated and the experimental timescales was also noticed.
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Affiliation(s)
- Dhrubajyoti Maji
- Department of Chemical and Biological Sciences, S. N. Bose National Centre for Basic Sciences, Block-JD, Sector III, Salt Lake, Kolkata, West Bengal 700106, India
| | - Ranjit Biswas
- Department of Chemical and Biological Sciences, S. N. Bose National Centre for Basic Sciences, Block-JD, Sector III, Salt Lake, Kolkata, West Bengal 700106, India
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5
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Zarzycki P. Distance-dependent dielectric constant at the calcite/electrolyte interface: Implication for surface complexation modeling. J Colloid Interface Sci 2023; 645:752-764. [PMID: 37172485 DOI: 10.1016/j.jcis.2023.04.169] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/10/2023] [Revised: 04/10/2023] [Accepted: 04/30/2023] [Indexed: 05/15/2023]
Abstract
HYPOTHESIS The electrical double layer formed at the mineral/electrolyte interface is often modeled using mean-field approaches based on a continuum description of the solvent whose dielectric constant is assumed to decrease monotonically with decreasing distance to the surface. In contrast, molecular simulations show that the solvent polarizability oscillates near the surface similar to the water density profile - as shown previously, for example, by Bonthuis et al. (D.J. Bonthuis, S. Gekle, R.R. Netz, Dielectric Profile of Interfacial Water and its Effect on Double-Layer Capacitance, Phys Rev Lett 107(16) (2011) 166102). We showed that molecular and mesoscale pictures agree by spatially averaging the dielectric constant obtained from molecular dynamics simulations over the distances relevant to the mean-field representation. In addition, the values of capacitances used to describe the electrical double layer in Surface Complexation Models (SCMs) of the mineral/electrolyte interface can be estimated using molecularly informed spatially averaged dielectric constants and positions of hydration layers. EXPERIMENTS First, we used molecular dynamics simulations to model the calcite 101¯4/electrolyte interface. Next, by using atomistic trajectories, we calculated the distance-dependent static dielectric constant and water density in the direction normal to the. Finally, we applied spatial compartmentalization consistent with the model of parallel-plate capacitors connected in series to estimate SCM capacitances. FINDINGS Computationally expensive simulations are required to determine the dielectric constant profile of interfacial water near the mineral surface. On the other hand, water density profiles are readily assessable from much shorter simulation trajectories. Our simulations confirmed that dielectric and water density oscillations at the interface are correlated. Here, we parametrized linear regression models to estimate the dielectric constant directly from the local water density. This is a significant computational shortcut compared to slowly converging calculations relying on total dipole moment fluctuations. The amplitude of the interfacial dielectric constant oscillation can exceed the dielectric constant of the bulk water, suggesting an ice-like frozen state, but only if there are no electrolyte ions. The interfacial accumulation of electrolyte ions causes a decrease in the dielectric constant due to the reduction of water density and re-orientation of water dipoles in ion hydration shells. Finally, we show how to use the computed dielectric properties to estimate SCM's capacitances.
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Affiliation(s)
- Piotr Zarzycki
- Energy Geosciences Division, Lawrence Berkeley National Laboratory, 1 Cyclotron Road, Berkeley, CA, United States.
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6
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Silva F, Veiga F, Paulo Jorge Rodrigues S, Cardoso C, Cláudia Paiva-Santos A. COSMO Models for the Pharmaceutical Development of Parenteral Drug Formulations. Eur J Pharm Biopharm 2023; 187:156-165. [PMID: 37120066 DOI: 10.1016/j.ejpb.2023.04.019] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/12/2023] [Revised: 03/31/2023] [Accepted: 04/21/2023] [Indexed: 05/01/2023]
Abstract
The aqueous solubility of active pharmaceutical ingredients is one of the most important features to be considered during the development of parenteral formulations in the pharmaceutical industry. Computational modelling has become in the last years an integral part of pharmaceutical development. In this context, ab initio computational models, such as COnductor-like Screening MOdel (COSMO), have been proposed as promising tools for the prediction of results without the effective use of resources. Nevertheless, despite the clear evaluation of computational resources, some authors had not achieved satisfying results and new calculations and algorithms have been proposed over the years to improve the outcomes. In the development and production of aqueous parenteral formulations, the solubility of Active Pharmaceutical Ingredients (APIs) in an aqueous and biocompatible vehicle is a decisive step. This work aims to study the hypothesis that COSMO models could be useful in the development of new parenteral formulations, mainly aqueous ones.
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Affiliation(s)
- Fernando Silva
- Department of Pharmaceutical Technology, Faculty of Pharmacy of the University of Coimbra, University of Coimbra, Coimbra, Portugal; REQUIMTE/LAQV, Group of Pharmaceutical Technology, Faculty of Pharmacy of the University of Coimbra, University of Coimbra, Coimbra, Portugal.
| | - Francisco Veiga
- Department of Pharmaceutical Technology, Faculty of Pharmacy of the University of Coimbra, University of Coimbra, Coimbra, Portugal; REQUIMTE/LAQV, Group of Pharmaceutical Technology, Faculty of Pharmacy of the University of Coimbra, University of Coimbra, Coimbra, Portugal
| | - Sérgio Paulo Jorge Rodrigues
- Coimbra Chemistry Centre, Chemistry Department, Faculty of Sciences and Technology of the University of Coimbra of the University of Coimbra, Coimbra, Portugal
| | - Catarina Cardoso
- Laboratórios Basi, Parque Industrial Manuel Lourenço Ferreira, lote 15, 3450-232 Mortágua, Portugal
| | - Ana Cláudia Paiva-Santos
- Department of Pharmaceutical Technology, Faculty of Pharmacy of the University of Coimbra, University of Coimbra, Coimbra, Portugal; REQUIMTE/LAQV, Group of Pharmaceutical Technology, Faculty of Pharmacy of the University of Coimbra, University of Coimbra, Coimbra, Portugal
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7
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Uskoković V. Learning from a dark brew: how traditional coffee-making can inspire the search for improved colloidal stability. J DISPER SCI TECHNOL 2023. [DOI: 10.1080/01932691.2023.2180387] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/27/2023]
Affiliation(s)
- Vuk Uskoković
- Advanced Materials and Nanobiotechnology Laboratory, TardigradeNano, Irvine, California, USA
- Department of Mechanical Engineering, San Diego State University, San Diego, California, USA
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8
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Singh A, Doan LC, Lou D, Wen C, Vinh NQ. Interfacial Layers between Ion and Water Detected by Terahertz Spectroscopy. J Chem Phys 2022; 157:054501. [DOI: 10.1063/5.0095932] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Dynamic fluctuations in hydrogen-bond network of water occur from femto- to nano-second timescale and provides insights into structural/dynamical aspects of water at ion-water interfaces. Employing terahertz spectroscopy assisted with molecular dynamics simulations, we study aqueous chloride solutions of five monovalent cations, namely, Li, Na, K, Rb and Cs. We show that ions modify the behavior of surrounding water molecules and form interfacial layers of water around them with physical properties distinct from that of bulk water. Small cations with high charge densities influence the kinetics of water well beyond the first solvation shell. At terahertz frequencies, we observe an emergence of fast relaxation processes of water with their magnitude following the ionic order Cs>Rb>K>Na>Li, revealing an enhanced population density of weakly coordinated water at ion-water interface. The results shed light on the structure breaking tendency of monovalent cations and provide insights into the properties of ionic solutions at the molecular level.
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Affiliation(s)
- Abhishek Singh
- Physics, Virginia Polytechnic Institute and State University, United States of America
| | - Luan C Doan
- Virginia Polytechnic Institute and State University, United States of America
| | - Djamila Lou
- Virginia Polytechnic Institute and State University, United States of America
| | - Chengyuan Wen
- Virginia Polytechnic Institute and State University - National Capital Region, United States of America
| | - Nguyen Q Vinh
- Department of Physics, Virginia Polytechnic Institute and State University, United States of America
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9
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Saravi SH, Panagiotopoulos AZ. Activity Coefficients and Solubilities of NaCl in Water-Methanol Solutions from Molecular Dynamics Simulations. J Phys Chem B 2022; 126:2891-2898. [PMID: 35411772 DOI: 10.1021/acs.jpcb.2c00813] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
We obtain activity coefficients and solubilities of NaCl in water-methanol solutions at 298.15 K and 1 bar from molecular dynamics (MD) simulations with the Joung-Cheatham, SPC/E, and OPLS-AA force fields for NaCl, water, and methanol, respectively. The Lorentz-Berthelot combining rules were adopted for the unlike-pair interactions of Na+, Cl-, and the oxygen site in SPC/E water, and geometric combining rules were utilized for the remainder of the cross interactions. We found that the selection of appropriate combining rules is important in obtaining physically realistic solubilities. The solvent compositions studied range from pure water to pure methanol. Several salt concentrations were investigated at each solvent composition, from the lowest concentrations permitted by the system size used up to the experimental solubilities. We first calculated individual ion activity coefficients (IIACs) for Na+ and Cl- from the free energy change due to the gradual insertion of a single cation or anion into the solution, accompanied by a neutralizing background. We obtained the salt solubilities by comparing the chemical potentials in solution with solid NaCl chemical potentials calculated previously using the Einstein crystal method. Mean ionic activity coefficients obtained from the IIACs are in reasonable agreement with experimental data, with deviations increasing for solutions of higher methanol content. Predictions for the salt solubility are in surprisingly good agreement with experimental data, despite well-known challenges in the simultaneous calculation of activity coefficients and solubilities with classical MD simulations. The present study demonstrates that good predictions for these two important phase equilibrium properties can be obtained for mixed-solvent electrolyte solutions using existing nonpolarizable models and further suggests that the previously proposed single ion insertion technique can be extended to complex mixed-solvent solutions as well.
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Affiliation(s)
- Sina Hassanjani Saravi
- Department of Chemical and Biological Engineering, Princeton University, Princeton, New Jersey 08544, United States
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10
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Saravi SH, Panagiotopoulos AZ. Activity coefficients of aqueous electrolytes from implicit-water molecular dynamics simulations. J Chem Phys 2021; 155:184501. [PMID: 34773944 DOI: 10.1063/5.0064963] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
We obtain activity coefficients in NaCl and KCl solutions from implicit-water molecular dynamics simulations, at 298.15 K and 1 bar, using two distinct approaches. In the first approach, we consider ions in a continuum with constant relative permittivity (ɛr) equal to that of pure water; in the other approach, we take into account the concentration-dependence of ɛr, as obtained from explicit-water simulations. Individual ion activity coefficients (IIACs) are calculated using gradual insertion of single ions with uniform neutralizing backgrounds to ensure electroneutrality. Mean ionic activity coefficients (MIACs) obtained from the corresponding IIACs in simulations with constant ɛr show reasonable agreement with experimental data for both salts. Surprisingly, large systematic negative deviations are observed for both IIACs and MIACs in simulations with concentration-dependent ɛr. Our results suggest that the absence of hydration structure in implicit-water simulations cannot be compensated by correcting for the concentration-dependence of the relative permittivity ɛr. Moreover, even in simulations with constant ɛr for which the calculated MIACs are reasonable, the relative positioning of IIACs of anions and cations is incorrect for NaCl. We conclude that there are severe inherent limitations associated with implicit-water simulations in providing accurate activities of aqueous electrolytes, a finding with direct relevance to the development of electrolyte theories and to the use and interpretation of implicit-solvent simulations.
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Affiliation(s)
- Sina Hassanjani Saravi
- Department of Chemical and Biological Engineering, Princeton University, Princeton, New Jersey 08544, USA
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11
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Vallem V, Roosa E, Ledinh T, Jung W, Kim TI, Rashid-Nadimi S, Kiani A, Dickey MD. A Soft Variable-Area Electrical-Double-Layer Energy Harvester. ADVANCED MATERIALS (DEERFIELD BEACH, FLA.) 2021; 33:e2103142. [PMID: 34462971 DOI: 10.1002/adma.202103142] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/25/2021] [Revised: 07/05/2021] [Indexed: 06/13/2023]
Abstract
The technological promise of soft devices-wearable electronics, implantables, soft robotics, sensors-has accelerated the demand for deformable energy sources. Devices that can convert mechanical energy to electrical energy can enable self-powered, tetherless, and sustainable devices. This work presents a completely soft and stretchable (>400% strain) energy harvester based on variable-area electrical-double-layer (EDL) capacitors (≈40 µF cm-2 ). Mechanically varying the EDL area, and thus the capacitance, disrupts equilibrium and generates a driving force for charge movement through an external circuit. Prior EDL capacitors varied the contact area by depressing water droplets between rigid electrodes. In contrast, here, the harvester consists of liquid-metal electrodes encased in a hydrogel. Deforming the device by ≈25% strain generates a power density ≈0.5 mW m-2 . This unconventional approach is attractive because: (1) it does not need an external voltage supply to provide charge; (2) the electrodes themselves deform; and (3) it can work under various modes of deformation such as pressing, stretching, bending, and twisting. The unique ability of the harvester to operate underwater shows promising applications in wearables that contact sweat, underwater sensing, and blue energy harvesting.
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Affiliation(s)
- Veenasri Vallem
- Department of Chemical and Biomolecular Engineering, North Carolina State University, Raleigh, NC, 27695, USA
| | - Erin Roosa
- Department of Chemical and Biomolecular Engineering, North Carolina State University, Raleigh, NC, 27695, USA
| | - Tyler Ledinh
- Department of Chemical and Biomolecular Engineering, North Carolina State University, Raleigh, NC, 27695, USA
| | - Woojin Jung
- School of Chemical Engineering, Sungkyunkwan University (SKKU), Suwon, 16419, Republic of Korea
| | - Tae-Il Kim
- School of Chemical Engineering, Sungkyunkwan University (SKKU), Suwon, 16419, Republic of Korea
| | - Sahar Rashid-Nadimi
- Department of Chemical and Biomolecular Engineering, North Carolina State University, Raleigh, NC, 27695, USA
| | - Abolfazl Kiani
- Department of Chemical and Biomolecular Engineering, North Carolina State University, Raleigh, NC, 27695, USA
- Department of Chemistry and Biochemistry, California State University, Bakersfield, Bakersfield, CA, 93311, USA
| | - Michael D Dickey
- Department of Chemical and Biomolecular Engineering, North Carolina State University, Raleigh, NC, 27695, USA
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12
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Xiao T, Zhou Y. A nonlocal electrostatics model for ions in concentrated primitive electrolyte solutions. Electrochim Acta 2021. [DOI: 10.1016/j.electacta.2021.139040] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/20/2022]
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13
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Sterling JD, Jiang W, Botello-Smith WM, Luo YL. Ion Pairing and Dielectric Decrement in Glycosaminoglycan Brushes. J Phys Chem B 2021; 125:2771-2780. [PMID: 33662212 DOI: 10.1021/acs.jpcb.0c11571] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Abstract
Cell-surface polysaccharides are essential to many aspects of physiology, serving as a highly conserved evolutionary feature of life and as an important part of the innate immune system in mammals. Here, as simplified biophysical models of these sugar coatings, we present results of molecular dynamics simulations of hyaluronic acid and heparin brushes that show important effects of ion pairing, water dielectric decrease, and coion exclusion. As in prior studies of macromolecular crowding under physiologically relevant salt concentrations, our results show equilibria with electroneutrality attained through screening and pairing of brush anionic charges by monovalent cations at the atomistic detail. Most surprising is the reversal of the Donnan potential obtained from both nonpolarizable and Drude polarizable force fields, in contrast to what would be expected based on electrostatic Boltzmann partitioning alone. Water dielectric decrement within the brush domain is also associated with Born hydration-driven cation exclusion from the brush. We observe that the primary partition energy attracting cations to attain brush electroneutrality is the ion pairing or salt-bridge energy. Potassium and sodium pairings to glycosaminoglycan carboxylates and sulfates show similar abundance of contact-pairing and solvent-separated pairing. We conclude that in these crowded macromolecular brushes, ion-pairing, Born-hydration, and electrostatic potential energies all contribute to attain electroneutrality and should therefore contribute in mean-field models to accurately represent brush electrostatics.
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Affiliation(s)
- James D Sterling
- Henry E. Riggs School of Applied Life Sciences, Keck Graduate Institute, 535 Watson Dr., Claremont, California 91711, United States
| | - Wenjuan Jiang
- College of Pharmacy, Western University of Health Sciences, 309 E. Second Street, Pomona, California 91766, United States
| | - Wesley M Botello-Smith
- College of Pharmacy, Western University of Health Sciences, 309 E. Second Street, Pomona, California 91766, United States
| | - Yun L Luo
- College of Pharmacy, Western University of Health Sciences, 309 E. Second Street, Pomona, California 91766, United States
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14
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Patel LA, Yoon TJ, Currier RP, Maerzke KA. NaCl aggregation in water at elevated temperatures and pressures: Comparison of classical force fields. J Chem Phys 2021; 154:064503. [PMID: 33588550 DOI: 10.1063/5.0030962] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022] Open
Abstract
The properties of water vary dramatically with temperature and density. This can be exploited to control its effectiveness as a solvent. Thus, supercritical water is of keen interest as solvent in many extraction processes. The low solubility of salts in lower density supercritical water has even been suggested as a means of desalination. The high temperatures and pressures required to reach supercritical conditions can present experimental challenges during collection of required physical property and phase equilibria data, especially in salt-containing systems. Molecular simulations have the potential to be a valuable tool for examining the behavior of solvated ions at these high temperatures and pressures. However, the accuracy of classical force fields under these conditions is unclear. We have, therefore, undertaken a parametric study of NaCl in water, comparing several salt and water models at 200 bar-600 bar and 450 K-750 K for a range of salt concentrations. We report a comparison of structural properties including ion aggregation, hydrogen bonding, density, and static dielectric constants. All of the force fields qualitatively reproduce the trends in the liquid phase density. An increase in ion aggregation with decreasing density holds true for all of the force fields. The propensity to aggregate is primarily determined by the salt force field rather than the water force field. This coincides with a decrease in the water static dielectric constant and reduced charge screening. While a decrease in the static dielectric constant with increasing NaCl concentration is consistent across all model combinations, the salt force fields that exhibit more ionic aggregation yield a slightly smaller dielectric decrement.
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Affiliation(s)
- Lara A Patel
- Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA
| | - Tae Jun Yoon
- Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA
| | - Robert P Currier
- Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA
| | - Katie A Maerzke
- Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA
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15
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Barman SS, Bhattacharyya S, Dutta P. Electrokinetic actuation of an uncharged polarizable dielectric droplet in charged hydrogel medium. Electrophoresis 2021; 42:920-931. [PMID: 33450075 DOI: 10.1002/elps.202000343] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/26/2020] [Revised: 12/20/2020] [Accepted: 01/04/2021] [Indexed: 12/21/2022]
Abstract
Electrokinetic transport of an uncharged nonconducting microsized liquid droplet in a charged hydrogel medium is studied. Dielectric polarization of the liquid drop under the action of an externally imposed electric field induces a non-homogeneous charge density at the droplet surface. The interactions of the induced surface charge of the droplet with the immobile charges of the hydrogel medium generates an electric force to the droplet, which actuates the drop through the charged hydrogel medium. A numerical study based on the first principle of electrokinetics is adopted. Dependence of the droplet velocity on its dielectric permittivity, bulk ionic concentration, and immobile charge density of the gel is analyzed. The surface conduction is significant in presence of charged gel, which creates a concentration polarization. The impact of the counterion saturation in the Debye layer due to the dielectric decrement of the medium is addressed. The modified Nernst-Planck equation for ion transport and the Poisson equation for the electric field is considered to take into account the dielectric polarization. A quadrupolar vortex around the uncharged droplet is observed when the gel medium is considered to be uncharged, which is similar to the induced charge electroosmosis around an uncharged dielectric colloid in free-solution. We find that the induced charge electrokinetic mechanism creates a strong recirculation of liquid within the droplet and the translational velocity of the droplet strongly depends on its size for the dielectric droplet embedded in a charged gel medium.
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Affiliation(s)
| | - Somnath Bhattacharyya
- Department of Mathematics, Indian Institute of Technology Kharagpur, Kharagpur, India
| | - Prashanta Dutta
- School of Mechanical and Materials Engineering, Washington State University, Pullman, USA
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17
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Saric D, Kohns M, Vrabec J. Dielectric constant and density of aqueous alkali halide solutions by molecular dynamics: A force field assessment. J Chem Phys 2020; 152:164502. [PMID: 32357782 DOI: 10.1063/1.5144991] [Citation(s) in RCA: 13] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022] Open
Abstract
The concentration dependence of the dielectric constant and the density of 11 aqueous alkali halide solutions (LiCl, NaCl, KCl, RbCl, CsCl, LiI, NaI, KI, CsI, KF, and CsF) is investigated by molecular simulation. Predictions using eight non-polarizable ion force fields combined with the TIP4P/ε water model are compared to experimental data. The influence of the water model and the temperature on the results for the NaCl brine are also addressed. The TIP4P/ε water model improves the accuracy of dielectric constant predictions compared to the SPC/E water model. The solution density is predicted well by most ion models. Almost all ion force fields qualitatively capture the decline of the dielectric constant with the increase of concentration for all solutions and with the increase of temperature for NaCl brine. However, the sampled dielectric constant is mostly in poor quantitative agreement with experimental data. These results are related to the microscopic solution structure, ion pairing, and ultimately the force field parameters. Ion force fields with excessive contact ion pairing and precipitation below the experimental solubility limit generally yield higher dielectric constant values. An adequate reproduction of the experimental solubility limit should therefore be a prerequisite for further investigations of the dielectric constant of aqueous electrolyte solutions by molecular simulation.
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Affiliation(s)
- Denis Saric
- Thermodynamics and Energy Technology, University of Paderborn, 33098 Paderborn, Germany
| | - Maximilian Kohns
- Laboratory of Engineering Thermodynamics, Technische Universität Kaiserslautern, 67633 Kaiserslautern, Germany
| | - Jadran Vrabec
- Thermodynamics and Process Engineering, Technical University Berlin, 10587 Berlin, Germany
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