1
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Sundar S, Sandilya AA, Priya MH. Unraveling the Influence of Osmolytes on Water Hydrogen-Bond Network: From Local Structure to Graph Theory Analysis. J Chem Inf Model 2021; 61:3927-3944. [PMID: 34379415 DOI: 10.1021/acs.jcim.1c00527] [Citation(s) in RCA: 11] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Water structure in aqueous osmolyte solutions, deduced from the slight alteration in the water-water radial distribution function, the decrease in water-water hydrogen bonding, and tetrahedral ordering based only on the orientation of nearest water molecules derived from the molecular dynamics simulations, appears to have been perturbed. A careful analysis, however, reveals that the hydrogen bonding and the tetrahedral ordering around a water molecule in binary solutions remain intact as in neat water when the contribution of osmolyte-water interactions is appropriately incorporated. Furthermore, the distribution of the water binding energies and the water excess chemical potential of solvation in solutions are also pretty much the same as in neat water. Osmolytes are, therefore, well integrated into the hydrogen-bond network of water. Indeed, osmolytes tend to preferentially hydrogen bond with water molecules and their interaction energies are strongly correlated to their hydrogen-bonding capability. The graph network analysis, further, illustrates that osmolytes act as hubs in the percolated hydrogen-bond network of solutions. The degree of hydrogen bonding of osmolytes predominantly determines all of the network properties. Osmolytes like ethanol that form fewer hydrogen bonds than a water molecule disrupt the water hydrogen-bond network, while other osmolytes that form more hydrogen bonds effectively increase the connectivity among water molecules. Our observation of minimal variation in the local structure and the vitality of osmolyte-water hydrogen bonds on the solution network properties clearly imply that the direct interaction between protein and osmolytes is solely responsible for the protein stability. Further, the relevance of hydrogen bonds on solution properties suggests that the hydrogen-bonding interaction among protein, water, and osmolyte could be the key determinant of the protein conformation in solutions.
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Affiliation(s)
- Smrithi Sundar
- Department of Biotechnology, Bhupat and Jyoti Mehta School of Biosciences, Indian Institute of Technology Madras, Chennai 600036, India
| | - Avilasha A Sandilya
- Department of Biotechnology, Bhupat and Jyoti Mehta School of Biosciences, Indian Institute of Technology Madras, Chennai 600036, India
| | - M Hamsa Priya
- Department of Biotechnology, Bhupat and Jyoti Mehta School of Biosciences, Indian Institute of Technology Madras, Chennai 600036, India
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2
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Asthagiri DN, Paulaitis ME, Pratt LR. Thermodynamics of Hydration from the Perspective of the Molecular Quasichemical Theory of Solutions. J Phys Chem B 2021; 125:8294-8304. [PMID: 34313434 DOI: 10.1021/acs.jpcb.1c04182] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023]
Abstract
The quasichemical organization of the potential distribution theorem, molecular quasichemical theory (QCT), enables practical calculations and also provides a conceptual framework for molecular hydration phenomena. QCT can be viewed from multiple perspectives: (a) as a way to regularize an ill-conditioned statistical thermodynamic problem; (b) as an introduction of and emphasis on the neighborship characteristics of a solute of interest; or (c) as a way to include accurate electronic structure descriptions of near-neighbor interactions in defensible statistical thermodynamics by clearly defining neighborship clusters. The theory has been applied to solutes of a wide range of chemical complexity, ranging from ions that interact with water with both long-ranged and chemically intricate short-ranged interactions, to solutes that interact with water solely through traditional van der Waals interations, and including water itself. The solutes range in variety from monatomic ions to chemically heterogeneous macromolecules. A notable feature of QCT is that, in applying the theory to this range of solutes, the theory itself provides guidance on the necessary approximations and simplifications that can facilitate the calculations. In this Perspective, we develop these ideas and document them with examples that reveal the insights that can be extracted using the QCT formulation.
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Affiliation(s)
- Dilipkumar N Asthagiri
- Department of Chemical and Biomolecular Engineering, Rice University, Houston, Texas 77005, United States
| | - Michael E Paulaitis
- Center for Nanomedicine, Johns Hopkins School of Medicine, Baltimore, Maryland 21231, United States
| | - Lawrence R Pratt
- Department of Chemical and Biomolecular Engineering, Tulane University, New Orleans, Louisiana 70118, United States
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3
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Utiramerur S, Paulaitis M. Analysis of Cooperativity and Group Additivity in the Hydration of 1,2-Dimethoxyethane. J Phys Chem B 2021; 125:1660-1666. [DOI: 10.1021/acs.jpcb.0c10729] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Sowmi Utiramerur
- William G. Lowrie Department of Chemical and Biomolecular Engineering, Ohio State University, Columbus, Ohio 43210, United States
| | - Michael Paulaitis
- William G. Lowrie Department of Chemical and Biomolecular Engineering, Ohio State University, Columbus, Ohio 43210, United States
- The Center for Nanomedicine at the Wilmer Eye Institute, Johns Hopkins University School of Medicine, Baltimore, Maryland 21231, United States
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4
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Eslami H, Das S, Zhou T, Müller-Plathe F. How Alcoholic Disinfectants Affect Coronavirus Model Membranes: Membrane Fluidity, Permeability, and Disintegration. J Phys Chem B 2020; 124:10374-10385. [PMID: 33172260 PMCID: PMC7670823 DOI: 10.1021/acs.jpcb.0c08296] [Citation(s) in RCA: 14] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/11/2020] [Revised: 10/28/2020] [Indexed: 01/17/2023]
Abstract
Atomistic molecular dynamics simulations have been carried out with a view to investigating the stability of the SARS-CoV-2 exterior membrane with respect to two common disinfectants, namely, aqueous solutions of ethanol and n-propanol. We used dipalmitoylphosphatidylcholine (DPPC) as a model membrane material and did simulations on both gel and liquid crystalline phases of membrane surrounded by aqueous solutions of varying alcohol concentrations (up to 17.5 mol %). While a moderate effect of alcohol on the gel phase of membrane is observed, its liquid crystalline phase is shown to be influenced dramatically by either alcohol. Our results show that aqueous solutions of only 5 and 10 mol % alcohol already have significant weakening effects on the membrane. The effects of n-propanol are always stronger than those of ethanol. The membrane changes its structure, when exposed to disinfectant solutions; uptake of alcohol causes it to swell laterally but to shrink vertically. At the same time, the orientational order of lipid tails decreases significantly. Metadynamics and grand-canonical ensemble simulations were done to calculate the free-energy profiles for permeation of alcohol and alcohol/water solubility in the DPPC. We found that the free-energy barrier to permeation of the DPPC liquid crystalline phase by all permeants is significantly lowered by alcohol uptake. At a disinfectant concentration of 10 mol %, it becomes insignificant enough to allow almost free passage of the disinfectant to the inside of the virus to cause damage there. It should be noted that the disinfectant also causes the barrier for water permeation to drop. Furthermore, the shrinking of the membrane thickness shortens the gap needed to be crossed by penetrants from outside the virus into its core. The lateral swelling also increases the average distance between head groups, which is a secondary barrier to membrane penetration, and hence further increases the penetration by disinfectants. At alcohol concentrations in the disinfectant solution above 15 mol %, we reliably observe disintegration of the DPPC membrane in its liquid crystalline phase.
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Affiliation(s)
- Hossein Eslami
- Eduard-Zintl-Institut
für Anorganische und Physikalische Chemie, Technische Universität Darmstadt, Alarich-Weiss-Str. 8, Darmstadt 64287, Germany
- Department
of Chemistry, College of Sciences, Persian
Gulf University, Boushehr 75168, Iran
| | - Shubhadip Das
- Eduard-Zintl-Institut
für Anorganische und Physikalische Chemie, Technische Universität Darmstadt, Alarich-Weiss-Str. 8, Darmstadt 64287, Germany
| | - Tianhang Zhou
- Eduard-Zintl-Institut
für Anorganische und Physikalische Chemie, Technische Universität Darmstadt, Alarich-Weiss-Str. 8, Darmstadt 64287, Germany
| | - Florian Müller-Plathe
- Eduard-Zintl-Institut
für Anorganische und Physikalische Chemie, Technische Universität Darmstadt, Alarich-Weiss-Str. 8, Darmstadt 64287, Germany
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5
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Muralidharan A, Pratt L, Chaudhari M, Rempe S. Quasi-chemical theory for anion hydration and specific ion effects: Cl-(aq) vs. F-(aq). ACTA ACUST UNITED AC 2019. [DOI: 10.1016/j.cpletx.2019.100037] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
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6
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Muralidharan A, Pratt LR, Chaudhari MI, Rempe SB. Quasi-Chemical Theory with Cluster Sampling from Ab Initio Molecular Dynamics: Fluoride (F -) Anion Hydration. J Phys Chem A 2018; 122:9806-9812. [PMID: 30475612 DOI: 10.1021/acs.jpca.8b08474] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023]
Abstract
Accurate predictions of the hydration free energy for anions typically has been more challenging than that for cations. Hydrogen bond donation to the anion in hydrated clusters such as F(H2O) n - can lead to delicate structures. Consequently, the energy landscape contains many local minima, even for small clusters, and these minima present a challenge for computational optimization. Utilization of cluster experimental results for the free energies of gas-phase clusters shows that even though anharmonic effects are interesting they need not be of troublesome magnitudes for careful applications of quasi-chemical theory to ion hydration. Energy-optimized cluster structures for anions can leave the central ion highly exposed, and application of implicit solvation models to these structures can incur more serious errors than those for metal cations. Utilizing cluster structures sampled from ab initio molecular dynamics simulations substantially fixes those issues.
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Affiliation(s)
- A Muralidharan
- Department of Chemical and Biomolecular Engineering , Tulane University , New Orleans , Louisiana 70118 , United States
| | - L R Pratt
- Department of Chemical and Biomolecular Engineering , Tulane University , New Orleans , Louisiana 70118 , United States
| | - M I Chaudhari
- Center for Biological and Engineering Sciences , Sandia National Laboratories , Albuquerque , New Mexico 87185 , United States
| | - S B Rempe
- Center for Biological and Engineering Sciences , Sandia National Laboratories , Albuquerque , New Mexico 87185 , United States
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7
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Dixit PD, Bansal A, Chapman WG, Asthagiri D. Mini-grand canonical ensemble: Chemical potential in the solvation shell. J Chem Phys 2018; 147:164901. [PMID: 29096517 DOI: 10.1063/1.4993178] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/12/2023] Open
Abstract
Quantifying the statistics of occupancy of solvent molecules in the vicinity of solutes is central to our understanding of solvation phenomena. Number fluctuations in small solvation shells around solutes cannot be described within the macroscopic grand canonical framework using a single chemical potential that represents the solvent bath. In this communication, we hypothesize that molecular-sized observation volumes such as solvation shells are best described by coupling the solvation shell with a mixture of particle baths each with its own chemical potential. We confirm our hypotheses by studying the enhanced fluctuations in the occupancy statistics of hard sphere solvent particles around a distinguished hard sphere solute particle. Connections with established theories of solvation are also discussed.
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Affiliation(s)
- Purushottam D Dixit
- Department of Systems Biology, Columbia University, New York City, New York 10032, USA
| | - Artee Bansal
- Department of Chemical and Biomolecular Engineering, Rice University, Houston, Texas 77251, USA
| | - Walter G Chapman
- Department of Chemical and Biomolecular Engineering, Rice University, Houston, Texas 77251, USA
| | - Dilip Asthagiri
- Department of Chemical and Biomolecular Engineering, Rice University, Houston, Texas 77251, USA
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8
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Marshall BD. Perturbation theory for water with an associating reference fluid. Phys Rev E 2017; 96:052602. [PMID: 29347741 DOI: 10.1103/physreve.96.052602] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/18/2017] [Indexed: 06/07/2023]
Abstract
The theoretical description of the thermodynamics of water is challenged by the structural transition towards tetrahedral symmetry at ambient conditions. As perturbation theories typically assume a spherically symmetric reference fluid, they are incapable of accurately describing the liquid properties of water at ambient conditions. In this paper we address this problem by introducing the concept of an associated reference perturbation theory (APT). In APT we treat the reference fluid as an associating hard sphere fluid which transitions to tetrahedral symmetry in the fully hydrogen bonded limit. We calculate this transition in a theoretically self-consistent manner without appealing to molecular simulations. This associated reference provides the reference fluid for a second order Barker-Henderson perturbative treatment of the long-range attractions. We demonstrate that this approach gives a significantly improved description of water as compared to standard perturbation theories.
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Affiliation(s)
- Bennett D Marshall
- ExxonMobil Research and Engineering, 22777 Springwoods Village Parkway, Spring, Texas 77389, USA
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9
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Chaudhari MI, Pratt LR, Paulaitis ME. Concentration dependence of the Flory-Huggins interaction parameter in aqueous solutions of capped PEO chains. J Chem Phys 2014; 141:244908. [DOI: 10.1063/1.4904386] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Affiliation(s)
- M. I. Chaudhari
- Department of Chemical and Biomolecular Engineering, Tulane University, New Orleans, Louisiana 70118, USA
| | - L. R. Pratt
- Department of Chemical and Biomolecular Engineering, Tulane University, New Orleans, Louisiana 70118, USA
| | - M. E. Paulaitis
- Department of Chemical and Biomolecular Engineering, The Ohio State University, Columbus, Ohio 43210, USA
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10
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Chaudhari MI, Sabo D, Pratt LR, Rempe SB. Hydration of Kr(aq) in Dilute and Concentrated Solutions. J Phys Chem B 2014; 119:9098-102. [DOI: 10.1021/jp508866h] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023]
Affiliation(s)
- Mangesh I. Chaudhari
- Center
for Biological and
Material Sciences, Sandia National Laboratories, Albuquerque, New Mexico 87123, United States
| | - Dubravko Sabo
- Department of Chemistry, New York University, New York, New York 10003, United States
| | - Lawrence R. Pratt
- Department of Chemical
and
Biomolecular Engineering, Tulane University, New Orleans, Louisiana 70118, United States
| | - Susan B. Rempe
- Center for Biological and
Material Sciences, Sandia National Laboratories, Albuquerque, New Mexico 87185, United States
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11
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Tomar DS, Weber V, Pettitt BM, Asthagiri D. Conditional solvation thermodynamics of isoleucine in model peptides and the limitations of the group-transfer model. J Phys Chem B 2014; 118:4080-7. [PMID: 24650057 PMCID: PMC3993919 DOI: 10.1021/jp500727u] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
Abstract
![]()
The
hydration thermodynamics of the amino acid X relative to the
reference G (glycine) or the hydration thermodynamics of a small-molecule
analog of the side chain of X is often used to model the contribution
of X to protein stability and solution thermodynamics. We consider
the reasons for successes and limitations of this approach by calculating
and comparing the conditional excess free energy, enthalpy, and entropy
of hydration of the isoleucine side chain in zwitterionic isoleucine,
in extended penta-peptides, and in helical deca-peptides. Butane in
gauche conformation serves as a small-molecule analog for the isoleucine
side chain. Parsing the hydrophobic and hydrophilic contributions
to hydration for the side chain shows that both of these aspects of
hydration are context-sensitive. Furthermore, analyzing the solute–solvent
interaction contribution to the conditional excess enthalpy of the
side chain shows that what is nominally considered a property of the
side chain includes entirely nonobvious contributions of the background.
The context-sensitivity of hydrophobic and hydrophilic hydration and
the conflation of background contributions with energetics attributed
to the side chain limit the ability of a single scaling factor, such
as the fractional solvent exposure of the group in the protein, to
map the component energetic contributions of the model-compound data
to their value in the protein. But ignoring the origin of cancellations
in the underlying components the group-transfer model may appear to
provide a reasonable estimate of the free energy for a given error
tolerance.
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Affiliation(s)
- Dheeraj S Tomar
- Department of Chemical and Biomolecular Engineering, Johns Hopkins University , 3400 North Charles Street, Baltimore, Maryland 21218, United States
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12
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Shi Y, Beck TL. Length scales and interfacial potentials in ion hydration. J Chem Phys 2013; 139:044504. [DOI: 10.1063/1.4814070] [Citation(s) in RCA: 33] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022] Open
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13
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Ren P, Chun J, Thomas DG, Schnieders MJ, Marucho M, Zhang J, Baker NA. Biomolecular electrostatics and solvation: a computational perspective. Q Rev Biophys 2012; 45:427-91. [PMID: 23217364 PMCID: PMC3533255 DOI: 10.1017/s003358351200011x] [Citation(s) in RCA: 135] [Impact Index Per Article: 11.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Abstract
An understanding of molecular interactions is essential for insight into biological systems at the molecular scale. Among the various components of molecular interactions, electrostatics are of special importance because of their long-range nature and their influence on polar or charged molecules, including water, aqueous ions, proteins, nucleic acids, carbohydrates, and membrane lipids. In particular, robust models of electrostatic interactions are essential for understanding the solvation properties of biomolecules and the effects of solvation upon biomolecular folding, binding, enzyme catalysis, and dynamics. Electrostatics, therefore, are of central importance to understanding biomolecular structure and modeling interactions within and among biological molecules. This review discusses the solvation of biomolecules with a computational biophysics view toward describing the phenomenon. While our main focus lies on the computational aspect of the models, we provide an overview of the basic elements of biomolecular solvation (e.g. solvent structure, polarization, ion binding, and non-polar behavior) in order to provide a background to understand the different types of solvation models.
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Affiliation(s)
- Pengyu Ren
- Department of Biomedical Engineering, The University of Texas at Austin
| | | | | | | | - Marcelo Marucho
- Department of Physics and Astronomy, The University of Texas at San Antonio
| | - Jiajing Zhang
- Department of Biomedical Engineering, The University of Texas at Austin
| | - Nathan A. Baker
- To whom correspondence should be addressed. Pacific Northwest National Laboratory, PO Box 999, MSID K7-29, Richland, WA 99352. Phone: +1-509-375-3997,
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14
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Weber V, Asthagiri D. Regularizing Binding Energy Distributions and the Hydration Free Energy of Protein Cytochrome C from All-Atom Simulations. J Chem Theory Comput 2012; 8:3409-15. [DOI: 10.1021/ct300505b] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
Affiliation(s)
| | - D. Asthagiri
- Department of Chemical and Biomolecular
Engineering, Johns Hopkins University, Baltimore, Maryland 21218,
United States
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15
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16
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Merchant S, Dixit PD, Dean KR, Asthagiri D. Ion-water clusters, bulk medium effects, and ion hydration. J Chem Phys 2011; 135:054505. [PMID: 21823710 DOI: 10.1063/1.3620077] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022] Open
Abstract
Thermochemistry of gas-phase ion-water clusters together with estimates of the hydration free energy of the clusters and the water ligands are used to calculate the hydration free energy of the ion. Often the hydration calculations use a continuum model of the solvent. The primitive quasichemical approximation to the quasichemical theory provides a transparent framework to anchor such efforts. Here we evaluate the approximations inherent in the primitive quasichemical approach and elucidate the different roles of the bulk medium. We find that the bulk medium can stabilize configurations of the cluster that are usually not observed in the gas phase, while also simultaneously lowering the excess chemical potential of the ion. This effect is more pronounced for soft ions. Since the coordination number that minimizes the excess chemical potential of the ion is identified as the optimal or most probable coordination number, for such soft ions the optimum cluster size and the hydration thermodynamics obtained with and without account of the bulk medium on the ion-water clustering reaction can be different. The ideas presented in this work are expected to be relevant to experimental studies that translate thermochemistry of ion-water clusters to the thermodynamics of the hydrated ion and to evolving theoretical approaches that combine high-level calculations on clusters with coarse-grained models of the medium.
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Affiliation(s)
- Safir Merchant
- Department of Chemical and Biomolecular Engineering, The Institute of NanoBioTechnology, Johns Hopkins University, Baltimore, Maryland 21218, USA
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17
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Toxvaerd S, Dyre JC. Role of the first coordination shell in determining the equilibrium structure and dynamics of simple liquids. J Chem Phys 2011; 135:134501. [DOI: 10.1063/1.3643123] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/16/2023] Open
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18
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Abstract
Monovalent ion hydration entropies are analyzed via energetic partitioning of the potential distribution theorem free energy. Extensive molecular dynamics simulations and free energy calculations are performed over a range of temperatures to determine the electrostatic and van der Waals components of the entropy. The far-field electrostatic contribution is negative and small in magnitude, and it does not vary significantly as a function of ion size, consistent with dielectric models. The local electrostatic contribution, however, varies widely as a function of ion size; the sign yields a direct indication of the kosmotropic (strongly hydrated) or chaotropic (weakly hydrated) nature of the ion hydration. The results provide a thermodynamic signature for specific ion effects in hydration and are consistent with experiments that suggest minimal perturbations of water structure outside the first hydration shell. The hydration entropies are also examined in relation to the corresponding entropies for the isoelectronic rare gas pairs; an inverse correlation is observed, as expected from thermodynamic hydration data.
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Affiliation(s)
- Thomas L Beck
- Department of Chemistry, University of Cincinnati, Cincinnati, Ohio 45221-0172, United States.
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19
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Rogers DM, Rempe SB. Probing the thermodynamics of competitive ion binding using minimum energy structures. J Phys Chem B 2011; 115:9116-29. [PMID: 21721551 DOI: 10.1021/jp2012864] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
Ion binding is known to affect the properties of biomolecules and is directly involved in many biochemical pathways. Because of the highly polar environments where ions are found, a quantum-mechanical treatment is preferable for understanding the energetics of competitive ion binding. Due to computational cost, a quantum mechanical treatment may involve several approximations, however, whose validity can be difficult to determine. Using thermodynamic cycles, we show how intuitive models for complicated ion binding reactions can be built up from simplified, isolated ion-ligand binding site geometries suitable for quantum mechanical treatment. First, the ion binding free energies of individual, minimum energy structures determine their intrinsic ion selectivities. Next, the relative propensity for each minimum energy structure is determined locally from the balance of ion-ligand and ligand-ligand interaction energies. Finally, the environment external to the binding site exerts its influence both through long-ranged dispersive and electrostatic interactions with the binding site as well as indirectly through shifting the binding site compositional and structural preferences. The resulting picture unifies field-strength, topological control, and phase activation viewpoints into a single theory that explicitly indicates the important role of solute coordination state on overall reaction energetics. As an example, we show that the Na(+) → K(+) selectivities can be recovered by correctly considering the conformational contribution to the selectivity. This can be done even when constraining configuration space to the neighborhood around a single, arbitrarily chosen, minimum energy structure. Structural regions around minima for K(+)- and Na(+)-water clusters are exhibited that display both rigid/mechanical and disordered/entropic selectivity mechanisms for both Na(+) and K(+). Thermodynamic consequences of the theory are discussed with an emphasis on the role of coordination structure in determining experimental properties of ions in complex biological environments.
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Affiliation(s)
- David M Rogers
- Center for Biological and Materials Sciences, MS 0895, Sandia National Laboratories, Albuquerque, New Mexico 87185, USA
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20
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Jiao D, Rempe SB. CO2solvation free energy using quasi-chemical theory. J Chem Phys 2011; 134:224506. [DOI: 10.1063/1.3598470] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
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21
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Merchant S, Shah JK, Asthagiri D. Water coordination structures and the excess free energy of the liquid. J Chem Phys 2011; 134:124514. [DOI: 10.1063/1.3572058] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023] Open
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22
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Weber V, Asthagiri D. Communication: Thermodynamics of water modeled using ab initio simulations. J Chem Phys 2011; 133:141101. [PMID: 20949978 DOI: 10.1063/1.3499315] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022] Open
Abstract
We regularize the potential distribution framework to calculate the excess free energy of liquid water simulated with the BLYP-D density functional. Assuming classical statistical mechanical simulations at 350 K model the liquid at 298 K, the calculated free energy is found in fair agreement with experiments, but the excess internal energy and hence also the excess entropy are not. The utility of thermodynamic characterization in understanding the role of high temperatures to mimic nuclear quantum effects and in evaluating ab initio simulations is noted.
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Affiliation(s)
- Valéry Weber
- Physical Chemistry Institute, University of Zurich, 8057 Zurich, Switzerland.
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23
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Weber V, Merchant S, Dixit PD, Asthagiri D. Molecular packing and chemical association in liquid water simulated using ab initio hybrid Monte Carlo and different exchange-correlation functionals. J Chem Phys 2010; 132:204509. [DOI: 10.1063/1.3437061] [Citation(s) in RCA: 14] [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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24
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Utiramerur S, Paulaitis ME. Cooperative hydrophobic/hydrophilic interactions in the hydration of dimethyl ether. J Chem Phys 2010; 132:155102. [DOI: 10.1063/1.3367977] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
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25
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Asthagiri D, Dixit PD, Merchant S, Paulaitis ME, Pratt LR, Rempe SB, Varma S. Ion selectivity from local configurations of ligands in solutions and ion channels. Chem Phys Lett 2010; 485:1-7. [PMID: 23750043 DOI: 10.1016/j.cplett.2009.12.013] [Citation(s) in RCA: 69] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/20/2022]
Abstract
Probabilities of numbers of ligands proximal to an ion lead to simple, general formulae for the free energy of ion selectivity between different media. That free energy does not depend on the definition of an inner shell for ligand-counting, but other quantities of mechanistic interest do. If analysis is restricted to a specific coordination number, then two distinct probabilities are required to obtain the free energy in addition. The normalizations of those distributions produce partition function formulae for the free energy. Quasi-chemical theory introduces concepts of chemical equilibrium, then seeks the probability that is simplest to estimate, that of the most probable coordination number. Quasi-chemical theory establishes the utility of distributions of ligand-number, and sharpens our understanding of quasi-chemical calculations based on electronic structure methods. This development identifies contributions with clear physical interpretations, and shows that evaluation of those contributions can establish a mechanistic understanding of the selectivity in ion channels.
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Affiliation(s)
- D Asthagiri
- Department of Chemical and Biomolecular Engineering and Institute of NanoBioTechnology, Johns Hopkins University, Baltimore, MD 21218, USA
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Merchant S, Asthagiri D. Thermodynamically dominant hydration structures of aqueous ions. J Chem Phys 2009; 130:195102. [PMID: 19466866 DOI: 10.1063/1.3132709] [Citation(s) in RCA: 49] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
The hydration free energy of an ion is separated into a chemical term, arising due to the interaction of the ion with water molecules within the defined coordination sphere (the inner shell), a packing contribution, accounting for forming an ion-free coordination sphere (the observation volume) in the solvent, and a long range correction, accounting for the interaction of the ion with the solvent outside the coordination sphere. The chemical term is recast as a sum over coordination states, with the nth term depending on the probability of observing n water molecules in the observation volume and the free energy of assembling the n water molecules around the ion in the presence of the outer-shell solvent. Each stepwise increment in the coordination number more fully accounts for the chemical contribution, and this molecular aufbau approach is used to interrogate the thermodynamic importance of various hydration structures X[H(2)O](n) of X(aq) (X = Na(+), K(+), F(-)) within a classical molecular mechanics framework. States with n less than (and at best equal to) the most probable coordination state ñ account for all of the chemical term and evince the role of the ion in drawing water molecules into the coordination sphere. For states with n > ñ, the influence of the ion is tempered and changes in coordination states due to density fluctuations in water also appear important. Thus the influence of the ion on the solvent matrix is local, and only a subset of water molecules (n < or = ñ) contributes dominantly to the hydration thermodynamics. The n = 4 state of Na(+) (ñ = 5) and K(+) (ñ = 7) and the n = 6 state of F(-) (ñ = 6) are thermodynamically dominant; adding a water molecule to the dominant state additionally contributes only about 2-3 k(B)T toward the chemical term, but removing a water molecule is very unfavorable.
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Affiliation(s)
- Safir Merchant
- Department of Chemical and Biomolecular Engineering and The Institute of NanoBioTechnology, Johns Hopkins University, Baltimore, Maryland 21218, USA
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Leung K, Rempe SB, von Lilienfeld OA. Ab initio molecular dynamics calculations of ion hydration free energies. J Chem Phys 2009; 130:204507. [PMID: 19485457 PMCID: PMC2736677 DOI: 10.1063/1.3137054] [Citation(s) in RCA: 108] [Impact Index Per Article: 7.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/12/2009] [Accepted: 04/25/2009] [Indexed: 11/14/2022] Open
Abstract
We apply ab initio molecular dynamics (AIMD) methods in conjunction with the thermodynamic integration or "lambda-path" technique to compute the intrinsic hydration free energies of Li(+), Cl(-), and Ag(+) ions. Using the Perdew-Burke-Ernzerhof functional, adapting methods developed for classical force field applications, and with consistent assumptions about surface potential (phi) contributions, we obtain absolute AIMD hydration free energies (DeltaG(hyd)) within a few kcal/mol, or better than 4%, of Tissandier et al.'s [J. Phys. Chem. A 102, 7787 (1998)] experimental values augmented with the SPC/E water model phi predictions. The sums of Li(+)/Cl(-) and Ag(+)/Cl(-) AIMD DeltaG(hyd), which are not affected by surface potentials, are within 2.6% and 1.2 % of experimental values, respectively. We also report the free energy changes associated with the transition metal ion redox reaction Ag(+)+Ni(+)-->Ag+Ni(2+) in water. The predictions for this reaction suggest that existing estimates of DeltaG(hyd) for unstable radiolysis intermediates such as Ni(+) may need to be extensively revised.
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Affiliation(s)
- Kevin Leung
- Department of Surface and Interface Sciences, MS 1415, Sandia National Laboratories, Albuquerque, New Mexico 87185, USA.
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Abstract
Hydrophobicity manifests itself differently on large and small length scales. This review focuses on large-length-scale hydrophobicity, particularly on dewetting at single hydrophobic surfaces and drying in regions bounded on two or more sides by hydrophobic surfaces. We review applicable theories, simulations, and experiments pertaining to large-scale hydrophobicity in physical and biomolecular systems and clarify some of the critical issues pertaining to this subject. Given space constraints, we cannot review all the significant and interesting work in this active field.
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Affiliation(s)
- Bruce J Berne
- Department of Chemistry, Columbia University, New York, New York 10027, USA.
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Rogers DM, Beck TL. Modeling molecular and ionic absolute solvation free energies with quasichemical theory bounds. J Chem Phys 2008; 129:134505. [DOI: 10.1063/1.2985613] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022] Open
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Ben-Amotz D, Underwood R. Unraveling water's entropic mysteries: a unified view of nonpolar, polar, and ionic hydration. Acc Chem Res 2008; 41:957-67. [PMID: 18710198 DOI: 10.1021/ar7001478] [Citation(s) in RCA: 110] [Impact Index Per Article: 6.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
[Figure: see text]. Most chemical processes on earth are intimately linked to the unique properties of water, relying on the versatility with which water interacts with molecules of varying sizes and polarities. These interactions determine everything from the structure and activity of proteins and living cells to the geological partitioning of water, oil, and minerals in the Earth's crust. The role of hydrophobic hydration in the formation of biological membranes and in protein folding, as well as the importance of electrostatic interactions in the hydration of polar and ionic species, are all well known. However, the underlying molecular mechanisms of hydration are often not as well understood. This Account summarizes and extends emerging understandings of these mechanisms to reveal a newly unified view of hydration and explain previously mystifying observations. For example, rare gas atoms (e.g., Ar) and alkali-halide ions (e.g., K+ and Cl-) have nearly identical experimental hydration entropies, despite the significant charge-induced reorganization of water molecules. Here, we explain how such previously mysterious observations may be understood as arising from Gibbs inequalities, which impose rigorous energetic upper and lower bounds on both hydration free energies and entropies. These fundamental Gibbs bounds depend only on the average interaction energy of a solute with water, thus providing a deep link between solute-water interaction energies and entropies. One of the surprising consequences of the emerging picture is the understanding that the hydration of an ion produces two large but nearly perfectly cancelling, entropic contributions: a negative ion-water interaction entropy and a positive water reorganization entropy. Recent work has also clarified the relationship between the strong cohesive energy of water and the free energy required to form an empty hole (cavity) in water. Here, we explain how linear response theory (whose roots may also be traced to Gibbs inequalities) can provide remarkably accurate descriptions of the process of filling aqueous cavities with nonpolar, polar, or charged molecules. The hydration of nonpolar molecules is well-described by first-order perturbation theory, which implies that turning on solute-water van der Waals interactions does not induce a significant change in water structure. The larger changes in water structure that are induced by polar and ionic solutes are well-described by second-order perturbation theory, which is equivalent to linear response theory. Comparisons of the free energies of nonpolar and polar or ionic solutes may be used to experimentally determine electrostatic contributions to water reorganization energies and entropies. The success of this approach implies that water's ability to respond to solutes of various polarities is far from saturated, as illustrated by simulations of acetonitrile (CH 3CN) in water, which reveal that even such a strongly dipolar solute only produces subtle changes in the structure of water.
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Affiliation(s)
- Dor Ben-Amotz
- Department of Chemistry, Purdue University, West Lafayette, Indiana 47907
| | - Robin Underwood
- Department of Chemistry, Purdue University, West Lafayette, Indiana 47907
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Asthagiri D, Merchant S, Pratt LR. Role of attractive methane-water interactions in the potential of mean force between methane molecules in water. J Chem Phys 2008; 128:244512. [DOI: 10.1063/1.2944252] [Citation(s) in RCA: 54] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
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Sabo D, Varma S, Martin MG, Rempe SB. Studies of the thermodynamic properties of hydrogen gas in bulk water. J Phys Chem B 2007; 112:867-76. [PMID: 18154326 DOI: 10.1021/jp075459v] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The thermodynamic properties of hydrogen gas in liquid water are investigated using Monte Carlo molecular simulation and the quasichemical theory of liquids. The free energy of hydrogen hydration obtained by Monte Carlo simulations agrees well with the experimental result, indicating that the classical force fields used in this work provide an adequate description of intermolecular interactions in the aqueous hydrogen system. Two estimates of the hydration free energy for hydrogen made within the framework of the quasichemical theory also agree reasonably well with experiment provided local anharmonic motions and distant interactions with explicit solvent are treated. Both quasichemical estimates indicate that the hydration free energy results from a balance between chemical association and molecular packing. Additionally, the results suggest that the molecular packing term is almost equally driven by unfavorable enthalpic and entropic components.
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Affiliation(s)
- Dubravko Sabo
- Sandia National Laboratories, Albuquerque, New Mexico 87185, USA.
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Shah JK, Asthagiri D, Pratt LR, Paulaitis ME. Balancing local order and long-ranged interactions in the molecular theory of liquid water. J Chem Phys 2007; 127:144508. [DOI: 10.1063/1.2766940] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
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Asthagiri D, Ashbaugh HS, Piryatinski A, Paulaitis ME, Pratt LR. Non-van der Waals Treatment of the Hydrophobic Solubilities of CF4. J Am Chem Soc 2007; 129:10133-40. [PMID: 17661465 DOI: 10.1021/ja071037n] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
A quasi-chemical theory implemented on the basis of molecular simulation is derived and tested for the hydrophobic hydration of CF4(aq). The theory formulated here subsumes a van der Waals treatment of solvation and identifies contributions to the hydration free energy of CF4(aq) that naturally arise from chemical contributions defined by quasi-chemical theory and fluctuation contributions analogous to Debye-Hückel or random phase approximations. The resulting Gaussian statistical thermodynamic model avoids consideration of hypothetical drying-then-rewetting problems and is physically reliable in these applications as judged by the size of the fluctuation contribution. The specific results here confirm that unfavorable tails of binding energy distributions reflect few-body close solute-solvent encounters. The solvent near-neighbors are pushed by the medium into unfavorable interactions with the solute, in contrast to the alternative view that a preformed interface is pulled by the solute-solvent attractive interactions into contact with the solute. The polyatomic model of CF4(aq) studied gives a satisfactory description of the experimental solubilities including the temperature dependence. The proximal distributions evaluated here for polyatomic solutes accurately reconstruct the observed distributions of water near these molecules which are nonspherical. These results suggest that drying is not an essential consideration for the hydrophobic solubilities of CF4, or of C(CH3)4 which is more soluble.
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Affiliation(s)
- D Asthagiri
- Department of Chemical & Biomolecular Engineering, Johns Hopkins University, Baltimore, Maryland 21218, USA
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