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Raposo DJ. Effect of Conformational Equilibrium on Solvation Properties of 1,2-DCE in Water: A Solvation Thermodynamics and 3D-RISM Study. J Phys Chem B 2023; 127:757-765. [PMID: 36626710 DOI: 10.1021/acs.jpcb.2c07836] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/12/2023]
Abstract
The contributions of the enthalpy and entropy of solvation for the study of chemical and biological systems are important in the prediction, interpretation, and manipulation of these processes. The relation between solvation Gibbs energies, enthalpies, and entropies of solvation, and their rigorous relation with the conformational equilibrium, are derived for the first time and applied with a computational method, in accordance with the Solvation Thermodynamics previous results, to 1,2-dichloroethane solvation in water. The rigid conformer calculations in solution were performed by using PC+/3D-RISM approach, with the conformational averaged results for enthalpy and solvation Gibbs energy reproducing the experimental results quite successfully. A qualitative agreement in the entropy of solvation predictions was also observed.
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Affiliation(s)
- Diego J Raposo
- Departamento de Química Fundamental, Universidade Federal de Pernambuco, Cidade Universitária, Recife, Pernambuco50740-560, Brazil
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2
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Phan A, Stamatakis M, Koh CA, Striolo A. Correlating Antiagglomerant Performance with Gas Hydrate Cohesion. ACS APPLIED MATERIALS & INTERFACES 2021; 13:40002-40012. [PMID: 34382786 DOI: 10.1021/acsami.1c06309] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/27/2023]
Abstract
Although inhibiting hydrate formation in hydrocarbon-water systems is paramount in preventing pipe blockage in hydrocarbon transport systems, the molecular mechanisms responsible for antiagglomerant (AA) performance are not completely understood. To better understand why macroscopic performance is affected by apparently small changes in the AA molecular structure, we perform molecular dynamics simulations. We quantify the cohesion energy between two gas hydrate nanoparticles dispersed in liquid hydrocarbons in the presence of different AAs, and we achieve excellent agreement against experimental data obtained at high pressure using the micromechanical force apparatus. This suggests that the proposed simulation approach could provide a screening method for predicting, in silico, the performance of new molecules designed to manage hydrates in flow assurance. Our results suggest that entropy and free energy of solvation of AAs, combined in some cases with the molecular orientation at hydrate-oil interfaces, are descriptors that could be used to predict performance, should the results presented here be reproduced for other systems as well. These insights could help speed up the design of new AAs and guide future experiments.
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Affiliation(s)
- Anh Phan
- Department of Chemical Engineering, University College London, London WC1E 7JE, U.K
| | - Michail Stamatakis
- Department of Chemical Engineering, University College London, London WC1E 7JE, U.K
| | - Carolyn A Koh
- Center for Hydrate Research, Chemical & Biological Engineering Department, Colorado School of Mines, Golden, Colorado 80401, United States
| | - Alberto Striolo
- Department of Chemical Engineering, University College London, London WC1E 7JE, U.K
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3
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Monroe JI, Shell MS. Decoding signatures of structure, bulk thermodynamics, and solvation in three-body angle distributions of rigid water models. J Chem Phys 2019; 151:094501. [PMID: 31492058 DOI: 10.1063/1.5111545] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022] Open
Abstract
A tetrahedral structure resulting from hydrogen bonding is a hallmark of liquid water and plays a significant role in determining its unique thermophysical properties. This water feature has helped understand anomalous properties and physically interpret and model hydrophobic solvation thermodynamics. Tetrahedrality is well described by the geometric relationship of any central water molecule with two of its nearest neighbors in the first coordination shell, as defined by the corresponding "three-body" angle. While order parameters and even full water models have been developed using specific or average features of the three-body angle distribution, here we examine the distribution holistically, tracking its response to changes in temperature, density, and the presence of model solutes. Surprisingly, we find that the three-body distribution responds by varying primarily along a single degree of freedom, suggesting a remarkably simplified view of water structure. We characterize three-body angle distributions across temperature and density space and identify principal components of the variations with state conditions. We show that these principal components embed physical significance and trace out transitions between tetrahedral and simple-fluid-like behavior. Moreover, we find that the ways three-body angles vary within the hydration shells of model colloids of different types and sizes are nearly identical to the variations seen in bulk water across density and temperature. Importantly, through the principal directions of these variations, we find that perturbations to the hydration-water distributions well predict the thermodynamics associated with colloid solvation, in particular, the relative entropy of this process that captures indirect, solvent-mediated contributions to the hydration free energy.
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Affiliation(s)
- Jacob I Monroe
- Department of Chemical Engineering, University of California, Santa Barbara, California 93106-9010, USA
| | - M Scott Shell
- Department of Chemical Engineering, University of California, Santa Barbara, California 93106-9010, USA
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5
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Fiedler J, Thiyam P, Kurumbail A, Burger FA, Walter M, Persson C, Brevik I, Parsons DF, Boström M, Buhmann SY. Effective Polarizability Models. J Phys Chem A 2017; 121:9742-9751. [DOI: 10.1021/acs.jpca.7b10159] [Citation(s) in RCA: 24] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Johannes Fiedler
- Physikalisches
Institut, Albert-Ludwigs-Universität Freiburg, Hermann-Herder-Strasse 3, 79104 Freiburg, Germany
| | - Priyadarshini Thiyam
- Department
of Materials Science and Engineering, KTH, Royal Institute of Technology, SE-100 44 Stockholm, Sweden
- Centre
for Materials Science and Nanotechnology, Department of Physics, University of Oslo, P.O.
Box 1048, Blindern, NO-0316 Oslo, Norway
| | - Anurag Kurumbail
- Department
of Energy and Process Engineering, Norwegian University of Science and Technology, NO-7491 Trondheim, Norway
| | - Friedrich A. Burger
- Physikalisches
Institut, Albert-Ludwigs-Universität Freiburg, Hermann-Herder-Strasse 3, 79104 Freiburg, Germany
| | - Michael Walter
- Physikalisches
Institut, Albert-Ludwigs-Universität Freiburg, Hermann-Herder-Strasse 3, 79104 Freiburg, Germany
- FIT Freiburg Centre for Interactive Materials and Bioinspired Technologies, Georges-Köhler-Allee 105, 79110 Freiburg, Germany
- Fraunhofer IWM, Wöhlerstrasse
11, D-79108 Freiburg
i. Br., Germany
| | - Clas Persson
- Department
of Materials Science and Engineering, KTH, Royal Institute of Technology, SE-100 44 Stockholm, Sweden
- Centre
for Materials Science and Nanotechnology, Department of Physics, University of Oslo, P.O.
Box 1048, Blindern, NO-0316 Oslo, Norway
| | - Iver Brevik
- Department
of Energy and Process Engineering, Norwegian University of Science and Technology, NO-7491 Trondheim, Norway
| | - Drew F. Parsons
- School
of Engineering and IT, Murdoch University, 90 South Street, Murdoch, WA 6150, Australia
| | - Mathias Boström
- Department
of Energy and Process Engineering, Norwegian University of Science and Technology, NO-7491 Trondheim, Norway
| | - Stefan Y. Buhmann
- Physikalisches
Institut, Albert-Ludwigs-Universität Freiburg, Hermann-Herder-Strasse 3, 79104 Freiburg, Germany
- Freiburg
Institute for Advanced Studies, Albert-Ludwigs-Universität Freiburg, Albertstrasse 19, 79104 Freiburg, Germany
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6
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Abstract
This review focuses on papers published since 2000 on the topic of the properties of solutes in water. More specifically, it evaluates the state of the art of our understanding of the complex relationship between the shape of a hydrophobe and the hydrophobic effect. To highlight this, we present a selection of references covering both empirical and molecular dynamics studies of small (molecular-scale) solutes. These include empirical studies of small molecules, synthetic hosts, crystalline monolayers, and proteins, as well as in silico investigations of entities such as idealized hard and soft spheres, small solutes, hydrophobic plates, artificial concavity, molecular hosts, carbon nanotubes and spheres, and proteins.
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Affiliation(s)
- Matthew B Hillyer
- Department of Chemistry, Tulane University, New Orleans, Louisiana 70118;
| | - Bruce C Gibb
- Department of Chemistry, Tulane University, New Orleans, Louisiana 70118;
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7
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Prasad S, Chakravarty C. Solvation of LiCl in model liquids with high to low hydrogen bond strengths. J Chem Phys 2017. [DOI: 10.1063/1.4982828] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022] Open
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8
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Yadav HOS, Chakravarty C. Thiolated gold nanoparticle solvation in near-critical fluids: The role of density, temperature, and topology. J Chem Phys 2017; 146:174902. [DOI: 10.1063/1.4982755] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Affiliation(s)
- Hari O. S. Yadav
- Department of Chemistry, Indian Institute of Technology-Delhi, New Delhi 110016, India
| | - Charusita Chakravarty
- Department of Chemistry, Indian Institute of Technology-Delhi, New Delhi 110016, India
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9
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Graziano G. Probability of cavity creation in water and corresponding Lennard-Jones liquid. J Mol Liq 2017. [DOI: 10.1016/j.molliq.2016.12.083] [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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Affiliation(s)
- Dor Ben-Amotz
- Department of Chemistry, Purdue University, West Lafayette, Indiana 47907;
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Cerdeiriña CA, Debenedetti PG. Water anomalous thermodynamics, attraction, repulsion, and hydrophobic hydration. J Chem Phys 2016; 144:164501. [DOI: 10.1063/1.4947062] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Affiliation(s)
- Claudio A. Cerdeiriña
- Departamento de Física Aplicada, Universidad de Vigo—Campus del Agua, Ourense 32004, Spain
| | - Pablo G. Debenedetti
- Department of Chemical and Biological Engineering, Princeton University, Princeton, New Jersey 08544, USA
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12
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Prasad S, Chakravarty C. Onset of simple liquid behaviour in modified water models. J Chem Phys 2014; 140:164501. [DOI: 10.1063/1.4870823] [Citation(s) in RCA: 30] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
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13
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Wuttke R, Hofmann H, Nettels D, Borgia MB, Mittal J, Best RB, Schuler B. Temperature-dependent solvation modulates the dimensions of disordered proteins. Proc Natl Acad Sci U S A 2014; 111:5213-8. [PMID: 24706910 PMCID: PMC3986154 DOI: 10.1073/pnas.1313006111] [Citation(s) in RCA: 146] [Impact Index Per Article: 14.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
For disordered proteins, the dimensions of the chain are an important property that is sensitive to environmental conditions. We have used single-molecule Förster resonance energy transfer to probe the temperature-induced chain collapse of five unfolded or intrinsically disordered proteins. Because this behavior is sensitive to the details of intrachain and chain-solvent interactions, the collapse allows us to probe the physical interactions governing the dimensions of disordered proteins. We find that each of the proteins undergoes a collapse with increasing temperature, with the most hydrophobic one, λ-repressor, undergoing a reexpansion at the highest temperatures. Although such a collapse might be expected due to the temperature dependence of the classical "hydrophobic effect," remarkably we find that the largest collapse occurs for the most hydrophilic, charged sequences. Using a combination of theory and simulation, we show that this result can be rationalized in terms of the temperature-dependent solvation free energies of the constituent amino acids, with the solvation properties of the most hydrophilic residues playing a large part in determining the collapse.
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Affiliation(s)
- René Wuttke
- Department of Biochemistry, University of Zurich, 8057 Zurich, Switzerland
| | - Hagen Hofmann
- Department of Biochemistry, University of Zurich, 8057 Zurich, Switzerland
| | - Daniel Nettels
- Department of Biochemistry, University of Zurich, 8057 Zurich, Switzerland
| | | | - Jeetain Mittal
- Department of Chemical Engineering, Lehigh University, Bethlehem, PA 18015; and
| | - Robert B. Best
- Laboratory of Chemical Physics, National Institute of Digestive and Diabetes and Kidney Diseases, National Institutes of Health, Bethesda, MD 20892-0520
| | - Benjamin Schuler
- Department of Biochemistry, University of Zurich, 8057 Zurich, Switzerland
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14
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Nayar D, Chakravarty C. Sensitivity of local hydration behaviour and conformational preferences of peptides to choice of water model. Phys Chem Chem Phys 2014; 16:10199-213. [DOI: 10.1039/c3cp55147d] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Secondary structural preferences of the beta-hairpin of the 2GB1 protein in the folded and unfolded ensembles are shown to be sensitive to the choice of water model.
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Affiliation(s)
- Divya Nayar
- Department of Chemistry
- Indian Institute of Technology-Delhi
- New Delhi: 110016, India
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15
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Fu CF, Tian SX. Different aggregation dynamics of benzene–water mixtures. Phys Chem Chem Phys 2014; 16:21957-63. [DOI: 10.1039/c4cp01537a] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
The differences between the molecular aggregations in benzene–water mixtures are identified using all-atom molecular dynamics simulations.
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Affiliation(s)
- Cen-Feng Fu
- Hefei National Laboratory for Physical Sciences at the Microscale and Department of Chemical Physics
- University of Science and Technology of China
- Hefei, China
| | - Shan Xi Tian
- Hefei National Laboratory for Physical Sciences at the Microscale and Department of Chemical Physics
- University of Science and Technology of China
- Hefei, China
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16
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Godec A, Smith JC, Merzel F. Soft collective fluctuations governing hydrophobic association. PHYSICAL REVIEW LETTERS 2013; 111:127801. [PMID: 24093302 DOI: 10.1103/physrevlett.111.127801] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/21/2013] [Revised: 08/02/2013] [Indexed: 06/02/2023]
Abstract
The interaction between two associating hydrophobic particles has traditionally been explained in terms of the release of entropically frustrated hydration shell water molecules. However, this picture cannot account for the kinetics of hydrophobic association and is therefore not capable of providing a microscopic description of the hydrophobic interaction (HI). Here, Monte Carlo simulations of a pair of molecular-scale apolar solutes in aqueous solution reveal the critical role of collective fluctuations in the hydrogen bond (HB) network for the microscopic picture of the HI. The main contribution to the HI is the relaxation of solute-water translational correlations. The existence of a heat capacity maximum at the desolvation barrier is shown to arise from softening of non-HB water fluctuations and the relaxation of many-body correlations in the labile HB network. The microscopic event governing the kinetics of hydrophobic association has turned out to be a relatively large critical collective fluctuation in hydration water displacing a substantial fraction of HB clusters from the inner to the outer region of the first hydration shell.
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Affiliation(s)
- Aljaž Godec
- National Institute of Chemistry, Hajdrihova 19, 1000 Ljubljana, Slovenia and Institute for Physics and Astronomy, University of Potsdam, 14476 Potsdam-Golm, Germany
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17
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Nayar D, Yadav HOS, Jabes BS, Chakravarty C. Relating Structure, Entropy, and Energy of Solvation of Nanoscale Solutes: Application to Gold Nanoparticle Dispersions. J Phys Chem B 2012; 116:13124-32. [DOI: 10.1021/jp307615f] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Divya Nayar
- Department
of Chemistry, Indian Institute of Technology-Delhi, New Delhi 110016, India
| | | | - B. Shadrack Jabes
- Department
of Chemistry, Indian Institute of Technology-Delhi, New Delhi 110016, India
| | - Charusita Chakravarty
- Department
of Chemistry, Indian Institute of Technology-Delhi, New Delhi 110016, India
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18
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Godec A, Merzel F. Physical origin underlying the entropy loss upon hydrophobic hydration. J Am Chem Soc 2012; 134:17574-81. [PMID: 23003674 DOI: 10.1021/ja306464u] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
The hydrophobic effect (HE) is commonly associated with the demixing of oil and water at ambient conditions and plays the leading role in determining the structure and stability of biomolecular assembly in aqueous solutions. On the molecular scale HE has an entropic origin. It is believed that hydrophobic particles induce order in the surrounding water by reducing the volume of configuration space available for hydrogen bonding. Here we show with computer simulation results that this traditional picture, based on average structural features of hydration water, configurational properties of single water molecules, and up to pairwise correlations, is not correct. Analyzing collective fluctuations in water clusters we are able to provide a fundamentally new picture of HE based on pronounced many-body correlations affecting the switching of hydrogen bonds (HBs) between molecules. These correlations emerge as a nonlocal compensation of reduced fluctuations of local electrostatic fields in the presence of an apolar solute. We propose an alternative view which may also be formulated as a maximization principle: The electrostatic noise acting on water molecules is maximized under the constraint that each water molecule on average maintains as many HBs as possible. In the presence of the solute the maximized electrostatic noise is a result of nonlocal fluctuations in the labile HB network giving rise to strong correlations among at least up to four water molecules.
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Affiliation(s)
- Aljaž Godec
- National Institute of Chemistry, Hajdrihova 19, 1000 Ljubljana, Slovenia.
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19
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Jabes BS, Nayar D, Dhabal D, Molinero V, Chakravarty C. Water and other tetrahedral liquids: order, anomalies and solvation. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2012; 24:284116. [PMID: 22739063 DOI: 10.1088/0953-8984/24/28/284116] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/01/2023]
Abstract
In order to understand the common features of tetrahedral liquids with water-like anomalies, the relationship between local order and anomalies has been studied using molecular dynamics simulations for three categories of such liquids: (a) atomistic rigid-body models for water (TIP4P, TIP4P/2005, mTIP3P, SPC/E), (b) ionic melts, BeF(2) (TRIM model) and SiO(2) (BKS potential) and (c) Stillinger-Weber liquids parametrized to model water (mW) and silicon. Rigid-body, atomistic models for water and the Stillinger-Weber liquids show a strong correlation between tetrahedral and pair correlation order and the temperature for the onset of the density anomaly is close to the melting temperature. In contrast, the ionic melts show weaker and more variable degrees of correlation between tetrahedral and pair correlation metrics, and the onset temperature for the density anomaly is more than twice the melting temperature. In the case of water, the relationship between water-like anomalies and solvation is studied by examining the hydration of spherical solutes (Na(+), Cl(-), Ar) in water models with different temperature regimes of anomalies (SPC/E, TIP4P and mTIP3P). For both ionic and nonpolar solutes, the local structure and energy of water molecules is essentially the same as in bulk water beyond the second-neighbour shell. The local order and binding energy of water molecules are not perturbed by the presence of a hydrophobic solute. In the case of ionic solutes, the perturbation is largely localized within the first hydration shell. The binding energies for the ions are strongly dependent on the water models and clearly indicate that the geometry of the partial charge distributions, and the associated multipole moments, play an important role. However the anomalous behaviour of the water network has been found to be unimportant for polar solvation.
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Affiliation(s)
- B Shadrack Jabes
- Department of Chemistry, Indian Institute of Technology-Delhi, New Delhi 110016, India
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20
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Baron R, Molinero V. Water-Driven Cavity–Ligand Binding: Comparison of Thermodynamic Signatures from Coarse-Grained and Atomic-Level Simulations. J Chem Theory Comput 2012; 8:3696-704. [DOI: 10.1021/ct300121r] [Citation(s) in RCA: 42] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Riccardo Baron
- Department of Medicinal Chemistry,
College of Pharmacy, and The Henry Eyring Center for Theoretical Chemistry,
The University of Utah, Salt Lake City, Utah 84112-5820, United States
| | - Valeria Molinero
- Department of Chemistry and
The Henry Eyring Center for Theoretical Chemistry, The University
of Utah, 315 South 1400 East, Salt Lake City, Utah 84112-0850, United
States
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21
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Head-Gordon T, Lynden-Bell RM, Dowdle JR, Rossky PJ. Predicting cavity formation free energy: how far is the Gaussian approximation valid? Phys Chem Chem Phys 2012; 14:6996-7004. [PMID: 22495173 DOI: 10.1039/c2cp00046f] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
We examine the range of validity of the Gaussian model for various water-like liquids whose intermolecular potentials differ from SPC/E water, to provide insight into the temperature dependence of the hydrophobic effect for small hard sphere solutes. We find that low compressibility liquids that have more close-packed network structures show much larger deviations from Gaussian fluctuations for low or zero occupancies relative to more compressible fluids with more open networks. Water appears to be a unique molecular fluid in possessing equilibrium density fluctuations that are faithfully described by the Gaussian theory. We ascribe this success to the fact, shown here, that the orientational correlations near a small hard sphere solute involve remarkably little reorganization from the bulk, which is a consequence of water's low solvent reorganization enthalpy and entropy.
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Affiliation(s)
- T Head-Gordon
- Department of Bioengineering, University of California, Berkeley, California 94720, USA
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22
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Nayar D, Agarwal M, Chakravarty C. Comparison of Tetrahedral Order, Liquid State Anomalies, and Hydration Behavior of mTIP3P and TIP4P Water Models. J Chem Theory Comput 2011; 7:3354-67. [PMID: 26598167 DOI: 10.1021/ct2002732] [Citation(s) in RCA: 39] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The relationship between local tetrahedral order, tagged particle potential energy, and coordination number is studied for mTIP3P and TIP4P models of water in the bulk as well as in the neighborhood of a small peptide. The tendency of water molecules with different binding or tagged particle potential energies to occupy environments with different degrees of disorder can be effectively illustrated by constructing tetrahedral order distributions and corresponding entropy metrics conditional on restricted ranges of local binding energy. At the state point corresponding to the onset of the density anomaly, the correlation between tetrahedral entropy versus tagged potential energy is strong and virtually identical for mTIP3P and TIP4P. In TIP4P, this correlation is retained up to temperatures as high as 300 K, while it is lost by 250 K in mTIP3P. In the 250-300 K regime that is important for biomolecular simulations, mTIP3P behaves essentially as a simple liquid while TIP4P shows the density and related anomalies characteristic of water. We also study the number of water molecules, the tetrahedral order, and the tagged molecule potential energies for water molecules as a function of the distance from the peptide for the 16-residue β-hairpin fragment of 2GB1 in mTIP3P and TIP4P solvents. The hydration shell coordination profiles (n(r)) of the number of water molecules are almost identical in the two solvents, but the radial variation in the local energies and local order show significant differences. The residue-wise variation in the tagged potential energy of water molecules within the first hydration shell is qualitatively similar in the two models. A comparison of the tetrahedral order distributions of water molecules lying at different distances from the biomolecular solute shows that the perturbation in the local tetrahedral order distributions of the bulk solvent due to the presence of the solute is marginal. Thus, in the 250-300 K regime, the mTIP3P and TIP4P water models show qualitatively different behavior in terms of the relationship between tetrahedral order and local energy, but as solvents in the neighborhood of a biomolecular solute, the differences between the two models are only quantitative and not qualitative.
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Affiliation(s)
- Divya Nayar
- Department of Chemistry, Indian Institute of Technology-Delhi , New Delhi 110016, India
| | - Manish Agarwal
- Department of Chemistry, Indian Institute of Technology-Delhi , New Delhi 110016, India
| | - Charusita Chakravarty
- Department of Chemistry, Indian Institute of Technology-Delhi , New Delhi 110016, India
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