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10 pages, 1984 KiB

Open AccessArticle

An Ab Initio Investigation of the Hydration of Antimony(III)

by Cory C. Pye and Champika Mahesh Gunasekara

Liquids 2024, 4(2), 322-331; https://doi.org/10.3390/liquids4020016 - 01 Apr 2024

Viewed by 779

The energies, structures, and vibrational frequencies of [Sb(H₂O)_n]³⁺, n = 0–9, 18 have been calculated at the Hartree–Fock and second-order Møller–Plesset levels of theory using the CEP, LANL2, and SDD effective core potentials in combination with their [...] Read more.

The energies, structures, and vibrational frequencies of [Sb(H₂O)_n]³⁺, n = 0–9, 18 have been calculated at the Hartree–Fock and second-order Møller–Plesset levels of theory using the CEP, LANL2, and SDD effective core potentials in combination with their associated basis sets, or with the 6-31G* and 6-31+G* basis sets. The metal–oxygen distances and totally symmetric stretching frequency of the aqua ions were compared with each other and with related crystal structure measurements where available. Full article

(This article belongs to the Special Issue Hydration of Ions in Aqueous Solution)

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15 pages, 4535 KiB

Open AccessArticle

An X-ray and Neutron Scattering Study of Aqueous MgCl₂ Solution in the Gigapascal Pressure Range

by Toshio Yamaguchi, Nami Fukuyama, Koji Yoshida, Yoshinori Katayama, Shinichi Machida and Takanori Hattori

Liquids 2023, 3(3), 288-302; https://doi.org/10.3390/liquids3030019 - 04 Jul 2023

Cited by 2 | Viewed by 1338

Abstract

The structure of electrolyte solutions under pressure at a molecular level is a crucial issue in the fundamental science of understanding the nature of ion solvation and association and application fields, such as geological processes on the Earth, pressure-induced protein denaturation, and supercritical [...] Read more.

The structure of electrolyte solutions under pressure at a molecular level is a crucial issue in the fundamental science of understanding the nature of ion solvation and association and application fields, such as geological processes on the Earth, pressure-induced protein denaturation, and supercritical water technology. We report the structure of an aqueous 2 m (=mol kg⁻¹) MgCl₂ solution at pressures from 0.1 MPa to 4 GPa and temperatures from 300 to 500 K revealed by X-ray- and neutron-scattering measurements. The scattering data are analyzed by empirical potential structure refinement (EPSR) modeling to derive the pair distribution functions, coordination number distributions, angle distributions, and spatial density functions (3D structure) as a function of pressure and temperature. Mg²⁺ forms rigid solvation shells extended to the third shell; the first solvation shell of six-fold octahedral coordination with about six water molecules at 0 GPa transforms into about five water molecules and one Cl⁻ due to the formation of the contact ion pairs in the GPa pressure range. The Cl⁻ solvation shows a substantial pressure dependence; the coordination number of a water oxygen atom around Cl⁻ increases from 8 at 0.1 MPa/300 K to 10 at 4 GPa/500 K. The solvent water transforms the tetrahedral network structure at 0.1 MPa/300 K to a densely packed structure in the GPa pressure range; the number of water oxygen atoms around a central water molecule gradually increases from 4.6 at 0.1 MPa/298 K to 8.4 at 4 GPa/500 K. Full article

(This article belongs to the Special Issue Hydration of Ions in Aqueous Solution)

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10 pages, 1770 KiB

Open AccessArticle

Hydration of Phosphate Ion in Polarizable Water: Effect of Temperature and Concentration

by Sandeep Verma and Arup Kumar Pathak

Liquids 2023, 3(3), 278-287; https://doi.org/10.3390/liquids3030018 - 21 Jun 2023

Viewed by 1355

Abstract

The hydration of phosphate ions, an essential component of many biological molecules, is studied using all-atom molecular dynamics (MD) simulation and quantum chemical methods. MD simulations are carried out by employing a mean-field polarizable water model. A good linear correlation between the self-diffusion [...] Read more.

The hydration of phosphate ions, an essential component of many biological molecules, is studied using all-atom molecular dynamics (MD) simulation and quantum chemical methods. MD simulations are carried out by employing a mean-field polarizable water model. A good linear correlation between the self-diffusion coefficient and phosphate anion concentration is ascertained from the computed mean-square displacement (MSD) profiles. The HB dynamics of the hydration of the phosphate anion is evaluated from the time-dependent autocorrelation function C_HB(t) and is determined to be slightly faster for the phosphate–anion system as compared to that of the water–water system at room temperature. The coordination number (CN) of the phosphate ion is found to be 15.9 at 298 K with 0.05 M phosphate ion concentration. The average CN is also calculated to be 15.6 for the same system by employing non-equilibrium MD simulation, namely, the well-tempered meta-dynamics method. A full geometry optimization of the PO₄³⁻·16H₂O cluster is investigated at the ωB97X-D/aug-cc-pVTZ level of theory, and the hydration of the phosphate anion is observed to have both singly and doubly bonded anion–water hydrogen bonds and inter-water hydrogen bonds in a range between 0.169–0.201 nm and 0.192–0.215 nm, respectively. Modified Stokes–Einstein relation is used to calculate the conductivity of the phosphate ion and is found to be in good agreement with the experimentally observed value. Full article

(This article belongs to the Special Issue Hydration of Ions in Aqueous Solution)

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9 pages, 1479 KiB

Open AccessArticle

An Ab Initio Investigation of the Hydration of Tin(II)

by Cory C. Pye and Champika Mahesh Gunasekara

Liquids 2022, 2(4), 465-473; https://doi.org/10.3390/liquids2040027 - 14 Dec 2022

Cited by 1 | Viewed by 1318

Abstract

The structure of tin(II) is not well known in aqueous solution. The energies, structures, and vibrational frequencies of [Sn(H₂O)_n,]²⁺ n = 0–9, 18 have been calculated at the Hartree–Fock and second order Møller–Plesset levels of theory using [...] Read more.

The structure of tin(II) is not well known in aqueous solution. The energies, structures, and vibrational frequencies of [Sn(H₂O)_n,]²⁺ n = 0–9, 18 have been calculated at the Hartree–Fock and second order Møller–Plesset levels of theory using the CEP, LANL2, and SDD effective core potentials in combination with their associated basis sets, or with the 6-31G* and 6-31+G* basis sets. The tin–oxygen distances and totally symmetric stretching frequency of the aquatin(II) ions were compared with each other, and with solution measurements where available. Full article

(This article belongs to the Special Issue Hydration of Ions in Aqueous Solution)

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20 pages, 1761 KiB

Open AccessArticle

Solvation Structure and Ion–Solvent Hydrogen Bonding of Hydrated Fluoride, Chloride and Bromide—A Comparative QM/MM MD Simulation Study

by Thomas S. Hofer

Liquids 2022, 2(4), 445-464; https://doi.org/10.3390/liquids2040026 - 09 Dec 2022

Cited by 2 | Viewed by 2003

Abstract

In this study, the correlated resolution-of-identity Møller–Plesset perturbation theory of second order (RIMP2) ab initio level of theory has been combined with the newly parameterised, flexible SPC-mTR2 water model to formulate an advanced QM/MM MD simulation protocol to study the solvation properties of [...] Read more.

In this study, the correlated resolution-of-identity Møller–Plesset perturbation theory of second order (RIMP2) ab initio level of theory has been combined with the newly parameterised, flexible SPC-mTR2 water model to formulate an advanced QM/MM MD simulation protocol to study the solvation properties of the solutes F

^{-}

, Cl

^{-}

and Br

^{-}

in aqueous solution. After the identification of suitable ion–water Lennard–Jones parameters for the QM/MM coupling, a total simulation period of 10 ps (equilibration) plus 25 ps (sampling) could be achieved for each target system at QM/MM conditions. The resulting simulation data enable an in-depth analysis of the respective hydration structure, the first shell ligand exchange characteristics and the impact of solute–solvent hydrogen bonding on the structural properties of first shell water molecules. While a rather unexpected tailing of the first shell ion–oxygen peak renders the identification of a suitable QM boundary region challenging, the presented simulation results provide a valuable primer for more advanced simulation approaches focused on the determination of single-ion thermodynamical properties. Full article

(This article belongs to the Special Issue Hydration of Ions in Aqueous Solution)

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15 pages, 1593 KiB

Open AccessArticle

Solvent Exchange around Aqueous Zn(II) from Ab Initio Molecular Dynamics Simulations

by Adrian Malinowski and Maciej Śmiechowski

Liquids 2022, 2(3), 243-257; https://doi.org/10.3390/liquids2030015 - 19 Sep 2022

Cited by 2 | Viewed by 1840

Abstract

Hydrated zinc(II) cations, due to their importance in biological systems, are the subject of ongoing research concerning their hydration shell structure and dynamics. Here, ab initio molecular dynamics (AIMD) simulations are used to study solvent exchange events around aqueous Zn²+, for [...] Read more.

Hydrated zinc(II) cations, due to their importance in biological systems, are the subject of ongoing research concerning their hydration shell structure and dynamics. Here, ab initio molecular dynamics (AIMD) simulations are used to study solvent exchange events around aqueous Zn²+, for which observation in detail is possible owing to the considerable length of the generated trajectory. While the hexacoordinated Zn(H₂O)₆²+ is the dominant form of Zn(II) in an aqueous solution, there is a non-negligible contribution of the pentacoordinated Zn(H₂O)₅²+ complex which presence is linked to the dissociative solvent exchange events around Zn²+. The pentacoordinated Zn(II) has a much tighter hydration sphere and is characterized by a trigonal bipyramidal structure, in contrast to the usual octahedral symmetry of the hexacoordinated complex. In total, two full exchange events are registered in the analyzed trajectory. AIMD simulations on an adequate length scale thus provide a direct way of studying such solvent exchange events around ions in molecular detail. Full article

(This article belongs to the Special Issue Hydration of Ions in Aqueous Solution)

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25 pages, 1425 KiB

Open AccessArticle

Solute-Induced Perturbation of the Solvent Microstructure in Aqueous Electrolyte Solutions: Some Uses and Misuses of Structure Making/Breaking Criteria

by Ariel A. Chialvo and Oscar D. Crisalle

Liquids 2022, 2(3), 106-130; https://doi.org/10.3390/liquids2030008 - 22 Jul 2022

Cited by 3 | Viewed by 1600

Abstract

In this article, we raise awareness about the misuses of frequently invoked criteria for structure making/breaking phenomena, resulting from the absence of any explicit cause–effect relationship between the proposed markers and the microstructural perturbation of the solvent induced by the solute. First, we [...] Read more.

In this article, we raise awareness about the misuses of frequently invoked criteria for structure making/breaking phenomena, resulting from the absence of any explicit cause–effect relationship between the proposed markers and the microstructural perturbation of the solvent induced by the solute. First, we support our assessment with rigorous molecular-based foundations to determine, directly and quantitatively, the solute-induced perturbation of the solvent structure leading to an unambiguous definition of a structure making/breaking event. Then, we highlight and discuss the sources of concealed ambiguities in two of the most frequently invoked structure making/breaking criteria, i.e., Hepler’s thermal expansivity-based and Jones–Dole’s

B

coefficient-based markers. Finally, we illustrate how the implementation of rigorous molecular-based arguments, in conjunction with the available experimental evidence on a variety of aqueous species at infinite dilution, rule out the validity of these two criteria as structure making/breaking markers and suggest their discontinuation to avoid the perpetuation of myths. Full article

(This article belongs to the Special Issue Hydration of Ions in Aqueous Solution)

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Review

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21 pages, 6351 KiB

Open AccessReview

Vibrational Raman Spectroscopy of the Hydration Shell of Ions

by Nishith Ghosh, Subhadip Roy, Anisha Bandyopadhyay and Jahur Alam Mondal

Liquids 2023, 3(1), 19-39; https://doi.org/10.3390/liquids3010003 - 27 Dec 2022

Cited by 5 | Viewed by 3550

Abstract

Ionic perturbation of water has important implications in various chemical, biological and environmental processes. Previous studies revealed the structural and dynamical perturbation of water in the presence of ions, mainly with concentrated electrolyte solutions having significant interionic interactions. These investigations highlighted the need [...] Read more.

Ionic perturbation of water has important implications in various chemical, biological and environmental processes. Previous studies revealed the structural and dynamical perturbation of water in the presence of ions, mainly with concentrated electrolyte solutions having significant interionic interactions. These investigations highlighted the need of selective extraction of the hydration shell water from a dilute electrolyte solution that is largely free from interionic interactions. Double-difference infrared (DDIR) and Raman multivariate curve resolution (Raman-MCR), as well as MD simulation, provided valuable insight in this direction, suggesting that the perturbed water mainly resides in the immediate vicinity of the ion, called the hydration shell. Recently, we have introduced Raman difference spectroscopy with simultaneous curve fitting (Raman-DS-SCF) analysis that can quantitatively extract the vibrational response of the perturbed water pertaining to the hydration shell of fully hydrated ions/solute. The DS-SCF analysis revealed novel hydrogen-bond (H-bond) structural features of hydration water, such as the existence of extremely weakly interacting water–OH (ν_max ~ 3600 cm⁻¹) in the hydration shell of high-charge-density metal ions (Mg²⁺, Dy³⁺). In addition, Raman-DS-SCF retrieves the vibrational response of the shared water in the water–shared-ion pair (WSIP), which is different from the hydration shell water of either the interacting cation and anion. Herein, we discuss the perturbation of water H-bonding in the immediate vicinity of cation, anion, zwitterion and hydrophobes and also the inter-ionic interactions, with a focus on the recent results from our laboratory using Raman-DS-SCF spectroscopy. Full article

(This article belongs to the Special Issue Hydration of Ions in Aqueous Solution)

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33 pages, 523 KiB

Open AccessReview

Structures of Hydrated Metal Ions in Solid State and Aqueous Solution

by Ingmar Persson

Liquids 2022, 2(3), 210-242; https://doi.org/10.3390/liquids2030014 - 07 Sep 2022

Cited by 14 | Viewed by 3272

Abstract

This review article summarizes the reported crystallographically determined structures of compounds containing a hydrated metal ion and the reported structures of hydrated metal ions in aqueous solution. A short overview of the methods available to study structures of metal complexes in solution is [...] Read more.

This review article summarizes the reported crystallographically determined structures of compounds containing a hydrated metal ion and the reported structures of hydrated metal ions in aqueous solution. A short overview of the methods available to study structures of metal complexes in solution is given. Full article

(This article belongs to the Special Issue Hydration of Ions in Aqueous Solution)

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