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Hydrophilic Versus Hydrophobic Coupling in the Pressure Dependence of the Chemical Potential of Alkali Metal and Halide Ions in Water

[Image: see text] We computed the chemical potential for some alkali metal ions (K(+), Rb(+), and Cs(+)) and two halide ions (Br(–) and I(–)) in aqueous solution at ambient T and various pressures in the range 1–8000 atm. Results were obtained from classic Monte Carlo simulations in the NPT ensemble...

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Autores principales: Tonti, Luca, Floris, Franca Maria
Formato: Online Artículo Texto
Lenguaje:English
Publicado: American Chemical Society 2022
Acceso en línea:https://www.ncbi.nlm.nih.gov/pmc/articles/PMC9677433/
https://www.ncbi.nlm.nih.gov/pubmed/36326490
http://dx.doi.org/10.1021/acs.jpcb.2c02373
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author Tonti, Luca
Floris, Franca Maria
author_facet Tonti, Luca
Floris, Franca Maria
author_sort Tonti, Luca
collection PubMed
description [Image: see text] We computed the chemical potential for some alkali metal ions (K(+), Rb(+), and Cs(+)) and two halide ions (Br(–) and I(–)) in aqueous solution at ambient T and various pressures in the range 1–8000 atm. Results were obtained from classic Monte Carlo simulations in the NPT ensemble by means of the free energy perturbation method. Here, the chemical potential is computed as the sum of a term relative to a Lennard-Jones solute and a term relative to the process in which this solute is transformed into the ion. Hydrophobic and hydrophilic features of these two components of the chemical potential show opposite behaviors under isothermal compression. The increase in pressure determines an increase in the hydrophobic component, which becomes more positive with a stronger effect for larger ions. Correspondingly, the values of the hydrophilic component become more negative for alkali ions, whereas they are only slightly affected by compression for halide ions. Hydrophobic–hydrophilic quasi-compensation in the slopes is observed for Rb(+). For a smaller ion, such as K(+), the dependence on pressure of the hydrophilic component is slightly dominant. For a larger ion, as observed in the cases of Cs(+), Br(–), and I(–), the hydrophobic component assumes the determinant role. Pressure dependence of the chemical potential is little affected by corrections introduced for molecular potential truncation. This view can change for possible boundary artifacts that could have affected the static electrostatic potential. Some inference is obtained from comparison with experimental data at 1 atm on the free energy of hydration. Discrepancies show the characteristic asymmetry between cations and anions. The further addition of a correction based on the static potential significantly reduces these discrepancies with important error cancellation on the sum of chemical potentials of ions of opposite charge. The correction is applied also at higher pressures, and results are compared with those obtained by adding an alternative correction that is based on the water number density. Regardless of the ion, changes of the chemical potential induced by an increase in pressure appear to be dominated by the hydrophobic component, in particular when using the alternative correction. For bromide and iodide electrolytes, the two corrections give chemical potentials in good agreement.
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spelling pubmed-96774332022-11-22 Hydrophilic Versus Hydrophobic Coupling in the Pressure Dependence of the Chemical Potential of Alkali Metal and Halide Ions in Water Tonti, Luca Floris, Franca Maria J Phys Chem B [Image: see text] We computed the chemical potential for some alkali metal ions (K(+), Rb(+), and Cs(+)) and two halide ions (Br(–) and I(–)) in aqueous solution at ambient T and various pressures in the range 1–8000 atm. Results were obtained from classic Monte Carlo simulations in the NPT ensemble by means of the free energy perturbation method. Here, the chemical potential is computed as the sum of a term relative to a Lennard-Jones solute and a term relative to the process in which this solute is transformed into the ion. Hydrophobic and hydrophilic features of these two components of the chemical potential show opposite behaviors under isothermal compression. The increase in pressure determines an increase in the hydrophobic component, which becomes more positive with a stronger effect for larger ions. Correspondingly, the values of the hydrophilic component become more negative for alkali ions, whereas they are only slightly affected by compression for halide ions. Hydrophobic–hydrophilic quasi-compensation in the slopes is observed for Rb(+). For a smaller ion, such as K(+), the dependence on pressure of the hydrophilic component is slightly dominant. For a larger ion, as observed in the cases of Cs(+), Br(–), and I(–), the hydrophobic component assumes the determinant role. Pressure dependence of the chemical potential is little affected by corrections introduced for molecular potential truncation. This view can change for possible boundary artifacts that could have affected the static electrostatic potential. Some inference is obtained from comparison with experimental data at 1 atm on the free energy of hydration. Discrepancies show the characteristic asymmetry between cations and anions. The further addition of a correction based on the static potential significantly reduces these discrepancies with important error cancellation on the sum of chemical potentials of ions of opposite charge. The correction is applied also at higher pressures, and results are compared with those obtained by adding an alternative correction that is based on the water number density. Regardless of the ion, changes of the chemical potential induced by an increase in pressure appear to be dominated by the hydrophobic component, in particular when using the alternative correction. For bromide and iodide electrolytes, the two corrections give chemical potentials in good agreement. American Chemical Society 2022-11-03 2022-11-17 /pmc/articles/PMC9677433/ /pubmed/36326490 http://dx.doi.org/10.1021/acs.jpcb.2c02373 Text en © 2022 The Authors. Published by American Chemical Society https://creativecommons.org/licenses/by/4.0/Permits the broadest form of re-use including for commercial purposes, provided that author attribution and integrity are maintained (https://creativecommons.org/licenses/by/4.0/).
spellingShingle Tonti, Luca
Floris, Franca Maria
Hydrophilic Versus Hydrophobic Coupling in the Pressure Dependence of the Chemical Potential of Alkali Metal and Halide Ions in Water
title Hydrophilic Versus Hydrophobic Coupling in the Pressure Dependence of the Chemical Potential of Alkali Metal and Halide Ions in Water
title_full Hydrophilic Versus Hydrophobic Coupling in the Pressure Dependence of the Chemical Potential of Alkali Metal and Halide Ions in Water
title_fullStr Hydrophilic Versus Hydrophobic Coupling in the Pressure Dependence of the Chemical Potential of Alkali Metal and Halide Ions in Water
title_full_unstemmed Hydrophilic Versus Hydrophobic Coupling in the Pressure Dependence of the Chemical Potential of Alkali Metal and Halide Ions in Water
title_short Hydrophilic Versus Hydrophobic Coupling in the Pressure Dependence of the Chemical Potential of Alkali Metal and Halide Ions in Water
title_sort hydrophilic versus hydrophobic coupling in the pressure dependence of the chemical potential of alkali metal and halide ions in water
url https://www.ncbi.nlm.nih.gov/pmc/articles/PMC9677433/
https://www.ncbi.nlm.nih.gov/pubmed/36326490
http://dx.doi.org/10.1021/acs.jpcb.2c02373
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