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Related Concept Videos

Intermolecular Forces03:13

Intermolecular Forces

Atoms and molecules interact through bonds (or forces): intramolecular and intermolecular. The forces are electrostatic as they arise from interactions (attractive or repulsive) between charged species (permanent, partial, or temporary charges) and exist with varying strengths between ions, polar, nonpolar, and neutral molecules. The different types of intermolecular forces are ion–dipole, dipole–dipole, hydrogen bonds, and dispersion; among these, dipole–dipole, hydrogen bonds, and dispersion...
Intermolecular Forces03:13

Intermolecular Forces

Atoms and molecules interact through bonds (or forces): intramolecular and intermolecular. The forces are electrostatic as they arise from interactions (attractive or repulsive) between charged species (permanent, partial, or temporary charges) and exist with varying strengths between ions, polar, nonpolar, and neutral molecules. The different types of intermolecular forces are ion–dipole, dipole–dipole, hydrogen bonds, and dispersion; among these, dipole–dipole, hydrogen bonds, and dispersion...
Aqueous Solutions and Heats of Hydration02:42

Aqueous Solutions and Heats of Hydration

Water and other polar molecules are attracted to ions. The electrostatic attraction between an ion and a molecule with a dipole is called an ion-dipole attraction. These attractions play an important role in the dissolution of ionic compounds in water.
When ionic compounds dissolve in water, the ions in the solid separate and disperse uniformly throughout the solution because water molecules surround and solvate the ions, reducing the strong electrostatic forces between them. This process...
Ionic Association01:28

Ionic Association

The ionic association is the association of oppositely charged ions in an electrolyte solution to form ion pairs. Bjerrum defined ion pairs as two oppositely charged ions whose electrostatic attraction exceeds the thermal energy of the system, typically expressed as 2kT. Electrostatic attraction depends on ionic charge, separation distance, and the dielectric constant of the medium. Thermal energy, represented by kT, reflects the tendency of ions to move independently due to molecular motion.
Theory of Strong Electrolytes01:23

Theory of Strong Electrolytes

The interionic forces of the strong electrolytes depend on the solvent's dielectric constant, which is the ability of a solvent to store electrical energy, based on its polarizability. and the solution's concentration. In high-dielectric solvents and in dilute solutions, weak electrostatic forces keep ions apart. However, in low-dielectric solvents or concentrated solutions, stronger interionic forces may cause ions to pair up as ionic doublets despite being fully ionized. The theory of strong...
Ions as Acids and Bases02:54

Ions as Acids and Bases

Salts with Acidic Ions
Salts are ionic compounds composed of cations and anions, either of which may be capable of undergoing an acid or base ionization reaction with water. Aqueous salt solutions, therefore, may be acidic, basic, or neutral, depending on the relative acid-base strengths of the salt’s constituent ions. For example, dissolving the ammonium chloride in water results in its dissociation, as described by the equation:

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Vibrational Spectra of a N719-Chromophore/Titania Interface from Empirical-Potential Molecular-Dynamics Simulation, Solvated by a Room Temperature Ionic Liquid
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Vibrational Spectra of a N719-Chromophore/Titania Interface from Empirical-Potential Molecular-Dynamics Simulation, Solvated by a Room Temperature Ionic Liquid

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Length scales and interfacial potentials in ion hydration.

Yu Shi1, Thomas L Beck

  • 1Department of Physics, University of Cincinnati, Cincinnati, Ohio 45221, USA.

The Journal of Chemical Physics
|August 2, 2013
PubMed
Summary

The Quasichemical Theory (QCT) reveals a universal 6.15 Å length scale for ion hydration free energy in alkali halides. This length scale unifies inner-shell and outer-shell contributions, simplifying solvation thermodynamics.

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Analyzing Protein Architectures and Protein-Ligand Complexes by Integrative Structural Mass Spectrometry
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Analyzing Protein Architectures and Protein-Ligand Complexes by Integrative Structural Mass Spectrometry

Published on: October 15, 2018

Area of Science:

  • Physical Chemistry
  • Computational Chemistry
  • Thermodynamics

Background:

  • The Quasichemical Theory (QCT) organizes solvation thermodynamics by length scales.
  • QCT has been applied to solutes from small molecules to proteins.
  • QCT decomposes free energy into inner-shell chemical, outer-shell packing, and outer-shell long-ranged terms.

Purpose of the Study:

  • To compute ion hydration free energy contributions using a regularized QCT and classical simulations.
  • To investigate these contributions for alkali halide ions at large cavity radii.
  • To assess approximations for the long-ranged term in QCT.

Main Methods:

  • Utilized a regularizing generalization of the Quasichemical Theory (QCT).
  • Employed classical simulations to compute solvation free energy contributions.
  • Examined eight ions from the alkali halide series.

Main Results:

  • Inner-shell contribution shows ion specificity below 4-5 Å.
  • A common length scale of 6.15 Å was identified where inner-shell contribution equals bulk hydration free energy for all ions.
  • The 6.15 Å scale relates to scaled-particle theory packing and Born estimates.

Conclusions:

  • The study identifies a universal length scale in ion hydration thermodynamics.
  • QCT provides a framework for understanding ion-specific and general solvation effects.
  • Approximations for long-ranged terms can be evaluated within this framework.