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Water-Mediated Ion Pairing: Occurrence and Relevance
Nico F A van der Vegt1, Kristoffer Haldrup2, Sylvie Roke3
1Eduard-Zintl-Institut für Anorganische und Physikalische Chemie and Center of Smart Interfaces, Technische Universität Darmstadt , Alarich-Weiss-Strasse 10, 64287 Darmstadt, Germany.
Chemical Reviews
|May 7, 2016
Summary
Ion pairing is common in aqueous solutions, not rare. Advanced spectroscopy and simulations reveal contact, solvent-shared, and solvent-separated ion pairs, crucial for biomolecular systems.
Area of Science:
- Physical Chemistry
- Solution Chemistry
- Biophysical Chemistry
Background:
- Ion pairing in aqueous media is fundamental to understanding electrolyte behavior.
- Previous studies often considered ion pairing a rare phenomenon.
- The role of specific ion-water and ion-ion interactions requires advanced investigation.
Purpose of the Study:
- To provide a comprehensive overview of ion pairing studies in aqueous media over the last decade.
- To highlight novel methodologies for investigating ion interactions.
- To elucidate the prevalence and types of ion pairs in various salt solutions.
Main Methods:
- Utilized advanced spectroscopic techniques: dielectric relaxation, far-infrared (terahertz) absorption, femtosecond mid-infrared, and X-ray spectroscopy/scattering.
- Employed molecular dynamics (MD) simulation methods for theoretical insights.
- Integrated experimental and computational approaches to study ion-ion and ion-water interactions.
Main Results:
- Ion pairing is a prevalent phenomenon, not limited to strongly interacting ions.
- Distinct concentrations of contact ion pairs (CIPs), solvent-shared ion pairs (SIPs), and solvent-separated ion pairs (2SIPs) were identified.
- Evidence for ion pairing was found in bulk salt solutions and at interfaces.
Conclusions:
- Ion pairing is a widespread characteristic of aqueous salt solutions.
- Specific ion-pairing interactions, such as Li+/Na+ with carboxylates/phosphates, are vital for macromolecular structure and function.
- The findings necessitate a re-evaluation of ion-pairing's significance in biological and chemical systems.
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