Hydration and ion association of aqueous choline chloride and chlorocholine chloride

  • Phys Chem Chem Phys. 2019 Jun 7;21(21):10970-10980. doi: 10.1039/c9cp01016e.
Saadia Shaukat  1 ,  Marina V Fedotova  2 ,  Sergey E Kruchinin  2 ,  Marija Bešter-Rogač  3 ,  Črtomir Podlipnik  3 ,  Richard Buchner  1
Affiliations
  • 1. Institute of Physical and Theoretical Chemistry, University of Regensburg, 93040 Regensburg, Germany. [email protected].
  • 2. G.A. Krestov Institute of Solution Chemistry, Russian Academy of Sciences, Akademicheskaya st. 1, 153045 Ivanovo, Russian Federation. [email protected].
  • 3. Faculty of Chemistry and Chemical Technology, Večna pot 113, University of Ljubljana, SI-1000 Ljubljana, Slovenia. [email protected].
PMID: 31107469 DOI: 10.1039/c9cp01016e
Abstract

The choline ion (Ch+) is ubiquitous in nature and also its synthetic homologue, chlorocholine (ClCh+), is widely used. Nevertheless, surprisingly little information on the hydration and counter-ion binding of these cations can be found in the literature. In this contribution we report effective hydration numbers, determined by dielectric relaxation spectroscopy, and ion-pair association constants with Cl-, determined by dilute-solution conductivity measurements. In combination with RISM calculations the obtained data suggest that for Ch+ water is bound to the hydroxy group via hydrogen bonds whereas for ClCh+ a rather stiff clathrate-like shell around the chlorine atom seems to be formed. With Cl- both cations form contact ion pairs with association constants of only ∼2 to 3 M-1.

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