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Ion pairing in ethanol/water solution probed by electrophoretic and diffusion NMR.
Fredrik Hallberg1, István Furó, Peter Stilbs
1Division of Physical Chemistry and Industrial NMR Centre, Department of Chemistry, Royal Institute of Technology, SE-10044 Stockholm, Sweden.
Journal of the American Chemical Society
|September 11, 2009
Summary
We developed a new method using NMR spectroscopy to quantify ion pairing in solutions. This technique reveals a Hofmeister effect on ion pairing, with divalent ions showing stronger pairing than monovalent ones.
Area of Science:
- Physical Chemistry
- Solution Chemistry
- Spectroscopy
Background:
- Ion pairing is crucial in understanding solution behavior.
- Quantifying ion pairing is challenging.
- The Hofmeister effect describes how ions influence protein solubility and other properties.
Purpose of the Study:
- To develop a quantitative method for measuring average ion charge in solution.
- To use this method to assess ion pairing.
- To investigate the Hofmeister effect on ion pairing.
Main Methods:
- Combined electrophoretic Nuclear Magnetic Resonance (NMR) and diffusion NMR experiments.
- Measured average charge carried by ions in solution.
- Analyzed ion pairing in 95% ethanol/water solutions.
Main Results:
- Successfully measured average ion charge to indicate ion pairing.
- Observed a Hofmeister relation in ion pairing between monovalent anions and tetramethylammonium cation.
- Found that divalent sulfate ion exhibited stronger ion pairing than monovalent anions.
Conclusions:
- Electrophoretic and diffusion NMR provide a quantitative measure of ion pairing.
- Ion pairing in ethanol/water solutions follows a Hofmeister trend.
- Divalent anions form stronger ion pairs than monovalent anions with tetramethylammonium cation.
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