Title

NMR pH Measurements using the 19F Chemical Shift of 2-Fluoro-3-hydroxymethylpyridine

Presenter Information

Kaysi Lee

Department

Chemistry

Research Advisor

Huang, Ming
Woelk, Klaus

Advisor's Department

Chemistry

Abstract

NMR chemical-shift information has long been used to determine the pH of aqueous solutions. Test molecules that qualify for conducting pH measurements must be sensitive to the solution’s H+ concentration and simultaneously change the electronic environment around the NMRsensitive nuclei. Especially 19F NMR has shown great potential because of the high NMR sensitivity of the 19F nucleus, the wide chemical-shift range, and the large chemical-shift response to the solution’s environment. Protonation of fluorinated molecules in acidic solutions or deprotonation in basic solution can alter the 19F chemical shift far enough to accurately determine the pH from prerecorded calibration curves. Around the pKa, fluoropyridines show a particularly large 19F chemical-shift dependence on pH. However, because fluoropyridines are generally insoluble in aqueous solutions, only the water-soluble fluoro-hydroxypyridines or fluorohydroxymethylpyridines are suitable candidates for chemical-shiftdependent pH test molecules. For the molecule 2-fluoro-3- hydroxymethylpyridine we have measured a substantial 19F chemical-shift dependence on pH.

Research Category

Sciences

Presentation Type

Poster Presentation

Document Type

Poster

Location

Upper Atrium

Presentation Date

17 Apr 2018, 9:00 am - 12:00 pm

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Apr 17th, 9:00 AM Apr 17th, 12:00 PM

NMR pH Measurements using the 19F Chemical Shift of 2-Fluoro-3-hydroxymethylpyridine

Upper Atrium

NMR chemical-shift information has long been used to determine the pH of aqueous solutions. Test molecules that qualify for conducting pH measurements must be sensitive to the solution’s H+ concentration and simultaneously change the electronic environment around the NMRsensitive nuclei. Especially 19F NMR has shown great potential because of the high NMR sensitivity of the 19F nucleus, the wide chemical-shift range, and the large chemical-shift response to the solution’s environment. Protonation of fluorinated molecules in acidic solutions or deprotonation in basic solution can alter the 19F chemical shift far enough to accurately determine the pH from prerecorded calibration curves. Around the pKa, fluoropyridines show a particularly large 19F chemical-shift dependence on pH. However, because fluoropyridines are generally insoluble in aqueous solutions, only the water-soluble fluoro-hydroxypyridines or fluorohydroxymethylpyridines are suitable candidates for chemical-shiftdependent pH test molecules. For the molecule 2-fluoro-3- hydroxymethylpyridine we have measured a substantial 19F chemical-shift dependence on pH.