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