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New class of 19F pH indicators: fluoroanilines
1Department of Physiology, University of Pennsylvania, Philadelphia 19104.
Biophysical Journal
|April 1, 1989
Summary
New fluorine-substituted aniline derivatives serve as effective 19F nuclear magnetic resonance (NMR) pH indicators. One compound shows slow proton exchange, enabling precise pH monitoring near physiological conditions.
Area of Science:
- Analytical Chemistry
- Organic Chemistry
- Physical Chemistry
Background:
- Fluorine-substituted aniline derivatives offer potential as pH indicators.
- 19F NMR spectroscopy provides a sensitive method for chemical shift analysis.
Purpose of the Study:
- To characterize the pH dependence of 19F chemical shifts in novel fluorine-substituted aniline derivatives.
- To evaluate these compounds as 19F NMR pH indicators.
- To investigate the factors influencing the performance of these indicators.
Main Methods:
- Synthesis of fluorine-substituted aniline derivatives.
- 19F NMR spectroscopy to measure chemical shifts across a range of pH values.
- Analysis of chemical shift dependence on pH to determine pKa and sensitivity.
Main Results:
- A new class of 19F NMR pH indicators was identified with sensitivities of 2-7 ppm/pH unit.
- Compounds exhibited total shifts of 5-15 ppm and pKa values from 1 to 7.
- N,N-(methyl-2-carboxyisopropyl)-4-fluoroaniline demonstrated a pKa of 6.8 and sensitivity of 5 ppm/pH unit.
- This specific compound showed significant 19F resonance broadening near its pKa, indicating slow proton exchange.
Conclusions:
- Fluorine-substituted anilines are viable 19F NMR pH indicators.
- The observed slow exchange in N,N-(methyl-2-carboxyisopropyl)-4-fluoroaniline is attributed to intramolecular hydrogen bond dissociation.
- This characteristic allows for precise pH measurements near neutral conditions.