NMR characterization of H₂O₂ hydrogen exchange

Area of Science:

• Analytical Chemistry
• Biochemistry
• Spectroscopy

Background:

• Accurate quantification of hydrogen peroxide (H2O2) is crucial across various scientific disciplines.
• Traditional indirect methods using fluorescent probes are limited by incomplete reactions and interfering substances.
• There is a need for a direct, sensitive, and reliable method for H2O2 measurement.

Purpose of the Study:

• To develop and optimize Nuclear Magnetic Resonance (NMR) detection for direct H2O2 quantification.
• To achieve sensitive H2O2 detection in the nanomolar range.
• To investigate the influence of pH and buffer catalysis on hydrogen exchange rates for optimal measurement conditions.

Main Methods:

• Optimization of NMR detection parameters for direct H2O2 quantification.
• Utilizing fast hydrogen exchange (HX) between H2O2 and water to enable short interscan delays and enhance sensitivity.
• Measurement of specific acid-, base-, and water-catalyzed HX rates at 2°C under varying pH conditions.
• Evaluation of buffer (MES, phosphate, imidazole, acetic acid) and salt (NaCl, azide) effects on HX rates.

Main Results:

• Direct quantification of H2O2 down to the nanomolar range (as low as 40 nM) is achieved using optimized NMR.
• Fast hydrogen exchange (HX) significantly increases sensitivity, allowing for rapid measurements.
• Minimum HX rate observed at pH 6.2, with accelerated exchange influenced by general acid/base catalysis.
• Specific buffer types and forms (protonated/unprotonated) exhibit varying catalytic effects on HX rates, while inorganic salts show negligible impact.

Conclusions:

• Optimized NMR detection provides a direct and highly sensitive method for quantifying H2O2 in aqueous solutions.
• Understanding and controlling hydrogen exchange kinetics is key to achieving nanomolar sensitivity.
• The developed method offers an improvement over indirect fluorescent probe assays, providing accurate H2O2 measurements in complex samples within hours.