A Stopped-Flow Instrument for Millisecond Timescale Reaction Monitoring on a Standard NMR Spectrometer

Area of Science:

• Analytical Chemistry
• Physical Chemistry
• Spectroscopy

Background:

• Standard NMR spectrometers are limited in analyzing fast chemical reactions.
• Rapid kinetic measurements are crucial for understanding reaction mechanisms.
• Existing stopped-flow techniques may not be compatible with standard NMR setups.

Purpose of the Study:

• To develop and characterize a novel stopped-flow instrument for rapid reaction initiation and analysis.
• To enable kinetic measurements of reactions with millisecond half-lives using standard NMR spectrometers.
• To provide a versatile tool for studying fast chemical kinetics without spectrometer modification.

Main Methods:

• Design and construction of a new stopped-flow instrument integrated with standard NMR spectrometers.
• Utilizing high-speed video, pressure, and NMR line-shape data for instrument characterization.
• Employing simulations to address dead time effects on observed rate constants.
• Demonstrating capabilities with base-mediated hydrolysis of methyl formate (¹H) and pentafluorophenyl boronic acid (¹⁹F).

Main Results:

• The instrument successfully performs kinetic measurements on reactions with half-lives as short as 5 milliseconds.
• Reproducible NMR data from fast reactions were generated, validating the instrument's performance.
• Reactant equilibration and efficient mixing ensure near-quantitative results.
• The system requires no permanent modifications to existing NMR spectrometers.

Conclusions:

• The developed stopped-flow instrument is effective for analyzing rapid reactions using standard NMR.
• It offers a valuable method for obtaining kinetic data from fast chemical processes with high reproducibility.
• The design facilitates integration with existing NMR setups, broadening accessibility for kinetic studies.