Rapid Hydrogen-Deuterium Exchange in Liquid Droplets

Area of Science:

• Analytical Chemistry
• Physical Chemistry
• Biophysical Chemistry

Background:

• Hydrogen-deuterium exchange (HDX) is a crucial technique for studying molecular dynamics and structure.
• Traditional methods like stopped-flow kinetics and NMR spectroscopy have limitations in temporal resolution for rapid exchange processes.
• Investigating HDX in microdroplets offers a novel approach to probe fast chemical reactions with high temporal resolution.

Purpose of the Study:

• To determine the rate of hydrogen-deuterium exchange (HDX) in aqueous droplets of phenethylamine with submillisecond temporal resolution.
• To investigate the influence of droplet confinement and microenvironment on HDX rates.
• To compare HDX rates in droplets with those measured in bulk solution.

Main Methods:

• Utilized nanoelectrospray ionization with a theta-capillary for generating aqueous droplets.
• Employed mass spectrometry for submillisecond temporal resolution of HDX.
• Measured microdroplet speed using microparticle image velocimetry.
• Modeled HDX kinetics using a system of ordinary differential equations.

Main Results:

• Observed accelerated HDX rates in aqueous droplets compared to bulk measurements.
• Determined rate constants for phenethylamine HDX: 3660 ± 290 s⁻¹ for -NH₂D⁺ formation and 3330 ± 270 s⁻¹ for -NHD₂⁺ formation.
• Found a 7-fold acceleration of HDX for angiotensin I in droplets versus bulk solution.
• Demonstrated droplet acceleration of approximately 30% during travel time.

Conclusions:

• HDX occurs significantly faster in aqueous droplets than in bulk solution, suggesting confinement effects influence reaction rates.
• The theta-capillary method enables rapid mixing and high-throughput analysis of fast exchange processes.
• This technique provides a powerful tool for studying molecular dynamics and kinetics with unprecedented temporal resolution.