Ultrafast Proton Transfer Pathways Mediated by Amphoteric Imidazole

Area of Science:

• Chemical Dynamics
• Physical Chemistry
• Spectroscopy

Background:

• Imidazole is an amphoteric molecule, acting as both an acid and a base.
• This property is crucial for proton transport in high-temperature fuel cells and biological proton channels.
• Understanding imidazole's acid-base reactivity is key to optimizing these systems.

Purpose of the Study:

• To investigate the proton transfer dynamics of imidazole.
• To explore the amphoteric properties of imidazole using a bifunctional photoacid, 7-hydroxyquinoline (7HQ).
• To elucidate the reaction pathway and kinetics of proton exchange involving imidazole.

Main Methods:

• Ultrafast ultraviolet-mid-infrared pump-probe spectroscopy.
• Analysis of molecular distribution functions.
• First-principles calculations of proton transfer reaction barriers.

Main Results:

• Observed an initial proton transfer from 7HQ to imidazole, contrary to typical acid-base expectations.
• Identified a subsequent proton transfer from imidazole back to 7HQ, completing the tautomerization.
• Determined the underlying reasons for this preferential reaction pathway through computational analysis.

Conclusions:

• Imidazole's proton transfer dynamics are complex and deviate from simple acid-base theory.
• The observed reaction pathway highlights a unique mechanism for proton exchange involving imidazole.
• This research provides fundamental insights into imidazole's role in proton transport processes.