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Multi PCET in symmetrically substituted benzimidazoles.

Emmanuel Odella¹, Maxim Secor², Mackenna Elliott¹

¹School of Molecular Sciences, Arizona State University Tempe Arizona 85287-1604 USA amoore@asu.edu.

Chemical Science

|October 27, 2021

Summary

Symmetrizing benzimidazole systems with two proton acceptors enables efficient two-proton transfer. This design ensures an uninterrupted hydrogen-bonded network, crucial for proton translocation in bioinspired constructs.

Area of Science:

Supramolecular Chemistry
Bioinorganic Chemistry
Physical Chemistry

Background:

Proton-coupled electron transfer (PCET) is vital in biological systems, exemplified by the TyrZ-His190 pair in Photosystem II.
Benzimidazole (BIP) systems mimic natural PCET sites, facilitating studies of electron oxidation and proton transfer.
Challenges in PCET arise from isomers disrupting intramolecular hydrogen bonds, hindering efficient proton translocation.

Purpose of the Study:

To design and investigate a novel symmetrized benzimidazole system for enhanced two-proton translocation.
To overcome limitations posed by isomeric forms in monosubstituted systems.
To explore the role of hydrogen-bond connectivity in facilitating multiple proton transfers.

Main Methods:

Synthesis of disubstituted benzimidazole systems with identical terminal proton acceptors (TPAs).
Nuclear Magnetic Resonance (NMR) spectroscopy to analyze isomeric forms and hydrogen bonding.
Infrared spectroelectrochemistry to monitor proton transfer events and redox potentials.
Computational studies to elucidate structural and energetic properties.

Main Results:

A strategic symmetrization yielded a disubstituted system with an uninterrupted intramolecular hydrogen-bonded network, irrespective of isomeric form.
NMR confirmed a single isomer in the disubstituted system, unlike the monosubstituted analogue in specific solvents.
Infrared spectroelectrochemistry demonstrated efficient two-proton transfer at a lower redox potential in the disubstituted system.
Computational analysis revealed stabilization of the oxidized state via bifurcated hydrogen bonding.

Conclusions:

Symmetrized benzimidazole constructs with dual TPAs effectively facilitate two-proton transfer by maintaining a robust hydrogen-bonded network.
This design overcomes isomer-induced disruptions, enabling more reliable proton translocation.
The findings provide a foundation for developing advanced, bioinspired nanoscale proton transport systems.

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