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Issue 26, 2018
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Interplay of proton and electron transfer to determine concerted behavior in the proton-coupled electron transfer of glutathione oxidation

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Abstract

Glutathione (GSH), whose thiol group dictates its redox chemistry, is oxidized to the thiyl radical (GS˙), which rapidly dimerizes to GSSG. Previously, we found that the oxidation rate of GSH by IrCl62− depends on the base (B) concentration and the pKa of its conjugate acid BH+, so that collateral to a stepwise mechanism, the concerted pathway GSH + IrCl62− + B = GS˙ + IrCl63− + BH+ was proposed as the rate determining step. Herein, this investigation is extended to include oxidant-base pairs that render exothermic and endothermic conditions of ΔG°′ for electron transfer (ET) and proton transfer (PT). Experiments were conducted by the reaction of GSH with an electrogenerated oxidant M+ and using digital simulations to infer the mechanism. Data analysis shows that despite parallel mechanisms, the concerted one seems to predominate for the oxidant-base pair that renders the most isoenergetic coupled state, whereby a PT with Image ID:c8cp01415a-t1.gif is capable of producing an ET with Image ID:c8cp01415a-t2.gif, as a result of the Nernstian shift of Image ID:c8cp01415a-t3.gif with pKa. In contrast, the stepwise PT–ET appears to dominate when GS grows in stability as Image ID:c8cp01415a-t4.gif becomes more negative. Understanding the interplay between ET and PT will help in the design of catalysts for energy harvesting processes that rely on proton-coupled electron transfer.

Graphical abstract: Interplay of proton and electron transfer to determine concerted behavior in the proton-coupled electron transfer of glutathione oxidation

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Supplementary files

Article information


Submitted
03 Mar 2018
Accepted
13 Jun 2018
First published
13 Jun 2018

Phys. Chem. Chem. Phys., 2018,20, 17666-17675
Article type
Paper

Interplay of proton and electron transfer to determine concerted behavior in the proton-coupled electron transfer of glutathione oxidation

K. Meng, J. Medina-Ramos, E. Yibeltal-Ashenafi and J. C. Alvarez, Phys. Chem. Chem. Phys., 2018, 20, 17666
DOI: 10.1039/C8CP01415A

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