Hydrogen Bond Switching among Flavin and Amino Acids Determines the Nature of Proton-Coupled Electron Transfer in BLUF Photoreceptors

2012 ◽  
Vol 3 (2) ◽  
pp. 203-208 ◽  
Author(s):  
Tilo Mathes ◽  
Jingyi Zhu ◽  
Ivo H. M. van Stokkum ◽  
M. L. Groot ◽  
Peter Hegemann ◽  
...  
Keyword(s):  
Amino Acids ◽  
Hydrogen Bond ◽  
Electron Transfer ◽  
Proton Coupled Electron Transfer

The water–boryl radical as a proton-coupled electron transfer reagent for carbon dioxide, formic acid, and formaldehyde — Theoretical approach

2013 ◽  
Vol 91 (2) ◽  
pp. 155-168
Author(s):  
Waled Tantawy ◽  
Ahmed Hashem ◽  
Nabil Yousif ◽  
Eman Flefel
Keyword(s):  
Carbon Dioxide ◽  
Hydrogen Bond ◽  
Electron Transfer ◽  
Hydrogen Atom ◽  
Transfer Process ◽  
Carbonyl Compounds ◽  
Hydrogen Atom Transfer ◽  
Transfer Reactions ◽  
Atom Transfer ◽  
Proton Coupled Electron Transfer

The thermochemistry of the hydrogen atom transfer reactions from the H2O–BX2 radical system (X = H, CH3, NH2, OH, F) to carbon dioxide, formic acid, and (or) formaldehyde, which produce hydroxyformyl, dihydroxymethyl, and hydroxymethyl radicals, respectively, were investigated theoretically at ROMP2/6–311+G(3DF,2P)//UB3LYP/6–31G(D) and UG3(MP2)-RAD levels of theory. Surprisingly, in the cases of a strong Lewis acid (X = H, CH3, F), the spin transfer process from the water–boryl radical to the carbonyl compounds was barrier-free and associated with a dramatic reduction in the B–H bond dissociation energy (BDE) relative to that of isolated water–borane complexes. Examining the coordinates of these reactions revealed that the entire hydrogen atom transfer process is governed by the proton-coupled electron transfer (PCET) mechanism. Hence, the elucidated mechanism has been applied in the cases of weak Lewis acids (X = NH2, OH), and the variation in the accompanied activation energy was attributed to the stereoelectronic effect interplaying in CO2 and HCOOH compared with HCHO. We ascribed the overall mechanism as a SA-induced five-center cyclic PCET, in which the proton transfers across the so-called complexation-induced hydrogen bond (CIHB) channel, while the SOMOB–LUMOC=O′ interaction is responsible for the electron migration process. Owing to previous reports that interrelate the hydrogen-bonding and the rate of proton-coupled electron-transfer reactions, we postulated that “the rate of the PCET reaction is expected to be promoted by the covalency of the hydrogen bond, and any factor that enhances this covalency could be considered an activator of the PCET process.” This postulate could be considered a good rationale for the lack of a barrier associated with the hydrogen atom transfer from the water-boryl radical system to the carbonyl compounds. Light has been shed on the water–boryl radical reagent from the thermodynamic perspective.

Electron transfer vs. proton-coupled electron transfer as the mechanism of reaction between amino acids and triplet-excited benzophenones revealed by time-resolved CIDNP

2018 ◽  
Vol 20 (32) ◽  
pp. 21127-21135 ◽  
Author(s):  
Olga B. Morozova ◽  
Mikhail S. Panov ◽  
Natalya N. Fishman ◽  
Alexandra V. Yurkovskaya
Keyword(s):  
Amino Acids ◽  
Electron Transfer ◽  
Reaction Mechanism ◽  
Hyperfine Coupling ◽  
Coupling Constants ◽  
Hyperfine Coupling Constants ◽  
Time Resolved ◽  
Proton Coupled Electron Transfer ◽  
Mechanism Of Reaction

We use proportionality between NMR signal enhancements in geminate products and hyperfine coupling constants in transient radicals to elucidate reaction mechanism in detail.

scholarly journals Hydrogen bond assisted photoinduced intramolecular electron transfer and proton coupled electron transfer in an ultrafast time domain using a ruthenium-anthraquinone dyad

2019 ◽  
Vol 18 (10) ◽  
pp. 2430-2441 ◽  
Author(s):  
Ananta Dey ◽  
Jayanta Dana ◽  
Sunil Aute ◽  
Amitava Das ◽  
Hirendra N. Ghosh
Keyword(s):  
Hydrogen Bond ◽  
Electron Transfer ◽  
Hydrogen Bonding ◽  
Time Domain ◽  
Transient Absorption ◽  
Transient Absorption Spectroscopy ◽  
Intramolecular Electron Transfer ◽  
Proton Coupled Electron Transfer ◽  
Femtosecond Transient Absorption ◽  
Femtosecond Transient Absorption Spectroscopy

PCET kinetics for the formation of charge-separated states was explored by using femtosecond transient absorption spectroscopy. Hydrogen bonding between water and the reduced anthraquinone accounted for thermodynamic and kinetic stabilization.

scholarly journals Multi PCET in Symmetrically Substituted Benzimidazoles

2021 ◽  
Author(s):  
Emmanuel Odella ◽  
Maxim Secor ◽  
Mackenna Elliot ◽  
Thomas L Groy ◽  
Thomas A. Moore ◽  
...  
Keyword(s):  
Hydrogen Bond ◽  
Electron Transfer ◽  
Proton Coupled Electron Transfer ◽  
Proton Donors

Proton-coupled electron transfer (PCET) reactions depend on the hydrogen-bond connectivity between sites of proton donors and acceptors. The 2-(2’-hydroxyphenyl) benzimidazole (BIP) based systems, which mimic the natural TyrZ-His190 pair of...

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