Proton-Coupled Electron Transfer from Tyrosine: A Strong Rate Dependence on Intramolecular Proton Transfer Distance

2011 ◽  
Vol 133 (34) ◽  
pp. 13224-13227 ◽  
Author(s):  
Ming-Tian Zhang ◽  
Tania Irebo ◽  
Olof Johansson ◽  
Leif Hammarström
Keyword(s):  
Electron Transfer ◽  
Proton Transfer ◽  
Intramolecular Proton Transfer ◽  
Rate Dependence ◽  
Transfer Distance ◽  
Proton Coupled Electron Transfer

scholarly journals C–H oxidation in fluorenyl benzoates does not proceed through a stepwise pathway: revisiting asynchronous proton-coupled electron transfer

2021 ◽  
Vol 12 (39) ◽  
pp. 13127-13136
Author(s):  
Scott C. Coste ◽  
Anna C. Brezny ◽  
Brian Koronkiewicz ◽  
James M. Mayer
Keyword(s):  
Electron Transfer ◽  
Proton Transfer ◽  
Intramolecular Proton Transfer ◽  
Proton Coupled Electron Transfer

2-Fluorenyl benzoates were recently shown to undergo C–H bond oxidation through intramolecular proton transfer coupled with electron transfer to an external oxidant.

QM/MM MD simulations reveal an asynchronous PCET mechanism for nitrite reduction by copper nitrite reductase

2020 ◽  
Vol 22 (36) ◽  
pp. 20922-20928
Author(s):  
Ronny Cheng ◽  
Chun Wu ◽  
Zexing Cao ◽  
Binju Wang
Keyword(s):  
Electron Transfer ◽  
Proton Transfer ◽  
Nitrite Reductase ◽  
Md Simulations ◽  
Nitrite Reduction ◽  
Proton Coupled Electron Transfer

The nitrite reduction in copper nitrite reductase is found to proceed through an asynchronous proton-coupled electron transfer (PCET) mechanism, with electron transfer from T1-Cu to T2-Cu preceding the proton transfer from Asp98 to nitrite.

scholarly journals Atomically manipulated proton transfer energizes water oxidation on silicon carbide photoanodes

2018 ◽  
Vol 6 (47) ◽  
pp. 24358-24366 ◽  
Author(s):  
Hao Li ◽  
Huan Shang ◽  
Yuchen Shi ◽  
Rositsa Yakimova ◽  
Mikael Syväjärvi ◽  
...  
Keyword(s):  
Silicon Carbide ◽  
Electron Transfer ◽  
Proton Transfer ◽  
Water Oxidation ◽  
Proton Coupled Electron Transfer ◽  
Rate Limiting Step ◽  
Limiting Step ◽  
Rate Limiting

Preferential exposure of Si-face of SiC will mechanistically shift the rate limiting step of water oxidation from sluggish proton-coupled electron transfer on C-face to a more energy-favorable electron transfer.

scholarly journals Proton-Coupled Electron Transfer in the Reaction of 3,4-Dihydroxyphenylpyruvic Acid with Reactive Species in Various Media

2015 ◽  
Vol 2015 ◽  
pp. 1-13 ◽  
Author(s):  
J. J. Fifen ◽  
Z. Dhaouadi ◽  
M. Nsangou ◽  
O. Holtomo ◽  
N. Jaidane
Keyword(s):  
Electron Transfer ◽  
Proton Transfer ◽  
Activation Barrier ◽  
Bond Cleavage ◽  
Hydrogen Atom Transfer ◽  
Free Energies ◽  
Solvent Interactions ◽  
Proton Coupled Electron Transfer ◽  
Nonpolar Solvents ◽  
One Step

The distinction of concerted proton-coupled electron transfer (CPCET) from sequential one as well as proton transfer-electron transfer (PT-ET) from electron transfer-proton transfer (ET-PT) in the O–H bond cleavage reactions in various media has always been a difficult task. In this work, the activation barrier of the CPCET mechanism, its rate constants, and reaction free energies related to ET-PT and PT-ET involving coreactive species were presented as good parameters to attempt the problem. DFT calculations were carried out studying the described pathways subsequent to the scavenging of OH• and OBr- by the 3,4-DHPPA in various media. The solvation was described in a hybrid manner using IEF-PCM model conjointly with a model that takes into account some solute-solvent interactions. As a result, we found that the scavenging of hydroxyl radical by 3,4-DHPPA is thermodynamically governed by a one-step hydrogen atom transfer (CPCET) from the acid to the radical in all media. In kinetic viewpoint, CPCET still dominates in the vacuum and in nonpolar solvents, but in polar solvents it could compete strongly with the ET-PT mechanism so that the latter could slightly dominate.

scholarly journals Design and synthesis of benzimidazole phenol-porphyrin dyads for the study of bioinspired photoinduced proton-coupled electron transfer

2019 ◽  
Vol 23 (11n12) ◽  
pp. 1336-1345
Author(s):  
S. Jimena Mora ◽  
Daniel A. Heredia ◽  
Emmanuel Odella ◽  
Uma Vrudhula ◽  
Devens Gust ◽  
...  
Keyword(s):  
Electron Transfer ◽  
Excited State ◽  
Photosystem Ii ◽  
Proton Transfer ◽  
Water Oxidation ◽  
Oxidation Catalyst ◽  
Design And Synthesis ◽  
Proton Coupled Electron Transfer ◽  
Anchoring Groups ◽  
High Redox Potential

Benzimidazole phenol-porphyrin dyads have been synthesized to study proton-coupled electron transfer (PCET) reactions induced by photoexcitation. High-potential porphyrins have been chosen to model P680, the photoactive chlorophyll cluster of photosynthetic photosystem II (PSII). They have either two or three pentafluorophenyl groups at the meso positions to impart the high redox potential. The benzimidazole phenol (BIP) moiety models the Tyr[Formula: see text]-His190 pair of PSII, which is a redox mediator that shuttles electrons from the water oxidation catalyst to P680[Formula: see text]. The dyads consisting of a porphyrin and an unsubstituted BIP are designed to study one-electron one-proton transfer (E1PT) processes upon excitation of the porphyrin. When the BIP moiety is substituted with proton-accepting groups such as imines, one-electron two-proton transfer (E2PT) processes are expected to take place upon oxidation of the phenol by the excited state of the porphyrin. The bis-pentafluorophenyl porphyrins linked to BIPs provide platforms for introducing a variety of electron-accepting moieties and/or anchoring groups to attach semiconductor nanoparticles to the macrocycle. The triads thus formed will serve to study the PCET process involving the BIPs when the oxidation of the phenol is achieved by the photochemically produced radical cation of the porphyrin.

scholarly journals Visualizing the protons in a metalloenzyme electron proton transfer pathway

2020 ◽  
Vol 117 (12) ◽  
pp. 6484-6490 ◽  
Author(s):  
Hanna Kwon ◽  
Jaswir Basran ◽  
Juliette M. Devos ◽  
Reynier Suardíaz ◽  
Marc W. van der Kamp ◽  
...  
Keyword(s):  
Crystal Structure ◽  
Electron Transfer ◽  
Hydrogen Bonding ◽  
Proton Transfer ◽  
Proton Donor ◽  
Biological Processes ◽  
Proton Coupled Electron Transfer ◽  
Neutron Structure ◽  
Bona Fide ◽  
Electron Proton Transfer

In redox metalloenzymes, the process of electron transfer often involves the concerted movement of a proton. These processes are referred to as proton-coupled electron transfer, and they underpin a wide variety of biological processes, including respiration, energy conversion, photosynthesis, and metalloenzyme catalysis. The mechanisms of proton delivery are incompletely understood, in part due to an absence of information on exact proton locations and hydrogen bonding structures in a bona fide metalloenzyme proton pathway. Here, we present a 2.1-Å neutron crystal structure of the complex formed between a redox metalloenzyme (ascorbate peroxidase) and its reducing substrate (ascorbate). In the neutron structure of the complex, the protonation states of the electron/proton donor (ascorbate) and all of the residues involved in the electron/proton transfer pathway are directly observed. This information sheds light on possible proton movements during heme-catalyzed oxygen activation, as well as on ascorbate oxidation.

EXCITED-STATE INTRAMOLECULAR ELECTRON TRANSFER COUPLED WITH EXCITED-STATE INTRAMOLECULAR PROTON TRANSFER IN PHOTOINDUCED ENOL TO KETO TAUTOMERIZATION

2009 ◽  
Vol 08 (supp01) ◽  
pp. 1073-1086
Author(s):  
YUANZUO LI ◽  
SHASHA LIU ◽  
LILI ZHAO ◽  
MAODU CHEN ◽  
FENGCAI MA ◽  
...  
Keyword(s):  
Electron Transfer ◽  
Excited State ◽  
Charge Transfer ◽  
Proton Transfer ◽  
Molecular Orbital ◽  
Energy Levels ◽  
Three Dimensional ◽  
Intramolecular Proton Transfer ◽  
Intramolecular Electron Transfer ◽  
Lowest Unoccupied Molecular Orbital

In this paper, the two-dimensional (2D) site and the three-dimensional (3D) cube representations [Sun MT, J Chem Phys124: 054903, 2006] have been further developed to study the charge transfer during excited-state relaxation. With these newly developed representations, we theoretically investigate the excited-state intramolecular electron transfer (ESIET) in enol excited-state geometry relaxation, and ESIET coupled with excited-state intramolecular proton transfer (ESIPT) in phototautomerization (in enol to keto transformation). The energy levels of highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) of HBODC in enol and keto absorption and fluorescence are compared to understand photoinduced ESIET and ESIPT process. The excited regions of molecule (where arrangement of electron density takes place during excited-state relaxation) are located with 2D site representation. 3D cube representations visualize the character of charge transfer (CT) in those regions. Results of the research indicate that the ability of charge transfer during enol excited-state geometry relaxation is much stronger than that in phototautomerization.

Shallow Distance Dependence for Proton-Coupled Tyrosine Oxidation in Oligoproline Peptides

2020 ◽  
Author(s):  
Brian Koronkiewicz ◽  
John R. Swierk ◽  
Kevin P. Regan ◽  
James Mayer
Keyword(s):  
Electron Transfer ◽  
Proton Transfer ◽  
Long Range ◽  
Rate Constants ◽  
High Energy ◽  
Transfer Distance ◽  
Tyrosine Oxidation ◽  
Donor And Acceptor ◽  
Distance Dependence ◽  
Biological Electron Transfer

We have explored the kinetic effect of increasing electron transfer distance in a biomimetic, proton coupled electron transfer system (PCET). Biological electron transfer is often simultaneous with proton transfer in order to avoid the high-energy, charged intermediates resulting from the stepwise transfer of protons and electrons. These concerted proton electron transfer (CPET) reactions are implicated in numerous biological electron transfer pathways. In many cases, proton transfer is coupled to long-range electron transfer. While many studies have shown that the rate of electron transfer is sensitive to the distance between the electron donor and acceptor, extensions to biological CPET reactions are sparse. The possibility of a unique electron transfer distance dependence for CPET reactions deserves further exploration, as this could have implications for how we understand biological electron transfer. We therefore explored the electron transfer distance dependence for the CPET oxidation of tyrosine in a model system. We prepared a series of metallopeptides with a tyrosine separated from a Ru(bpy)<sub>3</sub><sup>2+</sup> complex by an oligoproline bridge of increasing length. Rate constants for intramolecular tyrosine oxidation were measured using the flash-quench transient absorption technique in aqueous solutions. The rate constants for tyrosine oxidation decreased by 125-fold with three added prolines residues between tyrosine and the oxidant. By comparison, related intramolecular ET rate constants in very similar constructs were reported to decrease by 4-5 orders of magnitude over the same number of prolines. The observed shallow distance dependence for tyrosine oxidation is proposed to originate, at least in part, from the requirement for stronger oxidants, leading to a smaller hole transfer tunneling barrier height. The shallow distance dependence observed here and extensions to distance dependent CPET reactions have far-reaching implications for long-range charge transfers

scholarly journals Proton-coupled electron transfer and the role of water molecules in proton pumping by cytochrome c oxidase

2015 ◽  
Vol 112 (7) ◽  
pp. 2040-2045 ◽  
Author(s):  
Vivek Sharma ◽  
Giray Enkavi ◽  
Ilpo Vattulainen ◽  
Tomasz Róg ◽  
Mårten Wikström
Keyword(s):  
Electron Transfer ◽  
Free Energy ◽  
Proton Transfer ◽  
Short Circuit ◽  
Proton Pumping ◽  
Free Energy Calculations ◽  
Water Molecules ◽  
Transfer Event ◽  
Proton Coupled Electron Transfer ◽  
Dynamics Simulations

Molecular oxygen acts as the terminal electron sink in the respiratory chains of aerobic organisms. Cytochrome c oxidase in the inner membrane of mitochondria and the plasma membrane of bacteria catalyzes the reduction of oxygen to water, and couples the free energy of the reaction to proton pumping across the membrane. The proton-pumping activity contributes to the proton electrochemical gradient, which drives the synthesis of ATP. Based on kinetic experiments on the O–O bond splitting transition of the catalytic cycle (A → PR), it has been proposed that the electron transfer to the binuclear iron–copper center of O2 reduction initiates the proton pump mechanism. This key electron transfer event is coupled to an internal proton transfer from a conserved glutamic acid to the proton-loading site of the pump. However, the proton may instead be transferred to the binuclear center to complete the oxygen reduction chemistry, which would constitute a short-circuit. Based on atomistic molecular dynamics simulations of cytochrome c oxidase in an explicit membrane–solvent environment, complemented by related free-energy calculations, we propose that this short-circuit is effectively prevented by a redox-state–dependent organization of water molecules within the protein structure that gates the proton transfer pathway.

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