51
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Antioxidant Properties of Kanakugiol Revealed Through the Hydrogen Atom Transfer, Electron Transfer and M2+ (M2+ = Cu(II) or Co(II) Ion) Coordination Ability Mechanisms. A DFT Study In Vacuo and in Solution. FOOD BIOPHYS 2015. [DOI: 10.1007/s11483-015-9397-0] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
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52
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Abstract
An enormous variety of biological redox reactions are accompanied by changes in proton content at enzyme active sites, in their associated cofactors, in substrates and/or products, and between protein interfaces. Understanding this breadth of reactivity is an ongoing chemical challenge. A great many workers have developed and investigated biomimetic model complexes to build new ways of thinking about the mechanistic underpinnings of such complex biological proton-coupled electron transfer (PCET) reactions. Of particular importance are those model reactions that involve transfer of one proton (H(+)) and one electron (e(-)), which is equivalent to transfer of a hydrogen atom (H(•)). In this Current Topic, we review key concepts in PCET reactivity and describe important advances in biomimetic PCET chemistry, with a special emphasis on research that has enhanced efforts to understand biological PCET reactions.
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Affiliation(s)
- Jeffrey J. Warren
- Simon Fraser University, Department of Chemistry, 8888 University Drive, Burnaby BC, Canada V5A 1S6
| | - James M. Mayer
- Yale University, Department of Chemistry, P.O. Box 208107, 225 Prospect Street, New Haven, CT 06520-8107
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53
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Nomrowski J, Wenger OS. Photoinduced PCET in ruthenium-phenol systems: thermodynamic equivalence of uni- and bidirectional reactions. Inorg Chem 2015; 54:3680-7. [PMID: 25781364 DOI: 10.1021/acs.inorgchem.5b00318] [Citation(s) in RCA: 39] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023]
Abstract
Six termolecular reaction systems comprised of Ru(4,4′-bis(trifluoromethyl)-2,2′-bipyridine)32+, phenols with different para substituents, and pyridine in acetonitrile undergo proton-coupled electron transfer (PCET) upon photoexcitation of the metal complex. Five of these six phenols are found to release in concerted fashion an electron to the ruthenium photooxidant and a proton to the pyridine base. The kinetics for this concerted bidirectional PCET process and its relationship to the reaction free energy were compared to the driving-force dependence of reaction kinetics for unidirectional concerted proton–electron transfer (CPET) between the same phenols and Ru(2,2′-bipyrazine)32+, a combined electron/proton acceptor. The results strongly support the concept of thermodynamic equivalence between separated electron/proton acceptors and single-reagent hydrogen-atom acceptors. A key feature of the explored systems is the similarity between molecules employed for bi- and unidirectional CPET.
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Affiliation(s)
- Julia Nomrowski
- Department of Chemistry, University of Basel, St. Johanns-Ring 19, CH-4056 Basel, Switzerland
| | - Oliver S Wenger
- Department of Chemistry, University of Basel, St. Johanns-Ring 19, CH-4056 Basel, Switzerland
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54
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Proton-coupled electron transfer with photoexcited ruthenium(II), rhenium(I), and iridium(III) complexes. Coord Chem Rev 2015. [DOI: 10.1016/j.ccr.2014.03.025] [Citation(s) in RCA: 66] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
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55
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Salazar R, Vidal J, Martínez-Cifuentes M, Araya-Maturana R, Ramírez-Rodríguez O. Electrochemical characterization of hydroquinone derivatives with different substituents in acetonitrile. NEW J CHEM 2015. [DOI: 10.1039/c4nj01657b] [Citation(s) in RCA: 28] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
The effect of carbonyl groups in the ortho position with respect to a hydroxyl group on the electrochemical oxidation of hydroquinones in acetonitrile is studied.
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Affiliation(s)
- Ricardo Salazar
- Department of Environmental Sciences
- Faculty of Chemistry and Biology
- University of Santiago de Chile
- USACh
- Santiago
| | - Jorge Vidal
- Department of Environmental Sciences
- Faculty of Chemistry and Biology
- University of Santiago de Chile
- USACh
- Santiago
| | | | - Ramiro Araya-Maturana
- Department of Organic and Physical Chemistry
- Faculty of Chemical and Pharmaceutical Sciences
- University of Chile
- Santiago 1
- Chile
| | - Oney Ramírez-Rodríguez
- Department of Organic and Physical Chemistry
- Faculty of Chemical and Pharmaceutical Sciences
- University of Chile
- Santiago 1
- Chile
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56
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Chen J, Kuss-Petermann M, Wenger OS. Dependence of Reaction Rates for Bidirectional PCET on the Electron Donor–Electron Acceptor Distance in Phenol–Ru(2,2′-Bipyridine)32+ Dyads. J Phys Chem B 2014; 119:2263-73. [DOI: 10.1021/jp506087t] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Jing Chen
- Department of Chemistry, University of Basel, St. Johanns-Ring
19, CH-4056 Basel, Switzerland
| | - Martin Kuss-Petermann
- Department of Chemistry, University of Basel, St. Johanns-Ring
19, CH-4056 Basel, Switzerland
| | - Oliver S. Wenger
- Department of Chemistry, University of Basel, St. Johanns-Ring
19, CH-4056 Basel, Switzerland
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57
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Savéant JM, Tard C. Proton-Coupled Electron Transfer in Azobenzene/Hydrazobenzene Couples with Pendant Acid–Base Functions. Hydrogen-Bonding and Structural Effects. J Am Chem Soc 2014; 136:8907-10. [DOI: 10.1021/ja504484a] [Citation(s) in RCA: 34] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/24/2023]
Affiliation(s)
- Jean-Michel Savéant
- Laboratoire d’Electrochimie
Moléculaire, UMR 7591, CNRS, Université Paris Diderot, Sorbonne Paris Cité, 15 rue Jean-Antoine de Baïf, F-75205 Paris Cedex 13, France
| | - Cédric Tard
- Laboratoire d’Electrochimie
Moléculaire, UMR 7591, CNRS, Université Paris Diderot, Sorbonne Paris Cité, 15 rue Jean-Antoine de Baïf, F-75205 Paris Cedex 13, France
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58
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Salamone M, Amorati R, Menichetti S, Viglianisi C, Bietti M. Structural and Medium Effects on the Reactions of the Cumyloxyl Radical with Intramolecular Hydrogen Bonded Phenols. The Interplay Between Hydrogen-Bonding and Acid-Base Interactions on the Hydrogen Atom Transfer Reactivity and Selectivity. J Org Chem 2014; 79:6196-205. [DOI: 10.1021/jo5009367] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
Affiliation(s)
- Michela Salamone
- Dipartimento di Scienze e Tecnologie Chimiche, Università “Tor Vergata”, Via della Ricerca Scientifica, 1, I-00133 Rome, Italy
| | - Riccardo Amorati
- Dipartimento di Chimica “G.
Ciamician”, Università di Bologna, Via San Giacomo,
11, I-40126 Bologna, Italy
| | - Stefano Menichetti
- Dipartimento di
Chimica “U. Schiff”, Università di Firenze, Via della
Lastruccia, 3-13, I-50019 Sesto Fiorentino, Italy
| | - Caterina Viglianisi
- Dipartimento di
Chimica “U. Schiff”, Università di Firenze, Via della
Lastruccia, 3-13, I-50019 Sesto Fiorentino, Italy
| | - Massimo Bietti
- Dipartimento di Scienze e Tecnologie Chimiche, Università “Tor Vergata”, Via della Ricerca Scientifica, 1, I-00133 Rome, Italy
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59
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Martínez-González E, Frontana C. Inner reorganization limiting electron transfer controlled hydrogen bonding: intra- vs. intermolecular effects. Phys Chem Chem Phys 2014; 16:8044-50. [PMID: 24653999 DOI: 10.1039/c3cp55106g] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
In this work, experimental evidence of the influence of the electron transfer kinetics during electron transfer controlled hydrogen bonding between anion radicals of metronidazole and ornidazole, derivatives of 5-nitro-imidazole, and 1,3-diethylurea as the hydrogen bond donor, is presented. Analysis of the variations of voltammetric EpIcvs. log KB[DH], where KB is the binding constant, allowed us to determine the values of the binding constant and also the electron transfer rate k, confirmed by experiments obtained at different scan rates. Electronic structure calculations at the BHandHLYP/6-311++G(2d,2p) level for metronidazole, including the solvent effect by the Cramer/Truhlar model, suggested that the minimum energy conformer is stabilized by intramolecular hydrogen bonding. In this structure, the inner reorganization energy, λi,j, contributes significantly (0.5 eV) to the total reorganization energy of electron transfer, thus leading to a diminishment of the experimental k.
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Affiliation(s)
- Eduardo Martínez-González
- Centro de Investigación y Desarrollo Tecnológico en Electroquimica, S. Parque Tecnologico Queretaro Sanfandila Pedro Escobedo, Queretaro 76703, Mexico.
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60
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Migliore A, Polizzi NF, Therien M, Beratan DN. Biochemistry and theory of proton-coupled electron transfer. Chem Rev 2014; 114:3381-465. [PMID: 24684625 PMCID: PMC4317057 DOI: 10.1021/cr4006654] [Citation(s) in RCA: 345] [Impact Index Per Article: 34.5] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/19/2013] [Indexed: 02/01/2023]
Affiliation(s)
- Agostino Migliore
- Department
of Chemistry, Department of Biochemistry, and Department of Physics, Duke University, Durham, North Carolina 27708, United States
| | - Nicholas F. Polizzi
- Department
of Chemistry, Department of Biochemistry, and Department of Physics, Duke University, Durham, North Carolina 27708, United States
| | - Michael
J. Therien
- Department
of Chemistry, Department of Biochemistry, and Department of Physics, Duke University, Durham, North Carolina 27708, United States
| | - David N. Beratan
- Department
of Chemistry, Department of Biochemistry, and Department of Physics, Duke University, Durham, North Carolina 27708, United States
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61
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Affiliation(s)
- Joshua P. Layfield
- Department of Chemistry, 600 South Mathews Avenue, University of Illinois at Urbana-Champaign, Urbana, IL 61801
| | - Sharon Hammes-Schiffer
- Department of Chemistry, 600 South Mathews Avenue, University of Illinois at Urbana-Champaign, Urbana, IL 61801
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62
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Chen X, Ma G, Sun W, Dai H, Xiao D, Zhang Y, Qin X, Liu Y, Bu Y. Water Promoting Electron Hole Transport between Tyrosine and Cysteine in Proteins via a Special Mechanism: Double Proton Coupled Electron Transfer. J Am Chem Soc 2014; 136:4515-24. [DOI: 10.1021/ja406340z] [Citation(s) in RCA: 37] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Affiliation(s)
- Xiaohua Chen
- School
of Chemistry and Chemical Engineering, Chongqing University, Chongqing, 400030, China
| | - Guangcai Ma
- School
of Chemistry and Chemical Engineering, Shandong University, Jinan, Shandong 250100, China
| | - Weichao Sun
- School
of Chemistry and Chemical Engineering, Chongqing University, Chongqing, 400030, China
| | - Hongjing Dai
- School
of Chemistry and Chemical Engineering, Chongqing University, Chongqing, 400030, China
| | - Dong Xiao
- School
of Chemistry and Chemical Engineering, Chongqing University, Chongqing, 400030, China
| | - Yanfang Zhang
- School
of Chemistry and Chemical Engineering, Chongqing University, Chongqing, 400030, China
| | - Xin Qin
- School
of Chemistry and Chemical Engineering, Chongqing University, Chongqing, 400030, China
| | - Yongjun Liu
- School
of Chemistry and Chemical Engineering, Shandong University, Jinan, Shandong 250100, China
| | - Yuxiang Bu
- School
of Chemistry and Chemical Engineering, Shandong University, Jinan, Shandong 250100, China
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63
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Chen J, Kuss-Petermann M, Wenger OS. Distance Dependence of Bidirectional Concerted Proton-Electron Transfer in Phenol-Ru(2,2′-bipyridine)32+Dyads. Chemistry 2014; 20:4098-104. [DOI: 10.1002/chem.201304256] [Citation(s) in RCA: 30] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/31/2013] [Indexed: 11/08/2022]
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64
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Savéant JM. Concerted proton-electron transfers: fundamentals and recent developments. ANNUAL REVIEW OF ANALYTICAL CHEMISTRY (PALO ALTO, CALIF.) 2014; 7:537-560. [PMID: 25014349 DOI: 10.1146/annurev-anchem-071213-020315] [Citation(s) in RCA: 39] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/03/2023]
Abstract
Proton-coupled electron transfers (PCET) are ubiquitous in natural and synthetic processes. This review focuses on reactions where the two events are concerted. Semiclassical models of such reactions allow their kinetic characterization through activation versus driving force relationships, estimates of reorganization energies, effects of the nature of the proton acceptor, and H/D kinetic isotope effect as well as their discrimination from stepwise pathways. Several homogeneous reactions (through stopped-flow and laser flash-quench techniques) and electrochemical processes are discussed in this framework. Once the way has been rid of the improper notion of pH-dependent driving force, water appears as a remarkable proton acceptor in terms of reorganization energy and pre-exponential factor, thanks to its H-bonded and H-bonding properties, similarly to purposely synthesized "H-bond train" molecules. The most recent developments are in modeling and description of emblematic concerted proton-electron transfer (CPET) reactions associated with the breaking of a heavy-atom bond in an all-concerted process.
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Affiliation(s)
- Jean-Michel Savéant
- Laboratoire d'Electrochimie Moléculaire, Unité Mixte de Recherche, Université Paris Diderot, Sorbonne Paris Cité, CNRS 7591, 75205 Paris Cedex 13, France;
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65
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Savarese M, Netti PA, Rega N, Adamo C, Ciofini I. Intermolecular proton shuttling in excited state proton transfer reactions: insights from theory. Phys Chem Chem Phys 2014; 16:8661-6. [DOI: 10.1039/c4cp00068d] [Citation(s) in RCA: 34] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Abstract
The mechanism of intermolecular proton shuttling involved in a prototypical excited state proton transfer reaction is disclosed using DFT and TD-DFT.
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Affiliation(s)
- Marika Savarese
- Dipartimento di Chimica ‘Paolo Corradini’
- Università di Napoli Federico II
- Complesso Universitario di M.S.Angelo
- 80126 Napoli, Italy
- Center for Advanced Biomaterials for Health Care@CRIB
| | - Paolo A. Netti
- Dipartimento di Chimica ‘Paolo Corradini’
- Università di Napoli Federico II
- Complesso Universitario di M.S.Angelo
- 80126 Napoli, Italy
- Center for Advanced Biomaterials for Health Care@CRIB
| | - Nadia Rega
- Dipartimento di Chimica ‘Paolo Corradini’
- Università di Napoli Federico II
- Complesso Universitario di M.S.Angelo
- 80126 Napoli, Italy
- Center for Advanced Biomaterials for Health Care@CRIB
| | - Carlo Adamo
- LECIME
- Laboratoire d'Electrochimie
- Chimie des Interfaces et Modélisation pour l'Energie
- UMR
- France
| | - Ilaria Ciofini
- LECIME
- Laboratoire d'Electrochimie
- Chimie des Interfaces et Modélisation pour l'Energie
- UMR
- France
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66
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Savarese M, Netti PA, Adamo C, Rega N, Ciofini I. Exploring the Metric of Excited State Proton Transfer Reactions. J Phys Chem B 2013; 117:16165-73. [DOI: 10.1021/jp406301p] [Citation(s) in RCA: 48] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
Affiliation(s)
- Marika Savarese
- Dipartimento
di Chimica ‘Paolo Corradini’, Università di Napoli Federico II, Complesso Universitario di M.S. Angelo, via Cintia, 80126 Napoli, Italy
- Center
for Advanced Biomaterials for Health Care@CRIB, Istituto Italiano di Tecnologia, Largo Barsanti e Matteucci n, 53 80125 Napoli, Italy
| | - Paolo A. Netti
- Center
for Advanced Biomaterials for Health Care@CRIB, Istituto Italiano di Tecnologia, Largo Barsanti e Matteucci n, 53 80125 Napoli, Italy
| | - Carlo Adamo
- Laboratoire
d’Electrochimie, Chimie des Interfaces et Modelisation pour
l’Energie, CNRS UMR-7575, Ecole Nationale Supérieure de Chimie de Paris, Chimie ParisTech, 11 rue P. et M. Curie, F-75231 Paris Cedex 05, France
- Institut Universitaire de France, 103 Bd Saint-Michel, F-75005 Paris, France
| | - Nadia Rega
- Dipartimento
di Chimica ‘Paolo Corradini’, Università di Napoli Federico II, Complesso Universitario di M.S. Angelo, via Cintia, 80126 Napoli, Italy
- Center
for Advanced Biomaterials for Health Care@CRIB, Istituto Italiano di Tecnologia, Largo Barsanti e Matteucci n, 53 80125 Napoli, Italy
| | - Ilaria Ciofini
- Laboratoire
d’Electrochimie, Chimie des Interfaces et Modelisation pour
l’Energie, CNRS UMR-7575, Ecole Nationale Supérieure de Chimie de Paris, Chimie ParisTech, 11 rue P. et M. Curie, F-75231 Paris Cedex 05, France
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67
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Warren JJ, Herrera N, Hill MG, Winkler JR, Gray HB. Electron flow through nitrotyrosinate in Pseudomonas aeruginosa azurin. J Am Chem Soc 2013; 135:11151-8. [PMID: 23859602 DOI: 10.1021/ja403734n] [Citation(s) in RCA: 33] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023]
Abstract
We have designed ruthenium-modified Pseudomonas aeruginosa azurins that incorporate 3-nitrotyrosine (NO2YOH) between Ru(2,2'-bipyridine)2(imidazole)(histidine) and Cu redox centers in electron transfer (ET) pathways. We investigated the structures and reactivities of three different systems: RuH107NO2YOH109, RuH124NO2YOH122, and RuH126NO2YOH122. RuH107NO2YOH109, unlabeled H124NO2YOH122, and unlabeled H126NO2YOH122 were structurally characterized. The pKa's of NO2YOH at positions 122 and 109 are 7.2 and 6.0, respectively. Reduction potentials of 3-nitrotyrosinate (NO2YO(-))-modified azurins were estimated from cyclic and differential pulse voltammetry data: oxidation of NO2YO(-)122 occurs near 1.1 versus NHE; oxidation of NO2YO(-)109 is near 1.2 V. Our analysis of transient optical spectroscopic experiments indicates that hopping via NO2YO(-) enhances Cu(I) oxidation rates over single-step ET by factors of 32 (RuH107NO2YO(-)109), 46 (RuH126NO2YO(-)122), and 13 (RuH124NO2YO(-)122).
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Affiliation(s)
- Jeffrey J Warren
- Beckman Institute and Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, California 91125, USA
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68
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Abstract
Proton-coupled electron transfer (PCET) plays a crucial role in many enzymatic reactions and is relevant for a variety of processes including water oxidation, nitrogen fixation, and carbon dioxide reduction. Much of the research on PCET has focused on transfers between molecules in their electronic ground states, but increasingly researchers are investigating PCET between photoexcited reactants. This Account describes recent studies of excited-state PCET with d(6) metal complexes emphasizing work performed in my laboratory. Upon photoexcitation, some complexes release an electron and a proton to benzoquinone reaction partners. Others act as combined electron-proton acceptors in the presence of phenols. As a result, we can investigate photoinduced PCET involving electron and proton transfer in a given direction, a process that resembles hydrogen-atom transfer (HAT). In other studies, the photoexcited metal complexes merely serve as electron donors or electron acceptors because the proton donating and accepting sites are located on other parts of the molecular PCET ensemble. We and others have used this multisite design to explore so-called bidirectional PCET which occurs in many enzymes. A central question in all of these studies is whether concerted proton-electron transfer (CPET) can compete kinetically with sequential electron and proton transfer steps. Short laser pulses can trigger excited-state PCET, making it possible to investigate rapid reactions. Luminescence spectroscopy is a convenient tool for monitoring PCET, but unambiguous identification of reaction products can require a combination of luminescence spectroscopy and transient absorption spectroscopy. Nevertheless, in some cases, distinguishing between PCET photoproducts and reaction products formed by simple photoinduced electron transfer (ET) (reactions that don't include proton transfer) is tricky. Some of the studies presented here deal directly with this important problem. In one case study we employed a cyclometalated iridium(III) complex. Our other studies with ruthenium(II) complexes and phenols focused on systematic variations of the reaction free energies for the CPET, ET, and proton transfer (PT) steps to explore their influence on the overall PCET reaction. Still other work with rhenium(I) complexes concentrated on the question of how the electronic structure of the metal-to-ligand charge transfer (MLCT) excited states affects PCET. We used covalent rhenium(I)-phenol dyads to explore the influence of the electron donor-electron acceptor distance on bidirectional PCET. In covalent triarylamine-Ru(bpy)₃²⁺/Os(bpy)₃²⁺-anthraquinone triads (bpy = 2,2'-bipyridine), hydrogen-bond donating solvents significantly lengthened the lifetimes of photogenerated electron/hole pairs because of hydrogen-bonding to the quinone radical anion. Until now, comparatively few researchers have investigated this variation of PCET: the strengthening of H-bonds upon photoreduction.
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Affiliation(s)
- Oliver S. Wenger
- Departement Chemie, Universität Basel, Spitalstrasse 51, CH-4056 Basel, Switzerland
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69
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Kuss-Petermann M, Wenger OS. Photoacid Behavior versus Proton-Coupled Electron Transfer in Phenol–Ru(bpy)32+ Dyads. J Phys Chem A 2013; 117:5726-33. [DOI: 10.1021/jp402567m] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Martin Kuss-Petermann
- Institut für Anorganische
Chemie, Georg-August-Universität Göttingen, Tammannstraße 4, D-37077 Göttingen, Germany
| | - Oliver S. Wenger
- Departement für
Chemie, Universität Basel, Spitalstrasse 51, CH-4056 Basel, Switzerland
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70
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Tarantino KT, Liu P, Knowles RR. Catalytic ketyl-olefin cyclizations enabled by proton-coupled electron transfer. J Am Chem Soc 2013; 135:10022-5. [PMID: 23796403 DOI: 10.1021/ja404342j] [Citation(s) in RCA: 231] [Impact Index Per Article: 21.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
Concerted proton-coupled electron transfer is a key mechanism of substrate activation in biological redox catalysis. However, its applications in organic synthesis remain largely unexplored. Herein, we report the development of a new catalytic protocol for ketyl-olefin coupling and present evidence to support concerted proton-coupled electron transfer being the operative mechanism of ketyl formation. Notably, reaction outcomes were correctly predicted by a simple thermodynamic formalism relating the oxidation potentials and pKa values of specific Brønsted acid/reductant combinations to their capacity to act jointly as a formal hydrogen atom donor.
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Affiliation(s)
- Kyle T Tarantino
- Department of Chemistry, Princeton University, Princeton, New Jersey 08544, USA
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71
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Zhang Y, Yuan S, Lu R, Yu A. Ultrafast fluorescence quenching dynamics of Atto655 in the presence of N-acetyltyrosine and N-acetyltryptophan in aqueous solution: proton-coupled electron transfer versus electron transfer. J Phys Chem B 2013; 117:7308-16. [PMID: 23721323 DOI: 10.1021/jp404466f] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
We studied the ultrafast fluorescence quenching dynamics of Atto655 in the presence of N-acetyltyrosine (AcTyr) and N-acetyltryptophan (AcTrp) in aqueous solution with femtosecond transient absorption spectroscopy. We found that the charge-transfer rate between Atto655 and AcTyr is about 240 times smaller than that between Atto655 and AcTrp. The pH value and D2O dependences of the excited-state decay kinetics of Atto655 in the presence of AcTyr and AcTrp reveal that the quenching of Atto655 fluorescence by AcTyr in aqueous solution is via a proton-coupled electron-transfer (PCET) process and that the quenching of Atto655 fluorescence by AcTrp in aqueous solution is via an electron-transfer process. With the version of the semiclassical Marcus ET theory, we derived that the electronic coupling constant for the PCET reaction between Atto655 and AcTyr in aqueous solution is 8.3 cm(-1), indicating that the PCET reaction between Atto655 and AcTyr in aqueous solution is nonadiabatic.
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Affiliation(s)
- Ying Zhang
- Department of Chemistry, Renmin University of China, Beijing 100872, People's Republic of China
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72
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Markle TF, Tronic TA, DiPasquale AG, Kaminsky W, Mayer JM. Effect of basic site substituents on concerted proton-electron transfer in hydrogen-bonded pyridyl-phenols. J Phys Chem A 2012; 116:12249-59. [PMID: 23176252 PMCID: PMC3926939 DOI: 10.1021/jp311388n] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Separated concerted proton-electron transfer (sCPET) reactions of two series of phenols with pendent substituted pyridyl moieties are described. The pyridine is either attached directly to the phenol (HOAr-pyX) or connected through a methylene linker (HOArCH(2)pyX) (X = 4-NO(2), 5-CF(3), 4-CH(3), and 4-NMe(2)). Electron-donating and -withdrawing substituents have a substantial effect on the chemical environment of the transferring proton, as indicated by IR and (1)H NMR spectra, X-ray structures, and computational studies. One-electron oxidation of the phenols occurs concomitantly with proton transfer from the phenolic oxygen to the pyridyl nitrogen. The oxidation potentials vary linearly with the pK(a) of the free pyridine (pyX), with slopes slightly below the Nerstian value of 59 mV/pK(a). For the HOArCH(2)pyX series, the rate constants k(sCPET) for oxidation by NAr(3)(•+) or [Fe(diimine)(3)](3+) vary primarily with the thermodynamic driving force (ΔG°(sCPET)), whether ΔG° is changed by varying the potential of the oxidant or the substituent on the pyridine, indicating a constant intrinsic barrier λ. In contrast, the substituents in the HOAr-pyX series affect λ as well as ΔG°(sCPET), and compounds with electron-withdrawing substituents have significantly lower reactivity. The relationship between the structural and spectroscopic properties of the phenols and their CPET reactivity is discussed.
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Affiliation(s)
| | - Tristan A. Tronic
- Department of Chemistry, Campus Box 351700, University of Washington, Seattle, Washington 98195-1700
| | | | - Werner Kaminsky
- Department of Chemistry, Campus Box 351700, University of Washington, Seattle, Washington 98195-1700
| | - James M. Mayer
- Department of Chemistry, Campus Box 351700, University of Washington, Seattle, Washington 98195-1700
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