1
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Sheth S, Gotico P, Herrero C, Quaranta A, Aukauloo A, Leibl W. Proton Domino Reactions at an Imidazole Relay Control the Oxidation of a Tyr Z-His 190 Artificial Mimic of Photosystem II. Chemistry 2024; 30:e202400862. [PMID: 38676548 DOI: 10.1002/chem.202400862] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/29/2024] [Revised: 04/10/2024] [Accepted: 04/24/2024] [Indexed: 04/29/2024]
Abstract
A close mimic of P680 and the TyrosineZ-Histidine190 pair in photosystem II (PS II) has been synthesized using a ruthenium chromophore and imidazole-phenol ligands. The intramolecular oxidation of the ligands by the photoproduced Ru(III) species is characterized by a small driving force, very similar to PS II where the complexity of kinetics was attributed to the reversibility of electron transfer steps. Laser flash photolysis revealed biphasic kinetics for ligand oxidation. The fast phase (τ<50 ns) corresponds to partial oxidation of the imidazole-phenol ligand, proton transfer within the hydrogen bond, and formation of a neutral phenoxyl radical. The slow phase (5-9 μs) corresponds to full oxidation of the ligand which is kinetically controlled by deprotonation of the distant 1-nitrogen of the imidazolium. These results show that imidazole with its two protonatable sites plays a special role as a proton relay in a 'proton domino' reaction.
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Affiliation(s)
- Sujitraj Sheth
- CEA, CNRS, Institut de Biologie Intégrative de la Cellule (I2BC), Université Paris Saclay, 91198, Gif-sur-Yvette, France
- Current affiliation , National Key Laboratory of Green Pesticide, Guizhou University, Guiyang, 550025, Guizhou, China
| | - Philipp Gotico
- CEA, CNRS, Institut de Biologie Intégrative de la Cellule (I2BC), Université Paris Saclay, 91198, Gif-sur-Yvette, France
| | - Christian Herrero
- CNRS, Institut de Chimie Moléculaire et Des Matériaux d'Orsay (ICMMO), Université Paris Saclay, 91405, Orsay, France
| | - Annamaria Quaranta
- CEA, CNRS, Institut de Biologie Intégrative de la Cellule (I2BC), Université Paris Saclay, 91198, Gif-sur-Yvette, France
| | - Ally Aukauloo
- CEA, CNRS, Institut de Biologie Intégrative de la Cellule (I2BC), Université Paris Saclay, 91198, Gif-sur-Yvette, France
- CNRS, Institut de Chimie Moléculaire et Des Matériaux d'Orsay (ICMMO), Université Paris Saclay, 91405, Orsay, France
| | - Winfried Leibl
- CEA, CNRS, Institut de Biologie Intégrative de la Cellule (I2BC), Université Paris Saclay, 91198, Gif-sur-Yvette, France
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2
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Dey A, Ghorai N, Das A, Ghosh HN. Effects of hydrogen bonding on intramolecular/intermolecular proton-coupled electron transfer using a Ruthenium-anthraquinone dyad in ultrafast time domain. J Photochem Photobiol A Chem 2023. [DOI: 10.1016/j.jphotochem.2023.114709] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 03/30/2023]
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3
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Gotico P, Herrero C, Protti S, Quaranta A, Sheth S, Fallahpour R, Farran R, Halime Z, Sircoglou M, Aukauloo A, Leibl W. Proton-controlled Action of an Imidazole as Electron Relay in a Photoredox Triad. Photochem Photobiol Sci 2022; 21:247-259. [PMID: 34988933 DOI: 10.1007/s43630-021-00163-2] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/09/2021] [Accepted: 12/18/2021] [Indexed: 11/24/2022]
Abstract
Electron relays play a crucial role for efficient light-induced activation by a photo-redox moiety of catalysts for multi-electronic transformations. Their insertion between the two units reduces detrimental energy transfer quenching while establishing at the same time unidirectional electron flow. This rectifying function allows charge accumulation necessary for catalysis. Mapping these events in photophysical studies is an important step towards the development of efficient molecular photocatalysts. Three modular complexes comprised of a Ru-chromophore, an imidazole electron relay function, and a terpyridine unit as coordination site for a metal ion were synthesized and the light-induced electron transfer events studied by laser flash photolysis. In all cases, formation of an imidazole radical by internal electron transfer to the oxidized chromophore was observed. The effect of added base evidenced that the reaction sequence depends strongly on the possibility for deprotonation of the imidazole function in a proton-coupled electron transfer process. In the complex with MnII present as a proxy for a catalytic site, a strongly accelerated decay of the imidazole radical together with a decreased rate of back electron transfer from the external electron acceptor to the oxidized complex was observed. This transient formation of an imidazolyl radical is clear evidence for the function of the imidazole group as an electron relay. The implication of the imidazole proton and the external base for the kinetics and energetics of the electron trafficking is discussed.
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Affiliation(s)
- Philipp Gotico
- Institut de Biologie Intégrative de La Cellule (I2BC), Université Paris Saclay, CEA, CNRS, 91191, Gif-sur-Yvette, France
| | - Christian Herrero
- Institut de Chimie Moléculaire Et Des Matériaux d'Orsay (ICMMO), Université Paris Saclay, 91405, Orsay, France
| | - Stefano Protti
- PhotoGreen Lab, Department of Chemistry, University of Pavia, 27100, Pavia, Italy
| | - Annamaria Quaranta
- Institut de Biologie Intégrative de La Cellule (I2BC), Université Paris Saclay, CEA, CNRS, 91191, Gif-sur-Yvette, France
| | - Sujitraj Sheth
- Institut de Biologie Intégrative de La Cellule (I2BC), Université Paris Saclay, CEA, CNRS, 91191, Gif-sur-Yvette, France
| | - Reza Fallahpour
- Department of Chemistry, University of Zürich UZH, Freiestrasse 3, CH-3012, Bern, Switzerland
| | - Rajaa Farran
- Institut de Biologie Intégrative de La Cellule (I2BC), Université Paris Saclay, CEA, CNRS, 91191, Gif-sur-Yvette, France.,Lebanese International University, Mazraa, Beirut, 146404, Lebanon
| | - Zakaria Halime
- Institut de Chimie Moléculaire Et Des Matériaux d'Orsay (ICMMO), Université Paris Saclay, 91405, Orsay, France
| | - Marie Sircoglou
- Institut de Chimie Moléculaire Et Des Matériaux d'Orsay (ICMMO), Université Paris Saclay, 91405, Orsay, France
| | - Ally Aukauloo
- Institut de Chimie Moléculaire Et Des Matériaux d'Orsay (ICMMO), Université Paris Saclay, 91405, Orsay, France
| | - Winfried Leibl
- Institut de Biologie Intégrative de La Cellule (I2BC), Université Paris Saclay, CEA, CNRS, 91191, Gif-sur-Yvette, France.
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4
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Dey A, Ghorai N, Das A, Ghosh HN. Proton-Coupled Electron Transfer for Photoinduced Generation of Two-Electron Reduced Species of Quinone. J Phys Chem B 2020; 124:11165-11174. [PMID: 33241933 DOI: 10.1021/acs.jpcb.0c07809] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Purpose-built molecules that follow the fundamental process of photosynthesis have significance in developing better insight into the natural photosynthesis process. Quinones have a significant role as electron acceptors in natural photosynthesis, and their reduction is assisted through H-bond donation or protonation. The major challenge in such studies is to couple the multielectron and proton-transfer process and to achieve a reasonably stable charge-separated state for the elucidation of the mechanistic pathway. We have tried to address this issue through the design of a donor-acceptor-donor molecular triad (2RuAQ) derived from two equivalent [Ru(bpy)3]2+ derivatives and a bridging anthraquinone moiety (AQ). Photoinduced proton-coupled electron transfer (PCET) for this molecular triad was systematically investigated in the absence and presence of hexafluoroisopropanol and p-toluenesulfonic acid (PTSA) using time-resolved absorption spectroscopy in the ultrafast time domain. Results reveal the generation of a relatively long-lived charge-separated state in this multi-electron transfer reaction, and we could confirm the generation of AQ2- and RuIII as the transient intermediates. We could rationalize the mechanistic pathway and the dynamics associated with photoinduced processes and the role of H-bonding in stabilizing charge-separated states. Transient absorption spectroscopic studies reveal that the rates of intramolecular electron transfer and the mechanistic pathways associated with the PCET process are significantly different in different solvent compositions having different polarities. In acetonitrile, a concerted PCET mechanism prevails, whereas the stepwise PCET reaction process is observed in the presence of PTSA. The results of the present study represent a unique model for the mechanistic diversity of PCET reactions.
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Affiliation(s)
- Ananta Dey
- Analytical and Environmental Science Division and Centralized Instrument Facility, CSIR-Central Salt and Marine Chemicals Research Institute, Bhavnagar, Gujarat 364 002, India.,Academy of Scientific and Innovative Research (AcSIR), CSIR-Human Resource Development Centre, (CSIR-HRDC) Campus, Sector 19, Kamla Nehru Nagar, Ghaziabad, Uttar Pradesh 201 002, India
| | - Nandan Ghorai
- Institute of Nano Science and Technology, Mohali, Punjab 160062, India
| | - Amitava Das
- Academy of Scientific and Innovative Research (AcSIR), CSIR-Human Resource Development Centre, (CSIR-HRDC) Campus, Sector 19, Kamla Nehru Nagar, Ghaziabad, Uttar Pradesh 201 002, India.,Department of Chemical Sciences, Indian Institute of Science Education and Research Kolkata, Mohanpur, West Bengal 741 246, India
| | - Hirendra N Ghosh
- Institute of Nano Science and Technology, Mohali, Punjab 160062, India.,Radiation and Photochemistry Division, Bhabha Atomic Research Centre, Mumbai 400085, India
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5
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Li P, Soudackov AV, Koronkiewicz B, Mayer JM, Hammes-Schiffer S. Theoretical Study of Shallow Distance Dependence of Proton-Coupled Electron Transfer in Oligoproline Peptides. J Am Chem Soc 2020; 142:13795-13804. [PMID: 32664731 DOI: 10.1021/jacs.0c04716] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Long-range electron transfer is coupled to proton transfer in a wide range of chemically and biologically important processes. Recently the proton-coupled electron transfer (PCET) rate constants for a series of biomimetic oligoproline peptides linking Ru(bpy)32+ to tyrosine were shown to exhibit a substantially shallower dependence on the number of proline spacers compared to the analogous electron transfer (ET) systems. The experiments implicated a concerted PCET mechanism involving intramolecular electron transfer from tyrosine to Ru(bpy)33+ and proton transfer from tyrosine to a hydrogen phosphate dianion. Herein these PCET systems, as well as the analogous ET systems, are studied with microsecond molecular dynamics, and the ET and PCET rate constants are calculated with the corresponding nonadiabatic theories. The molecular dynamics simulations illustrate that smaller ET donor-acceptor distances are sampled by the PCET systems than by the analogous ET systems. The shallower dependence of the PCET rate constant on the ET donor-acceptor distance is explained in terms of an additional positive, distance-dependent electrostatic term in the PCET driving force, which attenuates the rate constant at smaller distances. This electrostatic term depends on the change in the electrostatic interaction between the charges on each end of the bridge and can be modified by altering these charges. On the basis of these insights, this theory predicted a less shallow distance dependence of the PCET rate constant when imidazole rather than hydrogen phosphate serves as the proton acceptor, even though their pKa values are similar. This theoretical prediction was subsequently validated experimentally, illustrating that long-range electron transfer processes can be tuned by modifying the nature of the proton acceptor in concerted PCET processes. This level of control has broad implications for the design of more effective charge-transfer systems.
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Affiliation(s)
- Pengfei Li
- Department of Chemistry, Yale University, 225 Prospect Street, New Haven, Connecticut 06520, United States
| | - Alexander V Soudackov
- Department of Chemistry, Yale University, 225 Prospect Street, New Haven, Connecticut 06520, United States
| | - Brian Koronkiewicz
- Department of Chemistry, Yale University, 225 Prospect Street, New Haven, Connecticut 06520, United States
| | - James M Mayer
- Department of Chemistry, Yale University, 225 Prospect Street, New Haven, Connecticut 06520, United States
| | - Sharon Hammes-Schiffer
- Department of Chemistry, Yale University, 225 Prospect Street, New Haven, Connecticut 06520, United States
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6
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Koronkiewicz B, Swierk J, Regan K, Mayer JM. Shallow Distance Dependence for Proton-Coupled Tyrosine Oxidation in Oligoproline Peptides. J Am Chem Soc 2020; 142:12106-12118. [PMID: 32510937 PMCID: PMC7545454 DOI: 10.1021/jacs.0c01429] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
Abstract
We have explored the kinetic effect of increasing electron transfer (ET) distance in a biomimetic, proton-coupled electron-transfer (PCET) system. Biological ET often occurs simultaneously with proton transfer (PT) 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 ET pathways. In many cases, PT is coupled to long-range ET. While many studies have shown that the rate of ET is sensitive to the distance between the electron donor and acceptor, extensions to biological CPET reactions are sparse. The possibility of a unique ET distance dependence for CPET reactions deserves further exploration, as this could have implications for how we understand biological ET. We therefore explored the ET 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)32+ 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 proline 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 in part from the requirement for stronger oxidants, leading to a smaller hole-transfer effective tunneling barrier height. The shallow distance dependence observed here and extensions to distance-dependent CPET reactions have potential implications for long-range charge transfers.
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Affiliation(s)
- Brian Koronkiewicz
- Department of Chemistry, Yale University, New Haven, Connecticut 06520-8107, United States
| | - John Swierk
- Department of Chemistry, Yale University, New Haven, Connecticut 06520-8107, United States
| | - Kevin Regan
- Department of Chemistry, Yale University, New Haven, Connecticut 06520-8107, United States
| | - James M Mayer
- Department of Chemistry, Yale University, New Haven, Connecticut 06520-8107, United States
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7
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Khade RV, Dutta Choudhury S, Pal H, Kumbhar AS. Excited State Interaction of Ruthenium (II) Imidazole Phenanthroline Complex [Ru(bpy) 2 ipH] 2+ with 1,4-Benzoquinone: Simple Electron Transfer or Proton-Coupled Electron Transfer? Chemphyschem 2018; 19:2380-2388. [PMID: 29873437 DOI: 10.1002/cphc.201800313] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/09/2018] [Indexed: 11/07/2022]
Abstract
The unidirectional proton coupled electron transfer (PCET) from the excited state of Ru(II) imidazole phenanthroline complex [Ru(bpy)2 ipH]2+ to 1,4-benzoquinone, was studied by steady-state (SS) and time-resolved (TR) fluorescence and transient absorption (TA) measurements. The pKa (9.7) and pKa * (8.6) values of the complex suggest that it behaves as a photoacid on excitation. The difference in the quenching rates obtained from SS and TR fluorescence studies indicate participation of both dynamic quenching and static quenching involving the hydrogen bonded ipH ligand of [Ru(bpy)2 ipH]2+ with the 1,4-benzoquinone quencher, formed in the ground state. Within the hydrogen bonded complex, the ruthenium centre acts as the electron donor, while the ipH ligand acts as the proton donor to the hydrogen bonded 1,4-benzoquinone that acts simultaneously both as the electron and proton acceptor. It is proposed that the static quenching in the hydrogen bonded [Ru(bpy)2 ipH]2+ -1,4-benzoquinone pairs occurs involving the PCET mechanism, while the dynamic quenching occurs through the simple ET mechanism, on diffusional encounter of the isolated 1,4-benzoquinone with the excited [Ru(bpy)2 ipH]2+ complex. The occurrence of broad TA bands around 420-430 nm suggests formation of both 1,4-benzoquinone radical anion as well as the 1,4-benzosemiquinone radical by the interaction of excited [Ru(bpy)2 ipH]2+ with 1,4-benzoquinone, thus supporting the ET process in the studied system.
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Affiliation(s)
- Rahul V Khade
- Department of Chemistry, Savitribai Phule Pune University, Pune, 411007, India
| | | | - Haridas Pal
- Radiation & Photochemistry Division, Bhabha Atomic Research Centre, Mumbai, 400085, India
| | - Avinash S Kumbhar
- Department of Chemistry, Savitribai Phule Pune University, Pune, 411007, India
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8
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Bowring MA, Bradshaw LR, Parada GA, Pollock TP, Fernández-Terán RJ, Kolmar SS, Mercado BQ, Schlenker CW, Gamelin DR, Mayer JM. Activationless Multiple-Site Concerted Proton-Electron Tunneling. J Am Chem Soc 2018; 140:7449-7452. [PMID: 29847111 PMCID: PMC6310214 DOI: 10.1021/jacs.8b04455] [Citation(s) in RCA: 21] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The transfer of protons and electrons is key to energy conversion and storage, from photosynthesis to fuel cells. Increased understanding and control of these processes are needed. A new anthracene-phenol-pyridine molecular triad was designed to undergo fast photoinduced multiple-site concerted proton-electron transfer (MS-CPET), with the phenol moiety transferring an electron to the photoexcited anthracene and a proton to the pyridine. Fluorescence quenching and transient absorption experiments in solutions and glasses show rapid MS-CPET (3.2 × 1010 s-1 at 298 K). From 5.5 to 90 K, the reaction rate and kinetic isotope effect (KIE) are independent of temperature, with zero Arrhenius activation energy. From 145 to 350 K, there are only slight changes with temperature. This MS-CPET reaction thus occurs by tunneling of both the proton and electron, in different directions. Since the reaction proceeds without significant thermal activation energy, the rate constant indicates the magnitude of the electron/proton double tunneling probability.
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Affiliation(s)
- Miriam A. Bowring
- Department of Chemistry, Yale University, New Haven, Connecticut 06520, United States
- Department of Chemistry, University of Washington, Seattle, Washington 98195, United States
- Department of Chemistry, Reed College, Portland, Oregon 97202, United States
| | - Liam R. Bradshaw
- Department of Chemistry, University of Washington, Seattle, Washington 98195, United States
| | - Giovanny A. Parada
- Department of Chemistry, Yale University, New Haven, Connecticut 06520, United States
| | - Timothy P. Pollock
- Department of Chemistry, University of Washington, Seattle, Washington 98195, United States
| | | | - Scott S. Kolmar
- Department of Chemistry, Yale University, New Haven, Connecticut 06520, United States
| | - Brandon Q. Mercado
- Department of Chemistry, Yale University, New Haven, Connecticut 06520, United States
| | - Cody W. Schlenker
- Department of Chemistry, University of Washington, Seattle, Washington 98195, United States
| | - Daniel R. Gamelin
- Department of Chemistry, University of Washington, Seattle, Washington 98195, United States
| | - James M. Mayer
- Department of Chemistry, Yale University, New Haven, Connecticut 06520, United States
- Department of Chemistry, University of Washington, Seattle, Washington 98195, United States
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9
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Sundin E, Abrahamsson M. Long-lived charge separation in dye–semiconductor assemblies: a pathway to multi-electron transfer reactions. Chem Commun (Camb) 2018; 54:5289-5298. [DOI: 10.1039/c8cc01071d] [Citation(s) in RCA: 20] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Key approaches to achieve long-lived charge separation and promote conduction band mediated electron transfer in dye-sensitized semiconductor assemblies.
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Affiliation(s)
- Elin Sundin
- Department of Chemistry and Chemical Engineering
- Chalmers University of Technology
- 412 96 Gothenburg
- Sweden
| | - Maria Abrahamsson
- Department of Chemistry and Chemical Engineering
- Chalmers University of Technology
- 412 96 Gothenburg
- Sweden
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10
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Rodríguez-Prieto F, Corbelle CC, Fernández B, Pedro JA, Ríos Rodríguez MC, Mosquera M. Fluorescence quenching of the N-methylquinolinium cation by pairs of water or alcohol molecules. Phys Chem Chem Phys 2018; 20:307-316. [DOI: 10.1039/c7cp07057h] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
The proposed mechanism involves an electron transfer from H2O/ROH to the excited quinolinium, concerted with proton transfer to the second hydroxy molecule.
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Affiliation(s)
- Flor Rodríguez-Prieto
- Centro Singular de Investigación en Química Biolóxica e Materiais Moleculares (CIQUS)
- Universidade de Santiago de Compostela
- E-15782 Santiago de Compostela
- Spain
- Departamento de Química Física
| | - Carlos Costa Corbelle
- Departamento de Química Física
- Facultade de Química
- Universidade de Santiago de Compostela
- E-15782 Santiago de Compostela
- Spain
| | - Berta Fernández
- Departamento de Química Física
- Facultade de Química
- Universidade de Santiago de Compostela
- E-15782 Santiago de Compostela
- Spain
| | - Jorge A. Pedro
- Centro Singular de Investigación en Química Biolóxica e Materiais Moleculares (CIQUS)
- Universidade de Santiago de Compostela
- E-15782 Santiago de Compostela
- Spain
| | - M. Carmen Ríos Rodríguez
- Centro Singular de Investigación en Química Biolóxica e Materiais Moleculares (CIQUS)
- Universidade de Santiago de Compostela
- E-15782 Santiago de Compostela
- Spain
- Departamento de Química Física
| | - Manuel Mosquera
- Centro Singular de Investigación en Química Biolóxica e Materiais Moleculares (CIQUS)
- Universidade de Santiago de Compostela
- E-15782 Santiago de Compostela
- Spain
- Departamento de Química Física
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11
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Lennox JC, Dempsey JL. Influence of Proton Acceptors on the Proton-Coupled Electron Transfer Reaction Kinetics of a Ruthenium-Tyrosine Complex. J Phys Chem B 2017; 121:10530-10542. [PMID: 29130684 DOI: 10.1021/acs.jpcb.7b06443] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
A polypyridyl ruthenium complex with fluorinated bipyridine ligands and a covalently bound tyrosine moiety was synthesized, and its photo-induced proton-coupled electron transfer (PCET) reactivity in acetonitrile was investigated with transient absorption spectroscopy. Using flash-quench methodology with methyl viologen as an oxidative quencher, a Ru3+ species is generated that is capable of initiating the intramolecular PCET oxidation of the tyrosine moiety. Using a series of substituted pyridine bases, the reaction kinetics were found to vary as a function of proton acceptor concentration and identity, with no significant H/D kinetic isotope effect. Through analysis of the kinetics traces and comparison to a control complex without the tyrosine moiety, PCET reactivity was found to proceed through an equilibrium electron transfer followed by proton transfer (ET-PT) pathway in which irreversible deprotonation of the tyrosine radical cation shifts the ET equilibrium, conferring a base dependence on the reaction. Comprehensive kinetics modeling allowed for deconvolution of complex kinetics and determination of rate constants for each elementary step. Across the five pyridine bases explored, spanning a range of 4.2 pKa units, a linear free-energy relationship was found for the proton transfer rate constant with a slope of 0.32. These findings highlight the influence that proton transfer driving force exerts on PCET reaction kinetics.
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Affiliation(s)
- J Christian Lennox
- Department of Chemistry, University of North Carolina , Chapel Hill, North Carolina 27599-3290, United States
| | - Jillian L Dempsey
- Department of Chemistry, University of North Carolina , Chapel Hill, North Carolina 27599-3290, United States
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12
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Dey A, Dana J, Aute S, Maity P, Das A, Ghosh HN. Proton-Coupled Electron-Transfer Processes in Ultrafast Time Domain: Evidence for Effects of Hydrogen-Bond Stabilization on Photoinduced Electron Transfer. Chemistry 2017; 23:3455-3465. [DOI: 10.1002/chem.201605594] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/30/2016] [Indexed: 11/11/2022]
Affiliation(s)
- Ananta Dey
- Organic Chemistry Division CSIR; National Chemical Laboratory; Pune, Maharashtra 411008 India
| | - Jayanta Dana
- Radiation and Photochemistry Division; Bhabha Atomic Research Centre; Mumbai 400085 India
| | - Sunil Aute
- Organic Chemistry Division CSIR; National Chemical Laboratory; Pune, Maharashtra 411008 India
| | - Partha Maity
- Radiation and Photochemistry Division; Bhabha Atomic Research Centre; Mumbai 400085 India
| | - Amitava Das
- Organic Chemistry Division CSIR; National Chemical Laboratory; Pune, Maharashtra 411008 India
- CSIR-Central Salt and Marine Chemicals Research Institute; Bhavnagar 364002 Gujarat India
| | - Hirendra N. Ghosh
- Radiation and Photochemistry Division; Bhabha Atomic Research Centre; Mumbai 400085 India
- Institute of Nano Science and Technology; Mohali Punjab 160062 India
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13
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Glover SD, Parada GA, Markle TF, Ott S, Hammarström L. Isolating the Effects of the Proton Tunneling Distance on Proton-Coupled Electron Transfer in a Series of Homologous Tyrosine-Base Model Compounds. J Am Chem Soc 2017; 139:2090-2101. [DOI: 10.1021/jacs.6b12531] [Citation(s) in RCA: 36] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Starla D. Glover
- Department of Chemistry−Ångström, Uppsala University, Box
532, SE-751 20, Uppsala, Sweden
| | - Giovanny A. Parada
- Department of Chemistry−Ångström, Uppsala University, Box
532, SE-751 20, Uppsala, Sweden
| | - Todd F. Markle
- Department of Chemistry−Ångström, Uppsala University, Box
532, SE-751 20, Uppsala, Sweden
| | - Sascha Ott
- Department of Chemistry−Ångström, Uppsala University, Box
532, SE-751 20, Uppsala, Sweden
| | - Leif Hammarström
- Department of Chemistry−Ångström, Uppsala University, Box
532, SE-751 20, Uppsala, Sweden
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14
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Pannwitz A, Prescimone A, Wenger OS. Ruthenium(II)-Pyridylimidazole Complexes as Photoreductants and PCET Reagents. Eur J Inorg Chem 2017. [DOI: 10.1002/ejic.201601403] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
Affiliation(s)
- Andrea Pannwitz
- Department of Chemistry; University of Basel; St. Johanns-Ring 19 and Spitalstrasse 51 4056 Basel Switzerland
| | - Alessandro Prescimone
- Department of Chemistry; University of Basel; St. Johanns-Ring 19 and Spitalstrasse 51 4056 Basel Switzerland
| | - Oliver S. Wenger
- Department of Chemistry; University of Basel; St. Johanns-Ring 19 and Spitalstrasse 51 4056 Basel Switzerland
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Kuss-Petermann M, Wenger OS. Unusual distance dependences of electron transfer rates. Phys Chem Chem Phys 2016; 18:18657-64. [DOI: 10.1039/c6cp03124b] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
There are regimes in which electron transfer rates increase with increasing donor–acceptor distance, leading to rate maxima at large donor–acceptor separations.
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Welker EA, Tiley BL, Sasaran CM, Zuchero MA, Tong WS, Vettleson MJ, Richards RA, Geruntho JG, Stoll S, Wolbach JP, Rhile IJ. Conformational Change with Steric Interactions Affects the Inner Sphere Component of Concerted Proton-Electron Transfer in a Pyridyl-Appended Radical Cation System. J Org Chem 2015; 80:8705-12. [PMID: 26270193 PMCID: PMC10758225 DOI: 10.1021/acs.joc.5b01427] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Proton-coupled electron transfer (PCET) model systems combine one-electron oxidants and bases to generate net hydrogen atom acceptors. We have generated two persistent pyridyl-appended radical cations: 10-(pyrid-2-yl)-10H-phenothiazinium (PPT•+) and 3-(pyrid-2-yl)-10-methyl-10H-phenothiazinium (MPTP•+). EPR spectra and corresponding calculations indicate phenothiazinium radical cations with minimal spin on the pyridine nitrogen. Addition of hindered phenols causes the radical cations to decay, and protonated products and the corresponding phenoxyl radicals to form. The ΔG° values for the formation of intermediates (determined through cyclic voltammetry and pKa measurements) rule out a stepwise mechanism, and kinetic isotope effects support concerted proton–electron transfer (CPET) as the mechanism. Calculations indicate that the reaction of PPT•+ + tBu3PhOH undergoes a significant conformational change with steric interactions on the diabatic surface while maintaining the hydrogen bond; in contrast, MPTP•+ + tBu3PhOH maintains its conformation throughout the reaction. This difference is reflected in both experiment and calculations with ΔG(⧧)MPTP•+ < ΔG(⧧)PPT•+ despite ΔG°MPTP•+ > ΔG°PPT•+. Experimental results with 2,6-di-tert-butyl-4-methoxyphenol are similar. Hence, despite the structural similarity between the compounds, differences in the inner sphere component for CPET affect the kinetics.
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Affiliation(s)
- Evan A. Welker
- Department of Chemistry and Biochemistry, Albright College, Reading, PA 19610-5234, United States
| | - Brittney L. Tiley
- Department of Chemistry and Biochemistry, Albright College, Reading, PA 19610-5234, United States
| | - Crina M. Sasaran
- Department of Chemistry and Biochemistry, Albright College, Reading, PA 19610-5234, United States
| | - Matthew A. Zuchero
- Department of Chemistry and Biochemistry, Albright College, Reading, PA 19610-5234, United States
| | - Wing-Sze Tong
- Department of Chemistry and Biochemistry, Albright College, Reading, PA 19610-5234, United States
| | - Melissa J. Vettleson
- Department of Chemistry and Biochemistry, Albright College, Reading, PA 19610-5234, United States
| | - Robert A. Richards
- Department of Chemistry and Biochemistry, Albright College, Reading, PA 19610-5234, United States
| | - Jonathan G. Geruntho
- Department of Chemistry and Biochemistry, Albright College, Reading, PA 19610-5234, United States
| | - Stefan Stoll
- Department of Chemistry, University of Washington, Seattle, WA 98195-1700, United States
| | | | - Ian J. Rhile
- Department of Chemistry and Biochemistry, Albright College, Reading, PA 19610-5234, United States
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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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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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