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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Bora JR, Mahalakshmi R. Photoradical-Mediated Catalyst-Independent Protein Cross-Link with Unusual Fluorescence Properties. Chembiochem 2023; 24:e202300380. [PMID: 37232210 PMCID: PMC7615464 DOI: 10.1002/cbic.202300380] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/24/2023] [Revised: 05/25/2023] [Accepted: 05/26/2023] [Indexed: 05/27/2023]
Abstract
Photo-actively modified natural amino acids have served as lucrative probes for precise mapping of the dynamics, interaction networks, and turnover of cytosolic proteins both in vivo and ex vivo. In our attempts to extend the utility of photoreactive reporters to map the molecular characteristics of vital membrane proteins, we carried out site-selective incorporation of 7-fluoro-indole in the human mitochondrial outer membrane protein VDAC2 (voltage-dependent anion channel isoform 2), with the aim of generating Trp-Phe/Tyr cross-links. Prolonged irradiation at 282 nm provided us with a surprisingly unusual fluorophore that displayed sizably red-shifted excitation (λex-max =280 nm→360 nm) and emission (λem-max =330 nm→430 nm) spectra that was reversible with organic solvents. By measuring the kinetics of the photo-activated cross-linking with a library of hVDAC2 variants, we demonstrate that formation of this unusual fluorophore is kinetically retarded, independent of tryptophan, and is site-specific. Using other membrane (Tom40 and Sam50) and cytosolic (MscR and DNA Pol I) proteins, we additionally show that formation of this fluorophore is protein-independent. Our findings reveal the photoradical-mediated accumulation of reversible tyrosine cross-links, with unusual fluorescent properties. Our findings have immediate applications in protein biochemistry and UV-mediated protein aggregation and cellular damage, opening avenues for formulating therapeutics that prolong cell viability in humans.
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Affiliation(s)
- Jinam Ravindra Bora
- Molecular Biophysics Laboratory Department of Biological Sciences Indian Institute of Science Education and Research Bhopal Bypass Road, Bhauri, Bhopal 462066, Madhya Pradesh (India)
| | - Radhakrishnan Mahalakshmi
- Molecular Biophysics Laboratory Department of Biological Sciences Indian Institute of Science Education and Research Bhopal Bypass Road, Bhauri, Bhopal 462066, Madhya Pradesh (India)
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3
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Hwang D, Wrigley LM, Lee M, Sobolewski AL, Domcke W, Schlenker CW. Local Hydrogen Bonding Determines Branching Pathways in Intermolecular Heptazine Photochemistry. J Phys Chem B 2023. [PMID: 37471476 DOI: 10.1021/acs.jpcb.3c01397] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 07/22/2023]
Abstract
Heptazine is the molecular core of the widely studied photocatalyst carbon nitride. By analyzing the excited-state intermolecular proton-coupled electron-transfer (PCET) reaction between a heptazine derivative and a hydrogen-atom donor substrate, we are able to spectroscopically identify the resultant heptazinyl reactive radical species on a picosecond time scale. We provide detailed spectroscopic characterization of the tri-anisole heptazine:4-methoxyphenol hydrogen-bonded intermolecular complex (TAHz:MeOPhOH), using femtosecond transient absorption spectroscopy and global analysis, to reveal distinct product absorption signatures at ∼520, 1250, and 1600 nm. We assign these product peaks to the hydrogenated TAHz radical (TAHzH•) based on control experiments utilizing 1,4-dimethoxybenzene (DMB), which initiates electron transfer without concomitant proton transfer, i.e., no excited-state PCET. Additional control experiments with radical quenchers, protonation agents, and UV-vis-NIR spectroelectrochemistry also corroborate our product peak assignments. These spectral assignments allowed us to monitor the influence of the local hydrogen-bonding environment on the resulting evolution of photochemical products from excited-state PCET of heptazines. We observe that the preassociation of heptazine with the substrate in solution is extremely sensitive to the hydrogen-bond-accepting character of the solvent. This sensitivity directly influences which product signatures we detect with time-resolved spectroscopy. The spectral signature of the TAHzH• radical assigned in this work will facilitate future in-depth analysis of heptazine and carbon nitride photochemistry. Our results may also be utilized for designing improved PCET-based photochemical systems that will require precise control over local molecular environments. Examples include applications such as preparative synthesis involving organic photoredox catalysis, on-site solar water purification, as well as photocatalytic water splitting and artificial photosynthesis.
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Affiliation(s)
- Doyk Hwang
- Department of Chemistry, University of Washington, Seattle, Washington 98195, United States
| | - Liam M Wrigley
- Department of Chemistry, University of Washington, Seattle, Washington 98195, United States
| | - Micah Lee
- Department of Chemistry, University of Washington, Seattle, Washington 98195, United States
| | | | - Wolfgang Domcke
- Department of Chemistry, Technical University of Munich, D-85747 Garching, Germany
| | - Cody W Schlenker
- Department of Chemistry, University of Washington, Seattle, Washington 98195, United States
- Molecular Engineering & Sciences Institute, University of Washington, Seattle, Washington 98195-1652, United States
- Clean Energy Institute, University of Washington, Seattle, Washington 98195-1653, United States
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4
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Zhu M, Wang S, Li Z, Li J, Xu Z, Liu X, Huang X. Tyrosine residues initiated photopolymerization in living organisms. Nat Commun 2023; 14:3598. [PMID: 37328460 PMCID: PMC10276049 DOI: 10.1038/s41467-023-39286-8] [Citation(s) in RCA: 4] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/09/2022] [Accepted: 06/07/2023] [Indexed: 06/18/2023] Open
Abstract
Towards intracellular engineering of living organisms, the development of new biocompatible polymerization system applicable for an intrinsically non-natural macromolecules synthesis for modulating living organism function/behavior is a key step. Herein, we find that the tyrosine residues in the cofactor-free proteins can be employed to mediate controlled radical polymerization under 405 nm light. A proton-coupled electron transfer (PCET) mechanism between the excited-state TyrOH* residue in proteins and the monomer or the chain transfer agent is confirmed. By using Tyr-containing proteins, a wide range of well-defined polymers are successfully generated. Especially, the developed photopolymerization system shows good biocompatibility, which can achieve in-situ extracellular polymerization from the surface of yeast cells for agglutination/anti-agglutination functional manipulation or intracellular polymerization inside yeast cells, respectively. Besides providing a universal aqueous photopolymerization system, this study should contribute a new way to generate various non-natural polymers in vitro or in vivo to engineer living organism functions and behaviours.
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Affiliation(s)
- Mei Zhu
- MIIT Key Laboratory of Critical Materials Technology for New Energy Conversion and Storage, School of Chemistry and Chemical Engineering, Harbin Institute of Technology, Harbin, 150001, P. R. China
| | - Shengliang Wang
- MIIT Key Laboratory of Critical Materials Technology for New Energy Conversion and Storage, School of Chemistry and Chemical Engineering, Harbin Institute of Technology, Harbin, 150001, P. R. China
| | - Zhenhui Li
- MIIT Key Laboratory of Critical Materials Technology for New Energy Conversion and Storage, School of Chemistry and Chemical Engineering, Harbin Institute of Technology, Harbin, 150001, P. R. China
| | - Junbo Li
- MIIT Key Laboratory of Critical Materials Technology for New Energy Conversion and Storage, School of Chemistry and Chemical Engineering, Harbin Institute of Technology, Harbin, 150001, P. R. China
| | - Zhijun Xu
- MIIT Key Laboratory of Critical Materials Technology for New Energy Conversion and Storage, School of Chemistry and Chemical Engineering, Harbin Institute of Technology, Harbin, 150001, P. R. China
| | - Xiaoman Liu
- MIIT Key Laboratory of Critical Materials Technology for New Energy Conversion and Storage, School of Chemistry and Chemical Engineering, Harbin Institute of Technology, Harbin, 150001, P. R. China.
| | - Xin Huang
- MIIT Key Laboratory of Critical Materials Technology for New Energy Conversion and Storage, School of Chemistry and Chemical Engineering, Harbin Institute of Technology, Harbin, 150001, P. R. China.
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5
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Zhou Z, Kong X, Liu T. Applications of Proton-Coupled Electron Transfer in Organic Synthesis. CHINESE J ORG CHEM 2021. [DOI: 10.6023/cjoc202106001] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
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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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Swords WB, Meyer GJ, Hammarström L. Excited-state proton-coupled electron transfer within ion pairs. Chem Sci 2020; 11:3460-3473. [PMID: 34109019 PMCID: PMC8152629 DOI: 10.1039/c9sc04941j] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
The use of light to drive proton-coupled electron transfer (PCET) reactions has received growing interest, with recent focus on the direct use of excited states in PCET reactions (ES-PCET). Electrostatic ion pairs provide a scaffold to reduce reaction orders and have facilitated many discoveries in electron-transfer chemistry. Their use, however, has not translated to PCET. Herein, we show that ion pairs, formed solely through electrostatic interactions, provide a general, facile means to study an ES-PCET mechanism. These ion pairs formed readily between salicylate anions and tetracationic ruthenium complexes in acetonitrile solution. Upon light excitation, quenching of the ruthenium excited state occurred through ES-PCET oxidation of salicylate within the ion pair. Transient absorption spectroscopy identified the reduced ruthenium complex and oxidized salicylate radical as the primary photoproducts of this reaction. The reduced reaction order due to ion pairing allowed the first-order PCET rate constants to be directly measured through nanosecond photoluminescence spectroscopy. These PCET rate constants saturated at larger driving forces consistent with approaching the Marcus barrierless region. Surprisingly, a proton-transfer tautomer of salicylate, with the proton localized on the carboxylate functional group, was present in acetonitrile. A pre-equilibrium model based on this tautomerization provided non-adiabatic electron-transfer rate constants that were well described by Marcus theory. Electrostatic ion pairs were critical to our ability to investigate this PCET mechanism without the need to covalently link the donor and acceptor or introduce specific hydrogen bonding sites that could compete in alternate PCET pathways.
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Affiliation(s)
- Wesley B Swords
- Department of Chemistry, Ångström Laboratories, Uppsala University Box 523 SE75120 Uppsala Sweden .,Department of Chemistry, University of North Carolina at Chapel Hill Chapel Hill 27599 USA
| | - Gerald J Meyer
- Department of Chemistry, University of North Carolina at Chapel Hill Chapel Hill 27599 USA
| | - Leif Hammarström
- Department of Chemistry, Ångström Laboratories, Uppsala University Box 523 SE75120 Uppsala Sweden
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8
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Biswas S, Bhattacharya I, Chakraborty T. Identification of an Emitting Metastable State of p-Fluorophenol-Ammonia 1:2 Complex by Laser-Induced Fluorescence Spectroscopy. J Phys Chem A 2019; 123:10563-10570. [PMID: 31714082 DOI: 10.1021/acs.jpca.9b07958] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
We have demonstrated here, for the first time to our knowledge, the formation of an emitting metastable species upon lowest electronic excitation (S1) of a hydrogen-bonded 1:2 complex of para-fluorophenol (pFP) with ammonia (NH3), which is known to be one of the smallest reactive complexes to undergo excited state H-atom transfer (HAT) reaction to produce •NH4(NH3) radical fragment. The emission spectrum of the species is characterized to be red-shifted, broad, and structureless. From the viewpoint of energy balance, an excited state proton transfer (ESPT) is unfavorable, but according to predicted electronic structure parameters, the metastable state species could be stabilized by charge transfer (CT) interaction at the hydrogen-bonded geometry of the complex. We propose that this species could act as an intermediate to the HAT process in the excited state. The observation of such a state could be valuable to understand the complex dynamics of similar events in biologically relevant systems.
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Affiliation(s)
- Souvick Biswas
- School of Chemical Sciences , Indian Association for the Cultivation of Science , 2A Raja S C Mullick Road, Jadavpur , Kolkata 700032 , India
| | - Indrani Bhattacharya
- School of Chemical Sciences , Indian Association for the Cultivation of Science , 2A Raja S C Mullick Road, Jadavpur , Kolkata 700032 , India
| | - Tapas Chakraborty
- School of Chemical Sciences , Indian Association for the Cultivation of Science , 2A Raja S C Mullick Road, Jadavpur , Kolkata 700032 , India
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9
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Yee EF, Dzikovski B, Crane BR. Tuning Radical Relay Residues by Proton Management Rescues Protein Electron Hopping. J Am Chem Soc 2019; 141:17571-17587. [PMID: 31603693 DOI: 10.1021/jacs.9b05715] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/11/2023]
Abstract
Transient tyrosine and tryptophan radicals play key roles in the electron transfer (ET) reactions of photosystem (PS) II, ribonucleotide reductase (RNR), photolyase, and many other proteins. However, Tyr and Trp are not functionally interchangeable, and the factors controlling their reactivity are often unclear. Cytochrome c peroxidase (CcP) employs a Trp191•+ radical to oxidize reduced cytochrome c (Cc). Although a Tyr191 replacement also forms a stable radical, it does not support rapid ET from Cc. Here we probe the redox properties of CcP Y191 by non-natural amino acid substitution, altering the ET driving force and manipulating the protic environment of Y191. Higher potential fluorotyrosine residues increase ET rates marginally, but only addition of a hydrogen bond donor to Tyr191• (via Leu232His or Glu) substantially alters activity by increasing the ET rate by nearly 30-fold. ESR and ESEEM spectroscopies, crystallography, and pH-dependent ET kinetics provide strong evidence for hydrogen bond formation to Y191• by His232/Glu232. Rate measurements and rapid freeze quench ESR spectroscopy further reveal differences in radical propagation and Cc oxidation that support an increased Y191• formal potential of ∼200 mV in the presence of E232. Hence, Y191 inactivity results from a potential drop owing to Y191•+ deprotonation. Incorporation of a well-positioned base to accept and donate back a hydrogen bond upshifts the Tyr• potential into a range where it can effectively oxidize Cc. These findings have implications for the YZ/YD radicals of PS II, hole-hopping in RNR and cryptochrome, and engineering proteins for long-range ET reactions.
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Affiliation(s)
- Estella F Yee
- Department of Chemistry and Chemical Biology , Cornell University , Ithaca , New York 14853 , United States
| | - Boris Dzikovski
- Department of Chemistry and Chemical Biology , Cornell University , Ithaca , New York 14853 , United States.,National Biomedical Center for Advanced ESR Technologies (ACERT) , Cornell University , Ithaca , New York 14850 , United States
| | - Brian R Crane
- Department of Chemistry and Chemical Biology , Cornell University , Ithaca , New York 14853 , United States
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10
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Lennox JC, Danilov EO, Dempsey JL. Delayed photoacidity produced through the triplet-triplet annihilation of a neutral pyranine derivative. Phys Chem Chem Phys 2019; 21:16353-16358. [PMID: 31309943 DOI: 10.1039/c9cp02929j] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
A novel pyranine derivative, EtHPTA-OH, was synthesized via the substitution of the anionic sulfonate groups with neutral diethylsulfonamide groups. The photophysical and photochemical properties of EtHPTA-OH were studied using photoluminescence quenching and transient absorption spectroscopy. The singlet state of EtHPTA-OH was found to be highly photoacidic (pKa* = 8.74 in acetonitrile). A series of aniline and pyridine bases were used to investigate excited-state proton transfer (ESPT) from singlet EtHPTA-OH, and rate constants for singlet quenching via ESPT were determined (kq = 5.18 × 109 to 1.05 × 1010 M-1 s-1). EtHPTA-OH was also found to exhibit a long-lived triplet state which reacts through a triplet-triplet annihilation (TTA) process to reform singlet EtHPTA-OH on timescales of up to 80 μs. Detection of ESPT photoproducts on timescales comparable to that of TTA singlet regeneration provides strong evidence for photoacidic behavior stemming from the regenerated singlet EtHPTA-OH.
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Affiliation(s)
- J Christian Lennox
- Department of Chemistry, University of North Carolina, Chapel Hill, North Carolina, USA27599.
| | - Evgeny O Danilov
- Department of Chemistry, North Carolina State University, Raleigh, North Carolina, USA27695
| | - Jillian L Dempsey
- Department of Chemistry, University of North Carolina, Chapel Hill, North Carolina, USA27599.
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11
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Dey A, Dana J, Aute S, Das A, Ghosh HN. Hydrogen bond assisted photoinduced intramolecular electron transfer and proton coupled electron transfer in an ultrafast time domain using a ruthenium-anthraquinone dyad. Photochem Photobiol Sci 2019; 18:2430-2441. [DOI: 10.1039/c9pp00135b] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
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.
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Affiliation(s)
- Ananta Dey
- CSIR-Central salt & Marine Chemicals Research Institute
- Bhavnagar 364002
- India
- Academy of Scientific and Innovative Research (AcSIR)
- Ghaziabad – 201002
| | - Jayanta Dana
- Radiation & Photochemistry Division
- Bhabha Atomic Research Centre
- Mumbai – 400085
- India
| | - Sunil Aute
- Academy of Scientific and Innovative Research (AcSIR)
- Ghaziabad – 201002
- India
- dCSIR National chemical Laboratory
- Pune
| | - Amitava Das
- CSIR-Central salt & Marine Chemicals Research Institute
- Bhavnagar 364002
- India
- Academy of Scientific and Innovative Research (AcSIR)
- Ghaziabad – 201002
| | - Hirendra N. Ghosh
- Radiation & Photochemistry Division
- Bhabha Atomic Research Centre
- Mumbai – 400085
- India
- Institute of Nano Science and Technology
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12
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Pannwitz A, Wenger OS. Recent advances in bioinspired proton-coupled electron transfer. Dalton Trans 2019; 48:5861-5868. [DOI: 10.1039/c8dt04373f] [Citation(s) in RCA: 18] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/17/2023]
Abstract
Fundamental aspects of PCET continue to attract attention. Understanding this reaction type is desirable for small-molecule activation and solar energy conversion.
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Affiliation(s)
- Andrea Pannwitz
- Department of Chemistry
- University of Basel
- 4056 Basel
- Switzerland
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13
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Lymar SV, Manbeck GF, Polyansky DE. Hydrogen bonding between hydroxylic donors and MLCT-excited Ru(bpy) 2(bpz) 2+ complex: implications for photoinduced electron–proton transfer. Chem Commun (Camb) 2019; 55:5870-5873. [DOI: 10.1039/c9cc01896d] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Rates of electron–proton transfer within the H-bonded exciplexes are evaluated using the free energy correlation with donor's H-bonding acidity.
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14
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Natali M, Amati A, Demitri N, Iengo E. Formation of a long-lived radical pair in a Sn(iv) porphyrin–di(l-tyrosinato) conjugate driven by proton-coupled electron-transfer. Chem Commun (Camb) 2018; 54:6148-6152. [DOI: 10.1039/c8cc03441a] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
A surprisingly long-lived radical pair state is achieved in a tin-porphyrin/l-tyrosine conjugate by exploiting a photochemical PCET quenching mechanism.
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Affiliation(s)
- Mirco Natali
- Department of Chemical and Pharmaceutical Sciences
- University of Ferrara and Centro Interuniversitario per la Conversione Chimica dell’Energia Solare (SOLARCHEM)
- 44121 Ferrara
- Italy
| | - Agnese Amati
- Department of Chemical and Pharmaceutical Sciences
- University of Trieste
- 34127 Trieste
- Italy
| | - Nicola Demitri
- Elettra–Sincrotrone Trieste
- S.S. 14 Km 163.5 in Area Science Park
- 34149 Basovizza, Trieste
- Italy
| | - Elisabetta Iengo
- Department of Chemical and Pharmaceutical Sciences
- University of Trieste
- 34127 Trieste
- Italy
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15
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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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16
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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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17
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Pannwitz A, Wenger OS. Photoinduced Electron Transfer Coupled to Donor Deprotonation and Acceptor Protonation in a Molecular Triad Mimicking Photosystem II. J Am Chem Soc 2017; 139:13308-13311. [PMID: 28906113 DOI: 10.1021/jacs.7b08761] [Citation(s) in RCA: 43] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
The first artificial donor-sensitizer-acceptor compound in which photoinduced long-range electron transfer is coupled to donor deprotonation and acceptor protonation is reported. The long-lived photoproduct stores energy in the form of a radical pair state in which the charges of the donor and the acceptor remain unchanged, much in contrast to previously investigated systems that exhibit charge-separated states comprised of electron-hole pairs. This finding is relevant for light-driven accumulation of redox equivalents, because it exemplifies how the buildup of charge can be avoided yet light energy can be stored. Proton-coupled electron transfer (PCET) reactions at a phenol donor and a monoquat acceptor triggered by excitation of a Ru(II) sensitizer enable this form of photochemical energy storage. Our triad emulates photosystem II more closely than previously investigated systems, because tyrosine Z is oxidized and deprotonated, whereas plastoquinone B is reduced and protonated.
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Affiliation(s)
- Andrea Pannwitz
- Department of Chemistry, University of Basel , St. Johanns-Ring 19, 4056 Basel, Switzerland
| | - Oliver S Wenger
- Department of Chemistry, University of Basel , St. Johanns-Ring 19, 4056 Basel, Switzerland
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18
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Lymar SV, Ertem MZ, Lewandowska-Andralojc A, Polyansky DE. Role of Hydrogen Bonding in Photoinduced Electron-Proton Transfer from Phenols to a Polypyridine Ru Complex with a Proton-Accepting Ligand. J Phys Chem Lett 2017; 8:4043-4048. [PMID: 28792768 DOI: 10.1021/acs.jpclett.7b01614] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/07/2023]
Abstract
Electron-proton transfer (EPT) from phenols to a triplet metal-to-ligand charge transfer (MLCT)-excited Ru polypyridine complex containing an uncoordinated nitrogen site, 1(T), can be described by a kinetic model that accounts for the H-bonding of 1(T) to phenol, 1(T) to solvent, and phenol to solvent. The latter plays a major role in the kinetic solvent effect and commonly precludes simultaneous determination of the EPT rate constant and 1(T)-phenol H-bonding constant. A number of these quantities previously reported for similar systems are shown to be in error due to inconsistent data analysis. Control experiments replacing either 1(T) by its structural isomer with a sterically screened nitrogen site or phenol by its H-bonding surrogate, trifluoroethanol, and the observation of negative activation enthalpies for the overall reactions between 1(T) and phenols lend support to the proposed model and provide evidence for the formation of a precursor H-bonded complex between the reactants, which is a prerequisite for EPT.
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Affiliation(s)
- Sergei V Lymar
- Chemistry Department, Brookhaven National Laboratory , Upton, New York 11973-5000, United States
| | - Mehmed Z Ertem
- Chemistry Department, Brookhaven National Laboratory , Upton, New York 11973-5000, United States
| | | | - Dmitry E Polyansky
- Chemistry Department, Brookhaven National Laboratory , Upton, New York 11973-5000, United States
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19
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Kuss-Petermann M, Wenger OS. Exceptionally Long-Lived Photodriven Multi-Electron Storage without Sacrificial Reagents. Chemistry 2017; 23:10808-10814. [DOI: 10.1002/chem.201701456] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/01/2017] [Indexed: 11/11/2022]
Affiliation(s)
- Martin Kuss-Petermann
- Department of Chemistry; University of Basel; St. Johanns-Ring 19 4056 Basel Switzerland
| | - Oliver S. Wenger
- Department of Chemistry; University of Basel; St. Johanns-Ring 19 4056 Basel Switzerland
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20
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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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21
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Zeng CH, Luo Z, Yao J. Porous hydrogen-bonded organic–inorganic frameworks: weak interactions and selective dye filtration. CrystEngComm 2017. [DOI: 10.1039/c6ce02367c] [Citation(s) in RCA: 25] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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22
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Manbeck GF, Fujita E, Concepcion JJ. Proton-Coupled Electron Transfer in a Strongly Coupled Photosystem II-Inspired Chromophore–Imidazole–Phenol Complex: Stepwise Oxidation and Concerted Reduction. J Am Chem Soc 2016; 138:11536-49. [DOI: 10.1021/jacs.6b03506] [Citation(s) in RCA: 44] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Gerald F. Manbeck
- Chemistry Division, Brookhaven National Laboratory, Upton, New York 11973-5000, United States
| | - Etsuko Fujita
- Chemistry Division, Brookhaven National Laboratory, Upton, New York 11973-5000, United States
| | - Javier J. Concepcion
- Chemistry Division, Brookhaven National Laboratory, Upton, New York 11973-5000, United States
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23
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Markle TF, Zhang MT, Santoni MP, Johannissen LO, Hammarström L. Proton-Coupled Electron Transfer in a Series of Ruthenium-Linked Tyrosines with Internal Bases: Evaluation of a Tunneling Model for Experimental Temperature-Dependent Kinetics. J Phys Chem B 2016; 120:9308-21. [DOI: 10.1021/acs.jpcb.6b05885] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Todd F. Markle
- Department of Chemistry − Ångström
Laboratory, Uppsala University, P.O. Box 523, S-75120 Uppsala, Sweden
| | - Ming-Tian Zhang
- Department of Chemistry − Ångström
Laboratory, Uppsala University, P.O. Box 523, S-75120 Uppsala, Sweden
| | - Marie-Pierre Santoni
- Department of Chemistry − Ångström
Laboratory, Uppsala University, P.O. Box 523, S-75120 Uppsala, Sweden
| | - Linus O. Johannissen
- Department of Chemistry − Ångström
Laboratory, Uppsala University, P.O. Box 523, S-75120 Uppsala, Sweden
| | - Leif Hammarström
- Department of Chemistry − Ångström
Laboratory, Uppsala University, P.O. Box 523, S-75120 Uppsala, Sweden
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24
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Shakib F, Hanna G. Mixed Quantum-Classical Liouville Approach for Calculating Proton-Coupled Electron-Transfer Rate Constants. J Chem Theory Comput 2016; 12:3020-9. [DOI: 10.1021/acs.jctc.6b00362] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Affiliation(s)
- Farnaz Shakib
- Department of Chemistry, University of Alberta, Edmonton, Alberta T6G 2G2, Canada
| | - Gabriel Hanna
- Department of Chemistry, University of Alberta, Edmonton, Alberta T6G 2G2, Canada
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25
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Miller DC, Tarantino KT, Knowles RR. Proton-Coupled Electron Transfer in Organic Synthesis: Fundamentals, Applications, and Opportunities. Top Curr Chem (Cham) 2016; 374:30. [PMID: 27573270 PMCID: PMC5107260 DOI: 10.1007/s41061-016-0030-6] [Citation(s) in RCA: 78] [Impact Index Per Article: 9.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/11/2015] [Accepted: 04/21/2016] [Indexed: 10/21/2022]
Abstract
Proton-coupled electron transfers (PCETs) are unconventional redox processes in which both protons and electrons are exchanged, often in a concerted elementary step. While PCET is now recognized to play a central a role in biological redox catalysis and inorganic energy conversion technologies, its applications in organic synthesis are only beginning to be explored. In this chapter, we aim to highlight the origins, development, and evolution of the PCET processes most relevant to applications in organic synthesis. Particular emphasis is given to the ability of PCET to serve as a non-classical mechanism for homolytic bond activation that is complimentary to more traditional hydrogen atom transfer processes, enabling the direct generation of valuable organic radical intermediates directly from their native functional group precursors under comparatively mild catalytic conditions. The synthetically advantageous features of PCET reactivity are described in detail, along with examples from the literature describing the PCET activation of common organic functional groups.
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Affiliation(s)
- David C Miller
- Department of Chemistry, Princeton University, Princeton, NJ, 08544, USA
| | - Kyle T Tarantino
- Department of Chemistry, Princeton University, Princeton, NJ, 08544, USA
| | - Robert R Knowles
- Department of Chemistry, Princeton University, Princeton, NJ, 08544, USA.
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26
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Shakib FA, Hanna G. New insights into the nonadiabatic state population dynamics of model proton-coupled electron transfer reactions from the mixed quantum-classical Liouville approach. J Chem Phys 2016; 144:024110. [DOI: 10.1063/1.4939586] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022] Open
Affiliation(s)
- Farnaz A. Shakib
- Department of Chemistry, University of Alberta, Edmonton, Alberta T6G 2G2, Canada
| | - Gabriel Hanna
- Department of Chemistry, University of Alberta, Edmonton, Alberta T6G 2G2, Canada
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27
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Carreño A, Gacitúa M, Fuentes JA, Páez-Hernández D, Peñaloza JP, Otero C, Preite M, Molins E, Swords WB, Meyer GJ, Manríquez JM, Polanco R, Chávez I, Arratia-Pérez R. Fluorescence probes for prokaryotic and eukaryotic cells using Re(CO)3+complexes with an electron withdrawing ancillary ligand. NEW J CHEM 2016. [DOI: 10.1039/c6nj00905k] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Re(CO)3+complexes with an ancillary ligand present an electron withdrawing effect suitable for cell imaging.
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28
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Choi GJ, Knowles RR. Catalytic Alkene Carboaminations Enabled by Oxidative Proton-Coupled Electron Transfer. J Am Chem Soc 2015; 137:9226-9. [PMID: 26166022 DOI: 10.1021/jacs.5b05377] [Citation(s) in RCA: 223] [Impact Index Per Article: 24.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
Abstract
Here we describe a dual catalyst system comprised of an iridium photocatalyst and weak phosphate base that is capable of both selectively homolyzing the N-H bonds of N-arylamides (bond dissociation free energies ∼ 100 kcal/mol) via concerted proton-coupled electron transfer (PCET) and mediating efficient carboamination reactions of the resulting amidyl radicals. This manner of PCET activation, which finds its basis in numerous biological redox processes, enables the formal homolysis of a stronger amide N-H bond in the presence of weaker allylic C-H bonds, a selectivity that is uncommon in conventional molecular H atom acceptors. Moreover, this transformation affords access to a broad range of structurally complex heterocycles from simple amide starting materials. The design, synthetic scope, and mechanistic evaluation of the PCET process are described.
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Affiliation(s)
- Gilbert J Choi
- Department of Chemistry, Princeton University, Princeton, New Jersey 08544, United States
| | - Robert R Knowles
- Department of Chemistry, Princeton University, Princeton, New Jersey 08544, United States
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29
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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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30
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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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31
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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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32
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Shakib FA, Hanna G. An analysis of model proton-coupled electron transfer reactions via the mixed quantum-classical Liouville approach. J Chem Phys 2014; 141:044122. [DOI: 10.1063/1.4890915] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022] Open
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33
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Eisenhart TT, Dempsey JL. Photo-induced proton-coupled electron transfer reactions of acridine orange: comprehensive spectral and kinetics analysis. J Am Chem Soc 2014; 136:12221-4. [PMID: 25046022 DOI: 10.1021/ja505755k] [Citation(s) in RCA: 60] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/21/2023]
Abstract
The triplet excited state of acridine orange ((3)*AO) undergoes a proton-coupled electron transfer (PCET) reaction with tri-tert-butylphenol ((ttb)PhOH) in acetonitrile. Each of the reaction components possesses a spectroscopic signature, providing a rare opportunity to monitor the individual proton transfer, electron transfer, and H(•)-transfer components in parallel via transient absorption spectroscopy. This enhanced optical tracking, along with excited-state thermochemical analysis, facilitates assignment of the mechanism of excited-state PCET reactivity. (3)*AO is quenched via concerted proton-electron transfer (CPET) from (ttb)PhOH to form acridine radical (AOH(•)) and (ttb)PhO(•) (kCPET = 3.7 × 10(8) M(-1) s(-1), KIE = 1.3). Subsequently, AOH(•) reduces the phenoxyl radical (kET = 5.5 × 10(9) M(-1) s(-1)), forming AOH(+) and (ttb)PhO(-), followed by proton transfer (kPT = 1.0 × 10(9) M(-1) s(-1)) to regenerate the starting reactants.
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Affiliation(s)
- Thomas T Eisenhart
- Department of Chemistry, University of North Carolina , Chapel Hill, North Carolina 27599-3290, United States
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34
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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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35
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Bronner C, Wenger OS. Long-range proton-coupled electron transfer in phenol–Ru(2,2′-bipyrazine)32+ dyads. Phys Chem Chem Phys 2014; 16:3617-22. [DOI: 10.1039/c3cp55071k] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
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36
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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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37
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Hewitt JT, Concepcion JJ, Damrauer NH. Inverse Kinetic Isotope Effect in the Excited-State Relaxation of a Ru(II)–Aquo Complex: Revealing the Impact of Hydrogen-Bond Dynamics on Nonradiative Decay. J Am Chem Soc 2013; 135:12500-3. [DOI: 10.1021/ja4037498] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Affiliation(s)
- Joshua T. Hewitt
- Department of Chemistry and
Biochemistry, University of Colorado, Boulder,
Colorado 80309, United States
| | - Javier J. Concepcion
- Department of Chemistry, The University of North Carolina, Chapel Hill, North
Carolina 27599-3290, United States
| | - Niels H. Damrauer
- Department of Chemistry and
Biochemistry, University of Colorado, Boulder,
Colorado 80309, United States
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38
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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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39
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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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40
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Capello MC, Broquier M, Dedonder-Lardeux C, Jouvet C, Pino GA. Fast excited state dynamics in the isolated 7-azaindole-phenol H-bonded complex. J Chem Phys 2013; 138:054304. [DOI: 10.1063/1.4789426] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
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41
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Haidasz EA, Li B, Pratt DA. Reaction mechanisms: radical and radical ion reactions. ACTA ACUST UNITED AC 2013. [DOI: 10.1039/c3oc90013d] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/22/2023]
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