1
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Geng H, Xu Y, Liu R, Xu J, Li X, Yang D, Dai X. Magnetic porous microspheres altering interfacial thermodynamics of sewage sludge to drive metabolic cooperation for efficient methanogenesis. WATER RESEARCH 2024; 261:122022. [PMID: 39002417 DOI: 10.1016/j.watres.2024.122022] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/08/2024] [Revised: 06/21/2024] [Accepted: 06/28/2024] [Indexed: 07/15/2024]
Abstract
Controllable and recyclable magnetic porous microspheres (MPMs) have been proposed as a means for enhancing the anaerobic digestion (AD) of sludge, as they do not require continuous replenishment and can serve as carriers for anaerobes. However, the effects of MPMs on the interfacial thermodynamics of sludge and the biological responses triggered by abiotic effects in AD systems remain to be clarified. Herein, the underlying mechanisms by which MPMs alter the solid-liquid interface of sludge to drive methanogenesis were investigated. A significant increase in the contents of 13C and 2H (D) in methane molecules was observed in the presence of MPMs, suggesting that MPMs might enhance the CO2-reduction methanogenesis and participation of water in methane generation. Experimental results demonstrated that the addition of MPMs did not promote the anaerobic bioconversion of soluble organics for methanogenesis, suggesting that the enhanced methanogenesis and water participation were not achieved through promotion of the bioconversion of original liquid-state organics in sludge. Analyses of the capillary force, surface adhesion force, and interfacial proton-coupled electron transfer (PCET) of MPMs revealed that MPMs can enhance mass transfer, effective contact, and electron-proton transfer with sludge. These outcomes were confirmed by the statistical analyses of variations in the interfacial thermodynamics and PCET of sludge with and without MPMs during AD. It was thus proposed that the MPMs enhanced the PCET of sludge and PCET-driven release of protons from water by promoting the interfacial Lewis acid-base interactions of sludge, thereby resulting in the enrichment of free and attached methanogenic consortia and the high energy-conserving metabolic cooperation. This proposition was further confirmed by identifying the predominant syntrophic partners, suggesting that PCET-based efficient methanogenesis was attributable to the enrichment of genomes harbouring CO2-reducing pathway and genes encoding water-mediated proton transfer. These findings offer new insights into how substrate properties can be altered by exogenous materials to enable highly efficient methanogenesis.
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Affiliation(s)
- Hui Geng
- State Key Laboratory of Pollution Control and Resource Reuse, School of Environmental Science and Engineering, Tongji University, Shanghai, 200092, China
| | - Ying Xu
- State Key Laboratory of Pollution Control and Resource Reuse, School of Environmental Science and Engineering, Tongji University, Shanghai, 200092, China; Shanghai Institute of Pollution Control and Ecological Security, Shanghai, 200092, China.
| | - Rui Liu
- State Key Laboratory of Pollution Control and Resource Reuse, School of Environmental Science and Engineering, Tongji University, Shanghai, 200092, China
| | - Jun Xu
- State Key Laboratory of Pollution Control and Resource Reuse, School of Environmental Science and Engineering, Tongji University, Shanghai, 200092, China
| | - Xiang Li
- State Key Laboratory of Pollution Control and Resource Reuse, School of Environmental Science and Engineering, Tongji University, Shanghai, 200092, China
| | - Dianhai Yang
- State Key Laboratory of Pollution Control and Resource Reuse, School of Environmental Science and Engineering, Tongji University, Shanghai, 200092, China
| | - Xiaohu Dai
- State Key Laboratory of Pollution Control and Resource Reuse, School of Environmental Science and Engineering, Tongji University, Shanghai, 200092, China; Shanghai Institute of Pollution Control and Ecological Security, Shanghai, 200092, China
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2
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Cole HD, Vali A, Roque JA, Shi G, Talgatov A, Kaur G, Francés-Monerris A, Alberto ME, Cameron CG, McFarland SA. Ru(II) Oligothienyl Complexes with Fluorinated Ligands: Photophysical, Electrochemical, and Photobiological Properties. Inorg Chem 2024; 63:9735-9752. [PMID: 38728376 PMCID: PMC11166183 DOI: 10.1021/acs.inorgchem.3c04382] [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] [Indexed: 05/12/2024]
Abstract
A series of Ru(II) complexes incorporating two 4,4'-bis(trifluoromethyl)-2,2'-bipyridine (4,4'-btfmb) coligands and thienyl-appended imidazo[4,5-f][1,10]phenanthroline (IP-nT) ligands was characterized and assessed for phototherapy effects toward cancer cells. The [Ru(4,4'-btfmb)2(IP-nT)]2+ scaffold has greater overall redox activity compared to Ru(II) polypyridyl complexes such as [Ru(bpy)3]2+. Ru-1T-Ru-4T have additional oxidations due to the nT group and additional reductions due to the 4,4'-btfmb ligands. Ru-2T-Ru-4T also exhibit nT-based reductions. Ru-4T exhibits two oxidations and eight reductions within the potential window of -3 to +1.5 V. The lowest-lying triplets (T1) for Ru-0T-2T are metal-to-ligand charge-transfer (3MLCT) excited states with lifetimes around 1 μs, whereas T1 for Ru-3T-4T is longer-lived (∼20-24 μs) and of significant intraligand charge-transfer (3ILCT) character. Phototoxicity toward melanoma cells (SK-MEL-28) increases with n, with Ru-4T having a visible EC50 value as low as 9 nM and PI as large as 12,000. Ru-3T and Ru-4T retain some of this activity in hypoxia, where Ru-4T has a visible EC50 as low as 35 nM and PI as high as 2900. Activity over six biological replicates is consistent and within an order of magnitude. These results demonstrate the importance of lowest-lying 3ILCT states for phototoxicity and maintaining activity in hypoxia.
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Affiliation(s)
- Houston D. Cole
- Department of Chemistry and Biochemistry, The University of Texas at Arlington, Arlington, Texas, 76019-0065 United States
| | - Abbas Vali
- Department of Chemistry and Biochemistry, The University of Texas at Arlington, Arlington, Texas, 76019-0065 United States
| | - John A. Roque
- Department of Chemistry and Biochemistry, The University of Texas at Arlington, Arlington, Texas, 76019-0065 United States
| | - Ge Shi
- Department of Chemistry and Biochemistry, The University of Texas at Arlington, Arlington, Texas, 76019-0065 United States
| | - Alisher Talgatov
- Department of Chemistry and Biochemistry, The University of Texas at Arlington, Arlington, Texas, 76019-0065 United States
| | - Gurleen Kaur
- Department of Chemistry and Biochemistry, The University of Texas at Arlington, Arlington, Texas, 76019-0065 United States
| | | | - Marta E. Alberto
- Dipartimento di Chimica e Tecnologie Chimiche, Università della Calabria, Arcavacata di Rende, 87036 Italy
| | - Colin G. Cameron
- Department of Chemistry and Biochemistry, The University of Texas at Arlington, Arlington, Texas, 76019-0065 United States
| | - Sherri A. McFarland
- Department of Chemistry and Biochemistry, The University of Texas at Arlington, Arlington, Texas, 76019-0065 United States
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3
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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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4
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Murray PD, Cox JH, Chiappini ND, Roos CB, McLoughlin EA, Hejna BG, Nguyen ST, Ripberger HH, Ganley JM, Tsui E, Shin NY, Koronkiewicz B, Qiu G, Knowles RR. Photochemical and Electrochemical Applications of Proton-Coupled Electron Transfer in Organic Synthesis. Chem Rev 2022; 122:2017-2291. [PMID: 34813277 PMCID: PMC8796287 DOI: 10.1021/acs.chemrev.1c00374] [Citation(s) in RCA: 154] [Impact Index Per Article: 77.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/01/2021] [Indexed: 12/16/2022]
Abstract
We present here a review of the photochemical and electrochemical applications of multi-site proton-coupled electron transfer (MS-PCET) in organic synthesis. MS-PCETs are redox mechanisms in which both an electron and a proton are exchanged together, often in a concerted elementary step. As such, MS-PCET can function as a non-classical mechanism for homolytic bond activation, providing opportunities to generate synthetically useful free radical intermediates directly from a wide variety of common organic functional groups. We present an introduction to MS-PCET and a practitioner's guide to reaction design, with an emphasis on the unique energetic and selectivity features that are characteristic of this reaction class. We then present chapters on oxidative N-H, O-H, S-H, and C-H bond homolysis methods, for the generation of the corresponding neutral radical species. Then, chapters for reductive PCET activations involving carbonyl, imine, other X═Y π-systems, and heteroarenes, where neutral ketyl, α-amino, and heteroarene-derived radicals can be generated. Finally, we present chapters on the applications of MS-PCET in asymmetric catalysis and in materials and device applications. Within each chapter, we subdivide by the functional group undergoing homolysis, and thereafter by the type of transformation being promoted. Methods published prior to the end of December 2020 are presented.
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Affiliation(s)
- Philip
R. D. Murray
- Department of Chemistry, Princeton
University, Princeton, New Jersey 08544, United States
| | - James H. Cox
- Department of Chemistry, Princeton
University, Princeton, New Jersey 08544, United States
| | - Nicholas D. Chiappini
- Department of Chemistry, Princeton
University, Princeton, New Jersey 08544, United States
| | - Casey B. Roos
- Department of Chemistry, Princeton
University, Princeton, New Jersey 08544, United States
| | | | - Benjamin G. Hejna
- Department of Chemistry, Princeton
University, Princeton, New Jersey 08544, United States
| | - Suong T. Nguyen
- Department of Chemistry, Princeton
University, Princeton, New Jersey 08544, United States
| | - Hunter H. Ripberger
- Department of Chemistry, Princeton
University, Princeton, New Jersey 08544, United States
| | - Jacob M. Ganley
- Department of Chemistry, Princeton
University, Princeton, New Jersey 08544, United States
| | - Elaine Tsui
- Department of Chemistry, Princeton
University, Princeton, New Jersey 08544, United States
| | - Nick Y. Shin
- Department of Chemistry, Princeton
University, Princeton, New Jersey 08544, United States
| | - Brian Koronkiewicz
- Department of Chemistry, Princeton
University, Princeton, New Jersey 08544, United States
| | - Guanqi Qiu
- 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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5
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Agarwal RG, Coste SC, Groff BD, Heuer AM, Noh H, Parada GA, Wise CF, Nichols EM, Warren JJ, Mayer JM. Free Energies of Proton-Coupled Electron Transfer Reagents and Their Applications. Chem Rev 2021; 122:1-49. [PMID: 34928136 DOI: 10.1021/acs.chemrev.1c00521] [Citation(s) in RCA: 134] [Impact Index Per Article: 44.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
We present an update and revision to our 2010 review on the topic of proton-coupled electron transfer (PCET) reagent thermochemistry. Over the past decade, the data and thermochemical formalisms presented in that review have been of value to multiple fields. Concurrently, there have been advances in the thermochemical cycles and experimental methods used to measure these values. This Review (i) summarizes those advancements, (ii) corrects systematic errors in our prior review that shifted many of the absolute values in the tabulated data, (iii) provides updated tables of thermochemical values, and (iv) discusses new conclusions and opportunities from the assembled data and associated techniques. We advocate for updated thermochemical cycles that provide greater clarity and reduce experimental barriers to the calculation and measurement of Gibbs free energies for the conversion of X to XHn in PCET reactions. In particular, we demonstrate the utility and generality of reporting potentials of hydrogenation, E°(V vs H2), in almost any solvent and how these values are connected to more widely reported bond dissociation free energies (BDFEs). The tabulated data demonstrate that E°(V vs H2) and BDFEs are generally insensitive to the nature of the solvent and, in some cases, even to the phase (gas versus solution). This Review also presents introductions to several emerging fields in PCET thermochemistry to give readers windows into the diversity of research being performed. Some of the next frontiers in this rapidly growing field are coordination-induced bond weakening, PCET in novel solvent environments, and reactions at material interfaces.
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Affiliation(s)
- Rishi G Agarwal
- Department of Chemistry, Yale University, New Haven, Connecticut 06520, United States
| | - Scott C Coste
- Department of Chemistry, Yale University, New Haven, Connecticut 06520, United States
| | - Benjamin D Groff
- Department of Chemistry, Yale University, New Haven, Connecticut 06520, United States
| | - Abigail M Heuer
- Department of Chemistry, Yale University, New Haven, Connecticut 06520, United States
| | - Hyunho Noh
- Department of Chemistry, Yale University, New Haven, Connecticut 06520, United States
| | - Giovanny A Parada
- Department of Chemistry, Yale University, New Haven, Connecticut 06520, United States.,Department of Chemistry, The College of New Jersey, Ewing, New Jersey 08628, United States
| | - Catherine F Wise
- Department of Chemistry, Yale University, New Haven, Connecticut 06520, United States
| | - Eva M Nichols
- Department of Chemistry, University of British Columbia, Vancouver, BC V6T 1Z1, Canada
| | - Jeffrey J Warren
- Department of Chemistry, Simon Fraser University, Burnaby, BC V5A 1S6, Canada
| | - James M Mayer
- Department of Chemistry, Yale University, New Haven, Connecticut 06520, United States
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6
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Cattaneo M, Parada GA, Tenderholt AL, Kaminsky W, Mayer JM. Structural, Electronic and Thermochemical preference for multi-PCET reactivity of Ruthenium(II)-Amine and Ruthenium(IV)-Amido Complexes. Eur J Inorg Chem 2021; 2021:4042. [PMID: 34776777 DOI: 10.1002/ejic.202100761] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
The multiredox reactivity of bioinorganic cofactors is often coupled to proton transfers. Here we investigate the structural, thermochemical, and electronic structure of ruthenium-amino/amido complexes with multi- proton-coupled electron transfer reactivity. The bis(amino)ruthenium(II) and bis(amido)ruthenium(IV) complexes [RuII(bpy)(en*)2]2+ (RuII-H0 ) and [RuIV(bpy)(en*-H2)2]2+ (RuIV-H2 ) interconvert reversibly with the transfer of 2e-/2H+ (bpy = 2,2'-bipyridine, en* = 2,3-diamino-2,3-dimethylbutane). X-ray structures allow correlations between the structural and electronic parameters, and the thermochemical data of the 2e-/2H+ multi-square grid scheme. Redox potentials, acidity constants and DFT calculations reveal potential intermediates implicated in 2e-/2H+ reactivity with organic reagents in non-protic solvents, which shows a strong inverted redox potential favouring 2e-/2H+ transfer. This is suggested to be an attractive system for potential one-step (concerted) transfer of 2e-and 2H+ due to the small changes of the pseudo-octahedral geometries and the absence of charge change, indicating a relatively small overall reorganization energy.
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Affiliation(s)
- Mauricio Cattaneo
- INQUINOA (CONICET-UNT), Facultad de Bioquímica, Química y Farmacia, Universidad Nacional de Tucumán, Ayacucho 471, (4000) San Miguel de Tucumán, Argentina
| | - Giovanny A Parada
- Department of Chemistry, Yale University, P.O. Box 208107, New Haven, CT 06520, USA.,Department of Chemistry, The College of New Jersey, Ewing, NJ 08628, USA. (as of 7/1/2021)
| | - Adam L Tenderholt
- Department of Chemistry, University of Washington, Seattle, Washington 98195-1700, USA
| | - Werner Kaminsky
- Department of Chemistry, University of Washington, Seattle, Washington 98195-1700, USA
| | - James M Mayer
- Department of Chemistry, Yale University, P.O. Box 208107, New Haven, CT 06520, USA
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7
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Cattaneo M, Parada GA, Tenderholt AL, Kaminsky W, Mayer JM. Structural, Electronic, and Thermochemical Preference for Multi‐PCET Reactivity of Ruthenium(II)‐Amine and Ruthenium(IV)‐Amido Complexes. Eur J Inorg Chem 2021. [DOI: 10.1002/ejic.202100604] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Affiliation(s)
- Mauricio Cattaneo
- INQUINOA (CONICET-UNT) Facultad de Bioquímica Química y Farmacia Universidad Nacional de Tucumán Ayacucho 471 4000 San Miguel de Tucumán Argentina
| | - Giovanny A. Parada
- Department of Chemistry Yale University P.O. Box 208107 New Haven CT 06520 USA
- Department of Chemistry The College of New Jersey Ewing NJ 08628 USA
| | - Adam L. Tenderholt
- Department of Chemistry University of Washington Seattle Washington 98195-1700 USA
| | - Werner Kaminsky
- Department of Chemistry University of Washington Seattle Washington 98195-1700 USA
| | - James M. Mayer
- Department of Chemistry Yale University P.O. Box 208107 New Haven CT 06520 USA
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8
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Coste SC, Brezny AC, Koronkiewicz B, Mayer JM. C-H oxidation in fluorenyl benzoates does not proceed through a stepwise pathway: revisiting asynchronous proton-coupled electron transfer. Chem Sci 2021; 12:13127-13136. [PMID: 34745543 PMCID: PMC8513817 DOI: 10.1039/d1sc03344a] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/21/2021] [Accepted: 09/09/2021] [Indexed: 11/21/2022] Open
Abstract
2-Fluorenyl benzoates were recently shown to undergo C–H bond oxidation through intramolecular proton transfer coupled with electron transfer to an external oxidant. Kinetic analysis revealed unusual rate-driving force relationships. Our analysis indicated a mechanism of multi-site concerted proton–electron transfer (MS-CPET) for all of these reactions. More recently, an alternative interpretation of the kinetic data was proposed to explain the unusual rate-driving force relationships, invoking a crossover from CPET to a stepwise mechanism with an initial intramolecular proton transfer (PT) (Costentin, Savéant, Chem. Sci., 2020, 11, 1006). Here, we show that this proposed alternative pathway is untenable based on prior and new experimental assessments of the intramolecular PT equilibrium constant and rates. Measurement of the fluorenyl 9-C–H pKa, H/D exchange experiments, and kinetic modelling with COPASI eliminate the possibility of a stepwise mechanism for C–H oxidation in the fluorenyl benzoate series. Implications for asynchronous (imbalanced) MS-CPET mechanisms are discussed with respect to classical Marcus theory and the quantum-mechanical treatment of concerted proton–electron transfer. 2-Fluorenyl benzoates were recently shown to undergo C–H bond oxidation through intramolecular proton transfer coupled with electron transfer to an external oxidant.![]()
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Affiliation(s)
- Scott C Coste
- Department of Chemistry, Yale University New Haven CT 06520-8107 USA
| | - Anna C Brezny
- Department of Chemistry, Skidmore College Saratoga Springs New York 12866 USA
| | | | - James M Mayer
- Department of Chemistry, Yale University New Haven CT 06520-8107 USA
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9
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Carreño A, Gacitúa M, Solis-Céspedes E, Páez-Hernández D, Swords WB, Meyer GJ, Preite MD, Chávez I, Vega A, Fuentes JA. New Cationic fac-[Re(CO) 3(deeb)B2] + Complex, Where B2 Is a Benzimidazole Derivative, as a Potential New Luminescent Dye for Proteins Separated by SDS-PAGE. Front Chem 2021; 9:647816. [PMID: 33842435 PMCID: PMC8027506 DOI: 10.3389/fchem.2021.647816] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/30/2020] [Accepted: 01/29/2021] [Indexed: 01/14/2023] Open
Abstract
Sodium-dodecyl-sulfate polyacrylamide gel electrophoresis (SDS-PAGE) can be used to separate proteins based mainly on their size such as in denaturing gels. Different staining methods have been reported to observe proteins in the gel matrix, where the most used dyes are generally anionic. Anionic dyes allow for interactions with protonated amino acids, retaining the dye in the proteins. Fluorescent staining is an alternative technique considered to be sensitive, safe, and versatile. Some anionic complexes based on d6 transition metals have been used for this purpose, where cationic dyes have been less explored in this context. In this work, we synthesized and characterized a new monocationic rhenium complex fac-[Re(CO)3(deeb)B2]+ (where deeb is 4,4′-bis(ethoxycarbonyl)-2,2′-bpy and B2 is 2,4-di-tert-butyl-6-(3H-imidazo[4,5-c]pyridine-2-yl)phenol). We carried out a structural characterization of this complex by MS+, FTIR, 1H NMR, D2O exchange, and HHCOSY. Moreover, we carried out UV-Vis, luminescence, and cyclic voltammetry experiments to understand the effect of ligands on the complex’s electronic structure. We also performed relativistic theoretical calculations using the B3LYP/TZ2P level of theory and R-TDDFT within a dielectric continuum model (COSMO) to better understand electronic transitions and optical properties. We finally assessed the potential of fac-[Re(CO)3(deeb)B2]+ (as well as the precursor fac-Re(CO)3(deeb)Br and the free ligand B2) to stain proteins separated by SDS-PAGE. We found that only fac-[Re(CO)3(deeb)B2]+ proved viable to be directly used as a luminescent dye for proteins, presumably due to its interaction with negatively charged residues in proteins and by weak interactions provided by B2. In addition, fac-[Re(CO)3(deeb)B2]+ seems to interact preferentially with proteins and not with the gel matrix despite the presence of sodium dodecyl sulfate (SDS). In future applications, these alternative cationic complexes might be used alone or in combination with more traditional anionic compounds to generate counterion dye stains to improve the process.
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Affiliation(s)
- Alexander Carreño
- Center of Applied NanoSciences (CANS), Facultad de Ciencias Exactas, Universidad Andres Bello, Santiago, Chile
| | | | - Eduardo Solis-Céspedes
- Escuela de Bioingeniería Médica, Facultad de Medicina, Universidad Católica del Maule, Talca, Chile.,Laboratorio de Bioinformática y Química Computacional, Facultad de Medicina, Universidad Católica del Maule, Talca, Chile
| | - Dayán Páez-Hernández
- Center of Applied NanoSciences (CANS), Facultad de Ciencias Exactas, Universidad Andres Bello, Santiago, Chile
| | - Wesley B Swords
- Department of Chemistry, University of North Carolina at Chapel Hill, Chapel Hill, NC, United States
| | - Gerald J Meyer
- Department of Chemistry, University of North Carolina at Chapel Hill, Chapel Hill, NC, United States
| | - Marcelo D Preite
- Departamento de Química Orgánica, Facultad de Química y Química y de Farmacia, Pontificia Universidad Católica de Chile, Santiago, Chile
| | - Ivonne Chávez
- Departamento de Química Inorgánica, Facultad de Química y Química y de Farmacia, Pontificia Universidad Católica de Chile, Santiago, Chile
| | - Andrés Vega
- Departamento de Ciencias Químicas, Facultad de Ciencias Exactas, Universidad Andres Bello, Viña del Mar, Chile.,Centro para el Desarrollo de la Nanociencia y la Nanotecnología Cedenna, Santiago, Chile
| | - Juan A Fuentes
- Laboratorio de Genética y Patogénesis Bacteriana, Facultad de Ciencias de la Vida, Universidad Andrés Bello, Santiago, Chile
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10
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Tyburski R, Liu T, Glover SD, Hammarström L. Proton-Coupled Electron Transfer Guidelines, Fair and Square. J Am Chem Soc 2021; 143:560-576. [PMID: 33405896 PMCID: PMC7880575 DOI: 10.1021/jacs.0c09106] [Citation(s) in RCA: 193] [Impact Index Per Article: 64.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/24/2020] [Indexed: 12/23/2022]
Abstract
Proton-coupled electron transfer (PCET) reactions are fundamental to energy transformation reactions in natural and artificial systems and are increasingly recognized in areas such as catalysis and synthetic chemistry. The interdependence of proton and electron transfer brings a mechanistic richness of reactivity, including various sequential and concerted mechanisms. Delineating between different PCET mechanisms and understanding why a particular mechanism dominates are crucial for the design and optimization of reactions that use PCET. This Perspective provides practical guidelines for how to discern between sequential and concerted mechanisms based on interpretations of thermodynamic data with temperature-, pressure-, and isotope-dependent kinetics. We present new PCET-zone diagrams that show how a mechanism can switch or even be eliminated by varying the thermodynamic (ΔGPT° and ΔGET°) and coupling strengths for a PCET system. We discuss the appropriateness of asynchronous concerted PCET to rationalize observations in organic reactions, and the distinction between hydrogen atom transfer and other concerted PCET reactions. Contemporary issues and future prospects in PCET research are discussed.
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Affiliation(s)
- Robin Tyburski
- Ångström
Laboratory, Department of Chemistry, Uppsala
University, Box 523, SE75120 Uppsala, Sweden
| | - Tianfei Liu
- Department
of Chemistry, University of North Carolina
at Chapel Hill, Chapel
Hill, North Carolina 27599-3290, United States
| | - Starla D. Glover
- Ångström
Laboratory, Department of Chemistry, Uppsala
University, Box 523, SE75120 Uppsala, Sweden
| | - Leif Hammarström
- Ångström
Laboratory, Department of Chemistry, Uppsala
University, Box 523, SE75120 Uppsala, Sweden
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11
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Berg N, Bergwinkl S, Nuernberger P, Horinek D, Gschwind RM. Extended Hydrogen Bond Networks for Effective Proton-Coupled Electron Transfer (PCET) Reactions: The Unexpected Role of Thiophenol and Its Acidic Channel in Photocatalytic Hydroamidations. J Am Chem Soc 2021; 143:724-735. [DOI: 10.1021/jacs.0c08673] [Citation(s) in RCA: 17] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
Affiliation(s)
- Nele Berg
- Institute of Organic Chemistry, University of Regensburg, D-93053 Regensburg, Germany
| | - Sebastian Bergwinkl
- Institute of Physical and Theoretical Chemistry, University of Regensburg, D-93053 Regensburg, Germany
| | - Patrick Nuernberger
- Institute of Physical and Theoretical Chemistry, University of Regensburg, D-93053 Regensburg, Germany
| | - Dominik Horinek
- Institute of Physical and Theoretical Chemistry, University of Regensburg, D-93053 Regensburg, Germany
| | - Ruth M. Gschwind
- Institute of Organic Chemistry, University of Regensburg, D-93053 Regensburg, Germany
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12
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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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13
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Yang JY, Kerr TA, Wang XS, Barlow JM. Reducing CO2 to HCO2– at Mild Potentials: Lessons from Formate Dehydrogenase. J Am Chem Soc 2020; 142:19438-19445. [DOI: 10.1021/jacs.0c07965] [Citation(s) in RCA: 27] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Affiliation(s)
- Jenny Y. Yang
- Department of Chemistry, University of California, Irvine, California 92697, United States
| | - Tyler A. Kerr
- Department of Chemistry, University of California, Irvine, California 92697, United States
| | - Xinran S. Wang
- Department of Chemistry, University of California, Irvine, California 92697, United States
| | - Jeffrey M. Barlow
- Department of Chemistry, University of California, Irvine, California 92697, United States
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14
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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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15
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Liu T, Tyburski R, Wang S, Fernández-Terán R, Ott S, Hammarström L. Elucidating Proton-Coupled Electron Transfer Mechanisms of Metal Hydrides with Free Energy- and Pressure-Dependent Kinetics. J Am Chem Soc 2019; 141:17245-17259. [PMID: 31587555 DOI: 10.1021/jacs.9b08189] [Citation(s) in RCA: 24] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Abstract
Proton-coupled electron transfer (PCET) was studied in a series of tungsten hydride complexes with pendant pyridyl arms ([(PyCH2Cp)WH(CO)3], PyCH2Cp = pyridylmethylcyclopentadienyl), triggered by laser flash-generated RuIII-tris-bipyridine oxidants, in acetonitrile solution. The free energy dependence of the rate constant and the kinetic isotope effects (KIEs) showed that the PCET mechanism could be switched between concerted and the two stepwise PCET mechanisms (electron-first or proton-first) in a predictable fashion. Straightforward and general guidelines for how the relative rates of the different mechanisms depend on oxidant and base are presented. The rate of the concerted reaction should depend symmetrically on changes in oxidant and base strength, that is on the overall ΔG0PCET, and we argue that an "asynchronous" behavior would not be consistent with a model where the electron and proton tunnel from a common transition state. The observed rate constants and KIEs were examined as a function of hydrostatic pressure (1-2000 bar) and were found to exhibit qualitatively different dependence on pressure for different PCET mechanisms. This is discussed in terms of different volume profiles of the PCET mechanisms as well as enhanced proton tunneling for the concerted mechanism. The results allowed for assignment of the main mechanism operating in the different cases, which is one of the critical questions in PCET research. They also show how the rate of a PCET reaction will be affected very differently by changes of oxidant and base strength, depending on which mechanism dominates. This is of fundamental interest as well as of practical importance for rational design of, for example, catalysts for fuel cells and solar fuel formation, which operate in steps of PCET reactions. The mechanistic richness shown by this system illustrates that the specific mechanism is not intrinsic to a specific synthetic catalyst or enzyme active site but depends on the reaction conditions.
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Affiliation(s)
- Tianfei Liu
- Department of Chemistry, Ångström Laboratory , Uppsala University , Box 532, SE-751 20 Uppsala , Sweden
| | - Robin Tyburski
- Department of Chemistry, Ångström Laboratory , Uppsala University , Box 532, SE-751 20 Uppsala , Sweden
| | - Shihuai Wang
- Department of Chemistry, Ångström Laboratory , Uppsala University , Box 532, SE-751 20 Uppsala , Sweden
| | - Ricardo Fernández-Terán
- Department of Chemistry, Ångström Laboratory , Uppsala University , Box 532, SE-751 20 Uppsala , Sweden
| | - Sascha Ott
- Department of Chemistry, Ångström Laboratory , Uppsala University , Box 532, SE-751 20 Uppsala , Sweden
| | - Leif Hammarström
- Department of Chemistry, Ångström Laboratory , Uppsala University , Box 532, SE-751 20 Uppsala , Sweden
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16
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Qiu G, Knowles RR. Understanding Chemoselectivity in Proton-Coupled Electron Transfer: A Kinetic Study of Amide and Thiol Activation. J Am Chem Soc 2019; 141:16574-16578. [PMID: 31573194 DOI: 10.1021/jacs.9b08398] [Citation(s) in RCA: 21] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Abstract
While the mechanistic understanding of proton-coupled electron transfer (PCET) has advanced significantly, few reports have sought to elucidate the factors that control chemoselectivity in these reactions. Here we present a kinetic study that provides a quantitative basis for understanding the chemoselectivity in competitive PCET activations of amides and thiols relevant to catalytic olefin hydroamidation reactions. These results demonstrate how the interplay between PCET rate constants, hydrogen-bonding equilibria, and rate-driving force relationships jointly determine PCET chemoselectivity under a given set of conditions. In turn, these findings predict reactivity trends in a model hydroamidation reaction, rationalize the selective activation of amide N-H bonds in the presence of much weaker thiol S-H bonds, and deliver strategies to improve the efficiencies of PCET reactions employing thiol co-catalysts.
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Affiliation(s)
- Guanqi Qiu
- 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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17
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Enomoto T, Kondo M, Masaoka S. Proton-Coupled Electron Transfer Induced by Near-Infrared Light. Chem Asian J 2019; 14:2806-2809. [PMID: 31290247 DOI: 10.1002/asia.201900863] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/25/2019] [Indexed: 11/06/2022]
Abstract
A proton-coupled electron transfer reaction induced by near-infrared light (>710 nm) has been achieved using a dye that shows intense NIR absorption property and electron/proton-accepting abilities. The developed system generated long-lived radical species and showed high reversibility and robustness. Mechanistic investigations suggested that the rate-determining step of the reaction involves the proton transfer process.
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Affiliation(s)
- Takafumi Enomoto
- Department of Life and Coordination-Complex Molecular Science, Institution for Molecular Science (IMS), 5-1 Higashiyama, Myodaiji, Okazaki, Aichi, 444-8787, Japan
| | - Mio Kondo
- Department of Life and Coordination-Complex Molecular Science, Institution for Molecular Science (IMS), 5-1 Higashiyama, Myodaiji, Okazaki, Aichi, 444-8787, Japan.,Division of Applied Chemistry, Graduate School of Engineering, Osaka University, 2-1 Yamadaoka, Suita, Osaka, 565-0871, Japan
| | - Shigeyuki Masaoka
- Department of Life and Coordination-Complex Molecular Science, Institution for Molecular Science (IMS), 5-1 Higashiyama, Myodaiji, Okazaki, Aichi, 444-8787, Japan.,Division of Applied Chemistry, Graduate School of Engineering, Osaka University, 2-1 Yamadaoka, Suita, Osaka, 565-0871, Japan
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18
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Schneider J, Bangle RE, Swords WB, Troian-Gautier L, Meyer GJ. Determination of Proton-Coupled Electron Transfer Reorganization Energies with Application to Water Oxidation Catalysts. J Am Chem Soc 2019; 141:9758-9763. [DOI: 10.1021/jacs.9b01296] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Affiliation(s)
- Jenny Schneider
- Department of Chemistry, University of North Carolina at Chapel Hill, Chapel Hill 27599, United States
| | - Rachel E. Bangle
- Department of Chemistry, University of North Carolina at Chapel Hill, Chapel Hill 27599, United States
| | - Wesley B. Swords
- Department of Chemistry, University of North Carolina at Chapel Hill, Chapel Hill 27599, United States
| | - Ludovic Troian-Gautier
- Department of Chemistry, University of North Carolina at Chapel Hill, Chapel Hill 27599, United States
| | - Gerald J. Meyer
- Department of Chemistry, University of North Carolina at Chapel Hill, Chapel Hill 27599, United States
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19
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Milić JV, Diederich F. The Quest for Molecular Grippers: Photo‐Electric Control of Molecular Gripping Machinery. Chemistry 2019; 25:8440-8452. [DOI: 10.1002/chem.201900852] [Citation(s) in RCA: 16] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/24/2019] [Revised: 03/25/2019] [Indexed: 11/08/2022]
Affiliation(s)
- Jovana V. Milić
- Laboratory of Photonics and InterfacesÉcole Polytechnique Fédéralé de Lausanne 1015 Lausanne Switzerland
| | - François Diederich
- Department of Chemistry and Applied BiosciencesETH Zurich Vladimir-Prelog-Weg 3 8010 Zurich Switzerland
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20
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Qiu G, Knowles RR. Rate-Driving Force Relationships in the Multisite Proton-Coupled Electron Transfer Activation of Ketones. J Am Chem Soc 2019; 141:2721-2730. [PMID: 30665301 DOI: 10.1021/jacs.8b13451] [Citation(s) in RCA: 48] [Impact Index Per Article: 9.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023]
Abstract
Here we present a detailed kinetic study of the multisite proton-coupled electron transfer (MS-PCET) activations of aryl ketones using a variety of Brønsted acids and excited-state Ir(III)-based electron donors. A simple method is described for simultaneously extracting both the hydrogen-bonding equilibrium constants and the rate constants for the PCET event from deconvolution of the luminescence quenching data. These experiments confirm that these activations occur in a concerted fashion, wherein the proton and electron are transferred to the ketone substrate in a single elementary step. The rates constants for the PCET events were linearly correlated with their driving forces over a range of nearly 19 kcal/mol. However, the slope of the rate-driving force relationship deviated significantly from expectations based on Marcus theory. A rationalization for this observation is proposed based on the principle of non-perfect synchronization, wherein factors that serve to stabilize the product are only partially realized at the transition state. A discussion of the relevance of these findings to the applications of MS-PCET in organic synthesis is also presented.
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Affiliation(s)
- Guanqi Qiu
- 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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21
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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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22
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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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23
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Huang T, Rountree ES, Traywick AP, Bayoumi M, Dempsey JL. Switching between Stepwise and Concerted Proton-Coupled Electron Transfer Pathways in Tungsten Hydride Activation. J Am Chem Soc 2018; 140:14655-14669. [PMID: 30362720 DOI: 10.1021/jacs.8b07102] [Citation(s) in RCA: 30] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/17/2023]
Abstract
Catalytic processes to generate (or oxidize) fuels such as hydrogen are underpinned by multiple proton-coupled electron transfer (PCET) steps that are associated with the formation or activation of metal-hydride bonds. Fully understanding the detailed PCET mechanisms of metal hydride transformations holds promise for the rational design of energy-efficient catalysis. Here we investigate the detailed PCET mechanisms for the activation of the transition metal hydride complex CpW(CO)2(PMe3)H (Cp = cyclopentadienyl) using stopped-flow rapid mixing coupled with time-resolved optical spectroscopy. We reveal that all three limiting PCET pathways can be accessed by changing the free energy for elementary proton, electron, and proton-electron transfers through the choice of base and oxidant, with the concerted pathway occurring exclusively as a secondary parallel route. Through detailed kinetics analysis, we define free energy relationships for the kinetics of elementary reaction steps, which provide insight into the factors influencing reaction mechanism. Rate constants for proton transfer processes in the limiting stepwise pathways reveal a large reorganization energy associated with protonation/deprotonation of the metal center (λ = 1.59 eV) and suggest that sluggish proton transfer kinetics hinder access to a concerted route. Rate constants for concerted PCET indicate that the concerted routes are asynchronous. Additionally, through quantification of the relative contributions of parallel stepwise and concerted mechanisms toward net product formation, the influence of various reaction parameters on reactivity are identified. This work underscores the importance of understanding the PCET mechanism for controlling metal hydride reactivity, which could lead to superior catalyst design for fuel production and oxidation.
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Affiliation(s)
- Tao Huang
- Department of Chemistry , University of North Carolina at Chapel Hill , Chapel Hill , North Carolina 27599-3290 , United States
| | - Eric S Rountree
- Department of Chemistry , University of North Carolina at Chapel Hill , Chapel Hill , North Carolina 27599-3290 , United States
| | - Andrew P Traywick
- Department of Chemistry , University of North Carolina at Chapel Hill , Chapel Hill , North Carolina 27599-3290 , United States
| | - Magd Bayoumi
- Department of Chemistry , University of North Carolina at Chapel Hill , Chapel Hill , North Carolina 27599-3290 , United States
| | - Jillian L Dempsey
- Department of Chemistry , University of North Carolina at Chapel Hill , Chapel Hill , North Carolina 27599-3290 , United States
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24
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25
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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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26
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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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27
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Thiyagarajan SK, Suresh R, Ramanan V, Ramamurthy P. Deciphering the incognito role of water in a light driven proton coupled electron transfer process. Chem Sci 2018; 9:910-921. [PMID: 29629158 PMCID: PMC5873145 DOI: 10.1039/c7sc03161k] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/19/2017] [Accepted: 11/10/2017] [Indexed: 01/26/2023] Open
Abstract
Light induced multisite electron proton transfer in two different phenol (simple and phenol carrying an intramolecularly hydrogen bonded base) pendants on acridinedione dye (ADD) and an NADH analogue was studied by following fluorescence quenching dynamics in an ultrafast timescale. In a simple phenol derivative (ADDOH), photo-excited acridinedione acquires an electron from phenol intramolecularly, coupled with the transfer of a proton to solvent water. But in a phenol carrying hydrogen bonded base (ADDDP), both electron and proton transfer occur completely intramolecularly. The sequence of this electron and proton transfer process was validated by discerning the pH dependency of the reaction kinetics. Since photo-excited ADDs are stronger oxidants, the sequential electron first proton transfer mechanism (ETPT) was observed in ADDOH and hence there is no change in the PCET reaction kinetics kETPT ∼ 6.57 × 109 s-1 in the entire pH range (pH 2-12). But the phenol carrying hydrogen bonded base (ADDDP) unleashes concerted electron proton transfer where the PCET reaction rate decreases upon decreasing the pH below its pKa. Noticeably, the concerted EPT process in ADDDP mimics the donor side of photosystem II and it occurs by two distinct pathways: (i) through direct intramolecular hydrogen bonding between the phenol and amine, kDEPT ∼ 12.5 × 1010 s-1 and (ii) through the bidirectional hydrogen bond extended by the water molecule trapped in between the proton donor and acceptor, which mediates the proton transfer and serves as a proton wire, kWMEPT ∼ 2.85 × 1010 s-1. These results unravel the incognito role played by water in mediating the proton transfer process when the structural elements do not favor direct hydrogen bonding between the proton donor and acceptor in a concerted PCET reaction.
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Affiliation(s)
- Senthil Kumar Thiyagarajan
- National Centre for Ultrafast Processes , University of Madras , Taramani Campus , Chennai - 600 113 , India .
| | - Raghupathy Suresh
- National Centre for Ultrafast Processes , University of Madras , Taramani Campus , Chennai - 600 113 , India .
| | - Vadivel Ramanan
- National Centre for Ultrafast Processes , University of Madras , Taramani Campus , Chennai - 600 113 , India .
| | - Perumal Ramamurthy
- National Centre for Ultrafast Processes , University of Madras , Taramani Campus , Chennai - 600 113 , India .
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28
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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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29
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Morris WD, Mayer JM. Separating Proton and Electron Transfer Effects in Three-Component Concerted Proton-Coupled Electron Transfer Reactions. J Am Chem Soc 2017; 139:10312-10319. [PMID: 28671470 DOI: 10.1021/jacs.7b03562] [Citation(s) in RCA: 55] [Impact Index Per Article: 7.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Multiple-site concerted proton-electron transfer (MS-CPET) reactions were studied in a three-component system. 1-Hydroxy-2,2,6,6-tetramethylpiperidine (TEMPOH) was oxidized to the stable radical TEMPO by electron transfer to ferrocenium oxidants coupled to proton transfer to various pyridine bases. These MS-CPET reactions contrast with the usual reactivity of TEMPOH by hydrogen atom transfer (HAT) to a single e-/H+ acceptor. The three-component reactions proceed by pre-equilibrium formation of a hydrogen-bonded adduct between TEMPOH and the pyridine base, and the adduct is then oxidized by the ferrocenium in a bimolecular MS-CPET step. The second-order rate constants, measured using stopped-flow kinetic techniques, spanned 4 orders of magnitude. An advantage of this system is that the MS-CPET driving force could be independently varied by changing either the pKa of the base or the reduction potential (E°) of the oxidant. Changes in ΔG°MS-CPET from either source had the same effect on the MS-CPET rate constants, and a combined Brønsted plot of ln(kMS-CPET) vs ln(Keq) was linear with a slope of 0.46. These results imply a synchronous concerted mechanism, in which the proton and electron transfer components of the CPET process make equal contributions to the rate constants. The only outliers to the Brønsted correlation are the reactions with sterically hindered pyridines, which apparently hinder the close approach of proton donor and acceptor that facilitates MS-CPET. These three-component reactions are compared with a related HAT reaction of TEMPOH, with the 2,4,6-tri-tert-butylphenoxyl radical. The MS-CPET and HAT oxidations of TEMPOH at the same driving force occurred with similar rate constants. While this is an imperfect comparison, the data suggest that the separation of the proton and electron to different reagents does not significantly inhibit the proton-coupled electron transfer process.
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Affiliation(s)
- Wesley D Morris
- Department of Chemistry, Yale University , New Haven, Connecticut 06511, United States
| | - James M Mayer
- Department of Chemistry, Yale University , New Haven, Connecticut 06511, United States
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30
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Skaisgirski M, Guo X, Wenger OS. Electron Accumulation on Naphthalene Diimide Photosensitized by [Ru(2,2′-Bipyridine)3]2+. Inorg Chem 2017; 56:2432-2439. [DOI: 10.1021/acs.inorgchem.6b02446] [Citation(s) in RCA: 31] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Affiliation(s)
- Michael Skaisgirski
- Department of Chemistry, University of Basel, St. Johanns-Ring 19, 4056 Basel, Switzerland
| | - Xingwei Guo
- 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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31
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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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32
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Dhar D, Yee GM, Markle TF, Mayer JM, Tolman WB. Reactivity of the copper(iii)-hydroxide unit with phenols. Chem Sci 2017; 8:1075-1085. [PMID: 28572905 PMCID: PMC5452261 DOI: 10.1039/c6sc03039d] [Citation(s) in RCA: 57] [Impact Index Per Article: 8.1] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/11/2016] [Accepted: 09/08/2016] [Indexed: 01/09/2023] Open
Abstract
Kinetic studies of the reactions of two previously characterized copper(iii)-hydroxide complexes (LCuOH and NO2 LCuOH, where L = N,N'-bis(2,6-diisopropylphenyl)-2,6-pyridine-dicarboxamide and NO2 L = N,N'-bis(2,6-diisopropyl-4-nitrophenyl)pyridine-2,6-dicarboxamide) with a series of para substituted phenols (XArOH where X = NMe2, OMe, Me, H, Cl, NO2, or CF3) were performed using low temperature stopped-flow UV-vis spectroscopy. Second-order rate constants (k) were determined from pseudo first-order and stoichiometric experiments, and follow the trends CF3 < NO2 < Cl < H < Me < OMe < NMe2 and LCuOH < NO2 LCuOH. The data support a concerted proton-electron transfer (CPET) mechanism for all but the most acidic phenols (X = NO2 and CF3), for which a more complicated mechanism is proposed. For the case of the reactions between NO2 ArOH and LCuOH in particular, competition between a CPET pathway and one involving initial proton transfer followed by electron transfer (PT/ET) is supported by multiwavelength global analysis of the kinetic data, formation of the phenoxide NO2 ArO- as a reaction product, observation of an intermediate [LCu(OH2)]+ species derived from proton transfer from NO2 ArOH to LCuOH, and thermodynamic arguments indicating that initial PT should be competitive with CPET.
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Affiliation(s)
- Debanjan Dhar
- Department of Chemistry , Center for Metals in Biocatalysis , University of Minnesota , 207 Pleasant St. SE , Minneapolis , MN 55455 , USA .
| | - Gereon M Yee
- Department of Chemistry , Center for Metals in Biocatalysis , University of Minnesota , 207 Pleasant St. SE , Minneapolis , MN 55455 , USA .
| | - Todd F Markle
- Department of Chemistry , Yale University , New Haven , Connecticut 06520-8107 , USA .
| | - James M Mayer
- Department of Chemistry , Yale University , New Haven , Connecticut 06520-8107 , USA .
| | - William B Tolman
- Department of Chemistry , Center for Metals in Biocatalysis , University of Minnesota , 207 Pleasant St. SE , Minneapolis , MN 55455 , USA .
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33
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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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34
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Direct observation of light-driven, concerted electron-proton transfer. Proc Natl Acad Sci U S A 2016; 113:11106-11109. [PMID: 27660239 DOI: 10.1073/pnas.1611496113] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The phenols 4-methylphenol, 4-methoxyphenol, and N-acetyl-tyrosine form hydrogen-bonded adducts with N-methyl-4, 4'-bipyridinium cation (MQ+) in aqueous solution as evidenced by the appearance of low-energy, low-absorptivity features in UV-visible spectra. They are assigned to the known examples of optically induced, concerted electron-proton transfer, photoEPT. The results of ultrafast transient absorption measurements on the assembly MeOPhO-H---MQ+ are consistent with concerted EPT by the instantaneous appearance of spectral features for MeOPhO·---H-MQ+ in the transient spectra at the first observation time of 0.1 ps. The transient decays to MeOPhO-H---MQ+ in 2.5 ps, accompanied by the appearance of oscillations in the decay traces with a period of ∼1 ps, consistent with a vibrational coherence and relaxation from a higher υ(N-H) vibrational level or levels on the timescale for back EPT.
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35
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Milić J, Zalibera M, Pochorovski I, Trapp N, Nomrowski J, Neshchadin D, Ruhlmann L, Boudon C, Wenger OS, Savitsky A, Lubitz W, Gescheidt G, Diederich F. Paramagnetic Molecular Grippers: The Elements of Six-State Redox Switches. J Phys Chem Lett 2016; 7:2470-2477. [PMID: 27300355 DOI: 10.1021/acs.jpclett.6b01094] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/06/2023]
Abstract
The development of semiquinone-based resorcin[4]arene cavitands expands the toolbox of switchable molecular grippers by introducing the first paramagnetic representatives. The semiquinone (SQ) states were generated electrochemically, chemically, and photochemically. We analyzed their electronic, conformational, and binding properties by cyclic voltammetry, ultraviolet/visible (UV/vis) spectroelectrochemistry, electron paramagnetic resonance (EPR) and transient absorption spectroscopy, in conjunction with density functional theory (DFT) calculations. The utility of UV/vis spectroelectrochemistry and EPR spectroscopy in evaluating the conformational features of resorcin[4]arene cavitands is demonstrated. Guest binding properties were found to be enhanced in the SQ state as compared to the quinone (Q) or the hydroquinone (HQ) states of the cavitands. Thus, these paramagnetic SQ intermediates open the way to six-state redox switches provided by two conformations (open and closed) in three redox states (Q, SQ, and HQ) possessing distinct binding ability. The switchable magnetic properties of these molecular grippers and their responsiveness to electrical stimuli has the potential for development of efficient molecular devices.
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Affiliation(s)
- Jovana Milić
- Laboratory of Organic Chemistry, ETH Zurich , Vladimir-Prelog-Weg 3, 8093 Zurich, Switzerland
| | - Michal Zalibera
- Max Planck Institute for Chemical Energy Conversion , Stiftstrasse 34-36, 45470 Mülheim an der Ruhr, Germany
- Institute of Physical Chemistry and Chemical Physics, Slovak University of Technology in Bratislava, Faculty of Chemical and Food Technology , Radlinského 9, 81237 Bratislava, Slovak Republic
| | - Igor Pochorovski
- Laboratory of Organic Chemistry, ETH Zurich , Vladimir-Prelog-Weg 3, 8093 Zurich, Switzerland
| | - Nils Trapp
- Laboratory of Organic Chemistry, ETH Zurich , Vladimir-Prelog-Weg 3, 8093 Zurich, Switzerland
| | - Julia Nomrowski
- Department of Chemistry, University of Basel , St. Johanns-Ring 19, 4056 Basel, Switzerland
| | - Dmytro Neshchadin
- Institute of Physical and Theoretical Chemistry, NAWI Graz, Graz University of Technology , Stremayrgasse 9/Z2, 8010 Graz, Austria
| | - Laurent Ruhlmann
- Université de Strasbourg, Laboratoire d'Électrochimie et Chimie Physique du Corps Solide, Institut de Chimie de Strasbourg, 4 rue Blaise Pascal, CS 90032, 67081 Strasbourg, France
| | - Corinne Boudon
- Université de Strasbourg, Laboratoire d'Électrochimie et Chimie Physique du Corps Solide, Institut de Chimie de Strasbourg, 4 rue Blaise Pascal, CS 90032, 67081 Strasbourg, France
| | - Oliver S Wenger
- Department of Chemistry, University of Basel , St. Johanns-Ring 19, 4056 Basel, Switzerland
| | - Anton Savitsky
- Max Planck Institute for Chemical Energy Conversion , Stiftstrasse 34-36, 45470 Mülheim an der Ruhr, Germany
| | - Wolfgang Lubitz
- Max Planck Institute for Chemical Energy Conversion , Stiftstrasse 34-36, 45470 Mülheim an der Ruhr, Germany
| | - Georg Gescheidt
- Institute of Physical and Theoretical Chemistry, NAWI Graz, Graz University of Technology , Stremayrgasse 9/Z2, 8010 Graz, Austria
| | - François Diederich
- Laboratory of Organic Chemistry, ETH Zurich , Vladimir-Prelog-Weg 3, 8093 Zurich, Switzerland
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36
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Pannwitz A, Wenger OS. Proton coupled electron transfer from the excited state of a ruthenium(ii) pyridylimidazole complex. Phys Chem Chem Phys 2016; 18:11374-82. [DOI: 10.1039/c6cp00437g] [Citation(s) in RCA: 27] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Transfer of one electron and one proton from [Ru(bpy)2pyimH]2+ to monoquat (MQ+) upon photoexcitation, corresponding to net transfer of a hydrogen atom.
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Affiliation(s)
- Andrea Pannwitz
- Department of Chemistry
- University of Basel
- 4056 Basel
- Switzerland
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37
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Rajeswari A, Ramdass A, Muthu Mareeswaran P, Rajagopal S. Electron Transfer Studies of Ruthenium(II) Complexes with Biologically Important Phenolic Acids and Tyrosine. J Fluoresc 2015; 26:531-43. [DOI: 10.1007/s10895-015-1738-3] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/11/2015] [Accepted: 11/27/2015] [Indexed: 01/24/2023]
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38
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Büldt LA, Prescimone A, Neuburger M, Wenger OS. Photoredox Properties of Homoleptic d6Metal Complexes with the Electron-Rich 4,4′,5,5′-Tetramethoxy-2,2′-bipyridine Ligand. Eur J Inorg Chem 2015. [DOI: 10.1002/ejic.201500670] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
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39
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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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