1
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Medagedara H, Teferi MY, Wanasinghe ST, Burson W, Kizi S, Zaslona B, Mardis KL, Niklas J, Poluektov OG, Rury AS. Decorrelated singlet and triplet exciton delocalization in acetylene-bridged Zn-porphyrin dimers. Chem Sci 2024; 15:1736-1751. [PMID: 38303928 PMCID: PMC10829018 DOI: 10.1039/d3sc03327a] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/29/2023] [Accepted: 12/12/2023] [Indexed: 02/03/2024] Open
Abstract
The controlled delocalization of molecular excitons remains an important goal towards the application of organic chromophores in processes ranging from light-initiated chemical transformations to classical and quantum information processing. In this study, we present a methodology to couple optical and magnetic spectroscopic techniques and assess the delocalization of singlet and triplet excitons in model molecular chromophores. By comparing the steady-state and time-resolved optical spectra of Zn-porphyrin monomers and weakly coupled dimers, we show that we can use the identity of substituents bound at specific positions of the macromolecules' rings to control the inter-ring delocalization of singlet excitons stemming from their B states through acetylene bridges. While broadened steady-state absorption spectra suggest the presence of delocalized B state excitons in mesityl-substituted Zn-tetraphenyl porphyrin dimers (Zn2U-D), we confirm this conclusion by measuring an enhanced ultrafast non-radiative relaxation from these inter-ring excitonic states to lower lying electronic states relative to their monomer. In contrast to the delocalized nature of singlet excitons, we use time-resolved EPR and ENDOR spectroscopies to show that the triplet states of the Zn-porphyrin dimers remain localized on one of the two macrocyclic sub-units. We use the analysis of EPR and ENDOR measurements on unmetallated model porphyrin monomers and dimers to support this conclusion. The results of DFT calculations also support the interpretation of localized triplet states. These results demonstrate researchers cannot conclude triplet excitons delocalize in macromolecular based on the presence of spatially extended singlet excitons, which can help in the design of chromophores for application in spin conversion and information processing technologies.
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Affiliation(s)
- Hasini Medagedara
- Department of Chemistry, Wayne State University Detroit MI 48202 USA
| | - Mandefro Y Teferi
- Chemical Sciences and Engineering Division, Argonne National Laboratory Lemont IL 60439 USA
| | | | - Wade Burson
- Department of Chemistry, Wayne State University Detroit MI 48202 USA
| | - Shahad Kizi
- Department of Chemistry, Wayne State University Detroit MI 48202 USA
| | - Bradly Zaslona
- Department of Chemistry, Wayne State University Detroit MI 48202 USA
| | - Kristy L Mardis
- Department of Chemistry, Physics, and Engineering Sciences, Chicago State University Chicago IL 60628 USA
| | - Jens Niklas
- Chemical Sciences and Engineering Division, Argonne National Laboratory Lemont IL 60439 USA
| | - Oleg G Poluektov
- Chemical Sciences and Engineering Division, Argonne National Laboratory Lemont IL 60439 USA
| | - Aaron S Rury
- Department of Chemistry, Wayne State University Detroit MI 48202 USA
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2
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Privitera A, Faccio D, Giuri D, Latawiec EI, Genovese D, Tassinari F, Mummolo L, Chiesa M, Fontanesi C, Salvadori E, Cornia A, Wasielewski MR, Tomasini C, Sessoli R. Challenges in the Direct Detection of Chirality-induced Spin Selectivity: Investigation of Foldamer-based Donor-acceptor Dyads. Chemistry 2023:e202301005. [PMID: 37677125 DOI: 10.1002/chem.202301005] [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: 03/29/2023] [Revised: 08/15/2023] [Accepted: 09/04/2023] [Indexed: 09/09/2023]
Abstract
Over the past two decades, the chirality-induced spin selectivity (CISS) effect was reported in several experiments disclosing a unique connection between chirality and electron spin. Recent theoretical works highlighted time-resolved Electron Paramagnetic Resonance (trEPR) as a powerful tool to directly detect the spin polarization resulting from CISS. Here, we report a first attempt to detect CISS at the molecular level by linking the pyrene electron donor to the fullerene acceptor with chiral peptide bridges of different length and electric dipole moment. The dyads are investigated by an array of techniques, including cyclic voltammetry, steady-state and transient optical spectroscopies, and trEPR. Despite the promising energy alignment of the electronic levels, our multi-technique analysis reveals no evidence of electron transfer (ET), highlighting the challenges of spectroscopic detection of CISS. However, the analysis allows the formulation of guidelines for the design of chiral organic model systems suitable to directly probe CISS-polarized ET.
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Affiliation(s)
- Alberto Privitera
- Department of Industrial Engineering, University of Florence, Via Santa Marta 3, 50139, Firenze, Italy
- Department of Chemistry and NIS Centre, University of Torino, Via Pietro Giuria 7, 10125, Torino, Italy
| | - Davide Faccio
- Department of Chemistry "Giacomo Ciamician", University of Bologna, Via Selmi 2, 40126, Bologna, Italy
| | - Demetra Giuri
- Department of Chemistry "Giacomo Ciamician", University of Bologna, Via Selmi 2, 40126, Bologna, Italy
| | - Elisabeth I Latawiec
- Department of Chemistry, Center for Molecular Quantum Transduction, and Paula M. Trienens Institute for Sustainability and Energy, Northwestern University, Evanston, IL, 60208-3113, USA
| | - Damiano Genovese
- Department of Chemistry "Giacomo Ciamician", University of Bologna, Via Selmi 2, 40126, Bologna, Italy
| | - Francesco Tassinari
- Department of Chemical and Geological Sciences and, INSTM Research Unit, University of Modena and Reggio Emilia, Via G. Campi 103, 41125, Modena, Italy
| | - Liviana Mummolo
- Department of Chemistry "Giacomo Ciamician", University of Bologna, Via Selmi 2, 40126, Bologna, Italy
| | - Mario Chiesa
- Department of Chemistry and NIS Centre, University of Torino, Via Pietro Giuria 7, 10125, Torino, Italy
| | - Claudio Fontanesi
- Department of Engineering "E. Ferrari", University of Modena and Reggio Emilia, Via P. Vivarelli 10, 41125, Modena, Italy
| | - Enrico Salvadori
- Department of Chemistry and NIS Centre, University of Torino, Via Pietro Giuria 7, 10125, Torino, Italy
| | - Andrea Cornia
- Department of Chemical and Geological Sciences and, INSTM Research Unit, University of Modena and Reggio Emilia, Via G. Campi 103, 41125, Modena, Italy
| | - Michael R Wasielewski
- Department of Chemistry, Center for Molecular Quantum Transduction, and Paula M. Trienens Institute for Sustainability and Energy, Northwestern University, Evanston, IL, 60208-3113, USA
| | - Claudia Tomasini
- Department of Chemistry "Giacomo Ciamician", University of Bologna, Via Selmi 2, 40126, Bologna, Italy
| | - Roberta Sessoli
- Department of Chemistry "U. Schiff" and INSTM Research Unit, University of Florence, Via della Lastruccia 3-13, 50019, Sesto Fiorentino, Italy
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3
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Tateno A, Masuzawa K, Nagashima H, Maeda K. Anisotropic and Coherent Control of Radical Pairs by Optimized RF Fields. Int J Mol Sci 2023; 24:ijms24119700. [PMID: 37298651 DOI: 10.3390/ijms24119700] [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: 04/30/2023] [Revised: 05/30/2023] [Accepted: 05/31/2023] [Indexed: 06/12/2023] Open
Abstract
Radical pair kinetics is determined by the coherent and incoherent spin dynamics of spin pair and spin-selective chemical reactions. In a previous paper, reaction control and nuclear spin state selection by designed radiofrequency (RF) magnetic resonance was proposed. Here, we present two novel types of reaction control calculated by the local optimization method. One is anisotropic reaction control and the other is coherent path control. In both cases, the weighting parameters for the target states play an important role in the optimizing of the RF field. In the anisotropic control of radical pairs, the weighting parameters play an important role in the selection of the sub-ensemble. In coherent control, one can set the parameters for the intermediate states, and it is possible to specify the path to reach a final state by adjusting the weighting parameters. The global optimization of the weighting parameters for coherent control has been studied. These manifest calculations show the possibility of controlling the chemical reactions of radical pair intermediates in different ways.
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Affiliation(s)
- Akihiro Tateno
- Department of Chemistry, Graduate School of Science and Engineering, Saitama University, 255 Shimo-okubo, Sakura-ku, Saitama 338-8570, Japan
| | - Kenta Masuzawa
- Department of Chemistry, Graduate School of Science and Engineering, Saitama University, 255 Shimo-okubo, Sakura-ku, Saitama 338-8570, Japan
| | - Hiroki Nagashima
- Department of Chemistry, Graduate School of Science and Engineering, Saitama University, 255 Shimo-okubo, Sakura-ku, Saitama 338-8570, Japan
| | - Kiminori Maeda
- Department of Chemistry, Graduate School of Science and Engineering, Saitama University, 255 Shimo-okubo, Sakura-ku, Saitama 338-8570, Japan
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Eschenbach P, Artiukhin DG, Neugebauer J. Reliable Isotropic Electron-Paramagnetic-Resonance Hyperfine Coupling Constants from the Frozen-Density Embedding Quasi-Diabatization Approach. J Phys Chem A 2022; 126:8358-8368. [DOI: 10.1021/acs.jpca.2c04959] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Patrick Eschenbach
- Theoretische Organische Chemie, Organisch-Chemisches Institut and Center for Multiscale Theory and Simulation, Westfälische Wilhelms-Universität Münster, Corrensstraße 36, 48149 Münster, Germany
| | - Denis G. Artiukhin
- Institut für Chemie und Biochemie, Freie Universität Berlin, Arnimallee 22, 14195 Berlin, Germany
| | - Johannes Neugebauer
- Theoretische Organische Chemie, Organisch-Chemisches Institut and Center for Multiscale Theory and Simulation, Westfälische Wilhelms-Universität Münster, Corrensstraße 36, 48149 Münster, Germany
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5
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Eschenbach P, Neugebauer J. Subsystem density-functional theory: A reliable tool for spin-density based properties. J Chem Phys 2022; 157:130902. [PMID: 36209003 DOI: 10.1063/5.0103091] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Subsystem density-functional theory compiles a set of features that allow for efficiently calculating properties of very large open-shell radical systems such as organic radical crystals, proteins, or deoxyribonucleic acid stacks. It is computationally less costly than correlated ab initio wave function approaches and can pragmatically avoid the overdelocalization problem of Kohn-Sham density-functional theory without employing hard constraints on the electron-density. Additionally, subsystem density-functional theory calculations commonly start from isolated fragment electron densities, pragmatically preserving a priori specified subsystem spin-patterns throughout the calculation. Methods based on subsystem density-functional theory have seen a rapid development over the past years and have become important tools for describing open-shell properties. In this Perspective, we address open questions and possible developments toward challenging future applications in connection with subsystem density-functional theory for spin-dependent properties.
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Affiliation(s)
- Patrick Eschenbach
- Theoretische Organische Chemie, Organisch-Chemisches Institut and Center for Multiscale Theory and Simulation, Westfälische Wilhelms-Universität Münster, Corrensstraße 36, 48149 Münster, Germany
| | - Johannes Neugebauer
- Theoretische Organische Chemie, Organisch-Chemisches Institut and Center for Multiscale Theory and Simulation, Westfälische Wilhelms-Universität Münster, Corrensstraße 36, 48149 Münster, Germany
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6
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Symmetry Breaking Charge Transfer in DNA-Templated Perylene Dimer Aggregates. MOLECULES (BASEL, SWITZERLAND) 2022; 27:molecules27196612. [PMID: 36235149 PMCID: PMC9571668 DOI: 10.3390/molecules27196612] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 09/03/2022] [Revised: 09/20/2022] [Accepted: 09/28/2022] [Indexed: 11/19/2022]
Abstract
Molecular aggregates are of interest to a broad range of fields including light harvesting, organic optoelectronics, and nanoscale computing. In molecular aggregates, nonradiative decay pathways may emerge that were not present in the constituent molecules. Such nonradiative decay pathways may include singlet fission, excimer relaxation, and symmetry-breaking charge transfer. Singlet fission, sometimes referred to as excitation multiplication, is of great interest to the fields of energy conversion and quantum information. For example, endothermic singlet fission, which avoids energy loss, has been observed in covalently bound, linear perylene trimers and tetramers. In this work, the electronic structure and excited-state dynamics of dimers of a perylene derivative templated using DNA were investigated. Specifically, DNA Holliday junctions were used to template the aggregation of two perylene molecules covalently linked to a modified uracil nucleobase through an ethynyl group. The perylenes were templated in the form of monomer, transverse dimer, and adjacent dimer configurations. The electronic structure of the perylene monomers and dimers were characterized via steady-state absorption and fluorescence spectroscopy. Initial insights into their excited-state dynamics were gleaned from relative fluorescence intensity measurements, which indicated that a new nonradiative decay pathway emerges in the dimers. Femtosecond visible transient absorption spectroscopy was subsequently used to elucidate the excited-state dynamics. A new excited-state absorption feature grows in on the tens of picosecond timescale in the dimers, which is attributed to the formation of perylene anions and cations resulting from symmetry-breaking charge transfer. Given the close proximity required for symmetry-breaking charge transfer, the results shed promising light on the prospect of singlet fission in DNA-templated molecular aggregates.
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7
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Hyperfine Decoupling of ESR Spectra Using Wavelet Transform. MAGNETOCHEMISTRY 2022. [PMID: 37475982 PMCID: PMC10357921 DOI: 10.3390/magnetochemistry8030032] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
The objective of spectral analysis is to resolve and extract relevant features from experimental data in an optimal fashion. In continuous-wave (cw) electron spin resonance (ESR) spectroscopy, both g values of a paramagnetic center and hyperfine splitting (A) caused by its interaction with neighboring magnetic nuclei in a molecule provide important structural and electronic information. However, in the presence of g- and/or A-anisotropy and/or large number of resonance lines, spectral analysis becomes highly challenging. Either high-resolution experimental techniques are employed to resolve the spectra in those cases or a range of suitable ESR frequencies are used in combination with simulations to identify the corresponding g and A values. In this work, we present a wavelet transform technique in resolving both simulated and experimental cw-ESR spectra by separating the hyperfine and super-hyperfine components. We exploit the multiresolution property of wavelet transforms that allow the separation of distinct features of a spectrum based on simultaneous analysis of spectrum and its varying frequency. We retain the wavelet components that stored the hyperfine and/or super-hyperfine features, while eliminating the wavelet components representing the remaining spectrum. We tested the method on simulated cases of metal–ligand adducts at L-, S-, and X-band frequencies, and showed that extracted g values, hyperfine and super-hyperfine coupling constants from simulated spectra, were in excellent agreement with the values of those parameters used in the simulations. For the experimental case of a copper(II) complex with distorted octahedral geometry, the method was able to extract g and hyperfine coupling constant values, and revealed features that were buried in the overlapped spectra.
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8
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Harvey SM, Wasielewski MR. Photogenerated Spin-Correlated Radical Pairs: From Photosynthetic Energy Transduction to Quantum Information Science. J Am Chem Soc 2021; 143:15508-15529. [PMID: 34533930 DOI: 10.1021/jacs.1c07706] [Citation(s) in RCA: 37] [Impact Index Per Article: 12.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Abstract
More than a half century ago, the NMR spectra of diamagnetic products resulting from radical pair reactions were observed to have strongly enhanced absorptive and emissive resonances. At the same time, photogenerated radical pairs were discovered to exhibit unusual electron paramagnetic resonance spectra that also had such resonances. These non-Boltzmann, spin-polarized spectra were observed in both chemical systems as well as in photosynthetic reaction center proteins following photodriven charge separation. Subsequent studies of these phenomena led to a variety of chemical electron donor-acceptor model systems that provided a broad understanding of the spin dynamics responsible for these spectra. When the distance between the two radicals is restricted, these observations result from the formation of spin-correlated radical pairs (SCRPs) in which the spin-spin exchange and dipolar interactions between the two unpaired spins play an important role in the spin dynamics. Early on, it was recognized that SCRPs photogenerated by ultrafast electron transfer are entangled spin pairs created in a well-defined spin state. These SCRPs can serve as spin qubit pairs (SQPs), whose spin dynamics can be manipulated to study a wide variety of quantum phenomena intrinsic to the field of quantum information science. This Perspective highlights the role of SCRPs as SQPs, gives examples of possible quantum manipulations using SQPs, and provides some thoughts on future directions.
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Affiliation(s)
- Samantha M Harvey
- Department of Chemistry, Center for Molecular Quantum Transduction, and Institute for Sustainability and Energy at Northwestern, Northwestern University, Evanston, Illinois 60208-3113, United States
| | - Michael R Wasielewski
- Department of Chemistry, Center for Molecular Quantum Transduction, and Institute for Sustainability and Energy at Northwestern, Northwestern University, Evanston, Illinois 60208-3113, United States
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9
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Richert S, Anderson HL, Peeks MD, Timmel CR. Probing the orientation of porphyrin oligomers in a liquid crystal solvent – a triplet state electron paramagnetic resonance study. Mol Phys 2019. [DOI: 10.1080/00268976.2018.1511868] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/28/2022]
Affiliation(s)
- Sabine Richert
- Centre for Advanced Electron Spin Resonance (CÆSR), University of Oxford, Oxford, UK
| | | | - Martin D. Peeks
- Chemistry Research Laboratory, University of Oxford, Oxford, UK
| | - Christiane R. Timmel
- Centre for Advanced Electron Spin Resonance (CÆSR), University of Oxford, Oxford, UK
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10
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Ivanov KL, Lukzen NN. Multiplet-to-net CIDEP conversion by MW-pulses with adiabatically ramped amplitude. Mol Phys 2019. [DOI: 10.1080/00268976.2018.1562121] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Affiliation(s)
- Konstantin L. Ivanov
- International Tomography Center, Siberian Branch of the Russian Academy of Science, Novosibirsk, Russia
- Novosibirsk State University, Novosibirsk, Russia
| | - Nikita N. Lukzen
- International Tomography Center, Siberian Branch of the Russian Academy of Science, Novosibirsk, Russia
- Novosibirsk State University, Novosibirsk, Russia
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11
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Kim W, Nowak-Król A, Hong Y, Schlosser F, Würthner F, Kim D. Solvent-Modulated Charge-Transfer Resonance Enhancement in the Excimer State of a Bay-Substituted Perylene Bisimide Cyclophane. J Phys Chem Lett 2019; 10:1919-1927. [PMID: 30892901 DOI: 10.1021/acs.jpclett.9b00357] [Citation(s) in RCA: 44] [Impact Index Per Article: 8.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/09/2023]
Abstract
Excimer, a configurational mixing between Frenkel exciton and charge-transfer resonance states, is typically regarded as a trap state that hinders desired energy or charge-transfer processes in artificial molecular assemblies. However, in recent days, the excimer has received much attention as a functional intermediate in the excited-state dynamics such as singlet fission or charge-separation processes. In this work, we show that the relative contribution to charge-transfer resonance of the excimer state in a bay-substituted perylene bisimide dimer cyclophane can be modulated by dielectric properties of the solvents employed. Solvent-dependent time-resolved fluorescence and absorption measurements reveal that an enhancement of charge-transfer resonance in the excimer state is reflected by incomplete symmetry-breaking charge-separation processes from the structurally relaxed excimer state by means of dipolar solvation processes in the high dielectric environment.
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Affiliation(s)
- Woojae Kim
- Department of Chemistry and Spectroscopy Laboratory for Functional π-Electronic Systems , Yonsei University , Seoul 03722 , Korea
| | - Agnieszka Nowak-Król
- Institut für Organische Chemie and Center for Nanosystems Chemistry , Universität Würzburg , Am Hubland , 97074 Würzburg , Germany
| | - Yongseok Hong
- Department of Chemistry and Spectroscopy Laboratory for Functional π-Electronic Systems , Yonsei University , Seoul 03722 , Korea
| | - Felix Schlosser
- Institut für Organische Chemie and Center for Nanosystems Chemistry , Universität Würzburg , Am Hubland , 97074 Würzburg , Germany
| | - Frank Würthner
- Institut für Organische Chemie and Center for Nanosystems Chemistry , Universität Würzburg , Am Hubland , 97074 Würzburg , Germany
| | - Dongho Kim
- Department of Chemistry and Spectroscopy Laboratory for Functional π-Electronic Systems , Yonsei University , Seoul 03722 , Korea
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12
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Möbius K, Lubitz W, Savitsky A. Jim Hyde and the ENDOR Connection: A Personal Account. APPLIED MAGNETIC RESONANCE 2017; 48:1149-1183. [PMID: 29151676 PMCID: PMC5668355 DOI: 10.1007/s00723-017-0959-9] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 09/29/2017] [Indexed: 06/07/2023]
Abstract
In this minireview, we report on our year-long EPR work, such as electron-nuclear double resonance (ENDOR), pulse electron double resonance (PELDOR) and ELDOR-detected NMR (EDNMR) at X-band and W-band microwave frequencies and magnetic fields. This report is dedicated to James S. Hyde and honors his pioneering contributions to the measurement of spin interactions in large (bio)molecules. From these interactions, detailed information is revealed on structure and dynamics of macromolecules embedded in liquid-solution or solid-state environments. New developments in pulsed microwave and sweepable cryomagnet technology as well as ultra-fast electronics for signal data handling and processing have pushed the limits of EPR spectroscopy and its multi-frequency extensions to new horizons concerning sensitivity of detection, selectivity of molecular interactions and time resolution. Among the most important advances is the upgrading of EPR to high magnetic fields, very much in analogy to what happened in NMR. The ongoing progress in EPR spectroscopy is exemplified by reviewing various multi-frequency electron-nuclear double-resonance experiments on organic radicals, light-generated donor-acceptor radical pairs in photosynthesis, and site-specifically nitroxide spin-labeled bacteriorhodopsin, the light-driven proton pump, as well as EDNMR and ENDOR on nitroxides. Signal and resolution enhancements are particularly spectacular for ENDOR, EDNMR and PELDOR on frozen-solution samples at high Zeeman fields. They provide orientation selection for disordered samples approaching single-crystal resolution at canonical g-tensor orientations-even for molecules with small g-anisotropies. Dramatic improvements of EPR detection sensitivity could be achieved, even for short-lived paramagnetic reaction intermediates. Thus, unique structural and dynamic information is revealed that can hardly be obtained by other analytical techniques. Micromolar concentrations of sample molecules have become sufficient to characterize stable and transient reaction intermediates of complex molecular systems-offering exciting applications for physicists, chemists, biochemists and molecular biologists.
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Affiliation(s)
- Klaus Möbius
- Department of Physics, Free University Berlin, Arnimallee 14, 14195 Berlin, Germany
- Max-Planck-Institute for Chemical Energy Conversion, 45470 Mülheim an der Ruhr, Germany
| | - Wolfgang Lubitz
- Max-Planck-Institute for Chemical Energy Conversion, 45470 Mülheim an der Ruhr, Germany
| | - Anton Savitsky
- Max-Planck-Institute for Chemical Energy Conversion, 45470 Mülheim an der Ruhr, Germany
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13
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Morozova OB, Yurkovskaya AV, Vieth HM, Sosnovsky DV, Ivanov KL. Light-induced spin hyperpolarisation in condensed phase. Mol Phys 2017. [DOI: 10.1080/00268976.2017.1363923] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/19/2022]
Affiliation(s)
- Olga B. Morozova
- Laboratory of Magnetic and Spin Phenomena, International Tomography Center SB RAS, Novosibirsk, 630090, Russia
- Laboratory of Magnetic Resonance in Chemistry, Biology and Medicine, Novosibirsk State University, Novosibirsk, 630090, Russia
| | - Alexandra V. Yurkovskaya
- Laboratory of Magnetic and Spin Phenomena, International Tomography Center SB RAS, Novosibirsk, 630090, Russia
- Laboratory of Magnetic Resonance in Chemistry, Biology and Medicine, Novosibirsk State University, Novosibirsk, 630090, Russia
| | - Hans-Martin Vieth
- Laboratory of Magnetic and Spin Phenomena, International Tomography Center SB RAS, Novosibirsk, 630090, Russia
- Department of Physics, Free University of Berlin, Berlin, 14195, Germany
| | - Denis V. Sosnovsky
- Laboratory of Magnetic and Spin Phenomena, International Tomography Center SB RAS, Novosibirsk, 630090, Russia
- Laboratory of Magnetic Resonance in Chemistry, Biology and Medicine, Novosibirsk State University, Novosibirsk, 630090, Russia
| | - Konstantin L. Ivanov
- Laboratory of Magnetic and Spin Phenomena, International Tomography Center SB RAS, Novosibirsk, 630090, Russia
- Laboratory of Magnetic Resonance in Chemistry, Biology and Medicine, Novosibirsk State University, Novosibirsk, 630090, Russia
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Richert S, Tait CE, Timmel CR. Delocalisation of photoexcited triplet states probed by transient EPR and hyperfine spectroscopy. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2017; 280:103-116. [PMID: 28579096 DOI: 10.1016/j.jmr.2017.01.005] [Citation(s) in RCA: 70] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/11/2016] [Revised: 01/05/2017] [Accepted: 01/07/2017] [Indexed: 05/22/2023]
Abstract
Photoexcited triplet states play a crucial role in photochemical mechanisms: long known to be of paramount importance in the study of photosynthetic reaction centres, they have more recently also been shown to play a major role in a number of applications in the field of molecular electronics. Their characterisation is crucial for an improved understanding of these processes with a particular focus on the determination of the spatial distribution of the triplet state wavefunction providing information on charge and energy transfer efficiencies. Currently, active research in this field is mostly focussed on the investigation of materials for organic photovoltaics (OPVs) and organic light emitting diodes (OLEDs). As the properties of triplet states and their spatial extent are known to have a major impact on device performance, a detailed understanding of the factors governing triplet state delocalisation is at the basis of the further development and improvement of these devices. Electron Paramagnetic Resonance (EPR) has proven a valuable tool in the study of triplet state properties and both experimental methods as well as data analysis and interpretation techniques have continuously improved over the last few decades. In this review, we discuss the theoretical and practical aspects of the investigation of triplet states and triplet state delocalisation by transient continuous wave and pulse EPR and highlight the advantages and limitations of the presently available techniques and the current trends in the field. Application of EPR in the study of triplet state delocalisation is illustrated on the example of linear multi-porphyrin chains designed as molecular wires.
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Affiliation(s)
- Sabine Richert
- Centre for Advanced Electron Spin Resonance (CAESR), Department of Chemistry, University of Oxford, South Parks Road, Oxford OX1 3QR, United Kingdom.
| | - Claudia E Tait
- Department of Chemistry, University of Washington, Seattle, WA 98195, United States.
| | - Christiane R Timmel
- Centre for Advanced Electron Spin Resonance (CAESR), Department of Chemistry, University of Oxford, South Parks Road, Oxford OX1 3QR, United Kingdom.
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15
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Hintze C, Steiner UE, Drescher M. Photoexcited Triplet State Kinetics Studied by Electron Paramagnetic Resonance Spectroscopy. Chemphyschem 2016; 18:6-16. [DOI: 10.1002/cphc.201600868] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/08/2016] [Revised: 10/07/2016] [Indexed: 11/08/2022]
Affiliation(s)
| | | | - Malte Drescher
- Fachbereich Chemie Universität Konstanz 78457 Konstanz Germany
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16
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Meyer A, Abdullin D, Schnakenburg G, Schiemann O. Single and double nitroxide labeled bis(terpyridine)-copper(ii): influence of orientation selectivity and multispin effects on PELDOR and RIDME. Phys Chem Chem Phys 2016; 18:9262-71. [DOI: 10.1039/c5cp07621h] [Citation(s) in RCA: 33] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Abstract
The structure of Jahn–Teller distorted copper–nitroxide complexes in neutral and acidic solutions is investigated using EPR distance measurements taking into account the influence of orientation selectivity and multispin effects.
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Affiliation(s)
- Andreas Meyer
- Institute of Physical and Theoretical Chemistry
- Rheinische Friedrich-Wilhelms-University Bonn
- 53115 Bonn
- Germany
| | - Dinar Abdullin
- Institute of Physical and Theoretical Chemistry
- Rheinische Friedrich-Wilhelms-University Bonn
- 53115 Bonn
- Germany
| | - Gregor Schnakenburg
- Institute of Inorganic Chemistry
- Rheinische Friedrich-Wilhelms-University Bonn
- 53121 Bonn
- Germany
| | - Olav Schiemann
- Institute of Physical and Theoretical Chemistry
- Rheinische Friedrich-Wilhelms-University Bonn
- 53115 Bonn
- Germany
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17
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Niklas J, Beaupré S, Leclerc M, Xu T, Yu L, Sperlich A, Dyakonov V, Poluektov OG. Photoinduced Dynamics of Charge Separation: From Photosynthesis to Polymer–Fullerene Bulk Heterojunctions. J Phys Chem B 2015; 119:7407-16. [DOI: 10.1021/jp511021v] [Citation(s) in RCA: 41] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Affiliation(s)
- Jens Niklas
- Chemical
Sciences and Engineering Division, Argonne National Laboratory, Argonne, Illinois 60439, United States
| | - Serge Beaupré
- Department
of Chemistry, Laval University, Quebec City, Quebec G1V 0A6, Canada
| | - Mario Leclerc
- Department
of Chemistry, Laval University, Quebec City, Quebec G1V 0A6, Canada
| | - Tao Xu
- Department
of Chemistry and James Franck Institute, University of Chicago, Chicago, Illinois 60637, United States
| | - Luping Yu
- Department
of Chemistry and James Franck Institute, University of Chicago, Chicago, Illinois 60637, United States
| | - Andreas Sperlich
- University of Würzburg and Bavarian Centre for Applied Energy
Research (ZAE Bayern), D-97074 Würzburg, Germany
| | - Vladimir Dyakonov
- University of Würzburg and Bavarian Centre for Applied Energy
Research (ZAE Bayern), D-97074 Würzburg, Germany
| | - Oleg G. Poluektov
- Chemical
Sciences and Engineering Division, Argonne National Laboratory, Argonne, Illinois 60439, United States
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18
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Tarasov VF, Jarocha LE, Avdievich NI, Forbes MDE. TREPR spectra of micelle-confined spin correlated radical pairs: I. Molecular motion and simulations. Photochem Photobiol Sci 2014; 13:439-53. [DOI: 10.1039/c3pp50328c] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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19
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Möbius K, Lubitz W, Savitsky A. High-field EPR on membrane proteins - crossing the gap to NMR. PROGRESS IN NUCLEAR MAGNETIC RESONANCE SPECTROSCOPY 2013; 75:1-49. [PMID: 24160760 DOI: 10.1016/j.pnmrs.2013.07.002] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/17/2013] [Revised: 07/15/2013] [Accepted: 07/15/2013] [Indexed: 06/02/2023]
Abstract
In this review on advanced EPR spectroscopy, which addresses both the EPR and NMR communities, considerable emphasis is put on delineating the complementarity of NMR and EPR concerning the measurement of molecular interactions in large biomolecules. From these interactions, detailed information can be revealed on structure and dynamics of macromolecules embedded in solution- or solid-state environments. New developments in pulsed microwave and sweepable cryomagnet technology as well as ultrafast electronics for signal data handling and processing have pushed to new horizons the limits of EPR spectroscopy and its multifrequency extensions concerning the sensitivity of detection, the selectivity with respect to interactions, and the resolution in frequency and time domains. One of the most important advances has been the extension of EPR to high magnetic fields and microwave frequencies, very much in analogy to what happens in NMR. This is exemplified by referring to ongoing efforts for signal enhancement in both NMR and EPR double-resonance techniques by exploiting dynamic nuclear or electron spin polarization via unpaired electron spins and their electron-nuclear or electron-electron interactions. Signal and resolution enhancements are particularly spectacular for double-resonance techniques such as ENDOR and PELDOR at high magnetic fields. They provide greatly improved orientational selection for disordered samples that approaches single-crystal resolution at canonical g-tensor orientations - even for molecules with small g-anisotropies. Exchange of experience between the EPR and NMR communities allows for handling polarization and resolution improvement strategies in an optimal manner. Consequently, a dramatic improvement of EPR detection sensitivity could be achieved, even for short-lived paramagnetic reaction intermediates. Unique structural and dynamic information is thus revealed that can hardly be obtained by any other analytical techniques. Micromolar quantities of sample molecules have become sufficient to characterize stable and transient reaction intermediates of complex molecular systems - offering highly interesting applications for chemists, biochemists and molecular biologists. In three case studies, representative examples of advanced EPR spectroscopy are reviewed: (I) High-field PELDOR and ENDOR structure determination of cation-anion radical pairs in reaction centers from photosynthetic purple bacteria and cyanobacteria (Photosystem I); (II) High-field ENDOR and ELDOR-detected NMR spectroscopy on the oxygen-evolving complex of Photosystem II; and (III) High-field electron dipolar spectroscopy on nitroxide spin-labelled bacteriorhodopsin for structure-function studies. An extended conclusion with an outlook to further developments and applications is also presented.
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Affiliation(s)
- Klaus Möbius
- Max Planck Institute for Chemical Energy Conversion, Stiftstrasse 34-36, D-45470 Mülheim an der Ruhr, Germany; Department of Physics, Free University Berlin, Arnimallee 14, D-14195 Berlin, Germany.
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20
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Eaton SS, Eaton GR. The world as viewed by and with unpaired electrons. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2012; 223:151-63. [PMID: 22975244 PMCID: PMC3496796 DOI: 10.1016/j.jmr.2012.07.025] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/27/2012] [Revised: 07/26/2012] [Accepted: 07/27/2012] [Indexed: 06/01/2023]
Abstract
Recent advances in electron paramagnetic resonance (EPR) include capabilities for applications to areas as diverse as archeology, beer shelf life, biological structure, dosimetry, in vivo imaging, molecular magnets, and quantum computing. Enabling technologies include multifrequency continuous wave, pulsed, and rapid scan EPR. Interpretation is enhanced by increasingly powerful computational models.
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Affiliation(s)
- Sandra S Eaton
- Department of Chemistry and Biochemistry, University of Denver, Denver, CO 80208, USA
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21
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WEIS VOLKER, VAN WILLIGEN HANS. FT-EPR Study of Spin-correlated Radical Pairs Formed by Electron Transfer Quenching of Porphyrin Triplets in Micellar Solution. J PORPHYR PHTHALOCYA 2012. [DOI: 10.1002/(sici)1099-1409(199807/10)2:4/5<353::aid-jpp87>3.0.co;2-z] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
The spin-correlated radical pairs (SCRPs) formed by photoinduced electron transfer from zinc tetrakis(4-sulfonatophenyl)porphyrin ( ZnTPPS ) to quinones in micelles of the cationic surfactant cetyltrimethylammonium chloride ( CTAC ) were studied by means of Fourier transform EPR (FT-EPR). It is shown that variation of the power of the microwave pulse allows the separation of EPR signals arising from SCRPs and free radicals. The measured kinetics of radical formation can be accounted for in terms of a statistical model taking into account the non-uniform distribution of the solutes over the micelles. The rate constant of electron transfer quenching (kq) of the ZnTPPS triplet state by duroquinone (DQ) is found to be 1.05 × 106 s−1. The FT-EPR measurements gave information also on the kinetics of the homogeneous electron transfer reaction DQ − + DQ → DQ + DQ − in CTAC solution in which the DQ − anion radicals were generated by light-induced electron transfer from ZnTPPS . It is found that the dependence of the rate of this reaction on quinone concentration deviates from the linear relationship found in homogeneous solutions. A statistical model is proposed to account for the data. Based on this model, the rate constant of the self-exchange reaction (k ex ) is 4.1 × 106 s−1. From results obtained with duroquinone and benzoquinone as acceptors, it is concluded that ZnTPPS is located at the micelle/water interface.
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Affiliation(s)
- VOLKER WEIS
- Department of Chemistry, University of Massachusetts at Boston, 100 Morrissey Boulevard, Boston, MA 02125, USA
| | - HANS VAN WILLIGEN
- Department of Chemistry, University of Massachusetts at Boston, 100 Morrissey Boulevard, Boston, MA 02125, USA
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22
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Vauthey E. Photoinduced Symmetry-Breaking Charge Separation. Chemphyschem 2012; 13:2001-11. [DOI: 10.1002/cphc.201200106] [Citation(s) in RCA: 133] [Impact Index Per Article: 11.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/07/2012] [Indexed: 11/08/2022]
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23
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Colvin MT, Ricks AB, Scott AM, Co DT, Wasielewski MR. Intersystem Crossing Involving Strongly Spin Exchange-Coupled Radical Ion Pairs in Donor–bridge–Acceptor Molecules. J Phys Chem A 2012; 116:1923-30. [DOI: 10.1021/jp212546w] [Citation(s) in RCA: 65] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Affiliation(s)
- Michael T. Colvin
- Department
of Chemistry and
Argonne-Northwestern Solar Energy Research (ANSER) Center, Northwestern University, Evanston, Illinois 60208-3113,
United States
| | - Annie Butler Ricks
- Department
of Chemistry and
Argonne-Northwestern Solar Energy Research (ANSER) Center, Northwestern University, Evanston, Illinois 60208-3113,
United States
| | - Amy M. Scott
- Department
of Chemistry and
Argonne-Northwestern Solar Energy Research (ANSER) Center, Northwestern University, Evanston, Illinois 60208-3113,
United States
| | - Dick T. Co
- Department
of Chemistry and
Argonne-Northwestern Solar Energy Research (ANSER) Center, Northwestern University, Evanston, Illinois 60208-3113,
United States
| | - Michael R. Wasielewski
- Department
of Chemistry and
Argonne-Northwestern Solar Energy Research (ANSER) Center, Northwestern University, Evanston, Illinois 60208-3113,
United States
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24
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Chatterjee R, Coates CS, Milikisiyants S, Poluektov OG, Lakshmi KV. Structure and Function of Quinones in Biological Solar Energy Transduction: A High-Frequency D-Band EPR Spectroscopy Study of Model Benzoquinones. J Phys Chem B 2011; 116:676-82. [DOI: 10.1021/jp210156a] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/14/2022]
Affiliation(s)
- Ruchira Chatterjee
- Department of Chemistry and Chemical Biology and The Baruch ’60 Center for Biochemical Solar Energy Research, Rensselaer Polytechnic Institute, Troy, New York 12180, United States
| | - Christopher S. Coates
- Department of Chemistry and Chemical Biology and The Baruch ’60 Center for Biochemical Solar Energy Research, Rensselaer Polytechnic Institute, Troy, New York 12180, United States
| | - Sergey Milikisiyants
- Department of Chemistry and Chemical Biology and The Baruch ’60 Center for Biochemical Solar Energy Research, Rensselaer Polytechnic Institute, Troy, New York 12180, United States
| | - Oleg G. Poluektov
- Chemical Sciences and Engineering Division, Argonne National Laboratory, 9700 South Cass Avenue, Argonne, Illinois 60439, United States
| | - K. V. Lakshmi
- Department of Chemistry and Chemical Biology and The Baruch ’60 Center for Biochemical Solar Energy Research, Rensselaer Polytechnic Institute, Troy, New York 12180, United States
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25
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Markovic V, Villamaina D, Barabanov I, Lawson Daku LM, Vauthey E. Photoinduced Symmetry-Breaking Charge Separation: The Direction of the Charge Transfer. Angew Chem Int Ed Engl 2011. [DOI: 10.1002/ange.201102601] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
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26
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Markovic V, Villamaina D, Barabanov I, Lawson Daku LM, Vauthey E. Photoinduced Symmetry-Breaking Charge Separation: The Direction of the Charge Transfer. Angew Chem Int Ed Engl 2011; 50:7596-8. [DOI: 10.1002/anie.201102601] [Citation(s) in RCA: 51] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/14/2011] [Indexed: 11/06/2022]
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27
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Su JH, Cox N, Ames W, Pantazis DA, Rapatskiy L, Lohmiller T, Kulik LV, Dorlet P, Rutherford AW, Neese F, Boussac A, Lubitz W, Messinger J. The electronic structures of the S(2) states of the oxygen-evolving complexes of photosystem II in plants and cyanobacteria in the presence and absence of methanol. BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 2011; 1807:829-40. [PMID: 21406177 DOI: 10.1016/j.bbabio.2011.03.002] [Citation(s) in RCA: 73] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/20/2011] [Revised: 03/02/2011] [Accepted: 03/04/2011] [Indexed: 01/25/2023]
Abstract
The electronic properties of the Mn(4)O(x)Ca cluster in the S(2) state of the oxygen-evolving complex (OEC) were studied using X- and Q-band EPR and Q-band (55)Mn-ENDOR using photosystem II preparations isolated from the thermophilic cyanobacterium T. elongatus and higher plants (spinach). The data presented here show that there is very little difference between the two species. Specifically it is shown that: (i) only small changes are seen in the fitted isotropic hyperfine values, suggesting that there is no significant difference in the overall spin distribution (electronic coupling scheme) between the two species; (ii) the inferred fine-structure tensor of the only Mn(III) ion in the cluster is of the same magnitude and geometry for both species types, suggesting that the Mn(III) ion has the same coordination sphere in both sample preparations; and (iii) the data from both species are consistent with only one structural model available in the literature, namely the Siegbahn structure [Siegbahn, P. E. M. Accounts Chem. Res.2009, 42, 1871-1880, Pantazis, D. A. et al., Phys. Chem. Chem. Phys.2009, 11, 6788-6798]. These measurements were made in the presence of methanol because it confers favorable magnetic relaxation properties to the cluster that facilitate pulse-EPR techniques. In the absence of methanol the separation of the ground state and the first excited state of the spin system is smaller. For cyanobacteria this effect is minor but in plant PS II it leads to a break-down of the S(T)=½ spin model of the S(2) state. This suggests that the methanol-OEC interaction is species dependent. It is proposed that the effect of small organic solvents on the electronic structure of the cluster is to change the coupling between the outer Mn (Mn(A)) and the other three Mn ions that form the trimeric part of the cluster (Mn(B), Mn(C), Mn(D)), by perturbing the linking bis-μ-oxo bridge. The flexibility of this bridging unit is discussed with regard to the mechanism of O-O bond formation.
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Affiliation(s)
- Ji-Hu Su
- Max-Planck-Institut für Bioanorganische Chemie, D-45470 Mülheim an der Ruhr, Germany
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28
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Witwicki M, Jezierska J. Effects of Solvents, Ligand Aromaticity, and Coordination Sphere on the g Tensor of Anionic o-Semiquinone Radicals Complexed by Mg2+ Ions: DFT Studies. J Phys Chem B 2011; 115:3172-84. [DOI: 10.1021/jp110515j] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Maciej Witwicki
- Faculty of Chemistry, Wroclaw University, 14 F. Joliot-Curie St., Wroclaw 50-283, Poland
| | - Julia Jezierska
- Faculty of Chemistry, Wroclaw University, 14 F. Joliot-Curie St., Wroclaw 50-283, Poland
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29
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Weber S, Biskup T, Okafuji A, Marino AR, Berthold T, Link G, Hitomi K, Getzoff ED, Schleicher E, Norris JR. Origin of light-induced spin-correlated radical pairs in cryptochrome. J Phys Chem B 2010; 114:14745-54. [PMID: 20684534 DOI: 10.1021/jp103401u] [Citation(s) in RCA: 47] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
Abstract
Blue-light excitation of cryptochromes and homologues uniformly triggers electron transfer (ET) from the protein surface to the flavin adenine dinucleotide (FAD) cofactor. A cascade of three conserved tryptophan residues has been considered to be critically involved in this photoreaction. If the FAD is initially in its fully oxidized (diamagnetic) redox state, light-induced ET via the tryptophan triad generates a series of short-lived spin-correlated radical pairs comprising an FAD radical and a tryptophan radical. Coupled doublet-pair species of this type have been proposed as the basis, for example, of a biological magnetic compass in migratory birds, and were found critical for some cryptochrome functions in vivo. In this contribution, a cryptochrome-like protein (CRYD) derived from Xenopus laevis has been examined as a representative system. The terminal radical-pair state FAD(•)···W324(•) of X. laevis CRYD has been characterized in detail by time-resolved electron-paramagnetic resonance (TREPR) at X-band microwave frequency (9.68 GHz) and magnetic fields around 345 mT, and at Q-band (34.08 GHz) at around 1215 mT. Different precursor states, singlet versus triplet, of radical-pair formation have been considered in spectral simulations of the experimental electron-spin polarized TREPR signals. Conclusively, we present evidence for a singlet-state precursor of FAD(•)···W324(•) radical-pair generation because at both magnetic fields, where radical pairs were studied by TREPR, net-zero electron-spin polarization has been detected. Neither a spin-polarized triplet precursor nor a triplet at thermal equilibrium can explain such an electron-spin polarization. It turns out that a two-microwave-frequency TREPR approach is essential to draw conclusions on the nature of the precursor electronic states in light-induced spin-correlated radical pair formations.
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Affiliation(s)
- Stefan Weber
- Institute of Physical Chemistry, Albert-Ludwigs-Universität Freiburg, 79104 Freiburg, Germany.
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30
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Algar WR, Tavares AJ, Krull UJ. Beyond labels: A review of the application of quantum dots as integrated components of assays, bioprobes, and biosensors utilizing optical transduction. Anal Chim Acta 2010; 673:1-25. [DOI: 10.1016/j.aca.2010.05.026] [Citation(s) in RCA: 406] [Impact Index Per Article: 29.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/18/2010] [Revised: 05/17/2010] [Accepted: 05/17/2010] [Indexed: 01/08/2023]
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31
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Kobori Y, Fuki M, Murai H. Electron Spin Polarization Transfer to the Charge-Separated State from Locally Excited Triplet Configuration: Theory and Its Application to Characterization of Geometry and Electronic Coupling in the Electron Donor−Acceptor System. J Phys Chem B 2010; 114:14621-30. [DOI: 10.1021/jp102330a] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/15/2023]
Affiliation(s)
- Yasuhiro Kobori
- Department of Chemistry, Faculty of Science, Shizuoka University, 836 Ohya Surugaku, Shizuoka 422-8529 Japan
| | - Masaaki Fuki
- Department of Chemistry, Faculty of Science, Shizuoka University, 836 Ohya Surugaku, Shizuoka 422-8529 Japan
| | - Hisao Murai
- Department of Chemistry, Faculty of Science, Shizuoka University, 836 Ohya Surugaku, Shizuoka 422-8529 Japan
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32
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Marchanka A, Savitsky A, Lubitz W, Möbius K, van Gastel M. B-Branch Electron Transfer in the Photosynthetic Reaction Center of a Rhodobacter sphaeroides Quadruple Mutant. Q- and W-Band Electron Paramagnetic Resonance Studies of Triplet and Radical-Pair Cofactor States. J Phys Chem B 2010; 114:14364-72. [DOI: 10.1021/jp1003424] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- A. Marchanka
- Max-Planck-Institut für Bioanorganische Chemie, Stiftstrasse 34-36, D-45470 Mülheim (Ruhr), Germany, Institut für Experimentalphysik, Freie Universität Berlin, Arnimallee 14, D-14195 Berlin, Germany
| | - A. Savitsky
- Max-Planck-Institut für Bioanorganische Chemie, Stiftstrasse 34-36, D-45470 Mülheim (Ruhr), Germany, Institut für Experimentalphysik, Freie Universität Berlin, Arnimallee 14, D-14195 Berlin, Germany
| | - W. Lubitz
- Max-Planck-Institut für Bioanorganische Chemie, Stiftstrasse 34-36, D-45470 Mülheim (Ruhr), Germany, Institut für Experimentalphysik, Freie Universität Berlin, Arnimallee 14, D-14195 Berlin, Germany
| | - K. Möbius
- Max-Planck-Institut für Bioanorganische Chemie, Stiftstrasse 34-36, D-45470 Mülheim (Ruhr), Germany, Institut für Experimentalphysik, Freie Universität Berlin, Arnimallee 14, D-14195 Berlin, Germany
| | - M. van Gastel
- Max-Planck-Institut für Bioanorganische Chemie, Stiftstrasse 34-36, D-45470 Mülheim (Ruhr), Germany, Institut für Experimentalphysik, Freie Universität Berlin, Arnimallee 14, D-14195 Berlin, Germany
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33
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Organic Dyes with Excited-State Transformations (Electron, Charge, and Proton Transfers). SPRINGER SERIES ON FLUORESCENCE 2010. [DOI: 10.1007/978-3-642-04702-2_7] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
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34
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TOYAMA NAMIKI, ASANO-SOMEDA MOTOKO, KAIZU YOUKOH. EPR spectra of gable-type copper(II) porphyrin dimers in fluid solution: extraction of exchange interaction in weakly coupled doublet pairs. Mol Phys 2009. [DOI: 10.1080/0026897021000054808] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Affiliation(s)
- NAMIKI TOYAMA
- a Department of Chemistry , Tokyo Institute of Technology , O-okayama, Meguro-ku , Tokyo , 152-8551 , Japan
| | - MOTOKO ASANO-SOMEDA
- a Department of Chemistry , Tokyo Institute of Technology , O-okayama, Meguro-ku , Tokyo , 152-8551 , Japan
| | - YOUKOH KAIZU
- a Department of Chemistry , Tokyo Institute of Technology , O-okayama, Meguro-ku , Tokyo , 152-8551 , Japan
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35
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Weyers AM, Chatterjee R, Milikisiyants S, Lakshmi KV. Structure and Function of Quinones in Biological Solar Energy Transduction: A Differential Pulse Voltammetry, EPR, and Hyperfine Sublevel Correlation (HYSCORE) Spectroscopy Study of Model Benzoquinones. J Phys Chem B 2009; 113:15409-18. [DOI: 10.1021/jp907379d] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Amanda M. Weyers
- Department of Chemistry and Chemical Biology and The Baruch ’60 Center for Biochemical Solar Energy Research, Rensselaer Polytechnic Institute, Troy, New York 12180
| | - Ruchira Chatterjee
- Department of Chemistry and Chemical Biology and The Baruch ’60 Center for Biochemical Solar Energy Research, Rensselaer Polytechnic Institute, Troy, New York 12180
| | - Sergey Milikisiyants
- Department of Chemistry and Chemical Biology and The Baruch ’60 Center for Biochemical Solar Energy Research, Rensselaer Polytechnic Institute, Troy, New York 12180
| | - K. V. Lakshmi
- Department of Chemistry and Chemical Biology and The Baruch ’60 Center for Biochemical Solar Energy Research, Rensselaer Polytechnic Institute, Troy, New York 12180
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36
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Jakob M, Berg A, Rubin R, Levanon H, Li K, Schuster DI. Photoinduced Electron Transfer in Porphyrin- and Fullerene/Porphyrin-Based Rotaxanes as Studied by Time-Resolved EPR Spectroscopy. J Phys Chem A 2009; 113:5846-54. [DOI: 10.1021/jp900331j] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Manuela Jakob
- Department of Physical Chemistry, Hebrew University of Jerusalem, Jerusalem 91904, Israel, and Department of Chemistry, New York University, New York, New York 10003
| | - Alexander Berg
- Department of Physical Chemistry, Hebrew University of Jerusalem, Jerusalem 91904, Israel, and Department of Chemistry, New York University, New York, New York 10003
| | - Roy Rubin
- Department of Physical Chemistry, Hebrew University of Jerusalem, Jerusalem 91904, Israel, and Department of Chemistry, New York University, New York, New York 10003
| | - Haim Levanon
- Department of Physical Chemistry, Hebrew University of Jerusalem, Jerusalem 91904, Israel, and Department of Chemistry, New York University, New York, New York 10003
| | - Ke Li
- Department of Physical Chemistry, Hebrew University of Jerusalem, Jerusalem 91904, Israel, and Department of Chemistry, New York University, New York, New York 10003
| | - David I. Schuster
- Department of Physical Chemistry, Hebrew University of Jerusalem, Jerusalem 91904, Israel, and Department of Chemistry, New York University, New York, New York 10003
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37
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Asher JR, Kaupp M. Car-Parrinello molecular dynamics simulations and EPR property calculations on aqueous ubisemiquinone radical anion. Theor Chem Acc 2008. [DOI: 10.1007/s00214-007-0408-1] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022]
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38
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High-Field/High-Frequency Electron Paramagnetic Resonance Involving Single- and Multiple-Transition Schemes. BIOPHYSICAL TECHNIQUES IN PHOTOSYNTHESIS 2008. [DOI: 10.1007/978-1-4020-8250-4_14] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
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Kacprzak S, Kaupp M, MacMillan F. Protein-cofactor interactions and EPR parameters for the Q(H) quinone binding site of quinol oxidase. A density functional study. J Am Chem Soc 2007; 128:5659-71. [PMID: 16637632 DOI: 10.1021/ja053988b] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Recent multifrequency EPR studies of the "high-affinity" quinone binding site of quinol oxidase (Q(H) site) have suggested a very asymmetric hydrogen-bonding environment for the semiquinone radical anion state. Single-sided hydrogen bonding to the O1 carbonyl position was one of the proposals, which contrasts with some previous experimental indications. Here density functional calculations of the EPR parameters (g-tensors, 13C, 1H, and 17O hyperfine tensors) for a wide variety of supermolecular model complexes have been used to provide insight into the detailed relations among structure, environment, and EPR parameters of ubisemiquinone radical anions. A single-sided binding model is not able to account for the experimentally observed low g(x) component of the g-tensor or for the observed magnitude of the asymmetry of the 13C carbonyl HFC tensors. Based on the detailed comparison between computation and experiment, a model with two hydrogen bonds to O1 and one hydrogen bond to O4 is suggested for the Q(H) site, but a model with one more hydrogen bond on each side cannot be excluded. Several general conclusions on the interrelations between EPR parameters and hydrogen bond patterns of ubisemiquinones in proteins are provided.
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Affiliation(s)
- Sylwia Kacprzak
- Institut für Anorganische Chemie, Universität Würzburg, Am Hubland, D 97074 Würzburg, Germany
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40
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Oganesyan VS. A novel approach to the simulation of nitroxide spin label EPR spectra from a single truncated dynamical trajectory. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2007; 188:196-205. [PMID: 17689278 DOI: 10.1016/j.jmr.2007.07.001] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/01/2007] [Revised: 07/06/2007] [Accepted: 07/09/2007] [Indexed: 05/16/2023]
Abstract
A simple effective method for calculation of EPR spectra from a single truncated dynamical trajectory of spin probe orientations is reported. It is shown that an accurate simulation can be achieved from the small initial fraction of a dynamical trajectory until the point when the autocorrelation function of re-orientational motion of spin label has relaxed. This substantially reduces the amount of time for spectra simulation compared to previous approaches, which require multiple full length trajectories (normally of several microseconds) to achieve the desired resolution of EPR spectra. Our method is applicable to trajectories generated from both Brownian dynamics and molecular dynamics (MD) calculations. Simulations of EPR spectra from Brownian dynamical trajectories under a variety of motional conditions including bi-modal dynamics with different hopping rates between the modes are compared to those performed by conventional method. Since the relatively short timescales of spin label motions are realistically accessible by modern MD computational methods, our approach, for the first time, opens the prospect of the simulation of EPR spectra entirely from MD trajectories of real proteins structures.
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Affiliation(s)
- V S Oganesyan
- CMSB, Centre for Metalloprotein Spectroscopy and Biology, Henry Wellcome Unit of Biological EPR, School of Chemical Sciences and Pharmacy, University of East Anglia, Norwich, UK.
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Olaso-Gonzalez G, Merchan M, Serrano-Andrés L. Ultrafast Electron Transfer in Photosynthesis: Reduced Pheophytin and Quinone Interaction Mediated by Conical Intersections. J Phys Chem B 2006; 110:24734-9. [PMID: 17134237 DOI: 10.1021/jp063915u] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The mechanism of electron transfer (ET) from reduced pheophytin (Pheo(-)) to the primary stable photosynthetic acceptor, a quinone (Q) molecule, is addressed by using high-level ab initio computations and realistic molecular models. The results reveal that the ET process involving the (Pheo(-) + Q) and (Pheo + Q(-)) oxidation states can be essentially seen as an ultrafast radiationless transition between the two hypersurfaces taking place via conical intersections (CIs). According to the present findings, an efficient ultrafast ET implies that the Pheo- and Q move toward each other in a given preferential parallel orientation, reaching the most effective arrangement for ET at intermolecular distances (R) around 5-3 Angstrom, where the lowest CIs are predicted. Favored donor/acceptor interactions are related to orientations with some overlap between the lowest occupied molecular orbitals (LUMO) of the two systems, and they lead to state-crossings at an earlier stage of the movement (larger R). Furthermore, when the topology of the interacting moieties does not make possible the LUMOs overlap, the corresponding diabatic potential energy curves do not intersect. Thus, it is anticipated that large scale motions, which are difficult to monitor experimentally, are actually occurring in the photosynthetic reaction centers of bacteria, algae, and higher plants, to fulfill the observed ultrafast ET processes.
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Affiliation(s)
- Gloria Olaso-Gonzalez
- Instituto de Ciencia Molecular, Universitat de València, Apartado 22085, ES-46071 Valencia, Spain
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Kandrashkin YE, Asano MS, van der Est A. Light-Induced Electron Spin Polarization in Vanadyl Octaethylporphyrin: II. Dynamics of the Excited States. J Phys Chem A 2006; 110:9617-26. [PMID: 16884195 DOI: 10.1021/jp062037x] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The dynamics of the low-lying excited states of vanadyl octaethylporphyrin (OEPVO) in frozen solution is investigated by transient electron paramagnetic resonance (TREPR). The observation of spin-polarized TREPR spectra from the lowest excited trip-quartet state of OEPVO, reported in the preceding paper, opens a new avenue for investigation of the excited states of such molecules. Here, a model based on the back-and-forth transitions between the trip-quartet and trip-doublet states is developed and used to explain the time dependence of the low-temperature laser flash-induced electron spin polarization of OEPVO. At early times, the TREPR spectra show predominantly multiplet polarization, whereas strong net polarization develops at later times. An analysis of the time dependence reveals two well-separated processes: (i) fast evolution of the polarization from the multiplet pattern to the net absorptive pattern and (ii) very slow decay of the net polarization. Both processes are temperature dependent and are faster at higher temperature. All of these observed features can be reproduced, and the experimental data can be simulated within the framework of the model. For simplicity, only the two nearly degenerate orbital states resulting from the a(1) --> e triplet excitation of the porphyrin are considered. Each of these is split into a trip-doublet and trip-quartet giving a total of four low-lying excited states. Transitions between the trip-doublet and trip-quartet states are assumed to be governed by spin-orbit coupling, which mixes the four low-lying states. It is known that following light excitation, the molecule initially decays to the lowest trip-doublet state and then to the trip-quartet state. In agreement with the observed TREPR spectra, the model predicts that this decay results in predominantly multiplet polarization of the trip-quartet. However, a small amount of net polarization is also predicted due to the spin selectivity associated with the Zeeman interaction. Because the energy gap between the trip-doublet and trip-quartet states is small, back-and-forth electronic transitions between the trip-doublet and trip-quartet are expected to occur as thermal equilibrium is established. The model predicts that it is these transitions that lead to the observed evolution of the initial multiplet polarization to net absorptive polarization.
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Affiliation(s)
- Yuri E Kandrashkin
- Department of Chemistry, Brock University, 500 Glenridge Ave., St. Catharines, Ontario, Canada L2S 3A1
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Di Valentin M, Bisol A, Agostini G, Moore AL, Moore TA, Gust D, Palacios RE, Gould SL, Carbonera D. Time-resolved EPR investigation of charge recombination to a triplet state in a carotene-diporphyrin triad. Mol Phys 2006. [DOI: 10.1080/00268970600638572] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/24/2022]
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44
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Photoinduced electron transfer through hydrogen bonds in a rod-like donor–acceptor molecule: A time-resolved EPR study. Chem Phys 2006. [DOI: 10.1016/j.chemphys.2005.11.044] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
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Kacprzak S, Kaupp M. Molecular Mechanical Devices Based on Quinone−Pyrrole and Quinone−Indole Dyads: A Computational Study. J Phys Chem B 2006; 110:8158-65. [PMID: 16610919 DOI: 10.1021/jp061105c] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
A set of intramolecularly connected dyads consisting of a quinone unit and a pyrrole or indole moiety have been designed and evaluated in quantum-chemical calculations. It is shown computationally for several systems, depending on the length and attachment points of the interconnecting chains, that a reduction of the quinone to the semiquinone radical anion or quinolate dianion state leads to a reversible intramolecular reorientation from a pi-stacked to a T-stacked arrangement. In the rearranged structures, a hydrogen bond from the pyrrole or indole N-H function to the semiquinone or quinolate pi-system is created upon reduction. In some systems, hydrogen bonds to the semiquinone or quinolate oxygen atoms are partly feasible and will be preferred over T-stacking. The choice of systems has been based on recent computational observations related to photosystem I. Systems with pyrrole or indole units should provide a better basis for the envisioned molecular motor than recently proposed quinone-benzene dyads. The intramolecular interactions modify the quinone redox potentials. Electronic g-tensors have been computed for the semiquinone states. These reflect characteristically the presence and nature of hydrogen bonds to the semiquinone and represent suitable electron paramagnetic resonance spectroscopic probes for the preferred structures. Intramolecular proton transfer is possible in the dianionic state.
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Affiliation(s)
- Sylwia Kacprzak
- Institut für Anorganische Chemie, Universität Würzburg, Am Hubland, D 97074 Würzburg, Germany
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Kandrashkin Y, Asano MS, van der Est A. Observation of a photoexcited state of a paramagnetic transition metal complex by time-resolved electron paramagnetic resonance spectroscopy. Phys Chem Chem Phys 2006; 8:2129-32. [PMID: 16751870 DOI: 10.1039/b602529c] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
The first observation of a spin polarized excited state of a paramagnetic metal-complex using time-resolved electron paramagnetic resonance (TREPR) spectroscopy is reported for octaethylporphinatooxovanadium(iv). The TREPR spectra show well resolved orientation dependent hyperfine splitting to the I = 7/2 vanadium nucleus. The reduction of the hyperfine splitting by a factor of 3 compared to the ground state and the observation of a multiplet pattern of spin polarization allow the TREPR spectra to be assigned to the excited quartet state of the complex. The spin polarization patterns evolve with time and it is postulated that this is a result of the equilibration between the lowest excited quartet and doublet states.
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Affiliation(s)
- Yuri Kandrashkin
- Department of Chemistry, Brock University, 500 Glenridge Ave., St. Catharines Ont., Canada L2S 3A1
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Di Valentin M, Bisol A, Agostini G, Carbonera D. Electronic Coupling Effects on Photoinduced Electron Transfer in Carotene−Porphyrin−Fullerene Triads Detected by Time-Resolved EPR. J Chem Inf Model 2005; 45:1580-8. [PMID: 16309257 DOI: 10.1021/ci050183e] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Photoinduced charge separation and recombination in a carotenoid-porphyrin-fullerene triad C-P-C60 (Bahr et al., 2000) have been followed by time-resolved electron paramagnetic resonance. The electron-transfer process has been characterized in a glass of 2-methyltetrahydrofuran and in the nematic phase of two uniaxial liquid crystals (E-7 and ZLI-1167). In all the different media, the molecular triad undergoes two-step photoinduced electron transfer, with the generation of a long-lived charge-separated state (C*+-P-C60*-), and charge recombination to the triplet state, localized in the carotene moiety, mimicking different aspects of the photosynthetic electron-transfer process. The magnetic interaction parameters have been evaluated by simulation of the spin-polarized radical pair spectrum. The weak exchange interaction parameter (J = +1.7 +/- 0.1 G) provides a direct measure of the dominant electronic coupling matrix element V between the C*+-P-C60*- radical pair state and the recombination triplet state 3C-P-C60. Comparison of the estimated values of V for this triad and a structurally related triad differing only in the porphyrin bridge (octaalkylporphyrin vs tetraarylporphyrin) explains in terms of an electronic coupling effect the approximately 6-fold variation of the recombination rate induced by the modification of the porphyrin bridge as derived by kinetic experiments (Bahr et al., 2000).
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Affiliation(s)
- Marilena Di Valentin
- Dipartimento di Scienze Chimiche, Università di Padova, via Marzolo 1, I-35131 Padova, Italy.
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48
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Kay CWM, Bittl R, Bacher A, Richter G, Weber S. Unambiguous Determination of the g-Matrix Orientation in a Neutral Flavin Radical by Pulsed Electron−Nuclear Double Resonance at 94 GHz. J Am Chem Soc 2005; 127:10780-1. [PMID: 16076154 DOI: 10.1021/ja051572s] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The recent observation of photoinduced radical pairs comprising a flavin radical and an oxidized amino acid residue in various blue-light-sensitive proteins has highlighted the need to gain a more complete understanding of the electronic structure of flavin radicals. In particular, precise knowledge of the anisotropy of the Zeeman interaction quantified by the g-tensor is necessary for attaining an unambiguous identification of flavin radicals by electron paramagnetic resonance (EPR). In a recent study of a protein-bound neutral flavin radical, we have determined the principal values of the g-tensor using high-frequency/high magnetic field EPR performed at 360 GHz/12.8 T. However, in those experiments, the orientation of the principal axes of g could not be unambiguously established with respect to the molecular frame of the isoalloxazine moiety. In this contribution we resolve this ambiguity by pulsed electron-nuclear double resonance (ENDOR) at 95 GHz/3.5 T (W-band). At such high values of the microwave frequency and the magnetic field, the g anisotropy provides improved spectral resolution compared to an ENDOR experiment performed at conventional 9.5 GHz/0.35 mT (X-band). This enables one to utilize Zeeman magnetoselection to obtain single-crystal-like data from disordered samples in frozen solution. Experiments exploiting this orientation selection have allowed us to use the hyperfine coupling of the methyl protons at C(8alpha) of the isoalloxazine ring to determine the angle between the molecular frame and the principal axes of g. Quite surprisingly, the g-tensor in FADH* is not oriented as one would have expected for a 1,3-semibenzoquinone radical. For the latter, the X-axis of g commonly bisects the smaller angle between the two axes along the C=O bonds. In FADH*, the large spin density on N(5) and C(4a) apparently contributes to a significant (44 degrees ) reorientation of the g-tensor axes.
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Di Valentin M, Bisol A, Agostini G, Liddell PA, Kodis G, Moore AL, Moore TA, Gust D, Carbonera D. Photoinduced Long-Lived Charge Separation in a Tetrathiafulvalene−Porphyrin−Fullerene Triad Detected by Time-Resolved Electron Paramagnetic Resonance. J Phys Chem B 2005; 109:14401-9. [PMID: 16852812 DOI: 10.1021/jp051345c] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Photoinduced electron transfer has been observed in a molecular triad, consisting of a porphyrin (P) covalently linked to a tetrathiafulvalene (TTF) and a fullerene derivative (C(60)), in the different phases of the liquid crystal E-7 and in a glass of 2-methyltetrahydrofuran (2-MeTHF) by means of time-resolved electron paramagnetic resonance (EPR) spectroscopy. In both solvents, an EPR signal observed immediately after excitation has been assigned to the radical pair TTF(*+)-P-C(60)(*-), based on its magnetic interaction parameters and spin polarization pattern. In the 2-MeTHF glass and the crystalline phase of E-7, the TTF(*+)-P-C(60)(*-) state is formed from the TTF-(1)P-C(60) singlet state via an initial TTF-P(*+)-C(60)(*-) charge-separated state. Long-lived charge separation ( approximately 8 mus) for the singlet-born radical pair is observed in the 2-MeTHF glass at cryogenic temperatures. In the nematic phase of E-7, a high degree of ordering in the liquid crystal is achieved by the molecular triad. In this phase, both singlet- and triplet-initiated electron transfer routes are concurrently active. At room temperature in the presence of the external magnetic field, the triplet-born radical pair (T)(TTF(*+)-P-C(60)(*-)) has a lifetime of approximately 7 mus, while that of the singlet-born radical pair (S)(TTF(*+)-P-C(60)(*-)) is much shorter (<1 mus). The difference in lifetimes is ascribed to spin dynamic effects in the magnetic field.
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Affiliation(s)
- Marilena Di Valentin
- Dipartimento di Scienze Chimiche, Università di Padova, via Marzolo 1, I-35131 Padova, Italy
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Stoica I. Force field impact and spin-probe modeling in molecular dynamics simulations of spin-labeled T4 lysozyme. J Mol Model 2005; 11:210-25. [PMID: 15806387 DOI: 10.1007/s00894-005-0255-8] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/15/2004] [Accepted: 01/26/2005] [Indexed: 11/25/2022]
Abstract
Several attempts have been made to compute electron paramagnetic resonance (EPR) spectra of biomolecules, using motional models or simulated trajectories to describe dynamics. Ideally, the simulated trajectories should capture "fast" (picosecond) snapshots of spin-probe rotations accurately, while being lengthy enough to ensure a proper Fourier integration of the time-domain signal. It is the interplay of the two criteria that poses computational challenges to the method. In this context, an analysis of the spin-probe and protein conformational sampling and equilibration, with different force fields and with explicit solvent, may be a useful attempt. The present work reports a comparative study of the effect of the molecular dynamics (MD) force field on conformational sampling and equilibration in two spin-labeled T4 lysozyme (T4L) variants, N40C and K48C. Ensembles of 10x 3 ns-trajectories per variant and per force field (OPLS/AMBER and AMBER99) are analyzed for a reliable assessment of convergence and sampling. It is found that subtle site-dependent differences in spin-probe rotations and torsions are more readily captured in the AMBER99 trajectories than in the OPLS/AMBER simulations. On the other hand, sampling and equilibration are found to be better with the OPLS/AMBER force field at equal trajectory lengths.
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Affiliation(s)
- Ileana Stoica
- National Research Council of Canada, Biotechnology Research Institute, 6100 Royalmount Avenue, Montréal, QC, H4P 2R2, Canada.
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