1
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Chiesa A, Chizzini M, Garlatti E, Salvadori E, Tacchino F, Santini P, Tavernelli I, Bittl R, Chiesa M, Sessoli R, Carretta S. Assessing the Nature of Chiral-Induced Spin Selectivity by Magnetic Resonance. J Phys Chem Lett 2021; 12:6341-6347. [PMID: 34228926 PMCID: PMC8397348 DOI: 10.1021/acs.jpclett.1c01447] [Citation(s) in RCA: 19] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/05/2021] [Accepted: 06/21/2021] [Indexed: 05/20/2023]
Abstract
Understanding chiral-induced spin selectivity (CISS), resulting from charge transport through helical systems, has recently inspired many experimental and theoretical efforts but is still the object of intense debate. In order to assess the nature of CISS, we propose to focus on electron-transfer processes occurring at the single-molecule level. We design simple magnetic resonance experiments, exploiting a qubit as a highly sensitive and coherent magnetic sensor, to provide clear signatures of the acceptor polarization. Moreover, we show that information could even be obtained from time-resolved electron paramagnetic resonance experiments on a randomly oriented solution of molecules. The proposed experiments will unveil the role of chiral linkers in electron transfer and could also be exploited for quantum computing applications.
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Affiliation(s)
- A. Chiesa
- Dipartimento
di Scienze Matematiche, Fisiche e Informatiche, Università di Parma, I-43124 Parma, Italy
- UdR
Parma, INSTM, I-43124 Parma, Italy
| | - M. Chizzini
- Dipartimento
di Scienze Matematiche, Fisiche e Informatiche, Università di Parma, I-43124 Parma, Italy
| | - E. Garlatti
- Dipartimento
di Scienze Matematiche, Fisiche e Informatiche, Università di Parma, I-43124 Parma, Italy
- UdR
Parma, INSTM, I-43124 Parma, Italy
| | - E. Salvadori
- Dipartimento
di Chimica & NIS Centre, Università
di Torino, Via P. Giuria
7, I-10125 Torino, Italy
| | - F. Tacchino
- IBM
Quantum, IBM Research—Zurich, Säumerstrasse 4, 8803 Rüschlikon, Switzerland
| | - P. Santini
- Dipartimento
di Scienze Matematiche, Fisiche e Informatiche, Università di Parma, I-43124 Parma, Italy
- UdR
Parma, INSTM, I-43124 Parma, Italy
| | - I. Tavernelli
- IBM
Quantum, IBM Research—Zurich, Säumerstrasse 4, 8803 Rüschlikon, Switzerland
| | - R. Bittl
- Freie
Universität Berlin, Fachbereich Physik, Berlin Joint EPR Lab, Arnimallee 14, D-14195 Berlin, Germany
| | - M. Chiesa
- Dipartimento
di Chimica & NIS Centre, Università
di Torino, Via P. Giuria
7, I-10125 Torino, Italy
| | - R. Sessoli
- Dipartimento
di Chimica “Ugo Schiff” & INSTM, Università Degli Studi di Firenze, I-50019 Sesto Fiorentino, Italy
| | - S. Carretta
- Dipartimento
di Scienze Matematiche, Fisiche e Informatiche, Università di Parma, I-43124 Parma, Italy
- UdR
Parma, INSTM, I-43124 Parma, Italy
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2
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Teki Y. Excited‐State Dynamics of Non‐Luminescent and Luminescent π‐Radicals. Chemistry 2019; 26:980-996. [DOI: 10.1002/chem.201903444] [Citation(s) in RCA: 30] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/29/2019] [Revised: 08/28/2019] [Indexed: 11/11/2022]
Affiliation(s)
- Yoshio Teki
- Division of Molecular Materials ScienceGraduate School of ScienceOsaka City University 3-3-138 Sugimoto Sumiyoshi-ku Osaka 558-8585 Japan
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3
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Horwitz NE, Phelan BT, Nelson JN, Mauck CM, Krzyaniak MD, Wasielewski MR. Spin Polarization Transfer from a Photogenerated Radical Ion Pair to a Stable Radical Controlled by Charge Recombination. J Phys Chem A 2017; 121:4455-4463. [DOI: 10.1021/acs.jpca.7b03468] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- Noah E. Horwitz
- Department
of Chemistry, ‡Argonne−Northwestern Solar Energy Research
(ANSER) Center, and §Institute for Sustainability and Energy at Northwestern, Northwestern University, Evanston, Illinois 60208-3113, United States
| | - Brian T. Phelan
- Department
of Chemistry, ‡Argonne−Northwestern Solar Energy Research
(ANSER) Center, and §Institute for Sustainability and Energy at Northwestern, Northwestern University, Evanston, Illinois 60208-3113, United States
| | - Jordan N. Nelson
- Department
of Chemistry, ‡Argonne−Northwestern Solar Energy Research
(ANSER) Center, and §Institute for Sustainability and Energy at Northwestern, Northwestern University, Evanston, Illinois 60208-3113, United States
| | - Catherine M. Mauck
- Department
of Chemistry, ‡Argonne−Northwestern Solar Energy Research
(ANSER) Center, and §Institute for Sustainability and Energy at Northwestern, Northwestern University, Evanston, Illinois 60208-3113, United States
| | - Matthew D. Krzyaniak
- Department
of Chemistry, ‡Argonne−Northwestern Solar Energy Research
(ANSER) Center, and §Institute for Sustainability and Energy at Northwestern, Northwestern University, Evanston, Illinois 60208-3113, United States
| | - Michael R. Wasielewski
- Department
of Chemistry, ‡Argonne−Northwestern Solar Energy Research
(ANSER) Center, and §Institute for Sustainability and Energy at Northwestern, Northwestern University, Evanston, Illinois 60208-3113, United States
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4
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Horwitz NE, Phelan BT, Nelson JN, Krzyaniak MD, Wasielewski MR. Picosecond Control of Photogenerated Radical Pair Lifetimes Using a Stable Third Radical. J Phys Chem A 2016; 120:2841-53. [PMID: 27108738 DOI: 10.1021/acs.jpca.6b02621] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Photoinduced electron transfer reactions in organic donor-acceptor systems leading to long-lived radical ion pairs (RPs) have attracted broad interest for their potential applications in fields as diverse as solar energy conversion and spintronics. We present the photophysics and spin dynamics of an electron donor - electron acceptor - stable radical system consisting of a meta-phenylenediamine (mPD) donor covalently linked to a 4-aminonaphthalene-1,8-dicarboximide (ANI) electron-accepting chromophore as well as an α,γ-bisdiphenylene-β-phenylallyl (BDPA) stable radical. Selective photoexcitation of ANI produces the BDPA-mPD(+•)-ANI(-•) triradical in which the mPD(+•)-ANI(-•) RP spins are strongly exchange coupled. The presence of BDPA is found to greatly increase the RP intersystem crossing rate from the initially photogenerated BDPA-(1)(mPD(+•)-ANI(-•)) to BDPA-(3)(mPD(+•)-ANI(-•)), resulting in accelerated RP recombination via the triplet channel to produce BDPA-mPD-(3*)ANI as compared to a reference molecule lacking the BDPA radical. The RP recombination rates observed are much faster than those previously reported for weakly coupled triradical systems. Time-resolved EPR spectroscopy shows that this process is also associated with strong spin polarization of the stable radical. Overall, these results show that RP intersystem crossing rates can be strongly influenced by stable radicals nearby strongly coupled RP systems, making it possible to use a third spin to control RP lifetimes down to a picosecond time scale.
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Affiliation(s)
- Noah E Horwitz
- Department of Chemistry, Argonne-Northwestern Solar Energy Research (ANSER) Center, and Institute for Sustainability and Energy at Northwestern, Northwestern University , Evanston, Illinois 60208-3113, United States
| | - Brian T Phelan
- Department of Chemistry, Argonne-Northwestern Solar Energy Research (ANSER) Center, and Institute for Sustainability and Energy at Northwestern, Northwestern University , Evanston, Illinois 60208-3113, United States
| | - Jordan N Nelson
- Department of Chemistry, Argonne-Northwestern Solar Energy Research (ANSER) Center, and Institute for Sustainability and Energy at Northwestern, Northwestern University , Evanston, Illinois 60208-3113, United States
| | - Matthew D Krzyaniak
- Department of Chemistry, Argonne-Northwestern Solar Energy Research (ANSER) Center, and Institute for Sustainability and Energy at Northwestern, Northwestern University , Evanston, Illinois 60208-3113, United States
| | - Michael R Wasielewski
- Department of Chemistry, Argonne-Northwestern Solar Energy Research (ANSER) Center, and Institute for Sustainability and Energy at Northwestern, Northwestern University , Evanston, Illinois 60208-3113, United States
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5
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Ishara Silva K, Jagannathan B, Golbeck JH, Lakshmi KV. Elucidating the design principles of photosynthetic electron-transfer proteins by site-directed spin labeling EPR spectroscopy. BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 2015; 1857:548-556. [PMID: 26334844 DOI: 10.1016/j.bbabio.2015.08.009] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/02/2015] [Accepted: 08/20/2015] [Indexed: 10/23/2022]
Abstract
Site-directed spin labeling electron paramagnetic resonance (SDSL EPR) spectroscopy is a powerful tool to determine solvent accessibility, side-chain dynamics, and inter-spin distances at specific sites in biological macromolecules. This information provides important insights into the structure and dynamics of both natural and designed proteins and protein complexes. Here, we discuss the application of SDSL EPR spectroscopy in probing the charge-transfer cofactors in photosynthetic reaction centers (RC) such as photosystem I (PSI) and the bacterial reaction center (bRC). Photosynthetic RCs are large multi-subunit proteins (molecular weight≥300 kDa) that perform light-driven charge transfer reactions in photosynthesis. These reactions are carried out by cofactors that are paramagnetic in one of their oxidation states. This renders the RCs unsuitable for conventional nuclear magnetic resonance spectroscopy investigations. However, the presence of native paramagnetic centers and the ability to covalently attach site-directed spin labels in RCs makes them ideally suited for the application of SDSL EPR spectroscopy. The paramagnetic centers serve as probes of conformational changes, dynamics of subunit assembly, and the relative motion of cofactors and peptide subunits. In this review, we describe novel applications of SDSL EPR spectroscopy for elucidating the effects of local structure and dynamics on the electron-transfer cofactors of photosynthetic RCs. Because SDSL EPR Spectroscopy is uniquely suited to provide dynamic information on protein motion, it is a particularly useful method in the engineering and analysis of designed electron transfer proteins and protein networks. This article is part of a Special Issue entitled Biodesign for Bioenergetics--the design and engineering of electronic transfer cofactors, proteins and protein networks, edited by Ronald L. Koder and J.L. Ross Anderson.
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Affiliation(s)
- K Ishara Silva
- Department of Chemistry and Chemical Biology, Rensselaer Polytechnic Institute, Troy, NY 12180; The Baruch '60 Center for Biochemical Solar Energy Research, Rensselaer Polytechnic Institute, Troy, NY 12180
| | - Bharat Jagannathan
- Department of Biochemistry and Molecular Biology, The Pennsylvania State University, University Park, PA 16802; Department of Chemistry, The Pennsylvania State University, University Park, PA 16802
| | - John H Golbeck
- Department of Biochemistry and Molecular Biology, The Pennsylvania State University, University Park, PA 16802; Department of Chemistry, The Pennsylvania State University, University Park, PA 16802.
| | - K V Lakshmi
- Department of Chemistry and Chemical Biology, Rensselaer Polytechnic Institute, Troy, NY 12180; The Baruch '60 Center for Biochemical Solar Energy Research, Rensselaer Polytechnic Institute, Troy, NY 12180.
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6
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Zarea M, Ratner MA, Wasielewski MR. Spin polarization transfer by the radical pair mechanism. J Chem Phys 2015; 143:054101. [DOI: 10.1063/1.4927589] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Affiliation(s)
- Mehdi Zarea
- Department of Chemistry and Argonne-Northwestern Solar Energy Research (ANSER) Center, Northwestern University, Evanston, Illinois 60208-3113, USA
| | - Mark A. Ratner
- Department of Chemistry and Argonne-Northwestern Solar Energy Research (ANSER) Center, Northwestern University, Evanston, Illinois 60208-3113, USA
| | - Michael R. Wasielewski
- Department of Chemistry and Argonne-Northwestern Solar Energy Research (ANSER) Center, Northwestern University, Evanston, Illinois 60208-3113, USA
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7
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Gardner DM, Chen HF, Krzyaniak MD, Ratner MA, Wasielewski MR. Large Dipolar Spin–Spin Interaction in a Photogenerated U-Shaped Triradical. J Phys Chem A 2015; 119:8040-8. [DOI: 10.1021/acs.jpca.5b03048] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Daniel M. Gardner
- Department of Chemistry and
Argonne-Northwestern Solar Energy Research (ANSER) Center, Northwestern University, Evanston, Illinois 60208-3113, United States
| | - Hsiao-Fan Chen
- Department of Chemistry and
Argonne-Northwestern Solar Energy Research (ANSER) Center, Northwestern University, Evanston, Illinois 60208-3113, United States
| | - Matthew D. Krzyaniak
- Department of Chemistry and
Argonne-Northwestern Solar Energy Research (ANSER) Center, Northwestern University, Evanston, Illinois 60208-3113, United States
| | - Mark A. Ratner
- 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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8
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Lukina EA, Popov AA, Uvarov MN, Kulik LV. Out-of-Phase Electron Spin Echo Studies of Light-Induced Charge-Transfer States in P3HT/PCBM Composite. J Phys Chem B 2015; 119:13543-8. [DOI: 10.1021/acs.jpcb.5b02142] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Ekaterina A. Lukina
- Voevodsky
Institute of Chemical Kinetics and Combustion of the Siberian Branch of the Russian Academy of Sciences, Institutskaya 3, Novosibirsk 630090, Russia
- Novosibirsk State University, Pirogova
2, Novosibirsk 630090, Russia
| | - Alexander A. Popov
- Voevodsky
Institute of Chemical Kinetics and Combustion of the Siberian Branch of the Russian Academy of Sciences, Institutskaya 3, Novosibirsk 630090, Russia
- Novosibirsk State University, Pirogova
2, Novosibirsk 630090, Russia
| | - Mikhail N. Uvarov
- Voevodsky
Institute of Chemical Kinetics and Combustion of the Siberian Branch of the Russian Academy of Sciences, Institutskaya 3, Novosibirsk 630090, Russia
| | - Leonid V. Kulik
- Voevodsky
Institute of Chemical Kinetics and Combustion of the Siberian Branch of the Russian Academy of Sciences, Institutskaya 3, Novosibirsk 630090, Russia
- Novosibirsk State University, Pirogova
2, Novosibirsk 630090, Russia
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9
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Zarea M, Carmieli R, Ratner MA, Wasielewski MR. Spin Dynamics of Radical Pairs with Restricted Geometries and Strong Exchange Coupling: The Role of Hyperfine Coupling. J Phys Chem A 2014; 118:4249-55. [DOI: 10.1021/jp5039283] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023]
Affiliation(s)
- Mehdi Zarea
- Department of Chemistry and Argonne−Northwestern
Solar Energy Research
(ANSER) Center, Northwestern University, Evanston, Illinois 60208-3113, United States
| | - Raanan Carmieli
- Department of Chemistry and Argonne−Northwestern
Solar Energy Research
(ANSER) Center, Northwestern University, Evanston, Illinois 60208-3113, United States
| | - Mark A. Ratner
- 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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10
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Colvin MT, Carmieli R, Miura T, Richert S, Gardner DM, Smeigh AL, Dyar SM, Conron SM, Ratner MA, Wasielewski MR. Electron Spin Polarization Transfer from Photogenerated Spin-Correlated Radical Pairs to a Stable Radical Observer Spin. J Phys Chem A 2013; 117:5314-25. [DOI: 10.1021/jp4045012] [Citation(s) in RCA: 40] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023]
Affiliation(s)
- Michael T. Colvin
- Department
of Chemistry and Argonne-Northwestern Solar
Energy Research (ANSER) Center, Northwestern University, Evanston, Illinois 60208-3113, United States
| | - Raanan Carmieli
- Department
of Chemistry and Argonne-Northwestern Solar
Energy Research (ANSER) Center, Northwestern University, Evanston, Illinois 60208-3113, United States
| | - Tomoaki Miura
- Department
of Chemistry and Argonne-Northwestern Solar
Energy Research (ANSER) Center, Northwestern University, Evanston, Illinois 60208-3113, United States
| | - Sabine Richert
- Department
of Chemistry and Argonne-Northwestern Solar
Energy Research (ANSER) Center, Northwestern University, Evanston, Illinois 60208-3113, United States
| | - Daniel M. Gardner
- Department
of Chemistry and Argonne-Northwestern Solar
Energy Research (ANSER) Center, Northwestern University, Evanston, Illinois 60208-3113, United States
| | - Amanda L. Smeigh
- Department
of Chemistry and Argonne-Northwestern Solar
Energy Research (ANSER) Center, Northwestern University, Evanston, Illinois 60208-3113, United States
| | - Scott M. Dyar
- Department
of Chemistry and Argonne-Northwestern Solar
Energy Research (ANSER) Center, Northwestern University, Evanston, Illinois 60208-3113, United States
| | - Sarah M. Conron
- Department
of Chemistry and Argonne-Northwestern Solar
Energy Research (ANSER) Center, Northwestern University, Evanston, Illinois 60208-3113, United States
| | - Mark A. Ratner
- 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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11
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Carmieli R, Smeigh AL, Mickley Conron SM, Thazhathveetil AK, Fuki M, Kobori Y, Lewis FD, Wasielewski MR. Structure and Dynamics of Photogenerated Triplet Radical Ion Pairs in DNA Hairpin Conjugates with Anthraquinone End Caps. J Am Chem Soc 2012; 134:11251-60. [DOI: 10.1021/ja303721j] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Raanan Carmieli
- Department of Chemistry and Argonne-Northwestern
Solar Energy Research (ANSER) Center, Northwestern University, Evanston, Illinois 60208-3113, United States
| | - Amanda L. Smeigh
- Department of Chemistry and Argonne-Northwestern
Solar Energy Research (ANSER) Center, Northwestern University, Evanston, Illinois 60208-3113, United States
| | - Sarah M. Mickley Conron
- Department of Chemistry and Argonne-Northwestern
Solar Energy Research (ANSER) Center, Northwestern University, Evanston, Illinois 60208-3113, United States
| | - Arun K. Thazhathveetil
- Department of Chemistry and Argonne-Northwestern
Solar Energy Research (ANSER) Center, Northwestern University, Evanston, Illinois 60208-3113, United States
| | - Masaaki Fuki
- Department of Chemistry, Faculty of Science, Shizuoka University, 836 Ohya Surugaku, Shizuoka 422-8529,
Japan
| | - Yasuhiro Kobori
- Department of Chemistry, Faculty of Science, Shizuoka University, 836 Ohya Surugaku, Shizuoka 422-8529,
Japan
- PRESTO, Japan Science and Technology Agency (JST), 4-1-8 Honcho
Kawaguchi, Saitama 332-0012, Japan
| | - Frederick D. Lewis
- 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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12
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Ivanov KL. Net and multiplet CIDEP of the observer spin in recombination of radical-biradical pair. J Phys Chem A 2005; 109:5160-7. [PMID: 16833871 DOI: 10.1021/jp0504524] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Net and multiplet chemically induced dynamic electron polarization (CIDEP) of the observer/catalyst spin formed in recombination of the radical-biradical pair is studied theoretically. We obtained analytical expressions for the observer spin CIDEP in the high magnetic field and for the multiplet polarization in zero magnetic field. Polarization in the vicinity of the so-called J resonance and its magnetic field dependence are investigated numerically. The observer spin methodology can be useful for probing magnetic interactions in the short-lived spin triads.
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Affiliation(s)
- K L Ivanov
- International Tomography Center, Novosibirsk 630090, Russia.
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13
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Xu W, Chitnis PR, Valieva A, van der Est A, Brettel K, Guergova-Kuras M, Pushkar YN, Zech SG, Stehlik D, Shen G, Zybailov B, Golbeck JH. Electron transfer in cyanobacterial photosystem I: II. Determination of forward electron transfer rates of site-directed mutants in a putative electron transfer pathway from A0 through A1 to FX. J Biol Chem 2003; 278:27876-87. [PMID: 12721306 DOI: 10.1074/jbc.m302965200] [Citation(s) in RCA: 90] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The directionality of electron transfer in Photosystem I (PS I) is investigated using site-directed mutations in the phylloquinone (QK) and FX binding regions of Synnechocystis sp. PCC 6803. The kinetics of forward electron transfer from the secondary acceptor A1 (phylloquinone) were measured in mutants using time-resolved optical difference spectroscopy and transient EPR spectroscopy. In whole cells and PS I complexes of the wild-type both techniques reveal a major, slow kinetic component of tau approximately 300 ns while optical data resolve an additional minor kinetic component of tau approximately 10 ns. Whole cells and PS I complexes from the W697FPsaA and S692CPsaA mutants show a significant slowing of the slow kinetic component, whereas the W677FPsaB and S672CPsaB mutants show a less significant slowing of the fast kinetic component. Transient EPR measurements at 260 K show that the slow phase is approximately 3 times slower than at room temperature. Simulations of the early time behavior of the spin polarization pattern of P700+A1-, in which the decay rate of the pattern is assumed to be negligibly small, reproduce the observed EPR spectra at 260 K during the first 100 ns following laser excitation. Thus any spin polarization from P700+FX- in this time window is very weak. From this it is concluded that the relative amplitude of the fast phase is negligible at 260 K or its rate is much less temperature-dependent than that of the slow component. Together, the results demonstrate that the slow kinetic phase results from electron transfer from QK-A to FX and that this accounts for at least 70% of the electrons. Although the assignment of the fast kinetic phase remains uncertain, it is not strongly temperature dependent and it represents a minor fraction of the electrons being transferred. All of the results point toward asymmetry in electron transfer, and indicate that forward transfer in cyanobacterial PS I is predominantly along the PsaA branch.
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Affiliation(s)
- Wu Xu
- Department of Biochemistry, Biophysics, and Molecular Biology, Iowa State University, Ames, Iowa 50011, USA
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