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Panariti D, Conron SM, Zhang J, Wasielewski MR, Di Valentin M, Tait CE. Control of excitation selectivity in pulse EPR on spin-correlated radical pairs with shaped pulses. Phys Chem Chem Phys 2024; 26:3842-3856. [PMID: 38221856 DOI: 10.1039/d3cp06009h] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/16/2024]
Abstract
Spin-correlated radical pairs generated by photoinduced electron transfer are characterised by a distinctive spin polarisation and a unique behaviour in pulse electron paramagnetic resonance (EPR) spectroscopy. Under non-selective excitation, an out-of-phase echo signal modulated by the dipolar and exchange coupling interactions characterising the radical pair is observed and allows extraction of geometric information in the two-pulse out-of-phase electron spin echo envelope modulation (ESEEM) experiment. The investigation of the role of spin-correlated radical pairs in a variety of biological processes and in the fundamental mechanisms underlying device function in optoelectronics, as well as their potential use in quantum information science, relies on the ability to precisely address and manipulate the spins using microwave pulses. Here, we explore the use of shaped pulses for controlled narrowband selective and broadband non-selective excitation of spin-correlated radical pairs in two model donor-bridge-acceptor triads, characterised by different spectral widths, at X- and Q-band frequencies. We demonstrate selective excitation with close to rectangular excitation profiles using BURP (band-selective, uniform response, pure-phase) pulses and complete non-selective excitation of both spins of the radical pair using frequency-swept chirp pulses. The use of frequency-swept pulses in out-of-phase ESEEM experiments enables increased modulation depths and, combined with echo transient detection and Fourier transformation, correlation of the dipolar frequencies with the EPR spectrum and therefore the potential to extract additional information on the donor-acceptor pair geometry.
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Affiliation(s)
- Daniele Panariti
- Department of Chemical Sciences, University of Padova, 35131 Padova, Italy
| | - Sarah M Conron
- Department of Chemistry, Applied Physics Program, and Center for Molecular Quantum Transduction, Northwestern University, Evanston, Illinois 60208-3113, USA
| | - Jinyuan Zhang
- Department of Chemistry, Applied Physics Program, and Center for Molecular Quantum Transduction, Northwestern University, Evanston, Illinois 60208-3113, USA
| | - Michael R Wasielewski
- Department of Chemistry, Applied Physics Program, and Center for Molecular Quantum Transduction, Northwestern University, Evanston, Illinois 60208-3113, USA
| | | | - Claudia E Tait
- Department of Chemistry, University of Oxford, Oxford OX1 3QZ, UK.
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Tait CE, Krzyaniak MD, Stoll S. Computational tools for the simulation and analysis of spin-polarized EPR spectra. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2023; 349:107410. [PMID: 36870248 DOI: 10.1016/j.jmr.2023.107410] [Citation(s) in RCA: 10] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/23/2022] [Revised: 02/10/2023] [Accepted: 02/18/2023] [Indexed: 06/18/2023]
Abstract
The EPR spectra of paramagnetic species induced by photoexcitation typically exhibit enhanced absorptive and emissive features resulting from sublevel populations that differ from thermal equilibrium. The populations and the resulting spin polarization of the spectra are dictated by the selectivity of the photophysical process generating the observed state. Simulation of the spin-polarized EPR spectra is crucial in the characterization of both the dynamics of formation of the photoexcited state as well as its electronic and structural properties. EasySpin, the simulation toolbox for EPR spectroscopy, now includes extended support for the simulation of the EPR spectra of spin-polarized states of arbitrary spin multiplicity and formed by a variety of different mechanisms, including photoexcited triplet states populated by intersystem crossing, charge recombination or spin polarization transfer, spin-correlated radical pairs created by photoinduced electron transfer, triplet pairs formed by singlet fission and multiplet states arising from photoexcitation in systems containing chromophores and stable radicals. In this paper, we highlight EasySpin's capabilities for the simulation of spin-polarized EPR spectra on the basis of illustrative examples from the literature in a variety of fields ranging across chemistry, biology, material science and quantum information science.
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Affiliation(s)
- Claudia E Tait
- Department of Chemistry, University of Oxford, Oxford OX1 3QZ, United Kingdom.
| | - Matthew D Krzyaniak
- Department of Chemistry, Center for Molecular Quantum Transduction and Institute for Sustainability and Energy at Northwestern, Northwestern University, Evanston 60208, IL, United States
| | - Stefan Stoll
- Department of Chemistry, University of Washington, Seattle, 98195, WA, United States
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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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Kanetomo T, Kihara T, Miyake A, Matsuo A, Tokunaga M, Kindo K, Nojiri H, Ishida T. Giant Exchange Coupling Evidenced with a Magnetization Jump at 52 T for a Gadolinium-Nitroxide Chelate. Inorg Chem 2017; 56:3310-3314. [PMID: 28281348 DOI: 10.1021/acs.inorgchem.6b02685] [Citation(s) in RCA: 26] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The Gd-radical complex [GdIII(hfac)3(6bpyNO)] (6bpyNO = 2,2'-bipyridin-6-yl tert-butyl nitroxide; Hhfac = 1,1,1,5,5,5-hexafluoropentane-2,4-dione) showed a magnetization jump at 52 T observed in a pulsed-field facility, corresponding to an exchange coupling constant of -17.4 K. Furthermore, hysteretic behavior due to a relatively slow magnetization reversal was recorded around 2 T. From the high-frequency EPR study, the exchange coupling between Gd and radical spins accompanies an anisotropic character, which is responsible for both the broad jump and the slow magnetization reversal.
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Affiliation(s)
- Takuya Kanetomo
- Department of Engineering Science, The University of Electro-Communications , Chofu, Tokyo 182-8585, Japan
| | - Takumi Kihara
- Institute for Materials Research, Tohoku University , Sendai, Miyagi 980-8577, Japan
| | - Atsushi Miyake
- Institute for Solid State Physics, The University of Tokyo , Kashiwa, Chiba 277-8581, Japan
| | - Akira Matsuo
- Institute for Solid State Physics, The University of Tokyo , Kashiwa, Chiba 277-8581, Japan
| | - Masashi Tokunaga
- Institute for Solid State Physics, The University of Tokyo , Kashiwa, Chiba 277-8581, Japan
| | - Koichi Kindo
- Institute for Solid State Physics, The University of Tokyo , Kashiwa, Chiba 277-8581, Japan
| | - Hiroyuki Nojiri
- Institute for Materials Research, Tohoku University , Sendai, Miyagi 980-8577, Japan
| | - Takayuki Ishida
- Department of Engineering Science, The University of Electro-Communications , Chofu, Tokyo 182-8585, Japan
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Karmova FM, Lebedeva VS, Mironov AF. Fullerene-containing porphyrins: Synthesis and potential practical applications. RUSS J GEN CHEM+ 2016. [DOI: 10.1134/s1070363216090322] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
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Richert S, Peeks MD, Tait CE, Anderson HL, Timmel CR. Photogenerated triplet states in supramolecular porphyrin ladder assemblies: an EPR study. Phys Chem Chem Phys 2016; 18:24171-5. [DOI: 10.1039/c6cp04444a] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Ladder formation and planarisation do not enhance delocalisation in the triplet excited states of linear porphyrin oligomers.
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Affiliation(s)
- Sabine Richert
- Centre for Advanced Electron Spin Resonance (CAESR)
- University of Oxford
- Oxford
- UK
| | | | - Claudia E. Tait
- Centre for Advanced Electron Spin Resonance (CAESR)
- University of Oxford
- Oxford
- UK
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Kelber JB, Panjwani NA, Wu D, Gómez-Bombarelli R, Lovett BW, Morton JJL, Anderson HL. Synthesis and investigation of donor-porphyrin-acceptor triads with long-lived photo-induced charge-separate states. Chem Sci 2015; 6:6468-6481. [PMID: 30090266 PMCID: PMC6054115 DOI: 10.1039/c5sc01830g] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/20/2015] [Accepted: 07/30/2015] [Indexed: 01/22/2023] Open
Abstract
Two donor-porphyrin-acceptor triads have been synthesized using a versatile Suzuki-coupling route. This synthetic strategy allows the powerful donor tetraalkylphenylenediamine (TAPD) to be introduced into tetraarylporphyrin-based triads without protection. The thermodynamics and kinetics of electron transfer in the new triads are compared with a previously reported octaalkyldiphenyl-porphyrin triad exhibiting a long-lived spin-polarized charge separate state (CSS), from theoretical and experimental perspectives, in both fluid solution and in a frozen solvent glass. We show that the less favorable oxidation potential of the tetraaryl-porphyrin core can be offset by using C60 , as a better electron-acceptor than triptycenenaphthoquinone (TNQ). The C60 -porphyrin-TAPD triad gives a spin-polarized charge-separated state that can be observed by EPR-spectroscopy, with a mean lifetime of 16 ms at 10 K, which is longer than in the previously reported TNQ-porphyrin-TAPD triad, following the predicted trend from calculated charge-recombination rates.
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Affiliation(s)
- Julien B Kelber
- Oxford University , Chemistry Research Laboratory , 12 Mansfield Road , OX1 3TA , Oxford , UK .
- University College London , London Centre for Nanotechnology , Gower Place , WC1E 6BT , London , UK .
| | - Naitik A Panjwani
- University College London , London Centre for Nanotechnology , Gower Place , WC1E 6BT , London , UK .
| | - Di Wu
- Oxford University , Chemistry Research Laboratory , 12 Mansfield Road , OX1 3TA , Oxford , UK .
| | - Rafael Gómez-Bombarelli
- Harvard University , Department of Chemistry and Chemical Biology , 12 Oxford St. 02138 , Cambridge , MA , USA
| | - Brendon W Lovett
- University of St Andrews , SUPA , School of Physics and Astronomy , KY16 9SS , St Andrews , UK .
| | - John J L Morton
- University College London , London Centre for Nanotechnology , Gower Place , WC1E 6BT , London , UK .
| | - Harry L Anderson
- Oxford University , Chemistry Research Laboratory , 12 Mansfield Road , OX1 3TA , Oxford , UK .
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Poddutoori PK, Zarrabi N, Moiseev AG, Gumbau-Brisa R, Vassiliev S, van der Est A. Long-Lived Charge Separation in Novel Axial Donor-Porphyrin-Acceptor Triads Based on Tetrathiafulvalene, Aluminum(III) Porphyrin and Naphthalenediimide. Chemistry 2013; 19:3148-61. [DOI: 10.1002/chem.201202995] [Citation(s) in RCA: 50] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/22/2012] [Indexed: 11/08/2022]
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9
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Pillai S, Ravensbergen J, Antoniuk-Pablant A, Sherman BD, van Grondelle R, Frese RN, Moore TA, Gust D, Moore AL, Kennis JTM. Carotenoids as electron or excited-state energy donors in artificial photosynthesis: an ultrafast investigation of a carotenoporphyrin and a carotenofullerene dyad. Phys Chem Chem Phys 2013; 15:4775-84. [DOI: 10.1039/c3cp50364j] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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Lee SH, Larsen AG, Ohkubo K, Cai ZL, Reimers JR, Fukuzumi S, Crossley MJ. Long-lived long-distance photochemically induced spin-polarized charge separation in β,β′-pyrrolic fused ferrocene-porphyrin-fullerene systems. Chem Sci 2012. [DOI: 10.1039/c1sc00614b] [Citation(s) in RCA: 82] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
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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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12
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Wagnert L, Berg A, Saltsman I, Gross Z, Rozenshtein V. Time-Resolved Electron Paramagnetic Resonance Study of Rhodium(III) Corrole Excited States. J Phys Chem A 2010; 114:2059-72. [DOI: 10.1021/jp909967b] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Linn Wagnert
- Department of Physical Chemistry, The Hebrew University of Jerusalem, Jerusalem 91904, Israel, and Schulich Faculty of Chemistry, Technion - Israel Institute of Technology, Haifa 32000, Israel
| | - Alexander Berg
- Department of Physical Chemistry, The Hebrew University of Jerusalem, Jerusalem 91904, Israel, and Schulich Faculty of Chemistry, Technion - Israel Institute of Technology, Haifa 32000, Israel
| | - Irena Saltsman
- Department of Physical Chemistry, The Hebrew University of Jerusalem, Jerusalem 91904, Israel, and Schulich Faculty of Chemistry, Technion - Israel Institute of Technology, Haifa 32000, Israel
| | - Zeev Gross
- Department of Physical Chemistry, The Hebrew University of Jerusalem, Jerusalem 91904, Israel, and Schulich Faculty of Chemistry, Technion - Israel Institute of Technology, Haifa 32000, Israel
| | - Vladimir Rozenshtein
- Department of Physical Chemistry, The Hebrew University of Jerusalem, Jerusalem 91904, Israel, and Schulich Faculty of Chemistry, Technion - Israel Institute of Technology, Haifa 32000, Israel
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13
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Kobori Y, Shibano Y, Endo T, Tsuji H, Murai H, Tamao K. Time-resolved EPR characterization of a folded conformation of photoinduced charge-separated state in porphyrin-fullerene dyad bridged by diphenyldisilane. J Am Chem Soc 2009; 131:1624-5. [PMID: 19159228 DOI: 10.1021/ja8073775] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
For development of the molecular solar-energy conversion systems, it is crucial to investigate how both the molecular geometry and electronic structure of electron donor-bridge-acceptor (D-B-A) molecules contribute to the electronic coupling for the charge-separation (CS) and charge-recombination (CR) processes. In a D-B-A system of a porphyrin-fullerene dyad (ZnP-C(60)) bridged by a diphenyldisilane spacer, we have characterized one specific folded molecular conformation in the CS state among several existing conformations using the time-resolved electron paramagnetic resonance (TREPR) method at low temperature. To determine the molecular conformation and spin-spin exchange coupling of the CS state, we have considered (1) the electron spin polarization transfer from the excited triplet state of the C(60) moiety to the CS state and (2) the sublevel-selective spin relaxations and CR in the CS state. In the CS state of this conformation, although the ZnP cation and C(60) anion radicals are in close proximity, direct overlap between their singly occupied molecular orbitals is small, resulting in detection of the long-lived CS state which has a totally different conformation from the optically detected, charge-transfer (CT) complex. It has been demonstrated that, among several folded and extended molecular conformations created by the flexibility of the -Si-Si- bridge, the EPR conformation can play a role on the prevention of the energy-wasting CR.
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Affiliation(s)
- Yasuhiro Kobori
- Department of Chemistry, Faculty of Science, Shizuoka University, 836 Ohya Surugaku, Shizuoka 422-8529, Japan
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Pulse ENDOR and density functional theory on the peridinin triplet state involved in the photo-protective mechanism in the peridinin–chlorophyll a–protein from Amphidinium carterae. BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 2008; 1777:295-307. [DOI: 10.1016/j.bbabio.2007.12.003] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/07/2007] [Revised: 12/21/2007] [Accepted: 12/28/2007] [Indexed: 11/21/2022]
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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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16
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Savitsky A, Möbius K. Photochemical Reactions and Photoinduced Electron-Transfer Processes in Liquids, Frozen Solutions, and Proteins as Studied by Multifrequency Time-Resolved EPR Spectroscopy. Helv Chim Acta 2006. [DOI: 10.1002/hlca.200690232] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
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17
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Kandrashkin YE, Asano MS, van der Est A. Light-Induced Electron Spin Polarization in Vanadyl Octaethylporphyrin: I. Characterization of the Excited Quartet State. J Phys Chem A 2006; 110:9607-16. [PMID: 16884194 DOI: 10.1021/jp0620365] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Laser flash induced spin-polarized transient electron paramagnetic resonance (TREPR) spectra for vanadyl octaethylporphyrin in isotropic and partially ordered frozen solutions are presented and compared with corresponding luminescence data. The TREPR spectra show well-resolved hyperfine couplings to the vanadium nucleus and a multiplet polarization pattern with features typical of zero-field splitting (ZFS). The principal values of the vanadium hyperfine coupling tensor evaluated from the spectra are 1/3 of the corresponding values found from steady-state EPR spectra of the ground state. On the basis of these characteristics and numerical simulations, the polarization patterns are assigned to the excited quartet state. The values of the ZFS parameters of the trip-quartet obtained from simulation of the spectra (D = 17.5 mT and E = 1.5 mT) are comparable to those of the triplet state of the zinc and free base octaethyl porphyrin. The lifetime of the spin polarization is found to be temperature dependent and is essentially the same as that of the optical emission. The temperature dependence is rationalized using a model in which the decay to the ground state occurs from both the trip-quartet and trip-doublet, which are in thermal equilibrium even at 15 K. A fit of the model to the observed spin polarization lifetimes yields an energy gap of 47 cm(-1) between the trip-quartet and trip-doublet. It is shown that the spin polarization evolves from a multiplet pattern at early times to a net absorptive pattern at late times following the laser flash. It is proposed that the establishment of thermal equilibrium leads to the evolution of the spin from multiplet to net 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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Kapko V, Matyushov DV. Dynamical Arrest of Electron Transfer in Liquid Crystalline Solvents. J Phys Chem B 2006; 110:13184-94. [PMID: 16805631 DOI: 10.1021/jp0615205] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
We argue that electron transfer reactions in slowly relaxing solvents proceed in the nonergodic regime, making the reaction activation barrier strongly dependent on the solvent dynamics. For typical dielectric relaxation times of polar nematics, electron transfer reactions in the subnanosecond time scale fall into nonergodic regime in which nuclear solvation energies entering the activation barrier are significantly lower than their thermodynamic values. The transition from isotropic to nematic phase results in weak discontinuities of the solvation energies at the transition point and the appearance of solvation anisotropy weakening with increasing solute size. The theory is applied to analyze experimental kinetic data for the electron transfer kinetics in the isotropic phase of 5CB liquid crystalline solvent. We predict that the energy gap law of electron transfer reactions in slowly relaxing solvents is characterized by regions of fast change of the rate at points where the reaction switches between the ergodic and nonergodic regimes. The dependence of the rate on the donor-acceptor separation may also be affected in a way of producing low values for the exponential falloff parameter.
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Affiliation(s)
- Vitaliy Kapko
- Department of Chemistry and Biochemistry and the Center for the Early Events in Photosynthesis, Arizona State University, P.O. Box 871604, Tempe, Arizona 85287-1604, USA
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Giacometti GM, Giacometti G. Twenty years of biophysics of photosynthesis in Padova, Italy (1984-2005): a tale of two brothers. PHOTOSYNTHESIS RESEARCH 2006; 88:241-58. [PMID: 16763879 DOI: 10.1007/s11120-006-9057-9] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/26/2006] [Accepted: 03/07/2006] [Indexed: 05/10/2023]
Abstract
This paper tells the history of two brothers, almost a generation apart in age, who met again, after having followed different academic paths, to introduce biophysical research in photosynthesis at the University of Padova. The development of two research groups, one in the Chemistry Department, the other in the Biology Department led to a comprehensive interdisciplinary group across academic barriers. The group of Giovanni Giacometti developed in Physical Chemistry, during the years before his retirement, with some roots which can be traced to the famous Linus Pauling school of the mid 1950s, and made possible, by the work of many students (especially Donatella Carbonera and Marilena Di Valentin) and of an older associate (Giancarlo Agostini). The group participated quite actively with a number of European and American laboratories in the application of physical techniques, especially Electron Spin Resonance (EPR) associated with Optical Spectroscopy (Optically Detected Magnetic Resonance; ODMR), and contributed to the development of the understanding of the structure-function relationships in photosynthetic membrane complexes, stimulated by the determination of the X-ray structure of the purple photosynthetic reaction center in the mid 1980s ( J. Deisenhofer, H. Michel, R. Huber and others). The younger brother of Giovanni, Giorgio Mario Giacometti, came to Padova after obtaining biochemical knowledge from the Rossi-Fanelli school in Rome, where Jeffries Wyman, Eraldo Antonini and Maurizio Brunori were the world masters of hemoglobin research. In Padova, together with a group of young scientists (at first Roberto Bassi and Roberto Barbato, now leaders of their own groups in Verona and in Alessandria respectively, followed soon by brilliant coworkers such as Fernanda Rigoni, Elisabetta Bergantino and more recently Ildikò Szabò and Paola Costantini), Giorgio approached more biochemical themes of oxygenic photosynthesis, such as purification and characterization of antenna chlorophyll-protein complexes, Photosystem II (PS II) particles and subunits, having always in mind structural and molecular problems at the level of the largest integrated particles, which are more difficult to investigate in detail by the spectroscopic techniques.
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Affiliation(s)
- Giorgio M Giacometti
- Department of Biology, University of Padova, Via Giuseppe Colombo 3, 35121 Padua, Italy.
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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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Santabarbara S, Kuprov I, Hore PJ, Casal A, Heathcote P, Evans MCW. Analysis of the Spin-Polarized Electron Spin Echo of the [P700+A1-] Radical Pair of Photosystem I Indicates That Both Reaction Center Subunits Are Competent in Electron Transfer in Cyanobacteria, Green Algae, and Higher Plants. Biochemistry 2006; 45:7389-403. [PMID: 16752928 DOI: 10.1021/bi060330h] [Citation(s) in RCA: 53] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
The decay of the light-induced spin-correlated radical pair [P700+ A1-] and the associated electron spin echo envelope modulation (ESEEM) have been studied in either thylakoid membranes, cellular membranes, or purified photosystem I prepared from the wild-type strains of Synechocystis sp. PCC 6803, Chlamydomonas reinhardtii, and Spinaceae oleracea. The decay of the spin-correlated radical pair is described in the wild-type membrane by two exponential components with lifetimes of 2-4 and 16-25 micros. The proportions of the two components can be altered by preillumination of the membranes in the presence of reductant at temperatures lower than 220 K, which leads to the complete reduction of the iron-sulfur electron acceptors F(A), F(B), and F(X) and partial photoaccumulation of the reduced quinone electron acceptor A1A-. The "out-of-phase" (OOP) ESEEM attributed to the [P700+ A1-] radical pair has been investigated in the three species as a function of the preillumination treatment. Values of the dipolar (D) and the exchange (J) interactions were extracted by time-domain fitting of the OOP-ESEEM. The results obtained in the wild-type systems are compared with two site-directed mutants of C. reinhardtii [Santabarbara et al. (2005) Biochemistry 44, 2119-2128], in which the spin-polarized signal on either the PsaA- or PsaB-bound electron transfer pathway is suppressed so that the radical pair formed on each electron transfer branch could be monitored selectively. This comparison indicates that when all of the iron-sulfur centers are oxidized, only the echo modulation associated with the A branch [P700+ A1A-] radical pair is observed. The reduction of the iron-sulfur clusters and the quinone A1 by preillumination treatment induces a shift in the ESEEM frequency. In all of the systems investigated this observation can be interpreted in terms of different proportions of the signal associated with the [P700+ A1A-] and [P700+ A1B-] radical pairs, suggesting that bidirectionality of electron transfer in photosystem I is a common feature of all species rather than being confined to green algae.
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Affiliation(s)
- Stefano Santabarbara
- School of Biological and Chemical Sciences, Queen Mary, University of London, Mile End Road, London E1 4NS, United Kingdom.
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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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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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Borrelli R, Di Donato M, Peluso A. Role of intramolecular vibrations in long-range electron transfer between pheophytin and ubiquinone in bacterial photosynthetic reaction centers. Biophys J 2005; 89:830-41. [PMID: 15894646 PMCID: PMC1366633 DOI: 10.1529/biophysj.105.060574] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The dynamics of the elementary electron transfer step between pheophytin and primary ubiquinone in bacterial photosynthetic reaction centers is investigated by using a discrete state approach, including only the intramolecular normal modes of vibration of the two redox partners. The whole set of normal coordinates of the acceptor and donor groups have been employed in the computations of the Hamiltonian matrix, to reliably account both for shifts and mixing of the normal coordinates, and for changes in vibrational frequencies upon ET. It is shown that intramolecular modes provide not only a discrete set of states more strongly coupled to the initial state but also a quasicontinuum of weakly coupled states, which account for the spreading of the wave packet after ET. The computed transition probabilities are sufficiently high for asserting that electron transfer from bacteriopheophytin to the primary quinone can occur via tunneling solely promoted by intramolecular modes; the transition times, computed for different values of the electronic energy difference and coupling term, are of the same order of magnitude (10(2) ps) of the observed one.
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