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Bindra JK, Malavath T, Teferi MY, Kretzschmar M, Kern J, Niklas J, Utschig LM, Poluektov OG. Light-Induced Charge Separation in Photosystem I from Different Biological Species Characterized by Multifrequency Electron Paramagnetic Resonance Spectroscopy. Int J Mol Sci 2024; 25:8188. [PMID: 39125759 PMCID: PMC11311511 DOI: 10.3390/ijms25158188] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/14/2024] [Revised: 07/15/2024] [Accepted: 07/19/2024] [Indexed: 08/12/2024] Open
Abstract
Photosystem I (PSI) serves as a model system for studying fundamental processes such as electron transfer (ET) and energy conversion, which are not only central to photosynthesis but also have broader implications for bioenergy production and biomimetic device design. In this study, we employed electron paramagnetic resonance (EPR) spectroscopy to investigate key light-induced charge separation steps in PSI isolated from several green algal and cyanobacterial species. Following photoexcitation, rapid sequential ET occurs through either of two quasi-symmetric branches of donor/acceptor cofactors embedded within the protein core, termed the A and B branches. Using high-frequency (130 GHz) time-resolved EPR (TR-EPR) and deuteration techniques to enhance spectral resolution, we observed that at low temperatures prokaryotic PSI exhibits reversible ET in the A branch and irreversible ET in the B branch, while PSI from eukaryotic counterparts displays either reversible ET in both branches or exclusively in the B branch. Furthermore, we observed a notable correlation between low-temperature charge separation to the terminal [4Fe-4S] clusters of PSI, termed FA and FB, as reflected in the measured FA/FB ratio. These findings enhance our understanding of the mechanistic diversity of PSI's ET across different species and underscore the importance of experimental design in resolving these differences. Though further research is necessary to elucidate the underlying mechanisms and the evolutionary significance of these variations in PSI charge separation, this study sets the stage for future investigations into the complex interplay between protein structure, ET pathways, and the environmental adaptations of photosynthetic organisms.
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Affiliation(s)
- Jasleen K. Bindra
- Argonne National Laboratory, Chemical Sciences and Engineering Division, 9700 South Cass Avenue, Lemont, IL 60439, USA; (J.K.B.); (T.M.); (M.Y.T.); (J.N.)
| | - Tirupathi Malavath
- Argonne National Laboratory, Chemical Sciences and Engineering Division, 9700 South Cass Avenue, Lemont, IL 60439, USA; (J.K.B.); (T.M.); (M.Y.T.); (J.N.)
| | - Mandefro Y. Teferi
- Argonne National Laboratory, Chemical Sciences and Engineering Division, 9700 South Cass Avenue, Lemont, IL 60439, USA; (J.K.B.); (T.M.); (M.Y.T.); (J.N.)
| | - Moritz Kretzschmar
- Lawrence Berkeley National Laboratory, Molecular Biophysics and Integrated Bioimaging Division, Berkeley, CA 94720, USA; (M.K.); (J.K.)
| | - Jan Kern
- Lawrence Berkeley National Laboratory, Molecular Biophysics and Integrated Bioimaging Division, Berkeley, CA 94720, USA; (M.K.); (J.K.)
| | - Jens Niklas
- Argonne National Laboratory, Chemical Sciences and Engineering Division, 9700 South Cass Avenue, Lemont, IL 60439, USA; (J.K.B.); (T.M.); (M.Y.T.); (J.N.)
| | - Lisa M. Utschig
- Argonne National Laboratory, Chemical Sciences and Engineering Division, 9700 South Cass Avenue, Lemont, IL 60439, USA; (J.K.B.); (T.M.); (M.Y.T.); (J.N.)
| | - Oleg G. Poluektov
- Argonne National Laboratory, Chemical Sciences and Engineering Division, 9700 South Cass Avenue, Lemont, IL 60439, USA; (J.K.B.); (T.M.); (M.Y.T.); (J.N.)
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Utschig LM, Brahmachari U, Mulfort KL, Niklas J, Poluektov OG. Biohybrid photosynthetic charge accumulation detected by flavin semiquinone formation in ferredoxin-NADP + reductase. Chem Sci 2022; 13:6502-6511. [PMID: 35756516 PMCID: PMC9172293 DOI: 10.1039/d2sc01546c] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/16/2022] [Accepted: 05/02/2022] [Indexed: 11/21/2022] Open
Abstract
Flavin chemistry is ubiquitous in biological systems with flavoproteins engaged in important redox reactions. In photosynthesis, flavin cofactors are used as electron donors/acceptors to facilitate charge transfer and accumulation for ultimate use in carbon fixation. Following light-induced charge separation in the photosynthetic transmembrane reaction center photosystem I (PSI), an electron is transferred to one of two small soluble shuttle proteins, a ferredoxin (Fd) or a flavodoxin (Fld) (the latter in the condition of Fe-deficiency), followed by electron transfer to the ferredoxin-NADP+ reductase (FNR) enzyme. FNR accepts two of these sequential one electron transfers, with its flavin adenine dinucleotide (FAD) cofactor becoming doubly reduced, forming a hydride which is then passed onto the substrate NADP+ to form NADPH. The two one-electron potentials (oxidized/semiquinone and semiquinone/hydroquinone) are similar to each other with the FNR protein stabilizing the hydroquinone, making spectroscopic detection of the intermediate semiquinone state difficult. We employed a new biohybrid-based strategy that involved truncating the native three-protein electron transfer cascade PSI → Fd → FNR to a two-protein cascade by replacing PSI with a molecular Ru(ii) photosensitizer (RuPS) which is covalently bound to Fd and Fld to form biohybrid complexes that successfully mimic PSI in light-driven NADPH formation. RuFd → FNR and RuFld → FNR electron transfer experiments revealed a notable distinction in photosynthetic charge accumulation that we attribute to the different protein cofactors [2Fe2S] and flavin. After freeze quenching the two-protein systems under illumination, an intermediate semiquinone state of FNR was readily observed with cw X-band EPR spectroscopy. The increased spectral resolution from selective deuteration allowed EPR detection of inter-flavoprotein electron transfer. This work establishes a biohybrid experimental approach for further studies of photosynthetic light-driven electron transfer chain that culminates at FNR and highlights nature's mechanisms that couple single electron transfer chemistry to charge accumulation, providing important insight for the development of photon-to-fuel schemes.
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Affiliation(s)
- Lisa M Utschig
- Chemical Sciences and Engineering Division, Argonne National Laboratory Lemont IL 60439 USA
| | - Udita Brahmachari
- Chemical Sciences and Engineering Division, Argonne National Laboratory Lemont IL 60439 USA
| | - Karen L Mulfort
- Chemical Sciences and Engineering Division, Argonne National Laboratory Lemont IL 60439 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
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Poluektov OG, Utschig LM. Quantum Sensing of Electron Transfer Pathways in Natural Photosynthesis Using Time-Resolved High-Field Electron Paramagnetic Resonance/Electron-Nuclear Double Resonance Spectroscopy. J Phys Chem B 2021; 125:4025-4030. [PMID: 33877826 DOI: 10.1021/acs.jpcb.1c00946] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Photosynthetic integral membrane reaction center (RC) proteins capture and convert sunlight into chemical energy via efficient charge separation achieved through a series of rapid, photoinitiated electron transfer steps. These fast electron transfers create an entangled spin qubit (radical) pair that contains detailed information about the weak magnetic interactions, structure, and dynamics of localized protein environments involved in charge separation events. Herein, we investigate how these entangled electron spin qubits interact with nuclear spins of the protein environment using the high spectral resolution of 130 GHz electron paramagnetic resonance (EPR) and electron-nuclear double resonance (ENDOR). Spectroscopic interrogation enabled the observation and probing of protons located in the electron transfer pathway between the membrane-spanning electron pair P+QA- (where P+ is the primary donor, a special pair of bacteriochlorophylls, and QA is the primary quinone acceptor) in the bacterial RC. Spectroscopic analysis reveals hydrogen-bonding interactions involved in regulating the route that light-induced electrons travel through the RC protein during charge separation.
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Affiliation(s)
- Oleg G Poluektov
- Chemical Sciences and Engineering Division, Argonne National Laboratory, 9700 South Cass Avenue, Lemont, Illinois 60439, United States
| | - Lisa M Utschig
- Chemical Sciences and Engineering Division, Argonne National Laboratory, 9700 South Cass Avenue, Lemont, Illinois 60439, United States
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Poluektov OG, Niklas J, Utschig LM. Spin-Correlated Radical Pairs as Quantum Sensors of Bidirectional ET Mechanisms in Photosystem I. J Phys Chem B 2019; 123:7536-7544. [DOI: 10.1021/acs.jpcb.9b06636] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Affiliation(s)
- Oleg G. Poluektov
- Chemical Sciences and Engineering Division, Argonne National Laboratory, 9700 S. Cass Avenue, Lemont, Illinois 60439, United States
| | - Jens Niklas
- Chemical Sciences and Engineering Division, Argonne National Laboratory, 9700 S. Cass Avenue, Lemont, Illinois 60439, United States
| | - Lisa M. Utschig
- Chemical Sciences and Engineering Division, Argonne National Laboratory, 9700 S. Cass Avenue, Lemont, Illinois 60439, United States
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Leonova MM, Fufina TY, Vasilieva LG, Shuvalov VA. Structure-function investigations of bacterial photosynthetic reaction centers. BIOCHEMISTRY (MOSCOW) 2012; 76:1465-83. [DOI: 10.1134/s0006297911130074] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
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Poluektov OG, Filippone S, Martín N, Sperlich A, Deibel C, Dyakonov V. Spin Signatures of Photogenerated Radical Anions in Polymer−[70]Fullerene Bulk Heterojunctions: High Frequency Pulsed EPR Spectroscopy. J Phys Chem B 2010; 114:14426-9. [DOI: 10.1021/jp1012347] [Citation(s) in RCA: 71] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Oleg G. Poluektov
- Chemical Sciences and Engineering Division, Argonne National Laboratory, 9700 Cass Avenue, Argonne, Illinois 60439, Departamento de Química Orgánica, Facultad de Ciencias Químicas, Universidad Complutense de Madrid, 28040, Madrid, Spain, IMDEA-Nanociencia, Campus Universidad Autónoma de Madrid, Spain, and Julius-Maximilians University of Würzburg and Bavarian Centre for Applied Energy Research e. V. (ZAE Bayern), D-97074 Würzburg, Germany
| | - Salvatore Filippone
- Chemical Sciences and Engineering Division, Argonne National Laboratory, 9700 Cass Avenue, Argonne, Illinois 60439, Departamento de Química Orgánica, Facultad de Ciencias Químicas, Universidad Complutense de Madrid, 28040, Madrid, Spain, IMDEA-Nanociencia, Campus Universidad Autónoma de Madrid, Spain, and Julius-Maximilians University of Würzburg and Bavarian Centre for Applied Energy Research e. V. (ZAE Bayern), D-97074 Würzburg, Germany
| | - Nazario Martín
- Chemical Sciences and Engineering Division, Argonne National Laboratory, 9700 Cass Avenue, Argonne, Illinois 60439, Departamento de Química Orgánica, Facultad de Ciencias Químicas, Universidad Complutense de Madrid, 28040, Madrid, Spain, IMDEA-Nanociencia, Campus Universidad Autónoma de Madrid, Spain, and Julius-Maximilians University of Würzburg and Bavarian Centre for Applied Energy Research e. V. (ZAE Bayern), D-97074 Würzburg, Germany
| | - Andreas Sperlich
- Chemical Sciences and Engineering Division, Argonne National Laboratory, 9700 Cass Avenue, Argonne, Illinois 60439, Departamento de Química Orgánica, Facultad de Ciencias Químicas, Universidad Complutense de Madrid, 28040, Madrid, Spain, IMDEA-Nanociencia, Campus Universidad Autónoma de Madrid, Spain, and Julius-Maximilians University of Würzburg and Bavarian Centre for Applied Energy Research e. V. (ZAE Bayern), D-97074 Würzburg, Germany
| | - Carsten Deibel
- Chemical Sciences and Engineering Division, Argonne National Laboratory, 9700 Cass Avenue, Argonne, Illinois 60439, Departamento de Química Orgánica, Facultad de Ciencias Químicas, Universidad Complutense de Madrid, 28040, Madrid, Spain, IMDEA-Nanociencia, Campus Universidad Autónoma de Madrid, Spain, and Julius-Maximilians University of Würzburg and Bavarian Centre for Applied Energy Research e. V. (ZAE Bayern), D-97074 Würzburg, Germany
| | - Vladimir Dyakonov
- Chemical Sciences and Engineering Division, Argonne National Laboratory, 9700 Cass Avenue, Argonne, Illinois 60439, Departamento de Química Orgánica, Facultad de Ciencias Químicas, Universidad Complutense de Madrid, 28040, Madrid, Spain, IMDEA-Nanociencia, Campus Universidad Autónoma de Madrid, Spain, and Julius-Maximilians University of Würzburg and Bavarian Centre for Applied Energy Research e. V. (ZAE Bayern), D-97074 Würzburg, Germany
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Kothe G, Thurnauer MC. What you get out of high-time resolution electron paramagnetic resonance: example from photosynthetic bacteria. PHOTOSYNTHESIS RESEARCH 2009; 102:349-365. [PMID: 19350413 DOI: 10.1007/s11120-009-9419-1] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/30/2008] [Accepted: 03/19/2009] [Indexed: 05/27/2023]
Abstract
The primary energy conversion steps of natural photosynthesis proceed via light-induced radical ion pairs as short-lived intermediates. Time-resolved electron paramagnetic resonance (EPR) experiments of photosynthetic reaction centers monitor the key charge separated state between the oxidized primary electron donor and reduced quinone acceptor, e.g., P(+)(865)Q(-)(A) of purple photosynthetic bacteria. The time-resolved EPR spectra of P(+)(865)Q(-)(A) are indicative of a spin-correlated radical pair that is created from the excited singlet state of P(865) in an ultra-fast photochemical reaction. Importantly, the spin-correlated radical pair nature of the charge separated state is a common feature of all photosynthetic reaction centers, which gives rise to several interesting spin phenomena such as quantum oscillations, observed at short delay times after optical excitation. In this review, we describe details of the quantum oscillation phenomenon and present a complete analysis of the data obtained from the charge separated state of purple bacteria, P(+)(865)Q(-)(A). The analysis and simulation of the quantum oscillations yield the three-dimensional structure of P(+)(865)Q(-)(A) in the photosynthetic membrane on a nanosecond time scale after light-induced charge separation. Comparison with crystallographic data reveals that the position of Q(-)(A) is essentially the same as in the X-ray structure. However, the head group of Q(-)(A) has undergone a 60° rotation in the ring plane relative to its orientation in the crystal structure. The results are discussed within the framework of the previously suggested conformational gating mechanism for electron transfer from Q(-)(A) to the secondary quinone acceptor Q(B).
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Affiliation(s)
- Gerd Kothe
- Department of Physical Chemistry, University of Freiburg, Albertstr. 21, 79104 Freiburg, Germany.
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Kulik L, Lubitz W. Electron-nuclear double resonance. PHOTOSYNTHESIS RESEARCH 2009; 102:391-401. [PMID: 19184518 PMCID: PMC2847154 DOI: 10.1007/s11120-009-9401-y] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/04/2008] [Accepted: 12/31/2008] [Indexed: 05/22/2023]
Abstract
The application of electron-nuclear double resonance (ENDOR) spectroscopy for the investigation of photosynthetic systems is reviewed. The basic principles of continuous wave and pulse ENDOR are presented. Selected examples of the application of the ENDOR technique for studying stable and transient paramagnetic species, including cofactor radical ions, radical pairs, triplet states, and the oxygen-evolving complex in plant Photosystem II (PSII) are discussed. Limitations and perspectives of ENDOR spectroscopy are outlined.
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Affiliation(s)
- Leonid Kulik
- Institute of Chemical Kinetics and Combustion, Institutskaya 3, 630090 Novosibirsk, Russia
| | - Wolfgang Lubitz
- Max-Planck-Institut für Bioanorganische Chemie, Stiftstrasse 34-36, 45470 Mülheim an der Ruhr, Germany
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Niklas J, Epel B, Antonkine ML, Sinnecker S, Pandelia ME, Lubitz W. Electronic Structure of the Quinone Radical Anion A1•− of Photosystem I Investigated by Advanced Pulse EPR and ENDOR Techniques. J Phys Chem B 2009; 113:10367-79. [DOI: 10.1021/jp901890z] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Jens Niklas
- Max-Planck-Institut für Bioanorganische Chemie, Stiftstrasse 34-36, 45470 Mülheim/Ruhr, Germany, and Institut für Experimentalphysik, Freie Universität Berlin, Arnimallee 14, 14195 Berlin, Germany
| | - Boris Epel
- Max-Planck-Institut für Bioanorganische Chemie, Stiftstrasse 34-36, 45470 Mülheim/Ruhr, Germany, and Institut für Experimentalphysik, Freie Universität Berlin, Arnimallee 14, 14195 Berlin, Germany
| | - Mikhail L. Antonkine
- Max-Planck-Institut für Bioanorganische Chemie, Stiftstrasse 34-36, 45470 Mülheim/Ruhr, Germany, and Institut für Experimentalphysik, Freie Universität Berlin, Arnimallee 14, 14195 Berlin, Germany
| | - Sebastian Sinnecker
- Max-Planck-Institut für Bioanorganische Chemie, Stiftstrasse 34-36, 45470 Mülheim/Ruhr, Germany, and Institut für Experimentalphysik, Freie Universität Berlin, Arnimallee 14, 14195 Berlin, Germany
| | - Maria-Eirini Pandelia
- Max-Planck-Institut für Bioanorganische Chemie, Stiftstrasse 34-36, 45470 Mülheim/Ruhr, Germany, and Institut für Experimentalphysik, Freie Universität Berlin, Arnimallee 14, 14195 Berlin, Germany
| | - Wolfgang Lubitz
- Max-Planck-Institut für Bioanorganische Chemie, Stiftstrasse 34-36, 45470 Mülheim/Ruhr, Germany, and Institut für Experimentalphysik, Freie Universität Berlin, Arnimallee 14, 14195 Berlin, Germany
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Poluektov OG, Paschenko SV, Utschig LM. Spin-dynamics of the spin-correlated radical pair in photosystem I. Pulsed time-resolved EPR at high magnetic field. Phys Chem Chem Phys 2009; 11:6750-6. [DOI: 10.1039/b906521k] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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Jones MR. Structural Plasticity of Reaction Centers from Purple Bacteria. THE PURPLE PHOTOTROPHIC BACTERIA 2009. [DOI: 10.1007/978-1-4020-8815-5_16] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
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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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High-Time Resolution Electron Paramagnetic Resonance Study of Quantum Beat Oscillations Observed in Photosynthetic Reaction Center Proteins. BIOPHYSICAL TECHNIQUES IN PHOTOSYNTHESIS 2008. [DOI: 10.1007/978-1-4020-8250-4_15] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
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Smirnova TI, Smirnov AI, Pachtchenko S, Poluektov OG. Geometry of hydrogen bonds formed by lipid bilayer nitroxide probes: a high-frequency pulsed ENDOR/EPR study. J Am Chem Soc 2007; 129:3476-7. [PMID: 17341078 PMCID: PMC2517987 DOI: 10.1021/ja068395v] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Solvent effects on magnetic parameters of nitroxide spin labels in combination with side-directed spin labeling EPR methods provide very useful means for elucidating polarity profiles in lipid bilayers and mapping local electrostatic effects in complex biomolecular systems. One major contributor to these solvent effects is the hydrogen bonds that could be formed between the nitroxide moiety and water and/or the available hydroxyl groups. Here, formation of hydrogen bonds between a lipid bilayer spin probe -5-doxyl stearic acid, 5DSA – and hydrogen bond donors has been studied using high-frequency (HF) pulsed ENDOR and EPR. A hydrogen-bonded deuteron was directly detected in HF ENDOR (130 GHz) spectra of 5DSA dissolved in several deuterated alcohols while the characteristic signal was absent in non-polar toluene-d 8. The length of the hydrogen bond, 1.74±0.06 Å, and its geometry were found to be essentially the same for all four alcohols studied, indicating that nearly identical hydrogen bonds have been formed regardless of the solvent dielectric constant. This strengthens a hypothesis that HF EPR spectra are exclusively sensitive to formation of hydrogen bonds and could be used for probing the hydrogen bond network in complex biomolecular assemblies and lipid bilayers with site-directed spin-labeling methods.
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Affiliation(s)
- Tatyana I. Smirnova
- Department of Chemistry, North Carolina State University, 2620 Yarbrough Dr., Raleigh, North Carolina 27695,
| | - Alex I. Smirnov
- Department of Chemistry, North Carolina State University, 2620 Yarbrough Dr., Raleigh, North Carolina 27695,
| | - Serguei Pachtchenko
- Chemistry Division, Argonne National Laboratory, 9700 South Cass Avenue, Argonne, Illinois 60439
| | - Oleg G. Poluektov
- Chemistry Division, Argonne National Laboratory, 9700 South Cass Avenue, Argonne, Illinois 60439
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Goldfarb D. High field ENDOR as a characterization tool for functional sites in microporous materials. Phys Chem Chem Phys 2006; 8:2325-43. [PMID: 16710481 DOI: 10.1039/b601513c] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
The determination of the details of the spatial and electronic structure of functional sites (centers) in any system, be it in materials chemistry or in biology, is the first step towards understanding their function. When such sites happen to be paramagnetic in any point of their activity cycle, the tool box offered by a variety of high resolution electron paramagnetic resonance (EPR) spectroscopic techniques becomes very attractive for their characterization. This tool box has been considerably expanded by the developments in high field (HF) EPR in general, and HF electron nuclear double resonance (ENDOR), in particular. These have led to numerous new applications in the fields of biology, physics, chemistry and materials sciences. This overview focuses specifically on recent applications of pulsed HF ENDOR spectroscopy to microporous materials, such as zeotype materials, presenting the new opportunities it offers. First, a brief description of the theoretical basis required for the analysis of the HF ENDOR spectrum is given, followed by a description of the pulsed techniques used to record spectra and assign the signals, along with a brief presentation of the required instrumentation. Next, specific applications are given, including transition metal ions and complexes exchanged into zeolite cages, transition metal substitution into frameworks of zeolites, aluminophosphate molecular sieves, and silicious mesoporous materials, the interaction of NO with Lewis sites in zeolite cages and trapped S. We end with a discussion of the advantages and the shortcomings of the method and conclude with a future outlook.
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Affiliation(s)
- Daniella Goldfarb
- Department of Chemical Physics, Weizmann Institute of Science, Rehovot, Israel.
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Current awareness in phytochemical analysis. PHYTOCHEMICAL ANALYSIS : PCA 2006; 17:63-70. [PMID: 16454478 DOI: 10.1002/pca.880] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/06/2023]
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