1
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Tran VA, Teucher M, Galazzo L, Sharma B, Pongratz T, Kast SM, Marx D, Bordignon E, Schnegg A, Neese F. Dissecting the Molecular Origin of g-Tensor Heterogeneity and Strain in Nitroxide Radicals in Water: Electron Paramagnetic Resonance Experiment versus Theory. J Phys Chem A 2023; 127:6447-6466. [PMID: 37524058 PMCID: PMC10424240 DOI: 10.1021/acs.jpca.3c02879] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/02/2023] [Revised: 07/01/2023] [Indexed: 08/02/2023]
Abstract
Nitroxides are common EPR sensors of microenvironmental properties such as polarity, numbers of H-bonds, pH, and so forth. Their solvation in an aqueous environment is facilitated by their high propensity to form H-bonds with the surrounding water molecules. Their g- and A-tensor elements are key parameters to extracting the properties of their microenvironment. In particular, the gxx value of nitroxides is rich in information. It is known to be characterized by discrete values representing nitroxide populations previously assigned to have different H-bonds with the surrounding waters. Additionally, there is a large g-strain, that is, a broadening of g-values associated with it, which is generally correlated with environmental and structural micro-heterogeneities. The g-strain is responsible for the frequency dependence of the apparent line width of the EPR spectra, which becomes evident at high field/frequency. Here, we address the molecular origin of the gxx heterogeneity and of the g-strain of a nitroxide moiety (HMI: 2,2,3,4,5,5-hexamethylimidazolidin-1-oxyl, C9H19N2O) in water. To treat the solvation effect on the g-strain, we combined a multi-frequency experimental approach with ab initio molecular dynamics simulations for structural sampling and quantum chemical EPR property calculations at the highest realistically affordable level, including an explicitly micro-solvated HMI ensemble and the embedded cluster reference interaction site model. We could clearly identify the distinct populations of the H-bonded nitroxides responsible for the gxx heterogeneity experimentally observed, and we dissected the role of the solvation shell, H-bond formation, and structural deformation of the nitroxide in the creation of the g-strain associated with each nitroxide subensemble. Two contributions to the g-strain were identified in this study. The first contribution depends on the number of hydrogen bonds formed between the nitroxide and the solvent because this has a large and well-understood effect on the gxx-shift. This contribution can only be resolved at high resonance frequencies, where it leads to distinct peaks in the gxx region. The second contribution arises from configurational fluctuations of the nitroxide that necessarily lead to g-shift heterogeneity. These contributions cannot be resolved experimentally as distinct resonances but add to the line broadening. They can be quantitatively analyzed by studying the apparent line width as a function of microwave frequency. Interestingly, both theory and experiment confirm that this contribution is independent of the number of H-bonds. Perhaps even more surprisingly, the theoretical analysis suggests that the configurational fluctuation broadening is not induced by the solvent but is inherently present even in the gas phase. Moreover, the calculations predict that this broadening decreases upon solvation of the nitroxide.
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Affiliation(s)
- Van Anh Tran
- Max-Planck-Institut
für Kohlenforschung, Kaiser-Wilhelm-Platz 1, 45470 Mülheim an der Ruhr, Germany
| | - Markus Teucher
- Max-Planck-Institut
für Chemische Energiekonversion, Stiftstraße 34-36, 45470 Mülheim an der Ruhr, Germany
| | - Laura Galazzo
- Department
of Physical Chemistry, University of Geneva, Quai Ernest Ansermet 30, 1211 Geneva, Switzerland
- Faculty
of Chemistry and Biochemistry, Ruhr-Universität
Bochum, 44780 Bochum, Germany
| | - Bikramjit Sharma
- Lehrstuhl
für Theoretische Chemie, Ruhr-Universität
Bochum, 44780 Bochum, Germany
| | - Tim Pongratz
- Fakultät
für Chemie und Chemische Biologie, Technische Universität Dortmund, Otto-Hahn-Str. 4a, 44227 Dortmund, Germany
| | - Stefan M. Kast
- Fakultät
für Chemie und Chemische Biologie, Technische Universität Dortmund, Otto-Hahn-Str. 4a, 44227 Dortmund, Germany
| | - Dominik Marx
- Lehrstuhl
für Theoretische Chemie, Ruhr-Universität
Bochum, 44780 Bochum, Germany
| | - Enrica Bordignon
- Department
of Physical Chemistry, University of Geneva, Quai Ernest Ansermet 30, 1211 Geneva, Switzerland
- Faculty
of Chemistry and Biochemistry, Ruhr-Universität
Bochum, 44780 Bochum, Germany
| | - Alexander Schnegg
- Max-Planck-Institut
für Chemische Energiekonversion, Stiftstraße 34-36, 45470 Mülheim an der Ruhr, Germany
| | - Frank Neese
- Max-Planck-Institut
für Kohlenforschung, Kaiser-Wilhelm-Platz 1, 45470 Mülheim an der Ruhr, Germany
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2
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Möbius K, Lubitz W, Savitsky A. CIDEP-Enhanced ENDOR of short-lived radicals. Recollections of first joint experiments with Renad Sagdeev. Russ Chem Bull 2022. [DOI: 10.1007/s11172-021-3366-1] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
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3
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Marko A, Sojka A, Laguta O, Neugebauer P. Simulation of nitrogen nuclear spin magnetization of liquid solved nitroxides. Phys Chem Chem Phys 2021; 23:17310-17322. [PMID: 34346404 PMCID: PMC8371994 DOI: 10.1039/d0cp06071b] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/23/2020] [Accepted: 06/25/2021] [Indexed: 12/15/2022]
Abstract
Nitroxide radicals are widely used in electron paramagnetic resonance (EPR) applications. Nitroxides are stable organic radicals containing the N-O˙ group with hyperfine coupled unpaired electron and nitrogen nuclear spins. In the past, much attention was devoted to studying nitroxide EPR spectra and electron spin magnetization evolution under various experimental conditions. However, the dynamics of nitrogen nuclear spin has not been investigated in detail so far. In this work, we performed quantitative prediction and simulation of nitrogen nuclear spin magnetization evolution in several magnetic resonance experiments. Our research was focused on fast rotating nitroxide radicals in liquid solutions. We used a general approach allowing us to compute electron and nitrogen nuclear spin magnetization from the same time-dependent spin density matrix obtained by solving the Liouville/von Neumann equation. We investigated the nitrogen nuclear spin dynamics subjected to various radiofrequency magnetic fields. Furthermore, we predicted a large dynamic nuclear polarization of nitrogen upon nitroxide irradiation with microwaves and analyzed its effect on the nitroxide EPR saturation factor.
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Affiliation(s)
- Andriy Marko
- Central European Institute of Technology, Brno University of TechnologyPurkynova-Str. 12361200BrnoCzech Republic
| | - Antonin Sojka
- Central European Institute of Technology, Brno University of TechnologyPurkynova-Str. 12361200BrnoCzech Republic
| | - Oleksii Laguta
- Central European Institute of Technology, Brno University of TechnologyPurkynova-Str. 12361200BrnoCzech Republic
| | - Petr Neugebauer
- Central European Institute of Technology, Brno University of TechnologyPurkynova-Str. 12361200BrnoCzech Republic
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4
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Bowen AM, Bertran A, Henbest KB, Gobbo M, Timmel CR, Di Valentin M. Orientation-Selective and Frequency-Correlated Light-Induced Pulsed Dipolar Spectroscopy. J Phys Chem Lett 2021; 12:3819-3826. [PMID: 33856805 PMCID: PMC8154851 DOI: 10.1021/acs.jpclett.1c00595] [Citation(s) in RCA: 9] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/23/2021] [Accepted: 03/31/2021] [Indexed: 06/12/2023]
Abstract
We explore the potential of orientation-resolved pulsed dipolar spectroscopy (PDS) in light-induced versions of the experiment. The use of triplets as spin-active moieties for PDS offers an attractive tool for studying biochemical systems containing optically active cofactors. Cofactors are often rigidly bound within the protein structure, providing an accurate positional marker. The rigidity leads to orientation selection effects in PDS, which can be analyzed to give both distance and mutual orientation information. Herein we present a comprehensive analysis of the orientation selection of a full set of light-induced PDS experiments. We exploit the complementary information provided by the different light-induced techniques to yield atomic-level structural information. For the first time, we measure a 2D frequency-correlated laser-induced magnetic dipolar spectrum, and we are able to monitor the complete orientation dependence of the system in a single experiment. Alternatively, the summed spectrum enables an orientation-independent analysis to determine the distance distribution.
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Affiliation(s)
- Alice M. Bowen
- Department
of Chemistry, Photon Science Institute and The National EPR Research
Facility, The University of Manchester, Oxford Road, Manchester M13 9PL, United Kingdom
- Centre
for Advanced Electron Spin Resonance and Inorganic Chemistry Laboratory,
Department of Chemistry, University of Oxford, South Parks Road, Oxford OX1 3QR, United Kingdom
| | - Arnau Bertran
- Centre
for Advanced Electron Spin Resonance and Inorganic Chemistry Laboratory,
Department of Chemistry, University of Oxford, South Parks Road, Oxford OX1 3QR, United Kingdom
| | - Kevin B. Henbest
- Centre
for Advanced Electron Spin Resonance and Inorganic Chemistry Laboratory,
Department of Chemistry, University of Oxford, South Parks Road, Oxford OX1 3QR, United Kingdom
| | - Marina Gobbo
- Department
of Chemical Sciences, University of Padova, Via Marzolo 1, 35131 Padova, Italy
| | - Christiane R. Timmel
- Centre
for Advanced Electron Spin Resonance and Inorganic Chemistry Laboratory,
Department of Chemistry, University of Oxford, South Parks Road, Oxford OX1 3QR, United Kingdom
| | - Marilena Di Valentin
- Department
of Chemical Sciences, University of Padova, Via Marzolo 1, 35131 Padova, Italy
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5
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Potapov A. Application of spherical harmonics for DEER data analysis in systems with a conformational distribution. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2020; 316:106769. [PMID: 32574865 DOI: 10.1016/j.jmr.2020.106769] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/03/2020] [Revised: 06/03/2020] [Accepted: 06/04/2020] [Indexed: 06/11/2023]
Abstract
Double electron-electron resonance (DEER) and other pulse electron paramagnetic resonance (EPR) techniques are valuable tools for determining distances between paramagnetic centres. DEER theory is well developed for a scenario where relative orientations of paramagnetic centres do not affect the DEER data. In particular, such theory enables a number of approaches for extracting distance distributions. However, in a more general case, when orientation selection effects become substantial, the analytical theory of DEER is less well developed, therefore quite commonly researchers rely on a comparison of some model-based simulations with experimental data. This work elaborates the theory of DEER with orientation selection effects, focusing on a scenario of a moderate conformational disorder, leading to an orientation distribution in a pair of paramagnetic centres. The analytical treatment based on expansions into spherical harmonics, provides important insights into the structure of DEER data. As follows from this treatment, DEER spectra with orientation selection can be represented as a linear combination of modified Pake pattern (MPP) components. The conformational disorder has a filtering effect on the weights of MPP components, specifically by significantly suppressing MPP components of higher degrees. The developed theory provides a pathway for model-based simulations of DEER data where orientation distribution is defined by analytical functions with parameters. The theory based on spherical harmonics expansions was also applied to develop an iterative processing algorithm based on Tikhonov regularization, which disentangles the distance and orientation information in a model-free manner. As an input, this procedure takes several DEER datasets measured at various positions of an EPR line, and outputs a distance distribution and orientation distribution information encoded in a set of coefficients related to the weights of MPP components. The model-based and model-free approaches based on the developed theory were validated for a nitroxide biradical and a spin-labelled protein.
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Affiliation(s)
- Alexey Potapov
- School of Physics and Astronomy, University of Nottingham, University Park, Nottingham NG7 2RD, UK.
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6
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Eckert H. Advanced Magnetic Resonance Techniques for the Structural Characterization of Aminoxyl Radicals and Their Inorganic-Organic Nanocomposite Systems. Chemistry 2017; 23:5893-5914. [PMID: 27862449 DOI: 10.1002/chem.201604685] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/05/2016] [Indexed: 11/10/2022]
Abstract
Electron and nuclear spins are extremely sensitive probes of their local structural and dynamic surroundings. Their Zeeman energy levels are modified by different types of local magnetic and electric fields created by their structural environment, which influence their magnetic resonance condition. For this reason, electron spin resonance (ESR) and nuclear magnetic resonance (NMR) spectroscopies have become extremely powerful tools of structural analysis, which are being widely used for the structural characterization of complex solids. Following a brief introduction into the basic theoretical foundations the most commonly used techniques and their application towards the structural characterization of paramagnetic solids based on aminoxyl radicals and their inorganic-organic nanocomposites will be described. Both ESR and NMR observables are useful for monitoring intermolecular interactions between unpaired electron spins, which are particularly important for the design of organically based ferromagnetic systems. ESR and NMR methods based on this effect can be used for monitoring the synthesis of polynitroxides and for evaluating the catalytic function of aminoxyl intercalation compounds. Finally, the sensitivity of ESR signals to motional dynamics can be exploited for characterizing molecule-surface interactions in nanocomposite systems. In the context of the latter work recently developed signal enhancement strategies are described, using polarization transfer from electron spins to nuclear spins for NMR spectroscopic detection.
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Affiliation(s)
- Hellmut Eckert
- Institut für Physikalische Chemie, WWU Münster, Corrensstraße 30, 48149, Münster, Germany.,Instituto de Física São Carlos, Universidade de São Paulo, CP 369, 13560-970, São Carlos, S.P., Brasil
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7
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Nalepa A, Malferrari M, Lubitz W, Venturoli G, Möbius K, Savitsky A. Local water sensing: water exchange in bacterial photosynthetic reaction centers embedded in a trehalose glass studied using multiresonance EPR. Phys Chem Chem Phys 2017; 19:28388-28400. [DOI: 10.1039/c7cp03942e] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023]
Abstract
Pulsed EPR spectroscopies and isotope labeled water are applied to detect and quantify the local water in a bacterial reaction center embedded into a trehalose glass.
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Affiliation(s)
- Anna Nalepa
- Max-Planck-Institut für Chemische Energiekonversion
- D-45470 Mülheim an der Ruhr
- Germany
| | - Marco Malferrari
- Laboratorio di Biochimica e Biofisica
- Dipartimento di Farmacia e Biotecnologie
- FaBiT
- Università di Bologna
- I-40126 Bologna
| | - Wolfgang Lubitz
- Max-Planck-Institut für Chemische Energiekonversion
- D-45470 Mülheim an der Ruhr
- Germany
| | - Giovanni Venturoli
- Laboratorio di Biochimica e Biofisica
- Dipartimento di Farmacia e Biotecnologie
- FaBiT
- Università di Bologna
- I-40126 Bologna
| | - Klaus Möbius
- Max-Planck-Institut für Chemische Energiekonversion
- D-45470 Mülheim an der Ruhr
- Germany
- Department of Physics
- Free University Berlin
| | - Anton Savitsky
- Max-Planck-Institut für Chemische Energiekonversion
- D-45470 Mülheim an der Ruhr
- Germany
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8
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Lohmiller T, Vibhute MA, Lubitz W, Savitsky A. Multifrequency Multiresonance EPR Investigation of Halogen-bonded Complexes Involving Neutral Nitroxide Radicals. ACTA ACUST UNITED AC 2016. [DOI: 10.1515/zpch-2016-0870] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
Abstract
Abstract
Halogen-bonded complexes with neutral nitroxide radicals as the Lewis base have been investigated in liquid and frozen solutions by multifrequency CW and pulse EPR spectroscopies, including ENDOR and ELDOR-detected NMR (EDNMR) techniques. The non-covalent interaction with iodopentafluorobenzene as halogen-bond donor is shown to affect a variety of EPR parameters of the stable nitroxide radicals. In liquid solution, only bulk effects on the EPR signal, i.e. isotropic g value, isotropic 14N hyperfine coupling and linewidth, are observed. Experiments on frozen solutions allow for a more in-depth dissection of complexing effects. W-band EPR spectra at cryogenic temperatures exhibit multiple signal components of different 14N hyperfine interactions and spectral widths. This demonstrates the coexistence of several halogen-bonded complexes that differ in donor-acceptor binding geometries. These complexes have different relaxation properties, which allow for their spectral discrimination. 19F ENDOR experiments prove the origin of these effects to be different specific intermolecular interactions rather than a consequence of changes in the solvation environment. The EPR spectra yet reveal a strong influence of solvent composition on the amount of the various complexes formed. The introduced methodology for the characterization of such adducts improves our understanding of halogen bonding and could be helpful in the development of tailor-made donors and complexes for specific applications.
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Affiliation(s)
- Thomas Lohmiller
- Max-Planck-Institut für Chemische Energiekonversion, 45470 Mülheim an der Ruhr, Germany
- Lehrstuhl für Organische Chemie II, Ruhr-Universität Bochum, 44780 Bochum, Germany
| | - Mahesh A. Vibhute
- Lehrstuhl für Physikalische Chemie II, Ruhr-Universität Bochum, 44780 Bochum, Germany
| | - Wolfgang Lubitz
- Max-Planck-Institut für Chemische Energiekonversion, 45470 Mülheim an der Ruhr, Germany
| | - Anton Savitsky
- Max-Planck-Institut für Chemische Energiekonversion, 45470 Mülheim an der Ruhr, Germany
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9
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Malferrari M, Savitsky A, Mamedov MD, Milanovsky GE, Lubitz W, Möbius K, Semenov AY, Venturoli G. Trehalose matrix effects on charge-recombination kinetics in Photosystem I of oxygenic photosynthesis at different dehydration levels. BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 2016; 1857:1440-1454. [DOI: 10.1016/j.bbabio.2016.05.001] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/18/2015] [Revised: 05/03/2016] [Accepted: 05/06/2016] [Indexed: 10/21/2022]
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10
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de Oliveira M, Knitsch R, Sajid M, Stute A, Elmer LM, Kehr G, Erker G, Magon CJ, Jeschke G, Eckert H. Aminoxyl Radicals of B/P Frustrated Lewis Pairs: Refinement of the Spin-Hamiltonian Parameters by Field- and Temperature-Dependent Pulsed EPR Spectroscopy. PLoS One 2016; 11:e0157944. [PMID: 27336303 PMCID: PMC4918942 DOI: 10.1371/journal.pone.0157944] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/13/2016] [Accepted: 06/07/2016] [Indexed: 11/18/2022] Open
Abstract
Q-band and X-band pulsed electron paramagnetic resonance spectroscopic methods (EPR) in the solid state were employed to refine the parameters characterizing the anisotropic interactions present in six nitroxide radicals prepared by N,N addition of NO to various borane-phosphane frustrated Lewis pairs (FLPs). The EPR spectra are characterized by the g-anisotropy as well as by nuclear hyperfine coupling between the unpaired electron and the 11B/10B, 14N and 31P nuclear magnetic moments. It was previously shown that continuous-wave spectra measured at X-band frequency (9.5 GHz) are dominated by the magnetic hyperfine coupling to 14N and 31P, whereas the g-tensor values and the 11B hyperfine coupling parameters cannot be refined with high precision from lineshape fitting. On the other hand, the X-band electron spin echo envelope modulation (ESEEM) and hyperfine sublevel correlation (HYSCORE) spectra are completely dominated by the nuclear hyperfine coupling to the 11B nuclei, allowing a selective determination of their interaction parameters. In the present work this analysis has been further validated by temperature dependent ESEEM measurements. In addition, pulsed EPR data measured in the Q-band (34 GHz) are reported, which present an entirely different situation: the g-tensor components can be measured with much higher precision, and the ESEEM and HYSCORE spectra contain information about all of the 10B, 11B, 14N and 31P hyperfine interaction parameters. Based on these new results, we report here high-accuracy and precision data of the EPR spin Hamiltonian parameters measured on six FLP-NO radical species embedded in their corresponding hydroxylamine host structures. While the ESEEM spectra at Q-band frequency turn out to be very complex (due to the multinuclear contribution to the overall signal) in the HYSCORE experiment the extension over two dimensions renders a better discrimination between the different nuclear species, and the signals arising from hyperfine coupling to 10B, 11B, 14N and 31P nuclei can be individually analyzed.
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Affiliation(s)
- Marcos de Oliveira
- Instituto de Física de São Carlos, Universidade de São Paulo, P.O. Box 369, 13560-970, São Carlos, São Paulo, Brazil
| | - Robert Knitsch
- Institut für Physikalische Chemie, WWU Münster, Corrensstr. 30, D 48149 Münster, Germany
| | - Muhammad Sajid
- Organisch-Chemisches Institut, WWU Münster, Corrensstr. 40, D 48149 Münster, Germany
| | - Annika Stute
- Organisch-Chemisches Institut, WWU Münster, Corrensstr. 40, D 48149 Münster, Germany
| | - Lisa-Maria Elmer
- Organisch-Chemisches Institut, WWU Münster, Corrensstr. 40, D 48149 Münster, Germany
| | - Gerald Kehr
- Organisch-Chemisches Institut, WWU Münster, Corrensstr. 40, D 48149 Münster, Germany
| | - Gerhard Erker
- Organisch-Chemisches Institut, WWU Münster, Corrensstr. 40, D 48149 Münster, Germany
| | - Claudio J. Magon
- Instituto de Física de São Carlos, Universidade de São Paulo, P.O. Box 369, 13560-970, São Carlos, São Paulo, Brazil
| | - Gunnar Jeschke
- Laboratorium für Physikalische Chemie, ETH Zürich, Vladimir-Prelog-Weg 2, 8049 Zürich, Switzerland
| | - Hellmut Eckert
- Instituto de Física de São Carlos, Universidade de São Paulo, P.O. Box 369, 13560-970, São Carlos, São Paulo, Brazil
- Institut für Physikalische Chemie, WWU Münster, Corrensstr. 30, D 48149 Münster, Germany
- * E-mail:
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11
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Bordignon E, Nalepa AI, Savitsky A, Braun L, Jeschke G. Changes in the Microenvironment of Nitroxide Radicals around the Glass Transition Temperature. J Phys Chem B 2015; 119:13797-806. [DOI: 10.1021/acs.jpcb.5b04104] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Enrica Bordignon
- Laboratory
of Physical Chemistry, ETH Zurich, Vladimir-Prelog-Weg 2, 8093 Zurich, Switzerland
- Berlin
Joint EPR Laboratories, Department of Experimental Physics, Free University of Berlin, Arnimallee 14, 14195 Berlin, Germany
| | - Anna I. Nalepa
- Max Planck Institute for Chemical Energy Conversion, Stiftstrasse 34−36, 45470 Mülheim an der Ruhr, Germany
| | - Anton Savitsky
- Max Planck Institute for Chemical Energy Conversion, Stiftstrasse 34−36, 45470 Mülheim an der Ruhr, Germany
| | - Lukas Braun
- Laboratory
of Physical Chemistry, ETH Zurich, Vladimir-Prelog-Weg 2, 8093 Zurich, Switzerland
| | - Gunnar Jeschke
- Laboratory
of Physical Chemistry, ETH Zurich, Vladimir-Prelog-Weg 2, 8093 Zurich, Switzerland
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12
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Marsh D. Bonding in nitroxide spin labels from 14N electric-quadrupole interactions. J Phys Chem A 2015; 119:919-21. [PMID: 25574852 DOI: 10.1021/jp512764w] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/21/2023]
Abstract
Nitrogen nuclear electric quadrupole couplings from FT-EPR of nitroxide spin labels can be used to deduce the covalent transfer πc in the N–O π-bond, and ionicities iσ(NO) and iσ(NC) of the N–O and N–C σ-bonds, if they are combined with the unpaired spin density on the nitrogen ρπ(N) obtained from the dipolar hyperfine couplings. Application to EPR data from an analogue of the MTSSL nitroxide that is used in site-directed spin-labeling demonstrates how environmental polarity and hydrogen bonding are reflected in the bonding parameters of the C–NO–C spin label moiety. Several recent publications erroneously claim to have deduced three independent bonding parameters from nitrogen quadrupole couplings alone.
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Affiliation(s)
- Derek Marsh
- Max-Planck-Institut für biophysikalische Chemie , Am Fassberg 11, 37077 Göttingen, Germany
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13
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Cox N, Nalepa A, Pandelia ME, Lubitz W, Savitsky A. Pulse Double-Resonance EPR Techniques for the Study of Metallobiomolecules. Methods Enzymol 2015; 563:211-49. [DOI: 10.1016/bs.mie.2015.08.016] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
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14
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Nalepa A, Möbius K, Lubitz W, Savitsky A. High-field ELDOR-detected NMR study of a nitroxide radical in disordered solids: towards characterization of heterogeneity of microenvironments in spin-labeled systems. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2014; 242:203-213. [PMID: 24685717 DOI: 10.1016/j.jmr.2014.02.026] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/21/2014] [Revised: 02/27/2014] [Accepted: 02/28/2014] [Indexed: 06/03/2023]
Abstract
The combination of high-field EPR with site-directed spin-labeling (SDSL) techniques employing nitroxide radicals has turned out to be particularly powerful in probing the polarity and proticity characteristics of protein/matrix systems. This information is concluded from the principal components of the nitroxide Zeeman (g), nitrogen hyperfine (A) and quadrupole (P) tensors of the spin labels attached to specific sites. Recent multi-frequency high-field EPR studies underlined the complexity of the problem to treat the nitroxide microenvironment in proteins adequately due to inherent heterogeneities which result in several principal x-components of the nitroxide g-tensor. Concomitant, but distinctly different nitrogen hyperfine components could, however, not be determined from high-field cw EPR experiments owing to the large intrinsic EPR linewidth in fully protonated guest/host systems. It is shown in this work that, using the W-band (95GHz) ELDOR- (electron-electron double resonance) detected NMR (EDNMR) method, different principal nitrogen hyperfine, Azz, and quadrupole, Pzz, tensor values of a nitroxide radical in glassy 2-propanol matrix can be measured with high accuracy. They belong to nitroxides with different hydrogen-bond situations. The satisfactory resolution and superior sensitivity of EDNMR as compared to the standard ENDOR (electron-nuclear double resonance) method are demonstrated.
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Affiliation(s)
- Anna Nalepa
- Max Planck Institute for Chemical Energy Conversion, Stiftstr. 34-36, D-45470 Mülheim an der Ruhr, Germany
| | - Klaus Möbius
- Max Planck Institute for Chemical Energy Conversion, Stiftstr. 34-36, D-45470 Mülheim an der Ruhr, Germany; Department of Physics, Free University Berlin, Arnimallee 14, D-14195 Berlin, Germany
| | - Wolfgang Lubitz
- Max Planck Institute for Chemical Energy Conversion, Stiftstr. 34-36, D-45470 Mülheim an der Ruhr, Germany
| | - Anton Savitsky
- Max Planck Institute for Chemical Energy Conversion, Stiftstr. 34-36, D-45470 Mülheim an der Ruhr, Germany.
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Gast P, Herbonnet RTL, Klare J, Nalepa A, Rickert C, Stellinga D, Urban L, Möbius K, Savitsky A, Steinhoff HJ, Groenen EJJ. Hydrogen bonding of nitroxide spin labels in membrane proteins. Phys Chem Chem Phys 2014; 16:15910-6. [DOI: 10.1039/c4cp01741b] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
On the basis of experiments at 275 GHz, we reconsider the dependence of the continuous-wave EPR spectra of nitroxide spin-labeled protein sites in sensory- and bacteriorhodopsin on the micro-environment.
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Affiliation(s)
- P. Gast
- Huygens-Kamerlingh Onnes Laboratory
- Department of Physics
- Leiden University
- NL-2300 RA Leiden, The Netherlands
| | - R. T. L. Herbonnet
- Huygens-Kamerlingh Onnes Laboratory
- Department of Physics
- Leiden University
- NL-2300 RA Leiden, The Netherlands
| | - J. Klare
- Department of Physics
- University of Osnabrück
- D-49076 Osnabrück, Germany
| | - A. Nalepa
- Max Planck Institute for Chemical Energy Conversion
- D-45470 Mülheim an der Ruhr, Germany
| | - C. Rickert
- Department of Physics
- University of Osnabrück
- D-49076 Osnabrück, Germany
| | - D. Stellinga
- Huygens-Kamerlingh Onnes Laboratory
- Department of Physics
- Leiden University
- NL-2300 RA Leiden, The Netherlands
| | - L. Urban
- Department of Physics
- University of Osnabrück
- D-49076 Osnabrück, Germany
| | - K. Möbius
- Max Planck Institute for Chemical Energy Conversion
- D-45470 Mülheim an der Ruhr, Germany
- Department of Physics
- Free University Berlin
- D-14195 Berlin, Germany
| | - A. Savitsky
- Max Planck Institute for Chemical Energy Conversion
- D-45470 Mülheim an der Ruhr, Germany
| | - H.-J. Steinhoff
- Department of Physics
- University of Osnabrück
- D-49076 Osnabrück, Germany
| | - E. J. J. Groenen
- Huygens-Kamerlingh Onnes Laboratory
- Department of Physics
- Leiden University
- NL-2300 RA Leiden, The Netherlands
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16
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Malferrari M, Nalepa A, Venturoli G, Francia F, Lubitz W, Möbius K, Savitsky A. Structural and dynamical characteristics of trehalose and sucrose matrices at different hydration levels as probed by FTIR and high-field EPR. Phys Chem Chem Phys 2013; 16:9831-48. [PMID: 24358471 DOI: 10.1039/c3cp54043j] [Citation(s) in RCA: 34] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Abstract
Some organisms can survive complete dehydration and high temperatures by adopting an anhydrobiotic state in which the intracellular medium contains large amounts of disaccharides, particularly trehalose and sucrose. Trehalose is most effective also in protecting isolated in vitro biostructures. In an attempt to clarify the molecular mechanisms of disaccharide bioprotection, we compared the structure and dynamics of sucrose and trehalose matrices at different hydration levels by means of high-field W-band EPR and FTIR spectroscopy. The hydration state of the samples was characterized by FTIR spectroscopy and the structural organization was probed by EPR using a nitroxide radical dissolved in the respective matrices. Analysis of the EPR spectra showed that the structure and dynamics of the dehydrated matrices as well as their evolution upon re-hydration differ substantially between trehalose and sucrose. The dehydrated trehalose matrix is homogeneous in terms of distribution of the residual water and spin-probe molecules. In contrast, dehydrated sucrose forms a heterogeneous matrix. It is comprised of sucrose polycrystalline clusters and several bulk water domains. The amorphous form was found only in 30% (volume) of the sucrose matrix. Re-hydration leads to a structural homogenization of the sucrose matrix, whilst in the trehalose matrix several domains develop differing in the local water/radical content and radical mobility. The molecular model of the matrices provides an explanation for the different protein-matrix dynamical coupling observed in dried ternary sucrose and trehalose matrices, and accounts for the superior efficacy of trehalose as a bioprotectant. Furthermore, for bacterial photosynthetic reaction centers it is shown that at low water content the protein-matrix coupling is modulated by the sugar/protein molar ratio in sucrose matrices only. This effect is suggested to be related to the preference for sucrose, rather than trehalose, as a bioprotective disaccharide in some anhydrobiotic organisms.
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Affiliation(s)
- M Malferrari
- Laboratorio di Biochimica e Biofisica, Dipartimento di Farmacia e Biotecnologie, FaBiT, Università di Bologna, via Irnerio 42, I-40126 Bologna, Italy
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17
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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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18
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Synthesis of a spin-labeled anti-estrogen as a dynamic motion probe for the estrogen receptor ligand binding domain. Bioorg Med Chem Lett 2012; 22:1743-6. [DOI: 10.1016/j.bmcl.2011.12.091] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/18/2011] [Revised: 12/14/2011] [Accepted: 12/19/2011] [Indexed: 11/21/2022]
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19
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Savitsky A, Dubinskii AA, Zimmermann H, Lubitz W, Möbius K. High-Field Dipolar Electron Paramagnetic Resonance (EPR) Spectroscopy of Nitroxide Biradicals for Determining Three-Dimensional Structures of Biomacromolecules in Disordered Solids. J Phys Chem B 2011; 115:11950-63. [DOI: 10.1021/jp206841v] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Anton Savitsky
- Max-Planck-Institut für Bioanorganische Chemie, 45470 Mülheim an der Ruhr, Germany
| | | | - Herbert Zimmermann
- Max-Planck-Institut für Medizinische Forschung, Abt. Biophysik, 69120 Heidelberg, Germany
| | - Wolfgang Lubitz
- Max-Planck-Institut für Bioanorganische Chemie, 45470 Mülheim an der Ruhr, Germany
| | - Klaus Möbius
- Max-Planck-Institut für Bioanorganische Chemie, 45470 Mülheim an der Ruhr, Germany
- Department of Physics, Free University Berlin, 14195 Berlin, Germany
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20
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Florent M, Kaminker I, Nagarajan V, Goldfarb D. Determination of the 14N quadrupole coupling constant of nitroxide spin probes by W-band ELDOR-detected NMR. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2011; 210:192-9. [PMID: 21459027 DOI: 10.1016/j.jmr.2011.03.005] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/20/2010] [Revised: 02/17/2011] [Accepted: 03/02/2011] [Indexed: 05/25/2023]
Abstract
Nitroxide spin probe electron paramagnetic resonance (EPR) has proven to be a very successful method to probe local polarity and solvent hydrogen bonding properties at the molecular level. The g(xx) and the (14)N hyperfine A(zz) principal values are the EPR parameters of the nitroxide spin probe that are sensitive to these properties and are therefore monitored experimentally. Recently, the (14)N quadrupole interaction of nitroxides has been shown to be also highly sensitive to polarity and H-bonding (A. Savitsky et al., J. Phys. Chem. B 112 (2008) 9079). High-field electron spin echo envelope modulation (ESEEM) was used successfully to determine the P(xx) and P(yy) principal components of the (14)N quadrupole tensor. The P(zz) value was calculated from the traceless character of the quadrupole tensor. We introduce here high-field (W-band, 95 GHz, 3.5 T) electron-electron double resonance (ELDOR)-detected NMR as a method to obtain the (14)N P(zz) value directly, together with A(zz). This is complemented by W-band hyperfine sublevel correlation (HYSCORE) measurements carried out along the g(xx) direction to determine the principal P(xx) and P(yy) components. Through measurements of TEMPOL dissolved in solvents of different polarities, we show that A(zz) increases, while |P(zz)| decreases with polarity, as predicted by Savitsky et al.
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Affiliation(s)
- Marc Florent
- Department of Chemical Physics, Weizmann Institute of Science, Rehovot 76100, Israel
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21
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Kaminker I, Florent M, Epel B, Goldfarb D. Simultaneous acquisition of pulse EPR orientation selective spectra. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2011; 208:95-102. [PMID: 21075028 DOI: 10.1016/j.jmr.2010.10.010] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/15/2010] [Revised: 10/14/2010] [Accepted: 10/14/2010] [Indexed: 05/30/2023]
Abstract
High resolution pulse EPR methods are usually applied to resolve weak magnetic electron-nuclear or electron-electron interactions that are otherwise unresolved in the EPR spectrum. Complete information regarding different magnetic interactions, namely, principal components and orientation of principal axis system with respect to the molecular frame, can be derived from orientation selective pulsed EPR measurements that are performed at different magnetic field positions within the inhomogeneously broadened EPR spectrum. These experiments are usually carried out consecutively, namely a particular field position is chosen, data are accumulated until the signal to noise ratio is satisfactory, and then the next field position is chosen and data are accumulated. Here we present a new approach for data acquisition of pulsed EPR experiments referred to as parallel acquisition. It is applicable when the spectral width is much broader than the excitation bandwidth of the applied pulse sequence and it is particularly useful for orientation selective pulse EPR experiments. In this approach several pulse EPR measurements are performed within the waiting (repetition) time between consecutive pulse sequences during which spin lattice relaxation takes place. This is achieved by rapidly changing the main magnetic field, B(0), to different values within the EPR spectrum, performing the same experiment on the otherwise idle spins. This scheme represents an efficient utilization of the spectrometer and provides the same spectral information in a shorter time. This approach is demonstrated on W-band orientation selective electron-nuclear double resonance (ENDOR), electron spin echo envelope modulation (ESEEM), electron-electron double resonance (ELDOR)--detected NMR and double electron-electron resonance (DEER) measurements on frozen solutions of nitroxides. We show that a factors of 3-6 reduction in total acquisition time can be obtained, depending on the experiment applied.
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Affiliation(s)
- Ilia Kaminker
- Department of Chemical Physics, Weizmann Institute of Science, Rehovot, Israel
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22
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Bobko AA, Kirilyuk IA, Gritsan NP, Polovyanenko DN, Grigor’ev IA, Khramtsov VV, Bagryanskaya EG. EPR and Quantum Chemical Studies of the pH-sensitive Imidazoline and Imidazolidine Nitroxides with Bulky Substituents. APPLIED MAGNETIC RESONANCE 2010; 39:437-451. [PMID: 22162912 PMCID: PMC3234120 DOI: 10.1007/s00723-010-0179-z] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/31/2023]
Abstract
The X- and W-band electron paramagnetic resonance (EPR) spectroscopies were employed to investigate a series of imidazolidine nitroxide radicals with different number of ethyl and methyl substituents at positions 2 and 5 of a heterocycle in liquid and frozen solutions. The influence of the substituents on the line shape and width was studied experimentally and analyzed using quantum chemical calculations. Each pair of the geminal ethyl groups in the positions 2 or 5 of the imidazolidine ring was found to produce an additional hyperfine splitting (hfs) of about 0.2 mT in the EPR spectra of the nitroxides. The effect was attributed to the hfs constant of only one of four methylene hydrogen atoms of two geminal ethyl substituents not fully averaged by ethyl group rotation and ring puckering. In accordance with this assumption, the substitution of hydrogen atoms of CH(2) groups in 2,2,5,5-tetraethyl-substituted imidazolidine nitroxides by deuterium leads to the substantial narrowing of EPR lines which could be useful for many biochemical and biomedical applications, including pH-monitoring. W-band EPR spectra of 2,2,5,5-tetraethyl-substituted imidazolidine nitroxide and its 2,2,5,5-tetraethyl-d(8) deuterium-substituted analog measured at low temperatures demonstrated high sensitivity of their g-factors to pH, which indicates their applicability as spin labels possessing high stability.
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Affiliation(s)
- A. A. Bobko
- Institute of Chemical Kinetics and Combustion, Russian Academy of Sciences, Novosibirsk 630090, Russia
- Dorothy M. Davis Heart and Lung Research Institute, The Ohio State University, Columbus, OH 43210, USA
| | - I. A. Kirilyuk
- Novosibirsk Institute of Organic Chemistry, Russian Academy of Sciences, Novosibirsk 630090, Russia
| | - N. P. Gritsan
- Institute of Chemical Kinetics and Combustion, Russian Academy of Sciences, Novosibirsk 630090, Russia
| | - D. N. Polovyanenko
- International Tomography Center, Russian Academy of Sciences, Institutskaya 3A, Novosibirsk 630090, Russia
| | - I. A. Grigor’ev
- Novosibirsk Institute of Organic Chemistry, Russian Academy of Sciences, Novosibirsk 630090, Russia
| | - V. V. Khramtsov
- Dorothy M. Davis Heart and Lung Research Institute, The Ohio State University, Columbus, OH 43210, USA
| | - E. G. Bagryanskaya
- International Tomography Center, Russian Academy of Sciences, Institutskaya 3A, Novosibirsk 630090, Russia
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23
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Ikryannikova LN, Ustynyuk LY, Tikhonov AN. DFT study of nitroxide radicals: explicit modeling of solvent effects on the structural and electronic characteristics of 4-amino-2,2,6,6-tetramethyl-piperidine-N-oxyl. MAGNETIC RESONANCE IN CHEMISTRY : MRC 2010; 48:337-349. [PMID: 20225189 DOI: 10.1002/mrc.2585] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/28/2023]
Abstract
An explicit DFT modeling of water surroundings on the electron paramagnetic resonance properties of 4-amino-2,2,6,6-tetramethyl-piperidine-N-oxyl (TA) has been performed. A stepwise hydration of TA is accompanied with certain changes in geometrical parameters (bond lengths and angles) and redistribution of partial electric charges in TA. An aqueous cluster of 45 water molecules can be considered as an appropriate model for a complete aqueous shell around TA, although most of the structural and electronic characteristics of TA already converge at about 10 water molecules. Water surroundings induce an increase in electron spin density on the nitrogen atom of the nitroxide fragment due to stabilization of the polar resonance structure > N(+*)-O(-) at the expense of less polar structure > N-O*. The water-induced rise of the isotropic splitting constant a(iso), calculated from the contact term of the hyperfine interaction, comprises Deltaa(iso)(rho(N2)) = 2.2-2.5 G, which is typical of experimental value for TA. There are two contributions to the solvent effect on the a(iso)(rho(N2)) value: the redistribution of spin density in the nitroxide fragment (polarity effect) and water-induced distortions of TA geometry. Microscopic variations in a hydrogen-bonded water network cause noticeable fluctuations of the splitting constant a(iso)(rho(N2)). Calculations of the atomic spin density (sigma(N2)) allowed us to compute the splitting constant from the relationship a(iso)(sigma(N2)) = Qsigma(N2), where Q = 36.2 G. A practical advantage of using this relationship is that it gives 'smoothed' values of the splitting constant, which are sensitive to the environment polarity but remain tolerant to microscopic fluctuations of the hydrogen-bonded water network around a spin-label molecule.
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Marsh D. Spin-Label EPR for Determining Polarity and Proticity in Biomolecular Assemblies: Transmembrane Profiles. APPLIED MAGNETIC RESONANCE 2010; 37:435-454. [PMID: 19960064 PMCID: PMC2784069 DOI: 10.1007/s00723-009-0078-3] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 04/29/2009] [Revised: 06/05/2009] [Indexed: 05/28/2023]
Abstract
Hyperfine couplings and g-values of nitroxyl spin labels are sensitive to polarity and hydrogen bonding in the environment probed. The dependences of these electronic paramagnetic resonance (EPR) properties on environmental dielectric permittivity and proticity are reviewed. Calibrations are given, in terms of the Block-Walker reaction field and local proton donor concentration, for the nitroxides that are commonly used in spin labeling of lipids and proteins. Applications to studies of the transverse polarity profiles in lipid bilayers, which constitute the permeability barrier of biological membranes, are reviewed. Emphasis is given to parallels with the permeation profiles of oxygen and nitric oxide that are determined from spin-label relaxation enhancements by using nonlinear continuous-wave EPR and saturation recovery EPR, and with permeation profiles of D(2)O that are determined by using (2)H electron spin echo envelope modulation spectroscopy.
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Affiliation(s)
- Derek Marsh
- Abteilung Spektroskopie, Max-Planck-Institut für biophysikalische Chemie, 37070 Göttingen, Germany
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25
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Savitsky A, Möbius K. High-field EPR. PHOTOSYNTHESIS RESEARCH 2009; 102:311-333. [PMID: 19468856 DOI: 10.1007/s11120-009-9432-4] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/24/2008] [Accepted: 04/29/2009] [Indexed: 05/27/2023]
Abstract
Among the numerous spectroscopic techniques utilized in photosynthesis research, high-field/high-frequency EPR and its pulse extensions ESE, ENDOR, ESEEM, and PELDOR play an important role in the endeavor to understand, on the basis of structure and dynamics data, dominant factors that control specificity and efficiency of light-induced electron- and proton-transfer processes in primary photosynthesis. Short-lived transient intermediates of the photocycle can be characterized by high-field EPR techniques, and detailed structural information can be obtained even from disordered sample preparations. The chapter describes how multifrequency high-field EPR methodology, in conjunction with mutation strategies for site-specific isotope or spin labeling and with the support of modern quantum-chemical computation methods for data interpretation, is capable of providing new insights into the photosynthetic transfer processes. The information obtained is complementary to that of protein crystallography, solid-state NMR and laser spectroscopy.
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Affiliation(s)
- Anton Savitsky
- Department of Physics, Free University Berlin, Arnimallee 14, 14195 Berlin, Germany
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26
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Eaton SS, Eaton GR. Frequency Dependence of Pulsed EPR Experiments. CONCEPTS IN MAGNETIC RESONANCE. PART A, BRIDGING EDUCATION AND RESEARCH 2009; 34A:315. [PMID: 20148127 PMCID: PMC2818603 DOI: 10.1002/cmr.a.20148] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/28/2023]
Abstract
The frequency dependence of the signal-to-noise ratio (S/N) that is theoretically possible for pulsed EPR experiments is the same as for continuous wave experiments. To select the optimum resonance frequency or frequencies for pulsed EPR experiments it is important to consider not only S/N, but also orientation selection, depth of spin echo modulation, and intensities of forbidden transitions. Evaluation of factors involved in selecting the optimum frequency for pulsed EPR measurements of distances between spins is discussed.
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Affiliation(s)
- Sandra S Eaton
- Department of Chemistry and Biochemistry, University of Denver, Denver, CO, USA 80208
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Annino G, Fittipaldi M, Martinelli M, Moons H, Van Doorslaer S, Goovaerts E. High-frequency EPR applications of open nonradiative resonators. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2009; 200:29-37. [PMID: 19523864 DOI: 10.1016/j.jmr.2009.05.011] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/03/2009] [Revised: 04/30/2009] [Accepted: 05/27/2009] [Indexed: 05/27/2023]
Abstract
A new class of open single-mode cavities, the nonradiative (NR) resonators, has recently been proposed in order to overcome the limitations of standard cylindrical cavities and Fabry-Perot resonators at millimeter wavelengths. This paper presents the first applications of a NR resonator in W-band pulsed electron paramagnetic resonance spectroscopy. It consists of a cylindrical cavity having a lateral aperture that represents about 35% of its total height. Electron-spin-echo measurements performed on different samples show that the signal-to-noise ratio and the optimal pulse length obtained with the proposed device are comparable to those obtained with the closed cavity used in the commercial W-band spectrometer, at both cryogenic and room temperature. Similar results have been obtained for paramagnetic species optically activated by means of an optical fiber inserted in the aperture of the resonator. The insertion losses estimated for the probe employed with the NR resonator are higher than those of the commercial probe, hence, demonstrating that the proposed cavity holds the promise of improved resonator performance.
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Affiliation(s)
- G Annino
- Istituto per i Processi Chimico-Fisici, CNR, via G. Moruzzi 1, 56124 Pisa, Italy.
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28
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Kulik LV, Rapatsky LL, Pivtsov AV, Surovtsev NV, Adichtchev SV, Grigor’ev IA, Dzuba SA. Electron-nuclear double resonance study of molecular librations of nitroxides in molecular glasses: Quantum effects at low temperatures, comparison with low-frequency Raman scattering. J Chem Phys 2009; 131:064505. [DOI: 10.1063/1.3206909] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
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