1
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Mullin KR, Johnson D, Freedman DE, Rondinelli JM. Systems-chart approach to the design of spin relaxation times in molecular qubits. Dalton Trans 2024. [PMID: 39347721 DOI: 10.1039/d4dt02311k] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/01/2024]
Abstract
Molecular qubits are a promising platform for future quantum information science technologies; however, to find success in novel devices requires that the molecules exhibit long spin relaxation times. Understanding and optimizing these relaxation times has been shown to be challenging and much experimental work has been done to understand how various chemical features of the molecular qubit influence relaxation times. Here we have curated a data set of relaxation times of metal complex molecular qubits and formulated systems design charts to provide a hierarchical organization of how chemical variables affect relaxation times via known physical processes. We demonstrate the utility of the systems charts by combining examples from the literature with calculated descriptors for molecules in the dataset. This approach helps reduce the complexity associated with de novo molecular design by providing a map of interdependencies and identifying features to prioritize during synthesis.
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Affiliation(s)
- Kathleen R Mullin
- Department of Materials Science and Engineering, Northwestern University, Evanston, Illinois 60208, USA.
| | - Dane Johnson
- Department of Chemistry, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA
| | - Danna E Freedman
- Department of Chemistry, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA
| | - James M Rondinelli
- Department of Materials Science and Engineering, Northwestern University, Evanston, Illinois 60208, USA.
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2
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Mullin KR, Greer RB, Waters MJ, Amdur MJ, Sun L, Freedman DE, Rondinelli JM. Detrimental Increase of Spin-Phonon Coupling in Molecular Qubits on Substrates. ACS APPLIED MATERIALS & INTERFACES 2024; 16:40160-40169. [PMID: 39016442 DOI: 10.1021/acsami.4c05728] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 07/18/2024]
Abstract
Molecular qubits are a promising platform for quantum information systems. Although single molecule and ensemble studies have assessed the performance of S = 1/2 molecules, it is understood that to function in devices, regular arrays of addressable qubits supported by a substrate are needed. The substrate imposes mechanical and electronic boundary conditions on the molecule; however, the impact of these effects on spin-lattice relaxation times is not well understood. Here we perform electronic structure calculations to assess the effects of a graphene (Cgr) substrate on the molecular qubit copper phthalocyanine (CuPc). We use a progressive Hessian approach to efficiently calculate and separate the substrate contributions. We also use a simple thermal model to predict the impact of these changes on the spin-phonon coupling from 0 to 200 K. Further analysis of the individual vibrational modes with and without Cgr shows that an overall increase in SPC between the vibrations modes of CuPc with the surface reduces the spin-lattice relaxation time T1. We explain these changes by examining how the substrate lifts symmetries of CuPc in the absorbed configuration. Our work shows that a surface can have a large unintentional impact on SPC and that ways to reduce this coupling need to be found to fully exploit arrays of molecular qubits in device architectures.
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Affiliation(s)
- Kathleen R Mullin
- Department of Materials Science and Engineering, Northwestern University, Evanston, Illinois 60208, United States
| | - Rianna B Greer
- Department of Chemistry, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, United States
| | - Michael J Waters
- Department of Materials Science and Engineering, Northwestern University, Evanston, Illinois 60208, United States
| | - M Jeremy Amdur
- Department of Chemistry, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, United States
| | - Lei Sun
- Center for Nanoscale Materials, Argonne National Laboratory, Lemont, Illinois 60439, United States
| | - Danna E Freedman
- Department of Chemistry, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, United States
| | - James M Rondinelli
- Department of Materials Science and Engineering, Northwestern University, Evanston, Illinois 60208, United States
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3
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Tubau À, Gómez-Coca S, Speed S, Font-Bardía M, Vicente R. New series of mononuclear β-diketonate cerium(III) field induced single-molecule magnets. Dalton Trans 2024; 53:9387-9405. [PMID: 38757803 DOI: 10.1039/d4dt00848k] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 05/18/2024]
Abstract
Five new β-diketonate Ce3+ mononuclear complexes, [Ce(Btfa)3(H2O)2] (1), [Ce(Btfa)3(phen)] (2), [Ce(Btfa)3(bipy)] (3), [Ce(Btfa)3(terpy)] (4) and [Ce(Btfa)3(bathophen)(DMF)] (5), where Btfa- = 4,4,4-trifluoro-1-phenyl-1,3-butanedionate, phen = 1,10-phenanthroline, bipy = 2,2'-bipyridyl, terpy = 2,2':6',2''-terpyridine and bathophen = 4,7-diphenyl-1,10-phenanthroline, have been synthesized and structurally characterized through X-ray diffraction of single crystals. The central Ce3+ atom displays a coordination number of 8 for 1, 2 and 3 and of 9 for 4 and 5. Under a 0 T external magnetic field, none of the given compounds exhibits single molecule magnet (SMM) behaviour. However, a small magnetic field, between 0.02 and 0.1 T, is enough for all the compounds to exhibit slow relaxation of the magnetization. A comprehensive magnetic analysis, with experimental magnetic data and ab initio calculations, was undertaken for all the complexes, and the study highlights the significance of the different spin relaxation mechanisms that must be considered for a Ce3+ lanthanide ion.
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Affiliation(s)
- Ànnia Tubau
- Departament de Química Inorgànica i Orgànica, Universitat de Barcelona, Martí i Franquès 1-11, 08028 Barcelona, Spain.
| | - Silvia Gómez-Coca
- Departament de Química Inorgànica i Orgànica, Universitat de Barcelona, Martí i Franquès 1-11, 08028 Barcelona, Spain.
- Institut de Química Teòrica i Computacional, Universitat de Barcelona, Diagonal 645, 08028 Barcelona, Spain
| | - Saskia Speed
- Departament de Química Inorgànica i Orgànica, Universitat de Barcelona, Martí i Franquès 1-11, 08028 Barcelona, Spain.
| | - Mercè Font-Bardía
- Departament de Mineralogia, Cristal lografia i Dipòsits Minerals and Unitat de Difracció de R-X. Centre Científic i Tecnològic de la Universitat de Barcelona (CCiTUB), Universitat de Barcelona, Solé i Sabarís 1-3, 08028 Barcelona, Spain
| | - Ramon Vicente
- Departament de Química Inorgànica i Orgànica, Universitat de Barcelona, Martí i Franquès 1-11, 08028 Barcelona, Spain.
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4
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Yamabayashi T, Horii Y, Li ZY, Yamashita M. Magnetic Relaxations of Chromium Nitride Porphyrinato Complexes Driven by the Anisotropic g-Factor. Chemistry 2024; 30:e202303082. [PMID: 37880199 DOI: 10.1002/chem.202303082] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/22/2023] [Revised: 10/20/2023] [Accepted: 10/25/2023] [Indexed: 10/27/2023]
Abstract
Molecule-based magnetic materials are useful candidates as the spin qubit due to their long coherence time and high designability. The anisotropy of the g-values of the metal complexes can be utilized to access the individual spin of the metal complexes, making it possible to achieve the scalable molecular spin qubit. For this goal, it is important to evaluate the effect of g-value anisotropy on the magnetic relaxation behaviour. This study reports the slow magnetic relaxation behaviour of chromium nitride (CrN2+ ) porphyrinato complex (1), which is structurally and magnetically similar with the vanadyl (VO2+ ) porphyrinato complex (2) which is known as the excellent spin qubit. Detailed analyses for vibrational and dynamical magnetism of 1 and 2 revealed that g-value anisotropy accelerates magnetic relaxations greater than the internal magnetic field from nuclear spin does. These results provide a design criterion for construction of multiple spin qubit based on g-tensor engineering.
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Affiliation(s)
- Tsutomu Yamabayashi
- Graduate School of Science, Tohoku University, 6-3 Aramaki-Aza-Aoba Aoba-ku, Sendai, Miyagi, 980-8578, Japan
| | - Yoji Horii
- Department of Chemistry, Faculty of Science, Nara Women's University, Nara, 630-8506, Japan
| | - Zhao-Yang Li
- School of Materials Science and Engineering, Nankai University, Tianjin, 300350, China
| | - Masahiro Yamashita
- Graduate School of Science, Tohoku University, 6-3 Aramaki-Aza-Aoba Aoba-ku, Sendai, Miyagi, 980-8578, Japan
- School of Chemical Science and Engineering, Tongji University, Siping Road 1239, Shanghai, 200092, P. R. China
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5
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Vujević L, Karadeniz B, Cindro N, Krajnc A, Mali G, Mazaj M, Avdoshenko SM, Popov AA, Žilić D, Užarević K, Kveder M. Improving the molecular spin qubit performance in zirconium MOF composites by mechanochemical dilution and fullerene encapsulation. Chem Sci 2023; 14:9389-9399. [PMID: 37712041 PMCID: PMC10498684 DOI: 10.1039/d3sc03089j] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/16/2023] [Accepted: 08/12/2023] [Indexed: 09/16/2023] Open
Abstract
Enlarging the quantum coherence times and gaining control over quantum effects in real systems are fundamental for developing quantum technologies. Molecular electron spin qubits are particularly promising candidates for realizing quantum information processing due to their modularity and tunability. Still, there is a constant search for tools to increase their quantum coherence times. Here we present how the mechanochemical introduction of active spin qubits in the form of 10% diluted copper(ii)-porphyrins in the diamagnetic PCN-223 and MOF-525 zirconium-MOF polymorph pair can be achieved. Furthermore, the encapsulation of fullerene during the MOF synthesis directs the process exclusively toward the rare PCN-223 framework with a controllable amount of fullerene in the framework channels. In addition to the templating role, the incorporation of fullerene increases the electron spin-lattice and phase-memory relaxation times, T1 and Tm. Besides decreasing the amount of nuclear spin-bearing solvent guests in the non-activated qubit frameworks, the observed improved relaxation times can be rationalized by modulating the phonon density of states upon fullerene encapsulation.
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Affiliation(s)
- Lucija Vujević
- Ruđer Bošković Institute Bijenička cesta 54 10000 Zagreb Croatia
| | - Bahar Karadeniz
- Ruđer Bošković Institute Bijenička cesta 54 10000 Zagreb Croatia
| | - Nikola Cindro
- Department of Chemistry, University of Zagreb 10000 Zagreb Croatia
| | - Andraž Krajnc
- National Institute of Chemistry Hajdrihova 19 SI-1001 Ljubljana Slovenia
| | - Gregor Mali
- National Institute of Chemistry Hajdrihova 19 SI-1001 Ljubljana Slovenia
| | - Matjaž Mazaj
- National Institute of Chemistry Hajdrihova 19 SI-1001 Ljubljana Slovenia
| | | | - Alexey A Popov
- Leibniz IFW Dresden Helmholtzstrasse 20 D-01069 Dresden Germany
| | - Dijana Žilić
- Ruđer Bošković Institute Bijenička cesta 54 10000 Zagreb Croatia
| | | | - Marina Kveder
- Ruđer Bošković Institute Bijenička cesta 54 10000 Zagreb Croatia
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6
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Wang Z, Balembois L, Rančić M, Billaud E, Le Dantec M, Ferrier A, Goldner P, Bertaina S, Chanelière T, Esteve D, Vion D, Bertet P, Flurin E. Single-electron spin resonance detection by microwave photon counting. Nature 2023; 619:276-281. [PMID: 37438594 DOI: 10.1038/s41586-023-06097-2] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/28/2022] [Accepted: 04/18/2023] [Indexed: 07/14/2023]
Abstract
Electron spin resonance spectroscopy is the method of choice for characterizing paramagnetic impurities, with applications ranging from chemistry to quantum computing1,2, but it gives access only to ensemble-averaged quantities owing to its limited signal-to-noise ratio. Single-electron spin sensitivity has, however, been reached using spin-dependent photoluminescence3-5, transport measurements6-9 and scanning-probe techniques10-12. These methods are system-specific or sensitive only in a small detection volume13,14, so that practical single-spin detection remains an open challenge. Here, we demonstrate single-electron magnetic resonance by spin fluorescence detection15, using a microwave photon counter at millikelvin temperatures16. We detect individual paramagnetic erbium ions in a scheelite crystal coupled to a high-quality-factor planar superconducting resonator to enhance their radiative decay rate17, with a signal-to-noise ratio of 1.9 in one second integration time. The fluorescence signal shows anti-bunching, proving that it comes from individual emitters. Coherence times up to 3 ms are measured, limited by the spin radiative lifetime. The method has the potential to be applied to arbitrary paramagnetic species with long enough non-radiative relaxation times, and allows single-spin detection in a volume as large as the resonator magnetic mode volume (approximately 10 μm3 in the present experiment), orders of magnitude larger than other single-spin detection techniques. As such, it may find applications in magnetic resonance and quantum computing.
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Affiliation(s)
- Z Wang
- Quantronics group, Université Paris-Saclay, CEA, CNRS, SPEC, Gif-sur-Yvette Cedex, France
- Département de Physique et Institut Quantique, Université de Sherbrooke, Sherbrooke, Québec, Canada
| | - L Balembois
- Quantronics group, Université Paris-Saclay, CEA, CNRS, SPEC, Gif-sur-Yvette Cedex, France
| | - M Rančić
- Quantronics group, Université Paris-Saclay, CEA, CNRS, SPEC, Gif-sur-Yvette Cedex, France
| | - E Billaud
- Quantronics group, Université Paris-Saclay, CEA, CNRS, SPEC, Gif-sur-Yvette Cedex, France
| | - M Le Dantec
- Quantronics group, Université Paris-Saclay, CEA, CNRS, SPEC, Gif-sur-Yvette Cedex, France
| | - A Ferrier
- Chimie ParisTech, PSL University, CNRS, Institut de Recherche de Chimie Paris, Paris, France
| | - P Goldner
- Chimie ParisTech, PSL University, CNRS, Institut de Recherche de Chimie Paris, Paris, France
| | - S Bertaina
- CNRS, Aix-Marseille Université, IM2NP (UMR 7334), Institut Matériaux Microélectronique et Nanosciences de Provence, Marseille, France
| | - T Chanelière
- Univ. Grenoble Alpes, CNRS, Grenoble INP, Institut Néel, Grenoble, France
| | - D Esteve
- Quantronics group, Université Paris-Saclay, CEA, CNRS, SPEC, Gif-sur-Yvette Cedex, France
| | - D Vion
- Quantronics group, Université Paris-Saclay, CEA, CNRS, SPEC, Gif-sur-Yvette Cedex, France
| | - P Bertet
- Quantronics group, Université Paris-Saclay, CEA, CNRS, SPEC, Gif-sur-Yvette Cedex, France
| | - E Flurin
- Quantronics group, Université Paris-Saclay, CEA, CNRS, SPEC, Gif-sur-Yvette Cedex, France.
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7
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Koyama S, Sato K, Yamashita M, Sakamoto R, Iguchi H. Observation of slow magnetic relaxation phenomena in spatially isolated π-radical ions. Phys Chem Chem Phys 2023; 25:5459-5467. [PMID: 36748343 DOI: 10.1039/d2cp06026d] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023]
Abstract
The use of molecular spins as quantum bits is fascinating because it offers a wide range of strategies through chemical modifications. In this regard, it is very interesting to search for organic radical ions that have small spin-orbit coupling values. On the other hand, the feature of the magnetic relaxation of π-organic radical ions is rarely exploited due to the difficulty of spin dilution, and π-stacking interaction. In this study, we focus on N,N',N''-tris(2,6-dimethylphenyl)benzenetriimide (BTI-xy), where three xylene moieties connected to the imide groups cover the π-plane of the BTI core. As a result, BTI-xy radical anions without π-stacking interaction were obtained. This led to the slow magnetization relaxation, which is reported for the first time in organic radicals. Furthermore, the relaxation times in a solution state revealed the importance of spin interaction.
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Affiliation(s)
- Shohei Koyama
- Department of Chemistry, Graduate School of Science, Tohoku University, 6-3 Aramaki-Aza-Aoba, Aoba-ku, Sendai, 980-8578, Japan.
| | - Kazunobu Sato
- Department of Chemistry, Graduate School of Science, Osaka Metropolitan University, 3-3-138 Sugimoto, Sumiyoshi-ku, Osaka 558-8585, Japan
| | - Masahiro Yamashita
- Department of Chemistry, Graduate School of Science, Tohoku University, 6-3 Aramaki-Aza-Aoba, Aoba-ku, Sendai, 980-8578, Japan. .,School of Materials Science and Engineering, Nankai University, Tianjin 300350, P. R. China
| | - Ryota Sakamoto
- Department of Chemistry, Graduate School of Science, Tohoku University, 6-3 Aramaki-Aza-Aoba, Aoba-ku, Sendai, 980-8578, Japan.
| | - Hiroaki Iguchi
- Department of Materials Chemistry, Graduate School of Engineering, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8603, Japan.
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8
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Moore W, Huffman JL, Driesschaert B, Eaton SS, Eaton GR. Impact of Chlorine Substitution on Electron Spin Relaxation of a Trityl Radical. APPLIED MAGNETIC RESONANCE 2022; 53:797-808. [PMID: 35601029 PMCID: PMC9122340 DOI: 10.1007/s00723-021-01405-3] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/03/2023]
Abstract
A perchlorotriarylmethyl tricarboxylic acid radical 99% enriched in 13C at the central carbon (13C1-PTMTC) was characterized in phosphate buffered saline solution (pH = 7.2) (PBS) at ambient temperature. Samples immobilized in 1:1 PBS:glycerol or in 9:1 trehalose:sucrose were studied as a function of temperature. Isotope enrichment at C1 creates a trityl that can be used to accurately measure microscopic viscosity. Understanding of the impact of the 13C hyperfine interaction on electron spin relaxation is important for application of this trityl in oximetry and distance measurements. The anisotropic 13C1 hyperfine couplings (Ax = Ay = 24 ± 2 MHz, Az = 200 ± 1 MHz) are larger than for the related 13C1-perdeuterated Finland trityl (13C1-dFT) and the g anisotropy (gx = 2.0013, gy = 2.0016, gz = 2.0042) is slightly larger than for 13C1-dFT. The tumbling correlation times (τR) for 13C1-PTMTC are 0.20 ± 0.02 ns in PBS and 0.40 ± 0.05 ns in 3:1 PBS:glycerol, which are shorter than for 13C1-dFT in the same solutions. T1 for 13C1-PTMTC is 3.5 ± 0.5 μs in PBS and 5.3 ± 0.4 μs in 3:1 PBS:glycerol, which are shorter than for 13C1-dFT due to faster tumbling, larger anisotropy of the 13C1 hyperfine, and about 30% larger contribution from the local mode. In immobilized samples T1 for 13C1-PTMTC is similar to that for 13C1-dFT and other trityls without chlorine or 13C1 substituents, indicating that the 13C1 and Cl substituents on the phenyl rings have little impact on T1. The temperature dependence of T1 was modeled with contributions from the direct, Raman, and local mode processes. Broadening of CW linewidths of about 0.6 G in fluid solution and about 2 G in rigid lattice is attributed to unresolved 35,37Cl hyperfine couplings.
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Affiliation(s)
- Whylder Moore
- Department of Chemistry and Biochemistry, University of Denver, Denver, CO 80210, USA
| | - Justin L. Huffman
- Department of Pharmaceutical Sciences, School of Pharmacy & In Vivo Multifunctional Magnetic Resonance Center, West Virginia University, Morgantown, WV 26506, USA
| | - Benoit Driesschaert
- Department of Pharmaceutical Sciences, School of Pharmacy & In Vivo Multifunctional Magnetic Resonance Center, West Virginia University, Morgantown, WV 26506, USA
| | - Sandra S. Eaton
- Department of Chemistry and Biochemistry, University of Denver, Denver, CO 80210, USA
| | - Gareth R. Eaton
- Department of Chemistry and Biochemistry, University of Denver, Denver, CO 80210, USA
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9
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Jardón-Álvarez D, Malka T, van Tol J, Feldman Y, Carmieli R, Leskes M. Monitoring electron spin fluctuations with paramagnetic relaxation enhancement. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2022; 336:107143. [PMID: 35085928 DOI: 10.1016/j.jmr.2022.107143] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/25/2021] [Revised: 12/30/2021] [Accepted: 01/03/2022] [Indexed: 06/14/2023]
Abstract
The magnetic interactions between the spin of an unpaired electron and the surrounding nuclear spins can be exploited to gain structural information, to reduce nuclear relaxation times as well as to create nuclear hyperpolarization via dynamic nuclear polarization (DNP). A central aspect that determines how these interactions manifest from the point of view of NMR is the timescale of the fluctuations of the magnetic moment of the electron spins. These fluctuations, however, are elusive, particularly when electron relaxation times are short or interactions among electronic spins are strong. Here we map the fluctuations by analyzing the ratio between longitudinal and transverse nuclear relaxation times T1/T2, a quantity which depends uniquely on the rate of the electron fluctuations and the Larmor frequency of the involved nuclei. This analysis enables rationalizing the evolution of NMR lineshapes, signal quenching as well as DNP enhancements as a function of the concentration of the paramagnetic species and the temperature, demonstrated here for LiMg1-xMnxPO4 and Fe(III) doped Li4Ti5O12, respectively. For the latter, we observe a linear dependence of the DNP enhancement and the electron relaxation time within a temperature range between 100 and 300 K.
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Affiliation(s)
- Daniel Jardón-Álvarez
- Department of Molecular Chemistry and Materials Science, Weizmann Institute of Science, Rehovot 76100, Israel
| | - Tahel Malka
- Department of Molecular Chemistry and Materials Science, Weizmann Institute of Science, Rehovot 76100, Israel
| | - Johan van Tol
- National High Magnetic Field Laboratory, Florida State University, 1800 E. Paul Dirac Dr, Tallahassee, FL 32310, United States
| | - Yishay Feldman
- Department of Chemical Research Support, Weizmann Institute of Science, Rehovot 76100, Israel
| | - Raanan Carmieli
- Department of Chemical Research Support, Weizmann Institute of Science, Rehovot 76100, Israel
| | - Michal Leskes
- Department of Molecular Chemistry and Materials Science, Weizmann Institute of Science, Rehovot 76100, Israel.
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10
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Mahapatro SN, Hovey TA, Ngendahimana T, Eaton SS, Eaton GR. Electron paramagnetic resonance characterization and electron spin relaxation of manganate ion in glassy alkaline LiCl solution and doped into Cs2SO4. J Inorg Biochem 2022; 229:111732. [DOI: 10.1016/j.jinorgbio.2022.111732] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/17/2021] [Revised: 12/23/2021] [Accepted: 01/15/2022] [Indexed: 11/26/2022]
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11
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Kazmierczak NP, Mirzoyan R, Hadt RG. The Impact of Ligand Field Symmetry on Molecular Qubit Coherence. J Am Chem Soc 2021; 143:17305-17315. [PMID: 34615349 DOI: 10.1021/jacs.1c04605] [Citation(s) in RCA: 23] [Impact Index Per Article: 7.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/15/2023]
Abstract
Developing quantum bits (qubits) exhibiting room temperature electron spin coherence is a key goal of molecular quantum information science. At high temperatures, coherence is often limited by electron spin relaxation, measured by T1. Here we develop a simple and powerful model for predicting relative T1 relaxation times in transition metal complexes from dynamic ligand field principles. By considering the excited state origins of ground state spin-phonon coupling, we derive group theory selection rules governing which vibrational symmetries can induce decoherence. Thermal weighting of the coupling terms produces surprisingly good predictions of experimental T1 trends as a function of temperature and explains previously confounding features in spin-lattice relaxation data. We use this model to evaluate experimental relaxation rates across S = 1/2 transition metal qubit candidates with diverse structures, gaining new insights into the interplay between spin-phonon coupling and molecular symmetry. This methodology elucidates the specific vibrational modes giving rise to decoherence, providing insight into the origin of room temperature coherence in transition metal complexes. We discuss the outlook of symmetry-based modeling and design strategies for understanding molecular coherence.
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Affiliation(s)
- Nathanael P Kazmierczak
- Division of Chemistry and Chemical Engineering, Arthur Amos Noyes Laboratory of Chemical Physics, California Institute of Technology, Pasadena, California 91125, United States
| | - Ruben Mirzoyan
- Division of Chemistry and Chemical Engineering, Arthur Amos Noyes Laboratory of Chemical Physics, California Institute of Technology, Pasadena, California 91125, United States
| | - Ryan G Hadt
- Division of Chemistry and Chemical Engineering, Arthur Amos Noyes Laboratory of Chemical Physics, California Institute of Technology, Pasadena, California 91125, United States
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12
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Mirzoyan R, Kazmierczak NP, Hadt RG. Deconvolving Contributions to Decoherence in Molecular Electron Spin Qubits: A Dynamic Ligand Field Approach. Chemistry 2021; 27:9482-9494. [PMID: 33855760 DOI: 10.1002/chem.202100845] [Citation(s) in RCA: 16] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/07/2021] [Indexed: 12/16/2022]
Abstract
In the past decade, transition metal complexes have gained momentum as electron spin-based quantum bit (qubit) candidates due to their synthetic tunability and long achievable coherence times. The decoherence of magnetic quantum states imposes a limit on the use of these qubits for quantum information technologies, such as quantum computing, sensing, and communication. With rapid recent development in the field of molecular quantum information science, a variety of chemical design principles for prolonging coherence in molecular transition metal qubits have been proposed. Here the spin-spin, motional, and spin-phonon regimes of decoherence are delineated, outlining design principles for each. It is shown how dynamic ligand field models can provide insights into the intramolecular vibrational contributions in the spin-phonon decoherence regime. This minireview aims to inform the development of molecular quantum technologies tailored for different environments and conditions.
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Affiliation(s)
- Ruben Mirzoyan
- Division of Chemistry and Chemical Engineering, Arthur Amos Noyes Laboratory of Chemical Physics, California Institute of Technology, Pasadena, CA 91125, USA
| | - Nathanael P Kazmierczak
- Division of Chemistry and Chemical Engineering, Arthur Amos Noyes Laboratory of Chemical Physics, California Institute of Technology, Pasadena, CA 91125, USA
| | - Ryan G Hadt
- Division of Chemistry and Chemical Engineering, Arthur Amos Noyes Laboratory of Chemical Physics, California Institute of Technology, Pasadena, CA 91125, USA
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13
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Jackson CE, Moseley IP, Martinez R, Sung S, Zadrozny JM. A reaction-coordinate perspective of magnetic relaxation. Chem Soc Rev 2021; 50:6684-6699. [PMID: 33949521 PMCID: PMC8215782 DOI: 10.1039/d1cs00001b] [Citation(s) in RCA: 23] [Impact Index Per Article: 7.7] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/01/2021] [Indexed: 11/21/2022]
Abstract
Understanding and utilizing the dynamic quantum properties of metal ions is the frontier of many next generation technologies. One property in particular, magnetic relaxation, is a complicated physical phenomenon that is scarcely treated in undergraduate coursework. Consequently, principles of magnetic relaxation are nearly impenetrable to starting synthetic chemists, who ultimately design the molecules that fuel new discoveries. In this Tutorial Review, we describe a new paradigm for thinking of magnetic relaxation in metal complexes in terms of a simple reaction-coordinate diagram to facilitate access to the field. We cover the main mechanisms of both spin-lattice (T1) and spin-spin (T2) relaxation times within this conceptual framework and how molecular and environmental design affects these times. Ultimately, we show that many of the scientific methods used by inorganic chemists to study and manipulate reactivity are also useful for understanding and controlling magnetic relaxation. We also describe the cutting edge of magnetic relaxation within this paradigm.
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Affiliation(s)
- Cassidy E Jackson
- Department of Chemistry, Colorado State University, Fort Collins, CO, USA.
| | - Ian P Moseley
- Department of Chemistry, Colorado State University, Fort Collins, CO, USA.
| | - Roxanna Martinez
- Department of Chemistry, Colorado State University, Fort Collins, CO, USA.
| | - Siyoung Sung
- Department of Chemistry, Colorado State University, Fort Collins, CO, USA.
| | - Joseph M Zadrozny
- Department of Chemistry, Colorado State University, Fort Collins, CO, USA.
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14
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Follmer AH, Ribson RD, Oyala PH, Chen GY, Hadt RG. Understanding Covalent versus Spin-Orbit Coupling Contributions to Temperature-Dependent Electron Spin Relaxation in Cupric and Vanadyl Phthalocyanines. J Phys Chem A 2020; 124:9252-9260. [PMID: 33112149 DOI: 10.1021/acs.jpca.0c07860] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Abstract
Recent interest in transition-metal complexes as potential quantum bits (qubits) has reinvigorated the investigation of fundamental contributions to electron spin relaxation in various ligand scaffolds. From quantum computers to chemical and biological sensors, interest in leveraging the quantum properties of these molecules has opened a discussion of the requirements to maintain coherence over a large temperature range, including near room temperature. Here we compare temperature-, magnetic field position-, and concentration-dependent electron spin relaxation in copper(II) phthalocyanine (CuPc) and vanadyl phthalocyanine (VOPc) doped into diamagnetic hosts. While VOPc demonstrates coherence up to room temperature, CuPc coherence times become rapidly T1-limited with increasing temperature, despite featuring a more covalent ground-state wave function than VOPc. As rationalized by a ligand field model, this difference is ascribed to different spin-orbit coupling (SOC) constants for Cu(II) versus V(IV). The manifestation of SOC contributions to spin-phonon coupling and electron spin relaxation in different ligand fields is discussed, allowing for a further understanding of the competing roles of SOC and covalency in electron spin relaxation.
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Affiliation(s)
- Alec H Follmer
- Division of Chemistry and Chemical Engineering, Arthur Amos Noyes Laboratory of Chemical Physics, California Institute of Technology, Pasadena, California 91125, United States
| | - Ryan D Ribson
- Division of Chemistry and Chemical Engineering, Arthur Amos Noyes Laboratory of Chemical Physics, California Institute of Technology, Pasadena, California 91125, United States
| | - Paul H Oyala
- Division of Chemistry and Chemical Engineering, Arthur Amos Noyes Laboratory of Chemical Physics, California Institute of Technology, Pasadena, California 91125, United States
| | - Grace Y Chen
- Division of Chemistry and Chemical Engineering, Arthur Amos Noyes Laboratory of Chemical Physics, California Institute of Technology, Pasadena, California 91125, United States
| | - Ryan G Hadt
- Division of Chemistry and Chemical Engineering, Arthur Amos Noyes Laboratory of Chemical Physics, California Institute of Technology, Pasadena, California 91125, United States
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15
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Fataftah MS, Krzyaniak MD, Vlaisavljevich B, Wasielewski MR, Zadrozny JM, Freedman DE. Metal-ligand covalency enables room temperature molecular qubit candidates. Chem Sci 2019; 10:6707-6714. [PMID: 31367325 PMCID: PMC6625489 DOI: 10.1039/c9sc00074g] [Citation(s) in RCA: 47] [Impact Index Per Article: 9.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/05/2019] [Accepted: 05/27/2019] [Indexed: 12/29/2022] Open
Abstract
Metal–ligand covalency enables observation of coherent spin dynamics to room temperature in a series of vanadium(iv) and copper(ii) catechol complexes.
Harnessing synthetic chemistry to design electronic spin-based qubits, the smallest unit of a quantum information system, enables us to probe fundamental questions regarding spin relaxation dynamics. We sought to probe the influence of metal–ligand covalency on spin–lattice relaxation, which comprises the upper limit of coherence time. Specifically, we studied the impact of the first coordination sphere on spin–lattice relaxation through a series of four molecules featuring V–S, V–Se, Cu–S, and Cu–Se bonds, the Ph4P+ salts of the complexes [V(C6H4S2)3]2– (1), [Cu(C6H4S2)2]2– (2), [V(C6H4Se2)3]2– (3), and [Cu(C6H4Se2)2]2– (4). The combined results of pulse electron paramagnetic resonance spectroscopy and ac magnetic susceptibility studies demonstrate the influence of greater M–L covalency, and consequently spin-delocalization onto the ligand, on elongating spin–lattice relaxation times. Notably, we observe the longest spin–lattice relaxation times in 2, and spin echos that survive until room temperature in both copper complexes (2 and 4).
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Affiliation(s)
- Majed S Fataftah
- Department of Chemistry , Northwestern University , Evanston , IL 60208 , USA . ;
| | - Matthew D Krzyaniak
- Department of Chemistry , Northwestern University , Evanston , IL 60208 , USA . ; .,The Institute for Sustainability and Energy at Northwestern , Northwestern University , Evanston , IL 60208 , USA
| | - Bess Vlaisavljevich
- Department of Chemistry , University of South Dakota , Vermillion , South Dakota 57069 , USA
| | - Michael R Wasielewski
- Department of Chemistry , Northwestern University , Evanston , IL 60208 , USA . ; .,The Institute for Sustainability and Energy at Northwestern , Northwestern University , Evanston , IL 60208 , USA
| | - Joseph M Zadrozny
- Department of Chemistry , Colorado State University , Fort Collins , Colorado 80523 , USA .
| | - Danna E Freedman
- Department of Chemistry , Northwestern University , Evanston , IL 60208 , USA . ;
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16
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Yu CJ, Krzyaniak MD, Fataftah MS, Wasielewski MR, Freedman DE. A concentrated array of copper porphyrin candidate qubits. Chem Sci 2019; 10:1702-1708. [PMID: 30842834 PMCID: PMC6368214 DOI: 10.1039/c8sc04435j] [Citation(s) in RCA: 50] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/05/2018] [Accepted: 11/20/2018] [Indexed: 01/04/2023] Open
Abstract
Synthetic chemistry offers a pathway to realize atomically precise arrays of qubits, the smallest unit of a quantum information science system. We harnessed framework chemistry to create an array of qubit candidates, featuring one qubit every 13.6 Å, by synthesizing the new copper(ii) variant of the porphyrinic metal-organic framework PCN-224. We subjected the framework to pulse-electron paramagnetic resonance (EPR) measurements, establishing spin coherence at temperatures up to 80 K within a fully spin concentrated framework. Observation of Rabi oscillations further support the viability of the qubits within these arrays. To interrogate the spin dynamics of qubit arrays, we investigated spin-lattice relaxation, T 1, through a combination of pulse-EPR and alternating current (ac) magnetic susceptibility measurements. These data revealed distinct vibrational environments within the frameworks that contribute to spin dynamics. The aggregate results establish a pathway for a synthetic approach to create spatially precise networks of qubits.
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Affiliation(s)
- Chung-Jui Yu
- Department of Chemistry , Northwestern University , Evanston , Illinois 60208 , USA .
| | - Matthew D Krzyaniak
- Department of Chemistry , Northwestern University , Evanston , Illinois 60208 , USA .
- Institute for Sustainability and Energy at Northwester , Northwestern University , Evanston , Illinois 60208-3113 , USA
| | - Majed S Fataftah
- Department of Chemistry , Northwestern University , Evanston , Illinois 60208 , USA .
| | - Michael R Wasielewski
- Department of Chemistry , Northwestern University , Evanston , Illinois 60208 , USA .
- Institute for Sustainability and Energy at Northwester , Northwestern University , Evanston , Illinois 60208-3113 , USA
| | - Danna E Freedman
- Department of Chemistry , Northwestern University , Evanston , Illinois 60208 , USA .
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17
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Eaton SS, Ngendahimana T, Eaton GR, Jupp AR, Stephan DW. Electron paramagnetic resonance of a 10B-containing heterocyclic radical. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2018; 290:76-84. [PMID: 29579535 DOI: 10.1016/j.jmr.2018.03.007] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/06/2017] [Revised: 03/14/2018] [Accepted: 03/15/2018] [Indexed: 06/08/2023]
Abstract
Electron paramagnetic resonance measurements for a 10B-containing heterocyclic phenanthrenedione radical, (C6F5)2B(O2C14H8), were made at X-band in 9:1 toluene:dichloromethane from 10 to 293 K and in toluene from 180 to 293 K. In well-deoxygenated 0.1 mM toluene solution at room temperature hyperfine couplings to 10B, four pairs of protons and five pairs of fluorines contribute to a continuous wave spectrum with many resolved lines. Hyperfine couplings were adjusted to provide the best fit for spectra of the radical enriched in 10B and the analogous radical synthesized with 10,11B in natural abundance, resulting in small refinements of the hyperfine coupling constants previously reported for the natural abundance sample. Electron spin relaxation rates at temperatures between 15 and 293 K were similar for samples containing 10B and natural isotope abundance. Analysis of electron spin echo envelope modulation and hyperfine correlation spectroscopy data at 80 K found Axx = -7.5 ± 0.3, Ayy = -8.5 ± 0.3, and Azz = -10.8 ± 0.3 MHz for 11B, which indicates small spin density on the boron. The spin echo and hyperfine spectroscopy data for the 10B -containing radical are consistent with the factor of 2.99 smaller hyperfine values for 10B than for 11B.
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Affiliation(s)
- Sandra S Eaton
- Department of Chemistry and Biochemistry, University of Denver, Denver, CO 80210, USA
| | - Thacien Ngendahimana
- Department of Chemistry and Biochemistry, University of Denver, Denver, CO 80210, USA
| | - Gareth R Eaton
- Department of Chemistry and Biochemistry, University of Denver, Denver, CO 80210, USA.
| | - Andrew R Jupp
- University of Toronto, 80 St. George St., Toronto, ON M5S 3H6, Canada
| | - Douglas W Stephan
- University of Toronto, 80 St. George St., Toronto, ON M5S 3H6, Canada
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18
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Ji X, Can TV, Mentink-Vigier F, Bornet A, Milani J, Vuichoud B, Caporini MA, Griffin RG, Jannin S, Goldman M, Bodenhausen G. Overhauser effects in non-conducting solids at 1.2 K. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2018; 286:138-142. [PMID: 29241045 PMCID: PMC5767554 DOI: 10.1016/j.jmr.2017.11.017] [Citation(s) in RCA: 19] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/05/2017] [Revised: 11/23/2017] [Accepted: 11/26/2017] [Indexed: 05/05/2023]
Abstract
Recently, it was observed that protons in non-conducting solids doped with 1,3-bisdiphenylene-2-phenylallyl (BDPA) or its sulfonated derivative (SA-BDPA) can be polarized through Overhauser effects via resonant microwave irradiation. These effects were present under magic angle spinning conditions in magnetic fields between 5 and 18.8 T and at temperatures near 100 K. This communication reports similar effects in static samples at 6.7 T and, more importantly, at temperatures as low as 1.2 K, in a different dynamic regime than in the previous study. Our results provide new information towards understanding the mechanism of the Overhauser effect in non-conducting solids. We discuss possible origins of the fluctuations that can give rise to an Overhauser effect at such low temperatures.
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Affiliation(s)
- X Ji
- Institut des Sciences et Ingénierie Chimiques, Ecole Polytechnique Fédérale de Lausanne, 1015 Lausanne, Switzerland; Departement de Chimie, Ecole Normale Superieure, PSL Research University, UPMC Univ Paris 06, CNRS, Laboratoire des Biomolecules (LBM), 24 rue Lhomond, 75005 Paris, France; Sorbonne Universites, UPMC Univ Paris 06, Ecole Normale Superieure, CNRS, Laboratoire des Biomolecules (LBM), Paris, France
| | - T V Can
- Department of Chemistry, Massachusetts Institute of Technology, Cambridge, MA 02139, USA; Francis Bitter Magnet Laboratory, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
| | - F Mentink-Vigier
- National High Magnetic Field Laboratory, Florida State University, Tallahassee, FL 32310, USA
| | - A Bornet
- Institut des Sciences et Ingénierie Chimiques, Ecole Polytechnique Fédérale de Lausanne, 1015 Lausanne, Switzerland; Univ Lyon, CNRS, Université Claude Bernard Lyon 1, ENS de Lyon, Institut des Sciences Analytiques, UMR 5280, 5 rue de la Doua, 69100 Villeurbanne, France
| | - J Milani
- Institut des Sciences et Ingénierie Chimiques, Ecole Polytechnique Fédérale de Lausanne, 1015 Lausanne, Switzerland; Univ Lyon, CNRS, Université Claude Bernard Lyon 1, ENS de Lyon, Institut des Sciences Analytiques, UMR 5280, 5 rue de la Doua, 69100 Villeurbanne, France
| | - B Vuichoud
- Institut des Sciences et Ingénierie Chimiques, Ecole Polytechnique Fédérale de Lausanne, 1015 Lausanne, Switzerland; Univ Lyon, CNRS, Université Claude Bernard Lyon 1, ENS de Lyon, Institut des Sciences Analytiques, UMR 5280, 5 rue de la Doua, 69100 Villeurbanne, France
| | - M A Caporini
- Amgen Inc., 360 Binney Street Cambridge, MA 02142, USA
| | - R G Griffin
- Department of Chemistry, Massachusetts Institute of Technology, Cambridge, MA 02139, USA; Francis Bitter Magnet Laboratory, Massachusetts Institute of Technology, Cambridge, MA 02139, USA.
| | - S Jannin
- Institut des Sciences et Ingénierie Chimiques, Ecole Polytechnique Fédérale de Lausanne, 1015 Lausanne, Switzerland; Univ Lyon, CNRS, Université Claude Bernard Lyon 1, ENS de Lyon, Institut des Sciences Analytiques, UMR 5280, 5 rue de la Doua, 69100 Villeurbanne, France
| | - M Goldman
- 2 Allée Geneviève Anthonioz de Gaulle, 93260 Les Lilas, France
| | - G Bodenhausen
- Departement de Chimie, Ecole Normale Superieure, PSL Research University, UPMC Univ Paris 06, CNRS, Laboratoire des Biomolecules (LBM), 24 rue Lhomond, 75005 Paris, France; Sorbonne Universites, UPMC Univ Paris 06, Ecole Normale Superieure, CNRS, Laboratoire des Biomolecules (LBM), Paris, France.
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19
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Boulon M, Fernandez A, Moreno Pineda E, Chilton NF, Timco G, Fielding AJ, Winpenny REP. Measuring Spin⋅⋅⋅Spin Interactions between Heterospins in a Hybrid [2]Rotaxane. Angew Chem Int Ed Engl 2017; 56:3876-3879. [PMID: 28276620 PMCID: PMC5434811 DOI: 10.1002/anie.201612249] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/17/2016] [Indexed: 12/29/2022]
Abstract
Use of molecular electron spins as qubits for quantum computing will depend on the ability to produce molecules with weak but measurable interactions between the qubits. Here we demonstrate use of pulsed EPR spectroscopy to measure the interaction between two inequivalent spins in a hybrid rotaxane molecule.
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Affiliation(s)
- Marie‐Emmanuelle Boulon
- The School of Chemistry and Photon Science InstituteThe University of ManchesterOxford RoadManchesterM13 9PLUK
| | - Antonio Fernandez
- The School of Chemistry and Photon Science InstituteThe University of ManchesterOxford RoadManchesterM13 9PLUK
| | - Eufemio Moreno Pineda
- The School of Chemistry and Photon Science InstituteThe University of ManchesterOxford RoadManchesterM13 9PLUK
| | - Nicholas F. Chilton
- The School of Chemistry and Photon Science InstituteThe University of ManchesterOxford RoadManchesterM13 9PLUK
| | - Grigore Timco
- The School of Chemistry and Photon Science InstituteThe University of ManchesterOxford RoadManchesterM13 9PLUK
| | - Alistair J. Fielding
- The School of Chemistry and Photon Science InstituteThe University of ManchesterOxford RoadManchesterM13 9PLUK
| | - Richard E. P. Winpenny
- The School of Chemistry and Photon Science InstituteThe University of ManchesterOxford RoadManchesterM13 9PLUK
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20
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Boulon ME, Fernandez A, Moreno Pineda E, Chilton NF, Timco G, Fielding AJ, Winpenny REP. Measuring Spin⋅⋅⋅Spin Interactions between Heterospins in a Hybrid [2]Rotaxane. Angew Chem Int Ed Engl 2017. [DOI: 10.1002/ange.201612249] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
Affiliation(s)
- Marie-Emmanuelle Boulon
- The School of Chemistry and Photon Science Institute; The University of Manchester; Oxford Road Manchester M13 9PL UK
| | - Antonio Fernandez
- The School of Chemistry and Photon Science Institute; The University of Manchester; Oxford Road Manchester M13 9PL UK
| | - Eufemio Moreno Pineda
- The School of Chemistry and Photon Science Institute; The University of Manchester; Oxford Road Manchester M13 9PL UK
| | - Nicholas F. Chilton
- The School of Chemistry and Photon Science Institute; The University of Manchester; Oxford Road Manchester M13 9PL UK
| | - Grigore Timco
- The School of Chemistry and Photon Science Institute; The University of Manchester; Oxford Road Manchester M13 9PL UK
| | - Alistair J. Fielding
- The School of Chemistry and Photon Science Institute; The University of Manchester; Oxford Road Manchester M13 9PL UK
| | - Richard E. P. Winpenny
- The School of Chemistry and Photon Science Institute; The University of Manchester; Oxford Road Manchester M13 9PL UK
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21
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Eaton SS, Huber K, Elajaili H, McPeak J, Eaton GR, Longobardi LE, Stephan DW. Electron spin relaxation of a boron-containing heterocyclic radical. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2017; 276:7-13. [PMID: 28081476 DOI: 10.1016/j.jmr.2016.12.013] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/10/2016] [Revised: 12/23/2016] [Accepted: 12/24/2016] [Indexed: 06/06/2023]
Abstract
Preparation of the stable boron-containing heterocyclic phenanthrenedione radical, (C6F5)2B(O2C14H8), by frustrated Lewis pair chemistry has been reported recently. Electron paramagnetic resonance measurements of this radical were made at X-band in toluene:dichloromethane (9:1) from 10 to 293K, in toluene from 180 to 293K and at Q-band at 80K. In well-deoxygenated 0.1mM toluene solution at room temperature hyperfine splittings from 11B, four pairs of 1H, and 5 pairs of 19F contribute to an EPR spectrum with many resolved lines. Observed hyperfine couplings were assigned based on DFT calculations and account for all of the fluorines and protons in the molecule. Rigid lattice g values are gx=2.0053, gy=2.0044, and gz=2.0028. Near the melting point of the solvent 1/Tm is enhanced due to motional averaging of g and A anisotropy. Increasing motion above the melting point enhances 1/T1 due to contributions from tumbling-dependent processes. The overall temperature dependence of 1/T1 from 10 to 293K was modeled with the sum of contributions of a process that is linear in T, a Raman process, spin rotation, and modulation of g anisotropy by molecular tumbling. The EPR measurements are consistent with the description of this compound as a substituted aromatic radical, with relatively small spin density on the boron.
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Affiliation(s)
- Sandra S Eaton
- Department of Chemistry and Biochemistry, University of Denver, Denver, CO 80210, USA
| | - Kirby Huber
- Department of Chemistry and Biochemistry, University of Denver, Denver, CO 80210, USA
| | - Hanan Elajaili
- Department of Chemistry and Biochemistry, University of Denver, Denver, CO 80210, USA
| | - Joseph McPeak
- Department of Chemistry and Biochemistry, University of Denver, Denver, CO 80210, USA
| | - Gareth R Eaton
- Department of Chemistry and Biochemistry, University of Denver, Denver, CO 80210, USA.
| | | | - Douglas W Stephan
- University of Toronto, 80 St. George St, Toronto, ON M5S 3H6, Canada
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22
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Graham MJ, Yu CJ, Krzyaniak MD, Wasielewski MR, Freedman DE. Synthetic Approach To Determine the Effect of Nuclear Spin Distance on Electronic Spin Decoherence. J Am Chem Soc 2017; 139:3196-3201. [DOI: 10.1021/jacs.6b13030] [Citation(s) in RCA: 51] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Affiliation(s)
- Michael J. Graham
- Department
of Chemistry and §Argonne-Northwestern Solar Energy Research Center, Northwestern University, 2145 Sheridan Road, Evanston, Illinois 60208-3113, United States
| | - Chung-Jui Yu
- Department
of Chemistry and §Argonne-Northwestern Solar Energy Research Center, Northwestern University, 2145 Sheridan Road, Evanston, Illinois 60208-3113, United States
| | - Matthew D. Krzyaniak
- Department
of Chemistry and §Argonne-Northwestern Solar Energy Research Center, Northwestern University, 2145 Sheridan Road, Evanston, Illinois 60208-3113, United States
| | - Michael R. Wasielewski
- Department
of Chemistry and §Argonne-Northwestern Solar Energy Research Center, Northwestern University, 2145 Sheridan Road, Evanston, Illinois 60208-3113, United States
| | - Danna E. Freedman
- Department
of Chemistry and §Argonne-Northwestern Solar Energy Research Center, Northwestern University, 2145 Sheridan Road, Evanston, Illinois 60208-3113, United States
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23
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Yu CJ, Graham MJ, Zadrozny JM, Niklas J, Krzyaniak MD, Wasielewski MR, Poluektov OG, Freedman DE. Long Coherence Times in Nuclear Spin-Free Vanadyl Qubits. J Am Chem Soc 2016; 138:14678-14685. [PMID: 27797487 DOI: 10.1021/jacs.6b08467] [Citation(s) in RCA: 91] [Impact Index Per Article: 11.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/11/2023]
Abstract
Quantum information processing (QIP) offers the potential to create new frontiers in fields ranging from quantum biology to cryptography. Two key figures of merit for electronic spin qubits, the smallest units of QIP, are the coherence time (T2), the lifetime of the qubit, and the spin-lattice relaxation time (T1), the thermally defined upper limit of T2. To achieve QIP, processable qubits with long coherence times are required. Recent studies on (Ph4P-d20)2[V(C8S8)3], a vanadium-based qubit, demonstrate that millisecond T2 times are achievable in transition metal complexes with nuclear spin-free environments. Applying these principles to vanadyl complexes offers a route to combine the previously established surface compatibility of the flatter vanadyl structures with a long T2. Toward those ends, we investigated a series of four qubits, (Ph4P)2[VO(C8S8)2] (1), (Ph4P)2[VO(β-C3S5)2] (2), (Ph4P)2[VO(α-C3S5)2] (3), and (Ph4P)2[VO(C3S4O)2] (4), by pulsed electron paramagnetic resonance (EPR) spectroscopy and compared the performance of these species with our recently reported set of vanadium tris(dithiolene) complexes. Crucially we demonstrate that solutions of 1-4 in SO2, a uniquely polar nuclear spin-free solvent, reveal T2 values of up to 152(6) μs, comparable to the best molecular qubit candidates. Upon transitioning to vanadyl species from the tris(dithiolene) analogues, we observe a remarkable order of magnitude increase in T1, attributed to stronger solute-solvent interactions with the polar vanadium-oxo moiety. Simultaneously, we detect a small decrease in T2 for the vanadyl analogues relative to the tris(dithiolene) complexes. We attribute this decrease to the absence of one nuclear spin-free ligand, which served to shield the vanadium centers against solvent nuclear spins. Our results highlight new design principles for long T1 and T2 times by demonstrating the efficacy of ligand-based tuning of solute-solvent interactions.
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Affiliation(s)
- Chung-Jui Yu
- Department of Chemistry, Northwestern University , Evanston, Illinois 60208, United States
| | - Michael J Graham
- Department of Chemistry, Northwestern University , Evanston, Illinois 60208, United States
| | - Joseph M Zadrozny
- Department of Chemistry, Northwestern University , Evanston, Illinois 60208, United States
| | - Jens Niklas
- Chemical Sciences and Engineering Division, Argonne National Laboratory , Argonne, Illinois 60439, United States
| | - Matthew D Krzyaniak
- Department of Chemistry, Northwestern University , Evanston, Illinois 60208, United States.,Argonne-Northwestern Solar Energy Research (ANSER) Center, Northwestern University , Evanston, Illinois 60208-3113, United States
| | - Michael R Wasielewski
- Department of Chemistry, Northwestern University , Evanston, Illinois 60208, United States.,Argonne-Northwestern Solar Energy Research (ANSER) Center, Northwestern University , Evanston, Illinois 60208-3113, United States
| | - Oleg G Poluektov
- Chemical Sciences and Engineering Division, Argonne National Laboratory , Argonne, Illinois 60439, United States
| | - Danna E Freedman
- Department of Chemistry, Northwestern University , Evanston, Illinois 60208, United States
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24
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Chen H, Maryasov AG, Rogozhnikova OY, Trukhin DV, Tormyshev VM, Bowman MK. Electron spin dynamics and spin-lattice relaxation of trityl radicals in frozen solutions. Phys Chem Chem Phys 2016; 18:24954-65. [PMID: 27560644 PMCID: PMC5482570 DOI: 10.1039/c6cp02649d] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Electron spin-lattice relaxation of two trityl radicals, d24-OX063 and Finland trityl, were studied under conditions relevant to their use in dissolution dynamic nuclear polarization (DNP). The dependence of relaxation kinetics on temperature up to 100 K and on concentration up to 60 mM was obtained at X- and W-bands (0.35 and 3.5 Tesla, respectively). The relaxation is quite similar at both bands and for both trityl radicals. At concentrations typical for DNP, relaxation is mediated by excitation transfer and spin-diffusion to fast-relaxing centers identified as triads of trityl radicals that spontaneously form in the frozen samples. These centers relax by an Orbach-Aminov mechanism and determine the relaxation, saturation and electron spin dynamics during DNP.
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Affiliation(s)
- Hanjiao Chen
- Department of Chemistry, The University of Alabama, Box 870336, Tuscaloosa, Alabama 35487-0336, USA.
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25
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Sarewicz M, Dutka M, Pietras R, Borek A, Osyczka A. Effect of H bond removal and changes in the position of the iron-sulphur head domain on the spin-lattice relaxation properties of the [2Fe-2S](2+) Rieske cluster in cytochrome bc(1). Phys Chem Chem Phys 2016; 17:25297-308. [PMID: 26355649 PMCID: PMC5716461 DOI: 10.1039/c5cp02815a] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023]
Abstract
Here, comparative electron spin–lattice relaxation studies of the 2Fe–2S iron–sulphur (Fe–S) cluster embedded in a large membrane protein complex – cytochrome bc1 – are reported.
Here, comparative electron spin–lattice relaxation studies of the 2Fe–2S iron–sulphur (Fe–S) cluster embedded in a large membrane protein complex – cytochrome bc1 – are reported. Structural modifications of the local environment alone (mutations S158A and Y160W removing specific H bonds between Fe–S and amino acid side chains) or in combination with changes in global protein conformation (mutations/inhibitors changing the position of the Fe–S binding domain within the protein complex) resulted in different redox potentials as well as g-, g-strain and the relaxation rates (T1–1) for the Fe–S cluster. The relaxation rates for T < 25 K were measured directly by inversion recovery, while for T > 60 K they were deduced from simulation of continuous wave EPR spectra of the cluster using a model that included anisotropy of Lorentzian broadening. In all cases, the relaxation rate involved contributions from direct, second-order Raman and Orbach processes, each dominating over different temperature ranges. The analysis of T1–1 (T) over the range 5–120 K yielded the values of the Orbach energy (EOrb), Debye temperature θD and Raman process efficiency CRam for each variant of the protein. As the Orbach energy was generally higher for mutants S158A and Y160W, compared to wild-type protein (WT), it is suggested that H bond removal influences the geometry leading to increased strength of antiferromagnetic coupling between two Fe ions of the cluster. While θD was similar for all variants (∼107 K), the efficiency of the Raman process generally depends on the spin–orbit coupling that is lower for S158A and Y160W mutants, when compared to the WT. However, in several cases CRam did not only correlate with spin–orbit coupling but was also influenced by other factors – possibly the modification of protein rigidity and therefore the vibrational modes around the Fe–S cluster that change upon the movement of the iron–sulphur head domain.
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Affiliation(s)
- Marcin Sarewicz
- Department of Molecular Biophysics, Faculty of Biochemistry, Biophysics and Biotechnology, Jagiellonian University, Kraków, Poland.
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Bradshaw M, Gaffney BJ. Fluctuations of an exposed π-helix involved in lipoxygenase substrate recognition. Biochemistry 2014; 53:5102-10. [PMID: 25036469 PMCID: PMC4131896 DOI: 10.1021/bi500768c] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/20/2014] [Revised: 07/16/2014] [Indexed: 01/14/2023]
Abstract
The second helix in lipoxygenases adapts to permit substrate access to the active site, but details of this process are varied and poorly understood. We therefore examined the dynamics of helix 2 in solutions of spin-labeled soybean lipoxygenase-1 and spin relaxation at 60 K of the spin-labels by catalytic iron. Helix 2 in soybean lipoxygenase structures is surface-exposed and contains one turn of π-helix, centrally located. A site-directed spin-label scan of 18 of the 21 helix 2 residues, and electron paramagnetic resonance, showed that the π-helical segment became unusually mobile, on a nanosecond time scale, under conditions favoring substrate binding (pH 9 and lipid addition), while segments before and after had relatively unchanged dynamics. Backbone dynamics of residues in the π-helical segment appeared to be correlated, at pH 9. Samples also were frozen to examine the polarity and proticity of the local environments, the effect of the local environment on intrinsic relaxation, and dipolar relaxation by two symmetries of catalytic iron. The average hyperfine tensor component, Azz, of four π-helix residues decreased by 1.75 G, with an increase in pH from 7 to 9, while it remained unaffected for nearby buried residues. Power saturation data suggested the change in polarity specific to the π-helix altered the intrinsic relaxation rates. Different symmetries of iron contributed to distance-dependent magnetic relaxation. We interpret these data to mean that a π-helix in the second helix of plant lipoxygenases is highly dynamic and is the site where lipid chains penetrate to inner helices that outline the substrate pocket.
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Affiliation(s)
- Miles
D. Bradshaw
- Department
of Biological
Science, Florida State University, Tallahassee, Florida 32306-4295, United States
| | - Betty J. Gaffney
- Department
of Biological
Science, Florida State University, Tallahassee, Florida 32306-4295, United States
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Pietras R, Sarewicz M, Osyczka A. Molecular organization of cytochrome c2 near the binding domain of cytochrome bc1 studied by electron spin-lattice relaxation enhancement. J Phys Chem B 2014; 118:6634-43. [PMID: 24845964 PMCID: PMC4065165 DOI: 10.1021/jp503339g] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
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Measurements
of specific interactions between proteins are challenging.
In redox systems, interactions involve surfaces near the attachment
sites of cofactors engaged in interprotein electron transfer (ET).
Here we analyzed binding of cytochrome c2 to cytochrome bc1 by measuring paramagnetic
relaxation enhancement (PRE) of spin label (SL) attached to cytochrome c2. PRE was exclusively induced by the iron atom
of heme c1 of cytochrome bc1, which guaranteed that only the configurations with
SL to heme c1 distances up to ∼30
Å were detected. Changes in PRE were used to qualitatively and
quantitatively characterize the binding. Our data suggest that at
low ionic strength and under an excess of cytochrome c2 over cytochrome bc1, several
cytochrome c2 molecules gather near the
binding domain forming a “cloud” of molecules. When
the cytochrome bc1 concentration increases,
the cloud disperses to populate additional available binding domains.
An increase in ionic strength weakens the attractive forces and the
average distance between cytochrome c2 and cytochrome bc1 increases. The spatial
arrangement of the protein complex at various ionic strengths is different.
Above 150 mM NaCl the lifetime of the complexes becomes so short that
they are undetectable. All together the results indicate that cytochrome c2 molecules, over the range of salt concentration
encompassing physiological ionic strength, do not form stable, long-lived
complexes but rather constantly collide with the surface of cytochrome bc1 and ET takes place coincidentally with one
of these collisions.
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Affiliation(s)
- Rafał Pietras
- Department of Molecular Biophysics, Faculty of Biochemistry, Biophysics and Biotechnology, Jagiellonian University , 30-387 Kraków, Poland
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28
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Siaw TA, Fehr M, Lund A, Latimer A, Walker SA, Edwards DT, Han SI. Effect of electron spin dynamics on solid-state dynamic nuclear polarization performance. Phys Chem Chem Phys 2014; 16:18694-706. [DOI: 10.1039/c4cp02013h] [Citation(s) in RCA: 42] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Optimum integral EPR saturation, determined by electron T1e and electron spin flip-flop rate, maximizes solid-state DNP performance using nitroxide radicals.
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Affiliation(s)
- Ting Ann Siaw
- Department of Chemical Engineering
- University of California Santa Barbara
- Santa Barbara, USA
| | - Matthias Fehr
- Department of Chemistry and Biochemistry
- University of California Santa Barbara
- Santa Barbara, USA
| | - Alicia Lund
- Department of Chemistry and Biochemistry
- University of California Santa Barbara
- Santa Barbara, USA
| | - Allegra Latimer
- Department of Chemistry and Biochemistry
- University of California Santa Barbara
- Santa Barbara, USA
| | - Shamon A. Walker
- Department of Chemical Engineering
- University of California Santa Barbara
- Santa Barbara, USA
| | - Devin T. Edwards
- Department of Physics
- University of California Santa Barbara
- Santa Barbara, USA
| | - Song-I Han
- Department of Chemical Engineering
- University of California Santa Barbara
- Santa Barbara, USA
- Department of Chemistry and Biochemistry
- University of California Santa Barbara
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29
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Lumata L, Kovacs Z, Sherry AD, Malloy C, Hill S, van Tol J, Yu L, Song L, Merritt ME. Electron spin resonance studies of trityl OX063 at a concentration optimal for DNP. Phys Chem Chem Phys 2013; 15:9800-7. [PMID: 23676994 PMCID: PMC3698225 DOI: 10.1039/c3cp50186h] [Citation(s) in RCA: 70] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
We have performed temperature-dependent electron spin resonance (ESR) measurements of the stable free radical trityl OX063, an efficient polarizing agent for dissolution dynamic nuclear polarization (DNP), at the optimum DNP concentration (15 mM). We have found that (i) when compared to the W-band electron spin-lattice relaxation rate T1e(-1) of other free radicals used in DNP at the same concentration, trityl OX063 has slower T1e(-1) than BDPA and 4-oxo-TEMPO. At T > 20 K, the T1e(-1)vs. T data of trityl OX063 appears to follow a power law dependence close to the Raman process prediction whereas at T < 10 K, electronic relaxation slows and approaches the direct process behaviour. (ii) Gd(3+) doping, a factor known to enhance DNP, of trityl OX063 samples measured at W-band resulted in monotonic increases of T1e(-1) especially at temperatures below 20-40 K while the ESR lineshapes remained essentially unchanged. (iii) The high frequency ESR spectrum can be fitted with an axial g-tensor with a slight g-anisotropy: g(x) = g(y) = 2.00319(3) and g(z) = 2.00258(3). Although the ESR linewidth D monotonically increases with field, the temperature-dependent T1e(-1) is almost unchanged as the ESR frequency is increased from 9.5 GHz to 95 GHz, but becomes faster at 240 GHz and 336 GHz. The ESR properties of trityl OX063 reported here may provide insights into the efficiency of DNP of low-γ nuclei performed at various magnetic fields, from 0.35 T to 12 T.
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Affiliation(s)
- Lloyd Lumata
- Advanced Imaging Research Center, University of Texas at Dallas, 800West Campbell Road, Richardson, Texas 75080 USA
| | - Zoltan Kovacs
- Advanced Imaging Research Center, University of Texas at Dallas, 800West Campbell Road, Richardson, Texas 75080 USA
| | - A. Dean Sherry
- Advanced Imaging Research Center, University of Texas at Dallas, 800West Campbell Road, Richardson, Texas 75080 USA
- Department of Chemistry
| | - Craig Malloy
- Advanced Imaging Research Center, University of Texas at Dallas, 800West Campbell Road, Richardson, Texas 75080 USA
- Molecular Biophysics, University of Texas at Dallas, 800West Campbell Road, Richardson, Texas 75080 USA
- VA North Texas Healthcare System, Dallas, TX 75216
| | - Stephen Hill
- Department of Physics, Florida State University, 77 Chieftan Way, Tallahassee, FL 32306 USA
- National High Magnetic Field Laboratory, Florida State University, 1800 East Paul Dirac Drive, Tallahassee, Florida 32310 USA
| | - Johan van Tol
- National High Magnetic Field Laboratory, Florida State University, 1800 East Paul Dirac Drive, Tallahassee, Florida 32310 USA
| | - Lu Yu
- National High Magnetic Field Laboratory, Florida State University, 1800 East Paul Dirac Drive, Tallahassee, Florida 32310 USA
| | - Likai Song
- National High Magnetic Field Laboratory, Florida State University, 1800 East Paul Dirac Drive, Tallahassee, Florida 32310 USA
| | - Matthew E. Merritt
- Advanced Imaging Research Center, University of Texas at Dallas, 800West Campbell Road, Richardson, Texas 75080 USA
- Biomedical Engineering, University of Texas at Dallas, 800West Campbell Road, Richardson, Texas 75080 USA
- Molecular Biophysics, University of Texas at Dallas, 800West Campbell Road, Richardson, Texas 75080 USA
- Department of Bioengineering
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Merunka D, Kveder M, Jokić M, Rakvin B. Effect of glassy modes on electron spin-lattice relaxation in solid ethanol. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2013; 228:50-58. [PMID: 23357426 DOI: 10.1016/j.jmr.2012.12.016] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/29/2012] [Revised: 12/20/2012] [Accepted: 12/21/2012] [Indexed: 06/01/2023]
Abstract
Electron spin-lattice relaxation (SLR) of TEMPO radical was measured in the crystalline and glassy states of deuterated ethanol in the temperature range 5-80K using X-band electron paramagnetic resonance (EPR). The measured SLR rates are higher in the glassy than in crystalline state and the excess SLR rate in glassy state is much lower than in ethanol. This result suggests that extra modes in glassy state, i.e. glassy modes, produce the excess SLR rate via the electron-nuclear dipolar (END) interaction between the electron spin of radical and the matrix protons or deuterons. Using the soft-potential model and assuming the END interaction between the electron spin and the matrix protons, the contributions to SLR rate of various mechanisms of glassy modes were theoretically analyzed. The evaluations of SLR rates in glassy ethanol indicate two main mechanisms of glassy modes: thermally activated relaxation of double-well systems and phonon-induced relaxation of quasi-harmonic local modes. The SLR rates induced by these mechanisms correlate well with the experimental data.
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Affiliation(s)
- Dalibor Merunka
- Ruer Bošković Institute, Bijenička cesta 54, HR-10000 Zagreb, Croatia.
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31
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Serra SC, Rosso A, Tedoldi F. Electron and nuclear spin dynamics in the thermal mixing model of dynamic nuclear polarization. Phys Chem Chem Phys 2013; 14:13299-308. [PMID: 22918556 DOI: 10.1039/c2cp41947e] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
A novel mathematical treatment is proposed for computing the time evolution of dynamic nuclear polarization processes in the low temperature thermal mixing regime. Without assuming any a priori analytical form for the electron polarization, our approach provides a quantitative picture of the steady state that agrees with the well known Borghini prediction based on thermodynamic arguments, as long as the electrons-nuclei transition rates are fast compared to the other relevant time scales. Substantially different final polarization levels are achieved instead when the latter assumption is relaxed in the presence of a nuclear leakage term, even though very weak, suggesting a possible explanation for the deviation between the measured steady state polarizations and the Borghini prediction. The proposed methodology also allows us to calculate nuclear polarization and relaxation times, once the electrons/nuclei concentration ratio and the typical rates of the microscopic processes involving the two spin species are specified. Numerical results are shown to account for the manifold dynamic behaviours of typical DNP samples.
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Affiliation(s)
- Sonia Colombo Serra
- Centro Ricerche Bracco, Bracco Imaging Spa, via Ribes 5, 10010 Colleretto Giacosa (TO), Italy.
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32
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Kirilyuk IA, Polienko YF, Krumkacheva OA, Strizhakov RK, Gatilov YV, Grigor’ev IA, Bagryanskaya EG. Synthesis of 2,5-Bis(spirocyclohexane)-Substituted Nitroxides of Pyrroline and Pyrrolidine Series, Including Thiol-Specific Spin Label: An Analogue of MTSSL with Long Relaxation Time. J Org Chem 2012; 77:8016-27. [DOI: 10.1021/jo301235j] [Citation(s) in RCA: 47] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Igor A. Kirilyuk
- N.N. Vorozhtsov Novosibirsk Institute of Organic Chemistry Sb RAS, Academician
Lavrentjev Ave. 9, Novosibirsk, 630090, Russia
| | - Yuliya F. Polienko
- N.N. Vorozhtsov Novosibirsk Institute of Organic Chemistry Sb RAS, Academician
Lavrentjev Ave. 9, Novosibirsk, 630090, Russia
| | - Olesya A. Krumkacheva
- International Tomography Center SB RAS, Institutskaya str. 3a, 630090, Novosibirsk,
Russia
| | - Rodion K. Strizhakov
- International Tomography Center SB RAS, Institutskaya str. 3a, 630090, Novosibirsk,
Russia
| | - Yurii V. Gatilov
- N.N. Vorozhtsov Novosibirsk Institute of Organic Chemistry Sb RAS, Academician
Lavrentjev Ave. 9, Novosibirsk, 630090, Russia
| | - Igor A. Grigor’ev
- N.N. Vorozhtsov Novosibirsk Institute of Organic Chemistry Sb RAS, Academician
Lavrentjev Ave. 9, Novosibirsk, 630090, Russia
| | - Elena G. Bagryanskaya
- N.N. Vorozhtsov Novosibirsk Institute of Organic Chemistry Sb RAS, Academician
Lavrentjev Ave. 9, Novosibirsk, 630090, Russia
- International Tomography Center SB RAS, Institutskaya str. 3a, 630090, Novosibirsk,
Russia
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Hoffmann SK, Goslar J, Lijewski S. Electron spin relaxation governed by Raman processes both for Cu²⁺ ions and carbonate radicals in KHCO₃ crystals: EPR and electron spin echo studies. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2012; 221:120-128. [PMID: 22750640 DOI: 10.1016/j.jmr.2012.06.001] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/19/2012] [Revised: 05/31/2012] [Accepted: 06/04/2012] [Indexed: 06/01/2023]
Abstract
EPR studies of Cu²⁺ and two free radicals formed by γ-radiation were performed for KHCO₃ single crystal at room temperature. From the rotational EPR results we concluded that Cu²⁺ is chelated by two carbonate molecules in a square planar configuration with spin-Hamiltonian parameters g(||)=2.2349 and A(||)=18.2 mT. Free radicals were identified as neutral HOCO· with unpaired electron localized on the carbon atom and a radical anion CO₃·⁻ with unpaired electron localized on two oxygen atoms. The hyperfine splitting of the EPR lines by an interaction with a single hydrogen atom of HOCO· was observed with isotropic coupling constants a₀=0.31 mT. Two differently oriented radical sites were identified in the crystal unit cell. Electron spin-lattice relaxation measured by electron spin echo methods shows that both Cu²⁺ and free radicals relax via two-phonon Raman processes with almost the same relaxation rate. The temperature dependence of the relaxation rate 1/T₁ is well described with the effective Debye temperature Θ(D)=175 K obtained from a fit to the Debye-type phonon spectrum. We calculated a more realistic Debye temperature value from available elastic constant values of the crystal as Θ(D)=246 K. This Θ(D)-value and the Debye phonon spectrum approximation give a much worse fit to the experimental results. Possible contributions from a local mode or an optical mode are considered and it is suggested that the real phonon spectrum should be used for the relaxation data interpretation. It is unusual that free radicals in KHCO₃ relax similarly to the well localized Cu²⁺ ions, which suggests a small destruction of the host crystal lattice by the ionizing irradiation allowing well coupling between radical and lattice dynamics.
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Affiliation(s)
- Stanislaw K Hoffmann
- Institute of Molecular Physics, Polish Academy of Sciences, Smoluchowskiego 17, 60-179 Poznan, Poland.
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34
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Mitrikas G. Pulsed EPR characterization of encapsulated atomic hydrogen in octasilsesquioxane cages. Phys Chem Chem Phys 2012; 14:3782-90. [PMID: 22323086 DOI: 10.1039/c2cp24057b] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Hydrogen atoms encapsulated in molecular cages are potential candidates for quantum computing applications. They provide the simplest two-spin system where the 1s electron spin, S = 1/2, is hyperfine-coupled to the proton nuclear spin, I = 1/2, with a large isotropic hyperfine coupling (A = 1420.40575 MHz for a free atom). While hydrogen atoms can be trapped in many matrices at cryogenic temperatures, it has been found that they are exceptionally stable in octasilsesquioxane cages even at room temperature [Sasamori et al., Science, 1994, 256, 1691]. Here we present a detailed spin-lattice and spin-spin relaxation study of atomic hydrogen encapsulated in Si(8)O(12)(OSiMe(2)H)(8) using X-band pulsed EPR spectroscopy. The spin-lattice relaxation times T(1) range between 1.2 s at 20 K and 41.8 μs at room temperature. The temperature dependence of the relaxation rate shows that for T < 60 K the spin-lattice relaxation is best described by a Raman process with a Debye temperature of θ(D) = 135 K, whereas for T > 100 K a thermally activated process with activation energy E(a) = 753 K (523 cm(-1)) prevails. The phase memory time T(M) = 13.9 μs remains practically constant between 200 and 300 K and is determined by nuclear spin diffusion. At lower temperatures T(M) decreases by an order of magnitude and exhibits two minima at T = 140 K and T = 60 K. The temperature dependence of T(M) between 20 and 200 K is attributed to dynamic processes that average inequivalent hyperfine couplings, e.g. rotation of the methyl groups of the cage organic substituents. The hyperfine couplings of the encapsulated proton and the cage (29)Si nuclei are obtained through numerical simulations of field-swept FID-detected EPR spectra and HYSCORE experiments, respectively. The results are discussed in terms of existing phenomenological models based on the spherical harmonic oscillator and compared to those of endohedral fullerenes.
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Affiliation(s)
- George Mitrikas
- Institute of Materials Science, NCSR Demokritos, Athens, Greece.
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35
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Merunka D, Kveder M, Rakvin B. Effect of thermally activated dynamics on electron spin–lattice relaxation in glasses. Chem Phys Lett 2011. [DOI: 10.1016/j.cplett.2011.08.088] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
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36
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Hoffmann SK, Goslar J, Lijewski S. Suppression of Raman electron spin relaxation of radicals in crystals. Comparison of Cu2+ and free radical relaxation in triglycine sulfate and Tutton salt single crystals. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2011; 23:345403. [PMID: 21841228 DOI: 10.1088/0953-8984/23/34/345403] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/31/2023]
Abstract
Electron spin-lattice relaxation was measured by the electron spin echo method in a broad temperature range above 4.2 K for Cu(2+) ions and free radicals produced by ionizing radiation in triglycine sulfate (TGS) and Tutton salt (NH4)(2)Zn(SO4)2 ⋅ 6H2O crystals. Localization of the paramagnetic centres in the crystal unit cells was determined from continuous wave electron paramagnetic resonance spectra. Various spin relaxation processes and mechanisms are outlined. Cu(2+) ions relax fast via two-phonon Raman processes in both crystals involving the whole phonon spectrum of the host lattice. This relaxation is slightly slower for TGS where Cu(2+) ions are in the interstitial position. The ordinary Raman processes do not contribute to the radical relaxation which relaxes via the local phonon mode. The local mode lies within the acoustic phonon band for radicals in TGS but within the optical phonon range in (NH4)(2)Zn(SO4)2 ⋅ 6H2O. In the latter the cross-relaxation was considered. A lack of phonons around the radical molecules suggested a local crystal amorphisation produced by x- or γ-rays.
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Affiliation(s)
- S K Hoffmann
- Institute of Molecular Physics, Polish Academy of Sciences, Smoluchowskiego 17, PL-60179 Poznan, Poland
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37
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Sato H, Kathirvelu V, Fielding A, Blinco JP, Micallef AS, Bottle SE, Eaton SS, Eaton GR. Impact of molecular size on electron spin relaxation rates of nitroxyl radicals in glassy solvents between 100 and 300 K. Mol Phys 2010. [DOI: 10.1080/00268970701724966] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022]
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38
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Scanned-probe detection of electron spin resonance from a nitroxide spin probe. Proc Natl Acad Sci U S A 2009; 106:22251-6. [PMID: 20018707 DOI: 10.1073/pnas.0908120106] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
We report an approach that extends the applicability of ultrasensitive force-gradient detection of magnetic resonance to samples with spin-lattice relaxation times (T (1)) as short as a single cantilever period. To demonstrate the generality of the approach, which relies on detecting either cantilever frequency or phase, we used it to detect electron spin resonance from a T (1) = 1 ms nitroxide spin probe in a thin film at 4.2 K and 0.6 T. By using a custom-fabricated cantilever with a 4 microm-diameter nickel tip, we achieve a magnetic resonance sensitivity of 400 Bohr magnetons in a 1 Hz bandwidth. A theory is presented that quantitatively predicts both the lineshape and the magnitude of the observed cantilever frequency shift as a function of field and cantilever-sample separation. Good agreement was found between nitroxide T (1) 's measured mechanically and inductively, indicating that the cantilever magnet is not an appreciable source of spin-lattice relaxation here. We suggest that the new approach has a number of advantages that make it well suited to push magnetic resonance detection and imaging of nitroxide spin labels in an individual macromolecule to single-spin sensitivity.
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Milikisyants S, Scarpelli F, Finiguerra MG, Ubbink M, Huber M. A pulsed EPR method to determine distances between paramagnetic centers with strong spectral anisotropy and radicals: the dead-time free RIDME sequence. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2009; 201:48-56. [PMID: 19758831 DOI: 10.1016/j.jmr.2009.08.008] [Citation(s) in RCA: 140] [Impact Index Per Article: 9.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/22/2009] [Revised: 07/15/2009] [Accepted: 08/07/2009] [Indexed: 05/09/2023]
Abstract
Methods to determine distances between paramagnetic metal centers and radicals are scarce. This is unfortunate because paramagnetic metal centers are frequent in biological systems and so far have not been employed much as distance markers. Successful pulse sequences that directly target the dipolar interactions cannot be applied to paramagnetic metal centers with fast relaxation rates and large g-anisotropy, if no echos can be detected and the excitation bandwidth is not sufficient to cover a sufficiently large part of the spectrum. The RIDME method Kulik et al. (2002) [20] circumvents this problem by making use of the T(1)-induced spin-flip of the transition-metal ion. Designed to measure distance between such a fast relaxing metal center and a radical, it suffers from a dead time problem. We show that this is severe because the anisotropy of the metal center broadens the dipolar curves, which therefore, only can be analyzed if the full curve is known. Here, we introduce five-pulse RIDME (5p-RIDME) that is intrinsically dead-time free. Proper functioning of the sequence is demonstrated on a nitroxide biradical. The distance between a low-spin Fe(III) center and a spin label in spin-labeled cytochrome f shows the complete dipolar trace of a transition-metal ion center and a spin label, yielding the distance expected from the structure.
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Affiliation(s)
- Sergey Milikisyants
- Department of Molecular Physics, Huygens Laboratory, Leiden University, 2300 RA Leiden, The Netherlands
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40
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Konovalova TA, Li S, Polyakov NE, Focsan AL, Dixon DA, Kispert LD. Measuring Ti(III)-carotenoid radical interspin distances in TiMCM-41 by pulsed EPR relaxation enhancement method. J Phys Chem B 2009; 113:8704-16. [PMID: 19492795 DOI: 10.1021/jp811369h] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/20/2023]
Abstract
Interspin distances between the Ti(3+) ions and the carotenoid radicals produced inside TiMCM-41 pores by photoinduced electron transfer from 7'-apo-7'-(4-carboxyphenyl)-beta-carotene (coordinated to Ti(3+)), canthaxanthin (formed as a random distribution of isomers), and beta-ionone (model for a short-chain polyene) to Ti(3+) framework sites were determined using the pulsed EPR relaxation enhancement method. To estimate the electron transfer distances, the temperature dependence of relaxation rates was analyzed in both siliceous and metal-substituted siliceous materials. The phase memory times, T(M), of the carotenoid radicals were determined from the best fits of two-pulse ESEEM curves. The spin-lattice relaxation times, T(1), of the Ti(3+) ion were obtained from the inversion recovery experiment with echo detection on a logarithmic time scale in the temperature range of 10-150 K. The relaxation enhancement for the carotenoid radicals in TiMCM-41 as compared to that in MCM-41 is consistent with an interaction between the radical and the fast relaxing Ti(3+) ion. For canthaxanthin and beta-ionone, a dramatic effect on the carotenoid relaxation rate, 1/T(M), occurs at 125 and 40 K, respectively, whereas for carboxy-beta-carotene 1/T(M) increases monotonically with increasing temperature. The interspin distances for canthaxanthin and beta-ionone were estimated from the 1/T(M) - 1/T(M0) difference, which corresponds to the Ti(3+) contribution at the temperature where the maximum enhancement in the relaxation rate occurs. Determination of the interspin distances is based on calculations of the dipolar interaction, taking into consideration the unpaired spin density distribution along the 20-carbon polyene chain, which makes it possible to obtain a fit over a wider temperature interval. A distribution of the interspin distances between the carotenoid radical and the Ti(3+) ion was obtained with the best fit at approximately 10 A for canthaxanthin and beta-ionone and approximately 9 A for 7'-apo-7'-(4-carboxyphenyl)-beta-carotene with an estimated error of +/-3 A. The interspin distances do not depend on 1/T(M) - 1/T(M0) for carboxy-beta-carotene which shows no prominent peak in the relaxation rate over the temperature range measured.
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Kathirvelu V, Sato H, Eaton SS, Eaton GR. Electron spin relaxation rates for semiquinones between 25 and 295K in glass-forming solvents. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2009; 198:111-120. [PMID: 19223213 PMCID: PMC2757793 DOI: 10.1016/j.jmr.2009.01.026] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/16/2008] [Revised: 01/13/2009] [Accepted: 01/22/2009] [Indexed: 05/27/2023]
Abstract
Electron spin lattice relaxation rates for five semiquinones (2,5-di-t-butyl-1,4-benzosemiquinone, 2,5-di-t-amyl-1,4-benzosemiquinone, 2,5-di-phenyl-1,4-benzosemiquinone, 2,6-di-t-butyl-1,4-benzosemiquinone, tetrahydroxy-1,4-benzosemiquione) were studied by long-pulse saturation recovery EPR in 1:4 glycerol:ethanol, 1:1 glycerol:ethanol, and triethanolamine between 25 and 295K. Although the dominant process changes with temperature, relaxation rates vary smoothly with temperature, even near the glass transition temperatures, and could be modeled as the sum of contributions that have the temperature dependence that is predicted for the direct, Raman, local mode and tumbling-dependent processes. At 85K, which is in a temperature range where the Raman process dominates, relaxation rates along the g(xx) (g approximately 2.006) and g(yy) (g approximately 2.005) axes are about 2.7-1.5 times faster than along the g(zz) axis (g=2.0023). In highly viscous triethanolamine, contributions from tumbling-dependent processes are negligible. At temperatures above 100K relaxation rates in triethanolamine are unchanged between X-band (9.5GHz) and Q-band (34GHz), so the process that dominates in this temperature interval was assigned as a local mode rather than a thermally activated process. Because the largest proton hyperfine couplings are only 2.2G, spin rotation makes a larger contribution than tumbling-dependent modulation of hyperfine anisotropy. Since g anisotropy is small, tumbling-dependent modulation of g anisotropy makes a smaller contribution than spin rotation at X-band. Although there was negligible impact of methyl rotation on T(1), rotation of t-butyl or t-amyl methyl groups enhances spin echo dephasing between 85 and 150K.
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Affiliation(s)
| | | | - Sandra S. Eaton
- Corresponding author: Professor Sandra S. Eaton, Department of Chemistry and Biochemistry, University of Denver Denver, CO 80208, 303-871-3102, Fax: 303-871-2254,
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Kathirvelu V, Eaton GR, Eaton SS. Impact of Chlorine Substitution on Spin Lattice Relaxation of Triarylmethyl and 1,4-Benzosemiquinone Radicals in Glass-forming Solvents between 25 and 295 K. APPLIED MAGNETIC RESONANCE 2009; 37:649. [PMID: 20126423 PMCID: PMC2814433 DOI: 10.1007/s00723-009-0086-3] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/19/2023]
Abstract
Spin-lattice relaxation rates measured by long-pulse saturation recovery in glassy solvents for chlorinated aromatic radicals: perchlorotriphenylmethyl radical, 2,5-dichloro-3,6-dihydroxy-1,4-benzosemiquinone, and tetrachloro-1,4-benzosemiquinone, were compared with relaxation rates for non-chlorinated analogs. The impact of the quadrupolar chlorines is small, and less than the effects of changing the rigidity of the glass. The temperature dependence of relaxation rates below the glass transition temperature could be modeled as the sum of contributions from the direct, Raman, and local mode processes.
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Affiliation(s)
- Velavan Kathirvelu
- Department of Chemistry and Biochemistry, University of Denver, Denver, CO 80208
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Jäger H, Koch A, Maus V, Spiess HW, Jeschke G. Relaxation-based distance measurements between a nitroxide and a lanthanide spin label. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2008; 194:254-263. [PMID: 18674941 DOI: 10.1016/j.jmr.2008.07.012] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/08/2008] [Revised: 07/15/2008] [Accepted: 07/15/2008] [Indexed: 05/26/2023]
Abstract
Distance measurements by electron paramagnetic resonance techniques between labels attached to biomacromolecules provide structural information on systems that cannot be crystallized or are too large to be characterized by NMR methods. However, existing techniques are limited in their distance range and sensitivity. It is anticipated by theoretical considerations that these limits could be extended by measuring the enhancement of longitudinal relaxation of a nitroxide label due to a lanthanide complex label at cryogenic temperatures. The relaxivity of the dysprosium complex with the macrocyclic ligand DOTA can be determined without direct measurements of longitudinal relaxation rates of the lanthanide and without recourse to model compounds with well defined distance by analyzing the dependence of relaxation enhancement on either temperature or concentration in homogeneous glassy frozen solutions. Relaxivities determined by the two calibration techniques are in satisfying agreement with each other. Error sources for both techniques are examined. A distance of about 2.7 nm is measured in a model compound of the type nitroxide-spacer-lanthanide complex and is found in good agreement with the distance in a modeled structure. Theoretical considerations suggest that an increase of the upper distance limit requires measurements at lower fields and temperatures.
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Affiliation(s)
- H Jäger
- Max Planck Institute for Polymer Research, Mainz, Germany
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Sato H, Kathirvelu V, Spagnol G, Rajca S, Rajca A, Eaton SS, Eaton GR. Impact of electron-electron spin interaction on electron spin relaxation of nitroxide diradicals and tetraradical in glassy solvents between 10 and 300 k. J Phys Chem B 2008; 112:2818-28. [PMID: 18284225 PMCID: PMC2731549 DOI: 10.1021/jp073600u] [Citation(s) in RCA: 69] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
To determine the impact of electron-electron spin-spin interactions on electron spin relaxation rates, 1/T1 and 1/Tm were measured for nitroxide monoradical, diradical, and tetraradical derivatives of 1,3-alternate calix[4]arenes, for two pegylated high-spin nitroxide diradicals, and for an azine-linked nitroxide diradical. The synthesis and characterization by SQUID (superconducting quantum interference device) magnetometry of one of the high-spin diradicals, in which nitroxides are conformationally constrained to be coplanar with the m-phenylene unit, is reported. The interspin distances ranged from about 5-9 A, and the magnitude of the exchange interaction ranged from >150 to >0.1 K. 1/T1 and 1/Tm were measured by long-pulse saturation recovery, three-pulse inversion recovery, and two-pulse echo decay at X-band (9.5 GHz) and Q-band (35 GHz). For a diradical with interspin distance about 9 A, relaxation rates were only slightly faster than for a monoradical with analogous structure. For interspin distances of about 5-6 A, relaxation rates in glassy solvents up to 300 K increased in the order monoradical < diradical < tetraradical. Modulation of electron-electron interaction enhanced relaxation via the direct, Raman, and local mode processes. The largest differences in 1/T1 were observed below 10 K, where the direct process dominates. For the three diradicals with comparable magnitude of dipolar interaction, 1/Tm and 1/T1 were faster for the molecules with more flexible structures. Relaxation rates were faster in the less rigid low-polarity sucrose octaacetate glass than in the more rigid 4:1 toluene/chloroform or in hydrogen-bonded glycerol glasses, which highlights the impact of motion on relaxation.
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Affiliation(s)
- Hideo Sato
- Department of Chemistry and Biochemistry, 2101 East Wesley Avenue, University of Denver, Denver, CO 80208-2436, USA
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Fielding AJ, Usselman RJ, Watmough N, Simkovic M, Frerman FE, Eaton GR, Eaton SS. Electron spin relaxation enhancement measurements of interspin distances in human, porcine, and Rhodobacter electron transfer flavoprotein-ubiquinone oxidoreductase (ETF-QO). JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2008; 190:222-32. [PMID: 18037314 PMCID: PMC2262937 DOI: 10.1016/j.jmr.2007.11.002] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/03/2007] [Revised: 10/20/2007] [Accepted: 11/02/2007] [Indexed: 05/25/2023]
Abstract
Electron transfer flavoprotein-ubiquinone oxidoreductase (ETF-QO) is a membrane-bound electron transfer protein that links primary flavoprotein dehydrogenases with the main respiratory chain. Human, porcine, and Rhodobacter sphaeroides ETF-QO each contain a single [4Fe-4S](2+,1+) cluster and one equivalent of FAD, which are diamagnetic in the isolated enzyme and become paramagnetic on reduction with the enzymatic electron donor or with dithionite. The anionic flavin semiquinone can be reduced further to diamagnetic hydroquinone. The redox potentials for the three redox couples are so similar that it is not possible to poise the proteins in a state where both the [4Fe-4S](+) cluster and the flavoquinone are fully in the paramagnetic form. Inversion recovery was used to measure the electron spin-lattice relaxation rates for the [4Fe-4S](+) between 8 and 18K and for semiquinone between 25 and 65K. At higher temperatures the spin-lattice relaxation rates for the [4Fe-4S](+) were calculated from the temperature-dependent contributions to the continuous wave linewidths. Although mixtures of the redox states are present, it was possible to analyze the enhancement of the electron spin relaxation of the FAD semiquinone signal due to dipolar interaction with the more rapidly relaxing [4Fe-4S](+) and obtain point-dipole interspin distances of 18.6+/-1A for the three proteins. The point-dipole distances are within experimental uncertainty of the value calculated based on the crystal structure of porcine ETF-QO when spin delocalization is taken into account. The results demonstrate that electron spin relaxation enhancement can be used to measure distances in redox poised proteins even when several redox states are present.
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Affiliation(s)
- Alistair J. Fielding
- Department of Chemistry and Biochemistry, University of Denver, Denver, CO 80208
| | - Robert J. Usselman
- Department of Chemistry and Biochemistry, University of Denver, Denver, CO 80208
| | - Nicholas Watmough
- Center for Metalloprotein Spectroscopy and Biology and School of Biological Sciences, University of East Anglia, Norwich, NR4 7TJ
| | - Martin Simkovic
- Department of Pediatrics, University of Colorado School of Medicine, Denver, CO 80262
| | - Frank E. Frerman
- Department of Pediatrics, University of Colorado School of Medicine, Denver, CO 80262
| | - Gareth R. Eaton
- Department of Chemistry and Biochemistry, University of Denver, Denver, CO 80208
| | - Sandra S. Eaton
- Department of Chemistry and Biochemistry, University of Denver, Denver, CO 80208
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Usselman RJ, Fielding AJ, Frerman FE, Watmough NJ, Eaton GR, Eaton SS. Impact of mutations on the midpoint potential of the [4Fe-4S]+1,+2 cluster and on catalytic activity in electron transfer flavoprotein-ubiquinone oxidoreductase (ETF-QO). Biochemistry 2007; 47:92-100. [PMID: 18069858 DOI: 10.1021/bi701859s] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Electron-transfer flavoprotein-ubiquinone oxidoreductase (ETF-QO) is an iron-sulfur flavoprotein that accepts electrons from electron-transfer flavoprotein (ETF) and reduces ubiquinone from the Q-pool. ETF-QO contains a single [4Fe-4S]2+,1+ cluster and one equivalent of FAD, which are diamagnetic in the isolated oxidized enzyme and can be reduced to paramagnetic forms by enzymatic donors or dithionite. Mutations were introduced by site-directed mutagenesis of amino acids in the vicinity of the iron-sulfur cluster of Rhodobacter sphaeroides ETF-QO. Y501 and T525 are equivalent to Y533 and T558 in the porcine ETF-QO. In the porcine protein, these residues are within hydrogen-bonding distance of the Sgamma of the cysteine ligands to the iron-sulfur cluster. Y501F, T525A, and Y501F/T525A substitutions were made to determine the effects on midpoint potential, activity, and EPR spectral properties of the cluster. The integrity of the mutated proteins was confirmed by optical spectra, EPR g-values, and spin-lattice relaxation rates, and the cluster to flavin point-dipole distance was determined by relaxation enhancement. Potentiometric titrations were monitored by changes in the CW EPR signals of the cluster and semiquinone. Single mutations decreased the midpoint potentials of the iron-sulfur cluster from +37 mV for wild type to -60 mV for Y501F and T525A and to -128 mV for Y501F/T525A. Lowering the midpoint potential resulted in a decrease in steady-state ubiquinone reductase activity and in ETF semiquinone disproportionation. The decrease in activity demonstrates that reduction of the iron-sulfur cluster is required for activity. There was no detectable effect of the mutations on the flavin midpoint potentials.
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Affiliation(s)
- Robert J Usselman
- Department of Chemistry and Biochemistry, University of Denver, Denver, Colorado 80208, USA
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Fielding AJ, Fox S, Millhauser GL, Chattopadhyay M, Kroneck PM, Fritz G, Eaton GR, Eaton SS. Electron spin relaxation of copper(II) complexes in glassy solution between 10 and 120 K. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2006; 179:92-104. [PMID: 16343958 PMCID: PMC2919208 DOI: 10.1016/j.jmr.2005.11.011] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/17/2005] [Revised: 11/17/2005] [Accepted: 11/18/2005] [Indexed: 05/05/2023]
Abstract
The temperature dependence, between 10 and 120 K, of electron spin-lattice relaxation at X-band was analyzed for a series of eight pyrrolate-imine complexes and for ten other copper(II) complexes with varying ligands and geometry including copper-containing prion octarepeat domain and S100 type proteins. The geometry of the CuN4 coordination sphere for pyrrolate-imine complexes with R=H, methyl, n-butyl, diphenylmethyl, benzyl, 2-adamantyl, 1-adamantyl, and tert-butyl has been shown to range from planar to pseudo-tetrahedral. The fit to the recovery curves was better for a distribution of values of T1 than for a single time constant. Distributions of relaxation times may be characteristic of Cu(II) in glassy solution. Long-pulse saturation recovery and inversion recovery measurements were performed. The temperature dependence of spin-lattice relaxation rates was analyzed in terms of contributions from the direct process, the Raman process, and local modes. It was necessary to include more than one process to fit the experimental data. There was a small contribution from the direct process at low temperature. The Raman process was the dominant contribution to relaxation between about 20 and 60 K. Debye temperatures were between 80 and 120 K. For samples with similar Debye temperatures the coefficient of the Raman process tended to increase as gz increased, as expected if modulation of spin-orbit coupling is a major factor in relaxation rates. Above about 60 K local modes with energies in the range of 260-360 K (180-250 cm-1) dominated the relaxation. For molecules with similar geometry, relaxation rates were faster for more flexible molecules than for more rigid ones. Relaxation rates for the copper protein samples were similar to rates for small molecules with comparable coordination spheres. At each temperature studied the range of relaxation rates was less than an order of magnitude. The spread was smaller between 20 and 60 K where the Raman process dominates, than at higher temperatures where local modes dominate the relaxation. Spin echo dephasing time constants, Tm, were calculated from two-pulse spin echo decays. Near 10 K Tm was dominated by proton spins in the surroundings. As temperature was increased motion and spin-lattice relaxation made increasing contributions to Tm. Near 100 K spin-lattice relaxation dominated Tm.
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Affiliation(s)
- Alistair J. Fielding
- Department of Chemistry and Biochemistry, University of Denver, Denver, CO 80208, USA
| | - Stephen Fox
- Department of Chemistry, University of Louisiana at Monroe, Monroe, LA 71219-0530, USA
| | - Glenn L. Millhauser
- Department of Chemistry and Biochemistry, University of California, Santa Cruz, CA 95064, USA
| | - Madhuri Chattopadhyay
- Department of Chemistry and Biochemistry, University of California, Santa Cruz, CA 95064, USA
| | | | - Günter Fritz
- Fachbereich Biologie, Universitat Konstanz, 78457 Konstanz, Germany
| | - Gareth R. Eaton
- Department of Chemistry and Biochemistry, University of Denver, Denver, CO 80208, USA
| | - Sandra S. Eaton
- Department of Chemistry and Biochemistry, University of Denver, Denver, CO 80208, USA
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48
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Direct evidence for the glass-crystalline transformation in solid ethanol by means of a nitroxide spin probe. Chem Phys Lett 2006. [DOI: 10.1016/j.cplett.2005.11.055] [Citation(s) in RCA: 16] [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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Nielsen RD, Canaan S, Gladden JA, Gelb MH, Mailer C, Robinson BH. Comparing continuous wave progressive saturation EPR and time domain saturation recovery EPR over the entire motional range of nitroxide spin labels. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2004; 169:129-163. [PMID: 15183364 DOI: 10.1016/j.jmr.2004.04.010] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/30/2003] [Revised: 04/08/2004] [Indexed: 05/24/2023]
Abstract
The measurement of spin-lattice relaxation rates from spin labels, such as nitroxides, in the presence and absence of spin relaxants provides information that is useful for determining biomolecular properties such as nucleic acid dynamics and the interaction of proteins with membranes. We compare X-band continuous wave (CW) and pulsed or time domain (TD) EPR methods for obtaining spin-lattice relaxation rates of spin labels across the entire range of rotational motion to which relaxation rates are sensitive. Model nitroxides and spin-labeled biological species are used to illustrate the potential complications that arise in extracting relaxation data under conditions typical to biological experiments. The effect of super hyperfine (SHF) structure is investigated for both CW and TD spectra. First and second harmonic absorption and dispersion CW spectra of the nitroxide spin label, TEMPOL, are all fit simultaneously to a model of SHF structure over a range of microwave amplitudes. The CW spectra are novel because all harmonics and microwave phases were acquired simultaneously using our homebuilt CW/TD spectrometer. The effect of the SHF structure on the pulsed free induction decay (FID) and pulsed saturation recovery spectrum is shown for both protonated and deuterated TEMPOL. We present novel pulsed saturation recovery measurements on biological molecules, including spin-lattice relaxation rates of spin-labeled proteins and spin-labeled double-stranded DNA. The impact of structure and dynamics on relaxation rates are discussed in the context of each of these examples. Collisional relaxation rates with oxygen and transition metal paramagnetic relaxants are extracted using both continuous wave and time domain methods. The extent of the errors inherent in the CW method and the advantages of pulsed methods for unambiguously measuring collisional relaxation rates are discussed. Spin-lattice relaxation rates, determined by both CW and pulsed methods, are used to determine the electrostatic potential on the surface of a protein.
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Affiliation(s)
- Robert D Nielsen
- Department of Chemistry, University of Washington, Seattle, WA 98195, USA
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50
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Vugman NV, de Araújo MB, Pinhal NM, Magon CJ, da Costa Filho AJ. Electron spin-relaxation via vibronic level of nickel (I) and nickel (III) cyanide complexes in NaCl single crystals. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2004; 168:132-136. [PMID: 15082258 DOI: 10.1016/j.jmr.2004.02.005] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/12/2003] [Revised: 02/05/2004] [Indexed: 05/24/2023]
Abstract
Electron spin-lattice relaxation rates for the low spin [Ni(CN)(4)](1-) and [Ni(CN)(4)](3-) complexes in NaCl host lattice were measured by the inversion recovery technique in the temperature range 7-50K. The data for both paramagnetic species fit very well to a relaxation process involving localized anharmonic vibration modes, also responsible for the g-tensor temperature dependence.
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Affiliation(s)
- N V Vugman
- Instituto de Física-Universidade Federal do Rio de Janeiro, Rio de Janeiro, RJ 21910-240, Brazil.
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