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Dubroca T, Wang X, Mentink-Vigier F, Trociewitz B, Starck M, Parker D, Sherwin MS, Hill S, Krzystek J. Terahertz EPR spectroscopy using a 36-tesla high-homogeneity series-connected hybrid magnet. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2023; 353:107480. [PMID: 37331305 DOI: 10.1016/j.jmr.2023.107480] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/08/2023] [Revised: 04/24/2023] [Accepted: 05/13/2023] [Indexed: 06/20/2023]
Abstract
Electron Paramagnetic Resonance (EPR) is a powerful technique to study materials and biological samples on an atomic scale. High-field EPR in particular enables extracting very small g-anisotropies in organic radicals and half-filled 3d and 4f metal ions such as MnII (3d5) or GdIII (4f7), and resolving EPR signals from unpaired spins with very close g-values, both of which provide high-resolution details of the local atomic environment. Before the recent commissioning of the high-homogeneity Series Connected Hybrid magnet (SCH, superconducting + resistive) at the National High Magnetic Field Laboratory (NHMFL), the highest-field, high-resolution EPR spectrometer available was limited to 25 T using a purely resistive "Keck" magnet at the NHMFL. Herein, we report the first EPR experiments performed using the SCH magnet capable of reaching the field of 36 T, corresponding to an EPR frequency of 1 THz for g = 2. The magnet's intrinsic homogeneity (25 ppm, that is 0.9 mT at 36 T over 1 cm diameter, 1 cm length cylinder) was previously established by NMR. We characterized the magnet's temporal stability (5 ppm, which is 0.2 mT at 36 T over one-minute, the typical acquisition time) using 2,2-diphenyl-1-picrylhydrazyl (DPPH). This high resolution enables resolving the weak g-anisotropy of 1,3-bis(diphenylene)-2-phenylallyl (BDPA), Δg = 2.5 × 10-4 obtained from measurements at 932 GHz and 33 T. Subsequently, we recorded EPR spectra at multiple frequencies for two GdIII complexes with potential applications as spin labels. We demonstrated a significant reduction in line broadening in Gd[DTPA], attributed to second order zero field splitting, and a resolution enhancement of g-tensor anisotropy for Gd[sTPATCN]-SL.
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Affiliation(s)
- Thierry Dubroca
- National High Magnetic Field Laboratory, Florida State University, Tallahassee, FL 32310, USA.
| | - Xiaoling Wang
- National High Magnetic Field Laboratory, Florida State University, Tallahassee, FL 32310, USA; Center for Molecular Magnetic Quantum Materials, University of Florida, Gainesville, FL 32611, USA
| | - Frédéric Mentink-Vigier
- National High Magnetic Field Laboratory, Florida State University, Tallahassee, FL 32310, USA
| | - Bianca Trociewitz
- National High Magnetic Field Laboratory, Florida State University, Tallahassee, FL 32310, USA
| | - Matthieu Starck
- Department of Chemistry, University of Durham, Durham DH13LE, UK
| | - David Parker
- Department of Chemistry, University of Durham, Durham DH13LE, UK
| | - Mark S Sherwin
- Department of Physics, University of California Santa Barbara, CA 93106, USA
| | - Stephen Hill
- National High Magnetic Field Laboratory, Florida State University, Tallahassee, FL 32310, USA; Center for Molecular Magnetic Quantum Materials, University of Florida, Gainesville, FL 32611, USA; Department of Physics, Florida State University, Tallahassee FL 32306, USA
| | - J Krzystek
- National High Magnetic Field Laboratory, Florida State University, Tallahassee, FL 32310, USA.
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Hagen WR. Conversion of a Single-Frequency X-Band EPR Spectrometer into a Broadband Multi-Frequency 0.1-18 GHz Instrument for Analysis of Complex Molecular Spin Hamiltonians. Molecules 2023; 28:5281. [PMID: 37446944 DOI: 10.3390/molecules28135281] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/13/2023] [Revised: 07/01/2023] [Accepted: 07/05/2023] [Indexed: 07/15/2023] Open
Abstract
A broadband EPR spectrometer is an instrument that can be tuned to many microwave frequencies over several octaves. Its purpose is the collection of multi-frequency data, whose global analysis affords interpretation of complex spectra by means of deconvolution of frequency-dependent and frequency-independent interaction terms. Such spectra are commonly encountered, for example, from transition-metal complexes and metalloproteins. In a series of previous papers, I have described the development of broadband EPR spectrometers around a vector network analyzer. The present study reports on my endeavor to start from an existing X-band spectrometer and to reversibly re-build it into a broadband machine, in a quest to drastically reduce design effort, building costs, and operational complexity, thus bringing broadband EPR within easy reach of a wide range of researchers.
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Affiliation(s)
- Wilfred R Hagen
- Department of Biotechnology, Delft University of Technology, Building 58, Van der Maasweg 9, 2629 HZ Delft, The Netherlands
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3
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Gibbs C, Fedoretz-Maxwell BP, MacNeil GA, Walsby CJ, Warren JJ. Proximal Methionine Amino Acid Residue Affects the Properties of Redox-Active Tryptophan in an Artificial Model Protein. ACS OMEGA 2023; 8:19798-19806. [PMID: 37305310 PMCID: PMC10249128 DOI: 10.1021/acsomega.3c01589] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 03/08/2023] [Accepted: 05/11/2023] [Indexed: 06/13/2023]
Abstract
Redox-active amino acid residues are at the heart of biological electron-transfer reactions. They play important roles in natural protein functions and are implicated in disease states (e.g., oxidative-stress-associated disorders). Tryptophan (Trp) is one such redox-active amino acid residue, and it has long been known to serve a functional role in proteins. Broadly speaking, there is still much to learn about the local features that make some Trp redox active and others inactive. Herein, we describe a new protein model system where we investigate how a methionine (Met) residue proximal to a redox-active Trp affects its reactivity and spectroscopy. We use an artificial variant of azurin from Pseudomonas aeruginosa to produce these models. We employ a series of UV-visible spectroscopy, electrochemistry, electron paramagnetic resonance, and density functional theory experiments to demonstrate the effect that placing Met near Trp radicals has in the context of redox proteins. The introduction of Met proximal to Trp lowers its reduction potential by ca. 30 mV and causes clear shifts in the optical spectra of the corresponding radicals. While the effect may be small, it is significant enough to be a way for natural systems to tune Trp reactivity.
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Ngueumaleu Y, Deutchoua ADD, Hanga SSP, Liendji RW, Dedzo GK, Ngameni E. Probing the reactivity of 2,2-diphenyl-1-picrylhydrazyl (DPPH) with metal cations and acids in acetonitrile by electrochemistry and UV-Vis spectroscopy. Phys Chem Chem Phys 2023; 25:5282-5290. [PMID: 36723192 DOI: 10.1039/d2cp05296b] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023]
Abstract
2,2-Diphenyl-1-picrylhydrazyl (DPPH) is certainly one of the most widely used free radicals in several applications, because of its high stability. Unfortunately, there are few works dealing with its stability in the presence of many chemical species that coexist during chemical processes. In this work, the stability of DPPH was investigated by electrochemistry and UV-Vis spectroscopy in the presence of some metal cations (Cu2+ and Zn2+) and acids (HClO4 and HNO3) in acetonitrile. In the presence of Cu2+, DPPH was oxidized to DPPH+ with the formation of an equivalent amount of Cu+. With Zn2+, DPPH undergoes a slow disproportionation with the formation of Zn(DPPH)+ and DPPH+, certainly favored by the acidity of the metal cation. This hypothesis was subsequently confirmed by studying the stability of DPPH in the presence of HClO4. This acid of appreciable strength in acetonitrile (pKa = 1.83) causes a fast disproportionation of DPPH with the formation of DPPH-H and DPPH+. This mechanism was confirmed both by UV-Vis spectroscopy and by electrochemistry, with a stoichiometry corresponding to 2 equivalents of DPPH for about 1 equivalent of HClO4. In the presence of nitric acid, which is about 107 weaker than HClO4 in acetonitrile, the disproportionation was much slower. These preliminary results are proof that many chemical species are likely to react with DPPH and indirectly induce sources of bias during its application, especially when evaluating antioxidant properties.
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Affiliation(s)
- Yannick Ngueumaleu
- Laboratory of Analytical Chemistry, Faculty of Sciences, University of Yaoundé I, B. P. 812 Yaoundé, Cameroon.
| | - Arlette Danelle Djitieu Deutchoua
- Laboratory of Analytical Chemistry, Faculty of Sciences, University of Yaoundé I, B. P. 812 Yaoundé, Cameroon. .,Department of Transformation and Quality Control of Fisheries Products, Institute of Fisheries and Aquatic Sciences at Yabassi, University of Douala, B. P. 7236 Douala, Cameroon
| | | | - Rossel Wendji Liendji
- Laboratory of Analytical Chemistry, Faculty of Sciences, University of Yaoundé I, B. P. 812 Yaoundé, Cameroon.
| | - Gustave Kenne Dedzo
- Laboratory of Analytical Chemistry, Faculty of Sciences, University of Yaoundé I, B. P. 812 Yaoundé, Cameroon.
| | - Emmanuel Ngameni
- Laboratory of Analytical Chemistry, Faculty of Sciences, University of Yaoundé I, B. P. 812 Yaoundé, Cameroon.
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5
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Krinichnyi VI, Yudanova EI. Magnetic-field-controlled charge transport in organic polymer composites. Chem Phys Lett 2021. [DOI: 10.1016/j.cplett.2021.138787] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/21/2022]
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6
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Marano S, Minnelli C, Ripani L, Marcaccio M, Laudadio E, Mobbili G, Amici A, Armeni T, Stipa P. Insights into the Antioxidant Mechanism of Newly Synthesized Benzoxazinic Nitrones: In Vitro and In Silico Studies with DPPH Model Radical. Antioxidants (Basel) 2021; 10:antiox10081224. [PMID: 34439472 PMCID: PMC8388956 DOI: 10.3390/antiox10081224] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/28/2021] [Revised: 07/21/2021] [Accepted: 07/27/2021] [Indexed: 11/16/2022] Open
Abstract
Synthetic nitrone spin-traps are being explored as therapeutic agents for the treatment of a wide range of oxidative stress-related pathologies, including but not limited to stroke, cancer, cardiovascular, and neurodegenerative diseases. In this context, increasing efforts are currently being made to the design and synthesis of new nitrone-based compounds with enhanced efficacy. The most researched nitrones are surely the ones related to α-phenyl-tert-butylnitrone (PBN) and 5,5-dimethyl-1-pyrroline N-oxide (DMPO) derivatives, which have shown to possess potent biological activity in many experimental animal models. However, more recently, nitrones with a benzoxazinic structure (3-aryl-2H-benzo[1,4]oxazin-N-oxides) have been demonstrated to have superior antioxidant activity compared to PBN. In this study, two new benzoxazinic nitrones bearing an electron-withdrawing methoxycarbonyl group on the benzo moiety (in para and meta positions respect to the nitronyl function) were synthesized. Their in vitro antioxidant activity was evaluated by two cellular-based assays (inhibition of AAPH-induced human erythrocyte hemolysis and cell death in human retinal pigmented epithelium (ARPE-19) cells) and a chemical approach by means of the α,α-diphenyl-β-picrylhydrazyl (DPPH) scavenging assay, using both electron paramagnetic resonance (EPR) spectroscopy and UV spectrophotometry. A computational approach was also used to investigate their potential primary mechanism of antioxidant action, as well as to rationalize the effect of functionalization on the nitrones reactivity toward DPPH, chosen as model radical in this study. Further insights were also gathered by exploring the nitrone electrochemical properties via cyclic voltammetry and by studying their kinetic behavior by means of EPR spectroscopy. Results showed that the introduction of an electron-withdrawing group in the phenyl moiety in the para position significantly increased the antioxidant capacity of benzoxazinic nitrones both in cell and cell-free systems. From the mechanistic point of view, the calculated results closely matched the experimental findings, strongly suggesting that the H-atom transfer (HAT) is likely to be the primary mechanism in the DPPH quenching.
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Affiliation(s)
- Stefania Marano
- Dipartimento di Scienze e Ingegneria della Materia, dell’Ambiente ed Urbanistica (SIMAU), Università Politecnica delle Marche, via Brecce Bianche, 60131 Ancona, Italy; (S.M.); (E.L.)
| | - Cristina Minnelli
- Dipartimento di Scienze della Vita e dell’Ambiente (DISVA), Università Politecnica delle Marche, via Brecce Bianche, 60131 Ancona, Italy; (C.M.); (G.M.)
| | - Lorenzo Ripani
- Dipartimento di Chimica, Università di Bologna, via Selmi 2, 40126 Bologna, Italy; (L.R.); (M.M.)
| | - Massimo Marcaccio
- Dipartimento di Chimica, Università di Bologna, via Selmi 2, 40126 Bologna, Italy; (L.R.); (M.M.)
| | - Emiliano Laudadio
- Dipartimento di Scienze e Ingegneria della Materia, dell’Ambiente ed Urbanistica (SIMAU), Università Politecnica delle Marche, via Brecce Bianche, 60131 Ancona, Italy; (S.M.); (E.L.)
| | - Giovanna Mobbili
- Dipartimento di Scienze della Vita e dell’Ambiente (DISVA), Università Politecnica delle Marche, via Brecce Bianche, 60131 Ancona, Italy; (C.M.); (G.M.)
| | - Adolfo Amici
- Dipartimento di Scienze Cliniche Specialistiche ed Odontostomatologiche-Sez. Biochimica, Biologia e Fisica, Università Politecnica delle Marche, 60131 Ancona, Italy; (A.A.); (T.A.)
| | - Tatiana Armeni
- Dipartimento di Scienze Cliniche Specialistiche ed Odontostomatologiche-Sez. Biochimica, Biologia e Fisica, Università Politecnica delle Marche, 60131 Ancona, Italy; (A.A.); (T.A.)
| | - Pierluigi Stipa
- Dipartimento di Scienze e Ingegneria della Materia, dell’Ambiente ed Urbanistica (SIMAU), Università Politecnica delle Marche, via Brecce Bianche, 60131 Ancona, Italy; (S.M.); (E.L.)
- Correspondence: ; Tel.: +39-071-2204409
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7
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Qi X, Xiao H, Han X, Wang Z, Xia D, Wang P, Li L. A broad range frequency measurement method for continuous and pulsed THz waves. THE REVIEW OF SCIENTIFIC INSTRUMENTS 2020; 91:014710. [PMID: 32012550 DOI: 10.1063/1.5120592] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/19/2019] [Accepted: 01/07/2020] [Indexed: 06/10/2023]
Abstract
This paper proposes a method to measure the frequency of terahertz (THz) waves based on the Zeeman effect and the high magnetic field technology with a wideband range from 60 GHz to 3 THz. As the frequency of THz waves absorbed by the sample is linear to the magnetic field in the Zeeman effect, the frequency can be measured by the magnetic field strength. A comparison study of THz frequency measurement was carried out in two magnet systems (a superconducting one and a pulsed one) to investigate the performance in two kinds of high magnetic fields. The experimental results of 60-700 GHz show that this method has high resolution (about 0.001%), excellent linearity, and good repeatability. Moreover, the proposed method can measure polychromatic signals simultaneously as well as the single pulse frequency in the order of tens of microseconds.
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Affiliation(s)
- Xin Qi
- Wuhan National High Magnetic Field Center, Huazhong University of Science and Technology, Wuhan 430074, China
| | - Houxiu Xiao
- Wuhan National High Magnetic Field Center, Huazhong University of Science and Technology, Wuhan 430074, China
| | - Xiaotao Han
- Wuhan National High Magnetic Field Center, Huazhong University of Science and Technology, Wuhan 430074, China
| | - Zhenxing Wang
- Wuhan National High Magnetic Field Center, Huazhong University of Science and Technology, Wuhan 430074, China
| | - Donghui Xia
- School of Electrical and Electronic Engineering, Huazhong University of Science and Technology, Wuhan 430074, China
| | - Pengbo Wang
- Wuhan National High Magnetic Field Center, Huazhong University of Science and Technology, Wuhan 430074, China
| | - Liang Li
- Wuhan National High Magnetic Field Center, Huazhong University of Science and Technology, Wuhan 430074, China
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8
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Lenz S, Hunger D, van Slageren J. Strong coupling between resonators and spin ensembles in the presence of exchange couplings. Chem Commun (Camb) 2020; 56:12837-12840. [DOI: 10.1039/d0cc04841k] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Exchange–dependent strong coupling between DPPH radical spins and 3D microwave cavity coupling up to room temperature.
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Affiliation(s)
- Samuel Lenz
- Institute of Physical Chemistry and Center for Integrated Quantum Science and Technology IQST
- University of Stuttgart
- Stuttgart 70569
- Germany
| | - David Hunger
- Institute of Physical Chemistry and Center for Integrated Quantum Science and Technology IQST
- University of Stuttgart
- Stuttgart 70569
- Germany
| | - Joris van Slageren
- Institute of Physical Chemistry and Center for Integrated Quantum Science and Technology IQST
- University of Stuttgart
- Stuttgart 70569
- Germany
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9
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Zhao S, Gao P, Miao D, Wu L, Qian Y, Chen S, Sharma VK, Jia H. Formation and Evolution of Solvent-Extracted and Nonextractable Environmentally Persistent Free Radicals in Fly Ash of Municipal Solid Waste Incinerators. ENVIRONMENTAL SCIENCE & TECHNOLOGY 2019; 53:10120-10130. [PMID: 31403286 DOI: 10.1021/acs.est.9b03453] [Citation(s) in RCA: 26] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/07/2023]
Abstract
Environmentally persistent free radicals (EPFRs) are emerging contaminants occurring in combustion-borne particulates and atmospheric particulate matter, but information on their formation and behavior on fly ash from municipal solid waste (MSW) incinerators is scarce. Here, we have found that MSW-associated fly ash samples contain an EPFR concentration of 3-10 × 1015 spins g-1, a line width (ΔHp-p) of ∼8.6 G, and a g-factor of 2.0032-2.0038. These EPFRs are proposed to be mixtures of carbon-centered and oxygen-centered free radicals. Fractionation of the fly ash-associated EPFRs into solvent-extracted and nonextractable radicals suggests that the solvent-extracted part accounts for ∼45-73% of the total amount of EPFRs. Spin densities of solvent-extracted EPFRs correlate positively with the concentrations of Fe, Cu, Mn, Ti, and Zn, whereas similar correlations are comparatively insignificant for nonextractable EPFRs. Under natural conditions, these two types of EPFRs exhibit different stabilization that solvent-extracted EPFRs are relatively unstable, whereas the nonextractable fraction possesses a long life span. Significant correlations between concentrations of solvent-extracted EPFRs and generation of hydroxyl and superoxide radicals are found. Overall, our results suggest that the fractionated solvent-extracted and nonextractable EPFRs may experience different formation and stabilization processes and health effects.
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Affiliation(s)
- Song Zhao
- College of Natural Resources and Environment; State Key Laboratory of Soil Erosion and Dryland Farming on Loess Plateau, Institute of Soil and Water Conservation , Northwest A & F University , Yangling 712100 , China
| | - Pin Gao
- College of Environmental Science and Engineering , Donghua University , Shanghai 201620 , China
| | - Duo Miao
- College of Natural Resources and Environment; State Key Laboratory of Soil Erosion and Dryland Farming on Loess Plateau, Institute of Soil and Water Conservation , Northwest A & F University , Yangling 712100 , China
| | - Lan Wu
- College of Natural Resources and Environment; State Key Laboratory of Soil Erosion and Dryland Farming on Loess Plateau, Institute of Soil and Water Conservation , Northwest A & F University , Yangling 712100 , China
| | - Yajie Qian
- College of Environmental Science and Engineering , Donghua University , Shanghai 201620 , China
| | - Shanping Chen
- Shanghai Environmental Sanitation Engineering Design Institute Co., Ltd. , Shanghai 200232 , China
| | - Virender K Sharma
- Program for the Environment and Sustainability, Department of Occupational and Environmental Health, School of Public Health , Texas A&M University , College Station , Texas 77843 , United States
| | - Hanzhong Jia
- College of Natural Resources and Environment; State Key Laboratory of Soil Erosion and Dryland Farming on Loess Plateau, Institute of Soil and Water Conservation , Northwest A & F University , Yangling 712100 , China
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10
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Matsumoto N, Itoh N. Measuring Number of Free Radicals and Evaluating the Purity of Di(phenyl)-(2,4,6-trinitrophenyl)iminoazanium [DPPH] Reagents by Effective Magnetic Moment Method. ANAL SCI 2018; 34:965-971. [PMID: 30101893 DOI: 10.2116/analsci.18p120] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
Abstract
Di(phenyl)-(2,4,6-trinitrophenyl)iminoazanium [DPPH] is widely used as a standard for measuring the number of free radicals. Here, we evaluated the number of free radicals of "DPPH" reagents from three manufacturers by effective magnetic moment method. Interestingly, the reagents from different manufacturers had varying temperature dependencies for both magnetic moment and g-value at low temperatures. As a result, the maximum relative difference among the three reagents on the number of free radicals per unit mass was 20%. Carbon hydrogen nitrogen (CHN) analyses, high-resolution EPR measurements, FT-IR measurement, and NMR measurement confirmed that a major component of only one among the three reagents was "pure" DPPH. The evaluated purity based on free radical content was 0.998 kg kg-1 with expanded uncertainty of 0.036 kg kg-1. The other two reagents were found to be contaminated by several % of benzene in the DPPH crystal structure.
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Affiliation(s)
- Nobuhiro Matsumoto
- National Metrology Institute of Japan (NMIJ), National Institute of Advanced Industrial Science and Technology (AIST)
| | - Nobuyasu Itoh
- National Metrology Institute of Japan (NMIJ), National Institute of Advanced Industrial Science and Technology (AIST)
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11
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Takahashi H, Okamoto T, Ishimura K, Hara S, Ohmichi E, Ohta H. Force-detected high-frequency electron spin resonance spectroscopy using magnet-mounted nanomembrane: Robust detection of thermal magnetization modulation. THE REVIEW OF SCIENTIFIC INSTRUMENTS 2018; 89:083905. [PMID: 30184643 DOI: 10.1063/1.5034529] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/12/2018] [Accepted: 07/29/2018] [Indexed: 06/08/2023]
Abstract
In this study, we report a conceptually novel broadband high-frequency electron spin resonance (HFESR) spectroscopic technique. In contrast to the ordinary force-detected electron spin resonance (ESR) technique, which detects the magnetization change due to the saturation effect, this method measures the magnetization change due to the change of the sample temperature at resonance. To demonstrate its principle, we developed a silicon nitride nanomembrane-based force-detected ESR spectrometer, which can be stably operated even at high magnetic fields. Test measurements were performed for samples with different spin relaxation times. We succeeded in obtaining a seamless ESR spectrum in magnetic fields of 15 T and frequencies of 636 GHz without significant spectral distortion. A high spin sensitivity of 1012 spins/G s was obtained, which was independent of the spin relaxation time. These results show that this technique can be used as a practical method in research fields where the HFESR technique is applicable.
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Affiliation(s)
- Hideyuki Takahashi
- Organization for Advanced and Integrated Research, Kobe University, 1-1, Rokkodai, Nada, Kobe 657-8501, Japan
| | - Tsubasa Okamoto
- Graduate School of Science, Kobe University, 1-1 Rokkodai-cho, Nada, Kobe 657-8501, Japan
| | - Kento Ishimura
- Graduate School of Science, Kobe University, 1-1 Rokkodai-cho, Nada, Kobe 657-8501, Japan
| | - Shigeo Hara
- Research Facility Center for Science and Technology, Kobe University, 1-1 Rokkodai-cho, Nada, Kobe 657-8501, Japan
| | - Eiji Ohmichi
- Graduate School of Science, Kobe University, 1-1 Rokkodai-cho, Nada, Kobe 657-8501, Japan
| | - Hitoshi Ohta
- Molecular Photoscience Research Center, Kobe University, 1-1 Rokkodai-cho, Nada, Kobe 657-8501, Japan
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Herb K, Tschaggelar R, Denninger G, Jeschke G. Double resonance calibration of g factor standards: Carbon fibers as a high precision standard. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2018; 289:100-106. [PMID: 29476927 DOI: 10.1016/j.jmr.2018.02.006] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/21/2017] [Revised: 02/08/2018] [Accepted: 02/10/2018] [Indexed: 06/08/2023]
Abstract
The g factor of paramagnetic defects in commercial high performance carbon fibers was determined by a double resonance experiment based on the Overhauser shift due to hyperfine coupled protons. Our carbon fibers exhibit a single, narrow and perfectly Lorentzian shaped ESR line and a g factor slightly higher than gfree with g=2.002644=gfree·(1+162ppm) with a relative uncertainty of 15ppm. This precisely known g factor and their inertness qualify them as a high precision g factor standard for general purposes. The double resonance experiment for calibration is applicable to other potential standards with a hyperfine interaction averaged by a process with very short correlation time.
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Affiliation(s)
- Konstantin Herb
- Laboratory of Physical Chemistry, ETH Zurich, Vladimir-Prelog-Weg 2, CH-8093 Zurich, Switzerland.
| | - Rene Tschaggelar
- Laboratory of Physical Chemistry, ETH Zurich, Vladimir-Prelog-Weg 2, CH-8093 Zurich, Switzerland.
| | - Gert Denninger
- 2. Physikalisches Institut, Universität Stuttgart, Pfaffenwaldring 57, D-70550 Stuttgart, Germany.
| | - Gunnar Jeschke
- Laboratory of Physical Chemistry, ETH Zurich, Vladimir-Prelog-Weg 2, CH-8093 Zurich, Switzerland.
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Vishtorskaya AA, Saverina EA, Pechennikov VM, Krylova IV, Lalov AV, Syroeshkin MA, Egorov MP, Jouikov VV. Assessing Ge-132 as an antioxidant in organic and water-containing media. J Organomet Chem 2018. [DOI: 10.1016/j.jorganchem.2018.01.004] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
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14
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Alkhorayef M, Mansour A, Sulieman A, Alnaaimi M, Alduaij M, Babikir E, Bradley D. Evaluation of dose uncertainty in radiation processing using EPR spectroscopy and butylated hydroxytoluene rods as dosimetry system. Radiat Phys Chem Oxf Engl 1993 2017. [DOI: 10.1016/j.radphyschem.2017.05.029] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
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15
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Ivanov MY, Nadolinny VA, Bagryanskaya EG, Grishin YA, Fedin MV, Veber SL. Bismuth germanate as a perspective material for dielectric resonators in EPR spectroscopy. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2016; 271:83-89. [PMID: 27569694 DOI: 10.1016/j.jmr.2016.08.009] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/18/2016] [Revised: 08/16/2016] [Accepted: 08/17/2016] [Indexed: 06/06/2023]
Abstract
High purity bismuth germanate (Bi4(GeO4)3, BGO) is proposed and implemented as an alternative material for dielectric EPR resonators. A significant improvement of the absolute sensitivity can be readily achieved by substituting the alumina insert (ring) by BGO-made one in commercially available X-band EPR probeheads. Four BGO dielectric inserts of 2, 3, 4 and 5mm inner diameter (ID) were made for comparison with standard 5mm inner diameter alumina insert. All inserts were introduced into commercial Bruker EPR resonator ER 4118X-MD-5W1, and their performance was investigated. The Q-values of empty resonators, B1 saturation curves and continuous wave EPR spectra of DPPH (2,2-diphenyl-1-picrylhydrazyl) were measured and analyzed in a temperature range 6-300K. BGO-made resonators were found superior in several important aspects. The background signals arising from BGO are much weaker compared to those of alumina at B=0-0.6T and T=6-300K; this is especially useful for measuring weak signals in the half-field region, as well as those near the central field. Moreover, mechanical properties of BGO allow easy fabrication of dielectric bodies having various shapes and sizes; in particular, small BGO resonators (e.g. ID=2 or 3mm) strongly enhance sensitivity for small samples due to increase of the filling factor. All these advantages have been also inspected in the pulse mode, proving that higher B1 fields and better filling factors can be achieved, contributing to the overall enhancement of the performance.
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Affiliation(s)
- Mikhail Y Ivanov
- International Tomography Center, SB RAS, Novosibirsk 630090, Russia; Novosibirsk State University, Novosibirsk 630090, Russia
| | | | - Elena G Bagryanskaya
- Novosibirsk State University, Novosibirsk 630090, Russia; N.N. Vorozhtsov Novosibirsk Institute of Organic Chemistry, SB RAS, Novosibirsk 630090, Russia
| | - Yuriy A Grishin
- Voevodsky Institute of Chemical Kinetics and Combustion, SB RAS, Novosibirsk 630090, Russia
| | - Matvey V Fedin
- International Tomography Center, SB RAS, Novosibirsk 630090, Russia; Novosibirsk State University, Novosibirsk 630090, Russia
| | - Sergey L Veber
- International Tomography Center, SB RAS, Novosibirsk 630090, Russia; Novosibirsk State University, Novosibirsk 630090, Russia.
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16
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Christian JH, Brogden DW, Bindra JK, Kinyon JS, van Tol J, Wang J, Berry JF, Dalal NS. Enhancing the Magnetic Anisotropy of Linear Cr(II) Chain Compounds Using Heavy Metal Substitutions. Inorg Chem 2016; 55:6376-83. [PMID: 26881994 DOI: 10.1021/acs.inorgchem.5b02545] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Magnetic properties of the series of three linear, trimetallic chain compounds Cr2Cr(dpa)4Cl2, 1, Mo2Cr(dpa)4Cl2, 2, and W2Cr(dpa)4Cl2, 3 (dpa = 2,2'-dipyridylamido), have been studied using variable-temperature dc and ac magnetometry and high-frequency EPR spectroscopy. All three compounds possess an S = 2 electronic ground state arising from the terminal Cr(2+) ion, which exhibits slow magnetic relaxation under an applied magnetic field, as evidenced by ac magnetic susceptibility and magnetization measurements. The slow relaxation stems from the existence of an easy-axis magnetic anisotropy, which is bolstered by the axial symmetry of the compounds and has been quantified through rigorous high-frequency EPR measurements. The magnitude of D in these compounds increases when heavier ions are substituted into the trimetallic chain; thus D = -1.640, -2.187, and -3.617 cm(-1) for Cr2Cr(dpa)4Cl2, Mo2Cr(dpa)4Cl2, and W2Cr(dpa)4Cl2, respectively. Additionally, the D value measured for W2Cr(dpa)4Cl2 is the largest yet reported for a high-spin Cr(2+) system. While earlier studies have demonstrated that ligands containing heavy atoms can enhance magnetic anisotropy, this is the first report of this phenomenon using heavy metal atoms as "ligands".
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Affiliation(s)
- Jonathan H Christian
- Department of Chemistry and Biochemistry, Florida State University , Tallahassee, Florida 32306, United States
| | - David W Brogden
- Department of Chemistry, University of Wisconsin - Madison , 1101 University Avenue Madison, Wisconsin 53706, United States
| | - Jasleen K Bindra
- Department of Chemistry and Biochemistry, Florida State University , Tallahassee, Florida 32306, United States
| | - Jared S Kinyon
- Department of Chemistry and Biochemistry, Florida State University , Tallahassee, Florida 32306, United States
| | - Johan van Tol
- National High Magnetic Field Laboratory, Florida State University , 1800 East Paul Dirac Drive, Tallahassee, Florida 32306, United States
| | - Jingfang Wang
- Department of Chemistry and Biochemistry, Florida State University , Tallahassee, Florida 32306, United States
| | - John F Berry
- Department of Chemistry, University of Wisconsin - Madison , 1101 University Avenue Madison, Wisconsin 53706, United States
| | - Naresh S Dalal
- Department of Chemistry and Biochemistry, Florida State University , Tallahassee, Florida 32306, United States
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17
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Xu N, Christian JH, Dalal NS, Abucayon EG, Lingafelt C, Powell DR, Richter-Addo GB. Six-coordinate ferric porphyrins containing bidentate N-t-butyl-N-nitrosohydroxylaminato ligands: structure, magnetism, IR spectroelectrochemisty, and reactivity. Dalton Trans 2015; 44:20121-30. [PMID: 26530148 DOI: 10.1039/c5dt03074a] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
NONOates (diazeniumdiolates) containing the [X{N2O2}](-) functional group are frequently employed as nitric oxide (NO) donors in biology, and some NONOates have been shown to bind to metalloenzymes. We report the preparation, crystal structures, detailed magnetic behavior, redox properties, and reactivities of the first isolable alkyl C-NONOate complexes of heme models, namely (OEP)Fe(η(2)-ON(t-Bu)NO) (1) and (TPP)Fe(η(2)-ON(t-Bu)NO) (2) (OEP = octaethylporphyrinato dianion, TPP = tetraphenylporphyrinato dianion). The compounds display the unusual NONOate O,O-bidentate binding mode for porphyrins, resulting in significant apical Fe displacements (+0.60 Å for 1, and +0.69 Å for 2) towards the axial ligands. Magnetic susceptibility and magnetization measurements made from 1.8-300 K at magnetic fields from 0.02 to 5 T, yielded magnetic moments of 5.976 and 5.974 Bohr magnetons for 1 and 2, respectively, clearly identifying them as high-spin (S = 5/2) ferric compounds. Variable-frequency (9.4 GHz and 34.5 GHz) EPR measurements, coupled with computer simulations, confirmed the magnetization results and yielded more precise values for the spin Hamiltonian parameters: g(avg) = 2.00 ± 0.03, |D| = 3.89 ± 0.09 cm(-1), and E/D = 0.07 ± 0.01 for both compounds, where D and E are the axial and rhombic zero-field splittings. IR spectroelectrochemistry studies reveal that the first oxidations of these compounds occur at the porphyrin macrocycles and not at the Fe-NONOate moieties. Reactions of 1 and 2 with a histidine mimic (1-methylimidazole) generate RNO and NO, both of which may bind to the metal center if sterics allow, as shown by a comparative study with the Cupferron complex (T(p-OMe)PP)Fe(η(2)-ON(Ph)NO). Protonation of 1 and 2 yields N2O as a gaseous product, presumably from the initial generation of HNO that dimerizes to the observed N2O product.
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Affiliation(s)
- Nan Xu
- Department of Chemistry and Biochemistry, University of Oklahoma, 101 Stephenson Parkway, Norman, OK 73019, USA. and Division of Mathematics and Natural Sciences, Penn State Altoona, 3000 Ivyside Park, Altoona, PA 16601, USA.
| | - Jonathan H Christian
- Department of Chemistry and Biochemistry, Florida State University, 95 Chieftan Way, Tallahassee, FL 32306, USA.
| | - Naresh S Dalal
- Department of Chemistry and Biochemistry, Florida State University, 95 Chieftan Way, Tallahassee, FL 32306, USA.
| | - Erwin G Abucayon
- Department of Chemistry and Biochemistry, University of Oklahoma, 101 Stephenson Parkway, Norman, OK 73019, USA.
| | - Colin Lingafelt
- Division of Mathematics and Natural Sciences, Penn State Altoona, 3000 Ivyside Park, Altoona, PA 16601, USA.
| | - Douglas R Powell
- Department of Chemistry and Biochemistry, University of Oklahoma, 101 Stephenson Parkway, Norman, OK 73019, USA.
| | - George B Richter-Addo
- Department of Chemistry and Biochemistry, University of Oklahoma, 101 Stephenson Parkway, Norman, OK 73019, USA.
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18
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Chen L, Willcock H, Wedge CJ, Hartl F, Colquhoun HM, Greenland BW. Efficient access to conjugated 4,4'-bipyridinium oligomers using the Zincke reaction: synthesis, spectroscopic and electrochemical properties. Org Biomol Chem 2015; 14:980-8. [PMID: 26626110 DOI: 10.1039/c5ob02211h] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
The cyclocondensation reaction between rigid, electron-rich aromatic diamines and 1,1'-bis(2,4-dinitrophenyl)-4,4'-bipyridinium (Zincke) salts has been harnessed to produce a series of conjugated oligomers containing up to twelve aromatic/heterocyclic residues. These oligomers exhibit discrete, multiple redox processes accompanied by dramatic changes in electronic absorption spectra.
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Affiliation(s)
- Long Chen
- Department of Chemistry, University of Reading, Whiteknights, Reading, RG6 6AD, UK.
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19
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Chong E, Xue W, Storr T, Kennepohl P, Schafer LL. Pyridonate-Supported Titanium(III). Benzylamine as an Easy-To-Use Reductant. Organometallics 2015. [DOI: 10.1021/acs.organomet.5b00469] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Eugene Chong
- Department
of Chemistry, University of British Columbia, 2036 Main Mall, Vancouver, British Columbia, Canada V6T 1Z1
| | - Wei Xue
- Department
of Chemistry, University of British Columbia, 2036 Main Mall, Vancouver, British Columbia, Canada V6T 1Z1
| | - Tim Storr
- Department
of Chemistry, Simon Fraser University, 8888 University Drive, Burnaby, British Columbia, Canada V5A 1S6
| | - Pierre Kennepohl
- Department
of Chemistry, University of British Columbia, 2036 Main Mall, Vancouver, British Columbia, Canada V6T 1Z1
| | - Laurel L. Schafer
- Department
of Chemistry, University of British Columbia, 2036 Main Mall, Vancouver, British Columbia, Canada V6T 1Z1
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20
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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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21
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Liu HY, Mahmood MHR, Qiu SX(S, Chang CK. Recent developments in manganese corrole chemistry. Coord Chem Rev 2013. [DOI: 10.1016/j.ccr.2012.12.017] [Citation(s) in RCA: 94] [Impact Index Per Article: 8.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
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22
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Lumata L, Merritt M, Khemtong C, Ratnakar SJ, van Tol J, Yu L, Song L, Kovacs Z. The efficiency of DPPH as a polarising agent for DNP-NMR spectroscopy. RSC Adv 2012. [PMID: 23205273 DOI: 10.1039/c2ra21853d] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
The free radical 2,2-diphenyl-1-pycrylhydrazyl (DPPH) was tested as a polarising agent for fast dissolution dynamic nuclear polarisation (DNP) NMR spectroscopy. DPPH was found to be reasonably soluble in sulfolane and the optimum concentration for DNP is 20-40 mM depending upon whether short polarisation times or the maximum signal intensity is needed. W-band ESR measurements revealed that the ESR linewidth D of DPPH is intermediate between that of BDPA and 4-oxo-TEMPO. Several thousand-fold NMR signal enhancements in the liquid-state were achieved for (13)C, (15)N, (89)Y, and (109)Ag compounds, demonstrating that DPPH can be added to the list of polarising agents for DNP-NMR spectroscopy. Furthermore, the hydrophobic DPPH free radical can be easily filtered out from the dissolution liquid when water is used as the dissolution solvent.
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Affiliation(s)
- Lloyd Lumata
- Advanced Imaging Research Center, University of Texas, Southwestern Medical Center, 5323 Harry Hines Boulevard, Dallas, Texas 75390 USA. ; Tel: +1-214-645-2750
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23
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Kozuki K, Nagashima T, Hangyo M. Measurement of electron paramagnetic resonance using terahertz time-domain spectroscopy. OPTICS EXPRESS 2011; 19:24950-24956. [PMID: 22273888 DOI: 10.1364/oe.19.024950] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/31/2023]
Abstract
We present a frequency-domain electron spin resonance (ESR) measurement system using terahertz time-domain spectroscopy. A crossed polarizer technique is utilized to increase the sensitivity in detecting weak ESR signals of paramagnets caused by magnetic dipole transitions between magnetic sublevels. We demonstrate the measurements of ESR signal of paramagnetic copper(II) sulfate pentahydrate with uniaxial anisotropy of the g-factor under magnetic fields up to 10 T. The lineshape of the obtained ESR signals agrees well with the theoretical predictions for a powder sample with the uniaxial anisotropy.
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Affiliation(s)
- Kohei Kozuki
- Institute of Laser Engineering, Osaka University, Suita, Osaka, Japan
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24
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Noipa T, Srijaranai S, Tuntulani T, Ngeontae W. New approach for evaluation of the antioxidant capacity based on scavenging DPPH free radical in micelle systems. Food Res Int 2011. [DOI: 10.1016/j.foodres.2011.01.034] [Citation(s) in RCA: 86] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
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25
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Stoll S, Ozarowski A, Britt RD, Angerhofer A. Atomic hydrogen as high-precision field standard for high-field EPR. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2010; 207:158-63. [PMID: 20813570 PMCID: PMC2956851 DOI: 10.1016/j.jmr.2010.08.006] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/18/2010] [Revised: 06/08/2010] [Accepted: 08/06/2010] [Indexed: 05/05/2023]
Abstract
We introduce atomic hydrogen trapped in an octaisobutylsilsesquioxane nanocage (H@iBuT₈) as a new molecular high-precision magnetic field standard for high-field EPR spectroscopy of organic radicals and other systems with signals around g=2. Its solid-state EPR spectrum consists of two 0.2 mT wide lines separated by about 51 mT and centered at g≈2. The isotropic g factor is 2.00294(3) and essentially temperature independent. The isotropic ¹H hyperfine coupling constant is 1416.8(2) MHz below 70 K and decreases slightly with increasing temperature to 1413.7(1) MHz at room temperature. The spectrum of the standard does not overlap with those of most organic radicals, and it can be easily prepared and is stable at room temperature.
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Affiliation(s)
- Stefan Stoll
- Department of Chemistry, University of California, One Shields Ave, Davis, California 95616, USA
| | - Andrew Ozarowski
- National High Magnetic Field Laboratory, Florida State University, 1800 East Paul Dirac Drive, Tallahassee, Florida 32310, USA
| | - R. David Britt
- Department of Chemistry, University of California, One Shields Ave, Davis, California 95616, USA
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26
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Zilić D, Pajić D, Jurić M, Molčanov K, Rakvin B, Planinić P, Zadro K. Single crystals of DPPH grown from diethyl ether and carbon disulfide solutions - crystal structures, IR, EPR and magnetization studies. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2010; 207:34-41. [PMID: 20833090 DOI: 10.1016/j.jmr.2010.08.005] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/24/2009] [Revised: 07/15/2010] [Accepted: 08/06/2010] [Indexed: 05/29/2023]
Abstract
Single crystals of the free radical 2,2-diphenyl-1-picrylhydrazyl (DPPH) obtained from diethyl ether (ether) and carbon disulfide (CS₂) were characterized by the X-ray diffraction, IR, EPR and SQUID magnetization techniques. The X-ray structural analysis and IR spectra showed that the DPPH form crystallized from ether (DPPH1) is solvent free, whereas that one obtained from CS₂ (DPPH2) is a solvate of the composition 4DPPH·CS₂. Principal values of the g-tensor were estimated by the X-band EPR spectroscopy at room and low (10 K) temperatures. Magnetization studies revealed the presence of antiferromagnetically coupled dimers in both types of crystals. However, the way of dimerization as well as the strength of exchange couplings are different in the two DPPH samples, which is in accord with their crystal structures. The obtained results improved parameters accuracy and enabled better understanding of properties of DPPH as a standard sample in the EPR spectrometry.
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Affiliation(s)
- Dijana Zilić
- Ruder Bošković Institute, Bijenička cesta 54, 10000 Zagreb, Croatia.
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27
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Chen O, Zhuang J, Guzzetta F, Lynch J, Angerhofer A, Cao YC. Synthesis of water-soluble 2,2'-diphenyl-1-picrylhydrazyl nanoparticles: a new standard for electron paramagnetic resonance spectroscopy. J Am Chem Soc 2009; 131:12542-3. [PMID: 19673526 DOI: 10.1021/ja905395u] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
This communication reports a size-controlled synthesis of water-soluble 2,2'-diphenyl-1-picrylhydrazyl (DPPH) nanoparticles (NPs). These nanoparticles exhibit size-dependent absorption spectra and fast spin exchange-narrowed single-line EPR spectra. The linewidths of the EPR spectra of these water-soluble nanoparticles are approximately 1.5-1.8 G, which are equal or close to the narrowest line width (1.5 G) of the common DPPH standard in the form of water-insoluble microcrystals. In addition, these NPs are stable over a wide pH range of 3.0 to 10.0. These properties make these water-soluble DPPH NPs suitable for use as a new type of EPR standard, which is important for fundamental research and practical applications in fields such as the food industry and the life sciences. Furthermore, the DPPH NPs can potentially be used as a spin probe in biomedical studies.
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Affiliation(s)
- Ou Chen
- Department of Chemistry, University of Florida, Gainesville, Florida 32611, USA
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28
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Cruickshank PAS, Bolton DR, Robertson DA, Hunter RI, Wylde RJ, Smith GM. A kilowatt pulsed 94 GHz electron paramagnetic resonance spectrometer with high concentration sensitivity, high instantaneous bandwidth, and low dead time. THE REVIEW OF SCIENTIFIC INSTRUMENTS 2009; 80:103102. [PMID: 19895049 DOI: 10.1063/1.3239402] [Citation(s) in RCA: 104] [Impact Index Per Article: 6.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/28/2023]
Abstract
We describe a quasioptical 94 GHz kW pulsed electron paramagnetic resonance spectrometer featuring pi/2 pulses as short as 5 ns and an instantaneous bandwidth of 1 GHz in nonresonant sample holders operating in induction mode and at low temperatures. Low power pulses can be as short as 200 ps and kilowatt pulses as short as 1.5 ns with timing resolution of a few hundred picoseconds. Phase and frequency can be changed on nanosecond time scales and complex high power pulse sequences can be run at repetition rates up to 80 kHz with low dead time. We demonstrate that the combination of high power pulses at high frequencies and nonresonant cavities can offer excellent concentration sensitivity for orientation selective pulsed electron double resonance (double electron-electron resonance), where we demonstrate measurements at 1 microM concentration levels.
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Affiliation(s)
- Paul A S Cruickshank
- School of Physics and Astronomy, University of St Andrews, North Haugh, St Andrews KY16 9SS, United Kingdom
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29
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Martincová J, Dostálová R, Dostál L, Růžička A, Jambor R. The Stannylene {2,6-(Me2NCH2)2C6H3}SnCl as a Ligand in Transition Metal Complexes of Palladium, Ruthenium, and Rhodium. Organometallics 2009. [DOI: 10.1021/om900393k] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Jana Martincová
- Department of General and Inorganic Chemistry, University of Pardubice, nám. Čs. legií 565, CZ-532 10, Pardubice, Czech Republic
| | - Romana Dostálová
- Department of General and Inorganic Chemistry, University of Pardubice, nám. Čs. legií 565, CZ-532 10, Pardubice, Czech Republic
| | - Libor Dostál
- Department of General and Inorganic Chemistry, University of Pardubice, nám. Čs. legií 565, CZ-532 10, Pardubice, Czech Republic
| | - Aleš Růžička
- Department of General and Inorganic Chemistry, University of Pardubice, nám. Čs. legií 565, CZ-532 10, Pardubice, Czech Republic
| | - Roman Jambor
- Department of General and Inorganic Chemistry, University of Pardubice, nám. Čs. legií 565, CZ-532 10, Pardubice, Czech Republic
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30
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Mattar SM, Sanford J. Role of the Geometry, Restricted Rotations and Solvents on the Computed 2,2′-Diphenyl-1-picrylhydrazyl Hyperfine Tensors. J Phys Chem A 2008; 112:11349-54. [DOI: 10.1021/jp806919k] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Saba M. Mattar
- Department of Chemistry and Centre for Laser, Atomic and Molecular Sciences, University of New Brunswick, Fredericton, NB, Canada E3B 6E2
| | - Jacob Sanford
- Department of Chemistry and Centre for Laser, Atomic and Molecular Sciences, University of New Brunswick, Fredericton, NB, Canada E3B 6E2
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31
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Sienkiewicz A, Krzystek J, Vileno B, Chatain G, Kosar AJ, Bohle DS, Forró L. Multi-frequency high-field EPR study of iron centers in malarial pigments. J Am Chem Soc 2007; 128:4534-5. [PMID: 16594665 DOI: 10.1021/ja058420h] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The multi-frequency high-field electron paramagnetic resonance (HFEPR) was used to study the magnetic properties of malarial pigment hemozoin and its synthetic analogue, beta-hematin. (FeIII-protoporphyrin-IX)2 dimers containing five-coordinate high-spin FeIII, S = 5/2, are the building blocks of these pigments. The fit of EPR spectra that were acquired in an unprecedented wide range of microwave frequencies of 34 and 94 GHz for hemozoin and 27-500 GHz for beta-hematin yielded a complete set of intrinsic spin Hamiltonian parameters: D = +5.85(1) cm-1, E = 0, g perpendicular = 1.95(1), g parallel = 2.00(1). These results point to the existence of largely axial symmetry of the iron environment in the bulk phase of hemozoin and beta-hematin.
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Affiliation(s)
- Andrzej Sienkiewicz
- Institute of Physics, Polish Academy of Sciences, Al. Lotników 32/46, 02-668 Warsaw, Poland
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Hartl F, Outersterp JWMV. Multistep Electrochemical Reduction Path of Clusters [Os3(CO)10(α-diimine)]: Comparison of Electrochemical and Photochemical Os-Os(α-diimine) Bond Cleavage. ACTA ACUST UNITED AC 2006. [DOI: 10.1135/cccc20060237] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
Abstract
Electrochemical reduction of the triangular clusters [Os3(CO)10(α-diimine)] (α-diimine = 2,2'-bipyridine (bpy), 2,2'-bipyrimidine (bpym)) and [Os3(CO)10(μ-bpym)ReBr(CO)3] produces primarily the corresponding radical anions. Their stability is strongly determined by the π-acceptor ability of the reducible α-diimine ligand, which decreases in the order μ-bpym > bpym >> bpy. Along this series, increasing delocalisation of the odd electron density in the radical anion over the Os(α-diimine) chelate ring causes weakening of the axial (CO)4Os-Os(CO)2(α-diimine) bond and its facile cleavage for α-diimine = bpy. In contrast, the cluster radical anion is inherently stable for the bridging bpym ligand, the strongest π-acceptor in the studied series. In the absence of the partial delocalisation of the unpaired electron over the Re(bpym) chelate bond, the Os3-core of the radical anion remains intact only at low temperatures. Subsequent one-electron reduction of [Os3(CO)10(bpym)]•- at T = 223 K gives the open-triosmium core (= Os3*) dianion, [Os3*(CO)10(bpym)]2-. Its oxidation leads to the recovery of parent [Os3(CO)10(bpym)]. At room temperature, [Os3*(CO)10(bpym)]2- is formed along a two-electron (ECE) reduction path. The chemical step (C) results in the formation of an open-core radical anion that is directly reducible at the cathodic potential of the parent cluster in the second electrochemical (E) step. In weakly coordinating tetrahydrofuran, [Os3*(CO)10(bpym)]2- rapidly attacks yet non-reduced parent cluster molecules, producing the relatively stable open-core dimer [Os3*(CO)10(bpym)]22- featuring two open-triangle cluster moieties connected with an (bpym)Os-Os(bpym) bond. In butyronitrile, [Os3*(CO)10(bpym)]2- is stabilised by the solvent and the dimer [Os3*(CO)10(bpym)]22- is then mainly formed by reoxidation of the dianion on reverse potential scan. The more reactive cluster [Os3(CO)10(bpy)] follows the same reduction path, as supported by spectroelectrochemical results and additional valuable evidence obtained from cyclic voltammetric scans. The ultimate process in the reduction mechanism is fragmentation of the cluster core triggered by the reduction of the dimer [Os3*(CO)10(α-diimine)]22-. The products formed are [Os2(CO)8]2- and {Os(CO)2(α-diimine)}2. The latter dinuclear fragments constitute a linear polymeric chain [Os(CO)2(α-diimine)]n that is further reducible at the α-diimine ligands. For α-diimine = bpy, the charged polymer is capable of reducing carbon dioxide. The electrochemical opening of the triosmium core in the [Os3(CO)10(α-diimine)] clusters exhibits several common features with their photochemistry. The same Os-α-diimine bond dissociates in both cases but the intimate mechanisms are different.
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Doux M, Mézailles N, Ricard L, Le Floch P, Vaz PD, Calhorda MJ, Mahabiersing T, Hartl F. Syntheses, X-ray structures, photochemistry, redox properties, and DFT calculations of interconvertible fac- and mer-[Mn(SPS)(CO)3] isomers containing a flexible SPS-based pincer ligand. Inorg Chem 2005; 44:9213-24. [PMID: 16323902 DOI: 10.1021/ic050774m] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The lithium salt of the anionic SPS pincer ligand composed of a central hypervalent lambda4-phosphinine ring bearing two ortho-positioned diphenylphosphine sulfide side arms reacts with [Mn(CO)5Br] to give fac-[Mn(SPS)(CO)3]. This isomer can be converted photochemically to mer-[Mn(SPS)(CO)3], with a very high quantum yield (0.80+/-0.05). The thermal backreaction is slow (taking ca. 8 h at room temperature), in contrast to rapid electrode-catalyzed mer-to-fac isomerization triggered by electrochemical reduction of mer-[Mn(SPS)(CO)3]. Both geometric isomers of [Mn(SPS)(CO)3] have been characterized by X-ray crystallography. Both isomers show luminescence from a low-lying 3IL (SPS-based) excited state. The light emission of fac-[Mn(SPS)(CO)3] is largely quenched by the efficient photoisomerization occurring probably from a low-lying Mn-CO dissociative excited state. Density functional theory (DFT) and time-dependent DFT calculations describe the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) of fac- and mer-[Mn(CO)3(SPS)] as ligand-centered orbitals, largely localized on the phosphinine ring of the SPS pincer ligand. In line with the ligand nature of its frontier orbitals, fac-[Mn(SPS)(CO)3] is electrochemically reversibly oxidized and reduced to the corresponding radical cation and anion, respectively. The spectroscopic (electron paramagnetic resonance, IR, and UV-vis) characterization of the radical species provides other evidence for the localization of the redox steps on the SPS ligand. The smaller HOMO-LUMO energy difference in the case of mer-[Mn(CO)3(SPS)], reflected in the electronic absorption and emission spectra, corresponds with its lower oxidation potential compared to that of the fac isomer. The thermodynamic instability of mer-[Mn(CO)3(SPS)], confirmed by the DFT calculations, increases upon one-electron reduction and oxidation of the complex.
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Affiliation(s)
- Marjolaine Doux
- Laboratoire Hétéroéléments et Coordination, UMR CNRS 7653, Département de Chimie, Ecole Polytechnique, 92128 Palaiseau Cédex, France
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Inclusion compounds of cystostatic active (C5H5)2VCl2 and (CH3C5H4)2VCl2 with α-, β- and γ-cyclodextrines: Synthesis, EPR study and microbiological behavior toward Escherichia coli. OPEN CHEM 2005. [DOI: 10.2478/bf02476239] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
AbstractThe inclusion of vanadocene dichloride (VDC) and 1,1′-dimethyl vanadocene dichloride (MeVDC) into cyclodextrines (α-CD, β-CD and γ-CD) was studied by EPR spectroscopy. It was found that VDC and MeVDC with β-CD and γ-CD form true inclusion compounds, but with α-CD, VDC and MeVDC gave only fine dispersion mixtures. The inclusion was validated by anisotropic EPR spectra of solid samples. In addition, the antimicrobial was validated by anisotropic EPR spectra of solid samples. In addition, the antimicrobial behavior (against E. coli) of each of the complexes was determined. It was established that not only did VDC and MeVDC cause elongation of E. coli, but also the new vanadocene inclusion complexes were effective in this regard.
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Hartl F, Mahabiersing T, Chardon-Noblat S, Da Costa P, Deronzier A. Redox-Active Polymers Based on Nonbridged Metal−Metal Bonds. Electrochemical Formation of [Os(bpy)(CO)(L)]n (bpy = 2,2‘-bipyridine; L = CO, MeCN) and of Their Reduced Forms: A Spectroelectrochemical Study. Inorg Chem 2004; 43:7250-8. [PMID: 15500366 DOI: 10.1021/ic049216i] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
IR, UV-vis, and EPR spectroelectrochemistry at variable temperatures and in different solvents were applied to investigate in situ the formation of electroactive molecular chains with a nonbridged Os-Os backbone, in particular, the polymer [Os(0)(bpy)(CO)(2)](n) (bpy = 2,2'-bipyridine), from a mononuclear Os(II) carbonyl precursor, [Os(II)(bpy)(CO)(2)Cl(2)]. The one-electron-reduced form, [Os(II)(bpy(.)(-))(CO)(2)Cl(2)](-), has been characterized spectroscopically at low temperatures. This radical anion is the key intermediate in the electrochemical propagation process responsible for the metal-metal bond formation. Unambiguous spectroscopic evidence has been gained also for the formation of [[Os(0)(bpy(*)(-))(CO)(2)](-)](n), the electron-rich electrocatalyst of CO(2) reduction. The polymer species are fairly well soluble in butyronitrile, which is important for their potential utilization in nanoscience, for example, as conducting molecular wires. We have also shown that complete solubility is accomplished for the monocarbonyl-acetonitrile derivative of the polymer, [Os(0)(bpy)(CO)(MeCN)(2)Cl](n).
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Affiliation(s)
- Frantisek Hartl
- Molecular Photonic Materials, van't Hoff Institute for Molecular Sciences, Universiteit van Amsterdam, Nieuwe Achtergracht 166, 1018 WV Amsterdam, The Netherlands.
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Vinklárek J, Paláčková H, Honzíček J. Experimental and Theoretical Study of the First Vanadocene(IV) Complexes of α-Amino Acids Prepared from Vanadocene Dichloride. ACTA ACUST UNITED AC 2004. [DOI: 10.1135/cccc20040811] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
Abstract
The first bioinorganic vanadocene(IV) complexes of α-amino acids ([Cp2V(aa)]Cl, Cp = η5-C5H5, aa = glycine, L-alanine, L-valine) were prepared by reaction of vanadocene dichloride ([Cp2VCl2]) and α-amino acids in aqueous methanol. Analogous cationic complexes with PF6- counterions were obtained by metathetical reactions of the chloride precursors with KPF6. These compounds are of great interest as model systems for the vanadocene moiety binding to proteins. All complexes have been characterized by elemental analyses and IR, Raman and EPR spectroscopies. On the basis of EPR spectra, a chelate in all the studied complexes was proposed, formed by the carboxylato and amino groups. This structure has also been confirmed by density functional theory (DFT) calculations.
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Krzystek J, Pardi LA, Brunel LC, Goldberg DP, Hoffman BM, Licoccia S, Telser J. High-frequency and -field electron paramagnetic resonance of high-spin manganese(III) in tetrapyrrole complexes. SPECTROCHIMICA ACTA. PART A, MOLECULAR AND BIOMOLECULAR SPECTROSCOPY 2002; 58:1113-1127. [PMID: 11993460 DOI: 10.1016/s1386-1425(01)00701-6] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
Abstract
High-field and -frequency electron paramagnetic resonance (HFEPR) spectroscopy has been used to study three complexes of high spin Manganese(III), 3d4, S = 2. The complexes studied were tetraphenylporphyrinatomanganese(III) chloride (MnTPPCI), phthalocyanatomanganese(III) chloride (MnPcCl), and (8,12-diethyl-2,3,7,13,17,18-hexamethylcorrolato)manganese(III) (MnCor). We demonstrate the ability to obtain both field-oriented (single-crystal like) spectra and true powder pattern HFEPR spectra of solid samples. The latter are obtained by immobilizing the powder, either in an n-eicosane mull or KBr pellet. We can also obtain frozen solution HFEPR spectra with good signal-to-noise, and yielding the expected true powder pattern. Frozen solution spectra are described for MnTPPCl in 2:3 (v/v) toluene/CH2Cl2 solution and for MnCor in neat pyridine (py) solution. All of the HFEPR spectra have been fully analyzed using spectral simulation software and a complete set of spin Hamiltonian parameters has been determined for each complex in each medium. Both porphyrinic complexes (MnTPPCl and MnPcCl) are rigorously axial systems, with similar axial zero-field splitting (zfs): D approximately -2.3 cm(-1), and g values quite close to 2.00. In contrast, the corrole complex, MnCor, exhibits slightly larger magnitude, rhombic zfs: D approximtely -2.6 cm(-1), absolute value(E) approximately 0.015 cm(-1), also with g values quite close to 2.00. These results are discussed in terms of the molecular structures of these complexes and their electronic structure. We propose that there is a significant mixing of the triplet (S = 1) excited state with the quintet (S= 2) ground state in Mn(III) complexes with porphyrinic ligands, which is even more pronounced for corroles.
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Affiliation(s)
- J Krzystek
- Center for Interdisciplinary Magnetic Resonance, National High Magnetic Field Laboratory, Florida State University, Tallahassee 32310, USA
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Zoleo A, Maniero AL, Prato M, Severin MG, Brunel LC, Kordatos K, Brustolon M. Anion Radicals of Mono- and Bisfulleropyrrolidines: g Tensors, Spin Density Distribution and Spin−Lattice Relaxation. J Phys Chem A 2000. [DOI: 10.1021/jp001518s] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Alfonso Zoleo
- Dipartimento di Chimica Fisica, Universitá di Padova, Via Loredan 2, I-35131 Padova, Italy, and Dipartimento di Scienze Farmaceutiche, Universitá di Trieste, Piazzale Europa, 34100 Trieste, Italy, and Center for Interdisciplinary Magnetic Resonance, National High Magnetic Field Laboratory, Florida State University, Tallahassee, Florida 32306
| | - Anna Lisa Maniero
- Dipartimento di Chimica Fisica, Universitá di Padova, Via Loredan 2, I-35131 Padova, Italy, and Dipartimento di Scienze Farmaceutiche, Universitá di Trieste, Piazzale Europa, 34100 Trieste, Italy, and Center for Interdisciplinary Magnetic Resonance, National High Magnetic Field Laboratory, Florida State University, Tallahassee, Florida 32306
| | - Maurizio Prato
- Dipartimento di Chimica Fisica, Universitá di Padova, Via Loredan 2, I-35131 Padova, Italy, and Dipartimento di Scienze Farmaceutiche, Universitá di Trieste, Piazzale Europa, 34100 Trieste, Italy, and Center for Interdisciplinary Magnetic Resonance, National High Magnetic Field Laboratory, Florida State University, Tallahassee, Florida 32306
| | - Maria Gabriella Severin
- Dipartimento di Chimica Fisica, Universitá di Padova, Via Loredan 2, I-35131 Padova, Italy, and Dipartimento di Scienze Farmaceutiche, Universitá di Trieste, Piazzale Europa, 34100 Trieste, Italy, and Center for Interdisciplinary Magnetic Resonance, National High Magnetic Field Laboratory, Florida State University, Tallahassee, Florida 32306
| | - Louis Claude Brunel
- Dipartimento di Chimica Fisica, Universitá di Padova, Via Loredan 2, I-35131 Padova, Italy, and Dipartimento di Scienze Farmaceutiche, Universitá di Trieste, Piazzale Europa, 34100 Trieste, Italy, and Center for Interdisciplinary Magnetic Resonance, National High Magnetic Field Laboratory, Florida State University, Tallahassee, Florida 32306
| | - Konstantinos Kordatos
- Dipartimento di Chimica Fisica, Universitá di Padova, Via Loredan 2, I-35131 Padova, Italy, and Dipartimento di Scienze Farmaceutiche, Universitá di Trieste, Piazzale Europa, 34100 Trieste, Italy, and Center for Interdisciplinary Magnetic Resonance, National High Magnetic Field Laboratory, Florida State University, Tallahassee, Florida 32306
| | - Marina Brustolon
- Dipartimento di Chimica Fisica, Universitá di Padova, Via Loredan 2, I-35131 Padova, Italy, and Dipartimento di Scienze Farmaceutiche, Universitá di Trieste, Piazzale Europa, 34100 Trieste, Italy, and Center for Interdisciplinary Magnetic Resonance, National High Magnetic Field Laboratory, Florida State University, Tallahassee, Florida 32306
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Annino G, Cassettari M, Fittipaldi M, Longo I, Martinelli M, Massa CA, Pardi LA. High-field, multifrequency EPR spectroscopy using whispering gallery dielectric resonators. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2000; 143:88-94. [PMID: 10698649 DOI: 10.1006/jmre.1999.1977] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
Abstract
High-field/high frequency EPR spectroscopy measurements are shown. Experiments were carried out at 240- and 316-GHz frequencies. The employed apparatus uses a novel combination of far infrared molecular lasers and of probehead exploiting dielectric resonators working in the whispering gallery modes. This approach constitutes a relatively simple method of multifrequency EPR spectroscopy and opens appealing perspectives in high-sensitivity EPR spectroscopy up to the THz regime.
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Affiliation(s)
- G Annino
- Istituto di Fisica Atomica e Molecolare del CNR, Via del Giardino 7, Pisa, 56127, Italy
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Hassan AK, Pardi LA, Krzystek J, Sienkiewicz A, Goy P, Rohrer M, Brunel LC. Ultrawide band multifrequency high-field EMR technique: A methodology for increasing spectroscopic information. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2000; 142:300-312. [PMID: 10648147 DOI: 10.1006/jmre.1999.1952] [Citation(s) in RCA: 234] [Impact Index Per Article: 9.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
Abstract
We report methodology that combines an ultrawide band multifrequency microwave system with technology of high magnetic fields for solving challenging problems in electron magnetic resonance (EMR) spectroscopy. This strategy has been made possible due to a novel EMR facility operating in an exceptionally wide range of microwave frequencies of 24 GHz to 3 THz, at magnetic fields up to 17 T, and in the temperature range of 1.6 to 330 K. The basic configuration of the multifrequency system works in a transmission mode and employs oversized cylindrical waveguides for routing the microwave power. A wide-band, low-noise, liquid helium cooled (4.2 K) InSb bolometer is used for signal detection. This approach results in an extremely wide-band performance, thus making it possible to employ a variety of solid-state millimeter and submillimeter microwave sources in combination with a far infrared laser microwave source for performing multifrequency EMR experiments. A complexity of resonant structures and related technical problems such as microphonics at high magnetic fields is virtually eliminated. The system is simple, yet sensitive, and has been revealed to be extremely advantageous while solving such problems as observation of AFMR transitions in spin-ordered systems, g-factor resolution enhancement in complex organic radicals, and resonance signal detection in EMR-silent spin systems having integer spin and large zero field splitting. A technical description of the multifrequency high-field EMR facility is presented and results of its performance tests are given. The potential utility of using the multifrequency high-field methodology in EMR studies is illustrated with selected examples of its recent applications.
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Affiliation(s)
- A K Hassan
- Center for Interdisciplinary Magnetic Resonance, National High Magnetic Field Laboratory, Florida State University, 1800 E. Paul Dirac Drive, Tallahassee, Florida 32310, USA
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Krzystek J, Telser J, Pardi LA, Goldberg DP, Hoffman BM, Brunel LC. High-Frequency and -Field Electron Paramagnetic Resonance of High-Spin Manganese(III) in Porphyrinic Complexes. Inorg Chem 1999; 38:6121-6129. [PMID: 11671322 DOI: 10.1021/ic9901970] [Citation(s) in RCA: 116] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
High-field and -frequency electron paramagnetic resonance (HFEPR) spectroscopy has been used to study two complexes of high-spin manganese(III), d(4), S = 2. The complexes studied were (tetraphenylporphyrinato)manganese(III) chloride and (phthalocyanato)manganese(III) chloride. Our previous HFEPR study (Goldberg, D. P.; Telser, J.; Krzystek, J.; Montalban, A. G.; Brunel, L.-C.; Barrett, A. G. M.; Hoffman, B. M. J. Am. Chem. Soc. 1997, 119, 8722-8723) included results on the porphyrin complex; however, we were unable to obtain true powder pattern HFEPR spectra, as the crystallites oriented in the intense external magnetic field. In this work we are now able to immobilize the powder, either in an n-eicosane mull or KBr pellet and obtain true powder pattern spectra. These spectra have been fully analyzed using spectral simulation software, and a complete set of spin Hamiltonian parameters has been determined for each complex. Both complexes are rigorously axial systems, with relatively low magnitude zero-field splitting: D approximately -2.3 cm(-)(1) and g values quite close to 2.00. Prior to this work, no experimental nor theoretical data exist for the metal-based electronic energy levels in Mn(III) complexes of porphyrinic ligands. This lack of information is in contrast to other transition metal complexes and is likely due to the dominance of ligand-based transitions in the absorption spectra of Mn(III) complexes of this type. We have therefore made use of theoretical values for the electronic energy levels of (phthalocyanato)copper(II), which electronically resembles these Mn(III) complexes. This analogy works surprisingly well in terms of the agreement between the calculated and experimentally determined EPR parameters. These results show a significant mixing of the triplet (S = 1) excited state with the quintet (S = 2) ground state in Mn(III) complexes with porphyrinic ligands. This is in agreement with the experimental observation of lower spin ground states in other metalloporphyrinic complexes, such as those of Fe(II) with S = 1.
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Affiliation(s)
- J. Krzystek
- Center for Interdisciplinary Magnetic Resonance, National High Magnetic Field Laboratory, Florida State University, Tallahassee, Florida 32310, Chemistry Program, Roosevelt University, Chicago, Illinois 60605, Istituto di Fisica Atomica e Molecolare, CNR, 56127 Pisa, Italy, Department of Chemistry, Johns Hopkins University, Baltimore, Maryland 21218, and Department of Chemistry, Northwestern University, Evanston, Illinois 60208
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Konovalova TA, Krzystek J, Bratt PJ, van Tol J, Brunel LC, Kispert LD. 95−670 GHz EPR Studies of Canthaxanthin Radical Cation Stabilized on a Silica−Alumina Surface. J Phys Chem B 1999. [DOI: 10.1021/jp990579r] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Tatyana A. Konovalova
- Department of Chemistry, P.O. Box 870336, University of Alabama, Tuscaloosa, Alabama 35487, Center for Interdisciplinary Magnetic Resonance, National High Magnetic Field Laboratory, Florida State University, Tallahassee, FL 32310, Department of Chemistry, P.O. Box 117200, University of Florida, Gainesville, FL 32611, and The Department of Biology, Darwin Building, University College London, Gower Street, London WC1H 9EW, United Kingdom
| | - J. Krzystek
- Department of Chemistry, P.O. Box 870336, University of Alabama, Tuscaloosa, Alabama 35487, Center for Interdisciplinary Magnetic Resonance, National High Magnetic Field Laboratory, Florida State University, Tallahassee, FL 32310, Department of Chemistry, P.O. Box 117200, University of Florida, Gainesville, FL 32611, and The Department of Biology, Darwin Building, University College London, Gower Street, London WC1H 9EW, United Kingdom
| | - Peter J. Bratt
- Department of Chemistry, P.O. Box 870336, University of Alabama, Tuscaloosa, Alabama 35487, Center for Interdisciplinary Magnetic Resonance, National High Magnetic Field Laboratory, Florida State University, Tallahassee, FL 32310, Department of Chemistry, P.O. Box 117200, University of Florida, Gainesville, FL 32611, and The Department of Biology, Darwin Building, University College London, Gower Street, London WC1H 9EW, United Kingdom
| | - J. van Tol
- Department of Chemistry, P.O. Box 870336, University of Alabama, Tuscaloosa, Alabama 35487, Center for Interdisciplinary Magnetic Resonance, National High Magnetic Field Laboratory, Florida State University, Tallahassee, FL 32310, Department of Chemistry, P.O. Box 117200, University of Florida, Gainesville, FL 32611, and The Department of Biology, Darwin Building, University College London, Gower Street, London WC1H 9EW, United Kingdom
| | - Louis-Claude Brunel
- Department of Chemistry, P.O. Box 870336, University of Alabama, Tuscaloosa, Alabama 35487, Center for Interdisciplinary Magnetic Resonance, National High Magnetic Field Laboratory, Florida State University, Tallahassee, FL 32310, Department of Chemistry, P.O. Box 117200, University of Florida, Gainesville, FL 32611, and The Department of Biology, Darwin Building, University College London, Gower Street, London WC1H 9EW, United Kingdom
| | - Lowell D. Kispert
- Department of Chemistry, P.O. Box 870336, University of Alabama, Tuscaloosa, Alabama 35487, Center for Interdisciplinary Magnetic Resonance, National High Magnetic Field Laboratory, Florida State University, Tallahassee, FL 32310, Department of Chemistry, P.O. Box 117200, University of Florida, Gainesville, FL 32611, and The Department of Biology, Darwin Building, University College London, Gower Street, London WC1H 9EW, United Kingdom
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Cage B, Weekley A, Brunel LC, Dalal NS. K3CrO8 in K3NbO8 as a Proposed Standard for g-Factor, Spin Concentration, and Field Calibration in High-Field EPR Spectroscopy. Anal Chem 1999. [DOI: 10.1021/ac9812330] [Citation(s) in RCA: 23] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Brant Cage
- Department of Chemistry, Department of Physics, and National High Magnetic Field Laboratory, Florida State University, Tallahassee, Florida 32306-4390
| | - April Weekley
- Department of Chemistry, Department of Physics, and National High Magnetic Field Laboratory, Florida State University, Tallahassee, Florida 32306-4390
| | - Louis-Claude Brunel
- Department of Chemistry, Department of Physics, and National High Magnetic Field Laboratory, Florida State University, Tallahassee, Florida 32306-4390
| | - Naresh S. Dalal
- Department of Chemistry, Department of Physics, and National High Magnetic Field Laboratory, Florida State University, Tallahassee, Florida 32306-4390
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Cage B, Cevc P, Blinc R, Brunel LC, Dalal NS. 1-370 GHz EPR linewidths for K3CrO8: a comprehensive test for the Anderson-Weiss model. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 1998; 135:178-184. [PMID: 9799692 DOI: 10.1006/jmre.1998.1569] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/22/2023]
Abstract
Electron paramagnetic resonance (EPR) measurements have been carried out over the frequency range of 1-370 GHz on single crystals of potassium peroxychromate (K3CrO8) with the view of examining the current models of exchange narrowing of EPR signals in solids. K3CrO8 has a simple (tetragonal) lattice structure, can be grown as single crystals pure or diluted with an isostructural diamagnetic host K3NbO8, and its paramagnetism can be described by a very simple (S = 12, I = 0) spin Hamiltonian. The measurements were made at various orientations of single crystals in the Zeeman field, with emphasis on the principal directions of the g-tensor. For essentially all orientations, the linewidth decreases monotonically for measurements at resonance frequencies, omega0, from 1 to about 100 GHz, and then starts to increase at higher omega0. In order to delineate the spin exchange effects from other sources of line broadening, the measurements were repeated with a diluted spin system, K3NbO8 containing approximately/= 0.5 mole % of K3CrO8, representing the broadening effect of all the magnetic field dependent terms, such as the broadening due to the g-strain and sample holder/waveguide magnetization at the high field utilized, up to 14 T. Using these data, the K3CrO8 linewidths were analyzed in terms of the current models of spin exchange narrowing in three-dimensional systems. A reasonably good agreement was found with the Anderson-Weiss model, when modified for various line broadening effects. The accuracy of the analysis procedure was confirmed by the comparison of the presently determined values of the exchange constant, J, and the dipolar field, Hp, with their values obtained by dc magnetic susceptibility measurements and theoretical analysis, respectively; the agreement was within 5% for J (=1.35 K) and about 25% for Hp (160 G). However, some deviations and unusual splittings were noted in measurements at 370 GHz, whose origin remains unclear.
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Affiliation(s)
- B Cage
- National High Magnetic Field Laboratory, Florida State University, Tallahassee, Florida, 32306-4390, USA
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Telser J, Pardi LA, Krzystek J, Brunel LC. EPR Spectra from “EPR-Silent” Species: High-Field EPR Spectroscopy of Aqueous Chromium(II). Inorg Chem 1998. [DOI: 10.1021/ic9806683] [Citation(s) in RCA: 78] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Joshua Telser
- Chemistry Program, Roosevelt University, Chicago, Illinois 60605, Center for Interdisciplinary Magnetic Resonance, National High Magnetic Field Laboratory, Florida State University, Tallahassee, Florida 32310, and Consorzio Interuniversitario Nazionale per la Scienza e Tecnologia dei Materiali, 50134 Florence, Italy
| | - Luca A. Pardi
- Chemistry Program, Roosevelt University, Chicago, Illinois 60605, Center for Interdisciplinary Magnetic Resonance, National High Magnetic Field Laboratory, Florida State University, Tallahassee, Florida 32310, and Consorzio Interuniversitario Nazionale per la Scienza e Tecnologia dei Materiali, 50134 Florence, Italy
| | - J. Krzystek
- Chemistry Program, Roosevelt University, Chicago, Illinois 60605, Center for Interdisciplinary Magnetic Resonance, National High Magnetic Field Laboratory, Florida State University, Tallahassee, Florida 32310, and Consorzio Interuniversitario Nazionale per la Scienza e Tecnologia dei Materiali, 50134 Florence, Italy
| | - Louis-Claude Brunel
- Chemistry Program, Roosevelt University, Chicago, Illinois 60605, Center for Interdisciplinary Magnetic Resonance, National High Magnetic Field Laboratory, Florida State University, Tallahassee, Florida 32310, and Consorzio Interuniversitario Nazionale per la Scienza e Tecnologia dei Materiali, 50134 Florence, Italy
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Goldberg DP, Telser J, Krzystek J, Montalban AG, Brunel LC, Barrett AGM, Hoffman BM. EPR Spectra from “EPR-Silent” Species: High-Field EPR Spectroscopy of Manganese(III) Porphyrins. J Am Chem Soc 1997. [DOI: 10.1021/ja971169o] [Citation(s) in RCA: 126] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- David P. Goldberg
- Department of Chemistry, Northwestern University Evanston, Illinois 60208 Chemistry Program, Roosevelt University Chicago, Illinois 60605 Center for Interdisciplinary Magnetic Resonance National High Magnetic Field Laboratory Florida State University, Tallahassee, Florida 32310 Department of Chemistry Imperial College of Science, Technology and Medicine London, UK SW7 2AY
| | - Joshua Telser
- Department of Chemistry, Northwestern University Evanston, Illinois 60208 Chemistry Program, Roosevelt University Chicago, Illinois 60605 Center for Interdisciplinary Magnetic Resonance National High Magnetic Field Laboratory Florida State University, Tallahassee, Florida 32310 Department of Chemistry Imperial College of Science, Technology and Medicine London, UK SW7 2AY
| | - J. Krzystek
- Department of Chemistry, Northwestern University Evanston, Illinois 60208 Chemistry Program, Roosevelt University Chicago, Illinois 60605 Center for Interdisciplinary Magnetic Resonance National High Magnetic Field Laboratory Florida State University, Tallahassee, Florida 32310 Department of Chemistry Imperial College of Science, Technology and Medicine London, UK SW7 2AY
| | - Antonio Garrido Montalban
- Department of Chemistry, Northwestern University Evanston, Illinois 60208 Chemistry Program, Roosevelt University Chicago, Illinois 60605 Center for Interdisciplinary Magnetic Resonance National High Magnetic Field Laboratory Florida State University, Tallahassee, Florida 32310 Department of Chemistry Imperial College of Science, Technology and Medicine London, UK SW7 2AY
| | - Louis-Claude Brunel
- Department of Chemistry, Northwestern University Evanston, Illinois 60208 Chemistry Program, Roosevelt University Chicago, Illinois 60605 Center for Interdisciplinary Magnetic Resonance National High Magnetic Field Laboratory Florida State University, Tallahassee, Florida 32310 Department of Chemistry Imperial College of Science, Technology and Medicine London, UK SW7 2AY
| | - Anthony G. M. Barrett
- Department of Chemistry, Northwestern University Evanston, Illinois 60208 Chemistry Program, Roosevelt University Chicago, Illinois 60605 Center for Interdisciplinary Magnetic Resonance National High Magnetic Field Laboratory Florida State University, Tallahassee, Florida 32310 Department of Chemistry Imperial College of Science, Technology and Medicine London, UK SW7 2AY
| | - Brian M. Hoffman
- Department of Chemistry, Northwestern University Evanston, Illinois 60208 Chemistry Program, Roosevelt University Chicago, Illinois 60605 Center for Interdisciplinary Magnetic Resonance National High Magnetic Field Laboratory Florida State University, Tallahassee, Florida 32310 Department of Chemistry Imperial College of Science, Technology and Medicine London, UK SW7 2AY
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