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Brown C, Lita A, Tao Y, Peek N, Crosswhite M, Mileham M, Krzystek J, Achey R, Fu R, Bindra JK, Polinski M, Wang Y, van de Burgt LJ, Jeffcoat D, Profeta S, Stiegman AE, Scott SL. Mechanism of Initiation in the Phillips Ethylene Polymerization Catalyst: Ethylene Activation by Cr(II) and the Structure of the Resulting Active Site. ACS Catal 2017. [DOI: 10.1021/acscatal.7b02677] [Citation(s) in RCA: 27] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- Carole Brown
- Department
of Chemistry and Biochemistry, Florida State University, Tallahassee, Florida 32306, United States
| | - Adrian Lita
- Department
of Chemistry and Biochemistry, Florida State University, Tallahassee, Florida 32306, United States
| | - Yuchuan Tao
- Department
of Chemistry and Biochemistry, Florida State University, Tallahassee, Florida 32306, United States
| | - Nathan Peek
- Department
of Chemistry and Biochemistry, Florida State University, Tallahassee, Florida 32306, United States
| | - Mark Crosswhite
- Department
of Chemistry and Biochemistry, Florida State University, Tallahassee, Florida 32306, United States
| | - Melissa Mileham
- Orbital ATK, Flight
Systems Group, Corinne, Utah 84307, United States
- Savannah River National Laboratory, Savannah River Site, Aiken, South Carolina 29808, United States
| | - J. Krzystek
- National High Magnetic Field Laboratory, Tallahassee, Florida 32310, United States
| | - Randall Achey
- Savannah River National Laboratory, Savannah River Site, Aiken, South Carolina 29808, United States
| | - Riqiang Fu
- National High Magnetic Field Laboratory, Tallahassee, Florida 32310, United States
| | - Jasleen K. Bindra
- Department
of Chemistry and Biochemistry, Florida State University, Tallahassee, Florida 32306, United States
| | - Matthew Polinski
- Department
of Chemistry and Biochemistry, Florida State University, Tallahassee, Florida 32306, United States
| | - Youhong Wang
- Department of Chemistry & Biochemistry, University of California, Santa Barbara, California 93106, United States
| | - Lambertus J. van de Burgt
- Department
of Chemistry and Biochemistry, Florida State University, Tallahassee, Florida 32306, United States
| | - David Jeffcoat
- Department
of Chemistry and Biochemistry, Florida State University, Tallahassee, Florida 32306, United States
| | - Salvatore Profeta
- Department
of Chemistry and Biochemistry, Florida State University, Tallahassee, Florida 32306, United States
| | - A. E. Stiegman
- Department
of Chemistry and Biochemistry, Florida State University, Tallahassee, Florida 32306, United States
- National High Magnetic Field Laboratory, Tallahassee, Florida 32310, United States
- Department
of Chemical Engineering, University of California, Santa Barbara, California 93106, United States
| | - Susannah L. Scott
- Department of Chemistry & Biochemistry, University of California, Santa Barbara, California 93106, United States
- Department
of Chemical Engineering, University of California, Santa Barbara, California 93106, United States
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Nieczyporowska E, Kita E, Katafias A, Bajek A, Kaźmierski Ł. Oxidation in vitro of chromium(III) dietary supplements mer-[Cr(pic)3] and trans(S,S)-[Cr(Cys)2]− by hydrogen peroxide. TRANSIT METAL CHEM 2017. [DOI: 10.1007/s11243-017-0168-2] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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Gutsev GL, Bozhenko KV, Gutsev LG, Utenyshev AN, Aldoshin SM. Transitions from Stable to Metastable States in the Cr2On and Cr2On– Series, n = 1–14. J Phys Chem A 2017; 121:845-854. [DOI: 10.1021/acs.jpca.6b11036] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- G. L. Gutsev
- Department of Physics, Florida A&M University, Tallahassee, Florida 32307, United States
| | - K. V. Bozhenko
- Institute of Problems of Chemical Physics, Russian Academy of Sciences, Chernogolovka 142432, Moscow Region, Russia
- Department
of Physical and Colloid Chemistry, Peoples’ Friendship University of Russia, Moscow 117198, Russia
| | - L. G. Gutsev
- Department
of Chemistry and Biochemistry, Florida State University, Tallahassee 32306, United States
| | - A. N. Utenyshev
- Institute of Problems of Chemical Physics, Russian Academy of Sciences, Chernogolovka 142432, Moscow Region, Russia
| | - S. M. Aldoshin
- Institute of Problems of Chemical Physics, Russian Academy of Sciences, Chernogolovka 142432, Moscow Region, Russia
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4
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Hydrolytic and redox transformations of chromium(III) bis-oxalato complexes with glutaminic acid and glutamine: a kinetic, UV–Vis and EPR, study. TRANSIT METAL CHEM 2016. [DOI: 10.1007/s11243-016-0039-2] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022]
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5
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Ramachandran V, van Tol J, McKenna AM, Rodgers RP, Marshall AG, Dalal NS. High Field Electron Paramagnetic Resonance Characterization of Electronic and Structural Environments for Paramagnetic Metal Ions and Organic Free Radicals in Deepwater Horizon Oil Spill Tar Balls. Anal Chem 2015; 87:2306-13. [DOI: 10.1021/ac504080g] [Citation(s) in RCA: 27] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Affiliation(s)
- Vasanth Ramachandran
- Department
of Chemistry and Biochemistry, Florida State University, 95 Chieftain
Way, Tallahassee, Florida 32306, United States
| | - Johan van Tol
- National High Magnetic Field Laboratory, 1800 East Paul Dirac Drive, Tallahassee, Florida 32310, United States
| | - Amy M. McKenna
- National High Magnetic Field Laboratory, 1800 East Paul Dirac Drive, Tallahassee, Florida 32310, United States
| | - Ryan P. Rodgers
- Department
of Chemistry and Biochemistry, Florida State University, 95 Chieftain
Way, Tallahassee, Florida 32306, United States
- National High Magnetic Field Laboratory, 1800 East Paul Dirac Drive, Tallahassee, Florida 32310, United States
| | - Alan G. Marshall
- Department
of Chemistry and Biochemistry, Florida State University, 95 Chieftain
Way, Tallahassee, Florida 32306, United States
- National High Magnetic Field Laboratory, 1800 East Paul Dirac Drive, Tallahassee, Florida 32310, United States
| | - Naresh S. Dalal
- Department
of Chemistry and Biochemistry, Florida State University, 95 Chieftain
Way, Tallahassee, Florida 32306, United States
- National High Magnetic Field Laboratory, 1800 East Paul Dirac Drive, Tallahassee, Florida 32310, United States
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6
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Kinetic studies on acid- and base-catalyzed aquation of bis-alaninatochromium(III) and on oxidation of tris- and bis-Aa–chromium(III) complexes (Aa = Gly, Ala, Asn) by H2O2. TRANSIT METAL CHEM 2014. [DOI: 10.1007/s11243-014-9809-x] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/25/2022]
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7
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Kiersikowska E, Marai H, Wrzeszcz G, Kita E. Kinetic studies on H+-catalyzed aquation and hydrogen peroxide oxidation of tris-asparaginatochromium(III). TRANSIT METAL CHEM 2013. [DOI: 10.1007/s11243-013-9727-3] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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8
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Samantaray R, Clark RJ, Choi ES, Dalal NS. Elucidating the mechanism of multiferroicity in (NH4)3Cr(O2)4 and its tailoring by alkali metal substitution. J Am Chem Soc 2012; 134:15953-62. [PMID: 22978349 DOI: 10.1021/ja3065705] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Abstract
The antiferromagnetic Cr(V) peroxychromates, M(3)Cr(O(2))(4), M = K, Rb, and Cs, become ferroelectric when mixed with NH(4)(+), but the underlying mechanism is not understood. Our dielectric relaxation, Raman scattering, and high-frequency EPR measurements on the M(3-x)(NH(4))(x)Cr(O(2))(4) family clarify this mechanism. At 295 K, (NH(4))(3)Cr(O(2))(4) is tetragonal (I42m), with the NH(4)(+) ions occupying two distinctly different sites, N1 and N2. A ferroelectric transition at T(c1) = 250 K is revealed by λ-type anomalies in C(p) and dielectric constant, and lowering of symmetry to Cmc2(1). Below T(c1), the N1 sites lose their tetrahedral symmetry and thus polarization develops. Raman detection of translational modes involving the NH(4)(+) ions around 193 cm(-1) supports this model. EPR around T(c1) revealed that the [Cr(O(2))(4)](3-) ions reorient by about 10°. A minor peak at T(c2) ≈ 207 K is attributed to a short-range ordering that culminates in a long-range, structural order at T(c3) ≈ 137 K. At T(c3), the symmetry is lowered to P1 with significant changes in the cell parameters. Rb(+) and Cs(+) substitutions that block the N1 and N2 sites selectively show that T(c1) is related to the torsional motion of the N1 site, while T(c2) and T(c3) are governed by the motional slowing down of the N2 site. These data show that the multiferroic behavior of this family is governed by the rotational and translational dynamics of the NH(4)(+) ions and is tunable by their controlled substitutions. Relevance to other classes of possible multiferroics is pointed out.
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Affiliation(s)
- Raghabendra Samantaray
- Department of Chemistry and Biochemistry, Florida State University, Tallahassee, Florida 32306, United States
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9
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Misra SK, Diehl S. Theory of EPR lineshape in samples concentrated in paramagnetic spins: effect of enhanced internal magnetic field on high-field high-frequency (HFHF) EPR lineshape. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2012; 219:53-60. [PMID: 22613039 DOI: 10.1016/j.jmr.2012.03.023] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/21/2012] [Revised: 03/28/2012] [Accepted: 03/28/2012] [Indexed: 05/20/2023]
Abstract
A theoretical treatment is provided for the calculation of EPR (electron paramagnetic resonance) lineshape as affected by interactions with paramagnetic ions in the vicinity. The internal fields seen by the various paramagnetic ions due to interactions with paramagnetic ions in their vicinity, as well as the resulting lineshapes, become quite significant at high magnetic fields required in high-frequency (HFHF) EPR. The resulting EPR signals for the various ions are therefore characterized by different g-shifts and lineshapes, so that the overall EPR lineshape, which is an overlap of these, becomes distorted, or even split in HFHF EPR, from that observed at lower frequencies. The observed EPR lineshapes in MnSO(4)⋅H(2)O powder and K(3)CrO(8) single-crystal samples have been simulated here taking into account g-shifts and modified lineshapes. These simulations show that in these samples, concentrated in paramagnetic spins, the position and lineshapes of EPR signals are significantly modified in HFHF EPR involving very high magnetic fields.
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Affiliation(s)
- Sushil K Misra
- Physics Department, Concordia University, 1455 de Maisonneuve Boulevard West, Montreal, Quebec, Canada H3G 1M8.
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10
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Wang J, Wang Z, Clark RJ, Ozarowski A, van Tol J, Dalal NS. A high-frequency EPR characterization of the S=2 linear tri-atomic chain in Cr3(dpa)4Cl2·CH2Cl2. Polyhedron 2011. [DOI: 10.1016/j.poly.2011.02.032] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
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11
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Zhao Q, Nellutla S, Son WJ, Vaughn SA, Ye L, Smith MD, Caignaert V, Lufaso M, Pekarek TM, Smirnov AI, Whangbo MH, zur Loye HC. Ba4KFe3O9: a novel ferrite containing discrete 6-membered rings of corner-sharing FeO4 tetrahedra. Inorg Chem 2011; 50:10310-8. [PMID: 21905756 PMCID: PMC3214634 DOI: 10.1021/ic201374g] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Single crystals of a new iron-containing oxide, Ba(4)KFe(3)O(9), were grown from a hydroxide melt, and the crystal structure was determined by single-crystal X-ray diffraction. This ferrite represents the first complex oxide containing isolated 6-membered rings of corner-sharing FeO(4) tetrahedra. Mössbauer measurements are indicative of two tetrahedral high-spin Fe(3+) coordination environments. The observed magnetic moment (~3.9 μ(B)) at 400 K is significantly lower than the calculated spin-only (~5.2 μ(B)) value, indicating the presence of strong antiferromagnetic interactions in the oxide. Our density functional theory calculations confirm the strong antiferromagnetic coupling between adjacent Fe(3+) sites within each 6-membered ring and estimate the nearest-neighbor spin-exchange integral as ~200 K; next-nearest-neighbor interactions are shown to be negligible. The lower than expected effective magnetic moment for Ba(4)KFe(3)O(9) calculated from χT data is explained as resulting from the occupation of lower-lying magnetic states in which more spins are paired. X-band (9.5 GHz) electron paramagnetic resonance (EPR) spectra of a powder sample consist of a single line at g ~ 2.01 that is characteristic of Fe(3+) ions in a tetrahedral environment, thus confirming the Mössbauer results. Further analysis of the EPR line shape reveals the presence of two types of Fe(6) magnetic species with an intensity ratio of ~1:9. Both species have Lorentzian line shapes and indistinguishable g factors but differ in their peak-to-peak line widths (δB(pp)). The line-width ratio δB(pp)(major)/δB(pp)(minor) ~ 3.6 correlates well with the ratio of the Weiss constants, θ(minor)/θ(major) ~ 4.
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Affiliation(s)
- Qingbiao Zhao
- Department of Chemistry and Biochemistry, University of South Carolina, Columbia, South Carolina 29208, USA
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12
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McGowan KP, Abboud KA, Veige AS. Trianionic NCN3– Pincer Complexes of Chromium in Four Oxidation States (CrII, CrIII, CrIV, CrV): Determination of the Active Catalyst in Selective 1-Alkene to 2-Alkene Isomerization. Organometallics 2011. [DOI: 10.1021/om200547u] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Affiliation(s)
- Kevin P. McGowan
- Department of Chemistry, Center for Catalysis, University of Florida, P.O. Box 117200, Gainesville, Florida 32611, United States
| | - Khalil A. Abboud
- Department of Chemistry, Center for Catalysis, University of Florida, P.O. Box 117200, Gainesville, Florida 32611, United States
| | - Adam S. Veige
- Department of Chemistry, Center for Catalysis, University of Florida, P.O. Box 117200, Gainesville, Florida 32611, United States
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13
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Samantaray R, Clark RJ, Choi ES, Zhou H, Dalal NS. M(3-x)(NH4)(x)CrO8 (M = Na, K, Rb, Cs): a new family of Cr5+-based magnetic ferroelectrics. J Am Chem Soc 2011; 133:3792-5. [PMID: 21355591 DOI: 10.1021/ja1117683] [Citation(s) in RCA: 40] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023]
Abstract
Upon consideration of the hydrogen-bonding properties of the NH(4)(+) cation, we synthesized a new class of compounds, M(3-x)(NH(4))(x)CrO(8) (M = Na, K, Rb, Cs). These magnetic compounds with the simple 3d(1) ground state become ferroelectric. X-ray studies confirmed that the phase transition involves a symmetry change from I42m to Cmc2(1) to P1. The transition temperature depends linearly on the composition variable x. The transitions are of the order-disorder type, with N-H···O bonding playing the central role in the mechanism. Extension of this idea to the introduction of ferroelectricity in several other classes of materials is suggested.
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Affiliation(s)
- Raghabendra Samantaray
- Department of Chemistry and Biochemistry, Florida State University, Tallahassee, Florida 32306-4390, United States
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Khan MI, Nome RC, Putrevu NR, McNeely JH, Cage B, Doedens RJ. Hybrid materials composed of tetravanadate motifs: Synthesis, structure and magnetic properties of the open framework structure solids [{M(C5H5N)4}2]V4O12 (M=Cu, Co). Inorganica Chim Acta 2010. [DOI: 10.1016/j.ica.2010.07.023] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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Chiu A, Shi XL, Lee WKP, Hill R, Wakeman TP, Katz A, Xu B, Dalal NS, Robertson JD, Chen C, Chiu N, Donehower L. Review of chromium (VI) apoptosis, cell-cycle-arrest, and carcinogenesis. JOURNAL OF ENVIRONMENTAL SCIENCE AND HEALTH. PART C, ENVIRONMENTAL CARCINOGENESIS & ECOTOXICOLOGY REVIEWS 2010; 28:188-230. [PMID: 20859824 PMCID: PMC4330561 DOI: 10.1080/10590501.2010.504980] [Citation(s) in RCA: 66] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/04/2023]
Abstract
Hexavalent chromium combines with glutathione in chloride intracellular channel carrier to form tetravalent and pentavalent chromium in plasma and organelle membranes. It also combines with NADH/NADPH to form pentavalent chromium in mitochondria. Tetravalent- and pentavalent- chromium (directly and indirectly) mediated DNA double strand breaks activate DNA damage signaling sensors: DNA-dependent-protein-kinase signals p53-dependent intrinsic mitochondrial apoptosis, and ataxia-telangiectasia-mutated and ataxia-telangiectasia-Rad3-related signal cell-arrest for DNA repair. Tetravalent chromium may be the most potent species since it causes DNA breaks and somatic recombination, but not apoptosis. Upon further failure of apoptosis and senescence/DNA-repair, damaged cells may become immortal with loss-of-heterozygosity and genetic plasticity.
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Affiliation(s)
- A Chiu
- National Center for Environmental Assessment DC, US Environmental Protection Agency, Washington, DC 20460, USA.
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O'Reilly M, Falkowski JM, Ramachandran V, Pati M, Abboud KA, Dalal NS, Gray TG, Veige AS. Catalytic aerobic oxidation by a trianionic pincer Cr(III)/Cr(V) couple. Inorg Chem 2010; 48:10901-3. [PMID: 19894679 DOI: 10.1021/ic9019469] [Citation(s) in RCA: 43] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Aerobic oxidation that incorporates both O atoms into a substrate (PPh(3)) is achieved by employing a Cr(III)/Cr(V)[triple bond]O catalytic couple. A terphenyl trianionic pincer ligand stabilizes a high oxidation state Cr(V)[triple bond]O complex, and both the reduced (Cr(III), IR/X-ray) and oxidized (Cr(V)[triple bond]O, electron paramagnetic resonance/IR/X-ray) participants in the catalytic cycle are characterized.
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Affiliation(s)
- Matthew O'Reilly
- University of Florida, Department of Chemistry, Center for Catalysis, P.O. Box 117200, Gainesville, Florida 32607, USA
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Cage B, McNeely JH, Russek SE, Halpern HJ. Thermomagnetic properties of the Finland trityl radical. JOURNAL OF APPLIED PHYSICS 2009; 105:43905. [PMID: 19529796 PMCID: PMC2685218 DOI: 10.1063/1.3073992] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/26/2008] [Accepted: 12/13/2008] [Indexed: 05/27/2023]
Abstract
The Finland trityl paramagnet is characterized by magnetic susceptibility and a new form of quantitative electron paramagnetic resonance (EPR) that utilizes a superconducting quantum interference device (SQUID) as a detection method. This radical is of interest due to its use as a dynamic nuclear polarization agent as well as a potential magnetic refrigerant and quantum computing bit. The SQUID-EPR data show that the EPR linewidth of a concentrated trityl powder decreases dramatically from 4.4 to 1.4 mT as the temperature is increased from 1.8 to 10 K. The quantitative nature of SQUID-EPR is used to thermodynamically quantify the EPR energy transfer times and saturated fractions. At 95 GHz and 1.8 K, only 40% of the spins are in resonance at the onset of saturation. Conventional dc magnetic susceptibility over 1.8-150 K indicates an S=12 Curie-Weiss relationship with little long range interaction. Magnetization versus applied field at 1.8 and 4 K fits a Brillouin function with >80% electronic polarization at a normalized field of gmu(B)mu(0)HkT approximately 3. These results provide information required for theoretical modeling and engineering of the trityl radical for a wide range of applications.
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Nellutla S, Choi KY, Pati M, van Tol J, Chiorescu I, Dalal NS. Coherent manipulation of electron spins up to ambient temperatures in Cr5+ (S = 1/2) doped K3NbO8. PHYSICAL REVIEW LETTERS 2007; 99:137601. [PMID: 17930636 DOI: 10.1103/physrevlett.99.137601] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/19/2007] [Indexed: 05/25/2023]
Abstract
We report coherent spin manipulation on Cr(5+) (S = 1/2, I = 0) doped K(3)NbO(8), which constitutes a dilute two-level model relevant for use as a spin qubit. Rabi oscillations are observed for the first time in a spin system based on transition metal oxides up to room temperature. At liquid helium temperature the phase coherence relaxation time T2 reaches approximately 10 micros and, with a Rabi frequency of 20 MHz, yields a single-qubit figure of merit Q(M) of about 500. This shows that a diluted ensemble of Cr(5+) (S = 1/2) doped K(3)NbO(8) is a potential candidate for solid-state quantum information processing.
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Affiliation(s)
- S Nellutla
- National High Magnetic Field Laboratory, Tallahassee, Florida 32310, USA
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20
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Cotton FA, Dalal NS, Huang P, Ibragimov SA, Murillo CA, Piccoli PMB, Ramsey CM, Schultz AJ, Wang X, Zhao Q. Better Understanding of the Species with the Shortest Re26+ Bonds and Related Re27+ Species with Tetraguanidinate Paddlewheel Structures. Inorg Chem 2007; 46:1718-26. [PMID: 17243673 DOI: 10.1021/ic062319b] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
A series of compounds has been made containing quadruply bonded Re2(hpp)4X2 species (hpp = the anion of 1,3,4,6,7,8-hexahydro-2H-pyrimido[1,2a]pyrimidine), where X is CF3SO3 (1), CF3CO2 (2), and F (3). The distances of 2.1562(7), 2.1711(5), and 2.1959(4) A for 1-3 show significant effects of the sigma and pi electron donating ability of the axial ligands on the metal-metal distance. With the weakly coordinating triflate ligand the Re-Re distance is the shortest for any quadruple bonded species known. In addition to examining the effects of axial ligands on the Re2(hpp)42+ core, our study of the Re2(hpp)43+ core is being extended beyond the preliminary results previously reported in only one compound [Re2(hpp)4Cl2]PF6 (Dalton Trans. 2003, 1218). We now report the structural characterization by both X-ray and neutron diffraction of the compound [Re2(hpp)4F](TFPB)2, 4 (TFPB = the anion tetrakis[3,5-bis(trifluoromethyl)phenyl]borate), and a detailed study by EPR spectroscopy of [Re2(hpp)4Cl2]PF6 at 9.5, 34.5, and 95 GHz frequencies, using dilute fluid solutions, frozen glass, and neat powder, show that the unpaired electron in the [Re2(hpp)4Cl2]+ ion is in an MO of predominant metal character with little mixing from the guanidinate ligands.
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Affiliation(s)
- F Albert Cotton
- Department of Chemistry and Laboratory of Molecular Structure and Bonding, P.O. Box 30012, Texas A&M University, College Station, Texas 77842-3012, USA.
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21
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Berry JF, Bill E, Bothe E, Cotton FA, Dalal NS, Ibragimov SA, Kaur N, Liu CY, Murillo CA, Nellutla S, North JM, Villagran D. A Fractional Bond Order of 1/2 in Pd25+−Formamidinate Species; The Value of Very High-Field EPR Spectra. J Am Chem Soc 2007; 129:1393-401. [PMID: 17263424 DOI: 10.1021/ja067328y] [Citation(s) in RCA: 45] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Reaction of Pd(2)(DAniF)(4), 1, (DAniF = di-p-anisylformamidinate) with 1 equiv of AgPF(6) in CH(2)Cl(2) at or below -10 degrees C produces the paramagnetic species [Pd(2)(DAniF)4]PF(6), 1-PF(6), that has been studied by X-ray crystallography, UV-vis spectroscopy, electrochemistry, and multifrequency (9.5, 34.5, 110, and 220 GHz) EPR spectroscopy. Upon oxidation of the precursor, the Pd-Pd distance decreases by 0.052 Angstrom from 2.6486(8) to 2.597(1) Angstrom. The EPR spectra show broad signals with line widths of about 1000 G. The spectra collected at high field show a large spread of g tensor components ( approximately 0.03), but these are masked at lower frequencies (9.5 and 34.5 GHz). A reinvestigation using high-field EPR of the p-tolyl analogue, which is the only other structurally characterized Pd(2)(5+) species (Cotton, F. A.; Matusz, M.; Poli, R.; Feng, X. J. Am. Chem. Soc. 1988, 110, 1144), shows that this species, which had been reported to give an isotropic 9.5 GHz EPR spectrum, also gives anisotropic 110 and 220 GHz EPR spectra with a similarly large spread of g tensor components consistent with the unpaired electron residing in a metal-based MO. The results of these studies and calculations using density functional theory are consistent with the oxidation being metal-based, resulting in an uncommon Pd(2)(5+) species with a Pd-Pd bond order of 1/2.
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Affiliation(s)
- John F Berry
- Department of Chemistry and Laboratory of Molecular Structure and Bonding, P.O. Box 30012, Texas A and M University, College Station, Texas 77842-3012, USA
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Barybin MV, Chisholm MH, Dalal NS, Holovics TH, Patmore NJ, Robinson RE, Zipse DJ. Long-Range Electronic Coupling of MM Quadruple Bonds (M = Mo or W) via a 2,6-Azulenedicarboxylate Bridge. J Am Chem Soc 2005; 127:15182-90. [PMID: 16248660 DOI: 10.1021/ja0541884] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The preparation of 2,6-azulenedicarboxylic acid (I) from its diester, 2-CO(2)(t)Bu-6-CO(2)-C(10)H(6) (II), is reported together with the crystal and molecular structure of the ester, II. From the reactions between the dicarboxylic acid I and the MM quadruply bonded complexes M(2)(O(2)C(t)Bu)(4), where M = Mo or W, the azulenedicarboxylate bridged complexes [M(2)(O(2)C(t)Bu)(3)](2)(mu-2,6-(CO(2))(2)-C(10)H(6)) have been isolated, III (M = Mo) and IV (M = W). The latter compounds provide examples of electronically coupled M(2) centers via a polar bridge. The compounds show intense electronic absorptions due to metal-to-bridge charge transfer. This occurs in the visible region of the spectrum for III (M = Mo) but in the near-IR for IV (M = W). One electron oxidation with Ag(+)PF(6)(-) in THF generates the radical cations III(+) and IV(+). By both UV-vis-NIR and EPR spectroscopy the molybdenum ion III(+) is shown to be valence trapped or Class II on the Robin and Day classification scheme. Electrochemical, UV-vis-NIR, and EPR spectroscopic data indicate that, in the tungsten complex ion IV(+), the single electron is delocalized over the two W(2) centers that are separated by a distance of ca. 13.6 A. Furthermore, from the hyperfine coupling to (183)W (I = (1)/(2)), the singly occupied highest molecular orbital is seen to be polarized toward one W(2) center in relationship to the other. Electronic structure calculations employing density functional theory indicate that the HOMO in compounds III and IV is an admixture of the two M(2) delta orbitals that is largely centered on the M(2) unit having proximity to the C(5) ring of the azulenedicarboxylate bridge. The energy of the highest occupied orbital of the bridge lies very close in energy to the M(2) delta orbitals. However, this orbital does not participate in electronic coupling by a hole transfer superexchange mechanism, and the electronic coupling in the radical cations of III and IV occurs by electron transfer through the bridge pi system.
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Affiliation(s)
- Mikhail V Barybin
- Department of Chemistry, The University of Kansas, Lawrence, Kansas 66045-7582, USA
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Chisholm MH, D'Acchioli JS, Pate BD, Patmore NJ, Dalal NS, Zipse DJ. Cations M2(O2CtBu)4+, Where M = Mo and W, and MoW(O2CtBu)4+. Theoretical, Spectroscopic, and Structural Investigations. Inorg Chem 2005; 44:1061-7. [PMID: 15859287 DOI: 10.1021/ic049081g] [Citation(s) in RCA: 51] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
With the aid of density function theory, the molecular and electronic structures of the molecules Mo2(O2CMe)4, MoW(O2CMe)4, and W2(O2CMe)4 and their single-electron oxidized radical cations have been determined; this includes calculated observables such as v(MM) and the delta --> delta* electronic transition energies. The calculated properties are compared with those for the corresponding pivalates, M2(O2CtBu)4 (M = Mo or W) and MoW(O2CtBu)4 and their radical cations prepared in situ by oxidation with Cp2FePF6. The EPR spectra of the radical cations are also reported. The EPR spectrum of the MoW(O2CtBu)4+ cation reveals that the unpaired electron is in a polarized MM delta orbital having 70% Mo and 30% W character. The MM stretching frequencies show good correlation with the MM bond lengths obtained from single-crystal X-ray diffraction studies of MoW(O2CtBu)4, W2(O2CtBu)4, and W2(O2CtBu)4+PF6- compounds, along with previously reported structures. These data provide benchmark parameters for valence trapped dicarboxylate bridged radical cations of the type [(tBuCO2)3M2]2(micro-O2C-X-CO2)+ (X = conjugated spacer).
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Affiliation(s)
- Malcolm H Chisholm
- Department of Chemistry, The Ohio State University, Columbus, Ohio 43210-1185, USA.
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Cotton FA, Dalal NS, Hillard EA, Huang P, Murillo CA, Ramsey CM. Applications of high-field (W-band) EPR to M-M bonded units (M = Cr, Mo): the first confirmed oxidation of a Cr2 4+ paddlewheel complex to a stable isostructural Cr2 5+ product. Inorg Chem 2003; 42:1388-90. [PMID: 12611500 DOI: 10.1021/ic0260670] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The EPR spectra of [Cr(2)[(PhN)(2)CN(CH(2))(4)](4)]PF(6) and [Mo(2)(TiPB)(4)]PF(6) (TiPB = anion of 2,4,6-triisopropylbenzoic acid) at W-band are shown to have g values significantly lower than 2.00 and exhibit parallel and perpendicular components (not resolved at X-band). Therefore the unpaired electrons of the M(2)(5+) units must reside on metal-based (not ligand-based) orbitals. Thus, the chromium compound must be considered as the first confirmed oxidation product of a Cr(2)(4+) paddlewheel complex comparable to the Mo(2)(5+) compounds.
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Affiliation(s)
- F Albert Cotton
- Department of Chemistry and Laboratory for Molecular Structure and Bonding, PO Box 30012, Texas A&M University, College Station 77842-3012, USA.
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Ranjit KT, Kevan L. Photoinduced Charge Separation of N,N,N‘N‘-Tetramethylbenzidine in Chromium Ion-Exchanged Zeolite X at Room Temperature. J Phys Chem B 2002. [DOI: 10.1021/jp021276r] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- Koodali T. Ranjit
- Department of Chemistry, University of Houston, Houston, Texas 77204-5003
| | - Larry Kevan
- Department of Chemistry, University of Houston, Houston, Texas 77204-5003
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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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Lay PA, Levina A. Activation of Molecular Oxygen during the Reactions of Chromium(VI/V/IV) with Biological Reductants: Implications for Chromium-Induced Genotoxicities1. J Am Chem Soc 1998. [DOI: 10.1021/ja974240z] [Citation(s) in RCA: 86] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Peter A. Lay
- Contribution from the School of Chemistry, University of Sydney, New South Wales 2006, Australia
| | - Aviva Levina
- Contribution from the School of Chemistry, University of Sydney, New South Wales 2006, Australia
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Zhang L, Lay PA. EPR Spectroscopic Studies on the Formation of Chromium(V) Peroxo Complexes in the Reaction of Chromium(VI) with Hydrogen Peroxide. Inorg Chem 1998. [DOI: 10.1021/ic971069j] [Citation(s) in RCA: 40] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Lianbo Zhang
- School of Chemistry, University of Sydney, Sydney, NSW 2006, Australia
| | - Peter A. Lay
- School of Chemistry, University of Sydney, Sydney, NSW 2006, Australia
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Hiromitsu I, Yamamoto H, Ito T. Three-dimensional antiferromagnetic transition of iodine-doped fluoro-aluminum phthalocyanine with a disordered polymer chain. PHYSICAL REVIEW. B, CONDENSED MATTER 1995; 52:7252-7259. [PMID: 9979667 DOI: 10.1103/physrevb.52.7252] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 04/12/2023]
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Abstract
Electron spin resonance (ESR) measurements provide evidence for the formation of Cr(V) intermediates in the enzymatic reduction of Cr(VI) by glutathione reductase (GSSG-R) in the presence of NADPH, indicating an initial single-electron transfer step in the reduction mechanism. Depending on the pH, at least two different Cr(V) species are generated which are relatively long-lived. In addition, we have detected the hydroxyl (.OH) radical formation during the GSSG-R catalyzed reduction of Cr(VI) by spin trapping, employing 5,5-dimethyl-1-pyrroline-N-oxide (DMPO) and alpha-(4-pyridyl-1-oxide)-N-tert-butylnitrone (4-POBN) as spin traps. Superoxide dismutase (SOD) causes only a minor effect on the .OH radical and Cr(V) formation, indicating that the O2- is not significantly involved in the reaction mechanism. Catalase enhances the Cr(V) formation and substantially inhibits the .OH radical formation, indicating the involvement of hydrogen peroxide (H2O2) in the reaction mechanism. Addition of H2O2 suppresses Cr(V) and enhances the .OH radical formation. Measurements involving N-ethylmaleimide show that the Cr(V) species, produced enzymatically by the reduction of Cr(VI) by GSSG-R, react with H2O2 to generate .OH radicals, which might participate in the initiation of Cr(VI) carcinogenicity.
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Affiliation(s)
- X L Shi
- Department of Chemistry, West Virginia University, Morgantown 26506
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Shi XL, Dalal NS. Evidence for a Fenton-type mechanism for the generation of .OH radicals in the reduction of Cr(VI) in cellular media. Arch Biochem Biophys 1990; 281:90-5. [PMID: 2166480 DOI: 10.1016/0003-9861(90)90417-w] [Citation(s) in RCA: 111] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
Electron spin resonance (ESR) spectroscopy has been employed to examine the role of tetraperoxochromate (V) ions (CrO3-8) and other Cr(V) species in the generation of hydroxyl (OH) radicals in the reaction of Cr(VI) with H2O2 in biological media. In contrast to earlier suggestions, the present ESR studies using crystalline K3CrO8 as a source of CrO3-8 show that decomposition of CrO3-8 in water or in H2O2 does not generate significant amounts of OH radicals. Addition of NADH to a solution containing CrO3-8 yields a Cr(V)-NADH complex, which readily reacts with H2O2 to generate OH radicals. Similar results obtained from several other biological reductants, including vitamin B2, indicate that a vacant coordination site on a Cr(V) complex facilitates its reaction with H2O2 to generate .OH radicals. We thus suggest that in biological media, reaction [3] instead of [1] or [2] is the major pathway for the .OH radical generation: [formula, see text]
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Affiliation(s)
- X L Shi
- Department of Chemistry, West Virginia University, Morgantown 26506
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Shi XG, Dalal NS. On the hydroxyl radical formation in the reaction between hydrogen peroxide and biologically generated chromium(V) species. Arch Biochem Biophys 1990; 277:342-50. [PMID: 2155579 DOI: 10.1016/0003-9861(90)90589-q] [Citation(s) in RCA: 142] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
Electron spin resonance (ESR) measurements on solutions and isolated powders provide direct evidence for the involvement of Cr(V) species in the reduction of Cr(VI) by NAD(P)H. ESR analysis of an isolated Cr(V)-NAD(P)H solid yields g parallel = 1.9831 and g perpendicular = 1.9772, indicating that the unpaired electron occupies the dz2 orbital of the Cr(V) ion, with square-pyramidal geometry. Addition of hydrogen peroxide (H2O2) to the NAD(P)H-Cr(VI) reaction mixtures suppresses the Cr(V) species and generates hydroxyl (.OH) radicals. The .OH radicals were detected via ESR spin trapping, employing 5,5-dimethyl-1-pyrroline-N-oxide and alpha-(4-pyridyl-1-oxide)-N-tert-butylnitrone as spin traps. The dependence of Cr(V) and .OH radical formation on the H2O2 and Cr(VI) concentrations indicates that the Cr(V) species react with H2O2 to generate the .OH radicals. Similar results were obtained by using various diols (arabinose, cellobiose, FAD, fructose, glyceraldehyde, ribose, and tartaric acid), alpha-hydroxycarboxylic acids, and glutathione. Investigations with superoxide dismutase showed no significant participation of O2- in the generation of .OH radicals. These results thus indicate that the Cr(V) complexes, produced in the reduction of Cr(VI) by cellular reductants, react with H2O2 to generate .OH radicals, which might be initiators of the primary events in the Cr(VI) cytotoxicity.
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Affiliation(s)
- X G Shi
- Department of Chemistry, West Virginia University, Morgantown 26506
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Shi XL, Dalal NS. On the mechanism of the chromate reduction by glutathione: ESR evidence for the glutathionyl radical and an isolable Cr(V) intermediate. Biochem Biophys Res Commun 1988; 156:137-42. [PMID: 2845969 DOI: 10.1016/s0006-291x(88)80815-5] [Citation(s) in RCA: 84] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023]
Abstract
With a view of elucidating the role of glutathione (GSH) in the biochemical pathways of the chromate-exposure related carcinogenesis, we carried out electron spin resonance (ESR) spectroscopic investigations of the chromate-GSH redox reactions. The ESR measurements, employing spin-traps, provide evidence for the involvement of the glutathione (GS) radical, as well as an isolable Cr(V)-glutathione intermediate. These results indicate a new mechanism for the reduction of chromate by GSH in in vitro cellular environment and help understand the (unexpected) increase in Cr(VI)-induced DNA strand breaks at elevated GSH levels.
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Affiliation(s)
- X L Shi
- Department of Chemistry, West Virginia University, Morgantown 26506
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The structure and reactivity of dioxygen complexes of the transition metals. TRANSITION METAL COMPLEXES STRUCTURES AND SPECTRA 1983. [DOI: 10.1007/bfb0111572] [Citation(s) in RCA: 111] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
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