Electron Spin Resonance of High-Spin d5 Systems

Dowsing, Roy D.; Gibson, J. F.

doi:10.1063/1.1670791

Cited by 270 publications

(60 citation statements)

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“…The theoretical framework that describes the origin of EPR spectra of Mn(II)-containing systems is well described elsewhere [31,[36][37][38][39][40][41] The first term describes the Zeeman effect whereby the applied static magnetic field B 0 interacts with the unpaired electrons, breaking the Kramers degeneracy. While generally, the matrix of g-values can exhibit significant anisotropy (i.e., differences from the free electron g-value = 2.0023), such is not the case for nearly all high-spi n mononuclear Mn(II) systems.…”

Section: Spin Physics For Mn(ii)mentioning

confidence: 99%

“…The theoretical framework that describes the origin of EPR spectra of Mn(II)-containing systems is well described elsewhere [31,[36][37][38][39][40][41] and only briefly summarized below. The energies of each spin level are understood in terms of the following effective spin Hamiltonian (2) The first term describes the Zeeman effect whereby the applied static magnetic field B 0 interacts with the unpaired electrons, breaking the Kramers degeneracy.…”

Section: Spin Physics For Mn(ii)mentioning

confidence: 99%

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Multifrequency pulsed EPR studies of biologically relevant manganese(II) complexes

et al. 2007

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Electron paramagnetic resonance studies at multiple frequencies (MF EPR) can provide detailed electronic structure descriptions of unpaired electrons in organic radicals, inorganic complexes, and metalloenzymes. Analysis of these properties aids in the assignment of the chemical environment surrounding the paramagnet and provides mechanistic insight into the chemical reactions in which these systems take part. Herein, we present results from pulsed EPR studies performed at three different frequencies (9, 31, and 130 GHz) on [Mn(II)(H 2 O) 6 ] 2+ , Mn(II) adducts with the nucleotides ATP and GMP, and the Mn(II)-bound form of the hammerhead ribozyme (MnHH). Through line shape analysis and interpretation of the zero-field splitting values derived from successful simulations of the corresponding continuous-wave and field-swept echodetected spectra, these data are used to exemplify the ability of the MF EPR approach in distinguishing the nature of the first ligand sphere. A survey of recent results from pulsed EPR, as well as pulsed electron-nuclear double resonance and electron spin echo envelope modulation spectroscopic studies applied to Mn(II)-dependent systems, is also presented. Mn-Containing Biological SystemsManganese operates as a cofactor in numerous proteins, serving both catalytic and structural roles [1][2][3][4]. Many Mn-dependent enzymes take advantage o f the rich redox chemistry available to the metal, accessing the +2, +3, +4, and perhaps even the +5 oxidation states during their turnover. For example, Mn-superoxide dismutase (MnSOD), which detoxifies the cell of the superoxide radical , cycles between the Mn(II) and Mn(III) oxidation states via the ping-pong type mechanism shown below [5][6][7][8][9].(1a) (1b) Other examples of such mononuclear redox-active enzymes include the manganese peroxidase responsible for lignin degradation by white-rot fungus [10][11][12]; a unique Mndependent form of lipoxygenase [13][14][15][16]; oxalate decarboxylase [17,18]; as well as an extradiol catechol dioxygenase [19][20][21]. NIH-PA Author ManuscriptNIH-PA Author Manuscript NIH-PA Author ManuscriptIn order to help minimize kinetic and thermodynamic penalties associated with electron transfer events and the execution of chemical reactions, two or more metal centers can be coupled together to provide active sites capable of conducting multiple electrons while still operating within a physiologically accessible range of reduction potentials [22]. Only three such examples of redox-active polynuclear Mn enzymes are known: Mn-catalase that disproportionates hydrogen peroxide [23][24][25][26]; a Mn form of ribonucleotide reductase (Mn-RNR) [27,28]; and, arguably the most recognized Mn-dependent enzyme, the photosynthetic core of green plants, algae, and certain cyanobacteria termed photosystem II (PSII) [29,30]. Through a series of photoinitiated electron transfer events, oxidizing equivalents are stored on the tetranuclear Mn core of PSII -the oxygen-evolving complex (OEC) -which then extracts four electr...

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Section: Spin Physics For Mn(ii)mentioning

confidence: 99%

Section: Spin Physics For Mn(ii)mentioning

confidence: 99%

Multifrequency pulsed EPR studies of biologically relevant manganese(II) complexes

et al. 2007

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“…In accordance with all previous experience g was assumed to be isotropic and set equal to 2.0024. Rough estimates of D and E were obtained from the observed fine structure splittings using the diagrams of Dowsing and Gibson 20 . Final values for the parameters D, E and a were obtained using a slightly modified least squares fitting computer program QCPE 69 developed by Gladney*.…”

Section: Resultsmentioning

confidence: 99%

EPR of Fe³⁺ in Low Quartz Isomorphs A(III)B(V)O₄

Krauß

Lehmann

1975

Zeitschrift Für Naturforschung A

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Electron spin resonance spectra of Fe 3+ in hydrothermally grown single crystals of A1P04 , GaP04, A1AS04 and GaAs04 were measured at X-band and analyzed using a Spin-Hamiltonian for rhombic symmetry. The zero field splitting was found to be between about one and two times the microwave frequency, increasing regularly from A1P04 to GaAs04. This increase is largely due to an increase in the axial parameter D whereas the second order rhombic parameter E is practically constant. The fourth order parameter a increases exponentially with the lattice parameter ratio c0/a0 . The variation of D indicates a site distortion for GaP04 about twice as large as in A1P04 . For the arsenates, influences of increased covalency are apparent in addition to site distortions of comparable size. Halfwidths in the range of 18 Gauss for the phosphates and 38 Gauss for the arsenates indicate hyperfine interactions with 31 P and 75 As, and estimates of 0.5 and 1% spin density resp. at these nuclei are obtained, again showing increased covalency for the arsenate compounds.

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“…Hagen 1992). In order to relate an amplitude ratio of the two signals, A g=4.3 /A g=6 , to a concentration ratio, [non-haemin Fe(III)]/[haemin Fe(III)], we assumed a small zero-field splitting, D<2 cm )1 , for the non-haemin iron (Dowsing & Gibson 1969), which implies 33% population of the observed doublet, and a D=10 cm )1 for the haemin signal (Van Kan et al 1998), which implies 84% of the observed doublet.…”

Section: Apoferritin Preparationmentioning

confidence: 99%

EPR Studies of Recombinant Horse L-Chain Apoferritin and its Mutant (E 53,56,57,60 Q) with Haemin

2006

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Structural similarities between ferritins and bacterioferritins have been extensively demonstrated. However, there is an essential difference between these two types of ferritins: whereas bacterioferritins bind haem, in-vivo, as Fe(II)-protoporphyrin IX (this haem is located in a hydrophobic pocket along the 2-fold symmetry axes and is liganded by two axial Met 52 residues), eukaryotic ferritins are non-haem iron proteins. However, in in-vivo studies, a cofactor has been isolated from horse spleen apoferritin similar to protoporphyrin IX; in in-vitro experiments, it has been shown that horse spleen apoferritin is able to interact with haemin (Fe(III)-protoporphyrin IX). Studies of haemin incorporation into horse spleen apoferritin have been carried out, which show that the metal free porphyrin is found in a pocket similar to that which binds haem in bacterioferritins (Pre´cigoux et al. 1994 Acta Cryst D50, 739-743). A mechanism of demetallation of haemin by L-chain apoferritins was subsequently proposed (Crichton et al. 1997 Biochem 36, 15049-15054) which involved four Glu residues (E 53,56,57,60) situated at the entrance of the hydrophobic pocket and appeared to be favoured by acidic conditions. To verify this mechanism, these four Glu have been mutated to Gln in recombinant horse L-chain apoferritin. We report here the EPR spectra of recombinant horse L-chain apoferritin and its mutant with haemin in basic and acidic conditions. These studies confirm the ability of recombinant L-chain apoferritin and its mutant to incorporate and demetallate the haemin in acidic and basic conditions.

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Electron Spin Resonance of High-Spin d5 Systems

Cited by 270 publications

References 22 publications

Multifrequency pulsed EPR studies of biologically relevant manganese(II) complexes

Multifrequency pulsed EPR studies of biologically relevant manganese(II) complexes

EPR of Fe³⁺ in Low Quartz Isomorphs A(III)B(V)O₄

EPR Studies of Recombinant Horse L-Chain Apoferritin and its Mutant (E 53,56,57,60 Q) with Haemin

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Electron Spin Resonance of High-Spin d5 Systems

Cited by 270 publications

References 22 publications

Multifrequency pulsed EPR studies of biologically relevant manganese(II) complexes

Multifrequency pulsed EPR studies of biologically relevant manganese(II) complexes

EPR of Fe3+ in Low Quartz Isomorphs A(III)B(V)O4

EPR Studies of Recombinant Horse L-Chain Apoferritin and its Mutant (E 53,56,57,60 Q) with Haemin

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EPR of Fe³⁺ in Low Quartz Isomorphs A(III)B(V)O₄