Water-exchange studies on manganese(II) nitrilotriacetate and ethylenediaminetetraacetate complexes by oxygen-17 nuclear magnetic resonance

Zetter, Mark S.; Grant, Michael W.; Wood, E.; Dodgen, Harold W.; Hunt, John P.

doi:10.1021/ic50117a026

Cited by 59 publications

(42 citation statements)

References 2 publications

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“…However, the obtained activation parameters, especially the small positive activation entropies and volumes (obtained for the first time for the seven-coordinate Mn(II) species) suggest an interchange (I d ) mechanism for the water exchange reactions on the seven-coordinate Mn(II) centres. The water exchange rate constants, k ex are mainly controlled by the p-acceptor abilities of the ligands and decrease with an increase 25 which is much faster than in the case of the Mn(II) complexes with neutral pentadentate ligands studied by us (Scheme 6). This increased lability is due to the strong p-donor ability and high negative charge of the EDTA ligand and also due to the fact that in [Mn(EDTA)(H 2 O)] 2the water molecule is in the sterically crowded equatorial plane with five donor atoms, whereas in our complexes water molecules are in the axial positions.…”

Section: Superoxide Activation Dismutation Catalyzed By Metal Centresmentioning

confidence: 68%

Metal complex-assisted activation of small molecules. From NO to superoxide and peroxides

Eldik

2008

Dalton Trans.

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Transition metal centres are one of the primary targets for nitric oxide (NO), superoxide (O2(-)) and hydrogen peroxide (H2O2), which are small molecules present in a biological milieu, and of industrial and environmental interest. Coordination to a metal centre modulates their redox behaviour in such a way that they become activated for an inner-sphere oxidation or reduction, depending on the electronic and redox properties of a particular transition metal ion. Since the related redox reactions play multiple roles in physiological and pathophysiological processes, as well as in chemical catalysis in terms of synthetic applications and exhaust gas purification, the elucidation of the mechanisms of the elementary reaction steps behind these complex processes is of fundamental importance. This review concentrates on our work in this area, where by applying low temperature and high pressure kinetic and thermodynamic techniques we shed more light on the mechanisms of the particular reaction steps involved in the activation of NO, O2(-) and various peroxides. The studies include work on solvent exchange reactions that control the binding of small molecules to the metal centre and subsequent electron-transfer processes. We paid special attention to different iron and manganese complexes with heme and non-heme ligand systems.

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Section: Superoxide Activation Dismutation Catalyzed By Metal Centresmentioning

confidence: 68%

Metal complex-assisted activation of small molecules. From NO to superoxide and peroxides

Eldik

2008

Dalton Trans.

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“…Usually such large values imply that the Mn(II) center is no longer in a pseudo-octahedral ligand field and is likely pentacoordinate [42,44,87] or some highly distorted tetrahedron [111]. However, NMR and X-ray crystallographic results clearly indicate that Mn(II)EDTA is seven-coordinate with a water ligand occupying an apical position [112,113]. The simulated EPR data presented in Fig.…”

Section: Pulsed Epr Studiesmentioning

confidence: 96%

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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“…There are a number of Mn II bispidine complexes known, especially with tetradentate bispidine ligands and, as expected for high spin d 5 systems, their geometries are generally octahedral with Mn-N distances significantly larger than those of the Fe II complexes. 27,29,41 Therefore and since heptacoordinate Mn II complexes ( pentagonal bipyramidal and monocapped trigonal prismatic) are not uncommon, [42][43][44] the hexacoordinating bispidine L was coordinated to Mn II . Diffusion of diethylether into the methanolic solution of [Mn II (L)Cl] + , obtained by the combination of a methanolic solution of MnCl 2 with an equimolar amount of ligand, produced practically colorless needles, suitable for X-ray diffraction.…”

Section: Transition Metal Coordination Chemistrymentioning

confidence: 99%

Synthesis and transition metal coordination chemistry of a novel hexadentate bispidine ligand

2015

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Reported is the new bispidine-derived hexadentate ligand (L = 3-(2-methylpyridyl)-7-(bis-2-methylpyridyl)-3,7-diazabicyclo[3.3.1]nonane) with two tertiary amine and four pyridine donor groups. This ligand can form heterodinuclear and mononuclear complexes and, in the mononuclear compounds discussed here, the ligand may coordinate as a pentadentate ligand, with one of the bispyridinemethane-based pyridine groups un- or semi-coordinated, or as a hexadentate ligand, leading to a pentagonal pyramidal coordination geometry or, with an additional monodentate ligand, to a heptacoordinate pentagonal bipyramidal structure. The solution and solid state data presented here indicate that, with the relatively small Cu(II) and high-spin Fe(II) ions the fourth pyridine group is only semi-coordinated for steric reasons and, with the larger high-spin Mn(II) ion genuine heptacoordination is observed but with a relatively large distortion in the pentagonal equatorial plane.

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Water-exchange studies on manganese(II) nitrilotriacetate and ethylenediaminetetraacetate complexes by oxygen-17 nuclear magnetic resonance

Cited by 59 publications

References 2 publications

Metal complex-assisted activation of small molecules. From NO to superoxide and peroxides

Metal complex-assisted activation of small molecules. From NO to superoxide and peroxides

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

Synthesis and transition metal coordination chemistry of a novel hexadentate bispidine ligand

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