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Query: UNIPROT:O14944 (EPR)
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Nitrosyl complexes with {Ru-NO} (6) and {Ru-NO} (7) configurations have been isolated in the framework of [Ru(trpy)(L)(NO)] ( n+ ) [trpy = 2,2':6',2''-terpyridine, L = 2-phenylimidazo[4,5- f]1,10-phenanthroline] as the perchlorate salts [ 4](ClO 4) 3 and [ 4](ClO 4) 2, respectively. Single crystals of protonated material [ 4-H (+)](ClO 4) 4.2H 2O reveal a Ru-N-O bond angle of 176.1(7) degrees and triply bonded N-O with a 1.127(9) A bond length. Structures were also determined for precursor compounds of [ 4] (3+) in the form of [Ru(trpy)(L)(Cl)](ClO 4).4.5H 2O and [Ru(trpy)(L-H)(CH 3CN)](ClO 4) 3.H 2O. In agreement with largely NO centered reduction, a sizable shift in nu(NO) frequency was observed on moving from [ 4] (3+) (1953 cm (-1)) to [ 4] (2+) (1654 cm (-1)). The Ru (II)-NO* in isolated or electrogenerated [ 4] (2+) exhibits an EPR spectrum with g 1 = 2.020, g 2 = 1.995, and g 3 = 1.884 in CH 3CN at 110 K, reflecting partial metal contribution to the singly occupied molecular orbital (SOMO); (14)N (NO) hyperfine splitting ( A 2 = 30 G) was also observed. The plot of nu(NO) versus E degrees ({RuNO} (6) --> {RuNO} (7)) for 12 analogous complexes [Ru(trpy)(L')(NO)] ( n+ ) exhibits a linear trend. The electrophilic Ru-NO (+) species [ 4] (3+) is transformed to the corresponding Ru-NO 2 (-) system in the presence of OH (-) with k = 2.02 x 10 (-4) s (-1) at 303 K. In the presence of a steady flow of dioxygen gas, the Ru (II)-NO* state in [ 4] (2+) oxidizes to [ 4] (3+) through an associatively activated pathway (Delta S++ = -190.4 J K (-1) M (-1)) with a rate constant ( k [s (-1)]) of 5.33 x 10 (-3). On irradiation with light (Xe lamp), the acetonitrile solution of paramagnetic [Ru(trpy)(L)(NO)] (2+) ([ 4] (2+)) undergoes facile photorelease of NO ( k NO = 2.0 x 10 (-1) min (-1) and t 1/2 approximately 3.5 min) with the concomitant formation of the solvate [Ru (II)(trpy)(L)(CH 3CN)] (2+) [ 2'] (2+). The photoreleased NO can be trapped as an Mb-NO adduct.
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PMID:Formation, reactivity, and photorelease of metal bound nitrosyl in [Ru(trpy)(L)(NO)](n+) (trpy = 2,2':6',2''-terpyridine, L = 2-phenylimidazo[4,5-f]1,10-phenanthroline). 1831 17

The iron(III) complexes of the 4N ligands 1,4-bis(2-pyridylmethyl)-1,4-diazepane (L1), 1,4-bis(6-methyl-2-pyridylmethyl)-1,4-diazepane (L2), and 1,4-bis(2-quinolylmethyl)-1,4-diazepane (L3) have been generated in situ in CH 3CN solution, characterized as [Fe(L1)Cl 2] (+) 1, [Fe(L2)Cl 2] (+) 2, and [Fe(L3)Cl 2] (+) 3 by using ESI-MS, absorption and EPR spectral and electrochemical methods and studied as functional models for the extradiol cleaving catechol dioxygenase enzymes. The tetrachlorocatecholate (TCC (2-)) adducts [Fe(L1)(TCC)](ClO 4) 1a, [Fe(L2)(TCC)](ClO 4) 2a, and [Fe(L3)(TCC)](ClO 4) 3a have been isolated and characterized by elemental analysis, absorption spectral and electrochemical methods. The molecular structure of [Fe(L1)(TCC)](ClO 4) 1a has been successfully determined by single crystal X-ray diffraction. The complex 1a possesses a distorted octahedral coordination geometry around iron(III). The two tertiary amine (Fe-N amine, 2.245, 2.145 A) and two pyridyl nitrogen (Fe-N py, 2.104, 2.249 A) atoms of the tetradentate 4N ligand are coordinated to iron(III) in a cis-beta configuration, and the two catecholate oxygen atoms of TCC (2-) occupy the remaining cis positions. The Fe-O cat bond lengths (1.940, 1.967 A) are slightly asymmetric and differ by 0.027 A only. On adding catecholate anion to all the [Fe(L)Cl 2] (+) complexes the linear tetradentate ligand rearranges itself to provide cis-coordination positions for bidentate coordination of the catechol. Upon adding 3,5-di- tert-butylcatechol (H 2DBC) pretreated with 1 equiv of Et 3N to 1- 3, only one catecholate-to-iron(III) LMCT band (648-800 nm) is observed revealing the formation of [Fe(L)(HDBC)] (2+) involving bidentate coordination of the monoanion HDBC (-). On the other hand, when H 2DBC pretreated with 2 equiv of Et 3N or 1 or 2 equiv of piperidine is added to 1- 3, two intense catecholate-to-iron(III) LMCT bands appear suggesting the formation of [Fe(L)(DBC)] (+) with bidentate coordination of DBC (2-). The appearance of the DBSQ/H 2DBC couple for [Fe(L)Cl 2] (+) at positive potentials (-0.079 to 0.165 V) upon treatment with DBC (2-) reveals that chelated DBC (2-) in the former is stabilized toward oxidation more than the uncoordinated H 2DBC. It is remarkable that the [Fe(L)(HDBC)] (2+) complexes elicit fast regioselective extradiol cleavage (34.6-85.5%) in the presence of O 2 unlike the iron(III) complexes of the analogous linear 4N ligands known so far to yield intradiol cleavage products exclusively. Also, the adduct [Fe(L2)(HDBC)] (2+) shows a higher extradiol to intradiol cleavage product selectivity ( E/ I, 181:1) than the other adducts [Fe(L3)(HDBC)] (2+) ( E/ I, 57:1) and [Fe(L1)(HDBC)] (2+) ( E/ I, 9:1). It is proposed that the coordinated pyridyl nitrogen abstracts the proton from chelated HDBC (-) in the substrate-bound complex and then gets displaced to facilitate O 2 attack on the iron(III) center to yield the extradiol cleavage product. In contrast, when the cleavage reaction is performed in the presence of a stronger base like piperidine or 2 equiv of Et 3N a faster intradiol cleavage is favored over extradiol cleavage suggesting the importance of bidentate coordination of DBC (2-) in facilitating intradiol cleavage.
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PMID:Novel iron(III) complexes of sterically hindered 4N ligands: regioselectivity in biomimetic extradiol cleavage of catechols. 1859 19

The reaction between Mn(ClO 4) 2 and di-(2-pyridyl)-ketone in the presence of the sodium salt of propanediol as a base in MeOH leads to the formation of a hexanuclear manganese cluster. This cluster has been characterized by the formula [Mn(II) 3Mn(III) 3O(OH)(CH 3pdol) 3(Hpdol) 3(pdol)](ClO 4) 4 ( 1). Molecular conductance measurements of a 10 (-3) M solution of compound 1 in CH 3CN, DMSO, or DMF give Lambda m = 529, 135, or 245 muS/cm, respectively, which suggests a 1:4 cation/anion electrolyte. The crystal structure of hexanuclear manganese cluster 1 consists of two distinct trinuclear units with a pseudocubane-like arrangement. The trinuclear units show two different valence distributions, Mn(II)/Mn(III)/Mn(II) and Mn(III)/Mn(II)/Mn(III). Additional features of interest for the compound include the fact that (a) two of the Mn(III) ions show a Jahn-Teller elongation, whereas the third ion shows a Jahn-Teller compression; (b) one bridge between Mn(III) atoms is an oxo (O (2-)) ion, whereas the bridge between Mn(II) and Mn(III) is a hydroxyl (OH (-)) group; and (c) the di-(2-pyridyl)-ketone ligand that is methanolyzed to methyl-Hpdol and R 2pdol (R = CH 3, H) acts in three different modes: methyl-pdol(-1), Hpdol(-1), and pdol(-2). For magnetic behavior, the general Hamiltonian formalism considers that (a) all of the interactions inside the two "cubanes" between Mn(II) and Mn(III) ions are equal to the J 1 constant, those between Mn(II) ions are equal to the J 2 constant, and those between the Mn(III) ions are equal to the J 3 constant and (b) the interaction between the two cubanes is equal to the J 4 constant. The fitting results are J 1 = J 2 = 0.7 cm (-1), J 3 approximately 0.0, J 4 = -6.2 cm (-1), and g = 2.0 (fixed). According to these results, the ground state is S = 1/2, and the next excited states are S = 3/2 and 5/2 at 0.7 and 1.8 cm (-1), respectively. The EPR spectra prove that the spin ground state at a low temperature is not purely S = 1/2 but is populated with the S = 3/2 state, which is in accordance with the susceptibility and magnetization measurements.
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PMID:Novel mixed-valence manganese cluster with two distinct Mn3(II/III/II) and Mn3(III/II/III) trinuclear units in a pseudocubane-like arrangement. 1867 72

Use of PhPyCNO (-)/X (-) "blends" (PhPyCNOH = phenyl 2-pyridyl ketoxime; X (-) = OH (-), alkanoato, ClO 4 (-)) in copper chemistry yielded trinuclear clusters that have been characterized as inverse-9-metallacrown-3 compounds and accommodate one or two guest ligands. The magnetic behavior showed a large antiferromagnetic interaction and a discrepancy between the low-temperature magnetic behavior observed experimentally and that predicted from a magnetic model. The discrepancy between the Brillouin curve and the experimental result provides clear evidence of the influence of the antisymmetric interaction. Introducing the antisymmetric terms derived from the fit of the susceptibility data into the magnetization formula caused the simulated curve to become nearly superimposable on the experimental one. The EPR data indicated that the compound [Cu 3(PhPyCNO) 3(mu 3-OH)(2,4,5-T) 2] ( 1), where 2,4,5-T is 2,4,5-trichlorophenoxyacetate, has isosceles or lower magnetic symmetry (delta not equal 0), that antisymmetric exchange is important ( G not equal 0), and that Delta E > hnu. The structures of the complexes 1 and [Cu 3(PhPyCNO) 3(mu 3-OH)(H 2O)(ClO 4) 2] ( 2) were determined using single-crystal X-ray crystallography. Theoretical calculations based on density functional theory were performed using the full crystal structures of 1, 2, [Cu 3(PhPyCNO) 3(OH)(CH 3OH) 2(ClO 4) 2] ( 3), and [Cu 3(PhPyCNO) 3(mu 3-OMe)(Cl)(ClO 4)] ( 4). The geometries of the model compounds [Cu 3(kappa (3) N, N, O-HNCHCHNO) 3(mu 3-OH)(mu 2-HCOO)(HCOO)] ( 5), [Cu 3(kappa (3) N, N, O-HNCHCHNO) 3(mu 2-HCOO)(HCOO)] (+) ( 6), [Cu 3(kappa (3) N, N, O-HNCHCHNO) 3(mu 3-O)] (+) ( 7), and [Cu 3(kappa (3) N, N, O-HNCHCHNO) 3] (3+) ( 8) were optimized at the same level of theory for both the doublet and quartet states, and vibrational analysis indicated that the resulting equilibrium geometries corresponded to minima on the potential energy surfaces. Both e g and t 2g magnetic orbitals seem to contribute to the magnetic exchange coupling. The latter contribution, although less important, might be due to overlap of the t 2g orbitals with the p-type orbitals of the central triply bridging oxide ligand, thereby affecting its displacement from the Cu 3 plane and contributing to the antiferromagnetic coupling. The crucial role of the triply bridging oxide (mu 3-O) ligand on the antiferromagnetic exchange coupling between the three Cu(II) magnetic centers is further evidenced by the excellent linear correlation of the coupling constant J with the distance of the mu 3-O ligand from the centroid of the Cu 3 triangle.
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PMID:Experimental and theoretical study of the antisymmetric magnetic behavior of copper inverse-9-metallacrown-3 compounds. 1868 22

Chlorite dismutase (Cld) is a heme b-dependent, O-O bond forming enzyme that transforms toxic chlorite (ClO(2)(-)) into innocuous chloride and molecular oxygen. The mechanism and specificity of the reaction with chlorite and alternate oxidants were investigated. Chlorite is the sole source of dioxygen as determined by oxygen-18 labeling studies. Based on ion chromatography and mass spectrometry results, Cld is highly specific for the dismutation of chlorite to chloride and dioxygen with no other side products. Cld does not use chlorite as an oxidant for oxygen atom transfer and halogenation reactions (using cosubstrates guaiacol, thioanisole, and monochlorodimedone, respectively). When peracetic acid or H(2)O(2) was used as an alternative oxidant, oxidation and oxygen atom transfer but not halogenation reactions occurred. Monitoring the reaction of Cld with peracetic acid by rapid-mixing UV-visible spectroscopy, the formation of the high valent compound I intermediate, [(Por(*+))Fe(IV) = O], was observed [k(1) = (1.28 +/- 0.04) x 10(6) M(-1) s(-1)]. Compound I readily decayed to form compound II in a manner that is independent of peracetic acid concentration (k(2) = 170 +/- 20 s(-1)). Both compound I and a compound II-associated tryptophanyl radical that resembles cytochrome c peroxidase (Ccp) compound I were observed by EPR under freeze-quench conditions. The data collectively suggest an O-O bond-forming mechanism involving generation of a compound I intermediate via oxygen atom transfer from chlorite, and subsequent recombination of the resulting hypochlorite and compound I.
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PMID:Mechanism of and exquisite selectivity for O-O bond formation by the heme-dependent chlorite dismutase. 1884 Jun 91

Some water-soluble polymer-copper(II) complexes, [Cu(phen)(l-phe)(BPEI)]ClO(4).4H(2)O (phen=1,10-phenanthroline, l-phe=l-phenylalanine, and BPEI=branched polyethyleneimine), with various amounts of copper(II) chelates in the polymer chain, were prepared by ligand substitution method in water-ethanol medium and characterized by infra-red, UV-visible, EPR spectral and elemental analysis methods. Binding of these complexes with calf thymus DNA (CT DNA) has been investigated by absorption spectroscopy, emission spectroscopy and gel electrophoresis techniques. The experimental results indicate that the amount of copper(II) chelate content in the polymer backbone have marked effect on the binding affinity to CT DNA. Interactions like electrostatic interaction, van der Waals interaction, hydrogen bonding and/or partial intercalation binding modes exist in this system. A sample of polymer-copper(II) complex was tested for its antibacterial and antifungal activity against certain human pathogenic organisms and it was found to have good antibacterial and antifungal activities.
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PMID:DNA binding and antimicrobial studies of polymer-copper(II) complexes containing 1,10-phenanthroline and L-phenylalanine ligands. 1905 79

A new iron(III) coordination compound exhibiting a two-step spin-transition behavior with a remarkably wide [HS-LS] plateau of about 45 K has been synthesized from a hydrazino Schiff-base ligand with an N,N,O donor set, namely 2-methoxy-6-(pyridine-2-ylhydrazonomethyl)phenol (Hmph). The single-crystal X-ray structure of the coordination compound {[Fe(mph)(2)](ClO(4))(MeOH)(0.5)(H(2)O)(0.5)}(2) (1) determined at 150 K reveals the presence of two slightly different iron(III) centers in pseudo-octahedral environments generated by two deprotonated tridentate mph ligands. The presence of hydrogen bonding interactions, instigated by the well-designed ligand, may justify the occurrence of the abrupt transitions. 1 has been characterized by temperature-dependent magnetic susceptibility measurements, EPR spectroscopy, differential scanning calorimetry, and (57)Fe Mossbauer spectroscopy, which all confirm the occurrence of a two-step transition. In addition, the iron(III) species in the high-spin state has been trapped and characterized by rapid cooling EPR studies.
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PMID:Two-step spin-transition iron(III) compound with a wide [high spin-low spin] plateau. 1923 71

In order to model the syn disposition of histidine residues in carboxylate-bridged non-heme diiron enzymes, we prepared a new dinucleating ligand, H(2)BPG(2)DEV, that provides this geometric feature. The ligand incorporates biologically relevant carboxylate functionalities, which have not been explored as extensively as nitrogen-only analogues. Three novel oxo-bridged diiron(III) complexes, [Fe(2)(mu-O)(H(2)O)(2)(BPG(2)DEV)](ClO(4))(2) (6), [Fe(2)(mu-O)(mu-O(2)CAr(iPrO))(BPG(2)DEV)](ClO(4)) (7), and [Fe(2)(mu-O)(mu-CO(3))(BPG(2)DEV)] (8), were prepared. Single-crystal X-ray structural characterization confirms that two pyridyl groups are bound syn with respect to the Fe-Fe vector in these compounds. The carbonato-bridged complex 8 forms quantitatively from 6 in a rapid reaction with gaseous CO(2) in organic solvents. A common maroon-colored intermediate (lambda(max) = 490 nm; epsilon = 1500 M(-1) cm(-1)) forms in reactions of 6, 7, or 8 with H(2)O(2) and NEt(3) in CH(3)CN/H(2)O solutions. Mass spectrometric analyses of this species, formed using (18)O-labeled H(2)O(2), indicate the presence of a peroxide ligand bound to the oxo-bridged diiron(III) center. The Mossbauer spectrum at 90 K of the EPR-silent intermediate exhibits a quadrupole doublet with delta = 0.58 mm/s and DeltaE(Q) = 0.58 mm/s. The isomer shift is typical for a peroxodiiron(III) species, but the quadrupole splitting parameter is unusually small compared to those of related complexes. These Mossbauer parameters are comparable to those observed for a peroxo intermediate formed in the reaction of reduced toluene/o-xylene monooxygenase hydroxylase with dioxygen. Resonance Raman studies reveal an unusually low-energy O-O stretching mode in the peroxo intermediate that is consistent with a short diiron distance. Although peroxodiiron(III) intermediates generated from 6, 7, and 8 are poor O-atom-transfer catalysts, they display highly efficient catalase activity, with turnover numbers up to 10,000. In contrast to hydrogen peroxide reactions of diiron(III) complexes that lack a dinucleating ligand, the intermediates generated here could be re-formed in significant quantities after a second addition of H(2)O(2), as observed spectroscopically and by mass spectrometry.
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PMID:Modeling the syn disposition of nitrogen donors in non-heme diiron enzymes. Synthesis, characterization, and hydrogen peroxide reactivity of diiron(III) complexes with the syn N-donor ligand H2BPG2DEV. 1975 95

The titanyl equilibria in strongly acidic solutions related to the hydrometallurgical production of titania have been investigated in the presence of inorganic ions (ClO(4)(-), NO(3)(-), Cl(-), SO(4)(2-), Fe(2+) and Fe(3+)) using spectroscopic (UV-Vis and EPR) methods. UV-Vis experiments showed no interaction or ion pairing effect in the acidic titanyl nitrate and titanyl perchlorate samples indicating that they would be suitable background electrolytes for further thermodynamic measurements. The stoichiometry of the titanyl chloride complex was determined as TiOCl(2)(0) and its stability constant was calculated (log beta(2) = 1.12 +/- 0.03). The interaction between titanyl and sulfate ions was quantified by determining the stoichiometry (1:1) and stability (log beta(1) = 1.64 +/- 0.06) of the titanyl sulfate species. Weak sulfate complexes were also detected with the ferric (log beta(1) = 2.00 +/- 0.10; log beta(2) = 2.49 +/- 0.08) and ferrous (log beta(1) = 1.52 +/- 0.06) ions under strongly acidic conditions. A double sulfato complex FeTiO(SO(4))(3)(2-) with relatively high stability (log beta = 7.13 +/- 0.07) was found in solutions containing titanyl, ferrous and sulfate ions in sulfuric acid medium. In addition, an EPR signal was assigned to the FeTiO(SO(4))(3)(2-) species. This double sulfato complex was found to be the major metal-containing species in the system similar to that used in the leaching process of ilmenite during the industrial production of titania.
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PMID:Spectroscopic characterisation of weak interactions in acidic titanyl sulfate-iron(II) sulfate solutions. 1975 45

A series of divalent metal flavonolate complexes of the general formula [(6-Ph(2)TPA)M(3-Hfl)]X (1-5-X; X = OTf(-) or ClO(4)(-); 6-Ph(2)TPA = N,N-bis((6-phenyl-2-pyridyl)methyl)-N-((2-pyridyl)methyl)amine; M = Mn(II), Co(II), Ni(II), Cu(II), Zn(II); 3-Hfl = 3-hydroxyflavonolate) were prepared and characterized by X-ray crystallography, elemental analysis, FTIR, UV-vis, (1)H NMR or EPR, and cyclic voltammetry. All of the complexes have a bidentate coordinated flavonolate ligand. The difference in M-O distances (Delta(M-O)) involving this ligand varies through the series, with the asymmetry of flavonolate coordination increasing in the order Mn(II) approximately Ni(II) < Cu(II) < Zn(II) < Co(II). The hypsochromic shift of the absorption band I (pi-->pi*) of the coordinated flavonolate ligand in 1-5-OTf (relative to that in free anion) increases in the order Ni(II) < Mn(II) < Cu(II) < Zn(II), Co(II). Previously reported 3-Hfl complexes of divalent metals fit well with this ordering. (1)H NMR studies indicate that the 3-Hfl complexes of Co(II), Ni(II), and Zn(II) exhibit a pseudo-octahedral geometry in solution. EPR studies suggest that the Mn(II) complex 1-OTf may form binuclear structures in solution. The mononuclear Cu(II) complex 4-OTf has a distorted square pyramidal geometry. The oxidation potential of the flavonolate ligand depends on the metal ion present and/or the solution structure of the complex, with the Mn(II) complex 1-OTf exhibiting the lowest potential, followed by the pseudo-octahedral Ni(II) and Zn(II) 3-Hfl complexes, and the distorted square pyramidal Cu(II) complex 4-OTf. The Mn(II) complex [(6-Ph(2)TPA)Mn(3-Hfl)]OTf (1-OTf) is unique in the series in undergoing ligand exchange reactions in the presence of M(ClO(4))(2).6H(2)O (M = Co, Ni, Zn) in CD(3)CN to produce [(6-Ph(2)TPA)M(CD(3)CN)(n)](X)(2), [Mn(3-Hfl)(2).0.5H(2)O], and MnX(2) (X = OTf(-) or ClO(4)(-)). Under similar conditions, the 3-Hfl complexes of Co(II), Ni(II), and Cu(II) undergo flavonolate ligand exchange to produce [(6-Ph(2)TPA)M(CD(3)CN)(n)](X)(2) (M = Co, Ni, Cu; n = 1 or 2) and [Zn(3-Hfl)(2).2H(2)O]. An Fe(II) complex of 3-Hfl, [(6-Ph(2)TPA)Fe(3-Hfl)]ClO(4) (8), was isolated and characterized by elemental analysis, FTIR, UV-vis, (1)H NMR, cyclic voltammetry, and a magnetic moment measurement. This complex reacts with O(2) to produce the diiron(III) mu-oxo compound [(6-Ph(2)TPAFe(3Hfl))(2)(mu-O)](ClO(4))(2) (6).
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PMID:Synthesis, characterization, and ligand exchange reactivity of a series of first row divalent metal 3-hydroxyflavonolate complexes. 1995 65


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