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Query: UNIPROT:O14944 (EPR)
 13,097 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The composition of the co-ordination sphere of Cu(II) dithiocarbamate mixed-ligand complexes Cu(Et2)dtc)X (X = Cl-, Br-) and Cu(Et2)dtc)(+)...Y- (Y- = ClO4-, NO3-) is studied from the combined analysis of spectrophotometric and EPR data. The results obtained about CT-photolysis of the complexes in EtOH and i-PrOH are compared with our previous data of photolysis in chloromethane/ROH solutions. Reaction mechanism and the role of alcohol are discussed on the ground of electronic and EPR spectra and quantum yield results.
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PMID:Structure of copper(II) dithiocarbamate mixed-ligand complexes and their photoreactivities in alcohols. 1513 27

Cobalt(II), nickel(II) and copper(II) complexes having the general composition M(L)X2 (where M = CO(II), Ni(II) and Cu(II), L = ligand, i.e. 3,4,12,13-tetraketo-2,5,11,14,19,20-hexaazatricyclo[13.3.1.1(6-10)]cosane; 1(19),6,8,10(20),15,17-hexaene and X stands for Cl-; NO3- and SO42-), have been prepared. The structure of the complexes has been elucidated by elemental analysis, molar conductance, magnetic susceptibility measurements, mass, IR, electronic and EPR spectral studies. The magnetic moment measurements of the complexes indicate that the metal ion is in high-spin state. On the basis of IR, electronic and EPR spectral studies an octahedral geometry was assigned for Co(II) and Ni(II) complexes whereas tetragonal geometry for Cu(II) complexes. This ligand and its complexes were also screened against bacteria and pathogenic fungi in vitro.
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PMID:EPR and electronic spectral studies on Co(II), Ni(II) and Cu(II) complexes with a new tetradentate [N4] macrocyclic ligand and their biological activity. 1514 99

Bacterial cytoplasmic assimilatory nitrate reductases are the least well characterized of all of the subgroups of nitrate reductases. In the present study the ferredoxin-dependent nitrate reductase NarB of the cyanobacterium Synechococcus sp. PCC 7942 was analyzed by spectropotentiometry and protein film voltammetry. Metal and acid-labile sulfide analysis revealed nearest integer values of 4:4:1 (iron/sulfur/molybdenum)/molecule of NarB. Analysis of dithionite-reduced enzyme by low temperature EPR revealed at 10 K the presence of a signal that is characteristic of a [4Fe-4S](1+) cluster. EPR-monitored potentiometric titration of NarB revealed that this cluster titrated as an n = 1 Nernstian component with a midpoint redox potential (E(m)) of -190 mV. EPR spectra collected at 60 K revealed a Mo(V) signal termed "very high g" with g(av) = 2.0047 in air-oxidized enzyme that accounted for only 10-20% of the total molybdenum. This signal disappeared upon reduction with dithionite, and a new "high g" species (g(av) = 1.9897) was observed. In potentiometric titrations the high g Mo(V) signal developed over the potential range of -100 to -350 mV (E(m) Mo(6+/5+) = -150 mV), and when fully developed, it accounted for 1 mol of Mo(V)/mol of enzyme. Protein film voltammetry of NarB revealed that activity is turned on at potentials below -200 mV, where the cofactors are predominantly [4Fe-4S](1+) and Mo(5+). The data suggests that during the catalytic cycle nitrate will bind to the Mo(5+) state of NarB in which the enzyme is minimally two-electron-reduced. Comparison of the spectral properties of NarB with those of the membrane-bound and periplasmic respiratory nitrate reductases reveals that it is closely related to the periplasmic enzyme, but the potential of the molybdenum center of NarB is tuned to operate at lower potentials, consistent with the coupling of NarB to low potential ferredoxins in the cell cytoplasm.
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PMID:Tuning a nitrate reductase for function. The first spectropotentiometric characterization of a bacterial assimilatory nitrate reductase reveals novel redox properties. 1516 46

Hydroxyurea reduces the incidence of painful crises in patients with sickle cell disease and has recently been approved for the treatment of this condition. A number of in vitro studies show that the oxidation of hydroxyurea results in the formation of nitric oxide, which also has drawn considerable interest as a sickle cell disease therapy. While patients on hydroxyurea demonstrate elevated levels of nitric oxide-derived metabolites, little information regarding the site or mechanism of the in vivo conversion of hydroxyurea to nitric oxide exists. Chemiluminescence detection experiments show the ability of catalase to catalyze the formation of nitrite and nitrate from hydroxyurea. Spectroscopic studies show that the reaction of hydroxyurea and catalase in the presence of a hydrogen peroxide generating system produces a ferrous-NO catalase complex. Trapping studies indicate the intermediacy of a nitroso species during this reaction. The proposed mechanism for this conversion includes initial hydrogen peroxide-dependent oxidation of hydroxyurea by catalase to form the nitroso species, hydrolysis of this nitroso species to produce nitroxyl, and reductive nitrosylation of the ferric heme of catalase by nitroxyl to yield the ferrous-NO catalase complex. Addition of Angeli's salt, a nitroxyl donor, to ferric catalase also produces the ferrous-NO catalase complex. Spectroscopic studies show that the ferrous-NO catalase complex releases nitric oxide as judged by the oxyhemoglobin assay and an NO specific EPR specific trap. These results demonstrate nitric oxide production from the ferric catalase oxidation of nitroxyl and identify a catalase-mediated pathway as a potential source of nitric oxide production from hydroxyurea.
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PMID:Catalase-mediated nitric oxide formation from hydroxyurea. 1521 77

The complexes of transition metal ions with an azamacrocyclic tetradentate nitrogen donor [N4] ligand viz. 2,6,12,16,21,22-hexaaza;3,5,13,15-tetramethyltricyclo[15.3.1.1(7-11)] docosa;1(21),2,5,7,9,11(22),12,15,17,19-decaene (L) have been synthesized. All the complexes were found to have general composition M(L)X2 [where M = manganese(II), cobalt(II), nickel(II) and copper(II) and X = Cl- & NO3-]. All the complexes are characterized by the elemental analysis, molar conductance measurements, magnetic susceptibility measurements, mass, 1H NMR, IR, electronic, EPR spectral and cyclic voltammetric studies. An octahedral geometry was assigned for Mn(II), Co(II) and Ni(II) complexes and tetragonal for Cu(II) complexes. The biological actions of the ligand and complexes have been screened in vitro against many bacteria and pathogenic fungi to study their comparative capacity to inhibit the growth.
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PMID:EPR, IR and electronic spectral studies on Mn(II), Co(II), Ni(II) and Cu(II) complexes with a new 22-membered azamacrocyclic [N4] ligand. 1524 47

Manganese(II), cobalt(II), nickel(II) and copper(II) complexes are synthesized with a novel tetradentate ligand viz. 1,3,9,11-tetraaza-4,8,12,16-tetraoxo-2,6,10,14-tetrathiacyclohexadecane (L) and characterized by the elemental analysis, molar conductance measurements, magnetic susceptibility measurements, electron impact mass, 1H NMR, IR, electronic and EPR spectral studies. The molar conductance measurements of the complexes in DMSO correspond to be nonelectrolytic nature for Mn(II), Co(II) and Cu(II) while 1:2 electrolytes for Ni(II) complexes. Thus these complexes may be formulated as [M(L)X2] and [Ni(L)]X2 (where M: Mn(II), Co(II), and Cu(II) and X = Cl- and NO3-). On the basis of IR, electronic and EPR spectral studies an octahedral geometry has been assigned for Mn(II) and Co(II) complexes, square-planar for Ni(II) whereas tetragonal for Cu(II) complexes. The ligand and its complexes were also evaluated against the growth of bacteria and pathogenic fungi in vitro.
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PMID:Spectroscopic characterization of tetradentate macrocyclic ligand: its transition metal complexes. 1535 Sep 11

New copper(II) complexes of indoxyl thiosemicarbazone (ITSC) of general composition CuL2X2 (where L: ITSC; X: Cl-, NO3-, ClO4-, NCS-) have been synthesized and characterized by elemental analysis, molar conductance, magnetic susceptibility measurements and spectral (electronic, IR, EPR, 1H NMR, Mass) studies. Cyclic voltammetry measurements show quasi-reversible Cu2+/Cu1+ couple. Various physico-chemical techniques suggest a tetragonal structure for these copper(II) complexes.
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PMID:Spectroscopic characterization of copper(II) complexes of indoxyl N(4)-methyl thiosemicarbazone. 1535 Sep 18

The reaction of *NO and NO2- with hemoglobin (Hb) is of pivotal importance to blood vessel function. Both species show at least two different reactions with Fe2+ Hb: one with deoxygenated Hb, in which the biological properties of *NO are preserved, and another with oxygenated hemoglobin (oxyHb), in which both species are oxidizes to NO3-. In this study we compared the oxidative reactions of *NO and NO2- and, in particular, the radical intermediates formed during transformation to NO3-. The reaction of NO2- with oxyHb was accelerated at high heme concentrations and produced stoichiometric amounts of NO3-. Direct EPR and spin trapping studies showed that NO2-, but not *NO, induced the formation of globin Tyr-, Trp-, and Cys-centered radicals. MS studies provided evidence of the formation of approximately 2% nitrotyrosine in both the alpha and beta subunits, suggesting that *NO2 diffuses in part away from the heme and reacts with Tyr radicals. No nitrotyrosines were detected in the reaction of *NO with oxyHb. Collectively, these results indicate that NO2- reaction with oxyHb causes an oxidative challenge not observed with *NO. The differences in oxidation mechanisms of *NO and NO2- are discussed.
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PMID:Scavenging of reactive nitrogen species by oxygenated hemoglobin: globin radicals and nitrotyrosines distinguish nitrite from nitric oxide reaction. 1545 Oct 64

The first structurally characterized Cr(V) dioxo complex, cis-[CrV(O)2(phen)2](BF4) (2, phen=1,10-phenanthroline) has been synthesized by the oxidation of a related Cr(III) complex, cis-[Cr(III)(phen)2(OH2)2](NO3)3.2.5H2O (1, characterized by X-ray crystallography), with NaOCl in aqueous solutions in the presence of excess NaBF4, and its purity has been confirmed by electrospray mass spectrometry (ESMS), EPR spectroscopy, and analytical techniques. Previously reported methods for the generation of Cr(V)-phen complexes, such as the oxidation of 1 with PbO2 or PhIO, have been shown by ESMS to lead to mixtures of Cr(III), Cr(V), Cr(VI), and in some cases Cr(IV) species, 3. Species 3 was assigned as [CrIV(O)(OH)(phen)2]+, based on ESMS and X-ray absorption spectroscopy measurements. A distorted octahedral structure for 2 (CrO, 1.63 A; Cr-N, 2.04 and 2.16 A) was established by multiple-scattering (MS) modeling of XAFS spectra (solid, 10 K). The validity of the model was verified by a good agreement between the results of MS XAFS fitting and X-ray crystallography for 1 (distorted octahedron; Cr-O, 1.95 A; Cr-N, 2.06 A). Unlike for the well-studied Cr(V) 2-hydroxycarboxylato complexes, 2 was equally or more stable in aqueous media (hours at pH=1-13 and 25 degrees C) compared with polar aprotic solvents. A stable Cr(III)-Cr(VI) dimer, [Cr(III)(Cr(VI)O4)(phen)2]+ (detected by ESMS), is formed during the decomposition of 2 in nonaqueous media. Comparative studies of the oxidation of 1 by NaOCl or PbO2 have shown that [Cr(V)(O)2(phen)2]+ was the active species responsible for the previously reported oxidative DNA damage, bacterial mutagenicity, and increased incidence of micronuclei in mammalian cells, caused by the oxidation products of 1 with PbO2. Efficient oxidation of 1 to a genotoxic species, [Cr(V)(O)2(phen)2]+, in neutral aqueous media by a biological oxidant, hypochlorite, supports the hypothesis on a significant role of reoxidation of Cr(III) complexes, formed during the intracellular reduction of Cr(VI), in Cr(VI)-induced carcinogenicity. Similar oxidation reactions may contribute to the reported adverse effects of a popular nutritional supplement, Cr(III) picolinate.
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PMID:Synthesis and characterization of a chromium(V) cis-dioxo bis(1,10-phenanthroline) complex and crystal and molecular structures of its chromium(III) precursor. 1555 50

The crystal structure of Escherichia coli nitrate reductase A (NarGHI) in complex with pentachlorophenol has been determined to 2.0 A of resolution. We have shown that pentachlorophenol is a potent inhibitor of quinol:nitrate oxidoreductase activity and that it also perturbs the EPR spectrum of one of the hemes located in the membrane anchoring subunit (NarI). This new structural information together with site-directed mutagenesis data, biochemical analyses, and molecular modeling provide the first molecular characterization of a quinol binding and oxidation site (Q-site) in NarGHI. A possible proton conduction pathway linked to electron transfer reactions has also been defined, providing fundamental atomic details of ubiquinol oxidation by NarGHI at the bacterial membrane.
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PMID:Structural and biochemical characterization of a quinol binding site of Escherichia coli nitrate reductase A. 1561 28


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