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Query: UNIPROT:Q86TM3 (cage)
 29,987 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

EPR spin trapping using the spin traps 5,5-dimethyl-1-pyrroline N-oxide (DMPO) and 3,5-dibromo-4-nitrosobenzene sulphonic acid (DBNBS) has been employed to examine the generation of radicals produced on reaction of a number of primary, secondary and lipid hydroperoxides with rat liver microsomal fractions in both the presence and absence of reducing equivalents. Two major mechanisms of radical generation have been elucidated. In the absence of NADPH or NADH, oxidative degradation of the hydroperoxide occurs to give initially a peroxyl radical which in the majority of cases can be detected as a spin adduct to DMPO; these radicals can undergo further reactions which result in the generation of alkoxyl and carbon-centered radicals. In the presence of NADPH (and to a lesser extent NADH) alkoxyl radicals are generated directly via reductive cleavage of the hydroperoxide. These alkoxyl radicals undergo further fragmentation and rearrangement reactions to give carbon-centered species which can be identified by trapping with DBNBS. The type of transformation that occurs is highly dependent on the structure of the alkoxyl radical with species arising from beta-scission, 1,2-hydrogen shifts and ring closure reactions being identified; these processes are in accord with previous chemical studies and are characteristic of alkoxyl radicals present in free solution. Studies using specific enzyme inhibitors and metal-ion chelators suggest that most of the radical generation occurs via a catalytic process involving haem proteins and in particular cytochrome P-450. An unusual species (an acyl radical) is observed with lipid hydroperoxides; this is believed to arise via a cage reaction after beta-scission of an initial alkoxyl radical.
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PMID:Detection of radicals produced by reaction of hydroperoxides with rat liver microsomal fractions. 131 69

With synchrotron radiation from the Bonn 2.5 GeV synchrotron, high-resolution absorption spectra have been measured at the vanadium K-edge of bromoperoxidase from the marine brown alga Ascophyllum nodosum and several model compounds. The near-edge structure (XANES) of these spectra was used to determine the charge state and the coordination geometry around the vanadium atom. For the active enzyme a coordination charge of 2.7 was found which is compatible with a formal valence of +5, assuming coordination by atoms with a high electronegativity such as oxygen or nitrogen. For the reduced enzyme the coordination charge value of 2.15 indicates the reduction of the valency by 1 unit. Our results suggest that the coordination sphere of the vanadium atom in the native enzyme consists of at least seven oxygen atoms in a distorted octahedral environment with an average bond length of about 2 A. Through the reduction process, the coordination sphere of the vanadium atom changes with a simultaneous decrease of the coordination cage. These results agree with those deduced from previous EPR and 51V-NMR measurements.
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PMID:Vanadium K-edge absorption spectrum of bromoperoxidase from Ascophyllum nodosum. 316 74

The complex of cytochrome c oxidase with NO and azide has been studied by EPR at 9.2 and 35 GHz. This complex which shows delta ms = 2 EPR triplet and strong anisotropic signals, due to the interaction of cytochrome a2+3 X NO (S = 1/2) and Cu2+B (S = 1/2), is photodissociable . Its action spectrum is similar to that of cytochrome a2+3 X NO with bands at 430, 560 and 595 nm, but shows an additional band in the near ultraviolet region. The quantum yield of the photodissociation process of cytochrome a2+3 X NO in the metal pair appears to depend on the redox state of CuB. When the photolysed sample was warmed to 77 K, a complex was observed with the EPR parameters of cytochrome a3+3 - N-3 - Cu1 +B (S = 1/2). This process of electron and ligand transfer can be reversed by heating the sample to 220 K. It is suggested that in the triplet species azide is bound to Cu2+B whereas NO is bridged between Cu2+B and the haem iron of the cytochrome a2+3. The complex has a triplet ground state and a singlet excited state with an exchange interaction J = -7.1 cm-1 between both spins. The anisotropy in the EPR spectra is mainly due to a magnetic dipole-dipole interaction between cytochrome a2+3 X NO and Cu2+B. From simulations of the triplet EPR spectra obtained at 9 and 35 GHz, a value for the distance between the nitroxide radical and Cu2+B of 0.33 nm was found. A model of the NO binding in the cytochrome a3-Cu pair shows a distance between the haem iron of cytochrome a3 and CuB of 0.45 nm. It is concluded that the cytochrome a3-CuB pair forms a cage in which the dioxygen molecule is bidentate coordinated to the two metals during the catalytic reaction.
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PMID:The cytochrome c oxidase-azide-nitric oxide complex as a model for the oxygen-binding site. 632 19

The interaction of Cu(II) with the ligand tdci (1,3,5-trideoxy-1,3,5-tris(dimethylamino)-cis-inositol) was studied both in the solid state and in solution. The complexes that were formed were also tested for phosphoesterase activity. The pentanuclear complex [Cu(5)(tdciH(-2))(tdci)(2)(OH)(2)(NO(3))(2)](NO(3))(4).6H(2)O consists of two dinuclear units and one trinuclear unit, having two shared copper(II) ions. The metal centers within the pentanuclear structure have three distinct coordination environments. All five copper(II) ions are linked by hydroxo/alkoxo bridges forming a Cu(5)O(6) cage. The Cu-Cu separations of the bridged centers are between 2.916 and 3.782 A, while those of the nonbridged metal ions are 5.455-5.712 A. The solution equilibria in the Cu(II)-tdci system proved to be extremely complicated. Depending on the pH and metal-to-ligand ratio, several differently deprotonated mono-, di-, and trinuclear complexes are formed. Their presence in solution was supported by mass, CW, and pulse EPR spectroscopic study, too. In these complexes, the metal ions are presumed to occupy tridentate [O(ax),N(eq),O(ax)] coordination sites and the O-donors of tdci may serve as bridging units between two metal ions. Additionally, deprotonation of the metal-bound water molecules may occur. The dinuclear Cu(2)LH(-3) species, formed around pH 8.5, provides outstanding rate acceleration for the hydrolysis of the activated phosphodiester bis(4-nitrophenyl)phosphate (BNPP). The second-order rate constant of BNPP hydrolysis promoted by the dinuclear complex (T = 298 K) is 0.95 M(-1) s(-1), which is ca. 47600-fold higher than that of the hydroxide ion catalyzed hydrolysis (k(OH)). Its activity is selective for the phosphodiester, and the hydrolysis was proved to be catalytic. The proposed bifunctional mechanism of the hydrolysis includes double Lewis acid activation and intramolecular nucleophilic catalysis.
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PMID:Highly efficient phosphodiester hydrolysis promoted by a dinuclear copper(II) complex. 1153 40

The cluster [Fe(5)RhN(CO)(15)](2)(-) was synthesized in 40% yield from [Fe(4)N(CO)(12)](-) and [Rh(CO)(4)](-) in refluxing tetrahydrofuran, whereas the analogous anion [Fe(5)IrN(CO)(15)](2)(-) was prepared in CH(3)CN at room temperature from [Fe(6)N(CO)(15)](3)(-) and [Ir(C(8)H(14))(2)Cl](2); the yields are higher than 60%. The monoanion [Fe(4)Rh(2)N(CO)(15)](-) was obtained in 70% yield from [Fe(5)RhN(CO)(15)](2)(-) and hydrated RhCl(3). The solid-state structures of the three anions were determined on their [PPh(4)](+) salts: the six metal atoms are arranged in octahedral cages and are coordinated to 3 edge-bridging and 12 terminal carbonyl ligands and to a &mgr;(6)-N ligand. The Rh and Ir atoms have less terminal COs than Fe, in order to equalize the excess electrons at the d(9) metal centers. The two rhodium atoms in [Fe(4)Rh(2)N(CO)(15)](-) are directly bound. The (15)N NMR spectra of the three compounds have been recorded; the signals of the nitride ligands were found at delta = 514 ppm for the dianions and 470 ppm for [Fe(4)Rh(2)N(CO)(15)](-); any group 9 atom shifts the resonance of nitrogen to higher fields. The coupling constants J((15)N-(103)Rh) are 8-9 Hz. The vibrational patterns of the metal cores have been interpreted on the basis of an idealized M(6) octahedral arrangement, subsequently modified by the perturbations given by different atomic masses and M-M stretching force constants. The motions of the nitrogen are related to the idealized symmetry of the cage; the M-N force constant values depend on the type of metal and on the charge of the anion. The dianions [Fe(5)MN(CO)(15)](2)(-) can be electrochemically oxidized at -20 degrees C to their short-lived monoanions, which can be characterized by EPR spectroscopy. In contrast, the cluster [Fe(4)Rh(2)N(CO)(15)](-) undergoes a single-step 2-electron reduction to the partially stable trianion [Fe(4)Rh(2)N(CO)(15)](3)(-), which was also characterized by EPR spectroscopy. The Fe-Rh nitride clusters are active catalysts for the hydroformylation of 1-pentene, but display low selectivity (35-65%) in n-hexanal and are demolished under catalytic conditions.
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PMID:Iron-Rhodium and Iron-Iridium Mixed-Metal Nitrido-Carbonyl Clusters. Synthesis, Characterization, Redox Properties, and Solid-State Structure of the Octahedral Clusters [Fe(5)RhN(CO)(15)](2)(-), [Fe(5)IrN(CO)(15)](2)(-), and [Fe(4)Rh(2)N(CO)(15)](-). Infrared and Nuclear Magnetic Resonance Spectroscopic Studies on the Interstitial Nitride. 1167 71

Endohedral fullerenes N@C(60) and N@C(70) were dissolved in the liquid crystal 4-methoxybenzylidene-4'-n-butylaniline (MBBA) and investigated by electron paramagnetic resonance. In both cases well resolved EPR spectra give proof for molecular orientation in the nematic mesophase. Spectral features are dominated by a nonvanishing zero-field interaction, indicating a deviation from spherical spin density distribution at the encased nitrogen atom. In N@C(70), a maximum order parameter O(33) = 0.18(3), correlated with the long axis of the cage, and a zero-field-splitting parameter D = -2.6(4) MHz were determined. A persistent zero-field splitting is also observed in C(60) via the quartet spin of the encapsulated nitrogen, although no assignment of the director with respect to the molecular frame is possible. The observed line splitting is indicative of pseudo orientation of the rapidly rotating cage in this case.
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PMID:Electron paramagnetic resonance investigation of endohedral fullerenes N@C(60) and N@C(70) in a liquid crystal. 1216 66

Dimeric (hydrated and anhydrated) complexes of Cu(II) with N,N'-bis(3-carboxy-1-oxo-2-prop-2-enyl)ethylenediamine(BCOPENH(2), A) and N,N'-bis(2-carboxy-1-oxo-phenylenyl)ethylenediamine(BCOPHENH(2), B) have been prepared and characterised by elemental analysis, magnetic susceptibility measurements, EPR, thermal and spectral (IR, UV/Vis) studies. EPR parameters and magnetic behaviour indicates that the complexes are antiferromagnetic in nature and most likely adopt the typical carboxylate cage structure. Interesting amide bonding patterns have been observed and various EPR parameters have been evaluated on the basis of these studies, tentative probable structures of the complexes have been proposed.
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PMID:Spectral studies of dimeric copper(II) complexes of acid amide derivatives as models for type III copper enzymes. 1449 38

The aqueous photochemistry of the sodium salt of 1-(N,N-diethylamino)-diazen-1-ium-1,2-diolate (3) has been investigated by both experimental and computational methods. Photolysis results in the formation of the N-nitrosodiethylamine radical anion (5) and nitric oxide (NO) via a triplet excited state. The nitrosamine radical anion either undergoes electron transfer with NO before cage escape to form triplet NO(-) and nitrosamine (minor process) or rapidly dissociates to form an additional molecule of NO and ultimately amine (major process). The production of nitrosamine radical anion 5 upon photolysis of diazeniumdiolate 3 is confirmed by low-temperature EPR spectroscopy. The calculated energetics for the ground and excited states of the parent diazeniumdiolate ion at the CIS and B3LYP levels of theory as well as B3LYP calculations on the fragmentation processes were very effective in rationalizing the observed photodissociation processes.
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PMID:Photochemistry of 1-(N,N-diethylamino)diazen-1-ium-1,2-diolate: an experimental and computational investigation. 1464 Jun 71

The use of nonporphyrin complexes encapsulated in zeolites as catalysts for oxidation reactions has been improved in the past decades by the discovery of increasing numbers of nonheme monoxygenases. The zeolite lattice can change the oxidative chemistry of the metallocomplexes, resulting in a catalytic effect different from those observed in homogeneous reactions. We report the encapsulation of iron and copper metallocomplexes with the ligand (2-hydroxybenzyl)(2-methylpyridyl)amine, Hbpa, and iron complexes with the ligand N,N'-bis(2-hydroxybenzyl)-N,N'-bis(2-methylpyridyl) ethylenediamine, H(2)bbpen. The zeolite-encapsulated metallocomplexes were prepared by diffusion of the ligands through the pores of the zeolites, already exchanged with the respective metal. The syntheses were performed in methanol and toluene solutions. Elemental analysis of solids with the Hbpa ligand have indicated better complexation for synthesis in toluene, where 74% of the iron atoms were coordinated by the ligand, against 37% for the synthesis in methanol. For the immobilization with the H(2)bbpen ligand in toluene it was observed that 46% of the iron atoms are coordinated, showing that the diffusion of the small ligand Hbpa through the zeolite cage was facilitated. The EPR spectra of the solids show signals at g = 2.0, which was attributed to an Fe-Fe interaction from the noncoordinated atoms, and g = 4.3 attributed to iron (III) in a rhombic geometry.
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PMID:Encapsulation of Fe(III) and Cu(II) complexes in NaY zeolite. 1527 50

We report a carboxylate triangle consisting of three manganese(II) centres which is made from manganese(II) carbonate and pivalic acid. The magnetic exchange within the triangle is extremely weak, and antiferromagnetic. Several models have been used to fit the magnetic data, and the best fit uses two weak antiferromagnetic coupling constants of J(1)=-0.588 cm(-1) and J(2)=-0.855 cm(-1). Exchange interactions between the metal centres has been calculated using DFT adopting all the three possible Heisenberg models for a trinuclear system and the results are compared with experimental values. Spin density distribution is used to analyse the nature of the coupling between the metal centres. EPR spectroscopy has been used to explore the nature of the ground state. Recrystallisation of the trinuclear compound from MeCN gives a polymer, while oxidation in air leads to a known compound--an edge-sharing bitetrahedral (MnIII2MnII4) cage.
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PMID:Synthesis and studies of a trinuclear Mn(II) carboxylate complex. 1530 71


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