Oxido complexes

This conversion is a clean reactivity model for the Mo enzyme trimethylamine A-oxide reductase. The molybdenum(VI) bis(oxido) complex has a distorted octahedral geometry [181],... 

A significant number of molybdenum oxido complexes either oxidize or reduce enzymatic substrates. Formally, many of these processes involve the inner sphere transfer of a neutral oxygen atom (O). This process is equivalent to the coupled transfer of 2 c and O2 in opposite direction [195],... 

Of the complexes studied, those with ancillary ligands that contain sulfur atoms have received the most attention. Among the most studied are the bis(dial-kyldithiocarbamate) molybdenum oxido complexes [196,197], Unfortunately, although these complexes react with certain enzyme substrates, their common problem as models for Moco active sites involves the propensity of the Movl dioxo and MoIV monoxo complexes to form a comproportionated Mov p-oxido dimer (Eq. 13 dtc = diethyldithiocarbamate). 

The importance of PCET and concerted proton electron transfer (EPT) in the activation of ruthenium oxido complexes was initially acknowledged for [Ru(bpy)2(py)OH2], but this complex failed to catalyse water oxidation. 

A substantial fraction of the named enzymes are oxido-reductases, responsible for shuttling electrons along metabolic pathways that reduce carbon dioxide to sugar (in the case of plants), or reduce oxygen to water (in the case of mammals). The oxido-reductases that drive these processes involve a small set of redox active cofactors , that is, small chemical groups that gain or lose electrons. These cofactors include iron porjDhyrins, iron-sulfur clusters and copper complexes as well as organic species that are ET active. 

Hydroxylamine, IV-benzoyl-lV-phenyl-in gravimetry, 1, 532 liquid-liquid extraction, 1, 544 Hydroxylamine, A -cinnamoyl-A -phenyl-liquid-liquid extraction, 1,544 Hydroxylamine, Ar,A -di-(-butyl-metal complexes, 2, 798 Hydroxylamine, Ay/V-diethyl-metal complexes, 2,798 Hydroxylamine, AAmethyl-metal complexes, 2,798 Hydroxylamine, A -2-naphthol-A -nitroso-ammonium salt — see Ncocupferron Hydroxylamine, A -nilrosophenyl-ammonium salt — see Cupferron Hydroxylamine ligands, 2, 101 Hydroxylamine oxido reductase, 6, 727 Hydroxylases molybdenum, 6,658,662 Hydroxylation arenes... 

The ferro-complex CD spectrum shows that reduction of the heme iron alters the heme environment. Redox-induced protein conformation changes could alter the S5unmetry in the heme pocket or produce two binding modes for the reduced complex whose asymmetries nearly cancel each other. Redox-linked conformational changes are especially interesting in view of recent findings of oxido-reductase activity associated with the heme-hemopexin-receptor interaction (89). 

Friedrich, T., VanHeek, P., Leif, H., Ohnishi, T., Forche, E., Kunze, B., Jansen, R., Trowitzsch-Kienast, W., Holfe, G., Reichenbach, H., and Weiss, H. Two binding sites of inhibitors in NADH ubiquinone oxidoreductase (complex I) relationship of one site with the ubiquinone oxido-reductase. Eur. J. Biochem., 219, 691, 1994. 

Thiosulfate cyanide sulfurtransferase symmetry in 78 TTiiouridine 234 Three-dimensional structures of aconitase 689 adenylate kinase 655 aldehyde oxido-reductase 891 D-amino acid oxidase 791 a-amylase, pancreatic 607 aspartate aminotransferase 57,135 catalytic intermediates 752 aspartate carbamyltransferase 348 aspartate chemoreceptor 562 bacteriophage P22 66 cadherin 408 calmodulin 317 carbonic acid anhydrase I 679 carboxypeptidase A 64 catalase 853 cholera toxin 333, 546 chymotrypsin 611 citrate synthase 702, 703 cutinase 134 cyclosporin 488 cytochrome c 847 cytochrome c peroxidase 849 dihydrofolate reductase 807 DNA 214, 223,228,229, 241 DNA complex... 

Complex III (ubiquinol-cytochrome c oxido-reductase or cytochrome bct complex). Mitochondrial complex III is a dimeric complex, each subunit of which contains 11 different subunits with a total molecular mass of 240 kDa per monomer.104-107 However, in many bacteria the complex consists of only three subunits, cytochrome b, cytochrome c , and the high potential ( 0.3 V) Rieske iron-sulfur protein, which is discussed in Chapter 16, Section A,7. These three proteins are present in all bc1 complexes. 

The average Mo=0 bond distance of the (MPT)Mo(0)2(S-eys) cofactor of sulfite oxidase is 1.68 A by EXAFS (Figure 14). The RR results are consistent with bis(oxido) coordination of MoVI and the two expected Mo=0 stretching modes are found at 903 and 881 cm-1 [119,139], Upon reduction and reoxidation in the presence of H2180 the Mo=0 bands shift to 890 and 848 cm-1, respectively [119,139], The difference in the 180 isotopic shifts for the symmetric and asymmetric bands is consistent with labeling of only one of the oxido ligands. This observation has precedent in the labeling of bis(oxido) model complexes and is supported by normal coordinate analysis [140],... 

Chemical systems of relevance to the molybdenum and tungsten enzymes include synthetic pterins, a-phosphorylated ketones (as precursor models), and a variety of molybdenum and tungsten oxido, sulfido, and 1,2-enedithiolate complexes. These compounds have been used to (1) confirm the identity of MPT derivatives (2) define steps in MPT biosynthesis (3) calibrate spectroscopic observations (4) give precise geometries and reactivities that can be used as input for theoretical studies and (5) provide options for mechanistic consideration. 

The realization that many of the Mo and W cofactors are 1,2-enedithiolate complexes with oxido or sulfido coordination has encouraged studies of complexes... 

In 1986, it was shown that MoIY0(bdt)22 could be prepared from Moiv02(CN)44 , and MovO(bdt)2 could be prepared from MovO(SPh)4 [176], The oxido bis(l,2-enedithiolate) Mo(V) and Mo(IV) complexes are readily inter-converted. Both complexes are square-pyramidal with an oxido as the apical ligand. The respective Mo-0 stretching frequencies are 941 and 905 cm1. 

V.E. Reactivity of Molybdenum and Tungsten Oxido Bis(1,2-Enedithiolate) Complexes... 

Recent work by Nakamura, Ueyama [177-185], Sarkar [186-191], and coworkers has led to the preparation and interconversion of several oxido bis(l,2-enedithiolate) complexes of Mo and W. These complexes take the form Movi02L2 and MIVOL2 where M = Mo or W and L is a 1,2-enedithiolate ligand, either (CN)2C2S22 (mnt2 ) or C6H4S22- (bdt2 ). 

The structures of all three oxidation states in the tungsten bdt series have been reported. The W(IV) and W(V) states are similar to the Mo analogs [178], The bis(oxido) W(VI) complex is a distorted octahedron. The W—S bonds tram to the oxido ligand are lengthened with W—S distances cis to the oxido at 2.425(4) A and tram to the oxido at 2.597(4) A, respectively. The W(VI) complex reacts with benzoin to give benzil (Eq. 12), but only reacts slowly with PPh3 [183],... 

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