1. Advantages of Chemical Redox Agents 878 2. Disadvantages of Chemical Redox Agents 879 C. Potentials in Nonaqueous Solvents 879 D. Reversible vs Irreversible ET Reagents 879 E. Categorization of Reagent Strength 881 II. Oxidants 881 A. Inorganic 881 1. Metal and Metal Complex Oxidants 881 2. Main Group Oxidants 887 B. Organic 891 1. Radical Cations 891 2. Carbocations 893 3. Cyanocarbons and Related Electron-Rich Compounds 894

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Chemical Redox Agents for Organometallic Chemistry

http://academic.oup.com/milmed/article-pdf/146/7/506/24126715/milmed-146-7-506.pdf

Goodman and Gilman's The Pharmacological Basis of Therapeutics

/pdf/polyoxometalates-in-medicine-3giyx6h3ls.pdf

Polyoxometalates in Medicine

Helicates as Versatile Supramolecular Complexes.

ion step follows the decarboxylation, which is consistent with the deuterium isotopic effects observed for thymine 7-hydroxylase which indicate that an irreversible step (or steps) occurs prior to the C-H bond breaking.395 It has also been shown for prolyl 4-hydroxylase that a substrate-derived radical is generated in the reaction, which is consistent with a rebound mechanism.437 It is important to point out that no oxygen intermediate (i.e., bridged superoxo or oxo-ferryl) has been observed for any R-KGdependent enzyme. This warrants future theoretical and experimental study. A detailed molecular mechanism has been proposed for IPNS based on spectroscopic and crystallographic studies.422 Resting IPNS/FeII is also 6C and thus relatively stable toward dioxygen. Substrate ACV binds directly to FeII IPNS through its thiolate group, providing an open coordination position at the FeII. O2 can then react to form an FeIII-superoxo intermediate. This intermediate is suggested422 to perform the first hydrogen-atom abstraction step and close the â-lactam ring, resulting in the formation of the first water molecule and generating an FeIVdO-II intermediate, which completes the second ringclosure process by hydrogen-atom abstraction forming a thiazolidine ring. Previously proposed mechanisms of ACCO involved direct binding of cosubstrate ascorbate to the iron before O2 as part of the oxygen activation process.438,439 The EPR and ESEEM studies of the NO complex of ACCO suggested a quite different molecular mechanism for ACCO.435 An FeIII-superoxo intermediate is proposed. Whether it is preceded by a 6C f 5C process with substrate binding is presently under study.440 This intermediate is thought to initiate a radical process by single hydrogen-atom abstraction or electron-coupled proton transfer (PT)ion or electron-coupled proton transfer (PT) from the bound amino group. The resulting substrate radical may undergo spontaneous conversion into products. The role of cosubstrate ascorbate is proposed to reduce the toxic peroxo byproduct to water. Alternatively, the two-electron reduction of FeIIIsuperoxo by the cosubstrate ascorbate could result in an FeIVdO-II intermediate which initiates the radical reaction.435 4. Rieske-Type Dioxygenases Biochemical Characterization. The Rieske ironsulfur center is a two iron-two sulfur cluster ([2Fe2S]) which has a 2His (on one iron), 2Cys (on the other iron) coordination environment, instead of the 4Cys present in plant ferredoxins. It plays a key role in the electron transport pathway in membranebound cytochrome complexes as well as in some dioxygenases.441 The latter are mainly comprised of two protein components: a reductase containing flavin and a ferredoxin [2Fe-2S], and a terminal oxygenase containing a Rieske [2Fe-2S] cluster and a non-heme iron active site.442 Except for the recently reported alkene monooxygenase that has a binuclear iron site in its terminal oxygenase,10 most of the Rieske-type oxygenases have a mononuclear iron site, which is believed to be the site of dioxygen activation and substrate oxygenation.442,443 The majority of the Rieske-type mononuclear non-heme oxygenases form a family of enzymes which are aromatic-ring-hydroxylating dioxygenases. These catalyze the regioand stereospecific cis-dihydroxylation of an aromatic ring using dioxygen and NAD(P)H (Table 1). Examples include benzene dioxygenase (BDO, EC 1.14.12.3),444 phthalate dioxygenase (PDO, EC 1.14.12.7),445 toluene dioxygenase (EC 1.14.12.11),446 and naphthalene 1,2-dioxygenase (NDO, EC 1.14.12.12),447 which initiate the aerobic degradation of aromatic compounds in the soil bacteria and are targets for bioengineering in bioremediation. This step is the first step in the pathway that ultimately leads to ring cleavage by the intraand extradiol dioxygenases (sections II.B.2 and II.C.1).443 Besides these bacterial dioxygenases, other Rieske-type mononuclear non-heme oxygenases include anthranilate 1,2-dioxygenase (EC 1.14.12.1),448 which deaminates and decarboxylates the substrate to produce catechol; chlorophenylacetate 3,4-dioxygenase (EC 1.14.2.13),449 which converts substrate to catechol with chloride elimination; and 4-methoxybenzoate O-demethylase (putidamonooxin),450 which catalyzes the conversion of 4-methoxybenzoic acid to 4-hydroxybenzoic acid and formaldehyde. The reductase component is usually a monomer (MW ) 12-15 kDa) and utilizes flavin to mediate ET from the two-electron donor NAD(P)H to the oneelectron acceptor [2Fe-2S] cluster and is specific to each terminal oxygenase; other electron donors do not support efficient oxygenation.442 The crystal structure of phthalate dioxygenase reductase is available.451 The terminal oxygenases are large protein aggregates (MW ) 150-200 kDa) containing either multiples of R subunits (BDO R2, PDO R4) or an equimolar combination of R and â subunits (toluene dioxygenase R2â2, NDO R3â3). The R subunits contain a Rieske [2Fe-2S] cluster and a catalytic non-heme FeII center. â subunits do not seem to be involved in the catalytic function (vide infra). Kinetics. Steady-state kinetic studies coupled with various rapid reaction studies of the partial reactions of PDO allowed Ballou et al. to propose a kinetic scheme (Scheme 15).443 On the basis of steady state 278 Chemical Reviews, 2000, Vol. 100, No. 1 Solomon et al.

Geometric and Electronic Structure/Function Correlations in Non-Heme Iron Enzymes

The syntheses and the solid state structural and spectroscopic solution characterizations of VO(Me-acac)2 and VO(Et-acac)2 (where Me-acac is 3-methyl-2,4-pentanedionato and Et-acac is 3-ethyl-2,4-pentanedionato) have been conducted since both VO(acac)2 and VO(Et-acac)2 have long-term in vivo insulin-mimetic effects in streptozotocin-induced diabetic Wistar rats. X-ray structural characterizations of VO(Me-acac)2 and VO(Et-acac)2 show that both contain five-coordinate vanadium similar to the parent VO(acac)2. The unit cells for VO(Et-acac)2 and VO(Me-acac)2 are both triclinic, P1, with a = 9.29970(10) A, b = 13.6117(2) A, c = 13.6642(2) A, alpha = 94.1770(10) degrees, beta = 106.4770(10) degrees, gamma = 106.6350(10) degrees for VO(Et-acac)2 and a = 7.72969(4) A, b = 8.1856(5) A, c = 11.9029(6) A, alpha = 79.927(2) degrees, beta = 73.988(2)degrees, gamma = 65.1790(10)degrees for VO(Me-acac)2. The total concentration of EPR-observable vanadium(IV) species for VO(acac)2 and derivatives in water solution at 20 degreesC was determined by double integration of the EPR spectra and apportioned between individual species on the basis of computer simulations of the spectra. Three species were observed, and the concentrations were found to be time, pH, temperature, and salt dependent. The three complexes are assigned as the trans-VO(acac)2.H2O adduct, cis-VO(acac)2.H2O adduct, and a hydrolysis product containing one vanadium atom and one R-acac- group. The reaction rate for conversion of species was slower for VO(acac)2 than for VO(malto)2, VO(Et-acac)2, and VO(Me-acac)2; however, in aqueous solution the rates for all of these species are slow compared to those of other vanadium species. The concentration of vanadium(V) species was determined by 51V NMR. The visible spectra were time dependent, consistent with the changes in species concentrations that were observed in the EPR and NMR spectra. EPR and visible spectroscopic studies of solutions prepared as for administration to diabetic rats documented both a salt effect on speciation and formation of a new halogen-containing complex. Compound efficacy with respect to long-term lowering of plasma glucose levels in diabetic rats traces the concentration of the hydrolysis product in the administration solution.

Chemistry and insulin-mimetic properties of bis(acetylacetonate)oxovanadium(IV) and derivatives

Models for iron-oxo proteins. Structures and properties of FeIIFeIII, ZnIIFeIII, and FeIIGaIII complexes with (.mu.-phenoxo)bis(.mu.-carboxylato)dimetal cores

Nonclassical Metal-Carbonyls - (Ag(Co))(+) and (Ag(Co)(2))(+)

X-ray Structure of (NH4)6(Gly-Gly)2V10O28.cntdot.4H2O: Model Studies for Polyoxometalate-Protein Interactions

Synthesis and characterization of phenolate-bridge copper dimers with a copper-copper separation of >3.5 .ANG.. Models for the active site of oxidized hemocyanin derivatives

Oren P. Anderson

Papers

Chemistry and insulin-mimetic properties of bis(acetylacetonate)oxovanadium(IV) and derivatives

Models for iron-oxo proteins. Structures and properties of FeIIFeIII, ZnIIFeIII, and FeIIGaIII complexes with (.mu.-phenoxo)bis(.mu.-carboxylato)dimetal cores

Nonclassical Metal-Carbonyls - (Ag(Co))(+) and (Ag(Co)(2))(+)

X-ray Structure of (NH4)6(Gly-Gly)2V10O28.cntdot.4H2O: Model Studies for Polyoxometalate-Protein Interactions

Synthesis and characterization of phenolate-bridge copper dimers with a copper-copper separation of >3.5 .ANG.. Models for the active site of oxidized hemocyanin derivatives