Mechanism Of Oxygen Atom Transfer Research Articles

New molybdenum catalysts for alkyl olefin epoxidation. Their implications for the mechanism of oxygen atom transfer.

We report here the design, synthesis, and characterization of new (dioxo)Mo(VI) epoxidation catalysts based on monoanionic tridentate ligands. Two important features distinguish these catalysts from those previously reported. First, their coordination environment remains well-defined during the epoxidation reaction. Second, the ligand design does not permit simultaneous coordination of olefin and alkyl hydroperoxide. Based on the study of these new catalysts, we conclude that direct oxygen atom transfer from coordinated alkyl peroxide to olefin remains the simplest mechanism consistent with the available data. We discuss literature discrepancies in this regard.

Resonance Raman Characterization of Biotin Sulfoxide Reductase: COMPARING OXOMOLYBDENUM ENZYMES IN THE Me2SO REDUCTASE FAMILY

Resonance Raman spectroscopy has been used to define active site structures for oxidized Mo(VI) and reduced Mo(IV) forms of recombinant Rhodobacter sphaeroides biotin sulfoxide reductase expressed in Escherichia coli. On the basis of (18)O/(16)O labeling studies involving water and the alternative substrate dimethyl sulfoxide and the close correspondence to the resonance Raman spectra previously reported for dimethyl sulfoxide reductase (Garton, S. D., Hilton, J., Oku, H., Crouse, B. R., Rajagopalan, K. V., and Johnson, M. K. (1997) J. Am. Chem. Soc. 119, 12906-12916), vibrational modes associated with a terminal oxo ligand and the two molybdopterin dithiolene ligands have been assigned. The results indicate that the enzyme cycles between mono-oxo-Mo(VI) and des-oxo-Mo(IV) forms with both molybdopterin dithiolene ligands remaining coordinated in both redox states. Direct evidence for an oxygen atom transfer mechanism is provided by (18)O/(16)O labeling studies, which show that the terminal oxo group at the molybdenum center is exchangeable with water during redox cycling and originates from the substrate in substrate-oxidized samples. Biotin sulfoxide reductase is not reduced by biotin or the nonphysiological products, dimethyl sulfide and trimethylamine. However, product-induced changes in the Mo=O stretching frequency provide direct evidence for a product-associated mono-oxo-Mo(VI) catalytic intermediate. The results indicate that biotin sulfoxide reductase is thermodynamically tuned to catalyze the reductase reaction, and a detailed catalytic mechanism is proposed.

Oxidation of sulfides by 3-hydroperoxy-4,4,5,5-tetramethyl-3-phenyl-1,2-dioxolane: Effect of solvent and sulfide substituent

The reaction of 3-hydroperoxy-4,4,5,5-tetramethyl-3-phenyl-1,2-dioxolane, 1, with a series of sulfides (2a = thioanisole, 2b = ethyl phenyl sulfide, 2c = 2-chloroethyl phenyl sulfide, and 2d = 2-chloroethyl methyl sulfide) at 34°C in various solvents yielded the corresponding sulfoxides and 3-hydroxy-1,2-dioxolane 3 in quantitative yields. The oxidations showed excellent second-order kinetic behavior overall. In CDCl3, the reactivity order was 2d > 2b > 2a > 2c. For 2a, the relative rate in various solvents was CDCl3 (17); CD3OD (7); C6D6 (∼3); CD3CN (1); CD3C(O)CD3 (∼0.3). Addition of ∼1 equivalent of acetic acid to reactions of 1 and 2a in CDCl3 and C6D6 resulted in small increases in the values of k2. The results are consistent with an electrophilic oxygen-atom transfer mechanism similar to that proposed for oxidations by α-azohydroperoxides. Since the precursor to 1, 3-hydroxy-1,2-dioxolane 3, is regenerated during the oxidation, the system has the potential to be developed as a cyclic process. © 1998 John Wiley & Sons, Inc. Heteroatom Chem 9:75–78, 1998

Resonance Raman as a direct probe for the catalytic mechanism of molybdenum oxotransferases

Recent studies of human sulfite oxidase and Rhodobacter sphaeroides DMSO reductase have demonstrated the ability of resonance Raman to probe in detail the coordination environment of the Mo active sites in oxotransferases via Mo=O, Mo-S(dithiolene), Mo-S(Cys) or Mo-O(Ser), dithiolene chelate ring and bound substrate vibrations. Furthermore, the ability to monitor the catalytically exchangeable oxo group via isotopic labeling affords direct mechanistic information and structures for the catalytically competent Mo(IV) and Mo(VI) species. The results clearly demonstrate that sulfite oxidase cycles between cis–di-oxo-Mo(VI) and mono-oxo-Mo(IV) states during catalytic turnover, whereas DMSO reductase cycles between mono-oxo-Mo(VI) and des-oxo-Mo(IV) states. In the case of DMSO reductase, 18O-labeling experiments have provided the first direct evidence for an oxygen atom transfer mechanism involving an Mo=O species. Of particular importance is that the active-site structures and detailed mechanism of DMSO reductase in solution, as determined by resonance Raman spectroscopy, are quite different to those reported or deduced in the three X-ray crystallographic studies of DMSO reductases from Rhodobacter species.

Unusual mechanism of oxygen atom transfer and product rearrangement in the catalytic reaction of 2-methyl-3-hydroxypyridine-5-carboxylic acid oxygenase.

The oxygenation reaction of 2-methyl-3-hydroxypyridine-5-carboxylic acid (MHPC) oxygenase with the substrate, MHPC, was investigated. Two oxygenated flavin intermediates C(4a)-hydroperoxy flavin and C(4a)-hydroxy flavin were found, implying that the enzyme functions similarly to flavoprotein hydroxylases. This finding is supported by the results of independent oxygen-18 tracer experiments, which showed that one atom of oxygen from 18O2 and one atom of oxygen from H218O are incorporated in the product. MHPC oxygenase normally catalyzes both the oxygenation and the hydrolytic ring opening of the pyridine ring of MHPC to yield the acyclic compound, alpha-(N-acetylaminomethylene)succinic acid. Using 5-hydroxynicotinic acid (5HN), which has no 2-methyl group, we tested whether the hydrolytic reaction was due to the presence of the 2-methyl group on MHPC (that prevented rearomatization of the initial product) or to the specific properties of MHPC oxygenase. Product analysis of the enzymatic reaction of 5HN and MHPC oxygenase shows that the enzyme catalyzes the hydroxylation and subsequent hydrolysis of the hydroxylated substrate to yield an acyclic product. The investigation of the oxygenation reaction demonstrates that the enzyme uses the same mechanism to catalyze the 5HN reaction as it does in the MHPC reaction.

Structure and reactivity of diamidoiron(III) hydroperoxide. The mechanism of oxygen-atom transfer to ammonia

Diamidoiron( 111) hydroperoxide has been examined as a highly simplified model for the hydroperoxide intermediate in hemoproteins such as peroxidases and cytochrome P-450. Equilibrium structures and transition states were optimized at the UHF and UMP2 levels using the 3-21G basis and the Wachters-Hay basis set (augmented with an f function on iron). The MP2 level was found to be essential for a proper description of the geometry and bonding. Diamidoiron(II1) hydroperoxide is a peroxo-bridged structure with Fe-0 bond lengths of 1.98 and 2.15 A. A CASSCF/ 3-21G geometry optimization also afforded a cyclic FeOOH structure with an Fe-0-0 bond angle of 70.4O. Similar calculations on (HO)3TiOOH yielded a bridged structure in excellent agreement with X-ray data. The barrier for oxygen transfer from diamidoiron(II1) hydroperoxide to ammonia is only 10.2 kcal/mol (MP4 energies using the Wachters-Hay basis), a barrier lower than that for LiOOH (20.0 kcallmol) and peroxyformic acid (17.8 kcal/mol). Protonated diamidoiron(II1) hydroperoxide is no longer bridged (R(Fe-O) = 2.01 and 2.85 A) and has a negative barrier for oxygen donation to NH3. Although these highly abbreviated models have many shortcomings, the present calculations suggest that in certain cases oxygen atom transfer from iron hemoproteins could precede the formation of the ferryl complex.

Mechanism of oxygen atom transfer from oxaziridine to a lithium enolate. A theoretical study

Mechanism of oxygen atom transfer from oxaziridine to a lithium enolate. A theoretical study

ChemInform Abstract: On the Mechanism of Oxygen Atom or Nitrene Group Transfer in Reactions of Epoxides and Aziridines with Tungsten(II) Compounds.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Possible chain mechanism of oxygen atom transfer

A chain mechanism is suggested for reactions in polar media which proceed according to the general scheme $$LO + B \to L + BO$$

ChemInform Abstract: Mechanism of Oxygen Atom Transfer from High Valent Iron Porphyrins to Olefins: Implications to the Biological Epoxidation of Olefins by Cytochrome P‐450.

ChemInform Abstract: Mechanism of Oxygen Atom Transfer from High Valent Iron Porphyrins to Olefins: Implications to the Biological Epoxidation of Olefins by Cytochrome P‐450.

Mechanism of oxygen atom transfer from high valent iron porphyrins to olefins: implications to the biological epoxidation of olefins by cytochrome P-450

Mechanism of oxygen atom transfer from high valent iron porphyrins to olefins: implications to the biological epoxidation of olefins by cytochrome P-450

The mechanism of oxygen atom transfer to tetraphenylporphinato chromic chloride

On etudie l'effet de la structure donneuse sur la facilite et le mecanisme de transfert d'oxygene

Photochemical reduction of the uranyl ion with dialkyl sulfides

The photochemical reduction of the uranyl ion by diethyl, di-n-propyl, and di-n-butyl sulfides has been investigated in acidified water-acetone medium by using radiations in the visible region (greater than or equal to 365 nm) from a medium-pressure mercury lamp. The photoreduction is independent of temperature. The quantum yield increases with an increase in dialkyl sulfide or hydrogen ion concentration. The plots of the reciprocal of the quantum yield vs. the reciprocal of initial dialkyl sulfide concentration are linear with intercepts on the ordinate axis. Stern-Volmer quenching constants have been calculated from luminescence measurements and indicated that physical and chemical quenching compete with each other. Electronic absorption spectra reveal that there is no ground-state interaction between the uranyl ion and the dialkyl sulfide. On the basis of product analysis, quantum yield of uranium(IV) formation, and Stern-Volmer quenching constants, a dynamic mechanism of oxygen atom transfer from the excited uranyl ion to dialkyl sulfide has been proposed. 33 references, 3 figures, 3 tables.

Epoxidation of olefins by cytochrome P-450 model compounds: mechanism of oxygen atom transfer.

The mechanism of the Mn(III) porphyrin-catalyzed epoxidation of olefins by lithium hypochlorite is examined. The active oxidant is thought to be a high-valent manganese-oxo complex. It is shown that a relatively stable intermediate is reversibly formed upon interaction of the olefin and the oxo complex. The decomposition of this intermediate to Mn(III) porphyrin and epoxide is the rate-determining step of the catalytic cycle. Some analogies to the biochemical epoxidation of olefins catalyzed by cytochrome P-450 are discussed.

Kinetics and mechanism of oxygen atom transfer from iodosylbenzene to certain cobalt(III) nitrosyl complexes

On montre que certains complexes de Co-nitrosyle reagissent avec l'iodosylbenzene pour donner les complexes nitro de Co correspondants. Les vitesses de reaction sont du 1er ordre; les reactions n'ont pas lieu en l'absence de base. Mecanisme mettant en jeu un preequilibre rapide suivi d'un processus du 2eme ordre determinant la vitesse

Catalytic oxidation of hydrocarbons using iodosylbenzene in the presence of a ruthenium(III) porphyrin complex

The ruthenium(III) octaethylporphyrin complex, Ru(OEP)(PPh 3)Br, 1,has been prepared by the oxidation of Ru(OEP)(PPh 3) 2 [1] with excess bromine, and fully characterized by spectroscopic and crystallographic methods [2]. We have found that CH 2Cl 2 solutions of 1 (5 × 10 −3 M) containing iodosylbenzene (0.1 M) catalyze at 20 °C the oxidation of certain olefins and cyclohexane (0.2–20.5 M). Some of the oxidation data are summarized in Table I. Groves et al. [3] have reported on corresponding oxidations using iron(III) porphyrins, and have presented evidence for involvement of an oxoiron(IV) porphyrin cation-radical intermediate, OFe IV(porp +•). This is equivalent electronically to iron(III) plus the oxygen atom (from iodosylbenzene), and is overall at the same oxidation level as the active species in the cytochrome P-450 enzyme cycle; the enzyme systems utilize molecular O 2 for alkene epoxidation and hydrocarbon hydroxylation, and active OFe IV(porp +•) intermediates have been implicated [3–5]. Studies with our ruthenium(III) system have led to isolation of closely related cation-radical species. Thus, reaction of 1 with PhIO yields a green complex tentatively formulated as 0Ru IV (OEP +•)Br, 2. A strong ESR signal at g = 2.00 (at 77 K or 20 °C), and a broad Soret band at 384 nm coupled with bands at 502 and 604 nm, are typical of cation-radical species [1, 4]; a stoichiometric spectrophotometric titration with PPh 3 (complex 2: PPh 3 = 2.0) to give quantitatively OPPh 3 and [Ru IV(OEP)Br] 2O [6] (see Scheme), and detection of bromine as cyclohexylbromide in the hydrocarbon oxidations (close to stoichiometric based on Ru, up to 85%, see Table) are consistent with the oxygen and bromine content of 2, and with 2 being the active oxidizing species via free-radical reactions [1, 9, 10]: ▪ ▪ An inactive green complex, isolated at the end of the oxidations, and also formed by decomposition of 2 in solution, is believed to be a ORu(OEP) species, 3, since it reacts quantitatively with PPh 3(1:1) to give the phosphine oxide and [Ru(OEP)] 2 [8]. Species 3, which is rapidly converted by trace amounts of base into [Ru(OEP)(OH)] 2O [7, 8], may contain an axial water ligand in which case it would resemble ORu(bipyridine) 2(py), which is known to oxidize PPh 3 by an oxygen atom transfer mechanism [11]. Spectroscopic studies are in progress in attempts to characterize more fully the putative oxo species 2 and 3.

Kinetics and mechanism of oxygen atom transfer from nitro compounds mediated by nickel(0) complexes

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTKinetics and mechanism of oxygen atom transfer from nitro compounds mediated by nickel(0) complexesR. S. Berman and J. K. KochiCite this: Inorg. Chem. 1980, 19, 1, 248–254Publication Date (Print):January 1, 1980Publication History Published online1 May 2002Published inissue 1 January 1980https://doi.org/10.1021/ic50203a050RIGHTS & PERMISSIONSArticle Views460Altmetric-Citations62LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (902 KB) Get e-Alerts Get e-Alerts

Oxidation by Molecular Oxygen. II. The Oxygen Atom Transfer Mechanism for Mixed-Function Oxidases and the Model for Mixed-Function Oxidases

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTOxidation by Molecular Oxygen. II. The Oxygen Atom Transfer Mechanism for Mixed-Function Oxidases and the Model for Mixed-Function OxidasesGordon A. HamiltonCite this: J. Am. Chem. Soc. 1964, 86, 16, 3391–3392Publication Date (Print):August 1, 1964Publication History Published online1 May 2002Published inissue 1 August 1964https://doi.org/10.1021/ja01070a037RIGHTS & PERMISSIONSArticle Views195Altmetric-Citations112LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (281 KB) Get e-Alerts Get e-Alerts