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Atom Transfer Reactions (atom + transfer_reaction)

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Chemistry100%

Selected Abstracts

Bis(dithiolene) Molybdenum Complex that Promotes Combined Coupled Electron,Proton Transfer and Oxygen Atom Transfer Reactions: A Water-Active Model of the Arsenite Oxidase Molybdenum Center

EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 22 2006
Hideki Sugimoto
Abstract Combined CEPT (coupled electron,proton transfer)/OAT (oxygen atom transfer) reactions were accomplished in (Bu4N)2[MoIVO(bdtCl2)2] (1) and (Bu4N)2[MoVIO2(bdtCl2)2] (2) complexes in aqueous media. The reaction mechanism of the CEPT reaction was analyzed electrochemically and the conversion of 1 to 2 was revealed to proceed by a two-proton two-electron oxidative process. The structural and reaction profiles provide a new model for the arsenite oxidase catalytic center. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006) [source]

Hydrogen Atom Transfer Experiments Provide Chemical Evidence for the Conformational Differences between C - and O -Disaccharides

EUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 27 2010
Elisa I. León
Abstract The glycopyran-6- O -yl radical promoted hydrogen atom transfer reaction (HAT) between the two pyranose units of ,- D -Manp -(1,4)-,- D -Glcp and ,- D -Manp -(1,4a)-4a-carba-,- D -Glcp disaccharides provides supporting chemical evidence for the conformational differences between O - and C -glycosyl compounds. In the O -disaccharide the 6-alkoxyl radical, generated under oxidative or reductive conditions, abstracts exclusively the hydrogen at C-5, via a completely regioselective 1,8-HAT reaction. This may be attributable to the conformational restriction of the glycosidic and aglyconic bonds due principally to steric and stereoelectronic effects. On the contrary, very little regioselectivity is observed in the homologous C -disaccharide and a mixture of compounds generated by 1,5-, 1,6-, and 1,8-HAT processes where the abstraction occurs at hydrogen atoms positioned at C-4a, C-1,, and C-5,, respectively, has been obtained. This study has been extended to simpler O - and C -glycosides, where the aglycon was a straight n -alkyl alcohol tether of five atoms; in general, all of the results obtained are shown to be consistent with a major conformational flexibility of the C -glycosidic bond. [source]

Studies on the oxygen atom transfer reactions of peroxomonosulfate: Catalytic effect of hemiacetal

INTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 10 2009
S. Shailaja
The reaction of peroxomonosulfate (PMS) with glycolic acid (GLYCA), an alpha hydroxy acid, in the presence of Ni(II) ions and formaldehyde was studied in the pH range 4.05,5.89 and at 31°C and 38°C. When formaldehyde and Ni(II) ions concentrations are ,5.0 × 10,4 M to 10.0 × 10,4 M, the reaction is second order in PMS concentration. The rate is catalyzed by formaldehyde, and the observed rate equation is (,d[PMS])/dt = (k,2[HCHO][Ni(II)][PMS]2)/{[H+](1+K2[GLYCA])}. The number of PMS decomposed for each mole of formaldehyde (turnover number) is 5,10, and the major reaction product is oxygen gas. The first step of the reaction mechanism is the formation of hemiacetal by the interaction of HCHO with the hydroxyl group of nickel glycolate. The peroxomonosulfate intermediate of the Ni-hemiacetal reacts with another molecule of PMS in the rate-limiting step to give the product. This reaction is similar to the thermal decomposition of PMS catalyzed by Ni(II) ions. © 2009 Wiley Periodicals, Inc. Int J Chem Kinet 41: 642,649, 2009 [source]

Studies on the oxygen atom transfer reactions of peroxomonosulfate: Oxidation of glycolic acid

INTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 3 2009
S. Shailaja
The kinetics of oxidation of glycolic acid, an ,-hydroxy acid, by peroxomonosulfate (PMS) was studied in the presence of Ni(II) and Cu(II) ions and in acidic pH range 4.05,5.89. The metal glycolate, not the glycolic acid (GLYCA), is oxidized by PMS. The rate is first order in [PMS] and metal ion concentrations. The oxidation of nickel glycolate is zero-order in [GLYCA] and inverse first order in [H+]. The increase of [GLYCA] decreases the rate in copper glycolate, and the rate constants initially increase and then remain constant with pH. The results suggest that the metal glycolate ML+ reacts with PMS through a metal-peroxide intermediate, which transforms slowly into a hydroperoxide intermediate by the oxygen atom transfer to hydroxyl group of the chelated GLYCA. The effect of hydrogen ion concentrations on kobs suggests that the structure of the metal-peroxide intermediates may be different in Ni(II) and Cu(II) glycolates. © 2008 Wiley Periodicals, Inc. Int J Chem Kinet 41: 160,167, 2009 [source]