Hydrogen atom abstraction

About: Hydrogen atom abstraction is a research topic. Over the lifetime, 7059 publications have been published within this topic receiving 151781 citations.

Lipoxygenase reaction mechanism: demonstration that hydrogen abstraction from substrate precedes dioxygen binding during catalytic turnover.

Abstract: Molecular oxygen is generally unreactive toward covalent bonds, due to spin conservation rules; a major role for oxygen-utilizing enzymes is, therefore, to activate dioxygen through a change in electronic configuration. In an effort to understand how lipoxygenase catalyzes lipid hydroperoxidation under conditions of catalytic turnover, kinetic deuterium isotope effects have been measured as a function of oxygen concentration. The properties of oxygen binding to lipoxygenase have also been pursued. The results presented herein show that, under steady state conditions, atmospheric oxygen enters the reaction pathway only after abstraction of hydrogen from substrate. Furthermore, it has not been possible to detect any form of lipoxygenase capable of binding molecular oxygen in the absence of activated substrate. We propose that molecular oxygen is not productively bound by lipoxygenase but rather interacts directly with the substrate radical lipoxygenase to form the hydroperoxyl radical of linoleate. A mechan...

Free-radical-induced formation of an 8,5'-cyclo-2'-deoxyguanosine moiety in deoxyribonucleic acid.

Abstract: Isolation and identification of a novel .OH-induced product, namely an 8,5′-cyclo-2′-deoxyguanosine moiety, in DNA and 2′-deoxyguanosine are described. .OH radicals were generated in dilute aqueous solutions by gamma-irradiation. Analyses of 2′-deoxyguanosine and enzymic hydrolysates of DNA by gas chromatography-mass spectrometry (g.c.-m.s.) after trimethylsilylation showed the presence of 8,5-cyclo-2′-deoxyguanosine on the basis of its fragment ions. This product was isolated by h.p.l.c. Its u.v. and n.m.r. spectra taken were in agreement with the structure suggested by its mass spectrum. Exact masses of the typical ions from the mass spectrum of the trimethylsilyl derivative of this product were measured by high-resolution m.s. The values found were in excellent agreement with the theoretical mass derived from the suggested fragmentation patterns. Both (5′R)- and (5′S)-epimers of 8,5′-cyclo-2′-deoxyguanosine were observed. These two diastereomers were separated from each other by g.c. as well as by h.p.l.c. The assignment of the epimers was accomplished on the basis of the n.m.r. data. The formation of 8,5′-cyclo-2′-deoxyguanosine was suppressed by the presence of O2 in the solutions. The use of g.c.-m.s. with the selected-ion monitoring technique facilitated the detection of 8,5′-cyclo-2′-deoxyguanosine in DNA at radiation doses as low as 1 Gy. Its mechanism of formation probably involves hydrogen atom abstraction by .OH radicals from the C-5′ of the 2′-deoxyguanosine moiety followed by intramolecular cyclization with the formation of a covalent bond between the C-5′ and C-8 and subsequent oxidation of the resulting N-7-centred radical.

Plasma chemistry aspects of a-Si:H deposition using an expanding thermal plasma

Abstract: The plasma chemistry of an argon/hydrogen expanding thermal arc plasma in interaction with silane injected downstream is analyzed using mass spectrometry. The dissociation mechanism and the consumption of silane are related to the ion and atomic hydrogen fluence emanating from the arc source. It is argued that as a function of hydrogen admixture in the arc, which has a profound decreasing effect on the ion-electron fluence emanating from the arc source, the dissociation mechanism of silane shifts from ion-electron induced dissociation towards atomic hydrogen induced dissociation. The latter case, the hydrogen abstraction of silane, leads to a dominance of the silyl (SiH3) radical whereas the ion-electron induced dissociation mechanism leads to SiHx (x<3) radicals. In the pure argon case, the consumption of silane is high and approximately two silane molecules are consumed per argon ion-electron pair. It is shown that this is caused by consecutive reactions of radicals SiHx (x<3) with silane. Almost indepe...

The Uranyl Cation as a Visible-Light Photocatalyst for C(sp(3) )-H Fluorination.

Abstract: The fluorination of unactivated C(sp(3) )-H bonds remains a desirable and challenging transformation for pharmaceutical, agricultural, and materials scientists. Previous methods for this transformation have used bench-stable fluorine atom sources; however, many still rely on the use of UV-active photocatalysts for the requisite high-energy hydrogen atom abstraction event. Uranyl nitrate hexahydrate is described as a convenient, hydrogen atom abstraction catalyst that can mediate fluorinations of certain alkanes upon activation with visible light.