scholarly journals Studies on the metal-ion and lipoxygenase-catalysed breakdown of hydroperoxides using electron-spin-resonance spectroscopy

1987 ◽  
Vol 245 (1) ◽  
pp. 167-173 ◽  
Author(s):  
M J Davies ◽  
T F Slater
Keyword(s):  
Metal Ion ◽  
Spin Trap ◽  
Cumene Hydroperoxide ◽  
Initial Step ◽  
Peroxyl Radicals ◽  
Resonance Spectroscopy ◽  
Alkoxy Radical ◽  
Alkoxyl Radical ◽  
Radical Adduct ◽  
Chemical Studies

The breakdown of cumene hydroperoxide and peroxidized fatty acids by iron is shown, by use of the spin trap 5,5-dimethyl-l-pyrroline-N-oxide, to be sensitive to (a) the oxidation state of the metal and (b) the nature of the chelating ligands. The initial step in the Fe2+-catalysed breakdown is the production of an alkoxyl radical by one-electron reduction, and this type of radical has been successfully trapped from each substrate. Subsequent reactions of this alkoxyl species produce both carbon-centred and peroxyl radicals, depending on the concentrations of the reagents present. The use of the same spin trap in microsomal systems undergoing either NADPH-supported or Fe2+-induced peroxidation led to the detection of low concentrations of radical adducts, among which are signals that are believed to be due to lipid alkoxyl radicals. Reaction of polyunsaturated fatty acid hydroperoxides with both Fe2+ and lipoxygenase under anaerobic conditions gives rise to signals not only from the alkoxy-radical adduct, but also from a further species which is tentatively identified as being due to an acyl [RC(O).]-radical adduct; chemical studies lend support to this assignment.

scholarly journals Studies on the photolytic breakdown of hydroperoxides and peroxidized fatty acids by using electron spin resonance spectroscopy. Spin trapping of alkoxyl and peroxyl radicals in organic solvents

1986 ◽  
Vol 240 (3) ◽  
pp. 789-795 ◽  
Author(s):  
M J Davies ◽  
T F Slater
Keyword(s):  
Fatty Acids ◽  
Spin Trap ◽  
Hydrogen Abstraction ◽  
Spin Trapping ◽  
Ring Closure ◽  
Peroxyl Radicals ◽  
Resonance Spectroscopy ◽  
Oxygen Oxygen ◽  
Low Levels ◽  
Trap Radical

Spin trapping using 5,5-dimethyl-1-pyrroline N-oxide (DMPO) has been used to detect and distinguish between the carbon-centred, alkoxyl, and peroxyl radicals produced during the photolytic decomposition of hydroperoxides. Photolysis of tert-butyl and cumene hydroperoxides, and peroxidized fatty acids, in toluene, with low levels of u.v. light, is shown to lead to the initial production of alkoxyl radicals by homolysis of the oxygen-oxygen bond. Subsequent reaction of these radicals with excess hydroperoxide leads, by hydrogen abstraction, to the production of peroxyl radicals that can be detected as their corresponding adducts with the spin trap. Subsequent breakdown of these adducts produces alkoxyl radicals and a further species that is believed to be the oxidized spin-trap radical 5,5-dimethyl-1-pyrrolidone-2-oxyl. No evidence was obtained at low hydroperoxide concentrations, with either the cumene or lipid alkoxyl radicals, for the occurrence of beta-scission reactions; the production of low levels of carbon-centred radicals is believed to be due to the alternative reactions of hydrogen abstraction, ring closure, and/or 1,2 hydrogen shifts. Analogous experiments with 3,3,5,5-tetramethyl-1-pyrroline N-oxide (TMPO) led only to the trapping of alkoxyl radicals with no evidence for peroxyl radical adducts, this is presumably due to a decreased rate of radical addition because of increased steric hindrance.

scholarly journals Formation of peroxide- and globin-derived radicals from the reaction of methaemoglobin and metmyoglobin with t-butyl hydroperoxide: an ESR spin-trapping investigation

1997 ◽  
Vol 322 (2) ◽  
pp. 633-639 ◽  
Author(s):  
Jolanda Van der ZEE
Keyword(s):  
Spin Trap ◽  
Hydrogen Abstraction ◽  
Spin Trapping ◽  
Tyrosyl Radical ◽  
Alkoxyl Radical ◽  
Butyl Hydroperoxide ◽  
Heterolytic Cleavage ◽  
Esr Spin Trapping ◽  
Radical Adduct ◽  
Protein Radicals

The reaction of human methaemoglobin and horse metmyoglobin with t-butyl hydroperoxide (t-BuOOH) was investigated with the ESR spin-trapping technique. With the spin trap 5,5-dimethyl-1-pyrroline N-oxide (DMPO) the formation of peroxyl, alkoxyl and methyl radicals derived from t-BuOOH could be detected. The relative contributions of these radicals were determined at various DMPO concentrations by computer simulation. From these data it could be concluded that the alkoxyl radical was the initial radical produced, which indicates that the hydroperoxide is cleaved homolytically. Further investigations, with the nitroso spin trap 2-methyl-2-nitrosopropane (MNP), showed the formation of globin-centred radicals. Non-specific proteolysis of the MNP adducts revealed isotropic three-line spectra, which means that the radical adducts were centred on a tertiary carbon with no bonds to a hydrogen or nitrogen. Comparison with MNP adducts of several amino acids indicated that in methaemoglobin the radical adduct was most probably located on a valine residue. With metmyoglobin the same adduct was obtained, whereas an additional adduct could be assigned to a tyrosyl radical. These protein radicals most probably resulted from hydrogen abstraction by the metal–oxo species, formed by heterolytic cleavage of the hydroperoxide. These results therefore show that homolytic cleavage of the hydroperoxide leads to the formation of peroxide-derived radicals, whereas concurrent heterolytic cleavage results in protein-derived radicals.

The aqueous chemistry of uranium minerals. Part I. Divalent cation zippeïte

1979 ◽  
Vol 43 (328) ◽  
pp. 539-541 ◽  
Author(s):  
David F. Haacke ◽  
Peter A. Williams
Keyword(s):  
Metal Ion ◽  
Metal Speciation ◽  
Divalent Metal ◽  
Free Energies ◽  
Naturally Occurring ◽  
Solution Studies ◽  
Chemical Studies ◽  
Divalent Metal Ion ◽  
Almost All ◽  
End Members

SynopsisFree energies of formation of divalent metal ion zippeïtes, M2(UO2)6(SO4)3(OH)10 ·nH2O, M = Mg,Co,Ni,Zn have been determined from solution studies and metal speciation calculations, in water. It is found that in the compounds, the number of molecules of water of crystallization is equal to 8. This is at variance with a previous report (Frondel et al., 1976), but it has been found that some at least of the water content of zippeite is either nonessential or very loosely bound in the structure. Based on the octahydrate formulation, values are −3506, −12695, −12683 and −12870±4 kJ mol−1 for the Mg,Co,Ni and Zn end-members, respectively. Almost all of the differences in the values are accounted for by those values for the metal ions alone with the exception of Znzippeïte where a discrepancy of some 22 kJ mol−1 is found. Even this value is small however, and the chemical studies indicate that extensive mutual solid solution between all end members is to be expected. These findings agree perfectly with observations on the composition of naturally occurring zippeite minerals of this group.

scholarly journals Spectroscopic glimpses of the transition state of ATP hydrolysis trapped in a bacterial DnaB helicase

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Alexander A. Malär ◽  
Nino Wili ◽  
Laura A. Völker ◽  
Maria I. Kozlova ◽  
Riccardo Cadalbert ◽  
...  
Keyword(s):  
Transition State ◽  
Metal Ion ◽  
Atp Hydrolysis ◽  
Magic Angle Spinning ◽  
Resonance Spectroscopy ◽  
Magic Angle ◽  
Aluminum Fluoride ◽  
Paramagnetic Resonance ◽  
Dnab Helicase ◽  
Fast Magic Angle Spinning

AbstractThe ATP hydrolysis transition state of motor proteins is a weakly populated protein state that can be stabilized and investigated by replacing ATP with chemical mimics. We present atomic-level structural and dynamic insights on a state created by ADP aluminum fluoride binding to the bacterial DnaB helicase from Helicobacter pylori. We determined the positioning of the metal ion cofactor within the active site using electron paramagnetic resonance, and identified the protein protons coordinating to the phosphate groups of ADP and DNA using proton-detected 31P,1H solid-state nuclear magnetic resonance spectroscopy at fast magic-angle spinning > 100 kHz, as well as temperature-dependent proton chemical-shift values to prove their engagements in hydrogen bonds. 19F and 27Al MAS NMR spectra reveal a highly mobile, fast-rotating aluminum fluoride unit pointing to the capture of a late ATP hydrolysis transition state in which the phosphoryl unit is already detached from the arginine and lysine fingers.

Chemical studies on antioxidant mechanism of garcinol: analysis of radical reaction products of garcinol with peroxyl radicals and their antitumor activities

Tetrahedron ◽  
2002 ◽  
Vol 58 (51) ◽  
pp. 10095-10102 ◽  
Author(s):  
Shengmin Sang ◽  
Chiung-Ho Liao ◽  
Min-Hsiung Pan ◽  
Robert T. Rosen ◽  
Shoei-Yn Lin-Shiau ◽  
...  
Keyword(s):  
Radical Reaction ◽  
Peroxyl Radicals ◽  
Reaction Products ◽  
Antitumor Activities ◽  
Antioxidant Mechanism ◽  
Chemical Studies

scholarly journals Mechanism in the reaction of cytochrome c oxidase with organic hydroperoxides: an ESR spin-trapping investigation

2002 ◽  
Vol 365 (2) ◽  
pp. 461-469 ◽  
Author(s):  
Yeong-Renn CHEN ◽  
Ronald P. MASON
Keyword(s):  
Cytochrome C ◽  
Cytochrome C Oxidase ◽  
Spin Trap ◽  
Spin Trapping ◽  
Initial Reaction ◽  
Radical Species ◽  
Alkoxyl Radical ◽  
Tyrosine Residues ◽  
Esr Spin Trapping ◽  
Organic Hydroperoxides

Organic hydroperoxides are of great utility in probing the reaction mechanism and the toxicological consequences of lipid peroxidation. In the present study, ESR spin-trapping was employed to investigate the peroxidation of mitochondrial cytochrome c oxidase (CcO) with t-butyl hydroperoxide (t-BuOOH) and cumene hydroperoxide (CumOOH). The spin trap 5,5-dimethyl-1-pyrroline N-oxide (DMPO) was used to detect the radical species formed from the reaction of CcO with t-BuOOH. The presence of t-BuOOH-derived alkoxyl radical (t-BuO˙) as the primary radical indicates reductive scission of the O—O bond by CcO. The ESR signal of DMPO/˙Ot-Bu can be partially abolished by cyanide, implying that the reductive cleavage involved the haem a3CuB binuclear site of CcO. A nitroso spin trap, 2-methyl-2-nitrosopropane (MNP), was used to detect and identify radical species from the reaction of CcO with CumOOH. In addition to the t-BuOOH-derived methyl, hydroxylmethyl and tertiary carbon-centred radicals, a protein-derived radical was detected. The intensity of the ESR signal from the protein radical increased with the CumOOH concentration at low CumOOH/CcO ratios, with maximal intensity at a ratio of 100mol of CumOOH/mol of CcO. The immobilized protein radical adduct of MNP was stable and persistent after dialysis; it was also resistant to proteolytic digestion, suggesting that it was formed in the transmembrane region, a region that is not accessible to proteases. Its signal was greatly enhanced when CcO cysteine residues were chemically modified by N-ethylmaleimide, when the tryptophan residues in CcO were oxidized by N-bromosuccimide, and when tyrosine residues on the surface of CcO were iodinated, showing that a radical equilibrium was established among the cysteine, tryptophan and tyrosine residues of the protein-centred radical. Pre-treatment of CcO with cyanide prevented detectable MNP adduct formation, confirming that the haem a3-CuB binuclear centre was the initial reaction site. When the CcO was pre-treated with 10mM (100 equivalents) of CumOOH, the enzyme activity decreased by more than 20%. This inhibition was persistent after dialysis, suggesting that the detected protein-centred radical was, in part, involved in the irreversible inactivation by CumOOH. Visible spectroscopic analysis revealed that the haem a of CcO was not affected during the reaction. However, the addition of pyridine to the reaction mixture under alkaline conditions resulted in the destruction of the haem centre of CcO, suggesting that its protein matrix rather than its haem a is the target of oxidative damage by the organic hydroperoxide.

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