Tryptophan-14 Is the Preferred Site of DBNBS Spin Trapping in the Self-Peroxidation Reaction of Sperm Whale Metmyoglobin with a Single Equivalent of Hydrogen Peroxide

2003 ◽  
Vol 16 (5) ◽  
pp. 652-660 ◽  
Author(s):  
Michael R. Gunther ◽  
Richard A. Tschirret-Guth ◽  
Olivier M. Lardinois ◽  
Paul R. Ortiz de Montellano
Keyword(s):  
Hydrogen Peroxide ◽  
Sperm Whale ◽  
Spin Trapping ◽  
The Self

scholarly journals Site-specific spin trapping of tyrosine radicals in the oxidation of metmyoglobin by hydrogen peroxide

1998 ◽  
Vol 330 (3) ◽  
pp. 1293-1299 ◽  
Author(s):  
R. Michael GUNTHER ◽  
Richard A. TSCHIRRET-GUTH ◽  
H. Ewa WITKOWSKA ◽  
C. Yang FANN ◽  
P. David BARR ◽  
...  
Keyword(s):  
Hydrogen Peroxide ◽  
Spin Trap ◽  
Sperm Whale ◽  
Spin Trapping ◽  
Tryptophan Residue ◽  
Radical Adduct ◽  
Unpaired Electron Density ◽  
Trapping Agent ◽  
Tyrosine Radical ◽  
Radical Yield

The reaction between metmyoglobin and hydrogen peroxide produces both a ferryl-oxo heme and a globin-centred radical(s) from the two oxidizing equivalents of the hydrogen peroxide. Evidence has been presented for localization of the globin-centred radical on one tryptophan residue and tyrosines 103 and 151. When the spin-trapping agent 5,5-dimethyl-1-pyrroline N-oxide (DMPO) is included in the reaction mixture, a radical adduct has been detected, but the residue at which that adduct is formed has not been determined. Replacement of either tryptophans 7 and 14 or tyrosines 146 and 151 with phenylalanine has no effect on the formation of DMPO adduct in the reaction with hydrogen peroxide. When tyrosine 103 is replaced with phenylalanine, however, only DMPOX, a product of the oxidation of the spin-trap, is detected. Tyrosine-103 is, therefore, the site of radical adduct formation with DMPO. The spin trap 2-methyl-2-nitrosopropane (MNP), however, forms radical adducts with any recombinant sperm whale metmyoglobin that contains either tyrosine 103 or 151. Detailed spectral analysis of the DMPO and MNP radical adducts of isotopically substituted tyrosine radical yield complete structural determinations. The multiple sites of trapping support a model in which the unpaired electron density is spread over a number of residues in the population of metmyoglobin molecules, at least some of which are in equilibrium with each other.

Spin trapping by use of nitrosodurene and its derivatives

1982 ◽  
Vol 60 (12) ◽  
pp. 1532-1541 ◽  
Author(s):  
Ryusei Konaka ◽  
Shigeru Terabe ◽  
Taiichi Mizuta ◽  
Shigeru Sakata
Keyword(s):  
Hydrogen Peroxide ◽  
Esr Spectra ◽  
Spin Trapping ◽  
Nitroso Compounds ◽  
Spin Adduct ◽  
Spin Traps ◽  
Spectral Pattern ◽  
Alkyl Radicals ◽  
Alkyl Hydroperoxides ◽  
Tert Butyl Hydroperoxide

In spin trapping the N-methyl-N-phenylaminomethyl radical with nitrosodurene, an esr spectmm exhibiting line width alternation was observed despite the normal spectral pattern found with the use of nitroso-tert-butane. Nitrosodurene derivatives, N-duryl nitrone and methyl N-duryl nitrone, have been revealed to be other excellent spin traps for the N-, 0-, and S-centered radicals. Spin adducts of these radicals, which can be independently prepared by spin trapping with nitrosodurene, are stable and can be easily discriminated by large differences in β-hydrogen splittings or characteristic patterns. Methyl N-duryl nitrone reacted with tert-butyl hydroperoxide to give a spin adduct which could be clearly distinguished in the esr spectra from the tert-butoxy adducts prepared independently from other sources. Accordingly, it seems to be the tert-butylperoxy adduct. Similarly, hydrogen peroxide gave a different spectrum from the hydroxy adducts. Alkyl hydroperoxides caused molecule-induced homolysis with the nitroso compounds to produce alkoxy adducts of the respective nitroso compounds. Some phenyl and duryl alkoxy nitroxides undergo decomposition to give alkyl radicals which were trapped by the nitroso compounds.

Benzoxathiete and related structures: experimental and quantum chemical studies

1990 ◽  
Vol 68 (11) ◽  
pp. 1950-1960 ◽  
Author(s):  
Ali Naghipur ◽  
Krzysztof Reszka ◽  
J. William Lown ◽  
Anne-Marie Sapse
Keyword(s):  
Hydrogen Peroxide ◽  
Acetic Acid ◽  
Quantum Chemical ◽  
Spin Trapping ◽  
Ring Closure ◽  
Paramagnetic Resonance ◽  
Valence Tautomerism ◽  
Carbon Centered Radical ◽  
Chemical Studies ◽  
Abinitio Calculations

The products, plausible intermediates, and their mechanisms of formation in the aprotic diazotization of 2-[(2-acetoxyethyl)-sulfinyl (and sulfonyl)]anilines with isoamyl nitrate have been investigated by experimental and quantum chemical methods. Oxidation of 1,2,3-benzthiadiazole with hydrogen peroxide in acetic acid affords 1,2,3-benzthiadiazole-1-oxide, 13. The thermal stability of 13 up to 135 °C, together with EPR evidence which disfavors an aryldiazenyl radical precursor, discount 13 as an intermediate in the formation of benzoxathiete 14 or its valence tautomer 17 during aprotic diazotization of the sulfinylanilines. Electron paramagnetic resonance evidence in conjunction with spin trapping indicates an intermediate arylaminyl radical. This evidence, taken together with abinitio calculations of optimized geometries energies and energy differences for biradical intermediate 15, favors a mechanism of formation of benzoxathiete 14 via aryldiazoate anhydride 5 thence to rapid ring closure of carbon-centered radical 8. Further oxidation of 1,2,3-benzthiadiazole-1-oxide, 13, with hydrogen peroxide in methanol – acetic acid affords biphenylene and dibenzo-1,4-oxathiane-S-oxide, 38. Rose bengal sensitized photooxidation of 1,2,3-benzthiadiazole affords 13, biphenylene, and 38. Formation of the latter, in which one of the original S—O bonds has been broken, requires the formation of benzoxathiete-S-oxide, 34, and its rapid valence tautomerism to ketosulfine 36 and (2 + 4) cycloaddition of 36 to the simultaneously generated dehydrobenzene to give 38. Both ring closure of singlet biradical 35 to 34 and valence tautomerism of the latter to 36 are predicted by abinitio calculations to be facile and exothermic. In contrast to the aprotic diazotization of 2-[(2-acetoxyethyl)sulfinyl]anilines, the reaction of isoamyl nitrite with the corresponding sulfonyl anilines may plausibly follow a mechanism via 1,2,3-benzthiadiazole-1,1-dioxide 33 owing to the thermal instability of the latter and supported by abinitio treatments of the energetics of the processes involved. In addition EPR evidence, in conjunction with spin trapping of carbon centered radicals, support the viability of the pathway via 23, 25, 28, and 16 to biphenylene 20. The abinitio calculations of the energy differences between the reaction intermediates and estimates of the activation energies elucidated several aspects of these novel reactions. Keywords: benzoxathiete, abinitio calculations, valence tautomerism.

Structural Variety of Copper(II)-Peroxide Adducts and Its Relevance to DNA Cleavage

1999 ◽  
Vol 54 (1-2) ◽  
pp. 94-99 ◽  
Author(s):  
Satoshi Nishino ◽  
Teruyuki Kobayashi ◽  
Mami Kunita ◽  
Sayo Ito ◽  
Yuzo Nishida
Keyword(s):  
Hydrogen Peroxide ◽  
High Activity ◽  
Dna Cleavage ◽  
Esr Spectroscopy ◽  
Spin Trapping ◽  
The Other ◽  
Experimental Conditions ◽  
Structural Variety ◽  
Supercoiled Form ◽  
Tetradentate Ligands

The reactivity of copper(II) compounds with several tetradentate ligands towards some spin-trapping reagents was studied in the presence of hydrogen peroxide. The compounds used in this study are roughly divided into two groups based on the reactivity towards 2 ,2 ,6 ,6 -tetramethyl-4-piperidinol(and also 2,2,6,6-tetramethyl-4-piperidone), which are trapping agents for singlet oxygen, 1O2 (1Δg); The A-group compounds exhibited a high activity to form the corresponding nitrone radical, which was detected by ESR spectroscopy, but corresponding activity of the B-group compounds was very low. The A-group compounds defined as above exhibited high activity for cleavage of DNA(supercoiled Form I) in the presence of hydrogen peroxide, yielding DNA Form II (relaxed circular) or Form III (linear duplex) under our experimental conditions ([Cu(II)]=0.1~0.5 mᴍ). On the other hand, the B-group compounds effected complete degradation of the DNA (double-strand scission) under the same experimental conditions, formation of Form II or Form III DNA was negligible. Two different DNA cleavage patterns observed for A-and B-group compounds were elucidated by the different structural property of the copper(II)-peroxide adducts, which is controlled by the interaction through both DNA and the peripheral group of the ligand system

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