Electron spin resonance of spin-trapped radicals of amines and polyamines. Hydroxyl radical reactions in aqueous solutions and γ-radiolysis in the solid state

Abstract

MAGDI M. MOSSOBA, IONEL ROSENTHAL, and PETER RIESZ. Can. J. Chem. 60, 1493 (1982). The reactions of hydroxyl radicals with methylamine, dimethylamine, trimethylamine, diethylamine, see-butylamine, ethylenediamine, 1,3-diaminopropane, putrescine, cadaverine, 1,7-diaminoheptane, ornithine, spermidine, spermine, agmatine, and arcaine in aqueous solutions have been investigated by spin-trapping and esr. Hydroxyl radicals were generated by the uv photolysis of H,O, and 2-methyl-2-nitrosopropane (MNP) was used as the spin-trap. The effects of ionizing radiation on the same polyamines in the polycrystalline state were also investigated. The free radicals produced by y-radiolysis of these solids at ro0.m temperature in the absence of air were identified by dissolution in aqueous solutions of MNP. The predominant reaction of OH with amines and polyamines below pH 7 was the abstraction of hydrogen atoms from a carbon that is not adjacent to the protonated amino group. For agmatine and arcaine which contain guanidinium groups abstraction occurred from the a-CH. Dimethylamine was oxidized to the dimethylnitroxyl radical by H,O, in the dark. y-Radiolysis of polyamines in the polycrystalline state generated radicals due to H-abstraction from either the a-CH or from a carbon atom in the middle of the alkyl chain. The deamination radical was obtained from ornithine. Faisant appel B la rpe et B I'utilisation de piegeurs de spin, on a itudiC la reaction des radicaux hydroxyles avec des solutions aqueuses des amines suivantes: methylamine, dimethylamine, trimethylamine, diethylamine, see-butylamine, Cthylknediamine, I diamino-1,3 propane, putrescine, cadavtrine, diamino-1,7 heptane, ornithine, spermidine, spermine, agmatine et arcaine. Les

H/D Kinetic Isotope Effect as a Tool to Elucidate the Reaction Mechanism of Methyl Radicals with Glycine in Aqueous Solutions

“…The redox potential for (NH 2 CHCOO •– /NH 2 CH 2 COO – ) is 0.8 V, and the redox potential for ( + NH 3 CHCOO •– / + NH 3 CH 2 COO – ) is 1.5 V, explaining the pH effect on k 7 . The observation that k 7 for H 2 NC(H 2 /D 2 )CO 2 – is orders of magnitude higher than that for + H 3 NC(H 2 /D 2 )CO 2 – is in accord with the analogous reaction of • OH radicals with glycine and other amino acids and amines. , This points out the effect of the delocalization, reorganization energy of the radical H 2 NC(H/D)CO 2 •– and the effect of the −NH 3 + /NH 2 groups on the bond dissociation energy of + H 3 NC(H 2 /D 2 )CO 2 – /H 2 NC(H 2 /D 2 )CO 2 – on the rate of the HAT.…”

Hydroxyl-Radical Reaction Pathways for the Fast Photochemical Oxidation of Proteins Platform As Revealed by 18O Isotopic Labeling

“…The delocalized positive charge increases the electron density on the adjacent δ-CH 2 to a greater extent than on γ-CH 2 and β-CH 2 . 36 Given that • H abstraction by • OH is an electrophilic process, the • OH preferentially reacts with the electron-rich δ-CH 2 . Higher electron density at δ-CH 2 also leads to a higher reaction rate of arginine toward • OH.…”

“…Under physiological conditions, the guanidyl is protonated, and its charge is delocalized over the guanidyl group. The delocalized positive charge increases the electron density on the adjacent δ-CH 2 to a greater extent than on γ-CH 2 and β-CH 2 . Given that • H abstraction by • OH is an electrophilic process, the • OH preferentially reacts with the electron-rich δ-CH 2 .…”

“…Despite its success, labeling pathways of • OH in a FPOP platform remain unclear even though the reaction mechanisms between • OH and free amino acids were extensively studied over decades by using electron paramagnetic resonance (EPR), − absorption spectroscopy, − MS, , NMR, and NMR-based hydrogen–deuterium exchange . The outcomes allowed key reaction intermediates and reaction pathways to be identified.…”

Spin-trapping with 2-methyl-2-nitrosopropane: photochemistry of carbonyl-containing compounds. Methyl radical formation from dimethyl sulfoxide

“…Thus, in the course of an investigation of free radicals derived from polyamines (27) it was found that when a dimethyl sulfoxide solution of MNP (1.5 mglmL) and dibenzoyl peroxide (5 mglmL) was saturated with 1,8-diaminooctane in the dark, at room temperature, the methyl spin adduct spectrum was exclusively observed. Control experiments indicated that all of these components were necessary for the formation of the methyl adduct.…”