The EPR spectra of thiyl radical spin adducts produced by photolysis of disulfides in the presence of 2,4,6-tri-tert-butylnitrosobenzene and 5,5-dimethyl-1-pyrroline N-oxide

Abstract

A series of thiyl radicals prepared by the photolysis of the parent disulfide have been trapped using 5,5-dimethyl-I -pyrroline N-oxide (DMPO) and 2,4,6-tri-tert-butylnitrosobenzene (BNB). The EPR spectra of the resulting spin adducts show proton hyperfine interactions from the 6-protons of the alkyl group of the thiyl, thus allowing definitive radical assignments to be made. For thiyl BNB spin adducts, a characteristic nitrogen coupling constant is observed. For secondary and tertiary thiyls, two adducts arise from addition to the nitrogen and oxygen of the nitroso group. The extent of reaction at the oxygen increases with increasing disulfide concentration. This is attributed to the formation of a complex between the thiyl and the parent disulfide, whose bulk favours its addition to the less sterically hindered oxygen position. The rate constant for the reaction of Pr'S' radicals with (PriS)2 to form the complex is 240 times lower than that for reaction with BNB. Direct addition of Pr'S' to the nitrogen of BNB is 11.5 times more efficient than to oxygen.

Aromatic thiol-mediated cleavage of N–O bonds enables chemical ubiquitylation of folded proteins

“…The spectrum exhibited six lines characteristic of DMPO-trapped thiyl radicals 22 , which could be simulated with a N =14.22 G and a H =16.16 G ( Fig. 3b ), giving a N < a H as expected for DMPO-thiyl radical adducts in aqueous solution 23 24 . The inclusion of 50 mM Na 2 HPO 4 , pH 7.5 in the reaction altered the appearance of the EPR spectrum ( Fig.…”

Kinetic Aspects of Spin Trapping

“…Clearly RO 2 • stands out as exceptionally unreactive towards spin traps. The rate of trapping of iso-PrS • by 2, 4, 6-tri-tert-butylnitrosobenzene (TNB) is ~240 times faster than the rate of complexation of iso-PrS • with (iso-PrS) 2 , and the rate of addition to the N-atom of BNB is ~10 times faster than that to the O-atom [116]. Ito and Matsuda [66] have found the rate of trapping of arenethiyl radicals by C 6 H 5 NO and MNP to lie in the range (1-2) ϫ 10 8 dm 3 mol -1 s -1 , Table 5.…”

Hydrogen radioisotopic labelling studies using muonium: properties of thiyl radicals potentially relevant to cellular membrane damage

“…Thiyl radicals have been detected indirectly in ESR/spin-trapping experiments, 4 but have never been detected directly by ESR in solution, although they may be trapped and thereby measured in solid matrices. 5,6 This has been ascribed to the formal orbital degeneracy of a thiyl radical, and an accordingly highly anisotropic g-tensor, 5,6 resulting in extremely broad lines; in addition, the high reactivity of RS ž radicals towards their precursors will favour the detection of product radicals such as RS-SR 2 6 or RSS ž .…”

“…Thus arrives the facility of the method, that muonium atoms ( C e ; Mu) may be formed in situ in a range of liquid-, solid-and gas-phase samples, when these adsorb muons which then combine with radiolytic electrons; when both have achieved near thermal energies [Eqn (4)]. …”