Structure and reactivity of peroxyl and sulphoxyl radicals from measurement of oxygen-17 hyperfine couplings: relationship with taft substituent parameters

Abstract

Radicals from Relationship withA series of peroxyl radicals (ROO') with substituent groups of varying electron withdrawing power have been investigated using electron paramagnetic resonance spectroscopy. Sixteen carbon-based radicals have been produced, identified and reacted with ' '0-labelled molecular oxygen to produce the corresponding peroxyl radical. Carboncentred radical precursors include alkyl, aromatic, halocarbon, lipid and alcohol radicals. The oxygen-17 hyperfine couplings are shown to monitor closely the spin density distribution on the oxygen atoms in the peroxyl radicals. The experimental 170 couplings suggest a value of -5.7 mT for the anisotropic coupling parameter, B , in good agreement with the theoretical value calculated from improved wavefunctions. An increase in the magnitude of the terminal oxygen coupling is shown to correlate with an increase in the reactivity of peroxyl radicals. In addition, the Taft substituent parameter (o*) is also correlated with the oxygen-17 couplings. The results allow estimation of peroxyl radical reactivity from oxygen-17 couplings and suggest that complexed superoxide ion may be more reactive than free 0;-. The cysteine sulphonyl peroxyl and thiol peroxyl radicals are discussed in light of the results for carbon-based peroxyl radicals. The sulphonyl peroxyl radical is suggested to be highly reactive and the thiyl peroxyl radical has unique properties which suggest it is of a different nature.

An EPR investigation of acetonitrile reactivity with superoxide radicals on polycrystalline TiO2

“…In the latter case, owing to the unequal distribution of spin in the -OO • fragment, two superimposed sextets should appear in the spectrum (due to -O 17 O • and -17 OO • ), as widely reported in the literature [30][31][32]. If O 2 -reacted with CH 3 CN at 210 K forming such a peroxy entity (i.e.…”

Density functional calculations on model tyrosyl radicals

“…Using experimental EPR data from studies of peroxide radicals, ROO (Sevilla et al, 1990;Broze et al, 1967) and the empirical McConnell-Strathdee relations (McConnell and Strathdee, 1959, and references therein), the Axx andAyy components and the spin density were then derived by Hoganson for the tyrosyl oxygen. The estimated values for the xx and yy components of the hyperfine tensor are quite low, however (+4.9 G, compared with our calculated values of + 13 G), as is the experimental oxygen spin density (exp.…”

Influence of Oxygen on the Repair of Direct Radiation Damage to DNA by Thiols in Model Systems

“…1989, Sevilla et al . 1990a) and that the RS0 2 00' radical is likely a highly reactive hydrogen abstracting agent (Sevilla et al . 1990b) .…”

“…However, RSOO' is not considered to be a good hydrogen abstractor (Sevilla et al 1990b) although one report suggests that it is an effective one-electron oxidant (Tamba et al 1986) . ESR work has shown that RSOO' is involved in a cyclic reaction sequence (reaction 6) which results in a highly reactive intermediate RS0 200' (Sevilla et al 1988(Sevilla et al , 1990a(Sevilla et al , 1990b .…”

“…ESR work has shown that RSOO' is involved in a cyclic reaction sequence (reaction 6) which results in a highly reactive intermediate RS0 200' (Sevilla et al 1988(Sevilla et al , 1990a(Sevilla et al , 1990b .…”