Vous avez des questions? Nous pouvons vous aider. Pour communiquer directement avec un auteur, consultez la première page de la revue dans laquelle son article a été publié afin de trouver ses coordonnées. Si vous n'arrivez pas à les repérer, communiquez avec nous à PublicationsArchive-ArchivesPublications@nrc-cnrc.gc.ca. Questions? Contact the NRC Publications Archive team atPublicationsArchive-ArchivesPublications@nrc-cnrc.gc.ca. If you wish to email the authors directly, please see the first page of the publication for their contact information. NRC Publications Archive Archives des publications du CNRCThis publication could be one of several versions: author's original, accepted manuscript or the publisher's version. / La version de cette publication peut être l'une des suivantes : la version prépublication de l'auteur, la version acceptée du manuscrit ou la version de l'éditeur. For the publisher's version, please access the DOI link below./ Pour consulter la version de l'éditeur, utilisez le lien DOI ci-dessous. NRC Publications Record / Notice d'Archives des publications de CNRC:http://nparc.cisti-icist.nrc-cnrc.gc.ca/eng/view/object/?id=124c64aa-fb51-4827-94c3-18efb61397d2 http://nparc.cisti-icist.nrc-cnrc.gc.ca/fra/voir/objet/?id=124c64aa-fb51-4827-94c3-18efb61397d2 Abstract: Absolute rate constants of ‚RfSO3 -radical addition to a series of water-soluble alkenes containing ionic, carboxylate substituents were measured by laser flash photolysis experiments in water. The observed rate constants were all considerably larger than those of structurally similar analogues in a nonpolar organic solvent, with rate factors of 3-9-fold being observed. It is concluded that such rate enhancements derive at least in part from stabilization of the polar transition state for addition of the electrophilic fluorinated radical to alkenes by the polar solvent water.

Two supercoiled (SC), double-stranded DNAs, pBR 322 and pUC 19, have been subjected to oxidative stress using horseradish peroxidase (HRP) and HRP + tert-butyl hydroperoxide (BOOH). HRP alone causes single-strand cleavage of these SC DNAs. Strand cleavage is enhanced substantially in the presence of commercial BOOH (which contains H 2 O 2 ) but is, at best, only very slightly enhanced in the presence of pure BOOH. In the HRP/pure BOOH system, the DNA single-strand-scission which does occur appears to be due to a direct action of oxidized HRP. It is not due to tert-butylperoxyl radicals because strand-scision is not even retarded by 10 mM Trolox, an outstanding water-soluble trap for peroxyl radicals. The present results are congruent with our earlier conclusion [Paul, T., et al. (2000) Biochemistry 39, 4129] that neutral alkylperoxyl radicals produce little or no direct single-strand-scission in SC DNAs.It was recently demonstrated in this laboratory that direct single-strand cleavage of (double-strand) supercoiled DNA by water-soluble alkylperoxyl radicals (1) 1 at 37°C was relatively facile when the peroxyl carried a positive charge but was generally below the level of detection when the peroxyl was uncharged or carried a negative charge (2). For example, with the positively charged peroxyl radical, (H 2 N) 2 + CC(CH 3 ) 2 OO • ( + ROO • ), 2 and the supercoiled (SC) plasmid DNA, pBR 322, it was found that ca. 50% of the SC DNA suffered a singlestrand break to afford relaxed (R) DNA at a + ROO • /bp ratio of 0.2 (2). Strand cleavage by a different positively changed peroxyl occurred with a similar efficiency (2). In contrast, the neutral, water-soluble peroxyl radical, HOCH 2 CH 2 NHC(O)C(CH 3 ) 2 OO • , generally produced no detectable strand-scission (i.e., no detectable R DNA) at a ROO • /bp ratio as high as 5:1 (2, 3), 3 and the negatively charged peroxyl radical, -O 3 SCH 2 CH 2 C(CH 3 )(CN)OO • , generally produced no strand-scission even at a ROO • / bp ratio of 24:1 (2). Essentially identical results were obtained with another SC DNA, pUC 19 (2). The uniquely strong DNA strand cleaving abilities of the positively charged peroxyl radicals was attributed to their Coulombic attraction to the negatively charged SC DNA polyanion (2).After these null-results on the neutral ROO • /DNA reaction were published (2), a paper appeared which caused us surprise and concern because it claimed that neutral alkylperoxyl radicals "generated in situ" from five different alkyl hydroperoxides and three different peroxidases generally produced single-strand breaks in pBR 322 (4). This strand-scission was not a consequence of the DNA having been subjected to very much higher ROO • /bp ratios than we had employed. 4 We were therefore prompted to investigate one of the peroxidase/alkyl hydroperoxide systems. We chose horseradish peroxidase (HRP) and tert-butyl hydroperoxide (BOOH) because both are readily available commercially and because the HRP/ BOOH pair had been reported to have "a substantial DNA-cleaving activity"(4). 5...

The role of electrostatic forces in free radical biology is very important but it is all too often overlooked. The radicals discussed in this review include positively-charged, negatively-charged and neutral water-soluble alkylperoxyls and superoxide. Important scientific insights have been gained by generating these radicals in known quantities by the thermal decomposition of simple, "clean", chemical precursors in the presence of potential bio-targets. For example, the abilities of these radicals to damage double-stranded DNA, a polyanion, are dictated by Coulombic forces with only the positively-charged peroxyls being capable of directly producing single-strand breaks. The Coulombic control of the reactions and reaction rates of water-soluble peroxyl radicals which are so evident with DNA do not manifest themselves with all electrostatically charged bio-targets, e.g., low density lipoprotein (LDL), probably because the charge on the surface of the LDL is not uniformly distributed.

Axial and equatorial cyclohexylacyl and tetrahydropyranyl-2-acyl radicals gave distinct EPR spectra thanks to surprisingly large beta-hydrogen atom hyperfine splittings that enabled them to be characterized and monitored. DFT computations indicated that the axial species (X = CH(2)) had a higher barrier to rotation about the (O)C(alpha)-C(beta) bond. The computed difference Delta H degrees for the axial and equatorial radicals (R = H, X = CH(2)) was 0.8 kcal mol(-)(1).