Neighboring group participation in radicals: pulse radiolysis studies on radicals with sulfur-oxygen interaction

Abstract

Acknowledgment. We thank the National Science Foundation (CHE-8510067) for support of this work and Donna Van Engen for a helpful discussion.Registry No. 1, 2, hexamethylbenzene, Supplementary Material Available: Bond lengths and bond angles, with standard deviations, for 2 (Tables IV and V), final anisotropic thermal parameters for chlorine (Table VI), and atomic parameters for hydrogen (Table VII) (3 pages). [The structure factor table is available from the author.] Ordering information is given on any current masthead page.

Oxidation of (Carboxyalkyl)thiopropionic Acid Derivatives by Hydroxyl Radicals. Mechanisms and Kinetics of Competitive Inter- and Intramolecular Formation of σ- and σ*-type Sulfuranyl Radicals

“…On the basis of 80% 8a,18c of the available • OH radicals (at pH 1.0, G total = 3.0) converting into 3a , we derive G (S∴S) + = 2.4 and the molar extinction coefficient ε 480 = 9200 M -1 cm -1 for 3a . It compares well with ε 480 - 500 = 4000−9000 M -1 cm -1 for other (R 2 S∴SR 2 ) + radical cations. 8a,12a,18bc,− …”

“…Under these experimental conditions, the radiation chemical yield of the hydroxyl radicals, available for reaction with 3-MTPA, was G ( • OH) = 5.3 (based on the formula given by Schuler et al which relates the G -value of solute radicals generated by • OH to the product of the rate constant for the reaction of • OH with the solute and the solute concentration). Assuming the yield of intramolecularly sulfur−oxygen bonded radicals to be equal to the initial yield of the hydroxysulfuranyl radicals, 〉 • S−OH (where these yields are equal to 80% of the total available • OH radicals), 8a,18c we derive G ( • S↔O) ≈ 4.25 and the molar aborption coefficient ε 390 = 2500 M -1 cm -1 for 2a which compares well with values of ε 390 - 400 = 2000−4000 M -1 cm -1 for other ( • S↔O)-bonded radicals. 18a, For a better comparison, all extinction coefficients derived for the various intermediates are summarized in Table .…”

Flavin-induced photodecomposition of sulfur-containing amino acids is decisive in the formation of beer lightstruck flavor

“…As no such species was detected with cysteine, the unpaired spin was suggested to be localized on the carbon bearing the two methyl groups. Indeed, homolytic cleavage of the C-S bond in intermediate iv, involving a twocenter three-electron bond between the neighbouring carboxylate and the sulfur-centered radical cation to form an intermediate five-membered-ring radical cation, 41 is favored by formation of the stabilized tertiary radical v. Next, a 1,3-hydrogen shift would result in a nitrogen-centered radical (vi), that after decarboxylation produced a sulfhydryl radical (iii) and imine 4, which was eventually hydrolyzed to 2-methylpropanal (5) and ammonia (6).…”

Computational Characterization of Sulfur−Oxygen Three-Electron-Bonded Radicals in Methionine and Methionine-Containing Peptides: Important Intermediates in One-Electron Oxidation Processes

“…28 nm, bringing the computed band to a little below the experimentally observed value (see Table 1). 18 Radicals 1b • and 1bH •+ exhibit vibrational frequencies of ca. 644 and 683 cm -1 , respectively, which can be assigned to the S-O bond-stretching modes.…”