Pulse radiolysis generation of sulfur radical cations stabilized by neighboring carboxylate and alcohol groups

Glass, Richard S.; Hojjatie, Massoud; Wilson, George S.; Mahling, Sabine; GOEBL, M.; Asmus, K.‐D.

doi:10.1021/ja00330a075

Cited by 39 publications

(22 citation statements)

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“…Intramolecular ( • S−O)-bonded radicals derived from 3-MTP and 3,3‘-DHP (see structures in reaction 8) were characterized in the Pulse Radiolysis section above. The presence of intramolecular ( • S−O)-bonded radicals was previously confirmed in pulse radiolysis − ,, and laser flash photolysis 18 experiments with sulfur-containing acids and amino acids. At pH = 9.8 resolutions of the experimental transient absorption spectra also led to the presence of the intermolecular S∴S-bonded radical cations and the intramolecular ( • S−O)-bonded radicals, but at this pH both species had much shorter lifetimes than did the corresponding species at lower pH.…”

Section: Resultsmentioning

confidence: 68%

“…In proteins, methionine residues are potentially surrounded by a variety of neighboring groups such as carboxylate, amino, hydroxy, and amide functionalities most of which have been shown to affect sulfide oxidations in simple organic model compounds. − The attacking oxidant usually induces formation of a distinct intermediate at the sulfide site, and the nature of this intermediate circumscribes the scope of any subsequent participation of neighboring groups. The nature and strength of the coupling of the neighboring group to any attacking oxidizing species and/or to the intermediate moiety formed at the sulfide site affects the ultimate course of the sulfide oxidation.…”

Section: Introductionmentioning

confidence: 99%

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Mechanism of One-Electron Oxidation of β-, γ-, and δ-Hydroxyalkyl Sulfides. Catalysis through Intramolecular Proton Transfer and Sulfur−Oxygen Bond Formation

et al. 1997

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The mechanism of photoinduced electron transfer between sulfur-containing alcohols and the 4-carboxybenzophenone (CB) triplet state in aqueous solution was investigated using laser flash photolysis and steady-state photolysis techniques. Bimolecular rate constants for quenching of the CB triplet state by five hydroxyalkyl sulfides, 2-(methylthio)ethanol (2-MTE), 2,2‘-dihydroxydiethyl sulfide (2,2‘-DHE), 3-(methylthio)propanol (3-MTP), 3,3‘-dihydroxydipropyl sulfide (3,3‘-DHP), and 4-(methylthio)butanol (4-MTB), with varying numbers of OH groups and varying locations with respect to the sulfur atom, were determined to be in the range (3.3−4.8) × 109 M-1 s-1 for neutral solutions. The intermediates identified were the CB ketyl radical anion (CB•-), the CB ketyl radical (CBH•), and intermolecularly (S∴S)-bonded radical cations. An additional absorption band at approximately 400 nm in the transient spectra for some of the hydroxyalkyl sulfides was assigned to the intramolecularly (•S−O)-bonded species (only for hydroxyalkyl sulfides which could adopt a five-membered ring structure). The spectra of appropriate (S∴S)+ and (•S−O) intermediates for the hydroxyalkyl sulfides were determined from complementary pulse radiolysis studies in acid and neutral aqueous solutions of the hydroxyalkyl sulfides, respectively. The observation of ketyl radical anions and intermolecular (S∴S)-bonded radical cations of the hydroxyalkyl sulfides was direct evidence for the participation of electron transfer in the mechanism of quenching. Quantum yields of formation of intermediates from flash photolysis experiments and quantum yields of formaldehyde formation from the steady-state measurements were determined. The values of these quantum yields indicated that the diffusion apart (escape of the radical ions) of the charge-transfer complex, formed as a primary photochemical step, is a minor photochemical pathway (with a contribution of ∼5−25% depending on the numbers of OH groups). Competing processes of proton transfer and back electron transfer within the CT complex gave significant contributions to these yields. Detailed mechanisms for the CB-sensitized photooxidation of sulfur-containing alcohols are proposed, discussed, and compared with that for the •OH-induced oxidation. One striking feature of the mechanisms is that there is a catalytic influence of neighboring groups on the radical reaction pathways during one-electron oxidation of the hydroxyalkyl sulfides in comparison to comparable reactions of nonsubstituted alkyl sulfides. Support for the mechanisms came in part from an analysis of observed solvent isotope effects on radical quantum yields.

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Section: Resultsmentioning

confidence: 68%

Section: Introductionmentioning

confidence: 99%

Mechanism of One-Electron Oxidation of β-, γ-, and δ-Hydroxyalkyl Sulfides. Catalysis through Intramolecular Proton Transfer and Sulfur−Oxygen Bond Formation

et al. 1997

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“…Another possible interpretation of the results is that the amido substituent of 1b , 1d , and 1f coordinates to the bromine atom involved in the hydrogen atom abstraction [Br∴NH(tBu)COR], thereby facilitating reaction. Similar three-electron-bonded species have been proposed as intermediates, for example, in the reaction of amino acids with hydroxyl radical [HO∴NH 2 CHRCO 2 - ] and in the radical-induced oxidation of sulfides [RR‘S∴OCOR‘‘], and sulfide coordination of the bromine atom [R 2 S∴Br] has been demonstrated . A third alternative is that the reactions of 1b , 1d , and 1f proceed via the corresponding N -bromoamides and involve intramolecular 1,4-hydrogen transfer to the amidyl radicals.…”

mentioning

confidence: 77%

Anchimeric Assistance in Hydrogen Atom Transfer Reactions on the Side Chains of Amino Acid Derivatives

Easton

Merrett

1996

J. Am. Chem. Soc.

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“…[9][10][11][12][13] Usually, the 1e-oxidation of sulfides leads to sulfide radical cations which can subsequently complex, preferentially intramolecularly, with oxygen-carrying substituents such as hydroxy, alkoxy, or carboxylate groups (reaction 1). [14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29][30] The stabilization of the 1e-oxidized sulfur through formation of sulfur-oxygen bonded sulfuranyl radicals might potentially accelerate oxidation and autoxidation processes of substituted sulfides and of Met in peptides and proteins. For example, the electrochemical oxidation of dialkyl sulfides showed lower peak potentials when appended with neighboring carboxylate and alcohol groups.…”

Section: Introductionmentioning

confidence: 99%

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

2003

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Density functional theory and semiempirical methods were employed to characterize the structure and properties of sulfur-oxygen-bonded radical cations formed during the one-electron oxidation of various organic sulfides and methionine-containing peptides. In general, all of the examined sulfur-oxygen bonds can be described as two-center, three-electron-bonded systems. The usefulness of approximate computational approaches (SCC-DFTB, AM1 and PM3) for the reliable description of three-electron-bonded species was examined.

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Pulse radiolysis generation of sulfur radical cations stabilized by neighboring carboxylate and alcohol groups

Cited by 39 publications

References 1 publication

Mechanism of One-Electron Oxidation of β-, γ-, and δ-Hydroxyalkyl Sulfides. Catalysis through Intramolecular Proton Transfer and Sulfur−Oxygen Bond Formation

Mechanism of One-Electron Oxidation of β-, γ-, and δ-Hydroxyalkyl Sulfides. Catalysis through Intramolecular Proton Transfer and Sulfur−Oxygen Bond Formation

Anchimeric Assistance in Hydrogen Atom Transfer Reactions on the Side Chains of Amino Acid Derivatives

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

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