- Novel model sulfur compounds as mechanistic probes for enzymatic and biomimetic oxidations
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To test for the intermediacy of sulfide radical cations in biomimetic and enzymatic oxidations, the sulfides PhSCH3 (1a), PhSCH2Ph (1b), PhSCHPh2 (1c), PhSCPh3 (1d), CH 3SCHPh2 (2), PhSCH2CH=CH2 (3), PhSCH2CH=CHPh (4) and CH3SCH2CH=CHPh (5) were studied, and their results were compared to those obtained for the corresponding chemical electron transfer (CET) and photoinduced electron transfer (PET) oxidations. The radical cations generated from 3-5 by CET in the presence of cerium(IV) ammonium nitrate (CAN) yielded only fragmentation products from the alkyl cations and the thiyl radicals (RS.), whereas 2.+ afforded both fragmentation and mainly α-deprotonation products. Photochemical treatment of the sulfides 1a and 1b with C(NO2) 4 gave only the corresponding sulfoxides, while fragmentation was the main pathway for the photoreactions of 1c, 2 and 5, and for 1d only this latter process was observed. These results support our selection of the sulfides RSCHPh2, RSCH2CH=CHPh (R = Me, Ph) and PhSCPh3 as models for the biomimetic and enzymatic studies. As evidenced by the sulfoxides and sulfones detected as unique products both in protic and in aprotic solvents, it is proposed that the mechanism of the biomimetic sulfoxidations of sulfides 1c and 2-5 by TPPFeIIICI is direct oxygen transfer. Three enzymes - Coprinus cinereus peroxidase (CiP), horseradish peroxidase (HRP) and chloroperoxidase (CPO) - were studied in the oxidation of sulfides 1a, 2, 4 and 5. The use of a racemic alkyl hydroperoxide in the CiP enzymatic oxidation of sulfides 5 and 2 yielded the corresponding sulfoxides (23 and 29%) and the aldehyde or benzophenone (5%), respectively. These results suggest the involvement of an ET process for the CiP-catalysed oxidation. Fragmentation products were observed in the enzymatic oxidation of sulfide 4 with HRP, which confirms the previously proposed ET mechanism. On the other hand, the CPO-enzymatic oxidation of sulfide 5 yielded only the corresponding sulfoxide, as would be expected for a direct oxygen-transfer or oxene mechanism. Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005.
- Penenory, Alicia B.,Argueello, Juan E.,Puiatti, Marcelo
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p. 114 - 122
(2007/10/03)
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- Photochemical Electron-Transfer Reactions between Sulfides and Tetranitromethane. Oxidation vs Fragmentation of the Sulfide Radical-Cation Intermediate
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Oxidation and/or fragmentation products are observed in the photochemical reaction of the alkyl phenyl sulfides 1a-d with tetranitromethane (TNM). The product distribution depends markedly on the substrate structure. Thus, methyl phenyl sulfide (1a) and benzyl phenyl sulfide (1b) give only the corresponding sulfoxides (oxidation). However, when the radical cation 1b?+ is generated by chemical oxidation with triarylaminium salts (Ar3N?+) in acetonitrile, in addition to oxidation fragmentation is also observed, and with an excess of Ar3N?+ oxidation is facilitated and no fragmentation is produced. For the photoreaction of diphenylmethyl phenyl sulfide (1c) with TNM, fragmentation is the main reaction, while for triphenylmethyl phenyl sulfide (1d) only this process is observed. The ease of C-S bond scission in these sulfur-centered radical cations 1.+ follows the ease of alkyl cation formation, i.e., Ph3C > Ph2CH > PhCH2 > CH3.
- Adam, Waldemar,Argueello, Juan E.,Penenory, Alicia B.
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p. 3905 - 3910
(2007/10/03)
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- Generation and decay of aryl sulfinyl and sulfenyl radicals: A transient absorption and computational study
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Absorption spectra and extinction coefficients of phenylsulfinyl and phenylsulfenyl (thiyl) radicals are determined by nanosecond laser photolysis in various solvents. Direct observation and characterization of arylsulfinyl radicals from the photolysis of
- Darmanyan, Alexander P.,Gregory, Daniel D.,Guo, Yushen,Jenks, William S.
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p. 6855 - 6863
(2007/10/03)
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