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One- and Two-Electron Transfer Oxidation of 1,4-Disilabenzene with Formation of Stable Radical Cations and Dications.

ABSTRACT: Electron-transferable oxidants such as B(C₆ F₅ )₃ /nBuLi, B(C₆ F₅ )₃ /LiB(C₆ F₅ )₄ , B(C₆ F₅ )₃ /LiHBEt₃ , Al(C₆ F₅ )₃ /(o-RC₆ H₄ )AlH₂ (R=N(CMe₂ CH₂ )₂ CH₂ ), B(C₆ F₅ )₃ /AlEt₃ , Al(C₆ F₅ )₃ , Al(C₆ F₅ )₃ /nBuLi, Al(C₆ F₅ )₃ /AlMe₃ , (CuC₆ F₅ )₄ , and Ag₂ SO₄ , respectively were employed for reactions with (L)₂ Si₂ C₄ (SiMe₃ )₂ (C₂ SiMe₃ )₂ (L=PhC(NtBu)₂ , 1). The stable radical cation [1]^+. was formed and paired with the anions [nBuB(C₆ F₅ )₃ ]^- (in 2), [B(C₆ F₅ )₄ ]^- (in 3), [HB(C₆ F₅ )₃ ]^- (in 4), [EtB(C₆ F₅ )₃ ]^- (in 5), {[(C₆ F₅ )₃ Al]₂ (μ-F)]^- (in 6), [nBuAl(C₆ F₅ )₃ ]^- (in 7), and [Cu(C₆ F₅ )₂ ]^- (in 8), respectively. The stable dication [1]²⁺ was also generated with the anions [EtB(C₆ F₅ )₃ ]^- (9) and [MeAl(C₆ F₅ )₃ ]^- (10), respectively. In addition, the neutral compound [(L)₂ Si₂ C₄ (SiMe₃ )₂ (C₂ SiMe₃ )₂ ][μ-O₂ S(O)₂ ] (11) was obtained. Compounds 2-11 are characterized by UV-vis absorption spectroscopy, X-ray crystallography, and elemental analysis. Compounds 2-8 are analyzed by EPR spectroscopy and compounds 9-11 by NMR spectroscopy. The structure features are discussed on the central Si₂ C₄ -rings of 1, [1]^+. , [1]²⁺ , and 11, respectively.

SUBMITTER: Chen Y

PROVIDER: S-EPMC9299862 | biostudies-literature | 2022 Jan

REPOSITORIES: biostudies-literature

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One- and Two-Electron Transfer Oxidation of 1,4-Disilabenzene with Formation of Stable Radical Cations and Dications.

Chen Yilin Y Chen Zhikang Z Jiang Liuyin L Li Jiancheng J Zhao Yiling Y Zhu Hongping H Roesky Herbert W HW

Chemistry (Weinheim an der Bergstrasse, Germany) 20211216 5

Electron-transferable oxidants such as B(C6 F5 )3 /nBuLi, B(C6 F5 )3 /LiB(C6 F5 )4 , B(C6 F5 )3 /LiHBEt3 , Al(C6 F5 )3 /(o-RC6 H4 )AlH2 (R=N(CMe2 CH2 )2 CH2 ), B(C6 F5 )3 /AlEt3 , Al(C6 F ...[more]

PMID: 34837718

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Project description:The one- and two-electron enzymic reduction of the bioreductive alkylating agents 2-methylmethoxynaphthoquinone (quinone I) and 2-chloromethylnaphthoquinone (quinone II) was studied with purified NADPH-cytochrome P-450 reductase and DT-diaphorase respectively, and characterized in terms of kinetic constants, oxyradical production, thiol oxidation and DNA-strand-break formation. The catalytic-centre activity values indicated that DT-diaphorase catalysed the reduction of quinone I far more efficiently than NADPH-cytochrome P-450 reductase, although the Km values of the two enzymes for this quinone were similar (1.2-3.0 microM). The one-electron-transfer flavoenzyme also catalysed the reduction of quinone II, but the behaviour of DT-diaphorase towards this quinone did not permit calculation of kinetic constants. A salient feature of the redox transitions caused by the one- and two-electron catalysis of these quinones was the different contributions of disproportionation and autoxidation reactions respectively. In the former case, about 26% of NADPH consumed was accounted for in terms of autoxidation (as H2O2 formation), whereas in the latter, the autoxidation component accounted for most (98%) of the NADPH consumed. This difference was abrogated by superoxide dismutase, which enhanced autoxidation during NADPH-cytochrome P-450 catalysis to a maximal value. E.s.r. analysis indicated the formation of superoxide radicals, the signal of which was suppressed by superoxide dismutase and unaffected by catalase. The one- and two-electron reduction of these quinones in the presence of GSH was accompanied by formation of thiyl radicals. Although superoxide dismutase suppressed the thiol radical e.s.r. signal in both instances, the enzyme enhanced GSSG accumulation during NADPH-cytochrome P-450 catalysis of quinone I, whereas it inhibited GSSG formation during reduction of the quinone by DT-diaphorase. One- and two-electron reduction of quinone I led to calf thymus DNA-strand-break formation, a process that (a) was substantially decreased in experiments performed with dialysed DNA and in the presence of desferal and (b) was partially sensitive to superoxide dismutase and/or catalase. These findings are rationalized in terms of the occurrence of metal ions ligated to DNA, protecting against the toxic effects of superoxide radicals generated during enzymic reduction of quinones.

Dataset Information

One- and Two-Electron Transfer Oxidation of 1,4-Disilabenzene with Formation of Stable Radical Cations and Dications.

Publications

One- and Two-Electron Transfer Oxidation of 1,4-Disilabenzene with Formation of Stable Radical Cations and Dications.

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