C(sp3)鈥揌 Bond Hydroxylation Catalyzed by Myoglobin Reconstituted with Manganese Porphycene

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• 作者：Koji Oohora ; Yushi Kihira ; Eiichi Mizohata ; Tsuyoshi Inoue ; Takashi Hayashi
• 刊名：Journal of the American Chemical Society
• 出版年：2013
• 出版时间：November 20, 2013
• 年：2013
• 卷：135
• 期：46
• 页码：17282-17285
• 全文大小：260K
• 年卷期：v.135,no.46(November 20, 2013)
• ISSN：1520-5126

文摘

Myoglobin reconstituted with manganese porphycene was prepared in an effort to generate a new biocatalyst and was characterized by spectroscopic techniques. The X-ray crystal structure of the reconstituted protein reveals that the artificial cofactor is located in the intrinsic heme-binding site with weak ligation by His93. Interestingly, the reconstituted protein catalyzes the H₂O₂-dependent hydroxylation of ethylbenzene to yield 1-phenylethanol as a single product with a turnover number of 13 at 25 掳C and pH 8.5. Native myoglobin and other modified myoglobins do not catalyze C鈥揌 hydroxylation of alkanes. Isotope effect experiments yield KIE values of 2.4 and 6.1 for ethylbenzene and toluene, respectively. Kinetic data, log k_obs versus BDE(C(sp³)鈥揌) for ethylbenzene, toluene, and cyclohexane, indicate a linear relationship with a negative slope. These findings clearly indicate that the reaction occurs via a rate-determining step that involves hydrogen-atom abstraction by a Mn(O) species and a subsequent rebound hydroxylation process which is similar to the reaction mechanism of cytochrome P450.