氧化态黄素对有机小分子的脱氢反应机理的理论研究

In order to explore the mechanisms of catalytic dehydrogenation of the small organic molecules by flavin in glucose oxidase, we detailed investigate the possible mechanisms of the dehydrogenation for alcohols, aldehydes, carboxylic acids by 7,8,10-trimethylisollxazine (instead of flavin, abbreviated as Fl) using M06-2X functional. Two possible reaction pathways are revealed, including a two-step reaction and a concerted reaction. In the two-steps reaction, a hydride (H-) is transferred from the small organic molecule to Fl via a single-proton-coupled double-electron transfer mechanism with a proton moving to the N5-atom of Fl and at the same time the small organic molecule binding to 4αC of Fl to form an intermediate. Then, the small molecule releases a proton to the N1 site of the Fl and the O-4αC bond is broken. In the concerted reaction, two hydrogen atoms of small organic fraction are transferred to Fl by a double-proton-coupled double-electron transfer mechanism with N5 and 4aC as the proton acceptors. After that, the proton of 4aC is transferred to the N1 position by a First-Third proton transfer mechanism. According to the comparison of the energy barriers, the concerted reaction favors the reactions of Fl with alcohols and the two-step reaction is more favorable for the dehydrogenation reactions of aldehydes and carboxylic acids by Fl. These findings are helpful to understand the reaction mechanisms between anode active center (Fl) and small organic molecules in the biofuel cell and provide the theoretical basis for expanding the diversity of fuels for biofuel cell. ?