One-Step versus Stepwise Mechanism in Protonated Amino Acid-Promoted Electron-Transfer Reduction of a Quinone by Electron Donors and Two-Electron Reduction by a Dihydronicotinamide Adenine Dinucleotide Analogue. Interplay between Electron Transfer and Hydrogen Bonding
作者:Junpei Yuasa、Shunsuke Yamada、Shunichi Fukuzumi
DOI:10.1021/ja8001452
日期:2008.4.1
Semiquinone radical anion of 1-(p-tolylsulfinyl)-2,5-benzoquinone (TolSQ(*-)) forms a strong hydrogen bond with protonated histidine (TolSQ(*-)/His x 2 H(+)), which was successfully detected by electron spin resonance. Strong hydrogen bonding between TolSQ(*-) and His x 2 H(+) results in acceleration of electron transfer (ET) from ferrocenes [R2Fc, R = C5H5, C5H4(n-Bu), C5H4Me] to TolSQ, when the one-electron
1-(p-tolylsulfinyl)-2,5-benzoquinone (TolSQ(*-)) 的半醌自由基阴离子与质子化组氨酸 (TolSQ(*-)/His x 2 H(+)) 形成强氢键,这是电子自旋共振检测成功。TolSQ(*-) 和 His x 2 H(+) 之间的强氢键导致从二茂铁 [R2Fc, R = C5H5, C5H4(n-Bu), C5H4Me] 到 TolSQ 的电子转移 (ET) 加速,当一个在存在 His x 2 H(+) 的情况下,TolSQ 的 - 电子还原电位很大程度上向正方向移动。His x 2 H(+) 促进的 ET 从 R2Fc 到 TolSQ 的速率表现出氘动力学同位素效应,这是由于在过渡态 His x 2 H(+) 中的 NH 键部分离解,当 His x 2 H(+) ) 被氘代化合物 (His x 2 D(+)-d6) 取代。观察到的氘动力学同位素效应