Proton-Coupled Electron Transfer Reactions with Photometric Bases Reveal Free Energy Relationships for Proton Transfer
作者:Thomas T. Eisenhart、William C. Howland、Jillian L. Dempsey
DOI:10.1021/acs.jpcb.6b04011
日期:2016.8.18
quinoline backbone, the driving force for proton transfer was systematically varied. Proton transfer rate constants (kPT,2 = (1.5–7.5) × 108 M–1 s–1, kPT,4 = (0.55–3.0) × 107 M–1 s–1) were found to correlate with the pKa of the conjugate acid of the proton acceptor, in agreement with anticipated free energy relationships for proton transfer processes in PCET reactions.
乙腈中对氨基苯酚的质子偶联电子转移(PCET)氧化是通过停止流快速混合进行的,并进行光谱监测。为了在存在7-(二甲基氨基)喹啉质子受体的情况下通过二茂铁进行氧化,可以在可见光区域对电子转移和质子转移组分进行光学监测。容易监测到二茂铁吸收率的衰减(λmax = 620 nm),以及2,4-取代的7-(二甲基氨基)喹啉衍生物的吸收率(λmax= 370–392 nm)在质子化过程中发生了红移(大约70 nm)。光谱分析表明反应是通过逐步的电子转移-质子转移过程进行的,对动力学曲线的建模可以监测二茂铁和喹啉鎓信号,从而为基本质子和电子转移步骤提供速率常数。由于所使用的2,4-R-7-(二甲氨基)喹啉衍生物的共轭酸的p K a值很容易通过改变喹啉骨架的2位和4位上的取代基来调节,因此质子转移是系统地变化的。质子传递速率常数(k PT,2 =(1.5–7.5)×10 8 M –1 s –1,kPT,4