The role of free energy change in coupled electron-proton transfer
The role of free energy change in coupled electron-proton transfer
复制标题
DOI：
10.1021/ja072558d
复制
发表时间：
2007-12-12
影响因子：
15
通讯作者：
Meyer, Thomas J.
中科院分区：
文献类型：
--
作者：
Fecenko, Christine J.;Thorp, H. Holden;Meyer, Thomas J.
采用催化循环伏安法研究了在25 ℃、含0.8M NaCl的0.5M缓冲溶液中，在外加碱（乙酸根、琥珀酸根、组氨酸、磷酸根和三羟甲基氨基甲烷）存在下，M（bPY）（3）（3+）（M = Os、Fe、Ru）氧化酪氨酸的动力学.如在早期研究中所报道的，氧化通过一系列途径发生-电子转移后质子转移（ET-PT）、质子转移后电子转移（PT-ET）和协同电子-质子转移（EPT）。后两者发生在酪氨酸和添加的碱基之间的氢键缔合复合物内。动力学分离用于集中在EPT途径，其中多位点电子质子转移（MS-EPT）发生与电子转移到氧化剂和质子转移到碱。测得的速率常数范围为k（EPT）= 5.0 x 10（3）至9.8 x 10（7）M-1 s（-1）。观察到RT Ink（EPT）随Δ G度的系统变化，RT Ink（EPT）随Δ G度增加，斜率类似于0.6，而不管Δ G度是否通过改变氧化剂的E度或碱的强度而改变。对于完整的数据集，在Δ G度的类似于0.7eV的变化上，Δ G度的变化与由O-H转移模式产生的量子效应的重要性一致，在类似于3000 cm（-1）处可能出现新的“量子拍”效应。
The kinetics of oxidation of tyrosine by the series of metal complex oxidants, M(bPY)(3)(3+) (M = Os, Fe, Ru), in the presence of added bases (acetate, succinate monoanion, histidine, phosphate, and tris), were investigated in 0.5 M buffer with 0.8 M NaCl at 25 degrees C by utilizing a catalytic cyclic voltammetry technique. As reported in an earlier study, oxidation occurs by a series of pathways-electron transfer followed by proton transfer (ET-PT), proton transfer followed by electron transfer (PT-ET), and concerted electron-proton transfer (EPT). The latter two occur within H-bonded association complex between tyrosine and the added base. Kinetic isolation was used to focus on the EPT pathway, in which multiple site-electron proton transfer (MS-EPT) occurs with electron transfer to the oxidant and proton transfer to the base. Measured rate constants varied from k (EPT) = 5.0 x 10(3) to 9.8 x 10(7) M-1 s(-1). Systematic 0 variations in RT In k (EPT) with Delta G degrees 'were observed with RT Ink (EPT) increasing with -Delta G degrees 'with a slope of similar to 0.6 regardless of whether Delta G degrees 'was varied either by varying E degrees 'for the oxidant or the strength of the base. Over the similar to 0.7 eV variation in Delta G degrees 'for the complete data set the variation with Delta G degrees 'is consistent with the importance of quantum effects arising from the O-H transfer mode with possible appearance of a novel "quantum beat" effect at similar to 3000 cm(-1).