In Situ Electrochemical EPR Studies of Charge Transfer across the Liquid/Liquid Interface
作者:Richard D. Webster、Robert A. W. Dryfe、Barry A. Coles、Richard G. Compton
DOI:10.1021/ac9708147
日期:1998.2.1
The in situ measurement of EPR spectra of radical ions generated at the polarized liquid/liquid interface is described in relation to the 7,7,8,8-tetracyanoquinodimethane (TCNQ), 2,3,5,6-tetrachloro-p-benzoquinone (TCBQ), and 2,3,5,6-tetrafluoro-p-benzoquinone (TFBQ) radical anions and the tetrathiafulvalene (TTF) radical cation. TCNQ and TTF were chosen as model compounds with which to quantify the performance of a novel liquid/liquid electrochemical EPR cell. The anion radical of TCNQ and the cation radical of TTF in 1,2-dichloroethane (DCE) were produced at the water interface by electron transfer from/to the aqueous-phase ferricyanide/ferrocyanide redox couple by applying a potential difference between the two phases with a four-electrode potentiostat. The EPR signal intensity (at constant magnetic field) of the resultant organic radicals was monitored during potential step experiments which indicated that the EPR data could be modeled in terms of diffusional transport. TCBQ and TFBQ were chosen as compounds to model the electron transfer behavior of biologically important quinones at the oil/water interface. The EPR and voltammetric data obtained from TCBQ/TCBQ-• and TFBQ/TFBQ-• indicated unambiguously that the two semiquinones are stable at the DCE/water interface and do not undergo immediate protonation.
在极化的液体/液体界面上生成的自由基离子的 EPR 光谱原位测量与 7,7,8,8-四氰基喹啉二甲烷(TCNQ)、2,3,5,6-四氯对苯醌(TCBQ)和 2,3,5,6-四氟对苯醌(TFBQ)自由基阴离子以及四硫富瓦烯(TTF)自由基阳离子有关。TCNQ 和 TTF 被选择为模型化合物,以量化新型液体/液体电化学 EPR 细胞的性能。通过在水界面施加相间电位差,使用四电极电位计从水相的铁氰化物/亚铁氰化物氧化还原对进行电子转移,在 1,2-二氯乙烯(DCE)中生成 TCNQ 的阴离子自由基和 TTF 的阳离子自由基。在潜在阶跃实验中,监测了生成的有机自由基的 EPR 信号强度(在恒定磁场下),这些结果表明 EPR 数据可以用扩散输运模型来描述。TCBQ 和 TFBQ 被选择作为模型化合物,以模拟在油/水界面上生物重要的醌类化合物的电子转移行为。从 TCBQ/TCBQ-• 和 TFBQ/TFBQ-• 获得的 EPR 和伏安数据明确表明,这两种半醌在 DCE/水界面上是稳定的,并且不会立即发生质子化。