ELECTROCHEMICAL AND THE ELECTRON-SPIN-RESONANCE STUDY ON THE INTERACTION BETWEEN ALPHA-CYCLODEXTRIN AND THE ELECTROCHEMICALLY GENERATED RADICAL INTERMEDIATE OF P-NITROPHENOLATE ANION

The interaction between α-cyclodextrin (α-CyD) and an electrogenerated intermediate radical of p-nitrophenolate anion (NP-) in aqueous solution was investigated by electrochemical and in-situ electrochemical electron spin resonance (ESR) spectroscopic techniques. The first step of the irreversible reduction of NP-was found to be the generation of the π-type anion radical of NP- (divalent anion radical; NP.2-). Fast scan cyclic voltammetry showed that α-CyD suppresses the subsequent reaction of NP.2- and causes a negative shift in the apparent half-wave potential of the NP-/NP.2- couple. The results were interpreted in terms of the formation of a 1:1 inclusion complex of α-CyD with NP.2- as well as with NP-, the estimated formation constant of the NP.2--α-CyD complex being 20 M-1. An ESR spectral study of NP.2- provided evidence for the incorporation of NP.2- into the α-CyD cavity: the addition of α-CyD suppressed the tumbling motion of NP.2- and then enhanced the anisotropic effect due to the hyperfine interaction of the 14N nucleus. These electrochemical and ESR data were analyzed quantitatively and the significance of the interactions between CyD and the intermediates is discussed. © 1990.