Host–Guest interaction of pesticide bifenox with cyclodextrin molecules. An electrochemical study.

The reduction of nitroaromatic compound bifenox (methyl 5-(2,4-dichlorophenoxy)-2-nitrobenzoate) was studied in aprotic solvents in the absence or presence of cyclodextrin (CD) molecules of different cavity sizes. bCD and gCD form complexes with bifenox in DMSO with the complex formation constants (5+-2) x 102 M-1 [bCD-bifenox] and (3+-1) x 102 M-1[gCD-bifenox], respectively. Bifenox yields a relatively stable anion radical in dimethyl sulfoxide, which is further reduced at more negative potentials by an overall addition of three electrons and four protons to the corresponding phenylhydroxylamine. In the presence of bCD the first reduction wave of bifenox becomes irreversible, it is shifted towards more positive potentials and the uptake of more than one electron is observed (up to four electrons during the exhaustive electrolysis). The first reduction wave of bifenox is not affected by the addition of glucose confirming that a simple availability of protons from the OH groups is not the main factor in further transformation of anion radical in the presence of bCD. The complex formation with bCD facilitates the protonation and additionally protects the molecule from disintegration into 2,4-dichlorophenol. A yield of 2,4-dichlorophenol decreases in the order bCD, gCD and aCD, respectively

Stochastic Resonance in Electron Transfer Oscillations of Extended Viologen

Selective generation of only odd harmonics and the absence of even harmonics were never described for electrochemical oscillators though this phenomenon is known in special fields of physics and in biological systems. The heterogeneous electron transfer to the extended viologen with four repetitive viologen units yields electrochemical current oscillations. Small perturbation of the applied voltage by only a few millivolts sine wave results in current oscillations, which selectively enhance only the odd harmonic higher frequencies. The effect is explained in terms of the theory of stochastic resonance occurring in driven oscillating reactions. The described interplay of heterogeneous and homogeneous coupled electron transfers complies with the behavior of a nonlinear potential-symmetric system

Electron Transfer Mechanism of Substituted Benzimidazoles: Dimer Switching, Oscillations, and Search for Singlet Fission Properties

Reduction and oxidation of 4,7-dimethyl-1,3-dimethoxybenzimidazolium cation (<b>1</b>) and the related dihydroxy analogue (<b>2</b>) were investigated by electrochemical and <i>in situ</i> spectroelectrochemical methods. Quantum chemical methods were applied to UV–vis spectra in native, reduced, and oxidized forms. Compounds were searched for possible formation of a cation radical and a dication radical suitable for the singlet fission effect. Indeed <b>1</b> yields by oxidation the target quinoidal structure. However, the reduction step for both compounds is coupled with very fast dimerization and prevents obtaining a stable target form. The complex mechanism of the reduction process yields electrochemical current oscillation. Estimation of the maximum Ljapunov exponent proves characteristics of the deterministic chaos