Polarographic Behavior of the Viologen Indicators

Abstract

The polarographic behavior of 1,1′-dimethyl- and 1,1′-dibenzyl-4,4′-bipyridinium dichloride has been investigated over the pH range of 1 to 13. Reversible reduction waves are obtained for the first single-electron step for both compounds. The second step is electrochemically irreversible but evidence is presented to indicate that the second step is fleetingly reversible at the dropping mercury electrode for methyl viologen but not benzyl viologen. Minor waves due to adsorption of the reduced viologen on the surface of the mercury have been observed.

Study of the Electrochemical Behavior and Sensitive Detection of Pesticides Using Microelectrodes Allied to Square-Wave Voltammetry

“…Based on those results, the electrochemical process related to peaks present a totally reversible behavior indicated by the presence of direct and reverse currents with similar values of peak current. In addition, the difference between peak potential for forward and reverse scan, presented values about 60 mV, which is indicative of the transfer of one electron during the redox process, a behavior similar to that published in other literature reports [12,32,33].…”

“…Like this, the frequency values of the 1000 s À1 were used in subsequent experiments. The influence of frequency on the peak potential, for paraquat and diquat pesticides, from the Equation 8, the slopes of the straight line obtained for the relationships DE p vs. Dlog(f) for Peak 1 and Peak 2 result in the value of n ¼ 1, for paraquat pesticide, (considering a ¼ 0.50), thus confirming the reaction pathway presented in proposed mechanisms [32,34]. For diquat the Equation 5 was used and the values obtained were similar to paraquat, indicating the similar redox mechanisms.…”

“…For paraquat and diquat pesticide, the cyclic voltammetric responses, for an Au-ME in 0.10 mol L À1 of Na 2 SO 4 , presented similar profiles and are shown in Figure 1A and Figure 1B, respectively. In the figures, Peaks 1 and 5, for both pesticides, represent the first process observed during the potential scan from À 0.0 to À 1.20 V and can be associated with the redox couple [32,33], where P represents the pesticide:…”

“…This electrode process was followed by a second one, represented by Peak 2 and is associated with a quasireversible adsorption controlled process hence generating the neutral molecule [32,33]:…”

E.P.R. studies and INDO calculations on the molecular structure of radicals derived from some N-alkylpyridinium salts

“…These compounds were first studied by Michaelis and Hill because of their biochemical properties [2], which result from the formation of a cation radical in a one-electron reduction step : This radical is relatively stable, and can be easily detected by its deep blue purple colour, The first reduction step is relatively fast and reversible and no protons are involved in the reaction [3]. A further reduction gives a neutral product [4], the N-N' disubstituted 4-4' dihydropyridine (III):…”