Electrochemistry of viologens at polypyrrole doped with sulfonated β–cyclodextrin

Abstract

The electrochemistry of methyl, ethyl and benzyl viologens was studied at polypyrrole doped with sulfonated cyclodextrin, PPysβ-CD, a cation exchange polymer. Three reduction waves were observed corresponding to the reduction of the viologen (V 2+ ) to the radical cation (V •+ ) followed by the neutral compound (V 0 ) and a third intense peak. This third reduction peak was associated with the ingress of V 2+ as the PPysβ-CD film is reduced. As the incorporated V 2+ is reduced to the neutral viologen, the influx of more V 2+ occurs to achieve charge balance and this repeated influx and reduction of V 2+ gives an intense reduction wave. These processes were only observed with sβ-CD as a dopant and this was attributed to the formation of an ion pair between the anionic cyclodextrin and the viologen. Lower diffusion coefficients and rate constants were observed for the reduction of V 2+ and V •+ on adding an excess of sβ-CD to the viologen solution. Linear calibration curves were obtained extending from 1.0 μM to 80 μM when the PPysβ-CD was employed as a sensor for methyl viologen. While the PPysβ-CD is not suitable for the detection of low nM concentrations, the uptake and extraction of MV 2+ was observed on polarising the PPysβ-CD in a solution of the viologen, highlighting the dual action of the polymer.

The selective electrochemical sensing of dopamine at a polypyrrole film doped with an anionic β−cyclodextrin

“…1, where the logarithm of the current is presented as a function of time, while a typical chargeÀtime plot recorded at a higher potential of 0.80 V vs SCE is shown in the inset. A near steadyÀstate current is observed within 30 s, indicating efficient polymerisation at the relatively low potential of 0.50 V in the presence of the anionic cyclodextrins without the presence of any other salts [26,27]. The chargeÀtime plot recorded at 0.80 V vs SCE shows a near linear increase in charge with increasing polarisation times, which is again consistent with efficient polymerisation and the deposition of conducting polymer layers.…”

“…It is clear that a prior reduction period gives rise to lower peak currents. This behaviour can be explained in terms of the cationÀexchange properties of the PPyÀSβCD films [26,34], where the ingress of Na þ ions occurs at lower applied potentials. This is illustrated in Fig.…”

“…Bidan and coÀworkers [23] and Temsamani et al [24] have elctrosynthesised polypyrrole doped with sulfonated βÀcyclodextrins, while Tamer et al [25] have prepared a threeÀdimensional network of branched fibres of polypyrrole doped with sulfonated βÀcyclodextrin through an interfacial polymerisation process. These anionic cyclodextrin doped polypyrrole films are particularly easy to prepare and they have been used to detect and uptake viologens [26] and in the controlled release of dopamine [27]. Also, polypyrrole has good biocompatibility properties [28] while cyclodextrins are well known in the drug delivery field [29], making these modified electrodes considerably more suitable for implantation compared to some of the more complex electrodes.…”

Cyclodextrins as Supramolecular Recognition Systems: Applications in the Fabrication of Electrochemical Sensors

“…As these are large and immobile dopants, they are not expelled as the polymer is reduced and are very well immobilized. These PPy/sβ-CD films have been employed in the electrochemical detection of dopamine [114,115], urea [116,117], and viologens [118]. Similar to the strategy employed with the PANI system, MWCNTs [119,120] and rGO [121][122][123] have been added to the PPy/CD polymers to enhance conductivity and the performance of the sensors.…”

Formation of benzyl viologen-containing films at copper and their protective properties

“…4(b). The two reduction peaks correspond to the two consecutive one-electron reductions, shown in Scheme 1, where the peak at À0.57 V vs SCE leads to the generation of the radical species, while the peak at À0.73 V vs SCE shows the conversion of the radical to the neutral compound [27]. On plotting the logarithm of the peak current for the reduction of the radical cation to the neutral species, at À0.73 V vs SCE, as a function of the logarithm of the scan rate, a linear plot was observed with a slope of 0.88, as illustrated in the inset in Fig.…”