Polypyrrole modified with sulfated β-cyclodextrin: characterization and application in the sensing of viologens
In this thesis a conducting polypyrrole (ppy) matrix doped with the anionic sulfated β-cyclodextrin (sβ-CD) was electrosynthesized and characterized. This modified polymer, ppysβ-CD, was used as a sensor for the detection of three compounds, methyl, ethyl and benzyl viologen. Methyl viologen is commonly known as paraquat and it is one of the most commonly used herbicides worldwide. The sβ-CD was permanently immobilized within the ppy backbone during the potentiostatic growth of the polymer. The incorporation of the macrocycle was confirmed by means of cyclic voltammetry (CV), quartz crystal microbalance (QCM) and differential scanning calorimetry (DSC). The large dopant was found not to significantly alter certain properties of the polymer such as diffusion of a probe analyte to the surface and charge transfer rate constant. The cyclodextrin modified polymer was shown to have cation exchange properties and this characteristic was used towards the sensing of the three electroactive viologen compounds. The three viologens were detected by means of differential pulse voltammetry (DPV), while for methyl viologen constant potential amperometry (CPA) experiments were also performed. These techniques gave a good linear response for the current measured at the polymer surface, as a function of the viologen concentration. Detection limits of 1.00 x 10-4 M for ethyl viologen (DPV), 2.50 x 10-5 M for benzyl viologen (DPV) and 1.56 x 10-5 M for methyl viologen (CPA) were measured experimentally. A detailed analysis was performed on the interaction of the sβ-CD with methyl, ethyl and benzyl viologen, using both electrochemistry (CV and RDV) and spectroscopy (UV-Vis, 1H NMR). It was established that a 1:1 interaction occurs between the sβ-CD and each of the viologens. The formation of inclusion complexes was verified not to occur. The generation of association complexes was instead suggested. These complexes result from an ion pairing interaction between the sβ-CD and the viologens, either in their dication state or in their radical state.
National University of Ireland - Maynooth
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