The incorporation and controlled release of dopamine from a sulfonated β–cyclodextrin–doped conducting polymer

Abstract

Pyrrole was electropolymerised in the presence of sulfonated β–cyclodextrin to give a conducting polypyrrole film doped with the anionic cyclodextrin, PPy–sβ–CD. On reduction of the polymer film at −0.80 V vs SCE, high concentrations of dopamine (DA) were incorporated and the DA was subsequently released at a potential of 0.10 V vs SCE. Much higher levels of DA were incorporated and released at PPy–sβ–CD compared to polypyrrole films doped with smaller anions and doped with the larger para–toluene sulfonic acid. In addition to releasing higher concentrations of DA, the DA was less prone to oxidation and degradation in the presence of the sulfonated β–cyclodextrin. This was attributed to the formation of an inclusion complex between the protonated DA molecule and the anionic CD. The higher release rates were explained in terms of the immobile nature of the large CD and the high charge density with approximately 9 sulfonated groups attached to the rim of the CD cavity, which facilitated the uptake of high levels of DA. Approximately 6.0 μmol cm⁻² of DA was released at 0.10 V vs SCE over 60 min on reducing the PPy–sβ–CD film for 30 min at −0.80 V vs SCE. Higher levels of 9.6 μmol cm⁻² were obtained on increasing the reduction period to 60 min, while levels of 14.0 μmol cm⁻² were achieved with thicker polymer films.

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