Electropolymerization of tetrakis(o-aminophenyl)porphyrin and relevant transition metal complexes from aqueous solution. The resulting modified electrodes as potentiometric sensors

The mechanism of electrogeneration of polyporphyrin from ortho-substituted phenylporphyrins, either free or complexing transition metals, is different when performed in aqueous solution from that operative in organic solvents, that has been reported in the literature. Polymerization occurs through the amino phenyl substituents, leading to a three dimensional 'cage' structure. The polymer is sensitive to morphology and nature of the surface it grows on. The mass deposited on a gold electrode was about 2 x 10(-4) g/cm(2). If the polymerization is performed under potentiodynamic conditions, the polymer forms essentially during the first scan, while no significant further growth is observed in subsequent potential cycles, from both free and metallated porphyrins. All polyporphyrin films, except the one obtained from CoTAPP, exhibit poor electrical conductivity, due to the three dimensional growth of the polymer chain that does not allow the necessary conjugation of pi orbitals inside the macromolecules. On the other hand, interesting properties are shown by the unmetallated as well as by metallated polymer films as possible coverages for 'coated wire' ion selective electrodes. The results obtained with respect to different ions and in particular, a selectivity study carried out on iodide ions are reported.