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 t he amino phenyl substituents, leading to a three dimensional 'cage' structu re. The polymer is sensitive to morphology and nature of the surface it gro ws 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 p olymer forms essentially during the first scan, while no significant furthe r growth is observed in subsequent potential cycles, from both free and met allated porphyrins. All polyporphyrin films, except the one obtained from C oTAPP, exhibit poor electrical conductivity, due to the three dimensional g rowth of the polymer chain that does not allow the necessary conjugation of pi orbitals inside the macromolecules. On the other hand, interesting prop erties are shown by the unmetallated as well as by metallated polymer films as possible coverages for 'coated wire' ion selective electrodes. The resu lts obtained with respect to different ions and in particular, a selectivit y study carried out on iodide ions are reported.