The tetra-cationic free base porphyrin, 4,4′,4″,4‴-(21H,23H-porphine-5,10,15,20-tetrayl) tetrakis[1-octylpyridinium]4+ (PTTO4+) shares the properties of both a long alkyl chain containing molecule with hydrophobic shell and a highly charged water soluble molecule with hydrophilic core. As a result, PTTO4+ is only very sparingly water soluble and tends to aggregate on suitable surfaces. It is shown here that the electrochemical reduction of PTTO4+ in aqueous media can be studied either by 'solid state voltammetry' or by 'membrane voltammetry' methodology with complementary results. When immobilised by adhering the microcrystalline powder to the surface of a basal plane pyrolytic graphite electrode, PTTO4+ exhibits two separate one electron-one proton reduction responses, which are both coupled to chemical follow-up processes (assumed here is a H-shift reaction). Both reduction responses become reversible at sufficiently high scan rates. In contrast, when accumulated into a TiO2 phytate membrane, PTTO4+ exhibits a chemically reversible 2 electron-2 proton reduction response. Upon increasing of the concentration of PTTO4+ in the membrane or upon increasing the thickness of the membrane more complex voltammetric responses are detected. High local 'concentration' conditions during solid state voltammetry experiments may be regarded as a limiting case of high concentration membrane voltammetry at very thin membranes.
|Number of pages||7|
|Journal||Indian Journal of Chemistry - Section A Inorganic, Physical, Theoretical and Analytical Chemistry|
|Publication status||Published - 1 Apr 2003|
ASJC Scopus subject areas
- Physical and Theoretical Chemistry
- Inorganic Chemistry