Porphyrins and metalloporphyrins are important catalysts and electrocatalysts for a variety of substrates, and their properties can be further improved by attaching transition metal complexes as cofactor groups, according to a supramolecular approach. During the last decade we synthesized, characterized and studied the properties of supermolecular species obtained by the coordination of ruthenium complexes to meso-tetrapyridylporphyrins, M(TPyP). Particularly interesting cofactor groups are [Ru(bipy)2Cl]+ and [Ru3O(Ac)6(py2)]+ which generate the M(TRPyP) and M(TCP) supramolecular species respectively, since the electronic properties of metal complexes can be tuned simply by changing their oxidation state. At the same time, they can act as redox equivalent reservoir, a charge transfer relay and as sites for intermolecular interactions. For example, GC electrodes modified with a Co(TCP) film performed the tetraelectronic reduction of O2 very efficiently, as confirmed by the RRDE voltammogram exhibiting almost no ring current.
Supramolecular porphyrin films can obtained by the electrostatic assembly of tetracationic M(TRPyP) and tetraanionic M(TPPS) species. These modified electrodes are electrocatalytic active toward the oxidation reaction of substrates such as nitrite, sulfite, phenol, dopamine and NADH. Accordingly, the application of that kind of supramolecular material in the preparation of chemical sensors has been pursued. The mechanism of the charge transport through the film and the kinetics of heterogeneous charge transfer at the film solution interface were studied by cyclic, RDE and RRDE voltammetry, chronoamperometry and electrochemical impedance spectroscopy. The intrinsic conductivity of thin films is relatively high, but becomes higher around the Ru(III/II) redox potential because of the contribution of the electron-hopping mechanism. The rate of the electrocatalytic reaction is controlled by the heterogeneous electron transfer from the substrates to the Ru(III) species generated on the film, which was found to be kf = 2.7x103 dm3 mol-1 s-1 for the oxidation of nitrite to nitrate. A faster process (kf = (6.2 ± 0.1) x 104 M-1 s-1) was found for an electropolymerized tetraruthenated porphyrin film. Tin oxide conducting glass slides covered with that porphyrin film are being proposed as disposable electrodes in a newly designed integrated gas diffusion flow injection analysis detectors. These showed to be durable enough to ensure more than a thousand analyses with reproducibility better than 1.5%, high sensibility (up to 0.1 µM) and throughput (more than 40 analysis per hour). Promising results were obtained as sensors of sulfite in wine and concentrates used in the sugar/alcohol industry. Similar results were obtained as sensors of nitrite/nitrate in cured meet, saliva and mineral water, also.