Formation And Characterization Of Self-assembly Monolayer Based On Thiol-terminal Porphyrins/Thiol

The thiol-terminal functionalized porphyrin and metalloporphyrin can be self-assembled on gold electrode surfaces to form a perfect monolayer, furthermore, the porphyrin and metalloporphyrin are the core of life-activity substance in all organism. Due to their larger surface area and particular rigidity of structure, the monolayers of porphyrin and metalloporphyrin become the best perfect model of genuine biomembrane, and have been used to study the basal course of life activity, such as photosynthesis, respiration, energy conversion, information transfer. Thus, the applications of porphyrins self-assembled monolayers in electroanalytical chemistry are reviewed, the future applications of porphyrins self-ssembled monolayers in electroanalytical chemistry are also given. Four applications are mentioned: the long distance electron transfer; the catalysis deoxidize; the identification of molecule; the biochemic sensor.In the experimentation, the mixed-monolayers of porphyrin/thiol and metalloporphyrin/thiol were self-assembled on gold surface and investigated by cyclic voltammetry(CV), electrochemical impedance spectroscopy(EIS) and scanning electrochemical microscopy(SECM). The results indicate that:(1) The preparation of mixed-SAMs by competition co-adsorption is feasible because the preferentially adsorbed longer-chain and gigantic-end porphyrin monolayer is unsaturated so remains some adsorption sites to be occupied by shorter-chain and thin thiol molecules. The course of competition co-adsorption is a dynamic equilibrium, the more thiol insertion, the more porphyrins are replaced.(2) The porphyrin monolayers can block the electron transfer from the redox couple [Fe(CN)₆]^3-/4- to gold electrode surface, effectively.. But with the coordination of cobalt ions into porphyrin rings, the electron transfer ability increases markedly due to the presence of cobalt(II) causing an other electron transfer way, i.e. depending on the mediator of cobalt( II), the bimolecular electron transfer occurs. Moreover, this way is dominating for metalloporphyrin. (3) The catalyzing-deoxidize ability of metalloporphyrins is disparate according to the different pH value. In the strong acidity condition, the ability of catalyzing-deoxidize is superexcellence due to the mechanism. In a word, there is 2e" transfer in the course of catalyzing-deoxidize and the resultant is H₂O₂.