CONICET | Buscador de Institutos y Recursos Humanos

A mathematical description of the kinetics of the hematin catalysed decolourization reaction of Orange IIalkaline solutions was constructed and validated under the assumption that hematin mimics the actionof peroxidases. The clean oxidant H2O2 was applied, however, hematin dismutated it, as catalases do,under reaction conditions. Thus, special attention was cared to the understanding of this ineffectiveside-reaction by the proposal of straightforward pathways concerning the catalatic or the pseudocatalaticcycles. Model validations were implemented by a parametrization procedure of relevant rateconstants under dynamic simulation fitting to selected experimental time-courses data. The peroxidaticcoupled to pseudo-catalatic mechanism gave predictions closer to experimental findings in a wide rangeof conditions. The initial rate method for data processing was successfully applied for providing reliableinitial rate constant guesses but also for the detection of unexpected rate depletion at high dye concentrations.This was considered in the model as unproductive dye coordination to hematin native state priorto H2O2 activation. The pseudo-catalatic pathway involves the production of superoxide and its coordinationto hematin native state to afford inactive but regenerable ferrous porphyrin. Model underestimationsof experimental data were interpreted as cooperative oxidation of Orange II molecules bysuperoxide whereas model deviations at high dye concentration (>400 mg/l) was assigned to furtherhematin catalysed oxidation of Orange II degraded products.

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