Catalytic and physical characteristics of axially modified cobalt (III) tetraphenyl porphyrin immobilized on chemically different supports
A newly synthesized binuclear cobalt (III) axial-methyl alcohol-hydrochloric acid-tetraphenyl porphyrin complex was supported on the surface of two carriers of different anchoring sites, silica gel as an inorganic carrier and DOWEX-50 HGR ion-exchange resin as an organic one. Complex loading ranged between 0.1 and 2.0% (w/w). The studied complex was shown to exhibit weaker interaction with silica gel surface, where it existed as mononuclear molecules in the diluted samples and as aggregated binuclear ones in the more concentrated samples. In the diluted samples on the resin, the complex molecules seemed to be inserted in the voids, freely and favorably oriented toward the ion exchange groups. With more concentration, part of the complex molecules was assumed to escape through diffusion from internal voids to the outer surface. The major part seemed to display associative ion exchange, where dissociation or break up of hydrogen-bonded sulphonate groups was the controlling step. The catalase-like activity of the various complex samples under study was shown to run in linear relationship with the dispersion parameter being a function of the mode of complex interaction with the support. The active site for the unsupported complex was suggested to involve both the π-electron cyclic system and the central cobalt ion. For supported complex samples, operating active sites seemed to be only the central cobalt ions, where the axial ligands, with the macro-ring system, might play the role of controlling the orientation, dispersion and distribution of complex molecules on the support surface.
Journal: Applied Catalysis A: General - Volume 300, Issue 1, 20 January 2006, Pages 14–23