Investigating axial ligand impact on pinch-porphyrin peroxidase activity with [bis(o-methylpyridino) (dimethylesterprotoporphyrinato)Fe(III)] chloride

Abstract

The synthesis and characterization of a novel hexacoordinated compound as a product of the reaction between chlorodimethylesterprotoprphyrin–Fe(III) 1 and 2–methylpiridine (2–CH3Py) was performed. The [bis(o–methylpyridino)(dimethylesterprotoporphyrinato)Fe(III)] chloride 2 is a compound of the family of the pinch–porphyrins, a model of peroxidase enzymes. We analyzed 2 using UV-Vis, 1H NMR, and EPR spectroscopies, as well as kinetic quantifications of its peroxidase activity and computational analysis, to evaluate the presence of the pinch-ligand coordinated to 1 in a series of pinch-ironprotoporphyrin complexes, as previously reported. Our investigation revealed that the oxidant activity of Compound I derived from peroxidase activity determination of 1 and 2, respectively, is better controlled when a heterohydrocarbonated chain is attached to the pyridyl groups that coordinate axially to 1; an effect evidenced by a decrease of the activation energy value associated with Compound 0 formation during the reaction performed by pinch–porphyrin, with the picdien axial ligand and hydrogen peroxide. When correlating the contribution of [Formula: see text]3/2 in the quantum mixed-spin state (qms), [Formula: see text]3/2, [Formula: see text]5/2, of iron(III)-based complexes with their peroxidase activity, we found that when the qms [Formula: see text]3/2, [Formula: see text]5/2, of iron(III) had 80% character [Formula: see text]3/2, the peroxide activity increased significantly. This could be a fundamental trait that could affect the peroxidase activity owing to the distortion of the iron geometry associated with its coordination number when [Formula: see text]methylpyridine is used as an axial ligand.