Structural and bio-catalytic aspects of nano crystallite iron(iii) complexes containing triazole-based ligands

Abstract

Three triazole-based ligands and their iron(III) complexes have been synthesized and characterized by several physical and chemical techniques. Elemental and thermal analysis in addition to molar conductance measurements assigned the molecular formulas while spectroscopic (¹H NMR, mass spectra, FTIR, UV-Vis and ESR) and magnetic investigations determined the bonding pattern and stereochemistry. The final and accurate structure of the present iron(III) complexes was confirmed using PXRD data combined with computational chemistry calculations. The distorted octahedral stereochemistry of the present iron(III) chelate is revealed based on the results of the different characterization techniques used. Using the stopped-flow technique, the bio-catalytic potential of the current Fe(III) complexes as mimetics of the blue copper proteins, catechol oxidase and phenoxazinone synthase was studied. Kinetic study showed that the catalytic aerobic oxidation reactions of the phenols under study are of the biphasic type and take place in the saturation pathway. Michael–Menten approach was adopted to estimate the kinetic parameters V_max, k_cat, K_M and k_cat/K_M. Cyclic voltammetry measurements were performed to determine the free energy (λ or ΔG°) of the ongoing oxidation reactions. The relationship between catalytic activity of triazole-based Fe(III) complexes with their structural properties and driving force (λ) is discussed. Possible mechanistic pathways for the catalytic oxidation reactions of the studied phenols are addressed.