Search

Synthetic and bioinspired metalloporphyrins are a class of redox-active catalysts able to emulate several enzymes such as cytochromes P450, ligninolytic peroxidases, and peroxygenases. Their ability to perform oxidation and degradation of recalcitrant compounds, including aliphatic hydrocarbons, phenolic and non-phenolic aromatic compounds, sulfides, and nitroso-compounds, has been deeply investigated. Such a broad substrate specificity has suggested their use also in the bleaching of textile plant wastewaters. In fact, industrial dyes belong to very different chemical classes, being their effective and inexpensive oxidation an important challenge from both economic and environmental perspective. Accordingly, we review here the most widespread synthetic metalloporphyrins, and the most promising formulations for large-scale applications. In particular, we focus on the most convenient approaches for immobilization to conceive economical affordable processes. Then, the molecular routes of catalysis and the reported substrate specificity on the treatment of the most diffused textile dyes are encompassed, including the use of redox mediators and the comparison with the most common biological and enzymatic alternative, in order to depict an updated picture of a very promising field for large-scale applications. [ABSTRACT FROM AUTHOR]

This paper describes the immobilization of 5,10,15,20-tetrakis(2,6-dichlorophenyl)porphine-manganese(III) through coordinative bond onto imidazolyl- and pyridyl-grafted silica, emulating the active site of ligninolytic peroxidases. To this purpose, plain silica gel was functionalized with two organosilanes: the first bearing an imidazolyl functionality, the other one bearing a pyridyl functionality. Manganese-porphine was then immobilized onto the two modified silicas. The two catalytic adducts have been fully characterized to point out the effect of the ligands on their catalytic features. Pyridine-immobilized metalloporphine was found to be a much more performant catalyst, giving significantly higher conversion rates with all the tested substrates: a lignin-model compound such as veratryl alcohol, the lignin peroxidase well-known substrate azure B, and recalcitrant textile dyes such as alizarin red S, phenosafranine, methylene blue, methyl green, xylenol orange, and methyl orange. Imidazole-immobilized metalloporphine on the contrary has proved to be more stable than its pyridine-based counterpart. Besides, the ligands seem to promote different catalytic pathways in the two adducts. These results allow giving rational and rigorous insights about the effect of the ligands during the immobilization of metalloporphines, thus helping in the design of catalysts with specific feature (i.e. stability, reactivity). [ABSTRACT FROM AUTHOR]

Abstract: Phenosafranine is a toxic, polluting dye, belonging to the N-phenylphenazinium class, whose inexpensive and environmentally friendly elimination from industrial effluents could be of interest. In this study we report phenosafranine degradation and concomitant decolorization of the corresponding wastewaters by H2O2 oxidation in the presence of 5,10,15,20-tetrakis(4-sulfonatophenyl)-porphine-Mn(III) catalyst immobilized on a modified silica support bearing imidazolyl functionality. Some operational features of the catalytic process are described and a chemical mechanism for the bleaching process is hypothesized. The proposed method was compared to others, based on the use of the oxidizing enzymes such as laccase, horseradish peroxidase, and lignin peroxidase. [Copyright &y& Elsevier]

Abstract: This paper describes the immobilization of the commercial synthetic tetrakis(pentafluorophenyl) porphine-iron(III) chloride on pyridyl-functionalized crosslinked poly(vinyl alcohol) and the catalytic activity of the adduct towards oxidation of selected organic substrates by hydrogen peroxide. The obtained adduct was characterized by UV/vis and IR spectroscopies. It showed a noticeable lignin-peroxidase-like catalytic activity; moreover a dramatic activity enhancement was observed in the presence of Mn2+ under certain experimental conditions, so the preparation could well be classified as a manganese-peroxidase-like catalyst leading to a transient Mn(III) species. Conversion yields for some aromatic compounds (bio)chemically related to lignin, kinetics and operational features of the adduct are also reported. [Copyright &y& Elsevier]