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Introduction to Heterogeneous Catalysis in Organic Transformation
Published in Varun Rawat, Anirban Das, Chandra Mohan Srivastava, Heterogeneous Catalysis in Organic Transformations, 2022
Garima Sachdeva, Gyandshwar Kumar Rao, Varun Rawat, Ved Prakash Verma, Kaur Navjeet
It is well known that depending on the chemical phase of the catalyst and reactants, different forms of catalysis can be distinguished. In homogeneous catalysis, the catalysts work in the same phase as the reactants and are often found in the liquid phase. It has been seen that mechanistic studies of homogeneous catalysts are comparatively easier than heterogeneous catalysts. The examples are Fe-porphyrin complexes active for the oxidation, Zn-complexes for decarboxylation reaction, Cu-imidazole (from histidine) complexes in hemocyanin, etc. [12].
Surface-Enhanced Spectro-Electrochemistry of Biological and Molecular Catalysts on Plasmonic Electrodes
Published in Marc Lamy de la Chapelle, Nordin Felidj, Plasmonics in Chemistry and Biology, 2019
Patrycja Kielb, Inez M. Weidinger
In synthetic chemistry, porphyrin complexes offer an impressive array of applications as models for biological electron transport or many catalytic reactions. The metal core serves as reactive active center responsible for performing a desired reaction such as oxygen or proton reduction [8–10]. Additional substituents at Cmeso positions of pyrrole rings can further tune the redox properties of a compound, whereas substituents at Cβ positions can modify their molecular flexibility [11].
Manganese Porphyrins as Pro-Oxidants in High-Molar-Mass Hyaluronan Oxidative Degradation
Published in Shrikaant Kulkarni, Neha Kanwar Rawat, A. K. Haghi, Green Chemistry and Green Engineering, 2020
Katarína Valachová, Peter Rapta, Ines Batinic-Haberle, Ladislav Šoltés
Metalloporphyrins catalyze numerous redox reactions, in particular, manganese porphyrins (MnPs) have been used as redox catalysts in several model systems relevant to biochemistry, for example, as superoxide dismutase and catalase. MnPs have been originally developed as SOD mimics based on a structure activity relationship correlating the metal-centered reduction potential and the rate constant for the catalysis of O•–2 dismutation. MnPs have several redox states and can reduce the levels of reactive species, which results in less damage of biological molecules and in the modulation of transcription factors, protein, and gene expression. The most effective MnPs have been tested in-vivo, which showed remarkable efficacy in cardiac, kidney, and liver ischemia, radioprotection, sickle cell disease, tumor suppression, diabetes, and disorders of central nervous system [13]. Porphyrin-based SOD mimics have a redox-active metal (Mn, Fe, and Cu) center and a stable porphyrin complex. The dismutation of O•–2 by Mn-porphyrin complexes involves two steps: in the first step Mn(III) are reduced by O•–2 to yield Mn(II) and O2 and in the second step Mn(II) are oxidized by O•–2 to yield H2O2 and return the manganese to its resting state as Mn(III) porphyrin. However, in the presence of a reductant such as ascorbate, MnPs function as O•–2 reductases rather than dismutases. Mn(III) can be reduced to Mn(II) by ascorbate while Mn(II) can react with O2 forming O•−2, which subsequently forms H2O2 and O2. The cytotoxic effects of two Mn(III) alkylpyridylporphyrins such as MnTE-2-PyP5+ and MnTnHex-2-PyP5+ and ascorbate have been demonstrated in Caco-2, HeLa, HCT116, and 4T1 cells. Given that several MnPs have already been tested in-vivo as SOD mimetics, and by themselves have shown low toxicities at micromolar levels, there is great potential for using MnPs as an adjuvant to enhance the efficacy of pharmacologic ascorbate [14].
Highly reactive μ-carbido diiron tetraphenylporphine oxo-species: chemical generation and the oxidation ability
Published in Journal of Coordination Chemistry, 2018
S. V. Zaitseva, E. Yu. Tyulyaeva, O. R. Simonova, S. A. Zdanovich, D. V. Tyurin, O. I. Koifman
Porphyrin complexes are widely used by nature in the active sites of enzymes responsible for catalytic aerobic oxidations, reduction and transport of dioxygen, metabolism of pharmaceuticals and destruction of peroxides. The peroxidase activity of iron-containing enzymes determined by their ability to initiate the metabolism and detoxification of peroxides by oxidation with the release of O2 is of great importance for the antioxidant system of the human body. Complexes with synthetic ligands can be also regarded as related to bioinspired chemistry. Dimeric metalloporphyrin species can exhibit even better catalytic properties than those of mononuclear counterparts [1–7]. Indeed, generation of active oxidizing species in the course of diiron macrocyclic constructions can increase their oxidation state by more than two redox equivalents. This high oxidation state is stabilized by charge delocalization at the two iron sites as well as at two aromatic ligands similar to the (P+•)FeIV=O (Compound I) species in cytochrome P-450 [8].