Manganese porphyrin complexes are efficient catalysts for oxidation reactions, and generally have longer lifetimes and higher yields over their iron porphyrin analogue. In particular, it can catalyze the oxidative desulfurization (ODS) of thiophenes and sulfides with different oxidants, but more effectively so in the presence of an N-donor ligand which stabilizes the formation of a high valent Mn=O intermediate. The goal of this work is to characterize the absorption spectral features of the manganese porphyrin protein resting state and high-valent intermediate(s) as influenced by the N-donor ligand bound to the Mn center. These artificial catalysts will then be tested for their ODS reactivity. Here, we utilize manganese protoporphyrin IX chloride (MnIIIPPIX) and bind it into human serum albumin (HSA) to form a [MnIIIPPIX]-HSA complex. Generation of a possible [MnIIIPPIX]-N(ligand) interaction can be achieved by incorporating an N-donor ligand, forming a N(ligand)-[MnIIIPPIX]-HSA complex. In solution, the artificial complexes constructed using imidazole and amine derivatives show the formation of a Mn intermediate upon addition of meta-chloroperoxybenzoic acid (mCPBA), but other N-donor groups are also being investigated. Conditions are currently being optimized in order to encase these complexes in a silica sol-gel matrix, enhancing stability without compromising their spectroscopic or catalytic properties. The effectivity of the sol-gel N(ligand)-[MnIIIPor]-HSA complexes will ultimately be tested for the ODS of thiophene derivatives such as benzothiophene, a commonly accepted model for organic sulfur in coal.

Effect of N-donor ligands on the formation of manganese porphyrin protein intermediates: Preparing catalysts for sulfoxidation reactions

ACS Spring 2022

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