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Spectroscopic properties and reactivity of a MnIII-Hydroperoxo complex that is stable at room temperature
Aghei, Zahra
Aghei, Zahra
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Abstract
The manganese lipoxygenase enzyme (MnLOX) which converts polyunsaturated fatty acids to alkyl hydroperoxides is found in fungi and plants to allow further metabolization of these substrates. It is proposed that the substrate oxidation is initiated by the transfer of a hydrogen atom from the C-H bond of the substrate to an active-site MnIII-hydroxo center. Inspired by these enzymes, there are many examples of synthesized model manganese complexes to study the active site of enzymes. These synthesized models were able to activate H2O2 to conduct a series of reactions such as sulfoxidation, olefin epoxidation and C-H bond activation with high selectivity. It is generally proposed that in both enzyme and synthesized Mn catalysts a MnV-oxo is the key intermediate which is formed from the O-O bond cleavage of a MnIII-hydroperoxo. This MnIII-hydroperoxo intermediate possesses critical role in Mn catalytic cycle but there are a few reports on them. In this study, we formed a MnIII-hydroperoxo supported by an amide-containing, pentadentate ligand (dpaq6Me). The MnIII-hydroxo complex [MnIII(OH)(6Medpaq)]+ reacted with H2O2 and HClO4 to form a green intermediate, with a UV-vis band at 615 nm. On the basis of 1H NMR, ESI-MS, EPR, FT-IR, and EPR data, we formulate this new intermediate as the MnIII-hyrdroperoxo complex [MnIII(OOH)(6Medpaq)]+. This complex reacts with 10 equivalences of PPh3 at 15 °C, and with 30 equivalences of TEMPOH at -35 °C. Based on kinetic studies, [MnIII(OOH)(6Medpaq)]+ reacts 600-fold faster with PPh3 than its MnIII-alkylperoxo analogue [MnIII(OOtBu)(6Medpaq)]+, and two-fold faster with TEMPOH than a similar MnIII-hydroperoxo complex [MnIII(OOH)(dpaq2Me)]+. Time dependent computations (TD-DFT) were applied to compare electronic features of [MnIII(OOH)(6Medpaq)]+ with analogous MnIII-hydroperoxo and MnIII-alkylperoxo complexes.
Description
This poster was presented at Gordon Bioinotganic Conference-GRS on 01/19/2025.
Date
2025-01-19
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University of Kansas
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Keywords
Manganese, Hydroperoxo, Density functional theory, Bio-inspired catalyst, Hydrogen transfer