scholarly journals Mimicking Elementary Reactions of Manganese Lipoxygenase Using Mn-hydroxo and Mn-alkylperoxo Complexes

Molecules ◽  
2021 ◽  
Vol 26 (23) ◽  
pp. 7151
Author(s):  
Adedamola A. Opalade ◽  
Elizabeth N. Grotemeyer ◽  
Timothy A. Jackson
Keyword(s):  
Active Site ◽  
Hydroxo Complex ◽  
Substrate Oxidation ◽  
Ligand Substitution ◽  
Oxidation Reactions ◽  
Elementary Reactions ◽  
Hydroxo Complexes ◽  
Alkyl Hydroperoxides ◽  
Ligand Substitution Reaction ◽  
Pentadentate Ligand

Manganese lipoxygenase (MnLOX) is an enzyme that converts polyunsaturated fatty acids to alkyl hydroperoxides. In proposed mechanisms for this enzyme, the transfer of a hydrogen atom from a substrate C-H bond to an active-site MnIII-hydroxo center initiates substrate oxidation. In some proposed mechanisms, the active-site MnIII-hydroxo complex is regenerated by the reaction of a MnIII-alkylperoxo intermediate with water by a ligand substitution reaction. In a recent study, we described a pair of MnIII-hydroxo and MnIII-alkylperoxo complexes supported by the same amide-containing pentadentate ligand (6Medpaq). In this present work, we describe the reaction of the MnIII-hydroxo unit in C-H and O-H bond oxidation processes, thus mimicking one of the elementary reactions of the MnLOX enzyme. An analysis of kinetic data shows that the MnIII-hydroxo complex [MnIII(OH)(6Medpaq)]+ oxidizes TEMPOH (2,2′-6,6′-tetramethylpiperidine-1-ol) faster than the majority of previously reported MnIII-hydroxo complexes. Using a combination of cyclic voltammetry and electronic structure computations, we demonstrate that the weak MnIII-N(pyridine) bonds lead to a higher MnIII/II reduction potential, increasing the driving force for substrate oxidation reactions and accounting for the faster reaction rate. In addition, we demonstrate that the MnIII-alkylperoxo complex [MnIII(OOtBu)(6Medpaq)]+ reacts with water to obtain the corresponding MnIII-hydroxo species, thus mimicking the ligand substitution step proposed for MnLOX.

Oxidase Catalysis via an Aerobically Generated Dess-Martin Periodinane Analogue

2018 ◽  
Author(s):  
Asim Maity ◽  
Sung-Min Hyun ◽  
Alan Wortman ◽  
David Powers
Keyword(s):  
Chemical Synthesis ◽  
Aerobic Oxidation ◽  
Substrate Oxidation ◽  
Oxidation Catalysis ◽  
Hypervalent Iodine ◽  
Oxidation Reactions ◽  
Broad Array ◽  
Oxidation Chemistry ◽  
Reactive Oxidants

<p>Hypervalent iodine(V) reagents, such as Dess-Martin periodinane (DMP) and 2-iodoxybenzoic acid (IBX), are broadly useful oxidants in chemical synthesis. Development of strategies to access these reagents from O2 would immediately enable use of O2 as a terminal oxidant in a broad array of substrate oxidation reactions. Recently we disclosed the aerobic synthesis of I(III) reagents by intercepting reactive oxidants generated during aldehyde autoxidation. Here, we couple aerobic oxidation of iodobenzenes with disproportionation of the initially generated I(III) compounds to generate I(V) reagents. The aerobically generated I(V) reagents exhibit substrate oxidation chemistry analogous to that of DMP. Further, the developed aerobic generation of I(V) has enabled the first application of I(V) intermediates in aerobic oxidation catalysis.</p>

A shared mechanistic pathway for pyridoxal phosphate–dependent arginine oxidases

2021 ◽  
Vol 118 (40) ◽  
pp. e2012591118
Author(s):  
Elesha R. Hoffarth ◽  
Kersti Caddell Haatveit ◽  
Eugene Kuatsjah ◽  
Gregory A. MacNeil ◽  
Simran Saroya ◽  
...  
Keyword(s):  
Active Site ◽  
Evolutionary History ◽  
Pyridoxal Phosphate ◽  
Computational Studies ◽  
Single Electron Transfer ◽  
Oxidation Reactions ◽  
Unified Framework ◽  
Precise Positioning ◽  
X Ray ◽  
Mechanistic Pathway

The mechanism by which molecular oxygen is activated by the organic cofactor pyridoxal phosphate (PLP) for oxidation reactions remains poorly understood. Recent work has identified arginine oxidases that catalyze desaturation or hydroxylation reactions. Here, we investigate a desaturase from the Pseudoalteromonas luteoviolacea indolmycin pathway. Our work, combining X-ray crystallographic, biochemical, spectroscopic, and computational studies, supports a shared mechanism with arginine hydroxylases, involving two rounds of single-electron transfer to oxygen and superoxide rebound at the 4′ carbon of the PLP cofactor. The precise positioning of a water molecule in the active site is proposed to control the final reaction outcome. This proposed mechanism provides a unified framework to understand how oxygen can be activated by PLP-dependent enzymes for oxidation of arginine and elucidates a shared mechanistic pathway and intertwined evolutionary history for arginine desaturases and hydroxylases.

scholarly journals Kinetics and mechanism of formation of the complex [Ru(CN)5INH]3− through the ligand substitution reaction between the aquapentacyanoruthenate(II) anion and isoniazid

2019 ◽  
Vol 44 (3) ◽  
pp. 244-256
Author(s):  
Rupal Yadav ◽  
Radhey Mohan Naik
Keyword(s):  
Ionic Strength ◽  
Substitution Reaction ◽  
Ligand Substitution ◽  
Yellow Colour ◽  
First Order ◽  
Charge Transfer Transitions ◽  
Colour Product ◽  
Pseudo First Order ◽  
Experimental Findings ◽  
Ligand Substitution Reaction

The formation kinetics of the complex, [Ru(CN)5INH]3−, formed through the ligand substitution reaction between isoniazid (INH) and aquapentacyanoruthenate(II) ([Ru(CN)5H2O]3−), have been investigated, under pseudo first-order conditions, as a function of concentrations of [INH] and [Ru(CN)5H2O]3−, ionic strength and temperature at pH = 4.0 ± 0.02 in 0.2 M NaClO4 spectrophotometrically at 502 nm ( λmax of intense yellow colour product [Ru(CN)5INH]3−) corresponding to metal-to-ligand charge-transfer transitions, in aqueous medium. The pseudo first-order condition was maintained by taking at least 10% excess of [INH] over [Ru(CN)5H2O]3−. The stoichiometry of the reaction product was found to be 1:1 which was further supported and characterized using elemental analysis, infrared, nuclear magnetic resonance and mass spectrometric techniques. Thermodynamic and kinetic parameters have also been computed, using the Eyring equation, and the values of ΔH≠, Ea, ΔG≠ and ΔS≠ were found to be 47.3 kJ mol−1, 49.8 kJ mol−1, −8.62 kJ mol−1 and 187.6 J K−1mol−1, respectively. The reaction was found to obey first-order kinetics with respect to [INH]. It exhibited a negative salt effect on the rate upon variation of ionic strength of the medium. A tentative mechanistic scheme was proposed on the basis of experimental findings.

Investigation of the active sites for NO oxidation reactions over MnOx–CeO2 catalysts

2017 ◽  
Vol 41 (8) ◽  
pp. 3106-3111 ◽  
Author(s):  
Zhihui Sun ◽  
Jun Wang ◽  
Jinxin Zhu ◽  
Chen Wang ◽  
Jianqiang Wang ◽  
...  
Keyword(s):  
Active Site ◽  
Active Sites ◽  
No Oxidation ◽  
Oxidation Reactions

Mn4+/Mn3+ is the active site for NO oxidation reactions, according to the TOF calculated with respect to the initial reducibility measured by H2-TPR quantification.

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