Kinetic and Computational Studies of Rhenium Catalysis for Oxygen Atom Transfer Reactions

2018 ◽  
Vol 71 (3) ◽  
pp. 149 ◽  
Author(s):  
Abdellatif Ibdah ◽  
Heba Bani Bakar ◽  
Salwa Alduwikat
Keyword(s):  
Oxygen Atom ◽  
Density Functional ◽  
Computational Study ◽  
Slow Step ◽  
Atom Transfer ◽  
Oxygen Atom Transfer ◽  
Functional Theory ◽  
Enthalpy Of Activation ◽  
Oxygen Atom Transfer Reactions ◽  
Rate Method

The rhenium(v)oxo dimer {MeReO(edt)}2 (edt = 1,2-ethanedithiolate) is an effective catalyst for the oxygen atom transfer (OAT) reaction from pyridine oxide and picoline oxide to triphenylarsine (Ph3As) as oxygen acceptor. Kinetics measurements were carried out by the initial rate method because of the monomerization reaction of the pyridine product with the {MeReO(edt)}2 catalysts. The derived rate is R = k[Re][NO] (where NO is picoline oxide or pyridine oxide) and independent of the Ph3As concentration. The rate constant at room temperature in chloroform is k(PicNO) = 268.1 ± 3.5 L mol−1 s−1 and k(PyNO) = 155.3 ± 2.3 L mol−1 s−1. The analogue rhenium(v)oxo dimer {MeReO(pdt)}2 (pdt = 1,3-propanedithiolate) does not monomerize with pyridine. However, {MeReO(edt)}2 rapidly monomerizes with pyridine. Density functional theory study of the enthalpy of the monomerization reaction shows that the {MeReO(edt)}2 reaction with pyridine is more thermodynamically favoured than {MeReO(pdt)}2 and this is attributed to the higher angle strain on the {MeReO(edt)}2 bridging sulfur. The computational study of the proposed slow step shows that enthalpy of activation (ΔH‡) of ReV oxidation to ReVII is unchanged by varying the substituent on the pyridine oxide.

A kinetic study of dimethyl sulfoxide reductase based on density functional theory

2010 ◽  
Vol 88 (8) ◽  
pp. 683-693 ◽  
Author(s):  
Elizabeth Hernandez-Marin ◽  
Tom Ziegler
Keyword(s):  
Density Functional Theory ◽  
Free Energy ◽  
Oxygen Atom ◽  
Dimethyl Sulfoxide ◽  
Density Functional ◽  
Synthetic Analogue ◽  
Atom Transfer ◽  
Oxygen Atom Transfer ◽  
Functional Theory ◽  
Model Complexes

We present a density functional theory study on the oxygen atom transfer (OAT) reaction of dimethyl sulfoxide (DMSO) with model complexes resembling a functional synthetic analogue of the molybdoenzyme DMSO reductase. The good agreement between our calculated Gibbs free energy profile and data derived from experimental kinetic parameters supports the reaction mechanisms of the oxygen atom transfer proposed in this study. When the mechanism involves the formation of a DMSO-bound intermediate, the calculations on the free energy surface provide valuable information that explains the origin of the apparent contradiction between the experimental findings and previous theoretical calculations with respect to the rate-limiting step of the reaction mechanism. The enzymatic mechanism of the OAT reaction is more complex than the mechanism of any synthetic analogue, mainly due to the formation of an enzyme-substrate adduct prior to the appearance of the substrate-bound intermediate. This study also presents a possible mechanism for the formation of such an adduct and the subsequent oxygen atom transfer. The mechanism involves a proton transfer to and from the substrate.

scholarly journals How Does Replacement of the Axial Histidine Ligand in Cytochrome c Peroxidase by Nδ-Methyl Histidine Affect Its Properties and Functions? A Computational Study

2020 ◽  
Vol 21 (19) ◽  
pp. 7133
Author(s):  
Calvin W. Z. Lee ◽  
M. Qadri E. Mubarak ◽  
Anthony P. Green ◽  
Sam P. de Visser
Keyword(s):  
Cytochrome C ◽  
Oxygen Atom ◽  
Density Functional ◽  
Computational Study ◽  
Cytochrome C Peroxidase ◽  
Electronic Configuration ◽  
Axial Ligand ◽  
Atom Transfer ◽  
Compound I ◽  
Oxygen Atom Transfer

Heme peroxidases have important functions in nature related to the detoxification of H2O2. They generally undergo a catalytic cycle where, in the first stage, the iron(III)–heme–H2O2 complex is converted into an iron(IV)–oxo–heme cation radical species called Compound I. Cytochrome c peroxidase Compound I has a unique electronic configuration among heme enzymes where a metal-based biradical is coupled to a protein radical on a nearby Trp residue. Recent work using the engineered Nδ-methyl histidine-ligated cytochrome c peroxidase highlighted changes in spectroscopic and catalytic properties upon axial ligand substitution. To understand the axial ligand effect on structure and reactivity of peroxidases and their axially Nδ-methyl histidine engineered forms, we did a computational study. We created active site cluster models of various sizes as mimics of horseradish peroxidase and cytochrome c peroxidase Compound I. Subsequently, we performed density functional theory studies on the structure and reactivity of these complexes with a model substrate (styrene). Thus, the work shows that the Nδ-methyl histidine group has little effect on the electronic configuration and structure of Compound I and little changes in bond lengths and the same orbital occupation is obtained. However, the Nδ-methyl histidine modification impacts electron transfer processes due to a change in the reduction potential and thereby influences reactivity patterns for oxygen atom transfer. As such, the substitution of the axial histidine by Nδ-methyl histidine in peroxidases slows down oxygen atom transfer to substrates and makes Compound I a weaker oxidant. These studies are in line with experimental work on Nδ-methyl histidine-ligated cytochrome c peroxidases and highlight how the hydrogen bonding network in the second coordination sphere has a major impact on the function and properties of the enzyme.

Nonclassical oxygen atom transfer reactions of an eight-coordinate dioxomolybdenum(vi) complex

2021 ◽  
Author(s):  
Leila G. Ranis ◽  
Jacqueline Gianino ◽  
Justin M. Hoffman ◽  
Seth N. Brown
Keyword(s):  
Oxygen Atom ◽  
Transfer Reaction ◽  
Transfer Reactions ◽  
Atom Transfer ◽  
Oxygen Atom Transfer ◽  
Oxygen Atom Transfer Reactions ◽  
Atom Transfer Reactions ◽  
Oxygen Atoms

Eight-coordinate MoO2(DOPOQ)2 can donate two oxygen atoms to substrates such as phosphines in a four-electron nonclassical oxygen atom transfer reaction.

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