ChemInform Abstract: Triphenylphosphine Reduction of Thiophene Endoperoxides: Nucleophilic Attack on Sulfur versus Biphilic Insertion into the Peroxide Bond.

ChemInform ◽  
2010 ◽  
Vol 27 (4) ◽  
pp. no-no
Author(s):  
W. ADAM ◽  
S. WEINKOETZ
Keyword(s):  
Nucleophilic Attack ◽  
Peroxide Bond

scholarly journals Selenium-Catalyzed Reduction of Hydroperoxides in Chemistry and Biology

Antioxidants ◽  
2021 ◽  
Vol 10 (10) ◽  
pp. 1560
Author(s):  
Laura Orian ◽  
Leopold Flohé
Keyword(s):  
Metabolic Regulation ◽  
Redox Regulation ◽  
Antioxidant Defense ◽  
Catalytic Efficiency ◽  
Antioxidant Defense System ◽  
Nucleophilic Attack ◽  
Glutathione Peroxidases ◽  
H2o2 Reduction ◽  
Thioredoxin Reductases ◽  
Peroxide Bond

Among the chalcogens, selenium is the key element for catalyzed H2O2 reduction. In organic synthesis, catalytic amounts of organo mono- and di-selenides are largely used in different classes of oxidations, in which H2O2 alone is poorly efficient. Biological hydroperoxide metabolism is dominated by peroxidases and thioredoxin reductases, which balance hydroperoxide challenge and contribute to redox regulation. When their selenocysteine is replaced by cysteine, the cellular antioxidant defense system is impaired. Finally, classes of organoselenides have been synthesized with the aim of mimicking the biological strategy of glutathione peroxidases, but their therapeutic application has so far been limited. Moreover, their therapeutic use may be doubted, because H2O2 is not only toxic but also serves as an important messenger. Therefore, over-optimization of H2O2 reduction may lead to unexpected disturbances of metabolic regulation. Common to all these systems is the nucleophilic attack of selenium to one oxygen of the peroxide bond promoting its disruption. In this contribution, we revisit selected examples from chemistry and biology, and, by using results from accurate quantum mechanical modelling, we provide an accurate unified picture of selenium’s capacity of reducing hydroperoxides. There is clear evidence that the selenoenzymes remain superior in terms of catalytic efficiency.

The mechanism of oxidation of 3-mercaptopropionic acid

1997 ◽  
Vol 75 (1) ◽  
pp. 9-13 ◽  
Author(s):  
Paula Forlano ◽  
José A. Olabe ◽  
Jorge F. Magallanes ◽  
Miguel A. Blesa
Keyword(s):  
Differential Pulse ◽  
Nucleophilic Attack ◽  
Differential Pulse Polarography ◽  
Acidic Ph ◽  
Mercaptopropionic Acid ◽  
Ph Dependency ◽  
Pulse Polarography ◽  
Mechanism Of Oxidation ◽  
Ph Range ◽  
Peroxide Bond

The mechanism of the oxidation of 3-mercaptopropionic acid (3-MPA) by hydrogen peroxide was studied in the acidic pH range. The nucleophilic attack by sulphur on the peroxide bond controls the rate. Extrapolation of the pH dependency suggests that the rate of attack by the deprotonated dianion is highest. Traces of Fe(III), at levels below 10−7 mol dm−3, do not catalyze efficiently the process through one-electron mechanisms; at higher concentrations, or on the surface of iron(III) oxides, this type of catalysis becomes important. The electrochemical oxidation of 3-MPA was also studied, using differential pulse polarography and cyclic voltammetry techniques. The mechanism is of the EC2E type, the second electron transfer step corresponding to the oxidation of the disulphide RS-SR. The rate constant for the dimerization of the RS• radicals was 1.8 × 103 mol−1 dm3 s−1; the slowness of this step agrees with the mechanisms observed in the course of one-electron oxidations by metal ions. Keywords: electrochemistry, kinetics, 3-mercaptopropionic acid, autooxidation.

A Conserved Asparagine in a Ubiquitin Conjugating Enzyme Positions the Substrate for Nucleophilic Attack

2018 ◽  
Author(s):  
Walker M. Jones ◽  
Aaron G. Davis ◽  
R. Hunter Wilson ◽  
Katherine L. Elliott ◽  
Isaiah Sumner
Keyword(s):  
Molecular Dynamics ◽  
Quantum Mechanics ◽  
Molecular Mechanics ◽  
Reaction Rates ◽  
Nucleophilic Attack ◽  
Classical Molecular Dynamics ◽  
Ubiquitin Conjugating Enzyme ◽  
Conjugating Enzyme

We present classical molecular dynamics (MD), Born-Oppenheimer molecular dynamics (BOMD), and hybrid quantum mechanics/molecular mechanics (QM/MM) data. MD was performed using the GPU accelerated pmemd module of the AMBER14MD package. BOMD was performed using CP2K version 2.6. The reaction rates in BOMD were accelerated using the Metadynamics method. QM/MM was performed using ONIOM in the Gaussian09 suite of programs. Relevant input files for BOMD and QM/MM are available.

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