Theoretical Calculations on an Enzyme Catalyzed Reaction Mechanism

1989 ◽  
pp. 345-355 ◽  
Author(s):  
Giuliano Alagona ◽  
Caterina Ghio
Keyword(s):  
Reaction Mechanism ◽  
Theoretical Calculations

Synthesis of 4-Aryl-3(5)-(2-hydroxyphenyl)pyrazoles by Reaction of Isoflavones and their 4-Thio Analogues with Hydrazine Derivatives

2007 ◽  
Vol 60 (12) ◽  
pp. 905 ◽  
Author(s):  
Albert Lévai ◽  
Artur M. S. Silva ◽  
José A. S. Cavaleiro ◽  
José Elguero ◽  
Ibon Alkorta ◽  
...  
Keyword(s):  
Reaction Mechanism ◽  
Nmr Spectroscopy ◽  
Hydrogen Bonds ◽  
Hydrazine Hydrate ◽  
1H Nmr ◽  
Theoretical Calculations ◽  
Intramolecular Hydrogen Bonds ◽  
Nmr Study ◽  
Intramolecular Hydrogen ◽  
New Compounds

4-Aryl-3(5)-2-(hydroxyphenyl)pyrazoles have been prepared by the reaction of isoflavones and their 4-thio analogues with hydrazine hydrate and phenylhydrazine in hot pyridine. The reaction mechanism for the formation of these pyrazoles is discussed. All the new compounds have been fully characterized by NMR spectroscopy. In [D6]DMSO, a 1H NMR study allows observation of the presence of both pyrazole annular tautomers, due to the presence of intramolecular hydrogen bonds in each tautomer (OH···N and NH···O). Theoretical calculations have been carried out on tautomers and conformers of compounds 20 (3(5)-(2-hydroxy-4-methoxyphenyl)-5(3)-methyl-4-phenylpyrazole) and 21 (3(5)-(2-hydroxy-4-methoxyphenyl)-4-(2-methoxyphenyl)-5(3)-methylpyrazole), including the absolute shieldings (GIAO/B3 LYP/6–311++G**) of 21.

scholarly journals Differentiation between Enamines and Tautomerizable Imines Oxidation Reaction Mechanism using Electron-Vibration-Vibration Two Dimensional Infrared Spectroscopy

Molecules ◽  
2019 ◽  
Vol 24 (5) ◽  
pp. 869 ◽  
Author(s):  
Fengqin Long ◽  
Zheng Chen ◽  
Keli Han ◽  
Lu Zhang ◽  
Wei Zhuang
Keyword(s):  
Reaction Mechanism ◽  
Reaction Mechanisms ◽  
Theoretical Calculations ◽  
Two Dimensional ◽  
Oxidation Reactions ◽  
Spectral Signatures ◽  
Potential Strength ◽  
Chemical Reaction Mechanisms ◽  
2Dir Spectroscopy ◽  
Two Dimensional Infrared Spectroscopy

Intermediates lie at the center of chemical reaction mechanisms. However, detecting intermediates in an organic reaction and understanding its role in reaction mechanisms remains a big challenge. In this paper, we used the theoretical calculations to explore the potential of the electron-vibration-vibration two-dimensional infrared (EVV-2DIR) spectroscopy in detecting the intermediates in the oxidation reactions of enamines and tautomerizable imines with 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO). We show that while it is difficult to identify the intermediates from their infrared and Raman signals, the simulated EVV-2DIR spectra of these intermediates have well resolved spectral features, which are absent in the signals of reactants and products. These characteristic spectral signatures can, therefore, be used to reveal the reaction mechanism as well as monitor the reaction progress. Our work suggests the potential strength of EVV-2DIR technique in studying the molecular mechanism of organic reactions in general.

scholarly journals Ag2O versus Cu2O in the Catalytic Isomerization of Coordinated Diaminocarbenes to Formamidines: A Theoretical Study

Materials ◽  
2022 ◽  
Vol 15 (2) ◽  
pp. 491
Author(s):  
Juan F. Van der Maelen ◽  
Javier Ruiz
Keyword(s):  
Reaction Mechanism ◽  
Nitrogen Atom ◽  
Carbon Atom ◽  
Transition State ◽  
Theoretical Study ◽  
Theoretical Calculations ◽  
Experimental Results ◽  
Similar Reaction ◽  
Isomerization Process ◽  
Catalytic Isomerization

DFT theoretical calculations for the Ag2O-induced isomerization process of diaminocarbenes to formamidines, coordinated to Mn(I), have been carried out. The reaction mechanism found involves metalation of an N-H residue of the carbene ligand by the catalyst Ag2O and the formation of a key transition state showing a μ-η2:η2 coordination of the formamidinyl ligand between manganese and silver, which allows a translocation process of Mn(I) and silver(I) ions between the carbene carbon atom and the nitrogen atom, before the formation of the formamidine ligand is completed. Calculations carried out using Cu2O as a catalyst instead of Ag2O show a similar reaction mechanism that is thermodynamically possible, but highly unfavorable kinetically and very unlikely to be observed, which fully agrees with experimental results.

scholarly journals Two-step reaction mechanism reveals new antioxidant capability of cysteine disulfides against hydroxyl radical attack

2020 ◽  
Vol 117 (31) ◽  
pp. 18216-18223
Author(s):  
Sarju Adhikari ◽  
Ramon Crehuet ◽  
Josep M. Anglada ◽  
Joseph S. Francisco ◽  
Yu Xia
Keyword(s):  
Reaction Mechanism ◽  
Hydroxyl Radical ◽  
Theoretical Calculations ◽  
Reaction Rates ◽  
Peroxyl Radicals ◽  
Thiyl Radical ◽  
Back Side ◽  
Sulfenic Acid ◽  
Acid Product ◽  
Sulfinyl Radical

Cysteine disulfides, which constitute an important component in biological redox buffer systems, are highly reactive toward the hydroxyl radical (•OH). The mechanistic details of this reaction, however, remain unclear, largely due to the difficulty in characterizing unstable reaction products. Herein, we have developed a combined approach involving mass spectrometry (MS) and theoretical calculations to investigate reactions of•OH with cysteine disulfides (Cys–S–S–R) in the gas phase. Four types of first-generation products were identified: protonated ions of the cysteine thiyl radical (+Cys–S•), cysteine (+Cys–SH), cysteine sulfinyl radical (+Cys–SO•), and cysteine sulfenic acid (+Cys–SOH). The relative reaction rates and product branching ratios responded sensitively to the electronic property of the R group, providing key evidence to deriving a two-step reaction mechanism. The first step involved•OH conducting a back-side attack on one of the sulfur atoms, forming sulfenic acid (–SOH) and thiyl radical (–S•) product pairs. A subsequent H transfer step within the product complex was favored for protonated systems, generating sulfinyl radical (–SO•) and thiol (–SH) products. Because sulfenic acid is a potent scavenger of peroxyl radicals, our results implied that cysteine disulfide can form two lines of defense against reactive oxygen species, one using the cysteine disulfide itself and the other using the sulfenic acid product of the conversion of cysteine disulfide. This aspect suggested that, in a nonpolar environment, cysteine disulfides might play a more active role in the antioxidant network than previously appreciated.

EXCITATION FUNCTIONS OF α-INDUCED REACTIONS IN COBALT AND PRE-EQUILIBRIUM EFFECTS

2004 ◽  
Vol 13 (03) ◽  
pp. 585-595 ◽  
Author(s):  
M. AFZAL ANSARI ◽  
MOUNER A. Abd. ALSLAM ◽  
N. P. M. SATHIK ◽  
M. ISMAIL ◽  
M. H. RASHID
Keyword(s):  
Experimental Data ◽  
Reaction Mechanism ◽  
Theoretical Calculations ◽  
Particle Energy ◽  
Activation Technique ◽  
Thermodynamical Equilibrium ◽  
Excitation Functions ◽  
Model Code ◽  
A Value ◽  
Stacked Foil Activation Technique

Excitation functions for the reactions (α,2n), (α,αn), (α,α2n), (α,α3n) and (α,2pn) have been measured using 57 Co as a target up to 50 MeV α-particle energy. The stacked foil activation technique and γ-ray spectroscopy method has been employed. Measured excitation functions are compared with the geometry dependent hybrid (GDH) model. A comparison shows that the pure equilibrium (EQ) compound reaction mechanism is incapable of reproducing the experimental data while the pre-equilibrium (PE) reaction mechanism along with equilibrium (EQ) decay, where it is considered that pre-equilibrium emission of particles take place prior to the establishment of the thermodynamical equilibrium of the system, is able to reproduce the experimental data. The GDH model code ALICE-91 has been used for theoretical calculations. A value of initial exciton number n0=4 with configuration (2 neutron + 2 proton + 0 hole) has been found to give the satisfactory reproduction of experimental excitation functions.

Insights into the reaction mechanism of propene H/D exchange over acidic zeolite catalysts from theoretical calculations

2016 ◽  
Vol 6 (16) ◽  
pp. 6328-6338 ◽  
Author(s):  
Xianfeng Yi ◽  
Lihong Ding ◽  
Guangchao Li ◽  
Zhiqiang Liu ◽  
Hongqiang Xia ◽  
...  
Keyword(s):  
Reaction Mechanism ◽  
Reaction Mechanisms ◽  
Theoretical Calculations ◽  
Zeolite Catalysts

The reaction mechanisms of propene H/D exchange over deuterated acidic ZSM-5 zeolite have been theoretically revealed.

The reaction mechanism of iron and manganese superoxide dismutases studied by theoretical calculations

2006 ◽  
Vol 27 (12) ◽  
pp. 1398-1414 ◽  
Author(s):  
Lubomír Rulíšek ◽  
Kasper P. Jensen ◽  
Kristoffer Lundgren ◽  
Ulf Ryde
Keyword(s):  
Reaction Mechanism ◽  
Theoretical Calculations ◽  
Superoxide Dismutases ◽  
Manganese Superoxide ◽  
Manganese Superoxide Dismutases ◽  
Iron And Manganese
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