Mechanism of the initial reaction of phenylhydrazine with oxyhemoglobin and effect of ring substitutions on the bimolecular rate constant of this reaction

Biochemistry ◽  
1982 ◽  
Vol 21 (10) ◽  
pp. 2421-2426 ◽  
Author(s):  
Harvey A. Itano ◽  
Jeanne L. Matteson
Keyword(s):  
Rate Constant ◽  
Initial Reaction ◽  
Bimolecular Rate Constant

From Reduction to Oxidation: pH Controlled Reaction of 1 Hydroxyethyl Radical with Caffeic Acid Analogues.

2021 ◽  
Vol 11 ◽  
Author(s):  
Laboni Das ◽  
Shashi P Shukla ◽  
Suchandra Chatterjee ◽  
Ashis K Satpati ◽  
Soumyakanti Adhikari
Keyword(s):  
Caffeic Acid ◽  
Rate Constant ◽  
Reduction Process ◽  
Phenoxyl Radical ◽  
Alpha Tocopherol ◽  
Side Chain ◽  
Product Analysis ◽  
Bimolecular Rate Constant ◽  
Ethyl Radical ◽  
Computational Calculations

Aims: The aim is to search for newer and better antioxidants through kinetic spectroscopic studies in combination with product analysis and computation. Background: Antioxidant effect of caffeic acid, its derivative, and analogues have been well reported. The antioxidative efficiencies are related to their molecular structure, and two reaction pathways are well accepted, H-atom transfer (HAT) or single electron transfer. 1-hydroxy ethyl radical (1-HER) being an ethanol-derived free radical might be causing the onset of liver injury detected after alcohol administration. 1-HER has also been reported to react with fatty acids and endogenous antioxidants such as glutathione, ascorbic acid, and alpha-tocopherol Objective: The present study is an attempt to understand the reaction mechanism of 1-HER with caffeic acid, its derivative, and analogues in detail. Method: Pulse radiolysis with kinetic absorption spectroscopy has been employed to follow the reaction pathway and identify the intermediates produced in the reaction. The reaction products have been detected using LCMS/MS. Based on these studies, a consolidated mechanism has been proposed. Cyclic voltammetry measurements and computational calculations have been used in support of the proposed mechanism. Result: In the reaction of 1-hydroxy ethyl radical (1-HER) with caffeic acid and its oligomers, reduction takes place below the pKa1, while oxidation occurs with the deprotonated phenolic moiety. The reduction of caffeic acid generates a carbon-centered radical at the double bond of the side chain with a bimolecular rate constant of 1.5x1010 dm3 mol-1 s-1. Notably, a low concentration of oxygen was able to regenerate a part of the caffeic acid molecules in the reduction process. At pH 10 a phenoxyl radical is formed due to oxidation with a much lower bimolecular rate constant (4.2x108 dm3 mol-1 s-1). In the case of di-hydrocaffeic acid, only phenoxyl radical is formed at pH 10 and, no reaction could be observed below pH 8. Conclusion: Change in reactive pattern from reduction to oxidation with change in pH within the same set of reactants has been evidently established in the present study. The results point towards the importance of  unsaturation in the side chain of caffeic acid oligomers for their reaction with 1-HER at neutral pH. The effect of oxygen concentration on the antioxidative protection offered by this class of molecules might be intriguing for the quest of the effectiveness of antioxidants at low concentrations. Other: It may be inferred that the effect of pH on the reactivity pattern as observed is not 1-HER, but substrate-specific, in the present case, phenolic acids. This study generates further scope for in-depth studies on other polyphenols where unsaturation exists in the side chain.

scholarly journals THE RATE CONSTANT OF THE REACTION BETWEEN FERROUS IONS AND HYDROGEN PEROXIDE IN ACID SOLUTION

1957 ◽  
Vol 35 (5) ◽  
pp. 428-436 ◽  
Author(s):  
T. J. Hardwick
Keyword(s):  
Hydrogen Peroxide ◽  
Acid Solution ◽  
Sulphuric Acid ◽  
Acid Concentration ◽  
Rate Constant ◽  
Perchloric Acid ◽  
Ferrous Ion ◽  
Ferrous Ions ◽  
Bimolecular Rate Constant

Identical values of the bimolecular rate constant of the ferrous ion – hydrogen peroxide reaction were obtained from intercomparisons of the methods previously used in following this reaction. In perchloric acid the bimolecular rate constant is unaffected by acid concentration; in sulphuric acid it increases slightly in acid concentrations above 10−2N. The results agree with and explain the differences between those obtained by Baxendale and by Dainton, but are only in marginal agreement with those recently reported by Weiss.

1,1,4-Derivatives of Thiosemicarbazide—New Non-Staining Antiozonants

1973 ◽  
Vol 46 (2) ◽  
pp. 517-523
Author(s):  
L. K. Zolotarevskaya ◽  
A. M. Lipkin ◽  
A. E. Grinberg ◽  
L. G. Angert
Keyword(s):  
Protective Effect ◽  
Rate Constant ◽  
Practical Interest ◽  
Initial Reaction ◽  
Inhibiting Activity ◽  
Thiourea Derivatives ◽  
New Class ◽  
Mechanism Of Reaction ◽  
Thiosemicarbazide Derivatives ◽  
Derivatives Of

Abstract In the nature of non-staining antiozonants, a new class of compounds, 1,1,4-derivatives of thiosemicarbazide, are proposed. The mechanism of reaction of thiosemicarbazide derivatives with ozone is analogous to the mechanism of this reaction with thiourea derivatives. Within this, the rate constant of the initial reaction of the thiosemicarbazide derivatives with ozone is somewhat higher than that of the thiourea derivatives. 1,1,4-Trialkyl-substituted thiosemicarbazides appear to be the most effective antiozonants, not changing the color of light vulcanizates. Of the investigated compounds, 1,1,4-tributylthiosemicarbazide, being distinguished by a large protective effect against ozone, inhibiting activity in the process of heat aging of the vulcanizates, and lesser ability for leaching out of the vulcanizates by water than tributylthiourea, presents the greatest practical interest.

Binding constants for tetramethylammonium ion determined with irreversible inhibitors of acetylcholinesterase

1976 ◽  
Vol 54 (10) ◽  
pp. 918-920 ◽  
Author(s):  
F. Iverson
Keyword(s):  
Rate Constant ◽  
Binding Constant ◽  
Binding Constants ◽  
Single Site ◽  
Reversible Binding ◽  
Bimolecular Rate Constant ◽  
Irreversible Inhibitors ◽  
Carbamate Inhibitors

The reversible binding constant (Ki) for tetramethylammonium ion (TMA) was determined from the decrease in the bimolecular rate constant (ki) observed with each of 21 organophosphate or carbamate inhibitors of acetylcholinesterase (EC 3.1.1.7). The Ki values obtained were reasonably constant (5.8 × 10−4 ± 0.38 M), and this is consistent with reports indicating that TMA binds to a single site on the enzyme.

Reaction of oxygen atoms with ethanol

1967 ◽  
Vol 45 (16) ◽  
pp. 1845-1861 ◽  
Author(s):  
A. Kato ◽  
R. J. Cvetanović
Keyword(s):  
Rate Constant ◽  
Vapor Phase ◽  
Room Temperature ◽  
Initial Reaction ◽  
Reaction Products ◽  
Absolute Value ◽  
Oxygen Atoms

Reaction of O(3P) atoms with ethanol in the vapor phase has been studied at room temperature. The principal initial reaction products are water, acetaldehyde, and 2,3-butanediol. The data are consistent with abstraction of an α-hydrogen from ethanol as the primary step in the reaction. Ethanol is found to react with O(3P) atoms about 3.5 times less rapidly than acetaldehyde. The approximate absolute value of the rate constant of the ethanol reaction at 25 °C is 6.2 × 1010 cm3 mole−1 s−1.As a corollary to the investigation of the reaction of oxygen atoms with ethanol, a brief study has been made of the mercury Hg 6(3P1) photosensitized decomposition of ethanol at room temperature.

Negative ion–molecule reactions in liquid argon following electron capture by N2O

1977 ◽  
Vol 55 (11) ◽  
pp. 2220-2224 ◽  
Author(s):  
George Bakale ◽  
Ulrich Sowada ◽  
Werner F. Schmidt
Keyword(s):  
Electron Capture ◽  
Rate Constant ◽  
Liquid Argon ◽  
Negative Ion ◽  
X Rays ◽  
Electron Current ◽  
Short Burst ◽  
Bimolecular Rate Constant ◽  
Ion Molecule Reactions

Electrons produced in liquid argon by a short burst of X rays react readily with dissolved N2O with a bimolecular rate constant of 5.8 × 10−10 cm3/s or 3.5 × 1011 M−1 s−1. The addition of H2 or CO to the Ar/N2O solution results in a fast and slower component in the decay of the electron current. We assume that O− ions are formed in the reaction of electrons with N2O and then react with H2 to give[Formula: see text]or with CO to give[Formula: see text]The addition of CH4 does not regenerate electrons since the reaction[Formula: see text]is thought to occur. Reaction 12 is in agreement with the fact that CO2 does not react with electrons in liquid argon.

Kinetics Of Thrombin, Antithrombin III And Heparin Interactions

1981 ◽  
Author(s):  
S T Olson ◽  
S A Evans ◽  
J D Shore
Keyword(s):  
Rate Constant ◽  
Antithrombin Iii ◽  
Heart Association ◽  
Slow Phase ◽  
Rapid Phase ◽  
Bimolecular Rate Constant ◽  
At Iii ◽  
Active Site Probe ◽  
Initial Binding ◽  
Kinetics Of

The rates of thrombin inactivation by AT III were studied by stopped-flow fluorimetry using p-aminobenzami- dine as an active site probe. p-Aminobenzamidine binds to thrombin with a of KD of 35 μM and a 50-fold fluorescence enhancement. The bimolecular rate constant for the thrombin-AT III reaction was 8.7 × 103 M-1 s-1 at 25° C and pH 7.4, with no diminished amplitude or evidence for a limiting rate at AT III concentrations as high as 10-4 M. Using lower AT III concentrations, an identical bimolecular rate constant was obtained by discontinuous assay of residual thrombin activity. Inactivation of thrombin by antithrombin III complexed with stoichiometric high affinity heparin at concentrations between 2.5 to 20 μM resulted in biphasic reactions: a rapid phase complete in less than 10 milliseconds and a slow phase with a rate constant of 4-6 s-1 . Relative amplitudes and slow phase rate constants showed slight changes over this AT III-heparin concentration range. These results are consistent with weak initial binding of AT III to thrombin in the absence of heparin (KD> 10-4 M), with a major part of the heparin rate enhancement due to a substantial decrease in the KD for the initial binding step. Supported by Michigan Heart Association and USPHS grant F32 HL06171-01.

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