Kinetic study on the reaction mechanism of pantothenase: existence of an acyl-enzyme intermediate and role of general acid catalysis

Biochemistry ◽  
1978 ◽  
Vol 17 (23) ◽  
pp. 4932-4938 ◽  
Author(s):  
R. Kalervo Airas
Keyword(s):  
Reaction Mechanism ◽  
Kinetic Study ◽  
Acid Catalysis ◽  
General Acid ◽  
Enzyme Intermediate

The kinetics and mechanism of the oxidation of mercaptoethanol by riboflavin

1977 ◽  
Vol 30 (6) ◽  
pp. 1387 ◽  
Author(s):  
JW Holden ◽  
L Main
Keyword(s):  
Kinetic Study ◽  
Acid Catalysis ◽  
Kinetics And Mechanism ◽  
Alternative Mechanism ◽  
Semiquinone Radical ◽  
Radical Intermediate ◽  
General Acid ◽  
Elimination Mechanism ◽  
Ph Range ◽  
Kinetic Form

Kinetic study of the oxidation of mercaptoethanol (RSH) by riboflavin (FlH) over the pH range 8.5-10.5 establishes that the rate is given by the term 0.036[FlH][RSH][RS-]]2 mol-2 s-1, there being no buffer catalysis. Any reactivity of the N 3-ionized riboflavin species (Fl-) is sufficiently low to be kinetically undetected. The kinetic form and lack of general acid catalysis are consistent with a nucleophilic (thiolate) 4a-addition-elimination mechanism previously proposed, but a possible alternative mechanism involving a flavin semiquinone (radical) intermediate is suggested.

scholarly journals Role of Carbonate Species on General Acid Catalysis of Bromide Oxidation by Hypochlorous Acid (HOCl) and Oxidation by Molecular Chlorine (Cl2)

2020 ◽  
Vol 54 (24) ◽  
pp. 16186-16194
Author(s):  
Samuel H. Brodfuehrer ◽  
David G. Wahman ◽  
Abdalrahman Alsulaili ◽  
Gerald E. Speitel ◽  
Lynn E. Katz
Keyword(s):  
Acid Catalysis ◽  
Hypochlorous Acid ◽  
Molecular Chlorine ◽  
General Acid ◽  
Carbonate Species

A KINETIC STUDY OF THE HYDROLYSIS OF BENZALANILINE

1953 ◽  
Vol 31 (4) ◽  
pp. 361-376 ◽  
Author(s):  
A. V. Willi ◽  
R. E. Robertson
Keyword(s):  
Kinetic Study ◽  
Acid Catalysis ◽  
Catalyst Concentration ◽  
Effect Of Substituents ◽  
General Acid ◽  
Acid Catalyzed ◽  
Interesting Special Case ◽  
Hydrolysis Of ◽  
Special Case

The rates of the acid catalyzed hydrolysis of a series of para substituted benzalanilines have been studied in 50/50 methanol–water in the presence of acetate buffers. Special and general acid catalysis were observed. The effect of para substituents on the rate is different for the charged and uncharged catalyst, and Hammett's relation cannot be applied. Similarly the effect of substituents on the Arrhenius constants for the two cases is different. The para dimethylamino derivative provides an interesting special case. For low buffer concentrations and in unbuffered solutions certain deviations were observed which show that the dependence of the rate on the catalyst concentration is more complicated than the equation[Formula: see text]

Rearrangement mechanisms for azoxypyridines and azoxypyridine N-oxides in the 100% H2SO4 region — The Wallach rearrangement story comes full circle

2009 ◽  
Vol 87 (8) ◽  
pp. 1127-1134 ◽  
Author(s):  
Erwin Buncel ◽  
Sam-Rok Keum ◽  
Srinivasan Rajagopal ◽  
Robin A. Cox
Keyword(s):  
Reaction Mechanism ◽  
Rate Constants ◽  
Acid Catalysis ◽  
Kinetic Studies ◽  
Linear Functions ◽  
Acidity Function ◽  
Full Circle ◽  
General Acid ◽  
Measurable Rate

Kinetic studies of the Wallach rearrangements of four azoxypyridines, four azoxypyridine N-oxides, and one azoxypyridine N-methiodide have been carried out in the 100% H2SO4 acidity region. For all of the β-isomers in the study the reactions proceeded at a spectrally measurable rate, and the log observed rate constants were found to be linear functions of the log H3SO4+ concentration, as previously found for azoxybenzene itself, suggesting that the reaction mechanism for these substrates is the same as that previously deduced for axozybenzene, i.e., a general-acid-catalysis A-SE2 process. For the α-azoxypyridines no reaction could be observed at all. The two α-azoxypyridine N-oxides in the study did react, albeit very slowly, but for these two compounds the log observed rate constants were not linear functions of the log H3SO4+ concentration, but were instead found to be linear in the H0 acidity function, which is known for the 100% H2SO4 acidity region. It follows that the reaction mechanism for these α-isomers is a different one, presumably an A1 process. This mechanism was proposed back in 1963 for azoxybenzene, but has never actually been observed for any substrate before the work reported in this study. Thus, the Wallach rearrangement story can be said to have come full circle.

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