1247. Hydrogen isotope effects in olefin hydration. The relationship of isotope effects to the mechanism of proton transfer from the hydronium ion

1965 ◽  
pp. 6718 ◽  
Author(s):  
V. Gold ◽  
M. A. Kessick
Keyword(s):  
Proton Transfer ◽  
Hydrogen Isotope ◽  
Isotope Effects ◽  
Hydronium Ion ◽  
Relationship Of ◽  
The Relationship

Vinyl ether hydrolysis. XXIV. 1-Methoxycyclooctene and the question of reversibility of the carbon protonation step

1991 ◽  
Vol 69 (1) ◽  
pp. 84-87 ◽  
Author(s):  
A. J. Kresge ◽  
Y. Yin
Keyword(s):  
Reaction Mechanism ◽  
Proton Transfer ◽  
Vinyl Ether ◽  
Isotope Effects ◽  
Hydrolysis Rate ◽  
Hydronium Ion ◽  
Mineral Acids ◽  
Dilute Aqueous Solutions ◽  
Solvent Isotope ◽  
Hydrolysis Of

An argument is presented which suggests that hydrolysis of the vinyl ether group of 1-methoxycyclooctene may occur by reversible proton transfer from a catalyzing acid to the β-carbon atom of the substrate, instead of by the conventional reaction mechanism in which this proton transfer is rate determining and not reversible. Hydrolysis of this substrate is then examined by measuring rates of reaction in dilute aqueous solutions of strong mineral acids (perchloric and hydrochloric) as well as in buffer solutions of seven carboxylic acids, biphosphate ion, and 1,1,1,3,3,3-hexafluoro-2-propanol. General acid catalysis is observed and a Brønsted relation with the exponent α = 0.73 is constructed. That, plus the isotope effects kH/kD = 2.9 and 6.0 for catalysis by hydronium ion and acetic acid respectively, as well as the lack of deuterium incorporation into the substrate when the reaction is carried out in D2O with D2PO4−/DPO42− buffer at pD = 8, show that carbon protonation of the substrate is not reversible and that the conventional reaction mechanism is operative. Key words: 1-methoxycyclooctene, vinyl ether hydrolysis, rate-determining proton transfer, Brønsted relation, solvent isotope effect.

scholarly journals Activation of the Proton Transfer Pathway in Catalysis by Iron Superoxide Dismutase

2002 ◽  
Vol 277 (51) ◽  
pp. 49282-49286 ◽  
Author(s):  
William B. Greenleaf ◽  
David N. Silverman
Keyword(s):  
Superoxide Dismutase ◽  
Proton Transfer ◽  
Hydrogen Isotope ◽  
Pulse Radiolysis ◽  
Ternary Complex ◽  
Isotope Effects ◽  
Order Rate Constant ◽  
Proton Acceptor ◽  
Primary Amines ◽  
Iron Superoxide Dismutase

Catalysis byEscherichia coliandPorphyromonas gingivalisiron superoxide dismutase was activated by addition of primary amines, as measured by pulse radiolysis and stopped-flow spectrophotometry. This activation was saturable for most amines investigated, and a free energy plot of the apparent second-order rate constant of activation was linear as a function of the pKaof the amine, indicating activation by proton transfer. Amines provide an alternate rather than the only pathway for proton transfer, and catalysis was appreciable in the absence of amines. Solvent hydrogen isotope effects were near unity for amine activation, which is consistent with rate-contributing proton transfer if the pKaof the proton acceptor on the enzyme is not in the region of the pKavalues of the amines studied, from 7.8 to 10.6. The activation of catalysis by these amines was uncompetitive with respect to superoxide, interpreted as proton transfer in a ternary complex of amine with the enzyme-bound peroxide dianion.

Vinyl ether hydrolysis. 9. Isotope effects on proton transfer from the hydronium ion

1977 ◽  
Vol 99 (22) ◽  
pp. 7228-7233 ◽  
Author(s):  
A. J. Kresge ◽  
D. S. Sagatys ◽  
H. L. Chen
Keyword(s):  
Proton Transfer ◽  
Vinyl Ether ◽  
Isotope Effects ◽  
Hydronium Ion
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