Reversible hydration of pteridine. General acid-base catalysis, solvent deuterium isotope effects, and transition state characterization

1975 ◽  
Vol 97 (19) ◽  
pp. 5540-5546 ◽  
Author(s):  
Y. Pocker ◽  
D. Bjorkquist ◽  
W. Schaffer ◽  
C. Henderson
Keyword(s):  
Transition State ◽  
Isotope Effects ◽  
Base Catalysis ◽  
Acid Base ◽  
General Acid ◽  
Deuterium Isotope Effects ◽  
Reversible Hydration

Mechanism of hydration and isomerisation of 4-ethylidene-2,6-di-tert-butyl-2,5-cyclohexadien-1-one. Kinetics, acid-base catalysis and solvent deuterium isotope effects

1979 ◽  
Vol 44 (1) ◽  
pp. 110-122 ◽  
Author(s):  
Jiří Velek ◽  
Bohumír Koutek ◽  
Milan Souček
Keyword(s):  
Aqueous Medium ◽  
Rate Equation ◽  
Kinetic Data ◽  
Isotope Effects ◽  
Base Catalysis ◽  
Quinone Methide ◽  
Reaction Products ◽  
Acid Base ◽  
Deuterium Isotope Effects ◽  
Hydroxybenzyl Alcohol

Competitive hydration and isomerisation of the quinone methide I at 25 °C in an aqueous medium in the region of pH 2.4-13.0 was studied spectrophotometrically. The only reaction products in the studied range of pH are 4-hydroxybenzyl alcohol (II) and 4-hydroxystyrene (III). The form of the overall rate equation corresponds to a general acid-base catalysis. The mechanism of both reactions for three markedly separated pH regions is discussed on the basis of kinetic data and solvent deuterium effect.

scholarly journals Crystal Structures of Streptomyces Coelicolor Methylmalonyl-CoA Epimerase with Substrate or Transition State Analog Contradicts a Simple General Acid-Base Catalytic Mechanism

2021 ◽  
Author(s):  
Lee M Stunkard ◽  
Aaron B Benjamin ◽  
James Bower ◽  
Tyler Huth ◽  
Jeremy Lohman
Keyword(s):  
Transition State ◽  
Crystal Structures ◽  
Conformational Changes ◽  
Catalytic Mechanism ◽  
Streptomyces Coelicolor ◽  
Base Catalysis ◽  
Acid Base ◽  
Transition State Analog ◽  
Catalytic Residues ◽  
General Acid

Crystal structures of Streptomyces coelicolor methylmalonyl-CoA epimerase in the holo-form, with substrate or the putative transition state analog, 2-nitroproionyl-CoA. The proposed catalytic mechanism is general acid-base catalysis. The proposed catalytic residues are too far from the substrate or analog, unless conformational changes take place or some other mechanism is used. <br>

Do Enzymes Change the Nature of Transition States? Mapping the Transition State for General Acid−Base Catalysis of a Serine Protease‡

Biochemistry ◽  
2003 ◽  
Vol 42 (36) ◽  
pp. 10545-10553 ◽  
Author(s):  
Richard R. Bott ◽  
Gina Chan ◽  
Blanca Domingo ◽  
Grant Ganshaw ◽  
Constance Y. Hsia ◽  
...  
Keyword(s):  
Transition State ◽  
Serine Protease ◽  
Transition States ◽  
Base Catalysis ◽  
Acid Base ◽  
General Acid

scholarly journals Crystal Structures of Streptomyces Coelicolor Methylmalonyl-CoA Epimerase with Substrate or Transition State Analog Contradicts a Simple General Acid-Base Catalytic Mechanism

2021 ◽  
Author(s):  
Lee M Stunkard ◽  
Aaron B Benjamin ◽  
James Bower ◽  
Tyler Huth ◽  
Jeremy Lohman
Keyword(s):  
Transition State ◽  
Crystal Structures ◽  
Conformational Changes ◽  
Catalytic Mechanism ◽  
Streptomyces Coelicolor ◽  
Base Catalysis ◽  
Acid Base ◽  
Transition State Analog ◽  
Catalytic Residues ◽  
General Acid

Crystal structures of Streptomyces coelicolor methylmalonyl-CoA epimerase in the holo-form, with substrate or the putative transition state analog, 2-nitroproionyl-CoA. The proposed catalytic mechanism is general acid-base catalysis. The proposed catalytic residues are too far from the substrate or analog, unless conformational changes take place or some other mechanism is used. <br>

Berechnung kinetischer Isotopeneffekte für die Reaktion von Methyljodid mit Cyanid-Ion

1966 ◽  
Vol 21 (9) ◽  
pp. 1377-1384
Author(s):  
A. V. Willi
Keyword(s):  
Transition State ◽  
Secular Equation ◽  
Isotope Effects ◽  
Force Constants ◽  
Bond Breaking ◽  
Bending Force ◽  
A Value ◽  
Order Of Magnitude ◽  
Deuterium Isotope Effects ◽  
The Difference

Kinetic carbon-13 and deuterium isotope effects are calculated for the SN2 reaction of CH3I with CN-. The normal vibrational frequencies of CH3I, the transition state I · · · CH3 · · · CN, and the corresponding isotope substituted reactants and transition states are evaluated from the force constants by solving the secular equation on an IBM 7094 computer.Values for 7 force constants of the planar CH3 moiety in the transition state (with an sp2 C atom) are obtained by comparison with suitable stable molecules. The stretching force constants related to the bonds being broken or newly formed (fCC, fCC and the interaction between these two stretches, /12) are chosen in such a way that either a zero or imaginary value for νʟ≠ will result. Agreement between calculated and experimental methyl-C13 isotope effects (k12/ k13) can be obtained only in sample calculations with sufficiently large values of f12 which lead to imaginary νʟ≠ values. Furthermore, the difference between fCI and fCC must be small (in the order of 1 mdyn/Å). The bending force constants, fHCI and fHCC, exert relatively little influence on k12/k13. They are important for the D isotope effect, however. As soon as experimental data on kH/kD are available it will be possible to derive a value for fHCC in the transition state if fHCI is kept constant at 0.205 mdynA, and if fCI, fCC and f12 are held in a reasonable order of magnitude. There is no agreement between experimental and calculated cyanide-C13 isotope effects. Possible explanations are discussed. — Since fCI and fCC cannot differ much it must be concluded that the transition state is relatively “symmetric”, with approximately equal amounts of bond making and bond breaking.

General acid base catalysis

1940 ◽  
pp. 204-248 ◽  
Author(s):  
R. P. Bell
Keyword(s):  
Base Catalysis ◽  
Acid Base ◽  
General Acid
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