Evidence for a rate-determining solvation change in methyl transfer to water. Solvent dependence of water-deuterium oxide kinetic isotope effects

1986 ◽  
Vol 108 (11) ◽  
pp. 2960-2968 ◽  
Author(s):  
Joseph L. Kurz ◽  
Jasun. Lee ◽  
Mark E. Love ◽  
Susan. Rhodes
Keyword(s):  
Deuterium Oxide ◽  
Isotope Effects ◽  
Kinetic Isotope Effects ◽  
Water Solvent ◽  
Kinetic Isotope ◽  
Methyl Transfer ◽  
Solvent Dependence

Theoretical simulation of Brønsted correlations for proton transfer and methyl transfer: the significance of the Brønsted coefficient β

1999 ◽  
Vol 77 (5-6) ◽  
pp. 830-841 ◽  
Author(s):  
Ian H Williams ◽  
Paul A Austin
Keyword(s):  
Proton Transfer ◽  
Isotope Effects ◽  
Kinetic Isotope Effects ◽  
Molecular Orbital Calculations ◽  
Theoretical Simulation ◽  
Kinetic Isotope ◽  
Methyl Transfer ◽  
Equilibrium Relationship ◽  
Substituted Pyridines ◽  
Very High

Brønsted correlations for proton transfer and methyl transfer between pairs of mimicked 4-substituted pyridines have been simulated by means of AM1 molecular orbital calculations. The enthalpies of activation and of reaction are well correlated by the Marcus relation. The Brønsted correlation is markedly curved for proton transfer for which the Marcus intrinsic barrier is very low (~ 5 kJ mol-1). Conversely, the Brønsted correlation is almost imperceptibly curved for methyl transfer for which the Marcus intrinsic barrier is very high (~ 152 kJ mol-1). The slope of the Brønsted correlation provides an approximate measure of the position of the transition structure along the reaction coordinate between the reactant and product encounter complexes. Primary kinetic isotope effects for proton transfer show a broad maximum, centered on ΔHrxn = 0, when plotted against reaction exo/endothermicity only if computed with respect to isolated acids and bases, but intracomplex kinetic isotope effects show a maximum displaced significantly towards the endothermic proton transfers.Key words: Brønsted correlation, rate-equilibrium relationship, transition state, isotope effect.

QM/MM Determination of Kinetic Isotope Effects for COMT-Catalyzed Methyl Transfer Does Not Support Compression Hypothesis

2004 ◽  
Vol 126 (28) ◽  
pp. 8634-8635 ◽  
Author(s):  
Giuseppe D. Ruggiero ◽  
Ian H. Williams ◽  
Maite Roca ◽  
Vicent Moliner ◽  
Iñaki Tuñón
Keyword(s):  
Isotope Effects ◽  
Kinetic Isotope Effects ◽  
Kinetic Isotope ◽  
Methyl Transfer

scholarly journals Horseradish peroxidase. XXIX. Reactions in water and deuterium oxide: cyanide binding, compound I formation, and reactions of compounds I and II with ferrocyanide

1978 ◽  
Vol 56 (22) ◽  
pp. 2844-2852 ◽  
Author(s):  
H. Brian Dunford ◽  
W. Donald Hewson ◽  
Håkan Steiner
Keyword(s):  
Hydrogen Peroxide ◽  
Horseradish Peroxidase ◽  
Kinetic Isotope Effect ◽  
Deuterium Oxide ◽  
Isotope Effects ◽  
Kinetic Isotope Effects ◽  
Compound I ◽  
Kinetic Isotope ◽  
Cyanide Binding ◽  
Compound Ii

The kinetics of the reactions of hydrogen peroxide and cyanide with native horseradish peroxidase, as well as reactions of compounds I and II with ferrocyanide have been studied in ordinary water and in deuterium oxide at 25 °C and ionic strength 0.11 using a stopped-flow apparatus. Rate constants for all reactions were measured over a wide range of acidity in both solvents from which equilibrium and kinetic isotope effects were evaluated. Protonation of an ionizable group on the enzyme with a pKa value of 4.15 ± 0.05 in water inhibits the reactions with both hydrogen peroxide and cyanide. A significant kinetic isotope effect, kH/kD = 1.6 ± 0.1, was measured for compound I formation whereas no significant kinetic isotope effect was found for cyanide binding. On the basis of these findings, a partial mechanism for compound I formation is proposed in which the group of pKa 4.15 plays a crucial role. The pH dependencies of the ferrocyanide reaction in the pH interval 4.5–10.8 confirmed the role of an acid group with a pKa of 5.2 for compound I and for compound II a pKa of 8.6 and another with a value lower than that encompassed by the pH range of the study. Equilibrium isotope effects were found but no kinetic isotope effects for either the reaction of compound I or of compound II This suggests that there are no rate-limiting proton transfers in the reactions between ferrocyanide and compounds I and II of horseradish peroxidase. The only reducing substrates which exhibit positive kH/kD values possess a labile proton.

Influence of Compression upon Kinetic Isotope Effects for SN2 Methyl Transfer:  A Computational Reappraisal

2000 ◽  
Vol 122 (44) ◽  
pp. 10895-10902 ◽  
Author(s):  
Vicent Moliner ◽  
Ian H. Williams
Keyword(s):  
Isotope Effects ◽  
Kinetic Isotope Effects ◽  
Kinetic Isotope ◽  
Methyl Transfer

scholarly journals Solvent Dependence of Primary Deuterium Kinetic Isotope Effects for Base-Catalyzed 1,3-Proton Transfer in the Indene System.

1990 ◽  
Vol 44 ◽  
pp. 845-850 ◽  
Author(s):  
Anita Hussénius ◽  
Olle Matsson ◽  
Bengt Långström ◽  
G. Alberti ◽  
M. Nielsen ◽  
...  
Keyword(s):  
Proton Transfer ◽  
Isotope Effects ◽  
Kinetic Isotope Effects ◽  
Kinetic Isotope ◽  
Solvent Dependence

scholarly journals Influence of Equatorial CH⋅⋅⋅O Interactions on Secondary Kinetic Isotope Effects for Methyl Transfer

2016 ◽  
Vol 55 (9) ◽  
pp. 3192-3195 ◽  
Author(s):  
Philippe B. Wilson ◽  
Ian H. Williams
Keyword(s):  
Isotope Effects ◽  
Kinetic Isotope Effects ◽  
Kinetic Isotope ◽  
Methyl Transfer

Kinetic Isotope Effects of Deuterium Oxide on Several α-Chymotrypsin-catalyzed Reactions

1962 ◽  
Vol 84 (13) ◽  
pp. 2570-2576 ◽  
Author(s):  
Myron L. Bender ◽  
Gordon A. Hamilton
Keyword(s):  
Deuterium Oxide ◽  
Isotope Effects ◽  
Kinetic Isotope Effects ◽  
Kinetic Isotope ◽  
Catalyzed Reactions
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