?-Secondary deuterium isotope effect and solvent isotope effects in catalysis by subtilisin BPN?

1990 ◽  
Vol 3 (4) ◽  
pp. 260-265 ◽  
Author(s):  
Ildiko M. Kovach ◽  
Son Do ◽  
Richard L. Schowen
Keyword(s):  
Isotope Effect ◽  
Isotope Effects ◽  
Deuterium Isotope Effect ◽  
Solvent Isotope ◽  
Solvent Isotope Effects

Solvent isotope effects in the oxidation of dipeptides by aqueous chlorine

1999 ◽  
Vol 77 (5-6) ◽  
pp. 997-1004 ◽  
Author(s):  
X L Armesto ◽  
M Canle L. ◽  
V García ◽  
J A Santaballa
Keyword(s):  
Isotope Effect ◽  
Deuterium Oxide ◽  
Isotope Effects ◽  
Second Step ◽  
Solvent Isotope Effect ◽  
General Base ◽  
Peptide Oxidation ◽  
Solvent Isotope ◽  
Hydrolysis Of ◽  
Solvent Isotope Effects

A kinetic study of the mechanism of oxidation of Ala-Gly and Pro-Gly by aqueous chlorine has been carried out. Among other experimental facts, the deuterium solvent isotope effects were used to clarify the mechanisms involved. In a first stage, N-chlorination takes place, and then the (N-Cl)-dipeptide decomposes through two possible mechanisms, depending on the acidity of the medium. The initial chlorination step shows a small isotope effect. In alkaline medium, two consecutive processes take place: first, the general base-catalyzed formation of an azomethine (β ca. 0.27), which has an inverse deuterium solvent isotope effect (kOH-/kOD- ~ 0.8). In a second step, the hydrolysis of the azomethine intermediate takes place, which is also general base-catalyzed, without deuterium solvent isotope effect, the corresponding uncatalyzed process having a normal deuterium solvent isotope effect (kH2O/kD2O ~ 2). In acid medium, the (N-Cl)-dipeptide undergoes disproportionation to a (N,N)-di-Cl-dipeptide, the very fast decomposition of the latter in deuterium oxide preventing a reliable estimation of the solvent isotope effect.Key words: chlorination, deuterium isotope effects, fractionation factors, peptide oxidation, water treatment.

Kinetic Solvent Isotope Effect for the Spontaneous Solvolysis Acetic and Propionic Anhydrides

1971 ◽  
Vol 49 (22) ◽  
pp. 3665-3670 ◽  
Author(s):  
R. E. Robertson ◽  
B. Rossall ◽  
W. A. Redmond
Keyword(s):  
Acetic Anhydride ◽  
Isotope Effect ◽  
Isotope Effects ◽  
Temperature Dependency ◽  
Solvent Isotope Effect ◽  
Propionic Anhydride ◽  
Solvent Isotope ◽  
Hydrolysis Of ◽  
Solvent Isotope Effects

The large kinetic solvent isotope effects for the neutral hydrolysis of acetic and propionic anhydride show unusual temperature dependency; the former passing through a maximum at about 15°, the latter showing a minimum at 30°. This unusual temperature dependency is the consequence of widely different values of the apparent ΔCp≠ in H2O and D2O: the value for acetic anhydride in H2O being −74 ± 2 cal deg−1 mol−1 but −32 ± 4 in D2O. The corresponding values for propionic anhydride being −31 ± 2 in H2O but −94 ± 10 in D2O. The implications of these differences are discussed.

Studies in Solvolysis. Part IV. Substituent and Solvent Isotope Effects in the Solvolysis of a Series of Benzyl Trifluoroacetates

1972 ◽  
Vol 50 (12) ◽  
pp. 1886-1890 ◽  
Author(s):  
June G. Winter ◽  
J. M. W. Scott
Keyword(s):  
Isotope Effect ◽  
Deuterium Oxide ◽  
Isotope Effects ◽  
The Other ◽  
Solvent Isotope Effect ◽  
Other Hand ◽  
Solvent Isotope ◽  
Hydrolysis Of ◽  
Solvent Isotope Effects

The rates of neutral hydrolysis of a series of 4-substituted benzyl trifluoroacetates 4-X-C6H4CH2OCOCF3, X = NO2, Cl, H, CH3, and OCH3 have been studied in water and deuterium oxide, both solvents containing 0.012 mol fraction of acetone. The alteration of the rates with the nature of the 4-substituent and the kinetic solvent isotope effect (k(H2O)/k(D2O)) are consistent with the proposal that the esters with X = NO2, Cl, H, and CH3 all react by an acyl–oxygen BAc2 mechanism. On the other hand, the same mechanistic criteria indicate that the 4-methoxybenzyl ester reacts by both the BAc2 and the SN1 alkyl–oxygen fission paths in equal amounts.

Kinetics and mechanism of acid-catalyzed hydrolysis of the diazo functional groups of 1-diazo-2-indanone and 2-diazo-1-indanone in aqueous solution

2005 ◽  
Vol 83 (9) ◽  
pp. 1202-1206 ◽  
Author(s):  
Yvonne Chiang ◽  
A Jerry Kresge ◽  
Oleg Sadovski ◽  
Xiaofeng Zeng ◽  
Yu Zhu
Keyword(s):  
Formic Acid ◽  
Isotope Effect ◽  
Isotope Effects ◽  
Diazo Compound ◽  
Acid Buffer ◽  
Buffer Solutions ◽  
Hydronium Ion ◽  
Solvent Isotope ◽  
Hydrolysis Of ◽  
Solvent Isotope Effects

Rates of hydrolysis of 1-diazo-2-indanone and 2-diazo-1-indanone were measured in dilute aqueous perchloric acid solutions using both H2O and D2O as the solvent, and rates of hydrolysis of the latter substrate were measured in dilute aqueous (H2O only) formic acid buffer solutions as well. The data for 1-diazo-2-indanone gave the hydronium ion catalytic coefficient kH+ = 5.7 × 10–3 (mol/L)–1 s–1 and the isotope effect kH+/kD+ = 2.9. The normal direction (kH/kD > 1) of this isotope effect was taken as evidence for a reaction mechanism involving rate-determining hydron transfer from the hydronium ion to the substrate's diazo carbon atom; followed by rapid displacement of diazo nitrogen by a water molecule, giving the observed 1-hydroxy-2-indanone product. The data for 2-diazo-1-indanone, on the other hand, gave a hydronium ion catalytic coefficient two orders of magnitude greater than the value for 1-diazo-2-indanone (kH+ = 5.9 × 10–1 (mol/L)–1 s–1), and an isotope effect near unity (kH+/kD+ = 1.2). It is argued that this isotope effect represents a situation in which diazo carbon hydronation and displacement of diazo nitrogen are each partly rate determining, a conclusion supported by incipient saturation of buffer catalysis in the formic acid buffer solutions. The 100-fold difference in hydronium ion catalytic coefficients for the two substrates is rationalized in terms of differing electron densities on the diazo carbon atoms.Key words: diazo compound hydrolysis, solution kinetics, acid catalysis, solvent isotope effects, buffer catalysis saturation.

scholarly journals Inverse Solvent Isotope Effects in Enzyme-Catalyzed Reactions

Molecules ◽  
2020 ◽  
Vol 25 (8) ◽  
pp. 1933
Author(s):  
Patrick L. Fernandez ◽  
Andrew S. Murkin
Keyword(s):  
Isotope Effect ◽  
Isotope Effects ◽  
Solvent Isotope Effect ◽  
Kinetic Isotope ◽  
Rate Limiting Step ◽  
Catalyzed Reactions ◽  
Enzyme Catalyzed Reactions ◽  
Solvent Isotope ◽  
Rate Limiting ◽  
Solvent Isotope Effects

Solvent isotope effects have long been used as a mechanistic tool for determining enzyme mechanisms. Most commonly, macroscopic rate constants such as kcat and kcat/Km are found to decrease when the reaction is performed in D2O for a variety of reasons including the transfer of protons. Under certain circumstances, these constants are found to increase, in what is termed an inverse solvent kinetic isotope effect (SKIE), which can be a diagnostic mechanistic feature. Generally, these phenomena can be attributed to an inverse solvent equilibrium isotope effect on a rapid equilibrium preceding the rate-limiting step(s). This review surveys inverse SKIEs in enzyme-catalyzed reactions by assessing their underlying origins in common mechanistic themes. Case studies for each category are presented, and the mechanistic implications are put into context. It is hoped that readers may find the illustrative examples valuable in planning and interpreting solvent isotope effect experiments.

Kinetic deuterium isotope effects and kinetic solvent isotope effects for the solvolyses in water and in water + acetonitrile mixtures related to a series of substituted benzyl nitrates

1980 ◽  
Vol 58 (20) ◽  
pp. 2142-2145 ◽  
Author(s):  
Mohammed Ahsan ◽  
Ross Elmore Robertson ◽  
Michael Jesse Blandamer ◽  
John Marshall William Scott
Keyword(s):  
Aqueous Solution ◽  
Benzene Ring ◽  
Isotope Effect ◽  
Isotope Effects ◽  
Bond Breaking ◽  
Relative Importance ◽  
Stage Process ◽  
Deuterium Isotope Effects ◽  
Solvent Isotope ◽  
Solvent Isotope Effects

In aqueous solution, the α-deuterium isotope effects in the solvolyses of benzyl nitrates derivatives depend on the nature of the substituent in the benzene ring. In addition, the isotope effect for some derivatives depends on mole fraction of added acetonitrile while for others the isotope effect is insensitive to solvent composition. However, the kinetic solvent isotope effects for para-methyl and meta-trifluoromethyl derivatives remain unchanged when acetonitrile is added. These observations are accounted for in terms of a model which describes the solvolytic reaction as a two-stage process and contrasts the relative importance of bond-making and bond-breaking.

Kinetic and solvent isotope effects in oxidation of halogen derivatives of tyramine catalyzed by monoamine oxidase A

2019 ◽  
Vol 167 (1) ◽  
pp. 49-54
Author(s):  
Małgorzata Pająk
Keyword(s):  
Monoamine Oxidase ◽  
Isotope Effect ◽  
Isotope Effects ◽  
Monoamine Oxidase A ◽  
Oxidative Deamination ◽  
Solvent Isotope Effect ◽  
Kinetic Isotope ◽  
Solvent Isotope ◽  
Derivatives Of ◽  
Solvent Isotope Effects

Abstract The isotope effects approach was used to elucidate the mechanism of oxidative deamination of 3′-halotyramines, catalyzed by monoamine oxidase A (EC 1.4.3.4). The numerical values of kinetic isotope effect (KIE) and solvent isotope effect (SIE) were established using a non-competitive spectrophotometric technique. Based upon KIE and SIE values, some of the mechanistic details of investigated reaction were discussed.

Medium isotope effect for isobutyrophenone in aqueous solution. Solvent isotope effects on carbonyl group hydration

1989 ◽  
Vol 67 (5) ◽  
pp. 792-793 ◽  
Author(s):  
J. R. Keeffe ◽  
A. J. Kresge
Keyword(s):  
Isotope Effect ◽  
Deuterium Oxide ◽  
Isotope Effects ◽  
Hydroxyl Group ◽  
Hydroxyl Groups ◽  
Solvent Isotope Effect ◽  
Fractionation Factor ◽  
Solvent Isotope ◽  
Solvent Isotope Effects ◽  
Fractionation Factors

A medium solvent isotope effect of Φ = 0.827 ± 0.013 was determined for transfer of isobutyrophenone from H2O to D2O. This result, in conjunction with the average solvent isotope effect on hydration of a number of carbonyl compounds, leads to [Formula: see text] as the fractionation factor for the hydroxyl group hydrogens of the hydration reactions' gem-diol products, which is consistent with the expectation that fractionation factors for uncharged hydroxyl groups should be unity. Keywords: isobutyrophenone, fractionation factors, solvent isotope effects, deuterium oxide.

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