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.

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.

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.

Solvent and substrate isotope effects on the enolization and carbon-acid ionization of isobutyrophenone

1996 ◽  
Vol 74 (12) ◽  
pp. 2481-2486 ◽  
Author(s):  
J.R. Keeffe ◽  
A.J. Kresge
Keyword(s):  
Isotope Effect ◽  
Isotope Effects ◽  
Isotopic Fractionation ◽  
Medium Effect ◽  
Solvent Isotope Effect ◽  
Fractionation Factor ◽  
Solvent Isotope ◽  
Carbon Acid ◽  
Fractionation Factors ◽  
Acid Ionization

Bromine scavenging was used to measure rates of acid-catalyzed enolization of isobutyrophenone in H2O and in D2O solution and of isobutyrophenone-α-d in D2O solution. The results provide the solvent isotope effect kH +/kD + = 0.56 and the substrate isotope effect kH/kD = 6.2 on the enolization reaction, both of which are consistent with the generally accepted mechanism for this process. The present results in combination with literature information also provide the solvent isotope effect on the enolization equilibrium, KE(H2O)/KE(D2O) = 0.92, and the solvent isotope effect on the ionization of isobutyrophenone as a carbon acid, kaK(H2O)/kaK(D2O) = 5.4, as well as the product of isotopic fractionation factor and medium effect, [Formula: see text], for isobutyrophenone enol and the medium effect, Φ = 0.47, for its enolate ion. The isotope effect on KE is the first ever determined for the keto–enol equilibrium of a simple aldehyde or ketone; its near-unit value is consistent with expectation on the basis of fractionation factors for the species involved. Key words: isobutyrophenone, keto–enol equilibrium, carbon-acid ionization, solvent isotope effects, isotopic fractionation factors.

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.

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.

SOLVOLYSIS IN HYDROGEN AND DEUTERIUM OXIDE: IV. HALIDES WITH NEIGHBORING GROUPS

1961 ◽  
Vol 39 (11) ◽  
pp. 2155-2162 ◽  
Author(s):  
P. M. Laughton ◽  
R. E. Robertson
Keyword(s):  
Deuterium Oxide ◽  
Isotope Effects ◽  
Solvation Shell ◽  
Hydroxyl Group ◽  
Activation Process ◽  
Anchimeric Assistance ◽  
Solvent Isotope ◽  
Hydrolysis Of ◽  
Related Compounds ◽  
Solvent Isotope Effects

Rate data for the hydrolysis of a series of halohydrins and related compounds in light and heavy water are reported. The solvent isotope effects [Formula: see text] from these measurements fall into three groups compared with those of simple halides. Thus the presence of a hydroxyl group in proximity to the seat of reaction may lead to increased, decreased, or normal solvent isotope ratios. The abnormal ratios can be interpreted in terms of the effect of anchimeric assistance on the solvation shell in the activation process.

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.

Sauerstoffisotopieeffekte und Hydratstruktur von Alkalihalogenid-Lösungen in H2O und D2O / Oxygen Isotope Effects and Hydrate Structure of Alkali Halide Solutions in H2O and D2O

1973 ◽  
Vol 28 (2) ◽  
pp. 137-141 ◽  
Author(s):  
D. Götz ◽  
K. Heinzinger
Keyword(s):  
Oxygen Isotope ◽  
Oxygen Isotopes ◽  
Alkali Halide ◽  
Isotope Effects ◽  
Bulk Water ◽  
Hydration Water ◽  
Solvent Isotope Effect ◽  
Anion Effect ◽  
Solvent Isotope ◽  
Fractionation Factors

The fractionation of the oxygen isotopes in solutions of LiCl, NaCl. KCl, KBr, KJ and CsCl with H2O and D2O as solvent has been measured at 25 °C by means of the CO2-equilibration technique. As opposed to earlier measurements a slight anion dependence for the potassium halides has been found in H2O. This anion effect is much more pronounced in D2O. It even leads to a change in the directions of the 180 enrichment between cationic hydration water and bulk water for KCl and KBr. The absolute values of the fractionation factors for LiCl and CsCl, which differ in sign in H2O in agreement with positive and negative cationic hydration, respectively, as known from other kinds of measurements, is increased for LiCl and decreased for CsCl in D2O. There is no fractionation of the oxygen isotopes between hydration water and bulk water in both solvents for NaCl.The solvent isotope effect is explained by the stronger anion influence on the structure of the bulk water in D2O as compared with H2O. This stronger influence is expected because of the higher structural order in D2O than in H2O at the same temperature.

?-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
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