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.

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.

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.

The Hydrolysis of Disubstituted Alkyl Phosphorochloridates and N,N,N′,N′-Tetra-stibstituted Phosphorodiamidic Chlorides in Water and Deuterium Oxide: Heat Capacity of Activation and Kinetic Solvent Isotope Effects

1973 ◽  
Vol 51 (4) ◽  
pp. 597-603 ◽  
Author(s):  
E. C. F. Ko ◽  
R. E. Robertson
Keyword(s):  
Heat Capacity ◽  
Thermodynamic Parameters ◽  
Alkyl Group ◽  
Deuterium Oxide ◽  
Isotope Effects ◽  
Potential Relationship ◽  
Mechanism Of Reaction ◽  
Solvent Isotope ◽  
Hydrolysis Of ◽  
Solvent Isotope Effects

The pseudo-thermodynamic parameters, ΔH≠, ΔS≠, and ΔCp≠ and the kinetic solvent isotope effects have been determined for the three alkyl-phosphorochloridates, where the alkyl group is ethylisopropyl and n-propyl; for tetra-methyl and tetra-ethyl phosphorodiamidic chlorides; the di-n-propyl and di-isopropyl analog, the di(isopropylmethylcarbinyl)phosphorochloridate and the tetra-ethylthiophosphorodiamidic chloride. These compounds have a potential relationship to compounds used as insecticides and as polymers. The mechanism of reaction is discussed on the basis of these data.

Studies in solvolysis. Part I. The neutral hydrolysis of some alkyl trifluoroacetates in water and deuterium oxide

1968 ◽  
Vol 46 (18) ◽  
pp. 2887-2894 ◽  
Author(s):  
June G. Winter ◽  
J. M. W. Scott
Keyword(s):  
Deuterium Oxide ◽  
Isotope Effects ◽  
Activation Process ◽  
Rate Data ◽  
Methyl Ethyl ◽  
Light Water ◽  
Carbonium Ion ◽  
Solvent Isotope ◽  
Hydrolysis Of ◽  
Solvent Isotope Effects

The temperature dependence of the rates of neutral hydrolysis of a series of alkyl trifluoroacetates (CF3COOR; R = methyl, ethyl, s-propyl, t-butyl) has been determined in both light and heavy water. From these studies the thermodynamic parameters (ΔH≠, ΔS≠) which characterize the activation process have been calculated. Sufficient rate data have been obtained in the case of the ethyl ester to calculate the heat capacity of activation (ΔCP≠) for the hydrolysis of this compound in light water. Both the entropies and enthalpies of activation as well as the solvent isotope effects are consistent with the proposal that the primary and secondary esters react by an acyl–oxygen BAc2 mechanism, in contrast to the tertiary ester, which appears to react either by a carbonium ion (SN1) process or by a route which combines both the BAc2 and SN1 paths.

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.

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.

scholarly journals A solvent-isotope-effect study of proton transfer during catalysis by Escherichia coli (lacZ) β-galactosidase

1990 ◽  
Vol 268 (2) ◽  
pp. 317-323 ◽  
Author(s):  
T Selwood ◽  
M L Sinnott
Keyword(s):  
Escherichia Coli ◽  
Isotope Effect ◽  
Kinetic Isotope Effect ◽  
Isotope Effects ◽  
Effect Study ◽  
Solvent Isotope Effect ◽  
Kinetic Isotope ◽  
Solvent Isotope ◽  
Paper Abstract ◽  
Hydrolysis Of

1. Michaelis-Menten parameters for the hydrolysis of 4-nitrophenyl β-D-galactopyranoside and 3,4-dinitrophenyl β-D-galactopyranoside Escherichia coli (lacZ) β-galactosidase were measured as a function of pH or pD (pL) in both 1H2O and 2H2O. 2. For hydrolysis of 4-nitrophenyl β-D-galactopyranoside by Mg2(+)-free enzyme, V is pL-independent below pL 9, but the V/Km-pL profile is sigmoid, the pK values shifting from 7.6 +/- 0.1 in 1H2O to 8.2 +/- 0.1 in 2H2O, and solvent kinetic isotope effects are negligible, in accord with the proposal [Sinnott, Withers & Viratelle (1978) Biochem. J. 175, 539-546] that glycone-aglycone fission without acid catalysis governs both V and V/Km. 3. V for hydrolysis of 4-nitrophenyl β-D-galactopyranoside by Mg2(+)-enzyme varies sigmoidally with pL, the pK value shifting from 9.19 +/- 0.09 to 9.70 +/- 0.07; V/Km shows both a low-pL fall, probably due to competition between Mg2+ and protons [Tenu, Viratelle, Garnier & Yon (1971) Eur. J. Biochem. 20, 363-370], and a high-pL fall, governed by a pK that shifts from 8.33 +/- 0.08 to 8.83 +/- 0.08. There is a negligible solvent kinetic isotope effect on V/Km, but one of 1.7 on V, which a linear proton inventory shows to arise from one transferred proton. 4. The variation of V and V/Km with pL is sigmoid for hydrolysis of 3,4-dinitrophenyl β-D-galactopyranoside by Mg2(+)-enzyme, with pK values showing small shifts, from 8.78 +/- 0.09 to 8.65 +/- 0.08 and from 8.7 +/- 0.1 to 8.9 +/- 0.1 respectively. There is no solvent isotope effect on V or V/Km for 3,4-dinitrophenyl β-D-galactopyranoside, despite hydrolysis of the galactosyl-enzyme intermediate governing V. 5. Identification of the ‘conformation change’ in the hydrolysis of aryl galactosides proposed by Sinnott & Souchard [(1973) Biochem. J. 133, 89-98] with the protolysis of the magnesium phenoxide arising from the action of enzyme-bound Mg2+ as an electrophilic catalyst rationalizes these data and also resolves the conflict between the proposals and the 18O kinetic-isotope-effect data reported by Rosenberg & Kirsch [(1981) Biochemistry 20, 3189-3196]. It should be noted that the actual Km values were determined to higher precision than can be estimated from the Figures in this paper.(ABSTRACT TRUNCATED AT 400 WORDS)

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