pH-Rate Profile for Hydrolysis of 4-Nitrophenyl β-D-Glucopyranoside: Unimolecular, Bimolecular and Intramolecular Cleavage Mechanisms

Aromatic Substitution ◽

Solvent Isotope Effect ◽

Dissociative Mechanism ◽

Neighboring Group ◽

Rate Determining Step ◽

Rate Profile ◽

Solvent Isotope ◽

1,2-trans-Glycosides hydrolyze through different mechanisms at different pH values, but systematic studies are lacking. Here we report the pH-rate constant profile for the hydrolysis of 4-nitrophenyl β-D-glucoside. An inverse kinetic isotope effect of k(H3O+)/k(D3O+ = 0.65 in the acidic region indicates that the mechanism requires the formation of the conjugate acid of the substrate for the reaction to proceed, with heterolytic cleavage of the glycosidic C-O bond. Reactions in the pH-independent region exhibit general catalysis with a single proton in flight, a normal solvent isotope effect of kH/kD = 1.5, and when extrapolated to zero buffer concentration show a small solvent isotope effect k(H2O)/k(D2O) = 1.1, consistent with water attack through a dissociative mechanism. In the basic region, solvolysis in 18O-labelled water and H2O/MeOH mixtures allowed detection of bimolecular hydrolysis and neighboring group participation, with a minor contribution of nucleophilic aromatic substitution. Under mildly basic conditions, a bimolecular concerted mechanism is implicated through an inverse solvent isotope effect of k(HO–)/k(DO–) = 0.5 and a strongly negative entropy of activation (DS‡ = –13.6 cal mol–1 K–1). Finally, at high pH, an inverse solvent isotope effect of k(HO–)/k(DO–) = 0.6 indicates that the formation of 1,2-anhydrosugar is the rate determining step.

pH Dependent Mechanisms of Hydrolysis of 4-Nitrophenyl β-D-Glucoside

10.26434/chemrxiv.13735084.v3 ◽

2021 ◽

Author(s):

Amani Alhifthi ◽

Spencer Williams

Keyword(s):

Isotope Effect ◽

Aromatic Substitution ◽

Solvent Isotope Effect ◽

Dissociative Mechanism ◽

Neighboring Group ◽

Rate Determining Step ◽

Solvent Isotope ◽

A Minor ◽

1,2-trans-Glycosides hydrolyze through different mechanisms at different pH values, but systematic studies are lacking. Here we report the pH-rate constant profile for the hydrolysis of 4-nitrophenyl β-D-glucoside. An inverse kinetic isotope effect (k(H3O+)/k(D3O+) = 0.63) in the acidic region indicates that the mechanism requires the formation of the conjugate acid of the substrate for the reaction to proceed, with heterolytic cleavage of the glycosidic C-O bond. Reactions in the pH-independent region exhibit general catalysis with a single proton in flight, a normal solvent isotope effect of kH/kD = 1.5, and when extrapolated to zero buffer concentration show a small solvent isotope effect k(H2O)/k(D2O) = 1.1, consistent with water attack through a dissociative mechanism. In the basic region, solvolysis in 18O-labelled water and H2O/MeOH mixtures allowed detection of bimolecular hydrolysis and neighboring group participation, with a minor contribution of nucleophilic aromatic substitution. Under mildly basic conditions, a bimolecular concerted mechanism is implicated through an inverse solvent isotope effect of k(HO–)/k(DO–) = 0.5 and a strongly negative entropy of activation (DS‡ = –13.6 cal mol–1 K–1). Finally, at high pH, an inverse solvent isotope effect of k(HO–)/k(DO–) = 0.6 indicates that the formation of 1,2-anhydrosugar is the rate determining step.

pH Dependent Mechanisms of Hydrolysis of 4-Nitrophenyl β-D-Glucoside

10.26434/chemrxiv.13735084 ◽

2021 ◽

Author(s):

Amani Alhifthi ◽

Spencer Williams

Keyword(s):

Isotope Effect ◽

Aromatic Substitution ◽

Solvent Isotope Effect ◽

Dissociative Mechanism ◽

Neighboring Group ◽

Rate Determining Step ◽

Solvent Isotope ◽

A Minor ◽

1,2-trans-Glycosides hydrolyze through different mechanisms at different pH values, but systematic studies are lacking. Here we report the pH-rate constant profile for the hydrolysis of 4-nitrophenyl β-D-glucoside. An inverse kinetic isotope effect (k(H3O+)/k(D3O+) = 0.63) in the acidic region indicates that the mechanism requires the formation of the conjugate acid of the substrate for the reaction to proceed, with heterolytic cleavage of the glycosidic C-O bond. Reactions in the pH-independent region exhibit general catalysis with a single proton in flight, a normal solvent isotope effect of kH/kD = 1.5, and when extrapolated to zero buffer concentration show a small solvent isotope effect k(H2O)/k(D2O) = 1.1, consistent with water attack through a dissociative mechanism. In the basic region, solvolysis in 18O-labelled water and H2O/MeOH mixtures allowed detection of bimolecular hydrolysis and neighboring group participation, with a minor contribution of nucleophilic aromatic substitution. Under mildly basic conditions, a bimolecular concerted mechanism is implicated through an inverse solvent isotope effect of k(HO–)/k(DO–) = 0.5 and a strongly negative entropy of activation (DS‡ = –13.6 cal mol–1 K–1). Finally, at high pH, an inverse solvent isotope effect of k(HO–)/k(DO–) = 0.6 indicates that the formation of 1,2-anhydrosugar is the rate determining step.

pH Dependent Mechanisms of Hydrolysis of 4-Nitrophenyl β-D-Glucoside

10.26434/chemrxiv.13735084.v2 ◽

2021 ◽

Author(s):

Amani Alhifthi ◽

Spencer Williams

Keyword(s):

Isotope Effect ◽

Aromatic Substitution ◽

Solvent Isotope Effect ◽

Dissociative Mechanism ◽

Neighboring Group ◽

Rate Determining Step ◽

Solvent Isotope ◽

A Minor ◽

1,2-trans-Glycosides hydrolyze through a range of mechanisms under conditions of different pH, but systematic studies are lacking. Here we report the pH-rate constant profile for the hydrolysis of 4-nitrophenyl β-D-glucoside. An inverse kinetic isotope effect (k(H3O+)/k(D3O+) = 0.63) in the acidic region indicates that the mechanism requires the formation of the conjugate acid of the substrate for the reaction to proceed, with heterolytic cleavage of the glycosidic C-O bond. Reactions in the pH-independent region exhibited general catalysis with a single proton in flight with a normal solvent isotope effect of kH/kD = 1.5, and when extrapolated to zero buffer concentration show a small solvent isotope effect k(H2O)/k(D2O) = 1.1, which is consistent with water attack through a dissociative mechanism. In the basic region, solvolysis in 18O-labelled water and H2O/MeOH mixtures allowed detection of bimolecular hydrolysis and neighboring group participation, and to a minor degree, nucleophilic aromatic substitution. Under mildly basic conditions, a bimolecular dissociative mechanism is implicated through an inverse solvent isotope effect of k(HO–)/k(DO–) = 0.5 and a strongly negative entropy of activation (deltaS‡ = –13.6 cal mol–1 K–1). Finally, at high pH, an inverse solvent isotope effect of k(HO–)/k(DO–) = 0.6 indicates that the formation of 1,2-anhydrosugar is the rate determining step.

Unimolecular, bimolecular and intramolecular hydrolysis mechanisms of 4-nitrophenyl β-D-glucopyranoside

10.26434/chemrxiv.13735084.v6 ◽

2021 ◽

Author(s):

Amani Alhifthi ◽

Spencer Williams

Keyword(s):

Isotope Effect ◽

Aromatic Substitution ◽

Solvent Isotope Effect ◽

Dissociative Mechanism ◽

Neighboring Group ◽

Rate Determining Step ◽

Conjugate Acid ◽

Solvent Isotope ◽

A Minor

1,2-trans-Glycosides hydrolyze through different mechanisms at different pH values, but systematic studies are lacking. Here we report the pH-rate constant profile for the hydrolysis of 4-nitrophenyl β-D-glucoside. An inverse kinetic isotope effect of k(H3O+)/k(D3O+ = 0.65 in the acidic region indicates that the mechanism requires the formation of the conjugate acid of the substrate for the reaction to proceed, with heterolytic cleavage of the glycosidic C-O bond. Reactions in the pH-independent region exhibit general catalysis with a single proton in flight, a normal solvent isotope effect of kH/kD = 1.5, and when extrapolated to zero buffer concentration show a small solvent isotope effect k(H2O)/k(D2O) = 1.1, consistent with water attack through a dissociative mechanism. In the basic region, solvolysis in 18O-labelled water and H2O/MeOH mixtures allowed detection of bimolecular hydrolysis and neighboring group participation, with a minor contribution of nucleophilic aromatic substitution. Under mildly basic conditions, a bimolecular concerted mechanism is implicated through an inverse solvent isotope effect of k(HO–)/k(DO–) = 0.5 and a strongly negative entropy of activation (DS‡ = –13.6 cal mol–1 K–1). Finally, at high pH, an inverse solvent isotope effect of k(HO–)/k(DO–) = 0.6 indicates that the formation of 1,2-anhydrosugar is the rate determining step.

pH Dependent Mechanisms of Hydrolysis of 4-Nitrophenyl β-D-Glucoside

10.26434/chemrxiv.13735084.v1 ◽

2021 ◽

Author(s):

Amani Alhifthi ◽

Spencer Williams

Keyword(s):

Isotope Effect ◽

Aromatic Substitution ◽

Solvent Isotope Effect ◽

Dissociative Mechanism ◽

Neighboring Group ◽

Negative Entropy ◽

Entropy Of Activation ◽

Solvent Isotope ◽

1,2-trans-Glycosides hydrolyze through a range of mechanisms under conditions of different pH, but systematic studies are lacking. Here we report the pH-rate constant profile for the hydrolysis of 4-nitrophenyl β-D-glucoside. An inverse kinetic isotope effect (k(H3O+)/k(D3O+) = 0.63) in the acidic region indicates that the mechanism requires the formation of the conjugate acid of the substrate for the reaction to proceed, with heterolytic cleavage of the glycosidic C-O bond. Reactions in the pH-independent region extrapolated to zero buffer concentration show a small inverse solvent isotope effect k(H2O)/k(D2O) = 1.1 and a positive entropy of activation (DS‡ = 3.07 cal mol–1 K–1), which is consistent with water attack through a dissociative mechanism. In the basic region, solvolysis in 18O-labelled water and H2O/MeOH mixtures allowed detection of bimolecular hydrolysis and neighboring group participation, and to a minor degree, nucleophilic aromatic substitution. Under mildly basic conditions, a bimolecular dissociative mechanism is implicated through a solvent isotope effect of k(HO-)/k(DO-) = 0.5 and a strongly negative entropy of activation (DS‡ = –13.6 cal mol–1 K–1). Finally, at high pH, an inverse solvent isotope effect of k(HO-)/k(DO-) = 0.6 and a weakly negative entropy of activation (DS‡ = –5.5 cal mol–1 K–1) indicates that the formation of 1,2-anhydrosugar is the rate determining step.

Unimolecular, bimolecular and intramolecular hydrolysis mechanisms of 4-nitrophenyl β-D-glucopyranoside

10.26434/chemrxiv.13735084.v8 ◽

2021 ◽

Author(s):

Amani Alhifthi ◽

Spencer Williams

Keyword(s):

Isotope Effect ◽

Aromatic Substitution ◽

Solvent Isotope Effect ◽

Dissociative Mechanism ◽

Neighboring Group ◽

Rate Determining Step ◽

Conjugate Acid ◽

Solvent Isotope ◽

A Minor

1,2-trans-Glycosides hydrolyze through different mechanisms at different pH values, but systematic studies are lacking. Here we report the pH-rate constant profile for the hydrolysis of 4-nitrophenyl β-D-glucoside. An inverse kinetic isotope effect of k(H3O+)/k(D3O)+ = 0.65 in the acidic region indicates that the mechanism requires the formation of the conjugate acid of the substrate for the reaction to proceed, with heterolytic cleavage of the glycosidic C-O bond. Reactions in the pH-independent region exhibit general catalysis with a single proton in flight, a normal solvent isotope effect of kH/kD = 1.5, and when extrapolated to zero buffer concentration show a small solvent isotope effect k(H2O)/k(D2O) = 1.1, consistent with water attack through a dissociative mechanism. In the basic region, solvolysis in 18O-labelled water and H2O/MeOH mixtures allowed detection of bimolecular hydrolysis and neighboring group participation, with a minor contribution of nucleophilic aromatic substitution. Under mildly basic conditions, a bimolecular concerted mechanism is implicated through an inverse solvent isotope effect of k(HO–)/k(DO–) = 0.5 and a strongly negative entropy of activation (DS‡ = –13.6 cal mol–1 K–1). Finally, at high pH, an inverse solvent isotope effect of k(HO–)/k(DO–) = 0.6 indicates that the formation of 1,2-anhydrosugar is the rate determining step.

Unimolecular, bimolecular and intramolecular hydrolysis mechanisms of 4-nitrophenyl β-D-glucopyranoside

10.26434/chemrxiv.13735084.v7 ◽

2021 ◽

Author(s):

Amani Alhifthi ◽

Spencer Williams

Keyword(s):

Isotope Effect ◽

Aromatic Substitution ◽

Solvent Isotope Effect ◽

Dissociative Mechanism ◽

Neighboring Group ◽

Rate Determining Step ◽

Conjugate Acid ◽

Solvent Isotope ◽

A Minor

1,2-trans-Glycosides hydrolyze through different mechanisms at different pH values, but systematic studies are lacking. Here we report the pH-rate constant profile for the hydrolysis of 4-nitrophenyl β-D-glucoside. An inverse kinetic isotope effect of k(H3O+)/k(D3O)+ = 0.65 in the acidic region indicates that the mechanism requires the formation of the conjugate acid of the substrate for the reaction to proceed, with heterolytic cleavage of the glycosidic C-O bond. Reactions in the pH-independent region exhibit general catalysis with a single proton in flight, a normal solvent isotope effect of kH/kD = 1.5, and when extrapolated to zero buffer concentration show a small solvent isotope effect k(H2O)/k(D2O) = 1.1, consistent with water attack through a dissociative mechanism. In the basic region, solvolysis in 18O-labelled water and H2O/MeOH mixtures allowed detection of bimolecular hydrolysis and neighboring group participation, with a minor contribution of nucleophilic aromatic substitution. Under mildly basic conditions, a bimolecular concerted mechanism is implicated through an inverse solvent isotope effect of k(HO–)/k(DO–) = 0.5 and a strongly negative entropy of activation (DS‡ = –13.6 cal mol–1 K–1). Finally, at high pH, an inverse solvent isotope effect of k(HO–)/k(DO–) = 0.6 indicates that the formation of 1,2-anhydrosugar is the rate determining step.

Neutral Solvolysis of Acyl Carbon and the Temperature Dependence of the Kinetic Solvent Isotope Effect

Canadian Journal of Chemistry ◽

10.1139/v75-121 ◽

1975 ◽

Vol 53 (6) ◽

pp. 869-877 ◽

Cited By ~ 6

Author(s):

B. Rossall ◽

R. E. Robertson

Keyword(s):

Temperature Dependence ◽

Isotope Effect ◽

Solvent Isotope Effect ◽

Acyl Carbon ◽

Rate Of Hydrolysis ◽

Solvent Isotope ◽

Neutral Conditions ◽

The temperature dependence of the rate of hydrolysis of benzoic, phthalic, and succinic anhydrides have been determined in H2O and D2O under "neutral" conditions. Corresponding data have been obtained for methyl trifluoroacetate. While both series supposedly react by the same BAc2 mechanism, remarkable differences are made obvious by this investigation. Possible sources of such differences are proposed.

One-proton catalysis by the α-l-arabinofuranosidase III of Monilinia fructigena

Biochemical Journal ◽

10.1042/bj2540899 ◽

1988 ◽

Vol 254 (3) ◽

pp. 899-901 ◽

Cited By ~ 5

Author(s):

T Selwood ◽

M L Sinnott

Keyword(s):

Isotopic Composition ◽

Isotope Effect ◽

Solvent Isotope Effect ◽

Monilinia Fructigena ◽

Single Proton ◽

Solvent Isotope ◽

1. Michaelis-Menten parameters for the hydrolysis of p-nitrophenyl alpha-L-arabinofuranoside were measured as a function of pL (pH or pD) in both 1H2O and 2H2O. 2. The variation of both Vmax. and Vmax./Km with pL is sigmoid, the pK governing Vmax. shifting from 6.34 +/- 0.05 in 1H2O to 6.84 +/- 0.07 in 2H2O, and that governing Vmax./Km from 5.89 +/- 0.03 in 1H2O to 6.38 +/- 0.05 in 2H2O. 3. In the plateau regions there is a small inverse solvent isotope effect on Vmax./Km (0.92), and one of 1.45 on Vmax. 4. The variation of Vmax. with isotopic composition is strictly linear, indicating that the isotope effect arises from the transfer of a single proton.