scholarly journals The kinetics of formation of horseradish peroxidase compound I by reaction with peroxobenzoic acids. pH and peroxo acid substituent effects

1976 ◽  
Vol 157 (1) ◽  
pp. 247-253 ◽  
Author(s):  
D M Davies ◽  
P Jones ◽  
D Mantle
Keyword(s):  
Horseradish Peroxidase ◽  
Active Site ◽  
Rate Constants ◽  
Ph Effect ◽  
Substituent Effects ◽  
Nucleophilic Attack ◽  
Compound I ◽  
Active Intermediate ◽  
Kinetics Of Formation ◽  
Kinetics Of

1. The kinetics of formation of horseradish peroxidase Compound I were studied by using peroxobenzoic acid and ten substituted peroxobenzoic acids as substrates. Kinetic data for the formation of Compound I with H2O2 and for the reaction of deuteroferrihaem with H2O2 and peroxobenzoic acids, to form a peroxidatically active intermediate, are included for comparison. 2. The observed second-order rate constants for the formation of Compound I with peroxobenzoic acids decrease with increasing pH, in the range pH 5-10, in contrast with pH-independence of the reaction with H2O2. The results imply that the formation of Compound I involves a reaction between the enzyme and un-ionized hydroperoxide molecules. 3. The maximal rate constants for Compound I formation with unhindered peroxobenzoic acids exceed that for H2O2. Peroxobenzoic acids with bulky ortho substituents show marked adverse steric effects. The pattern of substituent effects does not agree with expectations for an electrophilic oxidation of the enzyme by peroxoacid molecules in aqueous solution, but is in agreement with that expected for a reaction involving nucleophilic attack by peroxo anions. 4. Possible reaction mechanisms are considered by which the apparent conflict between the pH-effect and substituent-effect data may be resolved. A model in which it is postulated that a negatively charged ‘electrostatic gate’ controls access of substrate to the active site and may also activate substrate within the active site, provides the most satisfactory explanation for both the present results and data from the literature.

Kinetics of the oxidation of reduced nicotinamide adenine dinucleotide by horseradish peroxidase compounds I and II

1986 ◽  
Vol 64 (4) ◽  
pp. 323-327 ◽  
Author(s):  
Mohammed A. Kashem ◽  
H. Brian Dunford
Keyword(s):  
Horseradish Peroxidase ◽  
Active Site ◽  
Nicotinamide Adenine Dinucleotide ◽  
Ph Dependence ◽  
Transient State ◽  
Nicotinamide Adenine ◽  
Compound I ◽  
Single Ionization ◽  
Reduced Nicotinamide Adenine Dinucleotide ◽  
Kinetics Of

The transient state kinetics of the oxidation of reduced nicotinamide adenine dinucleotide (NADH) by horseradish peroxidase compound I and II (HRP-I and HRP-II) was investigated as a function of pH at 25.0 °C in aqueous solutions of ionic strength 0.11 using both a stopped-flow apparatus and a conventional spectrophotometer. In agreement with studies using many other substrates, the pH dependence of the HRP-I–NADH reaction can be explained in terms of a single ionization of pKa = 4.7 ± 0.5 at the active site of HRP-I. Contrary to studies with other substrates, the pH dependence of the HRP-H–NADH reaction can be interpreted in terms of a single ionization with pKa of 4.2 ± 1.4 at the active site of HRP-II. An apparent reversibility of the HRP-II–NADH reaction was observed. Over the pH range of 4–10 the rate constant for the reaction of HRP-I with NADH varied from 2.6 × 105 to5.6 × 102 M−1 s−1 and of HRP-II with NADH varied from 4.4 × 104 to 4.1 M−1 s−1. These rate constants must be taken into consideration to explain quantitatively the oxidase reaction of horseradish peroxidase with NADH.

scholarly journals Structure–property Effects in the Generation of Transient Aqueous Benzoic Acid Anhydrides by Carbodiimide Fuels

2019 ◽  
Author(s):  
Lasith Kariyawasam ◽  
Julie Kron ◽  
Run Jiang ◽  
André Sommer ◽  
Scott Hartley
Keyword(s):  
Atp Hydrolysis ◽  
Substituent Effects ◽  
Coupled Processes ◽  
Dissipative Systems ◽  
Nonequilibrium Systems ◽  
Structure Property ◽  
Ethylcarbodiimide Hydrochloride ◽  
Kinetics Of Formation ◽  
Acid Anhydrides ◽  
Kinetics Of

<div>The design of dissipative systems, which operate out-of-equilibrium by consuming chemical fuels, is challenging. As yet, there are few examples of privileged fuel chemistry that can be broadly applied in abiotic systems in the same way that ATP hydrolysis is exploited throughout biochemistry. The key issue is that designing nonequilibrium systems is inherently about balancing the relative rates of coupled processes. The use of carbodiimides as fuels to generate transient aqueous carboxylic anhydrides has recently been used in examples of new nonequilibrium materials and supramolecular assemblies. Here, we explore the kinetics of formation and decomposition of a series of benzoic anhydrides generated from the corresponding acids and EDC under prototypical conditions (EDC = <i>N</i>-(3-dimethylaminopropyl)-<i>N</i>′-ethylcarbodiimide hydrochloride). The reactions can be described by a simple mechanism that merges known behavior for the two processes independently. Structure–property effects in these systems are dominated by differences in anhydride decomposition rate. The kinetic parameters allow trends in concentration-dependent properties to be simulated, such as reaction lifetimes, peak anhydride concentrations, and efficiencies (i.e., total anhydride produced per equivalent of carbodiimide). For key properties there are diminishing returns with the addition of increasing amounts of fuel. This is particularly significant for the lifetimes, where substituent effects exert a much greater influence than fuel quantity under typical conditions. These results should provide useful guidelines for the design of functional systems making use of this chemistry.</div><div><br></div>

Rate constants for reactions of horseradish peroxidase compounds I and II with 4-substituted arylboronic acids

1994 ◽  
Vol 72 (10) ◽  
pp. 2159-2162 ◽  
Author(s):  
Weimei Sun ◽  
Xiaoying Ji ◽  
Larry J. Kricka ◽  
H. Brian Dunford
Keyword(s):  
Horseradish Peroxidase ◽  
Rate Constants ◽  
Compound I ◽  
Arylboronic Acid ◽  
Experimental Conditions ◽  
Kinetic Measurements ◽  
Arylboronic Acids ◽  
Total Ionic Strength ◽  
Compound Ii ◽  
Catalyzed Oxidation

The rate constants for the reactions of horseradish peroxidase compound I (k1) and compound II (k2) with three 4-substituted arylboronic acids, which enhance chemiluminescence in the horseradish peroxidase catalyzed oxidation of luminol by hydrogen peroxide, were determined at pH 8.6, total ionic strength 0.11 M, using stopped-flow kinetic measurements. For comparison, the rate constants of the reactions of 4-iodophenol with compounds I and II were also determined under the same experimental conditions. The three arylboronic acid derivatives and their rate constants are: 4-biphenylboronic acid, k1 = (1.21 ± 0.08) × 106 M−1 s−1, k2 = (4.6 ± 0.2) × 105 M−1 s−1; 4-bromophenylboronic acid, k1 = (5.5 ± 0.2) × 104 M−1 s−1, k2 = (3.6 ± 0.2) × 104 M−1 s−1; and 4-iodophenylboronic acid, k1 = (1.1 ± 0.2) × 105 M−1 s−1, k2 = (1.3 ± 0.1) × 104 M−1 s−1. 4-Biphenylboronic acid, which shows comparable luminescent enhancement to 4-iodophenol, has the highest reactivity in the reduction of both compounds I and II among the three arylboronic acid derivatives tested.

scholarly journals Structure–property Effects in the Generation of Transient Aqueous Benzoic Acid Anhydrides by Carbodiimide Fuels

2019 ◽  
Author(s):  
Lasith Kariyawasam ◽  
Julie Kron ◽  
André Sommer ◽  
Scott Hartley
Keyword(s):  
Atp Hydrolysis ◽  
Substituent Effects ◽  
Coupled Processes ◽  
Dissipative Systems ◽  
Nonequilibrium Systems ◽  
Structure Property ◽  
Ethylcarbodiimide Hydrochloride ◽  
Kinetics Of Formation ◽  
Acid Anhydrides ◽  
Kinetics Of

<div>The design of dissipative systems, which operate out-of-equilibrium by consuming chemical fuels, is challenging. As yet, there are few examples of privileged fuel chemistry that can be broadly applied in abiotic systems in the same way that ATP hydrolysis is exploited throughout biochemistry. The key issue is that designing nonequilibrium systems is inherently about balancing the relative rates of coupled processes. The use of carbodiimides as fuels to generate transient aqueous carboxylic anhydrides has recently been used in examples of new nonequilibrium materials and supramolecular assemblies. Here, we explore the kinetics of formation and decomposition of a series of benzoic anhydrides generated from the corresponding acids and EDC under prototypical conditions (EDC = <i>N</i>-(3-dimethylaminopropyl)-<i>N</i>′-ethylcarbodiimide hydrochloride). The reactions can be described by a simple mechanism that merges known behavior for the two processes independently. Structure–property effects in these systems are dominated by differences in anhydride decomposition rate. The kinetic parameters allow trends in concentration-dependent properties to be simulated, such as reaction lifetimes, peak anhydride concentrations, and efficiencies (i.e., total anhydride produced per equivalent of carbodiimide). For key properties there are diminishing returns with the addition of increasing amounts of fuel. This is particularly significant for the lifetimes, where substituent effects exert a much greater influence than fuel quantity under typical conditions. These results should provide useful guidelines for the design of functional systems making use of this chemistry.</div><div><br></div>

scholarly journals Kinetics of the reaction of 5-substituted orotic acids with diazodiphenylmethane

2004 ◽  
Vol 69 (11) ◽  
pp. 949-953 ◽  
Author(s):  
Bratislav Jovanovic ◽  
Fathi Assaleh ◽  
Aleksandar Marinkovic
Keyword(s):  
Rate Constants ◽  
Steric Effect ◽  
Substituent Effects ◽  
Electrical Effect ◽  
Kinetics Of

Rate konstants for the reaction of eight 5-substituted orotic acids with diazodiphenylmethane (DDM) in dimethylformamide (DMF) were determined at 30 ?C by the known spectrophotometricmethod. The determined rate constants were correlated with the equations: logk2 = ??1+??R+h logk2 = ??1+??R+??+h to detect the presence and investigate the influence of both electrical and steric substituent effects. The obtained results show that the electrical effect (the localized ? field and delocalized ? resonance) is predominant and that the steric effect, althought present, is releatively small in this reaction.

Kinetics of reactions of para-substituted phenyl isocyanates with amines and alcohols

1991 ◽  
Vol 56 (8) ◽  
pp. 1662-1670 ◽  
Author(s):  
Ivan Danihel ◽  
Falk Barnikol ◽  
Pavol Kristian
Keyword(s):  
Transition State ◽  
Solvent Effects ◽  
Rate Constants ◽  
Substituent Effects ◽  
Steric Effects ◽  
Stopped Flow ◽  
Partial Charges ◽  
Hammett Correlation ◽  
One Step ◽  
Kinetics Of

The reaction of para-substituted phenyl isocyanates with amines and alcohols was studied by stopped-flow method. The Hammett correlation obtained showed that the sensitivity of the above mentioned reactions toward substituent effects is the same as that of analogous reactions of phenyl isothiocyanates (ρ ~ 2). The rate constants of these reactions were found to be affected more by steric effects than by solvent effects. An one step multicentre mechanism with partial charges in transition state has been proposed for the title reactions.

Substituent effects on the reactivity of the silicon–carbon double bond. Arrhenius parameters for the reaction of 1,1 -diarylsilenes with alcohols and acetic acid

1997 ◽  
Vol 75 (10) ◽  
pp. 1393-1402 ◽  
Author(s):  
Christine J. Bradaric ◽  
William J. Leigh
Keyword(s):  
Acetic Acid ◽  
Proton Transfer ◽  
Rate Constants ◽  
Flash Photolysis ◽  
Substituent Effects ◽  
Activation Energies ◽  
Nucleophilic Attack ◽  
Acetonitrile Solution ◽  
Nanosecond Laser ◽  
Arrhenius Parameters

Absolute rate constants for the reaction of a series of ring-substituted 1,1 -diphenylsilene derivatives with methanol, tert-butanol, and acetic acid in acetonitrile solution have been determined using nanosecond laser flash photolysis techniques. The three reactions exhibit small positive Hammett ρ-values at 23 °C, consistent with a mechanism involving initial, reversible nucleophilic attack at silicon to form a σ-bonded complex that collapses to product via rate-limiting proton transfer. Deuterium kinetic isotope effects and Arrhenius parameters have been determined for the reactions of 1,1-di-(4-methylphenyl)silene and 1,1-di-(4-trifluoromethylphenyl)silene with methanol, and are compared to those for the parent compound. Proton transfer within the complex is dominated by entropic factors, resulting in negative activation energies for reaction. The trends in the data can be rationalized in terms of variations in the relative rate constants for reversion to reactants and proton transfer as a function of temperature and substituent. A comparison of the Arrhenius activation energies for reaction of acetic acid with 1,1-diphenylsilene (Ea = +1.9 ± 0.3 kcal/mol) and the more reactive di-trifluoromethyl analogue (Ea = +3.6 ± 0.5 kcal/mol) suggests that carboxylic acids also add by a stepwise mechanism, but with formation of the complex being rate determining. Keywords: silene, substituent effects, kinetics, Arrhenius, flash photolysis.

Studies on Horseradish Peroxidase. XII. A Kinetic Study of the Oxidation of Sulfite and Nitrite by Compounds I and II

1973 ◽  
Vol 51 (4) ◽  
pp. 588-596 ◽  
Author(s):  
R. Roman ◽  
H. B. Dunford
Keyword(s):  
Horseradish Peroxidase ◽  
Ground State ◽  
Ph Dependence ◽  
Intermediate Formation ◽  
Ion Concentration ◽  
Compound I ◽  
Hydrogen Ion Concentration ◽  
Ph Range ◽  
Compound Ii ◽  
Kinetics Of

The kinetics of the oxidation of sulfite and nitrite by horseradish peroxidase compounds I and II have been studied as a function of pH at 25° and ionic strength 0.11. The pH dependence of the rate of the reaction between compound I and sulfite over the pH range 2–7 is interpreted in terms of two ground state enzyme dissociations with pka values of 5.1 and 3.3, and that for the compound II reaction with sulfite in terms of a single ground state enzyme dissociation with a pKa value of 3.9. Whereas the reaction between compound I and sulfite produces the native enzyme without the intermediate formation of compound II, the reaction of compound I with nitrite yields compound II. The second-order rate constants for the reactions of compounds I and II with nitrite increase linearly with increasing hydrogen ion concentration over the pH range 6–8.

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