The kinetics of fluoride binding by lactoperoxidase

1968 ◽  
Vol 46 (12) ◽  
pp. 1471-1474 ◽  
Author(s):  
Raymond Segal ◽  
H. Brian Dunford ◽  
Martin Morrison
Keyword(s):  
Dissociation Rate ◽  
Specific Rate ◽  
Accurate Analysis ◽  
Binding Reaction ◽  
Reversible Binding ◽  
First Order Kinetics ◽  
Flow Apparatus ◽  
Absorbance Changes ◽  
Ph Range ◽  
Kinetics Of

The kinetics of the reversible binding of fluoride by ferric lactoperoxidase has been studied over the pH range 3.8–5.4 by means of a stopped-flow apparatus. Because of small absorbance changes upon the binding of fluoride by lactoperoxidase, the reaction was driven to completion by addition of a large excess of fluoride. Under these conditions the binding reaction obeys pseudo-first-order kinetics and an accurate analysis of the dissociation rate data is not possible. The results are consistent with a mechanism in which HF binds to the active site which contains no groups capable of ionization in the pH range of the present study. The specific rate constant for the binding reaction of HF to lactoperoxidase is (9.7 ± 0.4) × 102 M−1s−1.

Kinetic of oxidation of methyl orange by vanadium(V) under conditions VO2+ and decavanadates coexist: Catalysis by Triton X-100 micellar medium

2019 ◽  
Author(s):  
Chem Int
Keyword(s):  
Methyl Orange ◽  
Solution Ph ◽  
Vanadium Concentration ◽  
Limiting Behavior ◽  
First Order ◽  
First Order Kinetics ◽  
Ph Range ◽  
Kinetic Pattern ◽  
Triton X ◽  
Kinetics Of

The kinetics of oxidation of methyl orange by vanadium(V) {V(V)} has been investigated in the pH range 2.3-3.79. In this pH range V(V) exists both in the form of decavanadates and VO2+. The kinetic results are distinctly different from the results obtained for the same reaction in highly acidic solution (pH < 1) where V(V) exists only in the form of VO2+. The reaction obeys first order kinetics with respect to methyl orange but the rate has very little dependence on total vanadium concentration. The reaction is accelerated by H+ ion but the dependence of rate on [H+] is less than that corresponding to first order dependence. The equilibrium between decavanadates and VO2+ explains the different kinetic pattern observed in this pH range. The reaction is markedly accelerated by Triton X-100 micelles. The rate-[surfactant] profile shows a limiting behavior indicative of a unimolecular pathway in the micellar pseudophase.

Kinetics of formation of the primary compound (compound I) from hydrogen peroxide and turnip peroxidases

1978 ◽  
Vol 56 (7) ◽  
pp. 702-707 ◽  
Author(s):  
Dominique Job ◽  
Jacques Ricard ◽  
H. Brian Dunford
Keyword(s):  
Hydrogen Peroxide ◽  
Compound I ◽  
Ph Profile ◽  
Glycerol Water ◽  
Binding Reaction ◽  
Cyanide Binding ◽  
Kinetics Of Formation ◽  
Ph Range ◽  
Kinetics Of ◽  
Ionizable Groups

A kinetic study of the reaction of two turnip peroxidases (P1 and P7) with hydrogen peroxide to form the primary oxidized compound (compound I) has been carried out over the pH range from 2,4 to 10.8. In the neutral and acidic pH regions, the rates depend linearly on hydrogen peroxide concentration whereas at alkaline pH values the rates display saturation kinetics. A comparison is made with the cyanide binding reaction to peroxidases since the two reactions are influenced in the same manner by ionization of groups on the native enzymes. Two different ionization processes of peroxidase P1 with pKa values of 3.9 and 10 are required to explain the rate pH profile for the reaction with H2O2. Protonation of the former group and ionization of the latter causes a decrease in the rate of reaction of the enzyme with H2O2. In the case of peroxidase P7 a minimum model involves three ionizable groups with pKa values of 2.5, 4, and 9. Protonation of the former two groups and ionization of the latter lowers the reaction rate. In the pH-independent region, the rate of formation of compound I was measured as a function of temperature. From the Arrhenius plots the activation energy for the reaction was calculated to be 2.9 ± 0.1 kcal/mol for P1 and 5.4 ± 0.3 kcal/mol for P7. However, the rates are independent of viscosity in glycerol–water mixtures up to 30% glycerol.

scholarly journals Photodegradation of levofloxacin in aqueous and organic solvents: A kinetic study

2013 ◽  
Vol 63 (2) ◽  
pp. 223-229 ◽  
Author(s):  
Iqbal Ahmad ◽  
Raheela Bano ◽  
Muhammad Ali Sheraz ◽  
Sofia Ahmed ◽  
Tania Mirza ◽  
...  
Keyword(s):  
Dielectric Constant ◽  
Degradation Rate ◽  
Hplc Method ◽  
Ph Profile ◽  
Degree Of Ionization ◽  
First Order ◽  
First Order Kinetics ◽  
Anionic Species ◽  
Ph Range ◽  
Kinetics Of

The kinetics of photodegradation of levofloxacin in solution on UV irradiation in the pH range 2.0-12.0 has been studied using a HPLC method. Levofloxacin undergoes first-order kinetics in the initial stages of the reaction and the apparent first-order rate constants are of the order of 0.167 to 1.807×10-3 min-1. The rate-pH profile is represented by a curve indicating the presence of cationic, dipolar and anionic species during the reaction. The singly ionized form of the molecule is non-fluorescent and is less susceptible to photodegradation. The increase in the degradation rate in the pH range 5.0-9.0 may be due to greater reactivity of the ionized species existing in that range. The rate appears to vary with a change in the degree of ionization of the species present in a particular pH range and their susceptibility to photodegradation. Above pH 9, the decrease in the rate of photodegradation may be a result of deprotonation of the piperazinyl group. The levofloxacin molecule is more stable in the pH range around 7, which is then suitable for formulation purposes. The photodegradation of levofloxacin was found to be affected by the dielectric constant and viscosity of the medium

scholarly journals Temperature and pH effects on the kinetics of 2-aminophenol auto-oxidation in aqueous solution

2003 ◽  
Vol 1 (3) ◽  
pp. 233-241 ◽  
Author(s):  
Dumitru Oancea ◽  
Mihaela Puiu
Keyword(s):  
Experimental Data ◽  
Activation Energy ◽  
Aqueous Solution ◽  
Ph Effects ◽  
Influence Of Temperature ◽  
First Order ◽  
Incremental Methods ◽  
First Order Kinetics ◽  
Ph Range ◽  
Kinetics Of

AbstractThe kinetics of the auto-oxidation of 2-aminophenol (OAP) to 2-amino-phenoxazin-3-one (APX) was followed in air-saturated aqueous solutions and the influence of temperature and pH on the auto-oxidation rate was studied. The kinetic analysis was based on a spectrophotometric method following the increase of the absorbance of APX. The process follows first order kinetics according to the rate law—d[OAP]/dt=k′[OAP]. The experimental data, within the pH range 4–9.85, were analyzed using both differential and incremental methods. The temperature variation of the overall rate constant was studied at pH=9.85 within the range 25–50°C and the corresponding activation energy was evaluated.

Effect of pH, Buffer, and Viscosity on the Photolysis of Formylmethylflavin: A Kinetic Study

2013 ◽  
Vol 66 (5) ◽  
pp. 579 ◽  
Author(s):  
Iqbal Ahmad ◽  
Tania Mirza ◽  
Kefi Iqbal ◽  
Sofia Ahmed ◽  
Muhammad Ali Sheraz ◽  
...  
Keyword(s):  
Rate Constants ◽  
Anaerobic Conditions ◽  
First Order ◽  
Phosphate Ions ◽  
First Order Kinetics ◽  
Ph Buffer ◽  
Ph Range ◽  
Kinetics Of ◽  
Aerobic And Anaerobic ◽  
Aerobic And Anaerobic Conditions

The kinetics of the photolysis of formylmethylflavin, a major intermediate product in the aerobic and anaerobic photolysis of riboflavin, was studied in the pH range 2.0–11.0. Formylmethylflavin and its photoproducts, lumichrome and lumiflavin, were determined in degraded solutions using a specific multicomponent spectrophotometric method. The photolysis of formylmethylflavin in alkaline medium takes place by first-order kinetics and the rate constants (kobs) at pH 7.5–11.0 range from 0.27 × 10–4 to 3.88 × 10–4 and 0.36 × 10–4 to 5.63 × 10–4 s–1 under aerobic and anaerobic conditions respectively. In acid medium, the photolysis involves a second-order mechanism and the rate constants at pH 2.0–7.0 range from 1.37 to 2.11 and 2.03 to 2.94 M–1 s–1 under aerobic and anaerobic conditions respectively. The rate–pH profiles for the photolysis reactions indicate the highest rate of formylmethylflavin degradation is at ~pH 4 and above pH 10. In the alkaline region, the increase in rate with pH is due to higher reactivity of the flavin triplet state. The photolysis of formylmethylflavin is catalyzed by phosphate ions and is affected by the solvent viscosity.

scholarly journals Photoinitiated Polymerization of 2-Hydroxyethyl Methacrylate by Riboflavin/Triethanolamine in Aqueous Solution: A Kinetic Study

2013 ◽  
Vol 2013 ◽  
pp. 1-7 ◽  
Author(s):  
Iqbal Ahmad ◽  
Kefi Iqbal ◽  
Muhammad Ali Sheraz ◽  
Sofia Ahmed ◽  
Tania Mirza ◽  
...  
Keyword(s):  
Initial Rate ◽  
Hydroxyl Group ◽  
Hydroxyethyl Methacrylate ◽  
First Order ◽  
First Order Kinetics ◽  
Rate Of Polymerization ◽  
Rate Of Reaction ◽  
Ph Range ◽  
Kinetics Of ◽  
Increased Activity

The polymerization of 1–3 M 2-hydroxyethyl methacrylate (HEMA) initiated by riboflavin/triethanolamine system has been studied in the pH range 6.0–9.0. An approximate measure of the kinetics of the reaction during the initial stages (~5% HEMA conversion) has been made to avoid the effect of any variations in the volume of the medium. The concentration of HEMA in polymerized solutions has been determined by a UV spectrophotometric method at 208 nm with a precision of ±3%. The initial rate of polymerization of HEMA follows apparent first-order kinetics and the rates increase with pH. This may be due to the presence of a labile proton on the hydroxyl group of HEMA. The second-order rate constants for the interaction of triethanolamine and HEMA lie in the range of 2.36 to  M−1 s−1 at pH 6.0–9.0 suggesting an increased activity with pH. An increase in the viscosity of HEMA solutions from 1 M to 3 M leads to a decrease in the rate of polymerization probably as a result of the decrease in the reactivity of the flavin triplet state. The effect of pH and viscosity of the medium on the rate of reaction has been evaluated.

The formation and decay of the oxyferrous complex of beef adrenocortical cytochrome P-450scc. Rapid-scan and stopped-flow studies

1987 ◽  
Vol 65 (5) ◽  
pp. 486-492 ◽  
Author(s):  
Mohammed A. Kashem ◽  
H. Brian Dunford
Keyword(s):  
Rate Constant ◽  
Acid Group ◽  
Spontaneous Decay ◽  
Stopped Flow ◽  
Oxygen Binding ◽  
First Order Kinetics ◽  
Rapid Scan ◽  
Ph Range ◽  
Kinetics Of ◽  
Cytochrome P 450

The formation and spontaneous decay of the oxyferrous complex of purified beef adrenocortical cholesterol-bound (high spin) cytochrome P-450scc have been studied by means of rapid-scan spectrometry in the Soret region at 4 °C. The oxyferrous complex, the formation of which occurs within 40 ms with a Soret absorption peak at 422 nm, is unstable and decays spontaneously to the ferric cholesterol-bound cytochrome P-450scc. The rapid-scan spectra for both processes were recorded. Isosbestic points occur at the following wavelengths: between ferrous and oxyferrous complex at 418 nm, between oxyferrous complex and ferric cytochrome P-450scc at 411 nm. The kinetics of oxygen binding and spontaneous decay of the oxyferrous complex have also been studied at 4 °C by means of stopped-flow experiments in the pH range 5.1–8.8. The rate constant for oxygen binding is constant at 5.8 × 105 ± 0.8 × 105 M−1∙s−1 over the pH range of the study. On the other hand, the decay process exhibited pH-dependent monophasic first-order kinetics. The rate constant for the decay appears to be influenced by an acid group with a pKa of 7.1 on the oxyferrous complex of cholesterol-bound cytochrome P-450scc.

scholarly journals Single entity electrochemistry and the electron transfer kinetics of hydrazine oxidation

Nano Research ◽  
2021 ◽  
Author(s):  
Ruiyang Miao ◽  
Lidong Shao ◽  
Richard G. Compton
Keyword(s):  
Electron Transfer ◽  
Bulk Solution ◽  
Relative Contribution ◽  
Rate Determining Step ◽  
Multistep Process ◽  
Ph Range ◽  
Electro Catalytic Oxidation ◽  
Single Particle Impact ◽  
The Impact ◽  
Kinetics Of

AbstractThe mechanism and kinetics of the electro-catalytic oxidation of hydrazine by graphene oxide platelets randomly decorated with palladium nanoparticles are deduced using single particle impact electrochemical measurements in buffered aqueous solutions across the pH range 2–11. Both hydrazine, N2H4, and protonated hydrazine N2H5+ are shown to be electroactive following Butler-Volmer kinetics, of which the relative contribution is strongly pH-dependent. The negligible interconversion between N2H4 and N2H5+ due to the sufficiently short timescale of the impact voltammetry, allows the analysis of the two electron transfer rates from impact signals thus reflecting the composition of the bulk solution at the pH in question. In this way the rate determining step in the oxidation of each specie is deduced to be a one electron step in which no protons are released and so likely corresponds to the initial formation of a very short-lived radical cation either in solution or adsorbed on the platelet. Overall the work establishes a generic method for the elucidation of the rate determining electron transfer in a multistep process free from any complexity imposed by preceding or following chemical reactions which occur on the timescale of conventional voltammetry.

scholarly journals Empirical Validation of a Biogas Plant Simulation Model and Analysis of Biogas Upgrading Potentials

Energies ◽  
2021 ◽  
Vol 14 (9) ◽  
pp. 2424
Author(s):  
Jan Martin Zepter ◽  
Jan Engelhardt ◽  
Tatiana Gabderakhmanova ◽  
Mattia Marinelli
Keyword(s):  
Simulation Model ◽  
Biogas Production ◽  
Biogas Plant ◽  
Raw Material ◽  
Biogas Upgrading ◽  
Integrated Energy Systems ◽  
First Order Kinetics ◽  
Biogas Plants ◽  
Plant Simulation ◽  
Kinetics Of

Biogas plants may support the transformation towards renewable-based and integrated energy systems by providing dispatchable co-generation as well as opportunities for biogas upgrading or power-to-X conversion. In this paper, a simulation model that comprises the main dynamics of the internal processes of a biogas plant is developed. Based on first-order kinetics of the anaerobic digestion process, the biogas production of an input feeding schedule of raw material can be estimated. The output of the plant in terms of electrical and thermal energy is validated against empirical data from a 3-MW biogas plant on the Danish island of Bornholm. The results show that the model provides an accurate representation of the processes within a biogas plant. The paper further provides insights on the functioning of the biogas plant on Bornholm as well as discusses upgrading potentials of biogas to biomethane at the plant from an energy perspective.

scholarly journals Comparative Study of Chemical Stability of Two H1Antihistaminic Drugs, Terfenadine and ItsIn VivoMetabolite Fexofenadine, Using LC-UV Methods

2019 ◽  
Vol 2019 ◽  
pp. 1-10
Author(s):  
Anna Gumieniczek ◽  
Anna Berecka-Rycerz ◽  
Rafał Pietraś ◽  
Izabela Kozak ◽  
Karolina Lejwoda ◽  
...  
Keyword(s):  
Comparative Study ◽  
Chemical Stability ◽  
First Order ◽  
First Order Kinetics ◽  
Kinetics Of Degradation ◽  
Effects Of Temperature ◽  
High Doses ◽  
Antihistaminic Drugs ◽  
Kinetics Of

A comparative study of chemical stability of terfenadine (TER) and itsin vivometabolite fexofenadine (FEX) was performed. Both TER and FEX were subjected to high temperature at different pH and UV/VIS light at different pH and then quantitatively analyzed using new validated LC-UV methods. These methods were used to monitor the degradation processes and to determine the kinetics of degradation for both the compounds. As far as the effects of temperature and pH were concerned, FEX occurred more sensitive to degradation than TER. As far as the effects of UV/VIS light and pH were concerned, the both drugs were similarly sensitive to high doses of light. Using all stress conditions, the processes of degradation of TER and FEX followed the first-order kinetics. The results obtained for these two antihistaminic drugs could be helpful in developing their new derivatives with higher activity and stability at the same time.

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