THE ANODIC OXIDATION OF AMMONIA AT PLATINUM BLACK ELECTRODES IN AQUEOUS KOH ELECTROLYTE

1963 ◽  
Vol 41 (7) ◽  
pp. 1686-1694 ◽  
Author(s):  
H. G. Oswin ◽  
M. Salomon
Keyword(s):  
Anodic Oxidation ◽  
Hydrogen Oxidation ◽  
Reaction Pathway ◽  
Kinetic Scheme ◽  
Kinetic Studies ◽  
Platinum Black ◽  
Ammonia Vapor ◽  
Consecutive Reactions ◽  
Aqueous Potassium Hydroxide ◽  
Oxidation Of Ammonia

Electrochemical kinetic studies are reported on the anodic oxidation of ammonia in aqueous potassium hydroxide solutions at platinum black electrodes. A kinetic scheme of consecutive reactions is proposed; Tafel slopes are deduced for various rate-determining mechanisms and compared with the experimental behavior. The reaction pathway is correlated with that involved in the analogous catalyzed ammonia vapor decomposition. The exchange currents obtained, compared with those for hydrogen oxidation, render the system unfavorable for fuel cell applications.

scholarly journals Self-Assembled Bimetallic Aluminum-Salen Catalyst for the Cyclic Carbonates Synthesis

Molecules ◽  
2021 ◽  
Vol 26 (13) ◽  
pp. 4097
Author(s):  
Wooyong Seong ◽  
Hyungwoo Hahm ◽  
Seyong Kim ◽  
Jongwoo Park ◽  
Khalil A. Abboud ◽  
...  
Keyword(s):  
Hydrogen Bonding ◽  
Self Assembly ◽  
Reaction Pathway ◽  
Kinetic Studies ◽  
Cyclic Carbonate ◽  
Reaction Conditions ◽  
Formation Reaction ◽  
X Ray ◽  
Carbonate Formation ◽  
Salen Aluminum

Bimetallic bis-urea functionalized salen-aluminum catalysts have been developed for cyclic carbonate synthesis from epoxides and CO2. The urea moiety provides a bimetallic scaffold through hydrogen bonding, which expedites the cyclic carbonate formation reaction under mild reaction conditions. The turnover frequency (TOF) of the bis-urea salen Al catalyst is three times higher than that of a μ-oxo-bridged catalyst, and 13 times higher than that of a monomeric salen aluminum catalyst. The bimetallic reaction pathway is suggested based on urea additive studies and kinetic studies. Additionally, the X-ray crystal structure of a bis-urea salen Ni complex supports the self-assembly of the bis-urea salen metal complex through hydrogen bonding.

scholarly journals Time-dependent activation of the semicarbazide-sensitive amine oxidase (SSAO) from ox lung microsomes

2000 ◽  
Vol 351 (3) ◽  
pp. 789-794 ◽  
Author(s):  
Jose M. LIZCANO ◽  
Keith F. TIPTON ◽  
Mercedes UNZETA
Keyword(s):  
Amine Oxidase ◽  
Reaction Pathway ◽  
Substrate Inhibition ◽  
Kinetic Studies ◽  
Tryptophan Fluorescence ◽  
The Other ◽  
Time Dependent ◽  
High Substrate ◽  
Before And After ◽  
Lag Period

The activity of ox lung microsomal semicarbazide-sensitive amine oxidase (EC 1.4.3.6; SSAO) towards benzylamine increased 20-fold during incubation at 37°C. After an initial lag-period, activation was first-order with time and complete after approx. 20h. No significant changes in activity towards methylamine, histamine or 2-phenylethylamine were observed, although mixed-substrate experiments were consistent with the same enzyme being involved in the oxidation of all these substrates, both before and after time-dependent activation. The enzyme-tryptophan fluorescence increased on incubation at 37°C in parallel with the increase in activity towards benzylamine. Treatment of the activated-enzyme preparation with 6M guanidinium chloride followed by dialysis, caused both the activity towards benzylamine and the fluorescence to fall to that occurring before activation. However, incubation of this preparation at 37°C resulted in increases in fluorescence and activity similar to those seen with the unactivated enzyme. Benzylamine oxidation was inhibited, uncompetitively with respect to oxygen, by high substrate concentrations but no such inhibition was observed with the other amines. Activation resulted in an increase in Vmax for benzylamine oxidation, with no significant alterations in the Km or the Ksi for high-substrate inhibition. Kinetic studies were consistent with sequential mechanisms being followed for the oxidation of both benzylamine and methylamine but the dependence on oxygen concentration was complex. These results might indicate that benzylamine follows a different reaction pathway from the other substrates, with substrate-specific activation involving a reaction step that is rate-limiting for benzylamine oxidation but not for the others.

Photocatalytic Decomposition of Metoprolol and Its Intermediate Organic Reaction Products: Kinetics and Degradation Pathway

2016 ◽  
Vol 14 (3) ◽  
pp. 809-820 ◽  
Author(s):  
Alfonso Pinedo ◽  
Mariana López ◽  
Elisa Leyva ◽  
Brenda Zermeño ◽  
Benito Serrano ◽  
...  
Keyword(s):  
Uv Light ◽  
Reaction Pathway ◽  
Kinetic Studies ◽  
Initial Reaction Rate ◽  
Degradation Pathway ◽  
Photocatalytic Decomposition ◽  
Initial Reaction ◽  
Low Molecular Weight ◽  
Reaction Products ◽  
Constant Flow Rate

Abstract High purity metoprolol prepared by neutralization of an aqueous solution of metoprolol tartrate is efficiently mineralized to CO2 and water by photocatalysis with TiO2, UV light and a constant flow rate of oxygen. Since the tartrate anions were eliminated, all the HO• generated by photocatalysis reacted efficiently with the aromatic part of the medication. The reaction pathway includes two routes of degradation. The first one includes the transformation of metoprolol to hydroquinone via formation of 4-(2-methoxyethyl)phenol, 2-(4-hydroxyphenyl)ethanol and 4-hydroxybenzaldehyde. Metoprolol is also degraded directly to hydroquinone. Then, this aromatic compound is oxidized to 1,2,4-benzenetriol, which is rapidly oxidized to low molecular weight organic acids before being completely mineralized to CO2 and water. Kinetic studies indicated that the initial reaction rate of the degradation of metoprolol, 4-(2-methoxyethyl)phenol, 2-(4-hydroxyphenyl)ethanol and 4-hydroxybenzaldehyde is described by the LH-HW model.

scholarly journals Mechanistic studies of FosB: a divalent-metal-dependent bacillithiol-S-transferase that mediates fosfomycin resistance in Staphylococcus aureus

2013 ◽  
Vol 451 (1) ◽  
pp. 69-79 ◽  
Author(s):  
Alexandra A. Roberts ◽  
Sunil V. Sharma ◽  
Andrew W. Strankman ◽  
Shayla R. Duran ◽  
Mamta Rawat ◽  
...  
Keyword(s):  
Staphylococcus Aureus ◽  
Reaction Pathway ◽  
Catalytic Efficiency ◽  
Kinetic Studies ◽  
Competitive Inhibitor ◽  
Divalent Metal ◽  
Gram Positive ◽  
Gram Positive Bacteria ◽  
Nmr Characterization ◽  
Fosfomycin Resistance

FosB is a divalent-metal-dependent thiol-S-transferase implicated in fosfomycin resistance among many pathogenic Gram-positive bacteria. In the present paper, we describe detailed kinetic studies of FosB from Staphylococcus aureus (SaFosB) that confirm that bacillithiol (BSH) is its preferred physiological thiol substrate. SaFosB is the first to be characterized among a new class of enzyme (bacillithiol-S-transferases), which, unlike glutathione transferases, are distributed among many low-G+C Gram-positive bacteria that use BSH instead of glutathione as their major low-molecular-mass thiol. The Km values for BSH and fosfomycin are 4.2 and 17.8 mM respectively. Substrate specificity assays revealed that the thiol and amino groups of BSH are essential for activity, whereas malate is important for SaFosB recognition and catalytic efficiency. Metal activity assays indicated that Mn2+ and Mg2+ are likely to be the relevant cofactors under physiological conditions. The serine analogue of BSH (BOH) is an effective competitive inhibitor of SaFosB with respect to BSH, but uncompetitive with respect to fosfomycin. Coupled with NMR characterization of the reaction product (BS–fosfomycin), this demonstrates that the SaFosB-catalysed reaction pathway involves a compulsory ordered binding mechanism with fosfomycin binding first followed by BSH which then attacks the more sterically hindered C-1 carbon of the fosfomycin epoxide. Disruption of BSH biosynthesis in S. aureus increases sensitivity to fosfomycin. Together, these results indicate that SaFosB is a divalent-metal-dependent bacillithiol-S-transferase that confers fosfomycin resistance on S. aureus.

scholarly journals Kinetic studies of oxidized nicotinamide–adenine dinucleotide-facilitated reactions of d-glyceraldehyde 3-phosphate dehydrogenase

1974 ◽  
Vol 143 (2) ◽  
pp. 353-363 ◽  
Author(s):  
Patricia J. Harrigan ◽  
David R. Trentham
Keyword(s):  
Nicotinamide Adenine Dinucleotide ◽  
Temperature Jump ◽  
Reaction Pathway ◽  
Kinetic Studies ◽  
Rate Equations ◽  
First Order ◽  
Diffusion Controlled ◽  
Relaxation Temperature ◽  
Pig Muscle ◽  
Kinetics Of

The kinetics of the acylation of d-glyceraldehyde 3-phosphate dehydrogenase from pig muscle by 1,3-diphosphoglycerate in the presence of NAD+ has been analysed by using the relaxation temperature-jump method. At pH7.2 and 8°C the rate of acylation of the NAD+-bound (or holo-) enzyme was 3.3×105m−1·s−1 and the rate of phosphorolysis, the reverse reaction, was 7.5×103m−1·s−1. After a temperature-jump perturbation the equilibrium of NAD+ binding to the acyl-enzyme was re-established more rapidly than that of the acylation. The rate of phosphorolysis of the apoacylenzyme from sturgeon muscle and of aldehyde release from the d-glyceraldehyde 3-phosphate–apoenzyme complex were ≤40m−1·s−1 and ≤12s−1 respectively at pH8.0 and 22°C, which means that both processes are too slow to contribute significantly to the reaction pathway of the reversible NAD+-linked oxidative phosphorylation of d-glyceraldehyde 3-phosphate. Phosphorolysis of both acyl-apoenzyme and acyl-holoenzyme was first-order in Pi up to 100mm-Pi and more. PO43− could be the reactive species of the phosphorolysis of the acyl-holoenzyme, in which case phosphorolysis is a diffusion-controlled reaction, although other kinetically indistinguishable rate equations for the reaction are possible.

scholarly journals Efficient hydrothermal deoxygenation of tall oil fatty acids into n-paraffinic hydrocarbons and alcohols in the presence of aqueous formic acid

2020 ◽  
Author(s):  
Lakhya Jyoti Konwar ◽  
Benedetta Oliani ◽  
Ajaikumar Samikannu ◽  
Paolo Canu ◽  
Jyri-Pekka Mikkola
Keyword(s):  
Fatty Acids ◽  
Formic Acid ◽  
Rapeseed Oil ◽  
Reaction Pathway ◽  
Kinetic Studies ◽  
Tall Oil ◽  
Pd Catalysts ◽  
Catalytic Systems ◽  
Tall Oil Fatty Acids ◽  
Aqueous Formic Acid

Abstract Hydrothermal deoxygenation of tall oil fatty acids (TOFA) was investigated in the presence of aqueous formic acid (0.5–7.5 wt%) as a H2 donor in the presence of subcritical H2O pressure (569–599 K). Pd and Ru nanoparticles supported on carbon (5% Pd/CSigma, 5% Ru/CSigma, 10% Pd/CO850_DP, and 5% Ru/COPcomm_DP) were found to be efficient catalysts for deoxygenation of TOFA. The reaction pathway was mainly influenced by the concentration of formic acid and the catalyst. In case of Pd catalysts, in the presence of 0–2.5 wt% formic acid, decarboxylation was the dominant pathway producing n-paraffinic hydrocarbons with one less carbon atom (heptadecane yield up to 94 wt%), while with 5–7.5% formic acid, a hydrodeoxygenation/hydrogenation mechanism was favored producing C18 deoxygenation products octadecanol and octadecane as the main products (yields up to 70 wt%). In contrast, Ru catalysts produced a mixture of C5-C20 (n-and iso-paraffinic) hydrocarbons via decarboxylation, cracking and isomerization (up to 58 wt% C17 yield and total hydrocarbon yield up to 95 wt%) irrespective of formic acid concentration. Kinetic studies showed that the rates of deoxygenation displayed Arrhenius type behavior with apparent activation energies of 134.44 ± 31.36 kJ/mol and 148.92 ± 3.66 kJ/mol, for the 5% Pd/CSigma and 5% Ru/CSigma catalyst, respectively. Furthermore, the experiments with glycerol tristearate, rapeseed oil, sunflower oil, rapeseed biodiesel, and hydrolyzed rapeseed oil produced identical products confirming the versatility of the aforementioned catalytic systems for deoxygenation of C18 feedstocks.

KINETIC STUDIES OF THE AgO/Ag2O ELECTRODE IN ALKALINE SOLUTIONS

1964 ◽  
Vol 42 (11) ◽  
pp. 2488-2495 ◽  
Author(s):  
R. G. Barradas ◽  
G. H. Fraser
Keyword(s):  
Potassium Hydroxide ◽  
Potassium Hydroxide Solution ◽  
Kinetic Studies ◽  
Alkaline Solutions ◽  
Hyperbolic Function ◽  
Electron Number ◽  
Rate Determining Step ◽  
Symmetry Factor ◽  
Tafel Slopes ◽  
Aqueous Potassium Hydroxide

The anodic oxidation of Ag2O to AgO in normal aqueous potassium hydroxide solution was investigated quantitatively under both galvanostatic and potentiostatic conditions at 25 °C. A few results for similar experiments in N/40 KOH are also reported. Tafel slopes and other parameters were determined. The experimental results show the dependence of current density as a hyperbolic function of overpotential, i.e. i = 2i0 sinh (λFη/2RT). The electron number λ was found to be 2 and the symmetry factor β was confirmed to be 1/2. It is proposed that the rate-determining step for the formation of AgO from Ag2O occurs at the Ag2O/AgO interface and involves the transfer of O−2 ions.

scholarly journals Verification, Validation, and Testing of Kinetic Mechanisms of Hydrogen Combustion in Fluid-Dynamic Computations

2012 ◽  
Vol 2012 ◽  
pp. 1-11 ◽  
Author(s):  
Victor P. Zhukov
Keyword(s):  
Hydrogen Oxidation ◽  
Fluid Dynamic ◽  
Computational Cost ◽  
Kinetic Scheme ◽  
Time Step ◽  
Kinetic Schemes ◽  
Ignition Delay Times ◽  
Ansys Cfx ◽  
Kinetic Mechanisms ◽  
The Impact

A one-step, a two-step, an abridged, a skeletal, and four detailed kinetic schemes of hydrogen oxidation have been tested. A new skeletal kinetic scheme of hydrogen oxidation has been developed. The CFD calculations were carried out using ANSYS CFX software. Ignition delay times and speeds of flames were derived from the computational results. The computational data obtained using ANSYS CFX and CHEMKIN, and experimental data were compared. The precision, reliability, and range of validity of the kinetic schemes in CFD simulations were estimated. The impact of kinetic scheme on the results of computations was discussed. The relationship between grid spacing, time step, accuracy, and computational cost was analyzed.

Isothermal interpretations of oscillatory ignition during hydrogen oxidation in an open system II. Numerical analysis

1986 ◽  
Vol 405 (1828) ◽  
pp. 129-142 ◽  
Keyword(s):  
Hydrogen Oxidation ◽  
Effective Rate Constant ◽  
Kinetic Scheme ◽  
Effective Rate ◽  
Analytical Prediction ◽  
Third Body ◽  
Elementary Reactions ◽  
Stirred Reactor ◽  
Starting Point

Numerical methods are used to simulate oscillatory ignition under conditions resembling those associated with the second ignition limit for equimolar hydrogen and oxygen mixtures flowing through a well stirred reactor. The starting point is a scheme comprising 17 elementary reactions coupled to heat release and dissipation. The system of equations is then simplified without loss of the major qualitative features of the predicted time-dependent phenomena, first by eliminating the temperature change, so yielding an isothermal branching system, and then by reducing the kinetic scheme to seven elementary steps as follows: H 2 + O 2 → radicals, OH + H 2 → H 2 O + H, H + O 2 → OH + O, O + H 2 → OH + H, H + O 2 + M → HO 2 + M, HO 2 + H → H 2 O + O, HO 2 → inert. This scheme constitutes the minimum viable kinetic foundation from which isothermal chain-branching oscillations are predicted in H 2 + O 2 under flowing conditions. Its features are analysed and the role of each reaction explained. The change in overall third-body efficiency of M leading to HO 2 formation, as the composition within the reactor varies under flowing conditions, is a key kinetic prerequisite to oscillations. The interaction between H and HO 2 that follows is an essential additional feature. The overall third-body efficiency is highest immediately after ignition, when the concentration of water is highest. The displacement of water by inflowing hydrogen and oxygen reduces the overall efficiency, and hence the effective rate constant of the termolecular step relative to that for the branching reactions. This condition is in complete accord with the analytical prediction of periodicity presented in the previous paper.

scholarly journals Kinetic and Reaction Pathway Analysis in the Application of Botulinum Toxin A for Wound Healing

2012 ◽  
Vol 2012 ◽  
pp. 1-9 ◽  
Author(s):  
Frank J. Lebeda ◽  
Zygmunt F. Dembek ◽  
Michael Adler
Keyword(s):  
Wound Healing ◽  
Botulinum Toxin ◽  
Chronic Wounds ◽  
Clinical Symptoms ◽  
Reaction Pathway ◽  
Botulinum Toxin A ◽  
Case Reports ◽  
Healing Process ◽  
Kinetic Scheme ◽  
Pharmacokinetic Data

A relatively new approach in the treatment of specific wounds in animal models and in patients with type A botulinum toxin is the focus of this paper. The indications or conditions include traumatic wounds (experimental and clinical), surgical (incision) wounds, and wounds such as fissures and ulcers that are signs/symptoms of disease or other processes. An objective was to conduct systematic literature searches and take note of the reactions involved in the healing process and identify corresponding pharmacokinetic data. From several case reports, we developed a qualitative model of how botulinum toxin disrupts the vicious cycle of muscle spasm, pain, inflammation, decreased blood flow, and ischemia. We transformed this model into a minimal kinetic scheme for healing chronic wounds. The model helped us to estimate the rate of decline of this toxin's therapeutic effect by calculating the rate of recurrence of clinical symptoms after a wound-healing treatment with this neurotoxin.

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