Nonlinear Kinetic Analysis Research Articles

Non-linear kinetic analysis of catalytic hydrolysis of ethylenediamine bisborane with nano-structured Pd/TiO2 catalyst

In this study, the hydrogen generation from catalytic hydrolysis of ethylenediamine bisborane (EDAB) solution catalyzed by nanostructured titanium dioxide (TiO2) supported Pd metallic catalyst was carried out. TiO2 support material was synthesized by the sol-gel method from titanium (IV) ethoxide. Pd was loaded into TiO2 by the conventional impregnation-reduction method and reduction was carried out at 750 °C in an H2 atmosphere. The characterization of catalysts was done with SEM-EDX and multi-point BET analysis. To investigate the hydrogen production by catalytic hydrolysis of EDAB, parameters such as Pd loading (2–4% by weight) and temperature (40–80 °C) were chosen in the presence of ethylenediamine bisborane aqueous solution (0.034% by weight). Detailed non-linear kinetic analysis was applied to the experimental data by considering and Langmuir-Hinshelwood model and power law. The activation energy Ea was calculated as Ea = 33.61 kJ mol−1 and Ea = 36.32 kJ mol−1 according to Langmuir-Hinshelwood and power-law model respectively for the Pd/TiO2 catalyst.

Nonlinear Magnetochemical Effects in Nanotherapy of Walker-256 Carcinosarcoma.

The biological and medical aspects of magnetochemical effects in nanotherapy of tumors remain poorly studied. The present paper investigates the influence of nonlinear magnetochemical effects of anisotropic magnetic nanodots on an animal tumor model. The magnetic properties and electron spin resonance spectra of magnetic nanodots and doxorubicin were investigated after mechano-magnetochemical synthesis. The results obtained from the analysis of nonlinear kinetics and survival in Walker-256 carcinosarcoma-bearing animals found a nonlinear dependence between the value of the growth factor, braking ratio, survival rate, tumor redox state, and the treatment by the magnetic nanodot combined with a nonuniform constant magnetic field. To quantify the heterogeneity in microphotographs of Walker-256 carcinosarcoma sections, we applied the entropy parameter. The control (no treatment) group showed the greatest heterogeneity. The lowest value of tumor heterogeneity among animals given treatment was found in groups with the minimum growth factor. Similarly, the lowest entropy value was found in muscle tissue taken from inoculation areas of the tumor. The evidence from this study concluded that inhomogeneous constant magnetic fields with different strength applied to heterogeneous tumor tissues induced different magnetic anisotropy in the magnetic nanodot which had a significant influence on the nonlinear kinetics, redox state, and histological pattern of the tumor.

An optimal flattening algorithm for ship hull plate fabricated by thermal forming

Normally, ship hull plates contain compound curvature distributions and they can only be fabricated by integrating mechanical rolling with bending and following them with regional heating to achieve required configuration. This paper mainly proposes a comprehensive flattening process to determine optimal planar shape, shrinkage strain distribution and mapping relation for three typical ship hull plates by thermal forming, which practically benefit for automatic forming. An innovative geometric method is first presented to obtain initial planar approximation and strain square sum subject to negative principal strain constraints within each element from planar to desired surface is formulated based on nonlinear kinetic analysis. Then, we employ area equivalent method through transforming spatial quadrilateral into planar quadrilateral to simplify optimization model. Finally, initial planar approximations are regarded as iteration initial points to solve the model based on sequential quadratic programming. The results indicate that the proposed process can effectively achieve optimal planar shape, mapping relation and negative principal strain to help achieve all heating paths and heat source parameters at one time, thus automation.

A continuous spectrophotometric assay and nonlinear kinetic analysis of methionine γ-lyase catalysis

In this article, we present a new, easy-to-implement assay for methionine γ-lyase (MGL)-catalyzed γ-elimination reactions of l-methionine and its analogues that produce α-ketobutyrate (α-KB) as product. The assay employs ultraviolet–visible (UV–Vis) spectrophotometry to continuously monitor the rate of formation of α-KB by its absorbance at 315 nm. We also employ a nonlinear data analysis method that obviates the need for an “initial slope” determination, which can introduce errors when the progress curves are nonlinear. The spectrophotometric assay is validated through product analysis by 1H NMR (nuclear magnetic resonance), which showed that under the conditions of study l-methionine (l-met) and l-methionine sulfone (l-met sulfone) substrates were converted to α-KB product with greater than 99% yield. Using this assay method, we determined for the first time the Michaelis–Menten parameters for a recombinant form of MGL from Porphyromonas gingivalis, obtaining respective kcat and Km values of 328 ± 8 min−1 and 1.2 ± 0.1 mM for l-met γ-elimination and 2048 ± 59 min−1 and 38 ± 2 mM for l-met sulfone γ-elimination reactions. We envisage that this assay method will be useful for determining the activity of MGL γ-elimination reactions that produce α-KB as the end product.

A Study of Plant Char Oxidation: the Parallel Reactions and Their Chemical Kinetics

The present work explores the effects of the parallel reactions on the oxidation reactivity of plant chars formed at various heat treatment temperatures by using a multi-component parallel reaction model in conjunction with the non-linear kinetic analysis technique. Four plant species were selected. A plant char was prepared in a programme-controlled horizontal tube furnace under the atmosphere of N2 at a purity of 99.999%, and its heat treatment temperature was set at 450, 520 and 800 ℃, respectively. The aerial oxidation characteristics of plant chars were analyzed by using a simultaneous ther- mo-gravimetric analyzer and differential scanning calorimeter, and the kinetic data of the parallel reactions were then re- trieved by fitting both the mass change and mass loss rate data obtained during the oxidation measurements. It was confirmed that for the oxidation of the chars formed at moderate heat treatment temperatures (i.e. 450 and 520 ℃), the variation pat- terns of mass loss rate and the heat flow rate curves are contributed by the parallel oxidation reactions of lignin residue, amorphous carbon and the other reactive substances such as crude fat and protein, etc. When the heat treatment temperature reaches 800 ℃, the reactive substances stored in the char produced are mainly amorphous carbon, and the char oxidation can be simplified to an one-step reaction. Compared with the other two reaction components, lignin residue has the lowest activa- tion energy for oxidation with the range between 86 and 147 kJmol -1 , and its reaction temperatures vary between 300 and 480 ℃. The activation energy for the amorphous carbon fluctuates between 174 and 208 kJmol -1 with its reaction tempera- tures altering between 370 and 520 ℃. The other reactive substances undergo oxidation with the activation energy between 214 and 225 kJmol -1 and the corresponding reaction temperatures are between 420 and 510 ℃. It is obvious that the oxida- tion reactivity of plant chars mainly relies on the performance of lignin residue. With the increase in the heat treatment tem- perature for making a char, the oxidation reactivity of the plant char essentially reduces, which is essentially attributed to the decrease in the content of lignin residue and the increase in the activation energies for the other two components to oxidize. The established understanding lays the foundation for developing more effective methodologies for making use of the energy stored in plant chars and paves the way for identifying the role of plant chars in the spread of a wildland fire. Keywords plant char; oxidation; kinetic analysis; reaction temperature; reactivity

Distinctive in vivo kinetics of the new σ1 receptor ligands (R)-(+)- and (S)-(-)-18F-fluspidine in porcine brain.

Because of their involvement in growth and survival signaling cascades, the σ(1) receptors (σ(1)Rs) represent a novel target for the treatment of cancer and several brain diseases such as depression and neurodegeneration. From a series of σ1R-specific (18)F-fluoroalkylated spirocyclic piperidines, we have chosen (18)F-fluspidine for detailed investigation of the in vivo kinetics of the (R)-(+)- and (S)-(-)-enantiomers to identify their potential for imaging in humans. Enantiopure tosylate precursors for radiolabeling were obtained using chiral preparative high-performance liquid chromatography and used for radiosynthesis of both (18)F-fluspidine enantiomers by nucleophilic substitution with K-(18)F-F-Kryptofix 222-carbonate complex in a synthesis module. Brain pharmacokinetics were investigated by dynamic PET studies in piglets under baseline and blocking conditions using the highly selective σ1R agonist SA4503. Standardized uptake values (SUVs) were calculated for 24 MR-defined brain regions. Total distribution volume (V(T)) and binding potentials (k3'/k4) of (S)-(-)- and (R)-(+)-(18)F-fluspidine were estimated. Furthermore, V(T) values were estimated by graphical analysis using Logan plots. The (S)- and (R)-tosylates were obtained in excellent enantiomeric purities (>98% and >96% enantiomeric excess, respectively). (S)-(-)- and (R)-(+)-(18)F-fluspidine were synthesized within approximately 70 min (radiochemical yield, 35%-45%; specific activity, 650-870 GBq/μmol; radiochemical purity, >99%). Both radiotracers displayed different brain uptake kinetics. Although the initial brain uptake was similar, the SUV at the end of the study differed significantly (P < 0.05), with (R)-(+)-(18)F-fluspidine showing about 60%-150% higher values. Administration of SA4503 reduced SUV almost equally for both radiotracers by approximately 65%. Furthermore, k(3)' was significantly decreased under blocking conditions in almost all regions ((S)-(-)-(18)F-fluspidine, -90%-95%; (R)-(+)-(18)F-fluspidine, -70%-90%) whereas effects on k(4) differed according to the particular brain region. V(T) estimated by both graphical analysis using Logan plots and full nonlinear kinetic analysis revealed significant inhibition for both radiotracers under blocking conditions. Both (S)-(-)- and (R)-(+)-(18)F-fluspidine appear to be suitable for σ1R imaging in humans. The different pharmacokinetics of (S)-(-)-(18)F-fluspidine and (R)-(+)-(18)F-fluspidine may have the potential for application in the diagnostics of different pathologic conditions.

Nonlinear kinetic analysis of phenol adsorption onto peat soil

Phenolic compounds are considered as a serious organic pollutant containing in many industrial effluents particularly vulnerable when the plant discharge is disposed on land. In the present study, the phenol removal potential of peat soil as adsorption media was investigated as the adsorption process are gaining popular for polishing treatment of toxic materials in industrial wastewater. Batch experiments were performed in the laboratory to determine the adsorption isotherms of initial concentrations for 5, 8, 10, 15, and 20 mg/L and predetermined quantity of peat soil with size ranges between 425 and 200 μm poured into different containers. The effects of various parameters like initial phenol concentration, adsorbent quantity, pH, and contact time were also investigated. From experimental results, it was found that 42 % of phenol removal took place with optimized initial phenol concentration of 10 mg/L, adsorbent dose of 200 g/L, solution pH 6.0 for the equilibrium contact time of 6 h. The result exhibits that pseudo-first-order (R2 = 0.99) and Langmuir isotherm models are fitted reasonably (R2 = 0.91). Adams–Bohart, Thomas, Yoon–Nelson, and Wolborska models were also investigated to the column experimental data of different bed heights to predict the breakthrough curves and to determine the kinetic coefficient of the models using nonlinear regression analysis. It was found that the Thomas model is the best fitted model to predict the experimental breakthrough curves with the highest coefficient of determination, R2 = 0.99 and lowest root mean square error and mean absolute performance error values.

Nonlinear Kinetic Analysis of InP and InAs Metal Organic Vapor Phase Epitaxy by Selective Area Growth Technique

Kinetic analysis based on the combination of selective area metal organic vapor phase epitaxy (SA-MOVPE) and two-dimensional numerical simulation can be used to extract real surface kinetics, which usually remain unknown because the growth rate of deposited film is limited by diffusional mass-transfer rate in SA-MOVPE. To explain previously observed concentration dependency on surface reaction rate constant and to establish a more reliable model for the surface process, non-linear surface kinetics were used in this study to analyze SA-MOVPE process for InP and InAs. Surface reaction rate constant (ksn) and adsorption equilibrium constant (K) of a film precursor in a nonlinear model was successfully extracted in SA-MOVPE for InP and InAs. Results show that a nonlinear model that takes adsorption–desorption equilibrium into account can well explain the concentration dependency and can be potentially used in predicting growth behavior regardless of mask width or partial pressure influence.

Non-linear surface reaction kinetics in GaAs selective area MOVPE

Two-dimensional numerical simulation on growth rate non-uniformity of selective area growth (SAG) in metal-organic vapor phase epitaxy (MOVPE) is an effective method to examine the surface reaction kinetics, which is difficult to be investigated in mass-transport limited growth regime. Non-linear kinetic analysis based on the Langmuir–Hinshelwood mechanism is revealing the intrinsic process in MOVPE. Two important kinetic parameters, surface reaction rate constant ( k s n) and adsorption equilibrium coefficient ( K), were successfully extracted from GaAs SAG–MOVPE on (1 0 0) exact and 2° off misoriented substrates in the temperature range of 520–600 °C. The activation energy is 126–127 kJ/mol for k s n, and −53 to −59 kJ/mol for K. The surface coverage of Ga-species during the GaAs growth can be estimated from these kinetic parameters as 0.05–0.60. There is a critical temperature ( T c) for the conversion of GaAs surface reaction mode. When growth temperature is higher than T c, non-linear kinetic can be simplified as linear kinetic mode which is easier in calculation. T c was found to be 600 °C for (1 0 0) exact GaAs substrate and 650 °C for 2° off substrate.

Non-linear Surface Reaction Kinetics of GaAs MOVPE Explored by Selective Area Growth

Two-dimensional or three-dimensional numerical simulation on growth rate non-uniformity of selective area metalorganic vapor phase epitaxy in sub-millimeter scale can extract real surface kinetics, which is normally hindered by mass transport rate of film precursors. Non-linear surface kinetics is introduced to analyse group-III precursor concentration dependency for the first time and surface reaction rate constant (ksn) of adsorbed species and adsorption equilibrium constant (K) are extracted from GaAs-MOVPE at 575 C. The effect of misorientation angle of GaAs (100) substrate on these kinetic parameters is examined. It is found that ksn is about 3.4×10-5 mol/m2/s independent of the angle, whereas K is 6.9-12×10-5 m3/mol dependent on the angle. The obtained value of ksn can be converted to lifetime of adsorbed species on GaAs surface and it is 0.3 sec. This is mostly the same with gas-phase decomposition rate of trimethylgallium and supports the accuracy of our non-linear kinetic analysis.

Nonlinear Kinetics of GaAs MOVPE Examined by Selective Area Growth Technique

Two-dimensional or three-dimensional numerical simulation on growth rate nonuniformity of selective area metallorganic vapor phase epitaxy (SA-MOVPE) in sub-millimeter scale can extract real surface kinetics, which is normally hindered by mass transport rate of film precursors. Nonlinear surface kinetics is introduced to analyze group-III precursor concentration dependency of SA-MOVPE for the first time and surface reaction rate constant of adsorbed species and adsorption equilibrium constant are extracted from GaAs-MOVPE at . The effect of misorientation angle of GaAs(100) substrate on these kinetic parameters was examined. It was found that is about independent of ϕ, whereas ranged from dependent on ϕ. The obtained value of can be converted to lifetime of adsorbed species on GaAs surface and it is . This is mostly the same with gas-phase decomposition rate of trimethylgallium and supports the accuracy of our nonlinear kinetic analysis.

Non-linear kinetic analysis on GaAs selective area MOVPE combined with macro-scale analysis to extract major reaction mechanism

Numerical simulation on growth rate non-uniformity of selective area growth (SAG) in sub-millimeter scale can extract real surface kinetics in metal organic vapor phase epitaxy (MOVPE) process, which is normally hindered by mass transport rate of film precursors. SAG analysis with non-linear surface kinetics is introduced for the first time to analyze group-III precursor partial pressure dependency of GaAs-MOVPE. Important kinetic parameters, surface reaction rate constant, adsorption equilibrium constant and surface coverage, have been extracted and examined as various substrate misorientation angles. Such non-linear kinetic analysis using SAG (micro analysis) is combined with computational fluid dynamics (CFD) reactor-scale analysis (macro analysis) to elucidate the main reaction mechanism of GaAs-MOVPE process in the whole reactor. The reaction mechanism is different in different parts of the reactor. That means, we should use various kinetic parameters to preciously predict the growth procedure in the whole large-scale reactor.

Non-linear Kinetic Analysis of Decarburization and Deoxidization of Liquid Iron by Ar-CO-CO2 Gas Mixtures.

Decarburization and deoxidization of liquid iron in Ar-CO-CO 2 gas mixtures were investigated at 843 K using a cold crucible. The carbon or oxygen concentration decreased against their chemical potential gradients in the initial stage of the reactions. The concentration changes in the whole process were successfully reproduced by nonlinear equations based upon the two independent reactions in which the nonlinear reaction CO(g)=C+O was included. It has been shown that the decarburization of liquid iron in Ar-CO-CO 2 under reduced pressure can be also reasonably described by the nonlinear kinetic equations.

Comparison of the elimination of 10 and 20% TRAVAMULSION™ lipid emulsion from the blood of beagle dogs

Metabolic utilization of fat emulsions containing 20% lipid and 10% lipid were compared using beagles. The key parameter measured was elimination of the lipid from the bloodstream, which serves as an indication of the emulsion's availability for metabolism. Nonlinear kinetic analysis was used in this determination. Blood concentrations of free fatty acids, phospholipid, and cholesterol were also measured as additional ways of determining emulsion metabolism. The 10 and 20% emulsions appeared to be equivalent in elimination of the caloric substrate triglyceride from the blood stream. Results also showed an adaptation to emulsion infusion over time at both dosages administered (3 and 6 g/kg of body weight). This was indicated by increased elimination capacity and stabilization of each lipid class measured. However, blood concentrations of phospholipid and cholesterol indicate that the 20% emulsion provides a lesser lipid load for the amount of calories administered when compared to an emulsion containing 10% lipid.

Nonlinear kinetic analysis of the elimination of lipid emulsion administered intravenously to dogs.

A model based on a Michaelis-Menten nonlinear kinetic approach was used to analyze the kinetics of elimination of an intravenously infused lipid emulsion in the dog. The emulsion was administered at doses of 0.3, 3, or 6 g of lipid/kg of body weight. The model was applicable to all data regardless of the kinetic order of the elimination process operating. This can be either zero (linear), mixed, or first order (exponential). Furthermore, it was also found that parameters derived with the model can be used to predict the kinetics of elimination at different dosages. However, it was also shown that elimination parameters for a single bolus dose of lipid emulsion cannot be used to predict the manner in which a continuously infused dose will be eliminated.

Br*(2P1/2)+H2(v=0,1): Laser studies of the competition between reactive pathways and inelastic energy transfer channels

A systematic experimental study has been made on inelastic and reactive processes in the Br*(2P1/2)+H2(v=0,1) system. Laser photolysis and time-resolved infrared detection techniques allow direct observation of the previously unreported E–V equilibrium: Br*+H2(v=0)⇄kVEkEVBr +H2(v=1). A nonlinear kinetic analysis is presented that permits an estimate of the quantum efficiencies for the forward and reverse E–V processes, and provides an explanation for previous discrepancies in measured total Br* quenching rates with H2. In this work the quenching rate constant for Br*by H2 is determined at very low Br* concentrations to be 6.3(±1)×10−12 cm3 molecule−1 sec−1. At higher concentrations of Br*, second order processes involving collisions of Br*with H2(v=1) have been investigated. A substantial fraction of the Br*+H2(v=1) collisions react to form HBr(v=0)+H(2S1/2). It is suggested that the resonant E–V transfer pathway in the entrance channel Br*+H2(v=1) → Br+H2(v=2) may provide an efficient mechanism for potential surface crossing, thereby enhancing the reaction probability.

Evaluation of partial rate constants of competitive inhibition by analysis of nonlinear kinetics

The rate of binding of small ligands to proteins is usually measured by rapid reaction techniques and the detection relies on changes in physical properties of either enzyme or ligand. As physical changes are not specific, and small in magnitude, substrate concentrations of highly purified proteins are recommended. The same kind of information can be obtained using a methodology which avoids the need of high concentration of pure enzyme and, in some cases, of sophisticated instrumentation with high time resolution. The observed parameter in this method is the change in the rate of catalysis which is induced by the addition of a ligand reacting with a site which is already saturated by the substrate. The higher is the substrate concentration, the smaller is the free site concentration and the slower is the rate of the reaction with the ligand. The change in the rate of catalysis with time is subjected to mathematical presentation leading to equation suitable for calculating the rates of association and dissociation of the ligand. The example given below, the competitive inhibition of succinate dehydrogenase by malonate, demonstrates the advantages of the technique; the rate constants of association and dissociation of malonate are calculated using a catalytic amount of unpurified, membrane bound enzyme. The detection of the progress of the reaction is the usual method for monitoring the enzymic activity and