Initial Rate Approach Research Articles

Effect of Mg on the Structural, Optical and Thermoluminescence Properties of Li3Al3(BO3)4: Shift in Main Glow Peak

The doping of magnesium on lithium aluminium borate phosphor is reported in this study. A solid-state sintering technique was employed as the borate samples were synthesized. This report focuses on the structural, optical, thermoluminescence, and kinetic analyses of the main glow peak. The structural properties of lithium aluminium borates improved due to the magnesium dopants used. Differences in the crystallite size and particle size were 38.85-67.35 nm and 50-60 nm, respectively, and these results were obtained from the analyzed X-ray diffractogram and scanning electron spectroscopy. The energy band gaps obtained from the direct transition of borate phosphor materials were within the range of 3.00-4.40 eV, and the doped samples gave a higher energy band gap. A decrease in the TGA (%) exhibited a weight loss or water loss for the undoped, 0.1% Mg, and 0.3% Mg-doped lithium aluminium borate materials. The glow curve measured at a heat rate of 1 °C·s-1 after irradiation to 50 Gy revealed four peaks related to the magnesium doped lithium aluminium borate. The main glow peak was observed at 86 °C. Activation energy was extracted from the main glow peak by using kinetic analysis which involves the initial rise, deconvolution, and variable heating rate approach, and it was approximately 0.67 ± 0.03 eV. A shift in the main glow peak curve from 86 to 110 °C was recognized for the magnesium-doped lithium aluminium borate when it was irradiated from 1 to 300 Gy.

Electrochemical Oxidation of 6:2 Polyfluoroalkyl Phosphate Diester-Simulation of Transformation Pathways and Reaction Kinetics with Hydroxyl Radicals.

Polyfluoroalkyl phosphate diesters (diPAPs) are widely used for paper and cardboard impregnation and discharged via waste streams from production processes and consumer products. To improve the knowledge about the environmental fate of diPAPs, electrochemical oxidation (EO) was used to characterize the transformation pathways and reaction kinetics. 6:2 diPAP was transformed electrochemically to perfluorocarboxylic acids (C5-C7 PFCAs) and two intermediates (6:2 fluorotelomer carboxylic acid, FTCA, and 6:2 fluorotelomer unsaturated carboxylic acid, FTUCA). EO of potential intermediates 6:2 monoPAP and 6:2 fluorotelomer alcohol (FTOH) showed similar transformation products but with different ratios. We show that 6:2 diPAP is initiated by OH radical (•OH) reactions, as evidenced by the measured steady-state concentrations of •OH with the probe molecule terephthalic acid, quenching experiments, and pH dependency of the reaction. PFHpA was the main product of 6:2 diPAP oxidation, and it was formed in a pseudo-first-order reaction for which a bimolecular rate constant was estimated to be = 9.4(±1.4) × 107 M-1 s-1 by an initial rate approach. This can be utilized to estimate the environmental half-life of 6:2 diPAP for the reaction with •OH and the formation kinetics of persistent PFCAs.

7 - Kinetic Characterization of the Redox Regulation of OhrR

Pseudomonas aeruginosa is a pathogen that needs to cope with the oxidative insult imposed by the mammalian host. Organic Hydroperoxide Resistance protein (Ohr) is a Cys-based peroxidase that together with its transcriptional regulator Organic Hydroperoxide Resistance Regulator (OhrR) comprises a system that is central to the P. aeruginosa response towards organic hydroperoxides and peroxynitrite. Expression of Ohr gene is regulated by OhrR, which has the ability to bind to DNA, modulated by the oxidation of a critical Cys residue. Therefore, we investigate the kinetics of OhrR oxidation and reduction by the changes of its intrinsic fluorescence. The second-order rate constant for the reactions of OhrR from P. aeruginosa (PaOhrR) with tert-butyl hydroperoxide (tBHP) and with fatty acid hydroperoxides were in the 103 M-1 s-1 and in the 106M-1 s-1ranges, respectively. The second-order rate constant for the reaction between OhrR and peroxynitrite was determined as 6x105 M-1 s-1by initial rate approach. No redox dependent change in the fluorescence of PaOhrRC19S was observed, which is consistent with the notion that Cys19 is the reactive Cys. The OhrR from Chromobacterium violaceum (CvOhrR) was also investigated as its redox dependent ability to bind DNA was previously characterized. As PaOhrR, CvOhrR also reacted with tBHP with a rate constant in the 103 M-1 s-1 range. In contrast, reaction of CvOhrR with oleic acid hydroperoxide was considerably slower (103 M-1 s-1) than the equivalent reaction of PaOhrR. Concerning the reduction of CvOhrR, DTT and lipoamide were very poor reductants, whereas thioredoxin A (TrxA) reacted with the transcription factor with rate constants in the 104 M-1 s-1 range. Currently, we are investigating whether the binding of CvOhrR to its target DNA might affect its oxidation by distinct hydroperoxides. The kinetic characterization of OhrR proteins can improve our knowledge on the mechanisms underlying the response of bacteria to fatty acid hydroperoxides and peroxynitrite, two oxidants present at the host pathogen interface.

Pre-study and in-study validation of a size-exclusion chromatography method with different detection modes for the analysis of monoclonal antibody aggregates.

Size exclusion chromatography (SEC) with different detection modes was assessed as a means to characterize the type of bevacizumab aggregate that forms under thermal stress, quantitatively monitoring the aggregation kinetics. The combination of SEC with light-scattering (SEC/LS) detection was validated using in-study validation process. This was performed by applying a strategy based on a control chart to monitor the process parameters and by inserting quality control samples in routine runs. The SEC coupled with a differential refractive-index detector (SEC/RI) was validated using a pre-study validation process in accordance with the ICH-Q2 (R1) guidelines and in-study monitoring in accordance with the Analytical Target Profile (ATP) criteria. The total error and β-expectation tolerance interval rules were used to assess method suitability and control the risk of incorrectly accepting unsuitable analytical methods. The aggregation kinetics data were interpreted using a modified Lumry-Eyring model. The true order of the reaction was determined using the initial-rate approach. All the kinetic data show a linear Arrhenius dependence within the studied temperature range. The Arrhenius approach over-predicted the aggregation rate for 5°C, but provides an idea of the aggregation process and amount of aggregate formed. In any case, real-time stability data are necessary to establish the product shelf-life.

Assessment of four loss methods in simulation of flood hydrograph case study: Kasilian Basin

The aim of this study is to evaluate the effect of loss methods application on run-off volume and hydrograph shape used by hydrologic models. In this research, four loss methods including constant loss (φ index), initial loss-loss rate, SCS and constant fraction approach were applied to be evaluated. To do this, Clark Rainfall-Runoff model was applied for 24 storm events from Kasilain basin. Then, characteristics of calculated hydrographs including peak discharge, runoff volume and time to peak were compared with the same characteristics of the same observed hydrographs and analysed statistically. Statistical analysis of the effect of mentioned loss methods on characteristics of hydrographs using mean relative error, coefficient of determination (R²) and root mean square error, showed the relative superiority of the SCS, initial loss-loss rate, constant loss, and constant fraction (proportional loss) methods, respectively. Therefore, the initial losses have a significant effect on the rainfall abstraction for flood hydrographs simulation in forest areas.

A Kinetic Study on Sesame Cake Protein Hydrolysis by Alcalase

In the present study, the hydrolysis of sesame cake protein was performed by Alcalase, a bacterial protease produced by Bacillus licheniformis, to investigate the reaction kinetics of sesame cake hydrolysis and to determine decay and product inhibition effects for Alcalase. The reactions were carried out for 10 min in 0.1 L of aqueous solutions containing 10, 15, 20, 25, and 30 g protein/L at various temperature and pH values. To determine decay and product inhibition effects for Alcalase, a series of inhibition experiments were conducted with the addition of various amounts of hydrolysate. The reaction kinetics was investigated by initial rate approach. The initial reaction rates were determined from the slopes of the linear models that fitted to the experimental data. The kinetic parameters, K(m) and V(max), were estimated as 41.17 g/L and 9.24 meqv/L x min. The Lineweaver-Burk plots showed that the type of inhibition for Alcalase determined as uncompetitive, and the inhibition constant, K(i), was estimated as 38.24% (hydrolysate/substrate mixture). Practical Application: Plant proteins are increasingly being used as an alternative to proteins from animal sources to perform functional roles in food formulation. Knowledge of the kinetics of the hydrolysis reaction is essential for the optimization of enzymatic protein hydrolysis and for increasing the utilization of plant proteins in food products. Therefore, in the present study, the hydrolysis of sesame cake protein was performed by Alcalase, a bacterial protease produced by B. licheniformis, to investigate the reaction kinetics of sesame cake hydrolysis and to determine decay and product inhibition effects for Alcalase.

Gas Pressure Monitored Iodide-Catalyzed Decomposition Kinetics of H2O2: Initial-Rate and Integrated-Rate Methods in the General Chemistry Lab

The reaction kinetics of the iodide-catalyzed decomposition of H2O2 using the integrated-rate method is described. The method is based on the measurement of the total gas pressure using a datalogger and pressure sensor. This is a modification of a previously reported experiment based on the initial-rate approach.

Oxyfunctionalisation of adamantane using inorganic–organic hybrid materials based on isopoly and heteropoly anions: Kinetics and mechanistic studies

Oxyfunctionalisation of adamantane with 30% aq.H2O2 in butyronitrile solvent was efficiently catalyzed by inorganic–organic hybrid materials synthesized by the immobilisation of isopoly (WOx = sodium tungstate, MoOx = sodium molybdate and VOx = sodium metavanadate) and heteropoly anions (V1 = H4[PMo11VO40]·32·5H2O,and V3 = H6[PMo9V3O40]·34H2O, STA = silicotungstic acid, TPA = tungstophosphoric acid and MPA = molybdophosphoric acid) onto mesoporous silica (SBA-15). These catalysts were well characterized by standard techniques and it was found that polyoxometalate has been retained all its bulk characteristics upon immobilisation onto mesoporous silica. Among the catalysts 10-molybdo-2-vanadophosphoric acid (H5[PMo10V2O40]·32·5H2O) immobilized onto amine-functionalized SBA-15 gave the highest activity under the conditions in the liquid phase oxidation of adamantane with 30% aq.H2O2 in butyronitrile solvent and gave mainly 1-adamantanol. Kinetic parameter measurements were performed by following initial rate approach for determining the rate dependence of the reaction. In situ UV-vis and electron paramagnetic resonance (EPR) spectroscopic studies carried out showed that the vanadium (V) superoxo intermediate species formed was responsible for the CH bond activation of adamantane to give 1-adamentanol. Based on this, a plausible mechanism for the oxidation of adamantane to 1-adamantanol has been proposed. The catalysts leaching studies carried out by following a standard procedure ruled out any contribution by the active vanadium species that could leach into the reaction medium and catalysts were truly functioned as heterogeneous catalysts.

Chemoselective anti-Markovnikov hydroamination of α,β-ethylenic compounds with amines using montmorillonite clay

The catalytic activity of montmorillonite clays as a catalyst for the hydroamination of α,β-ethylenic compounds with amines was tested. Aniline and substituted anilines reacted with α,β-ethylenic compounds in the presence of catalytic amount of commercially available clay to afford exclusively anti-Markovnikov adduct in excellent yields. Aniline reacted with ethyl acrylate to yield only anti-Markovnikov adduct N-[2-(ethoxycarbonyl)ethyl]aniline (mono-addition product). No Markovnikov adduct ( N-[1-(ethoxycarbonyl)ethyl]aniline and double addition product N, N-bis[2-(ethoxycarbonyl)ethyl]aniline were formed under selected reaction conditions. For a better exploitation of the catalytic activity in terms of increased activity and improved selectivity for the mono-addition product, the reaction parameters were optimized in terms of temperature, solvent, reactant mole ratio. Under optimized reaction conditions, montmorillonite clay K-10 showed a superior catalytic performance in the hydroamination of ethyl acrylate with aniline with a conversion of aniline to mono-addition product (almost 100% chemoselectivity) with a high rate constant 0.3414 min −1 compared to the reported protocols. The dependence of conversion of aniline over different types of montmorillonite clays (K-10, K-20, K-30, Al-Pillared clay and untreated clay) has also been discussed. The activities of clay for the hydroamination of different aromatic and aliphatic amines have also been investigated. Under harsh reaction conditions (increased temperature and long reaction time) small amounts of di-addition products were observed. The kinetics data has been interpreted using the initial rate approach model.

Toward an Understanding of Biogenic-silica Dissolution in Seawater – An Initial Rate Approach Applied between 40 and 90 °C

The kinetics of phytoplankton frustule dissolution has generally been studied as the appearance of silicic acid in a batch reactor. Unfortunately, this approach, though often illuminating, has not so far been successful because of the difficulty of parameterising the full reaction curve. This current study shows how the initial rate approach to chemical kinetics offers a way around this bottleneck, thereby allowing much chemical kinetics information about frustule dissolution to be collected. The technique is shown to be flexible and suited to short reaction times which facilitate detailed quantitative kinetics investigation, indeed, as would be expected in a solution phase, kinetics study. The technique is exemplified by a dissolution study of uncleaned frustules of Cyclotella crypticaat 40 °C and above. The frustules were found to yield the same dissolution rate after 5 weeks dark storage, at 4 °C. Meanwhile, log dissolution rate was found to vary linearly with pH, with gradient 0.38 ± 0.01 (r 2=0.990). Linearity was upheld even at pHs as high as 14. Finally, a robust Arrhenius plot was established between 40 and 90 °C yielding an activation energy for dissolution of 84 ± 3 kJ mol −1. Follow through with the Eyring equation yielded an activation enthalpy, ΔH ‡, and an activation entropy, ΔS ‡, of 81 and 85 J mol −1 K −1, respectively. The discussion brings salient aspects of existing knowledge about diatom frustule dissolution kinetics into the wider context of silicate mineral dissolution.

Modeling the sequential photodechlorination of hexachlorobenzene in surfactant micelles

A five-stage consecutive irreversible model is derived to predict the photodegradation of hexachlorobenzene (HCB) in a surfactant solution, which was proven to be a useful treatment process following the surfactant-aided soil washing or remediation. The photodegradation of HCB in surfactant micelles is dominated by photodechlorination, which sequentially removes chlorides one at a time. The minor pathways of photoisomerization and photochlorination were neglected in the kinetic model. The results show that the derived consecutive irreversible model can accurately predict the decay of HCB and the formation (and decay) of its less-chlorinated congeners. The initial rate approach was used to identify the proper range of decay rate of each chlorinated benzene; so the overall rate constants can be determined easier by trial. The decreased performance of a completely mixed flow reactor (CMFR) with continuous input is also quantified compared to a batch reactor.

Kinetic study and analytical applications of micellar catalyzed reactions of 1-fluoro-2,4-dinitrobenzene with inorganic thioanions using a fluoride-selective electrode

A kinetic study and analytical applications of the CPC micellar catalyzed reactions of 1-fluoro-2,4-dinitrobenzene (FDNB) with inorganic thioanions (sulfide, sulfite and thiosulfafte) using a fluoride-selective electrode is described. Reaction orders (unity for both FDNB and thioanion) and experimental stoichiometric reaction-rate constants were calculated from initial slope measurements (Δ E/Δ t) at various pH values (4–9). Calibration graphs for quantitative determinations (4.5–45 μM for sulfide, 2.4–75 μM for thiosulfate and 6.6–75 μM for sulfite) are constructed using the initial rate approach. The proposed method has been applied to the determination of sulfide in spiked seawater samples using the multiple standard addition approach with a mean relative error of 5.5%. The application of this micellar catalyzed reaction in the differential kinetic analysis of binary mixtures of sulfide–thiosulfate and sulfite–thiosulfate, using the proportional equations approach at pH 5.5 and 8.0, was unsuccessful due to the interactions of the two analytes, which can be explained using the ion-exchange/pseudophase model of micellar catalysis. However, the use of multiple linear regression approach on a sufficient number of standard binary mixtures can confront this drawback.

Kinetics of oxidation of β-isophorone to keto-isophorone catalyzed by manganese Schiff base complex using molecular oxygen

Kinetic investigations were carried out on the oxidation of β-isophorone (β-IP) to keto-isophorone (KIP) catalyzed by [LMn(III)(Cl)], (where, L=bis-salicylaldehydeethylenedi-imine, salen) at temperature in the range 10–27°C and partial pressure 0.2–3 atm of molecular oxygen. β-IP gave mainly KIP as the oxidation product under the reaction conditions studied. Initial rate approach was adopted to evaluate kinetic parameters of the reaction. From the kinetic investigations, it was found that the rate of oxidation of β-IP showed a first-order dependence with respect to catalyst and substrate concentrations, and half-order dependence on the partial pressure of oxygen. The effect of temperature on the rates of oxidation was also investigated and from the Arrhenius plot of −ln rate vs. 1/ T, the activation energy estimated is 16.12 kcal mol −1. Thermodynamic activation parameters such as enthalpy, entropy and free energy of the reaction were calculated from the known thermodynamic equations. Based on the kinetic investigations, a plausible mechanism for manganese salen complex catalyzed oxidation of β-IP to KIP has been proposed.

Kinetics of Peroxynitrite Reaction with Amino Acids and Human Serum Albumin

An initial rate approach was used to study the reaction of peroxynitrite with human serum albumin (HSA) through stopped-flow spectrophotometry. At pH 7.4 and 37 degreesC, the second order rate constant for peroxynitrite reaction with HSA was 9.7 +/- 1.1 x 10(3) M-1 s-1. The rate constants for sulfhydryl-blocked HSA and for the single sulfhydryl were 5.9 +/- 0.3 and 3.8 +/- 0.8 x 10(3) M-1 s-1, respectively. The corresponding values for bovine serum albumin were also determined. The reactivity of sulfhydryl-blocked HSA increased at acidic pH, whereas plots of the rate constant with the sulfhydryl versus pH were bell-shaped. The kinetics of peroxynitrite reaction with all free L-amino acids were determined under pseudo-first order conditions. The most reactive amino acids were cysteine, methionine, and tryptophan. Histidine, leucine, and phenylalanine (and by extension tyrosine) did not affect peroxynitrite decay rate, whereas for the remaining amino acids plots of kobs versus concentration were hyperbolic. The sum of the contributions of the constituent amino acids of the protein to HSA reactivity was comparable to the experimentally determined rate constant, where cysteine and methionine (seven residues in 585) accounted for an estimated 65% of the reactivity. Nitration of aromatic amino acids occurred in HSA following peroxynitrite reaction, with nitration of sulfhydryl-blocked HSA 2-fold higher than native HSA. Carbon dioxide accelerated peroxynitrite decomposition, enhanced aromatic amino acid nitration, and partially inhibited sulfhydryl oxidation of HSA. Nitration in the presence of carbon dioxide increased when the sulfhydryl was blocked. Thus, cysteine 34 was a preferential target of peroxynitrite both in the presence and in the absence of carbon dioxide.

Alteration of glucose consumption kinetics with progression of baculovirus infection in Spodoptera frugiperda cells.

We have used the initial-rate approach to characterize changes in the glucose consumption kinetics of baculovirus-infected Spodoptera frugiperda clone 9 (Sf9) cells with the progression of the infection process. The specific glucose consumption rate (qG) of cultured baculovirus-infected Sf9 cells was measured at 4, 8, 12, 16, and 24 h postinfection (h.p.i.) in media containing 4-35 mM glucose. Higher medium glucose concentrations resulted in higher final extracellular virus and recombinant beta-galactosidase yields. qG was related to the extracellular glucose concentration by means of a Michaelis-Menten relationship. The apparent Michaelis-Menten constant (K(m)) for glucose consumption was found not to change significantly during the progression of the infection process, and remained between 6.2 and 7.2 mM. However, the maximal specific glucose consumption rate (qGmax) was found to rapidly increase after infection, peaking at 16 h.p.i. at a value four times that for uninfected Sf9 cells. The kinetic analysis of glucose consumption rates in baculovirus-infected Sf9 cells presented here will aid in the optimal design and operation of bioreactor systems for the large-scale production of recombinant products from the baculovirus/insect cell system.

Mathematical descriptions of hybridoma culture kinetics: I. Initial metabolic rates

The lack of quantitative descriptions of mammalian culture kinetics limits the ability to optimally design and control cell culture bioreactors. This limitation is ad dressed by developing mathematical equations relating the initial growth rate and the antibody productivity of the hybridoma cell line, CRL-1606, to its environmental state. This initial rate approach, in contrast with steady state analysis of chemostat cultures, approximates steady state behavior, since the rates were measured over brief time intervals and at low cell concentrations (< 50,000 cells/mL). The advantage of this approach is that it is much faster than the chemostat approach.An equation for the growth rate was developed that superimposed Monod equations in serum and glutamine with "noncompetitive" -type inhibition constants were inversely proportional to the lactate and ammonium concentrations. The Monod constant is critical for relating initial, low cell level culture states to other states.Lactate was found to be the only environmental parameter that significantly inhibited antifibronectin monoclonal antibody production by the CRL-1606 hybridomas. Volumetric productivity was strictly related to culture viability, which was observed to decline at growth rates below 0.02 h(-1). Lactate was also found to significantly inhibit ammonium production.

On the Estimation of the Partial Quantum Yields for phytochrome photoconversion by a nonlinear least‐squares method

AbstractA nonlinear least‐squares method is presented which enables the estimation of the partial quantum yields of a photoreversible two component system by fitting the corresponding kinetic equation directly to experimentally measured data.The principles of this method are discussed with reference to the photochromic transformation of phytochrome as an adequate model. It is demonstrated that this method yields sufficiently accurate and highly reliable results.In addition, the advantage of the nonlinear least‐squares method when compared with the so‐called formal integration method and with the initial rate approach is emphasized.

Simultaneous Determination of Silica and Phosphate in Water from a Single Experiment Using a Miniature Centrifugal fast Analyzer

Abstract The utility of Centrifugal Fast Analyzers for kinetic analyses of inorganic constituents is discussed and is illustrated for the simultaneous determination of silica and orthophosphate as the unreduced heteropoly acids. Silica is determined by an initial-rate approach, whereas the absorbance intercept is a measure of the orthophosphate content of the sample.

Random errors in kinetic data from a catalytic flow reactor

Kinetic measurements of cyclohexanol dehydration on alumina at 200 °C were conducted using a flow apparatus. The initial reaction rate approach was used to obtain data suitable for statistical evaluation of experimental error. The contribution of various error sources to the overall uncertainty of results was estimated either independently or by analysis of variance. Using the same procedure three sets of kinetic data from the work of other authors were also evaluated and information was obtained concerning the influence of minor changes of experimental technique on precision. The significance of errors found in dependent and independent variables is discussed and recommendations for improvement of experimental design are given.

Kinetics of catalytic oxidation of methane: Application of initial rate technique for mechanism determination

AbstractA kinetic investigation on the oxidation of methane using a palladium catalyst was conducted. Conversions of methane were small and limited to about 10% to facilitate the use of initial rate approach. Plots of initial rate against total pressure and varying feed composition were used to interpret the data qualitatively. Regression coefficients from linearized rate equations and criteria of best fit were used to arrive at a plausible mechanism. The experimental results indicated that the reaction rate is controlled by surface reaction in which the adsorbed oxygen and adsorbed methane react to produce adsorbed carbon dioxide and adsorbed water.