Kinetic aspects of ion exchange in KhFek[Fe(CN)(6)](l)center dot mH(2)O compounds: A combined electrical and mass transfer functions approach

The present paper quantifies and develops the kinetic aspects involved in the mechanism of interplay between electron and ions presented elsewhere(1) for KhFek[Fe(CN)(6)](l)center dot mH(2)O (Prussian Blue) host materials. Accordingly, there are three different electrochemical processes involved in the PB host materials: H3O+, K+, and H+ insertion/extraction mechanisms which here were fully kinetically studied by means of the use of combined electronic and mass transfer functions as a tool to separate all the processes. The use of combined electronic and mass transfer functions was very important to validate and confirm the proposed mechanism. This mechanism allows the electrochemical and chemical processes involved in the KhFek[Fe(CN)(6)](l)center dot mH(2)O host and Prussian Blue derivatives to be understood. In addition, a formalism was also developed to consider superficial oxygen reduction. From the analysis of the kinetic processes involved in the model, it was possible to demonstrate that the processes associated with K+ and H+ exchanges are reversible whereas the H3O+ insertion process was shown not to present a reversible pattern. This irreversible pattern is very peculiar and was shown to be related to the catalytic proton reduction reaction. Furthermore, from the model, it was possible to calculate the number density of available sites for each intercalation/deintercalation processes and infer that they are very similar for K+ and H+. Hence, the high prominence of the K+ exchange observed in the voltammetric responses has a kinetic origin and is not related to the amount of sites available for intercalation/deintercalation of the ions.

Non-isothermal kinetic of oxidation of tungsten carbide

Tungsten carbide, WC, has shown dissimilar thermal behavior when it is heated on changeable heating rate and flow of oxidant atmosphere. The oxidation of WC to WO3 tends to be in a single and slow kinetic step on slow heating rate and/or low flux of air. Kinetic parameters, on non-isothermal condition, could be evaluated to the oxidation of WC to heating rate below 15 degrees C min(-1) or low flow of air (10 mL min(-1)). The reaction is governed by nucleation and growth at 5 to 10 degrees C min(-1) then the tendency is to be autocatalytic, JMA and SB, respectively.

Kinetic parameters obtained for thermal decomposition of acrylic resins present in commercial paint emulsions

Samples of water based commercial acrylic resin paints were spread in a film form on slides, dried at room temperature and exposed to solar radiation for up to eight months.The characterization and quantification of resins and charges in the white paint emulsion were carried out for the thermal decomposition. Besides this, X-ray diffractometry was used to identify CaCO3 as charge and TiO2 (rutile phase) as pigment.It was observed through thermal techniques similar behavior to the samples even though with varied exposure time.Kinetic studies of the samples allowed to obtain the activation energy (Ea) and Arrhenius parameters (A) to the thermal decomposition of acrylic resin to three different commercial emulsion (called P-1, P-2, P-3) through non-isothermal procedures. The values of E. varied regarding the exposition time (eight months) and solar radiation from 173 to 197 U mol(-1) (P-1 sample), from 175 to 226 W mol(-1) (P-2 sample) and 206 to 197 kJ mol(-1) (P-3 sample).Kinetic Compensation Effect (KCE) observed for samples P-2 and P-3 indicate acrylic resin s present in these may be similar in nature. This aspect could be observed by a small difference in the thermal behavior of the TG curves from P I to P-2 and P-3 sample.The simulated kinetic model to all the samples was the autocatalytic estdk Berggreen.

Kinetic characterization of hypophosphatasia mutations with physiological substrates

We have analyzed 16 missense mutations of the tissue-nonspecific AP (TNAP) gene found in patients with hypophosphatasia. These mutations span the phenotypic spectrum of the disease, from the lethal perinatal/infantile forms to the less severe adult and odontohypophosphatasia. Site-directed mutagenesis was used to introduce a sequence tag into the TNAP cDNA and eliminate the glycosylphosphatidylinositol (GPI)-anchor recognition sequence to produce a secreted epitope-tagged TNAP (setTNAP). The properties of GPI-anchored TNAP (gpiTNAP) and setTNAP were found comparable. After introducing each single hypophosphatasia mutation, the setTNAP and mutant TNAP cDNAs were expressed in COS-1 cells and the recombinant flagged enzymes were affinity purified. We characterized the kinetic behavior, inhibition, and heat stability properties of each mutant using the artificial substrate p-nitrophenylphosphate (pNPP) at pH 9.8. We also determined the ability of the mutants to metabolize two natural substrates of TNAP, that is, pyridoxal-5'-phosphate (PLP) and inorganic pyrophosphate (PPi), at physiological pH. Six of the mutant enzymes were completely devoid of catalytic activity (R54C, R54P, A94T, R206W, G317D, and V365I), and 10 others (A16V, A115V, A160T, A162T, E174K, E174G, D277A, E281K, D361V, and G439R) showed various levels of residual activity. The A160T substitution was found to decrease the catalytic efficiency of the mutant enzyme toward pNPP to retain normal activity toward PPi and to display increased activity toward PLP. The A162T substitution caused a considerable reduction in the pNPPase, PPiase, and PLPase activities of the mutant enzyme. The D277A mutant was found to maintain high catalytic efficiency toward pNPP as substrate but not against PLP or PPi. Three mutations ( E174G, E174K, and E281K) were found to retain normal or slightly subnormal catalytic efficiency toward pNPP and PPi but not against PLP. Because abnormalities in PLP metabolism have been shown to cause epileptic seizures in mice null for the TNAP gene, these kinetic data help explain the variable expressivity of epileptic seizures in hypophosphatasia patients.

Determination of low-aliphatic aldehydes indoors by micellar electrokinetic chromatography using sample dissolution manipulation for signal enhancement

This work describes a novel approach for the analysis of selected aldehydes (formaldehyde, acetaldehyde, propionaldehyde, and acrolein) and acetone in environmental samples using micellar electrokinetic chromatography (MEKC). The method is based on the reaction of carbonyl compounds with 3-methyl-2-benzothiazoline hydrazone (MBTH) that gives an azine intermediate with maximum absorbance at 216 nm. A systematic evaluation of sample dissolution medium was conducted as a means to enhancing sensitivity. In the best condition, samples were dissolved in 0.030 mol.L-1 tetraborate solution. This condition presented enhancement factors in the range of 35-54 for the aldehydes under investigation, computed as the improvement of the concentration limits of detection (LODs) with reference to the sample dissolved in pure water. The running buffer was 0.020 mol.L-1 tetraborate, pH 9.3, containing 0.050 mol-L-1 sodium dodecyly sulfate (SIDS). The overall methodology presented several advantages over established methods for aldehydes. Worthy mentioning that MBTH is available in high purity degree, dispensing laborious reagent purification procedures. A few method validation parameters were determined revealing good migration time repeatability (< 2.5% coefficient of variation, CV) and area repeatability (< 4% CV), excellent linearity (20-120 mug/L, r > 0.995) and adequate sensitivity for environmental applications. The LODs with respect to each single aldehyde were in the range of 0.54-4.0 mug.L-1 and 11 mug.L-1 for acetone. The methodology was applied to the determination of aldehydes indoors. Samples were collected in an impinger flask containing 0.05% MBTH solution, at a flow rate of 0.80 L.min(-1), during 2.5 h, at different times during the day. The most abundant carbonyls in the samples were acetone, followed by formaldehyde and acetaldehyde, with estimate peak concentrations of 452, 5.2 and 2.2 ppbv, respectively.

KINETIC-PROPERTIES OF OSSEOUS PLATE ALKALINE-PHOSPHATASE FROM DIABETIC RATS

1. Increased levels of bone alkaline phosphatase activity were observed in diabetic rats. These animals exhibited impaired bone development without concomitant alterations of the sequence of cellular transformations.2. Alkaline phosphatase activity was delayed in diabetic rats but the kinetic parameters for the hydrolysis of p-Nitrophenylphosphate (PNPP) were virtually the same observed for controls (N = 1.2 and K0.5 = 43 muM).3. Alkaline phosphatase from diabetic rats had a better affinity (K0.5 = 38 muM) for magnesium ions than controls (K0.5 = 9 1 muM).4. Zinc ions affected alkaline phosphatase activity from control and diabetic rats in the same way (K0.5 = 10 muM).

Kinetic parameters of polymer degradation by SAPO-37

High density poly(ethylene) has been submitted to thermal degradation alone, and in the presence of silicoaluminophosphate SAPO-37. The processes were carried out in a reactor connected on line to a gas chromatograph/mass spectrometer in order to analyze the evolved products. Polymer degradation was also evaluated by thermogravimetry, from room temperature until 800 degreesC, under nitrogen dynamic atmosphere, with multiple heating rates. From TG curves, the activation energy related to degradation process was calculated using the Flynn and Wall multiple heating rate kinetic model for pure polymer (PE) and for polymer in the presence of catalyst (PE/S37). SAPO-37 showed good selectivity for low molecular mass hydrocarbons in PE catalytic degradation.

Kinetic studies on clavulanic acid degradation

Clavulanic acid (CA), a potent beta-lactamase inhibitor, is very sensitive to pH and temperature. It is produced by Streptomyces clavuligerus and to optimize both the fermentation step and the downstream process, the expression of the hydrolysis kinetics has to be determined. In the present work the CA degradation rate from various sources was investigated at temperatures of 10, 20, 25, 30 and 40degreesC and PH values of 6.2 and 7.0. The results showed that first-order kinetics explained very well the hydrolysis kinetics and the Arrhenius equation could be applied to establish a relationship between the degradation rate constant and temperature, at both pHs. It has been observed that CA from fermentation medium was much more unstable than that from standard solution and from a commercially available medicine. Also, it was observed that CA was more stable at PH 6.2 than at pH 7.0, irrespective of the CA source. (C) 2004 Elsevier B.V. All rights reserved.

Procedure optimization of silicate rocks dissolution in open vessels for ICP-AES analysis.

The main variables found on procedure of the dissolution silicate rocks using acid dissolution in teflon open vessel for analysis of micro elements by ICP-AES has been determined. The results obtained for some samples showed strong dependence of the rock mineralogical composition, then it was recommended an alkaline fusion step after acid dissolution. The decomposition procedure use 20 mi of an acid mixture of HF:HNO3 in the proportion 3:1 for a fraction of 250 mg pulverized sample. The recommended temperatures were 60 degrees C for attack and 90 degrees C for acid volatilization. The fusion step with 50 mg LiBO2 at 1000 degrees C may be used if non-attacked residue is observed in the solution. The whole time was 6 h per sample. Nine types os silicate rocks that show mineralogical and chemical different compositions were chosen for obtaining the optimization of the variables. The elements used were Ce, Y, Yb and Zr. In addition, ultrassonic nebulization has been used. The percentual standard deviations obtained for five determinations were 0.7 and 1.4 for triplicate samples. The mineralogical and textural information from the petrographical analysis of the samples indicated the need of increasing the fusion step on the optimized procedure.

Tin(II)-EDTA complex: kinetic of thermal decomposition by non-isothermal procedures

Tin on the oxide form, alone or doped with others metals, has been extensively used as gas sensor, thus, this work reports on the preparation and kinetic parameters regarding the thermal decomposition of Sn(II)-ethylenediaminetetraacetate as precursor to SnO2. Thus, the acquaintance with the kinetic model regarding the thermal decomposition of the tin complex may leave the door open to foresee, whether it is possible to get thin film of SnO2 using Sn(II)-EDTA as precursor besides the influence of dopants added.The Sn(II)-EDTA soluble complex was prepared in aqueous medium by adding of tin(II) chloride acid solution to equimolar amount of ammonium salt from EDTA under N-2 atmosphere and temperature of 50degreesC arising the pH similar to 4. The compound was crystallized in ethanol at low-temperature and filtered to eliminate the chloride ions, obtaining the heptacoordinated chelate with the composition H2SnH2O(CH2N(CH2COO)(2))(2).0.5H(2)O.Results from TG, DTG and DSC curves under inert and oxidizing atmospheres indicate the presence of water coordinated to the metal and that the ethylenediamine fraction is thermally more stable than carboxylate groups. The final residue from thermal decomposition was the SnO2 characterized by X-ray as a tetragonal rutile phase.Applying the isoconversional Wall-Flynn-Ozawa method on the DSC curves, average activation energy: E-a = 183.7 +/- 12.7 and 218.9 +/- 2.1 kJ mol(-1), and pre-exponential factor: log A = 18.85 +/- 0.27 and 19.10 +/- 0.27 min(-1), at 95% confidence level, could be obtained, regarding the loss of coordinated water and thermal decomposition of the carboxylate groups, respectively. The E-a and logA also could be obtained applying isoconventional Wall-Flynn method on the TG curves.From E-a and log A values, Dollimore and Malek procedures could be applied suggesting R3 (contracting volume) and SB (two-parameter model) as the kinetic model to the loss of coordinated water (177-244degreesC) and thermal decomposition of the carboxylate groups (283-315degreesC), respectively. Simulated and experimental normalized DTG and DSC curves besides analysis of residuals check these kinetic models. (C) 2003 Elsevier B.V. All rights reserved.

Bayesian L-optimal exact design of experiments for biological kinetic models

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Effects of Exercise Mode on the Oxygen Uptake Kinetic Response to Severe-Intensity Exercise in Prepubertal Children

The objective of this study was to verify the effect of the exercise mode on slow component of VO(2) (VO(2)SC) in children aged 11-12 years during severe-intensity exercise. After determination of the lactate threshold (LT) and peak VO(2) (VO(2)peak) in both cycling (CE) and running exercise (TR), fourteen active boys completed a series of "square-wave" transitions of 6-min duration at 75%Delta [75%Delta = LT + 0.75 X (VO(2)peak-LT)l to determine the VO(2) kinetics. The VO(2)SC was significantly higher in CE (180.5 +/- 155.8 ml . min(-1)) than in TR (113.0 +/- 84.2 ml . min(-1)). We can conclude that, although a VO(2)SC does indeed develop during TR in children, its magnitude is considerably lower than in CE during severe-intensity exercise.

Real-time monitoring and kinetic parameter estimation of the affinity interaction of jArtinM and rArtinM with peroxidase glycoprotein by the electrogravimetric technique

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Kinetic properties of glycerophosphate oxidase isolated from dry baker's yeast

The glycerophosphate oxidase is a flavoprotein responsible for the catalysis of the oxidation of the glycerophosphate to dihydroxyacetone phosphate, through the reduction of the oxygen to hydrogen peroxide. The glycerophosphate oxidase from baker's yeast was specific for L-alpha-glycerol phosphate. It was estimated by monitoring the consumption of oxygen with an oxygraph. An increase of 32% in consumption of oxygen was obtained when the enzyme was concentrated 16-fold. The assay of enzyme was determined by the peroxidase chromogen method followed at 500 nm. The procedure for the standardization of the activity of the glycerophosphate oxidase from baker's yeast was accomplished, and the pH and temperature stability showed that the enzyme presented a high stability at pH 8.0, and the thermal stability was maintained up to 60 degrees C during I h. Such method allowed quantifying in the range 92-230 mM of glycerol phosphate, an important intermediate metabolite from lipid biosynthesis and glycolytic routes. (C) 2007 Elsevier B.V. All rights reserved.