Kinetic parameters of soil β-glucosidase response to environmental temperature and moisture regimes

Soil β-glucosidase participates in the final step of cellulose biodegradation. It is significant in the soil C cycle and is used as an indicator of the biological fertility of soil. However, the response of its kinetic parameters to environmental temperature and moisture regimes is not well understood. This study tested the β-glucosidase response in the main agricultural soils (black soil, albic soil, brown soil, and cinnamon soil) of Northeast China. Incubation tests were conducted to measure the kinetic parameters Km, Vmax or Vmax/Km of soil β-glucosidase at environmental temperatures of 10, 20 and 30 ºC and at 10, 20 and 30 % soil moisture content. The insensitive response of the kinetic parameters to temperature changes indicates that soil β-glucosidase was present primarily in immobilized form. The significant response of the kinetic parameters of soil β-glucosidase to soil moisture rather than to environmental temperatures suggests that the catalytic ability of soil β-glucosidase was sensitive to changing soil moisture regimes.

Kinetic parameters of silicon uptake by rice cultivars

Silicon is considered an important chemical element for rice, because it can improve tolerance to biotic and abiotic stress. However, in many situations no positive effect of silicon was observed, probably due to genetic factors. The objective of this research was to monitor Si uptake kinetics and identify responses of rice cultivars in terms of Si uptake capacity and use. The experiment was carried out in a greenhouse of the São Paulo State University (UNESP), Brazil. The experiment was arranged in a completely randomized, factorial design with three replications. that consisted of two rice cultivars and two Si levels. Kinetic parameters (Vmax, Km, and Cmin), root morphology variables, dry matter yield, Si accumulation and levels in shoots and roots, uptake efficiency, utilization efficiency, and root/shoot ratio were evaluated. Higher Si concentrations in the nutrient solution did not increase rice dry matter. The development of the low-affinity silicon uptake system of the rice cultivar 'Caiapó' was better than of 'Maravilha'.

Effect of metal ions on the in vitro availability of enoxacin, its in vivo implications, kinetic and antibacterial studies

The present paper describes the effect of metals ions on the in vitro availability of enoxacin (a second generation quinolone antibiotic) owing to drug-metal interaction. These interaction studies were performed at 37 °C in different pH environments simulating human body compartments and were studied by UV spectroscopic technique. In order to determine the probability of these reactions different kinetic parameters (dissolution constants (K) and free energy change (ΔG)) for these reactions were also calculated. It is proposed that the structure of enoxacin contains various electron donating sites which facilitate its binding with metallic cations forming chelates. Hence taking food products, nutritional supplements or multivitamins containing multivalent cations at the same time as enoxacin, could reduce the absorption of the drug into the circulation and thus would decrease the effectiveness of the drug. In addition, the MIC of enoxacin for various microorganisms before and after interaction with metal ions was calculated which in most cases was increased which possibly could impair the clinical efficacy of the drug.

Dehydration and volatilization non isothermic kinetic of the solid state aluminium 8-hydroxyquinolinate

Al(C9H6ON)3.2.5H2O was precipitated from the mixture of an aqueous solution of aluminium ion and an acid solution of 8-hydroxyquinoline, by increasing the pH value to 9.5 with ammonia aqueous solution. The TG curves in nitrogen atmosphere present mass losses due to dehydration, partial volatilisation (sublimation plus vaporisation) of the anhydrous compound followed by thermal decomposition with the formation of a mixture of carbonaceous and residues. The relation between sublimation and vaporisation depends on the heating rate used. The non isothermic integral isoconventional methods as linear equations of Ozawa-Flynn-Wall and Kissinger-Akahira-Sunose (KAS) were used to obtain the kinetic parameters from TG and DTA curves, respectively. Despite the fact that both dehydration and volatilisation reactions follow the linearity by using both methods, only for the volatilisation reaction the validity condition, 20<= E/RT<= 50, was verified.

Kinetic behavior of nitrification in the post-treatment of poultry wastewater in a sequential batch reactor

A sequential batch reactor with suspended biomass and useful volume of 5 L was used in the removal of nutrients and organic matter in workbench scale under optimal conditions obtained by central composite rotational design (CCRD), with cycle time (CT) of 16 h (10.15 h, aerobic phase, and 4.35 h, anoxic phase) and carbon: nitrogen ratio (COD/NO2--N+NO3--N) equal to 6. Complete cycles (20), nitrification followed by denitrification, were evaluated to investigate the kinetic behavior of degradation of organic (COD) and nitrogenated (NH4+-N, NO2--N and NO3--N) matter present in the effluent from a bird slaughterhouse and industrial processing facility, as well as to evaluate the stability of the reactor using Shewhart control charts of individual measures. The results indicate means total inorganic nitrogen (NH4+-N+NO2- -N+NO3--N) removal of 84.32±1.59% and organic matter (COD) of 53.65±8.48% in the complete process (nitrification-denitrification) with the process under statistical control. The nitrifying activity during the aerobic phase estimated from the determination of the kinetic parameters had mean K1 and K2 values of 0.00381±0.00043 min-1 and 0.00381±0.00043 min-1, respectively. The evaluation of the kinetic behavior of the conversion of nitrogen indicated a possible reduction of CT in the anoxic phase, since removals of NO2--N and NO3--N higher than 90% were obtained with only 1 h of denitrification.

Modeling and kinetic study of bio-ethanol production from soy protein concentrate by-product

Abstract The aim of this work was to evaluate a non-agitated process of bioethanol production from soybean molasses and the kinetic parameters of fermentation using a strain of Saccharomyces cerevisiae (ATCC® 2345). Kinetic experiment was conducted in medium with 30% (w v-1) of soluble solids without supplementation or pH adjustment. The maximum ethanol concentration was in 44 hours, the ethanol productivity was 0.946 g L-1 h-1, the yield over total initial sugars (Y1) was 47.87%, over consumed sugars (Y2) was 88.08% and specific cells production rate was 0.006 h-1. The mathematical polynomial was adjusted to the experimental data and provided very similar parameters of yield and productivity. Based in this study, for one ton of soybean molasses can be produced 103 kg of anhydrous bioethanol.

Manganese uptake and redistribution in soybean as affected by glyphosate

Detrimental effects of glyphosate on plant mineral nutrition have been reported in the literature, particularly on Mn uptake and redistribution. However, in most of the experiments conducted so far glyphosate-susceptible plants were used. Effects of glyphosate on Mn absorption kinetics, accumulation, and distribution within the plant, as well as soybean response to Mn as affected by glyphosate were studied in three experiments. In the first experiment, in nutrient solution, the effect of glyphosate on soybean Mn uptake kinetic parameters (Imax, Km and Cmin) was determined. In a second experiment, also in nutrient solution, differential Mn accumulation and distribution were studied for a conventional soybean cultivar and its near-isogenic glyphosate-resistant counterpart as affected by glyphosate. In a third experiment, response of glyphosate-resistant soybean cultivars to Mn application was studied in the presence of glyphosate, in pots with Mn-deficient soil. Maximum Mn influx (Imax) was higher in the herbicide-resistant (GR) cultivar than in its conventional counterpart. Glyphosate applied to nutrient solution at low rates decreased Km and Cmin. A few days after herbicide treatment, RR soybean plants developed yellowish leaves, a symptom which, in the field, could be misinterpreted as Mn deficiency, but herbicide application had no effect on Mn uptake or distribution within the plant. In the soil experiment, soybean Mn uptake was increased by Mn application, with no effect of glyphosate. Under greenhouse conditions, there was no evidence of deleterious effects of glyphosate on Mn absorption, accumulation and distribution in the plant and on soybean cultivars response to Mn application.

Desenvolvimento e aplicação de células eletroquímicas em camada delgada

Theoretical and practical aspects concerning construction and use of a thin layer electrochemical cell are presented. Construction was realized by a simple technic and geometry was optimized in order to minimize the problems of electrical resistance. A well known redox system was studied ((Fe(III)(CN)6(3-)/Fe(II)(CN) 6(4-)) using two experimental methods, cyclic voltammetry and pulse chronopotentiometry. A numerical integration based-program was developed to calculate the voltammetric current in case of nernstian and non-nernstian behaviours and a diffusional model was used to treat the chronopotentiometric data. Thermodynamic (potential, concentration) and kinetic parameters (diffusion coefficient) were successfully determined for the redox system studied in this work.

Caracterização de catalisadores Cu/CeO2/Al2O3 por redução a temperatura programada e atividade para oxidação de CO

The kinetic parameters for the CO oxidation reaction using copper/alumina-modified ceria as catalysts were determined. The catalysts with different concentrations of the metals were prepared using impregnation methods. In addition, the reduction-oxidation behaviour of the catalysts were investigated by temperature-programmed reduction. The activity results show that the mechanism for CO oxidation is bifunctional : oxygen is activated on the anionic vacancies of ceria surface, while carbon monoxide is adsorbed preferentially on the higher oxidation copper site. Therefore, the reaction occurs on the interfacial active centers. Temperatures-programmed Reduction patterns show a higher disperdion when cerium oxide is present.

O eletrólito suporte e suas múltiplas funções em processos de eletrodo

The aim of this work is to present the principal properties and applications of supporting electrolytes (SE) to students, teachers and researchers interested in electrode processes. Different aspects are discussed including the importance of SE in maintaining constant the activity coefficients and the diffusion coefficients and reducing the transport number of electroactive species. Its effect on the electrochemical kinetic parameters is also presented.

Biossensor enzimático para detecção de fungicidas ditiocarbamatos: estudo cinético da enzima aldeído desidrogenase e otimização do biossensor

Initially, all major factors that affect the rate of the AldH-catalyzed reaction (enzyme concentration, substrate concentration, temperature and pH) were investigated. Optimal activity was observed between pH values of 7.5 and 9.5 in the temperature range of 25 to 50 ºC. Kinetic parameters, such as Km (2.92 µmol L-1) and Vmax (1.33 10-2 µmol min-1) demonstrate a strong enzyme-substrate affinity. The sensors were based on screen-printed electrodes modified with the Meldola Blue-Reinecke salt (MBRS) combination. Operational conditions (NAD+ and substrate contents, enzyme loading and response time) were optimized. Also, two enzyme immobilization procedures were tested: entrapment in poly(vinyl alcohol) bearing styrylpyridinium groups (PVA-SbQ) and crosslinking with glutaraldehyde. Chronoamperometry was employed to observe the biosensor responses during enzymatic hydrolysis of propionaldehyde and also to construct inhibition curves with maneb and zineb fungicides. Best results were found with the following conditions: [NAD+] = 0.25 mmol L-1; [propionaldehyde] = 80 µmol L-1; enzyme loading = 0.8 U per electrode; response time = 10 min, and inhibition time = 10 min. Current intensities around 103 ± 13 nA with the sensors and good stability was obtained for both immobilization procedures. Detection limits, calculated using 10% inhibition were 31.5 µg L-1 and 35 µg L-1 for maneb and zineb, respectively. Results obtained with other MBRS-modified electrodes consisting of mono and bi-enzymic sensors were compared. The ability to catalyze NADH oxidation by MB was also highlighted.

Estudo da decomposição térmica de propelente sólido compósito de baixa emissão de fumaça

The thermal decomposition of hydroxyl-terminated polybutadiene (HTPB)/ammonium nitrate (AN) based propellants, so called smokeless formulations, and raw materials were investigated by differential scanning calorimetry (DSC) and thermogravimetry (TG). The thermoanalytical profile of different components and of propellant were evaluated and the Arrhenius parameters for the thermal decomposition of the propellant sample were determined by the Ozawa method. The kinetic parameters of the thermal decomposition of propellant samples were determined by DSC measurements. The values obtained for activation energy (Ea) and pre-exponential factor were 163 kJ mol-1 and 1.94x10(6) min-1.

Tempo de vida útil de propelentes base-simples

The purpose of this work was to determine the safe shelf life of single-base propellants. The kinetic parameters relative to the consumption of the stabilizer diphenylamine (DPA) added to the propellant were determined as a function of the storage and ageing time. High Performance Liquid Chromatography (HPLC) with spectrophotometric detection was used to determine the DPA percentage before and after the artificial ageing at 60, 70 and 80 ºC. The experimental data were very well adjusted to a pseudo-first order kinetic model and the respective kinetic constants are 8.0-10-3 day-1 (60 ºC); 1.9-10-2 day-1 (70 ºC); 1.2-10-1 day-1 (80 ºC). The activation energy was calculated as 130 kJ mol-1 and the half-time for depletion of the DPA at the hypothetical temperature of 40 ºC of storage was estimated as being 6 years.

Estudo cinético da decomposição térmica do pentaeretritol-tetranitrado (PETN)

The pentaerythritol-tetranitrate (PETN) is a nitroether used in explosives and propellant formulations. Due to its suitable properties, PETN is used in booster manufacture. Knowing the thermal decomposition behavior of an energetic material is very important for storage and manipulation, and the purpose of this work is to study the kinetic parameters of the decomposition of PETN, compare the results with literature data and to study the decomposition activation energy differences between two crystalline forms of PETN (tetragonal and needle) by means of differential scanning calorimetry (DSC). Fourier transform infrared spectroscopy (FT-IR) is used to study the two crystalline forms.

Adsorção competitiva de inibidor de corrosão usado em poços de perfuração de petróleo sobre aço, esmectita e arenito

A commercial corrosion inhibitor used in petroleum production was characterized by means of infrared spectroscopy and energy dispersive spectroscopy (EDS). Predicting the adsorption behavior of corrosion inhibitor onto steel, sandstone and esmectite is the key to improve working conditions. In this study, the adsorption kinetics of inhibitor formulations in HCl 15% or in Mud Acid (HCl 13,5% and ammonium bifluoride) onto steel, sandstone and esmectite was determined by means of spectrophotometry. Kinetic parameters indicated that adsorption of inhibitor in the presence of bifluoride was favored. Moreover, the adsorption constant rate was the largest when the substrate was esmectite.