Values Of Kinetic Constants Research Articles

Immobilization of biosorbent in hydrogel as a new environmentally friendly fertilizer for micronutrients delivery

Abstract The aim of this work was to study the use of alginate-carboxymethyl cellulose-eggshell biocomposites as a material with controlled release of Cu2+ ions. The composition of biocomposites was optimized with Response Surface Methodology (5.0 wt% sodium alginate, 1.2 wt% carboxymethyl cellulose, 10.0 wt% eggshells). Physicochemical properties of biocomposites, kinetics and equilibrium of copper(II) ion sorption on structures were investigated. The General Rate Law model best described the kinetics data and the values of kinetic rate constants were 0.259, 0.358 min −1 for wet and dry capsules. The description of the sorption kinetics was also presented with the Weber-Morris diffusion model, which indicated a multi-stage process. The maximum sorption capacities for wet and dry biocomposites were 281 and 49 mg g−1. The composites presented a slow release of ions in the model soil solution (9 wt%/14 days). Studied biocomposites have a good potential as controlled release fertilizers fitting into the concept of sustainable development and precision agriculture. The new fertilizer formulations have the potential to by used as a new type of slow-release fertilizer that delivers micronutrient ions according to the plants uptake pattern with minimization of losses into the environment.

Kinetic modeling of cottonseed oil transesterification with ethanol

This study aimed to evaluate the kinetic behavior of cottonseed oil transesterification with ethanol based on a pseudo first order kinetic model. A 23 factorial planning with three central points was performed by considering temperature, catalyst concentration and alcohol/oil molar ratio as dependent variables and biodiesel concentration as response signal. It was observed that the highest conversion was obtained for the following conditions: temperature between 50 and 70 °C, high alcohol/oil molar ratio and low percentage of catalyst. All samples were collected during time intervals of 5–10–15–30–60 and 90 min. A set of kinetic constant values were obtained for each operating condition ranging from 72 to 23l min−1. Indeed, it was possible to obtain the kinetic parameters frequency factor k0 = 5807.05 dm3*mol−1*min−1 and Ea = 16.84 kJ*mol−1 for biodiesel production with ethanol.

Diesel exhaust emission soot adsorbent for the removal of dye from wastewater

Diesel exhaust emission soot (DEES) is waste soot particle that has been explored as an adsorbent for a dye rhodamine B (RB). DEES successfully adsorbed the RB from its aqueous solution. Equilibrium was achieved in 90 min. Basic medium (pH > 7) was more favorable than an acidic medium for the adsorption of RB. The study of kinetic of adsorption reveals that both pseudo-first-order and second-order kinetic models fit well to kinetic data of adsorption. Langmuir isotherm best explains the equilibrium study of adsorption. The values of various kinetic and isotherm constants of DEES are compared with that of candle soot, and it is found that DEES is slightly superior to candle soot as an adsorbent. Further, DEES was coated on a polyurethane foam and adsorption–desorption experiments were performed. Also, DEES-coated foam (DEES foam) was successfully reused for six cycles after desorption in ethanol.

Degradation of emerging organic pollutants in wastewater effluents by electrochemical photocatalysis on nanostructured TiO2 meshes

An immobilized photoactive TiO2 coating grown directly on titanium meshes was successfully exploited for the electrochemical photocatalytic degradation of carbamazepine in real secondary wastewater effluent. The catalyst was prepared by Plasma Electrolytic Oxidation and during the photocatalytic water treatment an electrical polarization (bias) was applied to the catalyst. The investigated process was compared with the conventional one employing suspended TiO2 powder (Degussa P25). Results showed that carbamazepine degradation rate follows the order UV/supported TiO2+bias ≈ UV/TiO2 Degussa P25 > UV/supported TiO2 > UV. The investigation also included the identification of other micropollutants and degradation products. This allowed the detection of 201 compounds present in the secondary wastewater effluent employed for the photocatalysis tests, 51 of them also successfully associated to compounds of emerging concern (CECs), and 194 to transformation products (TPs). The degradation of detected compounds followed first-order kinetics and the mean kinetic constant values of the 51 CECs resulted to be 0.048, 0.035 and 0.043 min−1 for the TiO2+Bias + UV, TiO2+UV and UV, respectively. As for TPs, results showed that the TiO2+Bias + UV treatment is much more efficient than both TiO2+UV and UV in minimizing the intensity of the organics in the real wastewater. Such a better performance was more pronounced at higher reaction time reaching 60% reduction of mean peak area of TPs at 90 min of reaction. Among the detected TPs also compounds belonging to known carbamazepine TPs were found. This allowed to propose a degradation pathway of carbamazepine. The supported catalyst was positively tested for 15 cycles demonstrating that it has the potential to be used in real wastewater tertiary steps aimed at removing CECs.

2-Ketogluconate Kinase from Cupriavidus necator H16: Purification, Characterization, and Exploration of Its Substrate Specificity.

We have cloned, overexpressed, purified, and characterized a 2-ketogluconate kinase (2-dehydrogluconokinase, EC 2.7.1.13) from Cupriavidus necator (Ralstonia eutropha) H16. Exploration of its substrate specificity revealed that three ketoacids (2-keto-3-deoxy-d-gluconate, 2-keto-d-gulonate, and 2-keto-3-deoxy-d-gulonate) with structures close to the natural substrate (2-keto-d-gluconate) were successfully phosphorylated at an efficiency lower than or comparable to 2-ketogluconate, as depicted by the measured kinetic constant values. Eleven aldo and keto monosaccharides of different chain lengths and stereochemistries were also assayed but not found to be substrates. 2-ketogluconate-6-phosphate was synthesized at a preparative scale and was fully characterized for the first time.

Dairy Wastewater Treatment Using Membrane Bioreactor

The paper presents the results of scientific researches in the field of biomembrane treatment of dairy products industry enterprises wastewater. Practical experiments confirmed the possibility of reducing the inhibition degree of the process of biological treatment of dairy products industry wastewater, which has been physically and chemically purified, by increasing the concentration of active sludge. This effect can be achieved while using membrane bioreactor technology (MBR). The experiments also showed that if dairy plants wastewater is pre-treated with coagulants and flocculants, specific speed of biocontamination oxidation decreases in 1, 2-2, 3 times at BODfull = 250 mg/l in comparison with the initial wastewater. It happens because of substrate inhibition rate of biochemical reactions. The identified dependencies show that it is advisable to exclude the stage of reagent flotation before the biological treatment of dairy products industry wastewater. It can reduce costs of using a large number of expensive reagents and simplify the technological scheme. During the experiments dairy plants wastewater was taken as a model. Later, the researchers used real wastewater and confirmed the main kinetic constants and coefficients for calculations of biological purification plants. These results are as follows: temperature constant χ, grad−1, for aerobic heterotrophic conversion – 0,079-0,091, for nitrification – 0.096; for denitrification – 0.13. Coefficients of inhibition by active sludge φ metabolic products amounted to (l/g): for organic substances oxidation by BODfull – 0,39-0,54; for nitrification – 0.19, for denitrification – 0.22; active reaction of the environment corresponding to the highest rate of oxidation of organic substances pHopt – 6.9 at pH-constant 150. The maximum specific speed of organic substances oxidation r’max is 82,5-101,1 mg/(g × h), the Michaelis constant Km – 15 mg/l. The maximum specific speed of nitrification r’max is 1.49 mg/(g × h), the Michaelis constant Km is 0.12 mg/l, the constant of inhibition a is 43. The maximum specific speed of denitrification r’max is 10.8 mg/(g × h), the Michaelis constant Km is 3.5 mg/l. The calculated values of kinetic coefficients and constants make it possible to calculate membrane bioreactors of sewage treatment plants of dairy industry to the specified degree of purification. The estimated annual economic effect for “Pestravskiy” diary plant of the Samara region equaled 4 mln. rub/year (at 2017 values).

Application of the concept of Linear Free Energy Relationships to the hydrogenation of levulinic acid and its corresponding esters

Biomass valorization to chemicals, biofuels or materials will be more and more important during this century. Production of γ-valerolactone (GVL) from the hydrogenation of levulinic acid is a good illustration of this tendency. GVL can also be produced from alkyl levulinates hydrogenation. Can we find a relationship between the structure and the kinetics of this reaction? Can we predict the kinetics of any alkyl levulinates by knowing the kinetics of another alkyl levulinate? This paper has studied these two questions by developing a kinetic model including the effect of gas-liquid mass transfer. We have demonstrated that the kinetics of hydrogenation of levulinic acid, methyl, ethyl and butyl levulinates to GVL using Ru/C follow the Taft equation, which is derived from Linear Free Energy Relationships. This equation measures the effects of polar and steric on a reaction series. We have demonstrated that polar effect of the reaction series is the most significant effect. This relationship can predict the values of kinetic constants just by knowing their structure.

Analysis of growth and intracellular product synthesis dynamics of a microalga cultivated in wastewater cocktail as medium

Kinetic modelling of cell growth and production dynamics (lipid and lutein) of Chlorella minutissima cultivated in cocktail wastewater medium following Taguchi’s L9 (4-factors-3-levels) array is reported. Monod model and a logistic equation were used to define cell growth whereas for lipid and lutein the Luedeking–Piret's equation was considered. Also, Kono-Asai’s model was used to analyze lipid product formation rate with growth rate. Monod kinetics constants: maximum specific growth rate (μmax) were highest for S5 and S3 (1.955 ± 0.01; 1.258 ± 0.03 d−1) and substrate affinity coefficient (KS) for S1 and S7 (345.4 ± 1.45; 35.25 ± 5.2 mg L−1). Kinetic constant values exhibited that Chlorella was able to grow faster under S3, S4, S5 and S7 cultivation conditions with high affinity for growth limiting substrate (nitrate), as indicated by low Ks value. Luedeking-Piret’s model predictions indicated that lipid was growth associated, whereas lutein was non-growth associated. Kono-Asai’s model reconfirmed Luedeking-Piret’s predictions for lipid. The models used would allow to select the dilution range of wastewaters and understand the product synthesis dynamics of the alga. Overall, highest growth yield and product yield coefficients were recorded for S3 and spectroflurometric analysis specified S3 cultivation condition to enhance the neutral lipid content up to 5.13 ± 0.18 μg mL−1.

Purification, characterization, and biodelignification potential of lignin peroxidase from immobilized Phanerochaete chrysosporium

Lignin peroxidase (LiP), which has been studied extensively in white-rot Basidiomycetes with regard to bio-pulping and bio-bleaching, plays a role in the biodegradation of plant cell wall lignin. In the current study, LiP obtained from a wild isolate of Phanerochaete chrysosporium immobilized on polyurethane foam cubes was purified 21-fold using ammonium sulphate precipitation and size exclusion chromatography. The enzyme with a molecular mass of 55 kDa exhibited a considerably higher pH tolerance and thermostability compared with the native enzyme. It showed a strong affinity for the substrate veratryl alcohol and had kinetic constant values of 142.86 µmol and 65 µM. Cysteine, sodium azide, mercaptoethanol, and silver nitrate inhibited the activity, while ethanol, EDTA, Cu2+, Mn+, Na+, and Fe2+ exhibited induction. Purified LiP completely decolorized (100%) bromo phenyl blue, bromothymol blue, and bromocresol green. The 96 and 72% degradation obtained with phenol and congo red was also higher compared to crude LiP. Treatment with LiP showed reduction in ADL as compared to untreated straws, with a maximum of 2.87 units obtained in JR followed by 2.66 units in PS. The digestibility of all straws increased, the response varying from a maximum of 21.27 units in PRM to a minimum of 12.32 units obtained in LM.

Hydrogel capsules with alfalfa as micronutrients carrier

The aim of this work was to study the properties of biocomposite based on sodium alginate and carboxymethyl cellulose with immobilized alfalfa as a material with controlled release of Cu2+ ions. Physicochemical (swelling, pHZPC) and sorption (kinetics, equilibrium) properties of the produced structures were investigated. Kinetic data were best described using a general rate law model, and the value of kinetic rate constant was 5.34 × 10−6. The sorption kinetics are also described using the Weber–Morris model, and the analysis revealed a three-step sorption. The maximum sorption capacity was determined using the Sips model and amounted to 9 mg g−1. Desorption of Cu2+ ions in soil solution (NaNO3 1 wt%) was carried out, and biocomposites released micronutrients in a slow way. The results showed that biocomposites with immobilized alfalfa are a very good material for potential applications in the agrochemical industry as a controlled released fertilizer.

Study of Anopheles gambiae 3-hydroxykynurenine transaminase activity and inhibition by LC-MS/MS method

In Anopheles gambiae, the most efficient vector of the malaria parasite Plasmodium falciparum, 3-hydroxykynurenine is endowed with a toxic potential. In adult mosquitoes, the excess of 3-hydroxykynurenine is removed by a specific transaminase (3-hydroxykynurenine transaminase, 3-HKT) which converts the compound into the more stable xanthurenic acid. Interfering with 3-hydroxykynurenine metabolism in A. gambiae is a potential approach for the development of transmission-blocking drugs and insecticides. Hence, the aims of this work were to develop and validate a new LC-MS/MS method for the evaluation of A. gambiae 3-hydroxykynurenine transaminase (Ag-HKT) activity and the determination of the potency of inhibitors of the enzyme. We set up a LC-MS/MS based enzymatic assay for the determination of kinetic constants values of the recombinant Ag-HKT enzyme and for the evaluation of Ag-HKT inhibition by a known protein inhibitor used as reference and a newly synthesized compound. The chromatographic separation was performed in a gradient mode on a Phenomenex Synergi Polar-RP (150 mm × 2.0, 4 μm) with methanol and water containing both 0.2% formic acid. Mass spectrometric detection was achieved with an ion trap equipped with an ESI source, in positive ionization scan, operating in SRM mode. The LC-MS/MS method was validated in terms of selectivity, linearity, precision and accuracy.

Anaerobic batch reactor treating acid mine drainage: Kinetic stability on sulfate and COD removal

The leaching of an acid solution containing metals and dissolved sulfate constitutes an environmental problem known as acid mine drainage (AMD). An anaerobic sequencing batch reactor designed for AMD treatment was evaluated regarding its capacity to accommodate an increase in metals concentrations. Time profiles were performed to verify chemical oxygen demand (COD) and sulfate removal kinetics. The resulting apparent kinetic constant values showed a decrease in the reaction rate at the same time that sulfate removal increased. An increase in Fe2+ concentration from 100 to 400 mg L−1 decreased the sulfate removal rate (KSap) from (0.20 ± 0.03) to (0.072 ± 0.004) h−1, and the COD removal rate (KCODap) from (0.057 ± 0.003) to (0.027 ± 0.002) h−1. Even with the reduction in the COD and sulfate removal rates, the system was stable for the cycle time of 48 h in all operation phases.

Quantitative Analysis of Cyclic Voltammetry of Redox Monolayers Adsorbed on Semiconductors: Isolating Electrode Kinetics, Lateral Interactions, and Diode Currents.

The design of devices whose functions span from sensing their environments to converting light into electricity or guiding chemical reactivity at surfaces often hinges around a correct and complete understanding of the factors at play when charges are transferred across an electrified solid-liquid interface. For semiconductor electrodes in particular, published values for charge-transfer kinetic constants are scattered. Furthermore, received wisdom suggests slower charge-transfer kinetics for semiconductors than for metal electrodes. We have used cyclic voltammetry of ferrocene-modified silicon photoanodes and photocathodes as the experimental model system and described a systematic analysis to separate charge-transfer kinetics from diode effects and interactions between adsorbed species. Our results suggest that literature values of charge-transfer kinetic constants at semiconductor electrodes are likely to be underestimates of their actual values. This is revealed by experiments and analytical models showing that the description of the potential distribution across the semiconductor-monolayer-electrolyte interface has been largely oversimplified.

Kinetic study of dye removal using TiO2 supported on polyethylene terephthalate by advanced oxidation processes through neural networks.

This work investigated the efficiency of polyethylene terephthalate (PET) as support material for TiO2 films in the photocatalytic degradation of red Bordeaux and yellow tartrazine dyes. The optimum operating conditions were determined by a factorial design, which resulted after 180 min of treatment in degradations of 99.5% and 99.1% for the UVC/H2O2/TiO2Sup and solar/H2O2/TiO2Sup systems, respectively. For the kinetic study, the experimental data fitted to the pseudo-first-order model and the calculated kinetic constants (k) values were 0.03 min-1 for the UVC/H2O2/TiO2Sup system and 0.0213 min-1 for the system solar/H2O2/TiO2Sup. It was verified that TiO2 supported in the PET remained with high degradation efficiency even after five cycles of reuse, indicating a good stability of the photocatalyst in the support. A significant reduction of TOC content was also observed along the reaction time. The phytotoxicity bioassay with Lactuca sativa demonstrated that after treatment with UVC/H2O2/TiO2Sup and solar/H2O2/TiO2SUP, an increase in IC50 and consequently lower toxicity was observed.

Bioassay-guided isolation of antioxidant and α-glucosidase inhibitory constituents from stem of Vigna angularis

Stem of Vigna angularis (Willd.) Ohwi & H. Ohashi (VAS) is a main byproduct with considerable bioactivities. In present study, a bioassay-guided phytochemical investigation was used and led to the isolation of 16 compounds including one new compound (1) and one compound (2) isolated from nature source firstly along with 14 known compounds (3–16). The structures of isolates were identified by NMR and HR-ESI-MS data. The ability of antioxidant and α-glucosidase inhibition of the compounds were measured in vitro. Most of the ingredients shown strong ABTS radical scavenging activity (IC50 = 4.21–14.93 μM) and α-glucosidase inhibitory activity (IC50 = 0.05–34.14 μM). Enzyme kinetic analysis and molecular docking of compounds 1 and 2 were conducted. Compounds 1 and 2 were competitive inhibitor for α-glucosidase, with the inhibition kinetic constant value of 1.03 and 1.06 μM, respectively. The potent α-glucosidase inhibitory ability of compounds 1 and 2 resulted from firm binding with the active site of α-glucosidase.

Microwave discharge electrodeless mercury lamp (Hg-MDEL): An energetic, mechanistic and kinetic approach to the degradation of Prozac®

A photochemical reactor composed of an Hg-MDEL was applied in photodegradation studies of fluoxetine (Prozac®). The reactor exhibited to be an efficient hydroxyl radical generation system, since the O•H quantification studies conducted with coumarin (COU), 4-hydroxycoumarin (4HC) and 7-hydroxycoumarin (7HC) solutions resulted in the kinetics constant of formation of O•H kOH = 3.14 ± 0.18 min−1. When the Hg-MDEL reactor was applied for degradation of Prozac®, the study of variation of the microwave power allowed a significant increase in the rate of degradation of the Prozac®, indicating that the hydroxyl radical formation is optimized through the adjustment of this parameter. An increase in the initial concentration of Prozac from 33 to 134 μmol L−1 resulted in a 21% decrease in the kinetic constant value, the mean kinetic constant was k = 10.64 ± 1.25 min −1 and R 2 = 0.943 ± 0.131. The Prozac® photodegradation studies showed that the application of the pseudo-first-order kinetics should be limited to the time of up to 0.50 min for the respective system, due to the influence exerted by the transformation products. In general, the total removal of Prozac® was 100% for its highest concentration (134 μmol L−1) at the time of 0.75 min. As for the solution of Prozac® 101 μmol L−1, the energy consumption was 6 kW h g−1, achieving a removal of 99%. Finally, the photochemical system presented in this work demonstrates a high efficiency in the formation of hydroxyl radicals, a high degradation rate of organic compounds (Prozac®, COU and 7HC) and low energy consumption.

Kinetic models of the cyclohexene hydromethoxycarbonylation catalyzed by the Pd(OAc)2/trans‐2,3‐bis(diphenylphosphinomethyl)norbornane/p‐toluensulfonic acid

AbstractOperating over the entire length from the region of initial rates to deep conversions of cyclohexene, hydromethoxycarbonylation kinetic models have been obtained in the temperature range of 358–378 K. At 378 K, a conclusion on a higher stability of the diphosphine complex [HPd(TBDPN)(CH3OH)]OTs compared to [HPd(CO)2OTs] under hydromethoxycarbonylation conditions has been made based on the comparison of the kinetic model constant values.

Coupled X-ray Absorption/UV-vis Monitoring of Fast Oxidation Reactions Involving a Nonheme Iron-Oxo Complex.

Time-resolved X-ray absorption (XAS) and UV-vis spectroscopies with millisecond resolution are used simultaneously to investigate oxidation reactions of organic substrates by nonheme iron activated species. In particular, the oxidation processes of arylsulfides and benzyl alcohols by a nonheme iron-oxo complex have been studied. We show for the first time that the pseudo-first-order rate constants of fast bimolecular processes in solution (milliseconds and above) can be determined by time-resolved XAS technique. By following the Fe K-edge energy shift, it is possible to detect the rate of iron oxidation state evolution that matches that of the bimolecular reaction in solution. The kinetic constant values obtained by XAS are in perfect agreement with those obtained by means of the concomitant UV-vis detection. This combined approach has the potential to provide unique insights into reaction mechanisms in the liquid phase that involve changes of the oxidation state of a metal center, and it is particularly useful in complex chemical systems where possible interferences from species present in solution could make it impossible to use other detection techniques.

Commercial steel wool used for Zero Valent Iron and as a source of dissolved iron in a combined red-ox process for pentachlorophenol degradation in tap water

Pentachlorophenol solutions in tap water were treated with a combined process of zero valent iron (ZVI) reduction followed by a photo-Fenton oxidation. Commercial steel wool was used as ZVI source, demonstrating its effectivity for pentachlorophenol de-chlorination at acidic pH values. The reductive pathway was monitored by the use of excitation emission matrices, showing the transformation of the initial compound into the fluorescent species 4-chlorophenol and phenol.While the use of tap water represented a drawback in photo-Fenton oxidative reactions (at least half kinetic constants values) an improvement was achieved when the reductive stage was applied in the studied pH range. The transformation of pentachlorophenol into phenol produced an increase in oxidative stage rate of about 8 times. This fact could be related to the treatment time and hydrogen peroxide consumption of the photo-Fenton process, enhancing the economic viability. Furthermore, the de-chlorination of the pentachlorophenol minimized the possibility of releasing toxic by-products in the photo-Fenton process.

Stability and repeatability improvement of horseradish peroxidase by immobilization on amino-functionalized bacterial cellulose

Abstract Bacterial cellulose (BC) is a biodegradable material with many excellent properties for enzyme immobilization. However, hydroxyl groups of low reactivity in glucose units cannot directly react with the amines of enzymatic proteins. In this work, amino-functionalized bacterial cellulose was firstly used as carrier to immobilize horseradish peroxidase (HRP) via glutaraldehyde coupling. SEM, FT-IR, XPS, BET, and TGA were used to characterize the properties of modified BC and showed that it is more suitable for enzyme immobilization. The optimum pH range for immobilized HRP (pH 5.5–8.5) was wider than that of free enzyme (pH 6–8), and the immobilized HRP exhibited good adaptability to environmental alkalinity. The relative activity of immobilized HRP at 25–40 °C was greater than 90%, significantly surpassing that of free HRP. Furthermore, the obtained kinetic constant values showed that modified BC had decreased affinity for the substrate. Additionally, modified BC-immobilized HRP was reused efficiently for 10 cycles with greater than 70% of its original activity retained. Under optimal conditions, coupling ratio and specific activity could reach 86.7% and 41.7 Ug -1 min -1 , respectively. These results show that the immobilization of HRP on amino-functionalized BC enhanced its appropriateness for a future use in various biotechnological and environmental applications.