Stoichiometry Of Reaction Research Articles

Evaluation of thermodynamic parameters via reaction stoichiometry and the corrected Langmuir parameter for sorption of Cu(II) on chitosan and chitosan blended PVA films

Natural Chitosan (C) and Chitosan blended with Poly vinyl Alcohol (PVA) C + P film was prepared by solution casting method for the sorption of Cu(II) from aqueous solution. The FTIR studies revealed that the amino group of chitosan played key roles in the copper uptake and FE-SEM and EDAX studies confirmed the formation of Cu-amino complex in 1:1 ratio of metal to ligand. The prime objective of present studies is the evaluation of thermodynamic parameters (ΔG0, ΔH0 and ΔS0) via reaction stoichiometry and the corrected Langmuir parameter for sorption of Cu(II) on chitosan (C) and (C + P) films. The surface morphology, stability and Cu(II) adsorption efficiency of the films were investigated. The C + P film showed enhanced chemical and mechanical endurance over the C film. The batch adsorption studies exhibited that the adsorption capacity of both the films was pH dependant and the maximum adsorption obtained was 55.56 mg g−1 for C film and 35.71 mg g−1 for C + P film at pH 5.5. The adsorption process was described by Langmuir adsorption model and was found to follow pseudo first order kinetics. The Gibbs free energies calculated using the formation constant Kn and the corrected dimensionless Langmuir constant KL(C) were in good agreement with each other thereby confirming the formation of pendant complex [Cu-NH2]2+. The C + P film could be reused till 5 desorption cycles using EDTA as the desorbing agent and could recover around 169.16 mg of Cu(II) per g of the material.

A mathematical model for persistent post-CSD vasoconstriction.

Cortical spreading depression (CSD) is the propagation of a relatively slow wave in cortical brain tissue that is linked to a number of pathological conditions such as stroke and migraine. Most of the existing literature investigates the dynamics of short term phenomena such as the depolarization and repolarization of membrane potentials or large ion shifts. Here, we focus on the clinically-relevant hour-long state of neurovascular malfunction in the wake of CSDs. This dysfunctional state involves widespread vasoconstriction and a general disruption of neurovascular coupling. We demonstrate, using a mathematical model, that dissolution of calcium that has aggregated within the mitochondria of vascular smooth muscle cells can drive an hour-long disruption. We model the rate of calcium clearance as well as the dynamical implications on overall blood flow. Based on reaction stoichiometry, we quantify a possible impact of calcium phosphate dissolution on the maintenance of F0F1-ATP synthase activity.

Determination of Metoclopramide Hydrochloride in Pharmaceuticals and Spiked Human Urine through Diazotization Reaction

Three simple, rapid, sensitive and cost-effective titrimetric and spectrophotometric methods were described for the determination of metoclopramide (MCP) in its pharmaceutical dosage forms and spiked human urine. The titrimetric methods were based on the diazotization reaction involving the primary amine group of MCP and NaNO2 in acid medium with visual (method A) and potentiometric (method B) end point detection. The spectrophotometric method (method C) depends upon the diazotization of MCP in acid medium followed by coupling with diphenylamine to give a red colored chromogen with a wavelength of maximum absorption at 530 nm. The experimental conditions were optimized. Both the titrimetric methods were applicable over the concentration range of 1.0-20.0 mg and the calculations were based on a 1 : 1 (MCP: NaNO2) reaction stoichiometry. In the spectrophotometric method, Beer's law was obeyed over the concentration range or 0.3-7.5 ug/mL with a molar absorptivity of 4.73 x 10^4 L/mol cm and Sandell's sensitivity being 0.007 μg/cm^2. The limit of detection and the limit of quantification were calculated to be 0.22 and 0.67 μg/mL, respectively. The proposed methods were applied to the determination of MCP in tablets, injection and also in spiked human urine.

Cyclic square wave voltammetry of electrode reactions with nonunity stoichiometry

Abstract A general and easy-to-manage analytical theory is presented for the square wave voltammetry (SWV) of reversible electrode reactions with complex stoichiometry, aO + ne− ⇌ bR, at macroelectrodes valid for any value of the stoichiometric and diffusion coefficients of the redox species. A comprehensive study of the SWV in cyclic mode is performed, investigating the effect of all the key variables for different stoichiometries a:b stoichiometries. As reported in literature, these reactions are of interest in the electrochemistry of hydrogen, halides and mercury complexes, among others. The concentration-dependence of the position of the SWV signal along with the peak height, width and symmetry are demonstrated to be sensitive to the reaction stoichiometry, offering rapid and simple diagnostic clues. Then, the quantitative analysis of the peak current, peak potential and half-peak width with the theory here presented allows for the determination of the stochiometric coefficients and number of electrons transferred. Also, the diffusion coefficients of the oxidized and reduced species and/or the formal potential of the redox couple can be extracted. For this, accurate procedures are proposed on the basis of simple explicit equations and working curves, proving the remarkable value of the SWV method.

Leaching of a pyrite-based ore containing copper using sulfuric acid and hydrogen peroxide

The oxidation of sulfide-based ores is industrially relevant as it facilitates the extraction of valuable metals and eliminates undesired elements from an ore. Even though oxidation can be done thermally (pyrometallurgy), solution-based (hydrometallurgical) methods are currently sought as they represent a more sustainable option. Here, the leaching of a sulfide ore (32% Fe, 2% Cu) is investigated using a mixture of sulfuric acid and hydrogen peroxide (0.15 M H2SO4 and 0.5 M H2O2), in proportions forming a slurry 10% w/w. The leaching process is found to occur in two stages, the first corresponding to an exothermic, peroxide-mediated dissolution, and the second corresponding to an acid-mediated reaction, which appears to be thermoneutral. Control experiments performed with only peroxide confirm that this oxidant is involved in the first stage of the dissolution process. The leaching process leads to copper and iron dissolution (15% and 5%, respectively), as determined using atomic absorption spectrometry (AAS). The mass of pyrite dissolved is estimated from AAS measurements and, from the stoichiometry of the peroxide-mediated dissolution reaction, it is found that ~ 80% of the peroxide participates in the dissolution, with the other 20% being decomposed, in a reaction catalyzed by ferric (Fe+3) ions produced during the first stage of the dissolution.

In situ Crosslinking System of Gelatin with Acrylated β-cyclodextrin Towards the Fabrication of Hydrogels for Sustained Drug Release

Cyclodextrins (CDs) are of interest in fabrication of various polymeric platforms; especially the crosslinked networks that possess unique advantages in biomedical applications. Benefiting from the abilities of CDs to form inclusion complexes with hydrophobic drug molecules, hydrogel-based sustained drug platforms employ CDs as nano-buckets in the network structure. In the current study, we report on the fabrication of gelatin based hydrogels chemically crosslinked with acrylated β-cyclodextrin (β-CD) as sustained drug release platforms. A simple and practical synthesis of crosslinked networks was achieved by Michael addition reaction of gelatin amino functionalities onto acryloyl groups of modified β-CD. Tunable synthesis of hydrogels incorporating different amount of β-CD molecules were maintained by simple adjustment of the reaction stoichiometry between amine and acrylate groups. The resulting hydrogels were characterized by their equilibrium swelling ratios and rheological properties. Thus obtained hydrogels were evaluated in terms of their drug loading capacities and sustained release efficiencies. The results demonstrated that the amount of drug loading and prolonged release is dependent on the amount of β-CD in the gel network. Owing to their in situ gel forming abilities, these hydrogels can be used as injectable formulations for various biomedical applications.

Removal of PCE/TCE from groundwater by peroxydisulfate activated with citric acid chelated ferrous iron at 13 °C

Chlorinated organic compounds (CVOCs), such as tetrachloroethene (PCE) and trichloroethene (TCE) belong to the most abundant groundwater contaminants across the world. Over the last 15 years, in situ chemical oxidation (ISCO) using peroxydisulfate (PDS) activated by citric acid chelated ferrous ion (Fe(II)-CA) has been proposed as a suitable method for CVOCs removal from groundwater. However, published studies examining Fe(II)-CA activated PDS systems under laboratory conditions (T ≈ 20 °C) and in demineralized water have not provided a picture of the desired behavior of Fe(II)-CA activated PDS systems for CVOCs degradation at a lower temperature (T ≈ 13 °C) that are typical for shallow groundwater of larger areas of Europe and North America and in the presence of typical groundwater constituents, such as chlorides and bicarbonates. To resolve this knowledge gap, a series of batch experiments were conducted to investigate PCE, TCE and combined PCE/TCE degradation performance in Fe(II)-CA (fixed molar ratio Fe(II)/CA = 2/3) activated and unactivated PDS systems based on their PDS/Fe(II) initial molar ratios (1/2.5; 1/1; 2.5/1; 5/1; 7.5/1; 10/1; 15/10). The experiments were conducted in artificially prepared groundwater (0.5 mmol⋅L−1 CaCl2 ⋅H2O, 0.5 mmol⋅L−1 MgCl2 ⋅H2O, 0.5 mmol⋅L−1 NaHCO3 and 0.5 mmol⋅L−1 KHCO3) at 13 °C. The results indicated that the most efficient PDS/Fe(II) initial molar ratios in terms of CVOCs removal efficiency and reaction stoichiometry efficiency (RSE) were 10/1 for PCE, and 15/1 for both TCE and combined PCE/TCE. Surprisingly, the efficiency of unactivated PDS systems was comparable to Fe(II)-CA activated PDS systems. The results therefore suggest that unactivated PDS could be an appropriate option for field applications and should not be disregarded within feasibility studies at given thermal and hydro-chemical conditions. Overall, conclusions made in this study deepened the knowledge of ISCO using PDS at lower than laboratory temperatures and in the presence of typical groundwater constituents, therefore, could be exploited by remediation practitioners as well as in future research work.

The effect of chloride ions on copper solvent extraction from sulfate-chloride medium using LIX 984N

The supply of fresh water is becoming an increasingly important issue in hydrometallurgical treatment of mineral ores. The problem may significantly reduce if the extraction process can incorporate the usage of saltwater throughout the whole hydrometallurgical operation. Seawater as the main source of saltwater is a potential alternative to freshwater. In this research, the effect of the chloride ions, in a range of 0 to 40 g/L, on the solvent extraction of copper with LIX 984N was studied. LIX 984N has been commercially used in copper solvent extraction around the world. Increasing the concentration of Cl− was shown to increase the H+ activity and formation of CuCl+ and CuCl2 species. The solution acidity did not have a negative effect on the extent of copper extraction and extraction rate, in the presence and absence of chloride ion, in contrast to recent studies. The chloride addition was even showed to have a positive impact on copper extraction at pHs below 2 and at shorter mixing times. Through thermodynamic studies, it was shown that increasing chloride concentration results in both higher H+ activity and an increase in the activity of copper chloride complexes, of which the latter factor counteracts the former and overall improves the extent of copper extraction. Increasing the chloride concentration was found to negatively affect the copper extraction isotherms. The impact became more significant at lower concentrations of the extractant. It is therefore suggested that cupric chloride complex ion inhibits copper extraction by lowering the extraction driving forces. Also, it was shown that increasing aqueous chloride concentration promotes involvement of more extractant molecules per Cu2+ species in the extraction reaction in contrast to the reaction without chloride ions. The negative effect of chloride ions on copper solvent extraction then is due to the change in the reaction stoichiometry and decrease in the extraction driving force rather than the types of aqueous Cu2+ speciation. The effect of wash stages on the removal of the chloride ion from loaded organic solution was then investigated and the optimum conditions for the wash stage were found at wash solution to loaded organic ratio of 1 to 7 and sulfuric acid concentration of 10 g/L.

Detail data of reactive extraction of caproic acid using tri-Butyl phosphate and Sunflower and Soybean oils as diluents.

Caproic acid can be produced by fermentation technology. Reactive extraction method is a promising technology for separating the acid from the carboxylic mixture in the fermenter [1], [2], [3], [4]. To achieve it, tri‑butyl phosphate (TBP) is used as the reactive extractant and sunflower and soybean oils are used as the diluents. The performance of both the physical and reactive extraction processes was analysed by different parameters like distribution coefficient, loading ratio, and extraction efficiency. To meet the purpose, concentration of caproic acid in aqueous phase was measured by doing acid-base titration by caustic solution Further, reaction equilibrium constant, stoichiometry and distribution of complex, free acid and dimer concentrations in the organic phase were analysed. The data are related to the published (https://doi.org/10.1016/j.cep.2020.107926) paper in Chemical Engineering and Processing: Process Intensification [5]. The data shown in the current article are not provided in the mentioned published paper. Moreover, data are useful for understanding the physical and chemical behavior of the caproic acid extraction process and also can be used to design the process in industrial scale.

Specific Features of Oxidation of Sodium Tetradecahydroundecaborate to Decaborane with Manganese Dioxide

Oxidation of tetradecahydroundecaborate ion with manganese dioxide is considered. The influence exerted by the structure of the crystal lattice of manganese dioxide polymorphic modifications (α, β, γ, δ) on the MnO2 activity in tetradecahydroundecaborate ion oxidation is analyzed. The decaborane yield reaches a maximum if MnO2 prepared by the reaction of aqueous solutions of MnSO4 and KMnO4 under varied conditions has predominantly amorphous form (δ-MnO2). Based on the experimental results, a new stoichiometry of the oxidation reaction is suggested, taking into account the influence of different activity of MnO2 polymorphic modifications on the decaborane formation.

L2Zn and LZnX complexes bearing half-salphen ligands and their catalysis of ring-opening polymerization of ε -caprolactone

Zinc complexes L2Zn and LZnX were prepared by template synthesis from ZnX2, N1,N1-dimethylbenzene-1,2-diamine and substituted salicylaldehyde (SA). A systematic exploration of this synthetic route revealed the subtle role of choice of Zn source and SA substitution pattern on the reaction stoichiometry and enabled synthesis of pure Zn complexes. Use of poorly coordinating counterions (such as CF3SO3−) and apolar substituents on the SA component favours formation of pentacoordinate L2Zn, while more coordinating counterions tend to produce LZnX, (LZnX)2 or even binuclear LZn(O2CR)Zn(O2CR)2 not reported before. The complexes (LZnX)2 and LZn(O2CR)·Zn(O2CR)2 (L = L2 or L4) could be activated with BnOH/LiMe for ring-opening polymerization of ε-caprolactone; bis(ligand) complexes L2Zn show low or vanishing activity when activated either by BnOH or BnOH/LiMe.

Development of porphyrin-based chemosensor for highly selective sensing of fluoride ion in aqueous media

A porphyrin-based receptor to sense fluoride ion via hydrogen bonding has been prepared and investigated in aqueous media. The interactions between receptor and fluoride ion are confirmed by absorption and emission spectroscopy, and the influence of pH on the sensor performance has also been investigated. A dramatic color change from wine red to green, and photoswitching from the fluorescent on-state to the non-fluorescent off-state were observed after addition of fluoride ion to chemosensor POR. The detection limit for fluoride ion was calculated to be around 10 µM by both the colorimetric and fluorometric methods, which is under the tolerable amounts in drinking water by WHO guidelines. The Jobs plot showed a 1:2 reaction stoichiometry between POR and fluoride ion, which was further confirmed by mass analysis. The experimental results are fully supported by the DFT theoretical calculations. Furthermore, the changes in structural alignment of POR during fluoride detection were also proposed.

The impact of reagents concentration on the efficiency of obtaining high-purity magnesium hydroxide

Abstract The work presents the impact of reagents concentration and the drying process on the efficiency of obtaining magnesium hydroxide and its specific surface area. Magnesium sulphate(VI) within the concentration range of 0.7–2.0 mol/dm3 was used in the research as magnesium feedstock and sodium hydroxide was used as a precipitating agent within the same concentration range. The process of obtaining magnesium hydroxide was carried out with a 25% excess of the precipitating agent in relation to the reaction stoichiometry. The obtained suspension was separated by way of multi-stage sedimentation with the use of acetone and freezing samples. Depending on the concentration of reagents the efficiency of obtaining magnesium hydroxide fell within the range of 88–99%, whereas the specific surface area – within 115–609 m2/g, while the high purity of samples above 99% of magnesium hydroxide was maintained.

Application of dynamic metabolic flux analysis for process modeling: Robust flux estimation with regularization, confidence bounds, and selection of elementary modes.

In macroscopic dynamic models of fermentation processes, elementary modes (EM) derived from metabolic networks are often used to describe the reaction stoichiometry in a simplified manner and to build predictive models by parameterizing kinetic rate equations for the EM. In this procedure, the selection of a set of EM is a key step which is followed by an estimation of their reaction rates and of the associated confidence bounds. In this paper, we present a method for the computation of reaction rates of cellular reactions and EM as well as an algorithm for the selection of EM for process modeling. The method is based on the dynamic metabolic flux analysis (DMFA) proposed by Leighty and Antoniewicz (2011, Metab Eng, 13(6), 745–755) with additional constraints, regularization and analysis of uncertainty. Instead of using estimated uptake or secretion rates, concentration measurements are used directly to avoid an amplification of measurement errors by numerical differentiation. It is shown that the regularized DMFA for EM method is significantly more robust against measurement noise than methods using estimated rates. The confidence intervals for the estimated reaction rates are obtained by bootstrapping. For the selection of a set of EM for a given st oichiometric model, the DMFA for EM method is combined with a multiobjective genetic algorithm. The method is applied to real data from a CHO fed‐batch process. From measurements of six fed‐batch experiments, 10 EM were identified as the smallest subset of EM based upon which the data can be described sufficiently accurately by a dynamic model. The estimated EM reaction rates and their confidence intervals at different process conditions provide useful information for the kinetic modeling and subsequent process optimization.

Experimental and theoretical analysis of reactive extraction of caproic acid by using TBP in green diluents

Use of toxic diluent is harmful for producing caproic acid from fermentation unit. It led to consider green and non-toxic diluents: sunflower and soybean oils in the current study along with tributyl phosphate (TBP) as the reactive extractant. Important performance indicator parameters were estimated over the temperature range of 298 K–318 K. The changed of enthalpy and entropy because of mass transfer of caproic acid from aqueous phase to the interfaces, complexation reaction and overall acid transfer from aqueous phase to organic phase were estimated and analyzed. Best model among considered different acid concentration dependent distribution co-efficient models was identified following a newly developed method. Sunflower oil is identified as more efficient diluent than soybean oil. The new method has successfully determined the equilibrium complexation reaction stoichiometry. Further, concentrations of complex, free acid and dimer in the organic phase were determined which never were estimated previously. In spite of low loading ratio, less than 0.5 in the current experimental study, the estimated m has appeared greater than 1.0 for n=1. Current work has suggested to use presently studied microorganism friendly green and nontoxic diluents (sunflower and soybean oil) in biorefinary industry for recovering caproic acid from fermentation unit.

Spectrofluorometric method for the determination of ascorbic acid in pharmaceutical preparation using l-tyrosine as fluorescence probe.

Ascorbic acid is a vital nutrient and antioxidant that is commonly used as an additive in commercial products. Quantitation of ascorbic acid is highly desired in the medical, food, and cosmetic industries. A spectrofluorometric assay for sensitive determination of ascorbic acid was developed using l-tyrosine as a fluorescent probe. The native fluorescence intensity of tyrosine was quenched using ascorbic acid. The linear range was 0.03-30.00 μM, and the limit of detection was 0.01 μM. The method exhibited excellent precision, accuracy, specificity, and robustness. Components of pharmaceutical preparations that are commonly found with ascorbic acid did not interfere with detection. The procedure was successfully employed for determination of ascorbic acid content in pharmaceutical tablets, injections, and nutrient supplements with satisfactory results. A Stern-Volmer plot and fluorescence lifetime revealed that quenching was attributed to the inner filter effect and static quenching. Isothermal titration calorimetry confirmed the formation of a complex between tyrosine and ascorbic acid, with a binding constant of 1.68 × 103 M-1 and reaction stoichiometry of 0.94. Thermodynamic parameters suggested spontaneous complexation via hydrophobic interactions as the dominant binding force. This method is promising for the simple and rapid determination of ascorbic in the pharmaceutical industry.

Analysis of clozapine in its tablets using two novel spectrophotometric reactions targeting its tertiary amino group.

Two simple spectrophotometric methodologies have been proposed and validated for the measurement of an atypical antipsychotic drug Clozapine (CLZ). Method A depends on interaction of CLZ with N-bromosuccinimide(NBS) resulting in formation of a yellowish orange colored product, measured at 320nm. The linearity range was 5.0-70.0μg/mL. Method B depends on condensation of the same drug with acetic acid mixed anhydride reagent producing a purple colored product, measured at 319nm. The linearity range was 8.0-24.0μg/mL. All parameters affecting the reaction condition (volume of both reagent, temperature, time and the different diluting solvents) were optimized. Both methods were successfully applied to assay CLZ in its pure form and tablets giving mean percentage recoveries of (98.87±1.8 and 100±1.7) for method A, and corresponding values of (98.6±0.96 and 99.5±1) for method B. Besides, the study of reactions stoichiometry was performed and the reaction mechanisms were proposed.

Elucidation of the reaction mechanism of catalytic reaction coupling of ethylbenzene dehydrogenation with nitrobenzene hydrogenation over MoO3/TiO2 catalysts

Catalytic coupling of ethylbenzene (EB) dehydrogenation with nitrobenzene (NB) hydrogenation offers potential economical and energetic benefits. However, several studies in the literature have shown that NB conversion could be higher than that of EB, violating the law of mass conversion. This work provides a new understanding of this reaction coupling scheme over MoO3/TiO2 catalysts to elucidate this scientific mystery. Our results suggest that EB and NB have different adsorption rates on the TiO2 surfaces, resulting in higher NB conversion. In addition, three distinct reaction schemes, each follows a different EB to NB stoichiometric ratio, were identified on the MoO3 surfaces. The occurrence of the reactions is dependent on catalyst pretreatment by hydrogen reduction and the amount of oxygen vacancies on the surfaces. Our work explains why mass conservation was not satisfied in some previous studies due to the incorrect reaction stoichiometry used for analyzing the reactant conversions.

Structural conserved moiety splitting of a stoichiometric matrix

Characterising biochemical reaction network structure in mathematical terms enables the inference of functional biochemical consequences from network structure with existing mathematical techniques and spurs the development of new mathematics that exploits the peculiarities of biochemical network structure. The structure of a biochemical network may be specified by reaction stoichiometry, that is, the relative quantities of each molecule produced and consumed in each reaction of the network. A biochemical network may also be specified at a higher level of resolution in terms of the internal structure of each molecule and how molecular structures are transformed by each reaction in a network. The stoichiometry for a set of reactions can be compiled into a stoichiometric matrix N∈Zm×n, where each row corresponds to a molecule and each column corresponds to a reaction. We demonstrate that a stoichiometric matrix may be split into the sum of m−rank(N) moiety transition matrices, each of which corresponds to a subnetwork accessible to a structurally identifiable conserved moiety. The existence of this moiety matrix splitting is a property that distinguishes a stoichiometric matrix from an arbitrary rectangular matrix.

Landing microextraction sediment phase onto surface enhanced Raman scattering to enhance sensitivity and selectivity for chromium speciation in food and environmental samples

The current study explores the first full mode liquid microextraction technique coupled with surface-enhanced Raman spectroscopy (SERS), and has been successfully applied for chromium speciation in food and environmental matrices. Herein, chromium as chlorochromate anion [CrO3Cl]− and the cationic rhodamine 6G [RG]+ dye has been extracted in organic phase as a complex ion associate [RG+.CrO3Cl−.nS]org at pH ≤ 1.0. Afterwards, the extracted phase was deposited on the surface of the nano-flower shaped silver nanoparticles substrate and the SERS response was monitored against the reagent blank at 1505 cm−1. Substrate characterizations, reaction mechanism assignment, stoichiometry, speciation, analytical applications, selectivity and validation were performed. The analytical procedure exhibits a detection limit of 0.03 µg L−1 under the optimized experimental conditions. The accuracy of the proposed strategy was validated by inductively coupled plasma optical emission spectrometry method using student's t- and F tests at 95% confidence.