Reagent Concentration Research Articles

Catalytic effect of the in-situ rhodium(III) complexes in surfactant medium on the auto-oxidation of 1,2-hydroxyphenylthiourea: A theoretical and experimental study for rhodium(III) sensing

1,2-hydroxyphenylthiourea(HPTU) undergoes auto-oxidation to form an yellow colored dimer. The process of auto-oxidation is enhanced by the presence of trace quantities of transition metal ions and transition metal complexes that act as catalysts. In the current study, catalytic potential of rhodium(III) complexes on the auto-oxidation of 1,2-hydroxyphenylthiourea(HPTU) was studied theoretically using quantum mechanical calculations and experiments were carried out using photometry and fluorometry. DFT studies inferred that [Rh(Py)6]Cl3 showed a better catalytic activity in the dimerization of HPTU. Theoretical studies were subsequently validated through experiments using photometric methods and the range of detection was determined to be 6 ng/mL–100 ng/mL. The detection limit was observed to be 2 ng/mL. Analytical parameters such as pH, reagent concentration, metal ion concentration, appropriate activators and surfactants were established.

Continuous-flow analysis of nitrogen compounds in environmental water using a copper–zinc reduction coil

The copper–cadmium reduction method has been applied to determine nitrogen compounds in heavily contaminated environmental water. However, there is an international demand to reduce the use of cadmium because it is harmful to humans and environment. Hence, a copper–zinc reduction continuous flow analysis system without using cadmium was developed for nitrogen‐compound determination. However, the effects of seawater contaminants on this analytical method remains unknown. Therefore, in this study, the effects of contaminants on the developed method are investigated, and the applicability of the method to environmental water analysis is examined. Resultantly, interference due to magnesium precipitation is confirmed; however, this could be prevented by adjusting the concentration of the analytical reagent, i.e,. ethylenediaminetetraacetic acid disodium. The measurement of certified reference materials under the new conditions, with precipitation countermeasures, show good results, with an accuracy of over 96%. Additionally, a recovery study using actual environmental water afforded good results, with recovery of >95% for all samples. These results indicate that the proposed method is an excellent, cadmium-free analytical method capable of analyzing environmental water as effectively as conventional methods.

Programmable C−N Bond Formation through Radical‐Mediated Chemistry in Plasma‐Microdroplet Fusion

AbstractNon‐thermal plasma discharge produced in the wake of charged microdroplets is found to facilitate catalyst‐free radical mediated hydrazine cross‐coupling reactions without the use of external light source, heat, precious metal complex, or trapping agents. A plasma‐microdroplet fusion platform is utilized for introduction of hydrazine reagent that undergoes homolytic cleavage forming radical intermediate species. The non‐thermal plasma discharge that causes the cleavage originates from a chemically etched silica capillary. The coupling of the radical intermediates gives various products. Plasma‐microdroplet fusion occurs online in a programmable reaction platform allowing direct process optimization and product validation via mass spectrometry. The platform is applied herein with a variety of hydrazine substrates, enabling i) self‐coupling to form secondary amines with identical N‐substitutions, ii) cross‐coupling to afford secondary amine with different N‐substituents, iii) cross‐coupling followed by in situ dehydrogenation to give the corresponding aryl‐aldimines with two unique N‐substitutions, and iv) cascade heterocyclic carbazole derivatives formation. These unique reactions were made possible in the charged microdroplet environment through our ability to program conditions such as reagent concentration (i. e., flow rate), microdroplet reactivity (i. e., presence or absence of plasma), and reaction timescale (i. e., operational mode of the source). The selected program is implemented in a co‐axial spray format, which is found to be advantageous over the conventional one‐pot single emitter electrospray‐based microdroplet reactions.

Programmable C-N Bond Formation through Radical-Mediated Chemistry in Plasma-Microdroplet Fusion.

Non-thermal plasma discharge produced in the wake of charged microdroplets is found to facilitate catalyst-free radical mediated hydrazine cross-coupling reactions without the use of external light source, heat, precious metal complex, or trapping agents. A plasma-microdroplet fusion platform is utilized for introduction of hydrazine reagent that undergoes homolytic cleavage forming radical intermediate species. The non-thermal plasma discharge that causes the cleavage originates from a chemically etched silica capillary. The coupling of the radical intermediates gives various products. Plasma-microdroplet fusion occurs online in a programmable reaction platform allowing direct process optimization and product validation via mass spectrometry. The platform is applied herein with a variety of hydrazine substrates, enabling i) self-coupling to form secondary amines with identical N-substitutions, ii) cross-coupling to afford secondary amine with different N-substituents, iii) cross-coupling followed by in situ dehydrogenation to give the corresponding aryl-aldimines with two unique N-substitutions, and iv) cascade heterocyclic carbazole derivatives formation. These unique reactions were made possible in the charged microdroplet environment through our ability to program conditions such as reagent concentration (i. e., flow rate), microdroplet reactivity (i. e., presence or absence of plasma), and reaction timescale (i. e., operational mode of the source). The selected program is implemented in a co-axial spray format, which is found to be advantageous over the conventional one-pot single emitter electrospray-based microdroplet reactions.

Towards the clinical translation of a silver sulfide nanoparticle contrast agent: large scale production with a highly parallelized microfluidic chip.

Ultrasmall silver sulfide nanoparticles (Ag2S-NP) have been identified as promising contrast agents for a number of modalities and in particular for dual-energy mammography. These Ag2S-NP have demonstrated marked advantages over clinically available agents with the ability to generate higher contrast with high biocompatibility. However, current synthesis methods for inorganic nanoparticles are low-throughput and highly time-intensive, limiting the possibility of large animal studies or eventual clinical use of this potential imaging agent. We herein report the use of a scalable silicon microfluidic system (SSMS) for the large-scale synthesis of Ag2S-NP. Ag2S-NP produced using this system were compared to bulk synthesis and a commercially available microfluidic device through characterization, contrast generation, in vivo imaging, and clearance profiles. Using SSMS chips with 1 channel, 10 parallelized channels, and 256 parallelized channels, we determined that the Ag2S-NP produced were of similar quality as measured by core size, concentration, UV-visible spectrometry, and in vitro contrast generation. Moreover, by combining parallelized chips with increasing reagent concentration, we were able to increase output by an overall factor of 5,100. We also found that in vivo imaging contrast generation was consistent across synthesis methods and confirmed renal clearance of the ultrasmall nanoparticles. Finally, we found best-in-class clearance of the Ag2S-NP occurred within 24h. These studies have identified a promising method for the large-scale production of Ag2S-NP, paving the way for eventual clinical translation.

Optimization of waste biomass demineralization through response surface methodology and enhancement of thermochemical and fusion properties

This study examines the impact of leaching with dilute hydrochloric acid solution on the reduction of ash content and the thermal degradation behavior of sugarcane bagasse. Response surface methodology (RSM) was used to statistically design the experiments and investigate the effect of three independent variables: treatment time, solid-to-liquid ratio, and reagent concentration. The leaching conditions were further optimized and experimentally validated for maximum ash reduction for suitability of treated biomass as feedstock for thermochemical conversion technologies. Reagent concentration and treatment time directly affected ash reduction, while the solid-to-liquid ratio inversely influenced it. Concentration had the highest impact, and treatment duration had the least. The maximum 78.2% ash reduction was achieved by treating the biomass with 1 M HCl for 80 min at a solid-to-liquid ratio of 50:1 (wt/vol). This ash reduction also resulted in a 9.82% increase in higher heating value (HHV). Hemicellulose hydrolysis during leaching was observed through chemical composition and Fourier-transform infrared spectroscopy (FTIR). Ash fusion temperatures increased, indicating more thermally stable biomass. Thermogravimetric analysis (TGA) showed elevated maximum degradation temperature and activation energy.

Parameters of Collision and Adhesion Process Between a Rising Bubble and Quartz in Long-Chain Amine Solution and Their Correlation with Flotation

The successful adhesion of air bubbles to mineral particles is the crucial to flotation technology. This paper systematically investigates the parameters variation in the dynamic interaction process between a rising bubble and a quartz plate in long-chain amine solutions (dodecylamine, tedecylamine, and octadecylamine). The results show that the type and concentration of long-chain amine affected the collision and adhesion process between bubbles and quartz plates remarkably. The maximum rebound distance (rebound distance after the first collision) of bubbles and the stable-state liquid film thickness gradually decreases with the increase of reagent concentration. Additionally, the collision-rebound duration and induction time shorten accordingly, the surface tension of the solution decreases, the surface hydrophobicity of quartz increases, and the deformation degree and average movement velocity of bubbles decrease. With the increase in carbon chain length, the adsorption form of the amine collector and quartz surface becomes closer to vertical, and the density of water molecules decreases. The recovery of quartz particles is highest with octadecylamine systems, corresponding well with the changing trend in steady-state liquid film thickness. This research provides an effective method for in-depth analysis of the microscopic interaction mechanism between bubbles and mineral surfaces and the prediction of flotation results.

Tailoring metabolic activity assays for tumour-engineered 3D models

Monitoring cell behaviour in hydrogel-based 3D models is critical for assessing their growth and response to cytotoxic treatment. Resazurin-based PrestoBlue and AlamarBlue reagents are frequently used metabolic activity assays when determining cell responses. However, both assays are largely applied to cell monolayer cultures but yet to have a defined protocol for use in hydrogel-based 3D models. The assays' performance depends on the cell type, culture condition and measurement sensitivity. To better understand how both assays perform, we grew pancreatic cancer cells in gelatin methacryloyl and collagen hydrogels and evaluated their metabolic activity using different concentrations and incubation times of the PrestoBlue and AlamarBlue reagents. We tested reagent concentrations of 4 % and 10 % and incubation times of 45 min, 2 h and 4 h. In addition, we co-cultured cancer cells together with cancer-associated fibroblasts and peripheral blood mononuclear cells in gelatin methacryloyl hydrogels and subjected them to gemcitabine and nab-paclitaxel to evaluate how both assays perform when characterising cell responses upon drug treatment. CyQuant assays were conducted on the same samples and compared to data from the metabolic activity assays. In cancer monocultures, higher reagent concentration and incubation time increased fluorescent intensity. We found a reagent concentration of 10 % and an incubation time of 2 h suitable for all cell lines and both hydrogels. In multicellular 3D cultures, PrestoBlue and AlamarBlue assays detected similar cell responses upon drug treatment but overestimated cell growth. We recommend to assess cell viability and growth in conjunction with CyQuant assays that directly measure cell functions.

Thiol‐Ene Coupling Reaction for Functionalization of Non‐Activated Alkenes: An Experimental Study on the Chemistry of the Methyl Oleate Amination

AbstractThis work investigates the functionalization of molecules with non‐activated internal double bonds via thiol‐ene coupling (TEC) reaction. A comprehensive study of the reaction between cysteamine hydrochloride (CAHC) and methyl oleate (MO) was carried out. A series of reactions were conducted under different operating conditions in order to assess their effect on conversion and selectivity. Different conditions were considered like the type of atmospheres and solvents, a portionwise addition of CAHC, reagents concentrations, and excess of CAHC. Maximum conversion and selectivity were reached under inert atmosphere, diluted conditions, ethanol as solvent, and the addition of CAHC at the beginning of the reaction with a molar ratio of CAHC/MO of 3/1. This provides an approach for analyzing more complex reaction systems.

A hybrid predictive modeling approach for catalyzed polymerization reactors

Polymerization reactions are characterized by complex, nonlinear behaviors that pose significant challenges for conventional modeling techniques. Accurate and reliable models are crucial for advancing material science and enabling technological innovations across various industries. Conventional first-principles models often fall short in capturing the intricate dynamics of polymeric systems, leading to limitations in predictive accuracy. In this work, we propose a novel hybrid modeling approach that combines a conventional first-principles model with the strengths of a data-driven multi-layer perceptron (MLP) model and also a linear regression (LR) model to enhance the predictability of polymerization processes. Utilizing this hybrid approach significantly reduces the mean absolute error for predicting the concentrations of main reagents by 84% and 86%, respectively, in experiments with significantly deviant outcomes. Our results indicate that the model is capable of predicting the concentrations of both the main and side products with a maximum error margin of 3.5%.

Characterization of complexation of uracil with peptides through its volumetric properties in buffer saline solution at different temperatures

Densities of mixtures of uracil (Ura) with glycyl-glycine (GlyGly) and glycyl-phenylalanine (GlyPhe) in a buffered saline (pH 7.4) were measured at T=(288.15, 293.15, 298.15, 303.15, 308.15 and 313.15) K using the density meter DMA 5000 M (Anton Paar). The apparent molar volumes, limiting apparent molar volumes at infinite dilution and their derivatives with respect to temperature have been evaluated. Interactions of uracil (Ura) with glycylpeptides (GlyGly, GlyPhe, GlyTyr, GlyGlu) were studied with using review volumetric properties obtained early for Ura in GlyTyr and GlyGlu buffered solutions. The effect of concentration, ionic state and hydrophobicity of reagents on the Ura volume properties were discussed. The results indicate the complex formation between Ura and glycylpeptides with 1:1 stoichiometry. It was shown that the complexation of uracil with the glycylpeptides is accompanied by the positive changes of molar volume of Ura. The positive values of Hepler parameter indicate an increase in the ordering of the solvent in the environment of uracil with the addition of peptides. Uracil acts as a structure maker and its structure-making ability increases in series: Ura < GlyPhe < GlyGly < GlyGlu < GlyTyr.

The importance of factorial design on the optimization of biosensor performance: immobilization of glucose oxidase as a case study.

Conventionally, the optimization of glucose biosensors is achieved by varying the concentrations of the individual reagents used to immobilize the enzyme. In this work, the effect and interaction between glucose oxidase enzyme (GOx), ferrocene methanol (Fc), and multi-walled carbon nanotubes (MWCNTs) at different concentrations were investigated by a design of experiments (DoE). For this analysis, a factorial design with three factors and two levels each was used with the software RStudio for statistical analysis. The data were obtained by electrochemical experiments on the immobilization of GOx-Fc/MWCNT at different concentrations. The results showed that the factorial DoE method was confirmed by the non-normality of the residuals and the outliers of the experiment. When examining the effects of the variables, analyzing the half-normal distribution and the effects and contrasts for GOx-Fc/MWCNT, the factors that showed the greatest influence on the electrochemical response were GOx, MWCNT, Fc, and MWCNT:Fc, and there is a high correlation between the factors GOx, MWCNT, Fc, and MWCNT:Fc, as shown by the analysis of homoscedasticity and multicollinearity. With these statistical analyses and experimental designs, it was possible to find the optimal conditions for different factors: 10mMmL-1 GOx, 2mgmL-1 Fc, and 15mgmL-1 MWCNT show a greater amperometric response in the glucose oxidation. This work contributes to advancing enzyme immobilization strategies for glucose biosensor applications. Systematic investigation of DoE leads to optimized immobilization for GOx, enables better performance as a glucose biosensor, and allows the prediction of some outcomes.

The Power of Reagent Titration in Flow Cytometry.

Flow cytometry facilitates the detection of multiple cell parameters simultaneously with a high level of resolution and throughput, enabling in-depth immunological evaluations. High data resolution in flow cytometry depends on multiple factors, including the concentration of reagents used in the staining protocol, and reagent validation and titration should be the first step in any assay optimization. Titration is the process of finding the concentration of the reagent that best resolves a positive signal from the background, with the saturation of all binding sites, and minimal antibody excess. The titration process involves the evaluation of serial reagent dilutions in cells expressing the antigen target for the tested antibody. The concentration of antibody that provides the highest signal to noise ratio is calculated by plotting the percentage of positive cells and the intensity of the fluorescence of the stained cells with respect to the negative events, in a concentration-response curve. The determination of the optimal antibody concentration is necessary to ensure reliable and reproducible results and is required for each sample type, reagent clone and lot, as well as the methods used for cell collection, staining, and storage conditions. If the antibody dilution is too low, the signal will be too weak to be accurately determined, leading to suboptimal data resolution, high variability across measurements, and the underestimation of the frequency of cells expressing a specific marker. The use of excess antibodies could lead to non-specific binding, reagent misuse, and detector overloading with the signal off scale and higher spillover spreading. In this publication, we summarized the titration fundamentals and best practices, and evaluated the impact of using a different instrument, sample, staining, acquisition, and analysis conditions in the selection of the optimal titer and population resolution.

Insights into the methodological perspectives for screening polyunsaturated fatty acids-containing bacteria.

Polyunsaturated fatty acids (PUFA) are vital molecules in the pharmaceutical, medical, and nutritional industries. Exploration of bacterial strains capable of producing significant amounts of PUFAs offers a promising avenue for biotechnological applications and industrial-scale production. However, an extensive screening of several samples from diverse sources is highly needed to identify a potential strain. The present study provides the results of the evaluation of 15 different screening methodologies (including changes in existing protocols in terms of reagent concentration, incubation temperature and time) for identifying PUFA-producing bacteria in comparison to the gold standard method (Gas chromatography-mass spectrometry), for the first time. The results determined the most effective techniques for each critical PUFA, leading to an optimized screening process that saves time and resources. The H2O2 plate assay using 0.5% or 1% H2O2 for 72 & 96h of incubation at 15 °C consistently outperformed others for finding bacteria containing total nutritionally important long chain-PUFA (LC-PUFA), linoleic acid, and arachidonic acid. Whereas the 2,3,5-triphenyl tetrazolium chloride broth assay at 10-15 °C was the most effective and semiquantitative screening methodology for eicosapentaenoic acid (EPA) and alpha-linolenic acid-containing bacteria. Apart from the methodological perspectives, the study also revealed certain potential strains to be targeted in the ongoing research on PUFA-containing bacteria. Further, the manuscript forms the first report on the presence of docosahexaenoic acid (DHA) in Shewanella decolorationis, EPA in Psychrobacter maritimus and Micrococcus aloeverae, and both EPA and DHA in Arthrobacter rhombi. Altogether, the paper generates several thought-provoking insights on the methodological perspectives and identifies potential PUFA-containing bacteria with practical applications in future bacteria-based PUFA research.

Safety method, Spectrophotometric Determination of Sulfamethaxazole drug in bulk and Pharmaceutical Preparations

A simple, cheap, fast, accurate, Safety and sensitive spectrophotometric method for the determination of sulfamethaxazole (SFMx), in pure form and pharmaceutical dosage forms. has been described The Method is based on the diazotization of the drug by sodium nitrite in acidic medium at 5Cº followed by coupling with salbutamol sulphate (SBS) drug to form orange color the product was stabilized and measured at 452 nm Beer’s law is obeyed in the concentration range of 2.5-87.5 ?g ml-1 with molar absorptivity of 2.5x104 L mole-1 cm-1. All variables including the reagent concentration, reaction time, color stability period, and sulfamethaxazole /salbutamol ratio were studied in order to optimize the reaction conditions. No interferences were observed Results of analysis were validated statistically and by recovery studies. These methods are successfully employed for the determination of sulfamethaxazole in some pharmaceutical preparations.. The developed method is easy to use and accurate for routine studies relative to HPLC and other techniques.

Spectrofluorimetric determination of acetone in water samples with solid-phase extraction and a new benzaldehyde derivative

A new method is described for acetone (C(CH3)2O) determination in water samples. The method is based on the reaction with 4-(dimethylamino)benzaldehyde (DMAB) in dimethyl sulfoxide (DMSO) in slightly basic medium, resulting in a highly fluorescent compound with fluorescent wavelengths undisturbed by other common fluorescent compounds. Experimental conditions were optimized (reagents concentrations, reaction time) to reach optimal sensitivity. For the analysis of aqueous samples, a preconcentration step of acetone by solid-phase extraction (SPE) followed by an elution step in DMSO was optimized using Isolute ENV + columns. A highly satisfactory low detection limit of 0.014 μM (0.8 μg L−1) was achieved by combining these two steps, with a linear range from 0.048 to 5 μM and relative standard deviations between 5.7 % and 6.9 %. The protocol was validated on complex real water samples such as river water and wastewater, and our fluorimetric method with DMAB was in good agreement with the reference LC-UV method with DNPH.

Identifying synthetic variables influencing the reproducible microfluidic synthesis of ZIF nano- and micro-particles

The reproducible synthesis of nano- and -micro particles is a critical step in multiple synthetic and industrial processes. Microfluidic synthesis offers numerous advantages for development of precise, reliable, and industrially useful synthesis protocols. However, the influence of different synthetic variables on reproducibility in microfluidic synthesis is underexplored. In this work, we systematically study the influence of key synthetic parameters on the microfluidic synthesis of four Zeolitic Imidazolate Frameworks (ZIFs): ZIF-7, ZIF-8, ZIF-9, and ZIF-67. Utilizing a coiled tube microfluidic setup, we explore the influence of key synthetic parameters such as reagent concentration, stoichiometry, aging time, and nine modulators (pH-altering agents, surfactants, and polar polymers). Most importantly, we evaluate the impact of these variables in combination with the role of mixing, using the Dean flow model. Lastly, we focus on the reproducibility problems that a coiled reactor presents at specific flowrates and how these problems can be recognized and avoided. Overall, the insights collected from this work inform the design of synthetic protocols and enhance material reproducibility and control in microfluidic nano- and micro-particle synthesis.

Electrolytic Conversion of Nitro Compounds into Amines in a Membrane Reactor.

Aromatic and aliphatic amines are key intermediates in the synthesis of pharmaceuticals, dyes, and agrochemicals. These amines are often sourced from nitro compounds. The hydrogenation of nitro compounds into amines requires harsh reaction conditions (e.g., high pressures and high temperatures) or additives that are usually toxic. Here we demonstrate the electrochemically-driven hydrogenation of nitro compounds into amines in the hydrogenation compartment of a membrane reactor. The hydrogen is sourced from water in an adjacent electrolysis compartment separated by a hydrogen-permeable palladium membrane. Modifications of the palladium membrane with catalyst coatings enabled a wide range of commercially relevant nitro compounds to be hydrogenated into amines, without any additives, at ambient pressure and room temperature. This membrane reactor also enables nitro hydrogenation at high reagent concentrations with high functional group tolerance.

Exfoliation of Ti3 C2 MXene using (NH4 )2TiF6 Etchant and Simultaneous Synthesis of Ti3 C2 MXene/NH4 TiOF3 Mesocrystals Hybrids

Abstract A new single-step method is suggested to fabricate block structures consisting of NH4TiOF3 wrapped around Ti3C2 MXene (Ti3C2) by etching Ti3AlC2 MAX phase with (NH4)2TiF6. The optimal reaction conditions for Ti3AlC2 MAX phase and (NH4)2TiF6 are systematically investigated. (NH4)2TiF6 selectively etches the Al in the Ti3AlC2 MAX phase and promotes promoting the mild hydrolysis reaction of (NH4)2TiF6 to form NH4TiOF3 crystals. The exterior shapes of Ti3C2/NH4TiOF3 hybrids can be tuned by adjusting the reagent concentration, reaction temperature. The phase composition, morphology and photophysical properties of the Ti3C2/NH4TiOF3 hybrids are investigated using various characterization techniques. Ti3AlC2 MAX phase reacts with (NH4)2TiF6 at 60 °C for 24 h to form hybrids which are surrounded by NH4TiOF3 crystals simultaneously with the formation of Ti3C2 nanosheet. The resulting Ti3C2/NH4TiOF3 are porous and finely structured, showing potential for various applications in biotechnology, sensing, and environmental fields. This method provides important insights into future applications of Ti3C2/NH4TiOF3 hybrids.

Kinetics of chemical reactions in spray

The number of observations demonstrating a significant effect of droplet sizes on the kinetics of chemical processes has increased with the expansion of the scope of application of spray technology. The equations linking the concentrations of reagents, the volume of droplets, the initial composition of the solution, the composition of the gas medium and the speed of processes are formulated within the framework of formal chemical kinetics. Using the example of second-order reactions (coupling, exchange, condensation, polymerization, polycondensation), it is shown that size kinetic effects occur when chemical processes are accompanied by changes in the droplet sizes in equilibrium with the gas medium. The results of computer simulation of condensation reaction and polycondensation process reproducing size effects are presented. Kinetic curves obtained by modeling the polycondensation process are compared with experimental data.