Reagent Concentration Research Articles

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.

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., flowrate), microdroplet reactivity (i.e., presence or absence of plasma), and reaction timescale (i.e., operational mode source). The selected program is implemented in a co‐axial spray format.

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., flowrate), microdroplet reactivity (i.e., presence or absence of plasma), and reaction timescale (i.e., operational mode source). The selected program is implemented in a co-axial spray format.

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%.

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.

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.

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.

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.

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.

A comparative study of discharging and leaching of spent lithium-ion battery recycling

Accelerated production of lithium-ion batteries (LIBs) implies an increase in the raw materials demand, especially for metals like lithium, cobalt, and nickel. Spent LIBs recycling guarantees the regeneration and reincorporation of valuable materials into the manufacturing industry; therefore, recycling methods and techniques must be optimized. In this investigation, alkaline and reductive acid leaching processes were evaluated and compared in order to determine the effect of parameters such as pH, temperature, and reagents concentrations to achieve selective leaching processes. This study demonstrated that strongly alkaline solutions (NaOH) do not ensure selective lithium and aluminum dissolution. Also, a solid compound, LiAl2(OH)6OH(s) can be formed at pH ∼14, negatively affecting the lithium extraction. On the other hand, reductive acid leaching, with acid sulfuric and hydrazine sulfate (H2SO4 + N2H6SO4) solutions resulted in an efficient system, extracting ≥90 % of Ni, Co, and Mn at 40 °C. Hydrazine is essential as a reductant, although it must be added in excess (40 % excess with respect to the Co, Ni, and Mn content) to suppress copper dissolution. Furthermore, this work demonstrated the possibility of processing the entire spent LIBs sample once the discharge and crushing stages were concluded, avoiding physical separation, without affecting the leaching efficiency and contributing to process economy.

Fluorescence-based determination of tobramycin using a portable smartphone-based device

The study presents the development of a robust portable smartphone-based device for determining tobramycin in drugs and urine by a fluorescence-based method. As existing analytical methods for the determination of tobramycin often require complex equipment and time-consuming procedures, the proposed approach offers simplicity, portability and real-time monitoring capabilities. The spectrofluorimetric method is based on the reaction of tobramycin and fluorescamine in an alkaline medium. The measurement of analytical signals was enabled with a specially designed device integrating a 3D printed adapter, LEDs, a macro lens, an Arduino-based microcontroller, and asmartphone. The traditional spectrofluorimetry was used as a reference method. Preliminary and optimisation studies were conducted to select the most suitable experimental conditions (e.g. reagent concentration and reaction time) as well as instrumental parameters (e.g. selection of the appropriate RGB model component, ISO, and white balance). The performance of the method was validated, and then verified against conventional spectrofluorimetry, showing comparable accuracy and precision. The method implemented in a smartphone-based device showed a linear range of 0.10–1.00 mgL-1 with a detection limit of 0.03 mgL-1. Synthetic samples were tested to verify analytical usability, followed by analysis of pharmaceutical and urine samples. The method showed good precision (CV<3.4 %) and recovery values (92.3–114.1 %), consistent with spectrofluorimetric results (CV<5.9 %, recovery 92.3–119.8 %). Comparison with other methods highlighted the simplicity and efficiency of the developed approach. The research reveals that it is competitive with existing well-established methods. The proposed device offers reliable results with low reagent and sample consumption, making itsuitable for on-the-go analysis in non-laboratory conditions.

Optimization of ion-pairing HPLC method for mutual separation of rare earth elements: unveiling the “diad-effect” appraisal utilizing periodic variations in their properties

A new ion-pairing HPLC method has been developed for the analytical separation of rare earth elements (REEs), utilizing the unique “diad-effect” of the lanthanides. A chemometric approach was used to optimize the separation process, examining the impact of mobile phase pH and ion-pairing reagent concentration on resolution and elution time. A triple gradient elution program was proposed, involving changes in the pH of the mobile phase from 3.5 to 4.5, the ion-pairing reagent concentration from 25 mM to 0.05 M, and the mobile phase complexing additive (hydroxyisobutyric acid) concentration from 0.05 M to 0.5 M. With the proposed method, all REEs, including pairs that are typically difficult to separate (Pr–Nd, Eu–Gd, and Dy–Y), were effectively separated in less than eight minutes. The method validation conducted following ICH guidelines showed accurate results, with an accuracy of 99–108% across a concentration range of 50–150% of the target concentration for REEs. It also exhibited good linearity (0.9998–0.9992) across a concentration range of 5–15 µg/mL for REEs and a detection limit of 0.27–0.98 µg/mL for the various species. The proposed HPLC method proved reliable and successfully separated a commercial sample of yttrium-group oxides.

Improved synthesis of the unnatural base NaM, and evaluation of its orthogonality in in vitro transcription and translation.

Unnatural base pairs (UBP) promise to diversify cellular function through expansion of the genetic code. Some of the most successful UBPs are the hydrophobic base pairs 5SICS:NaM and TPT3:NaM developed by Romesberg. Much of the research on these UBPs has emphasized strategies to enable their efficient replication, transcription and translation in living organisms. These experiments have achieved spectacular success in certain cases; however, the complexity of working in vivo places strong constraints on the types of experiments that can be done to optimize and improve the system. Testing UBPs in vitro, on the other hand, offers advantages including minimization of scale, the ability to precisely control the concentration of reagents, and simpler purification of products. Here we investigate the orthogonality of NaM-containing base pairs in transcription and translation, looking at background readthrough of NaM codons by the native machinery. We also describe an improved synthesis of NaM triphosphate (NaM-TP) and a new assay for testing the purity of UBP containing RNAs.

SONOCHEMICAL SYNTHESIS OF SILVER NANOPARTICLES FOR GAS-DIFFUSION ELECTRODES APPLICATION

The aim of the current study is to explore the application of silver nanoparticles (AgNPs) as a catalyst in air gas-diffusion electrodes (AGDE). AgNPs have been successfully synthesized through an original sonochemical method. The effects of reagent concentrations, temperature and reaction time were studied as well. Composites of AgNPs and activated carbon (Norit NK) were prepared by using two adsorption methods to demonstrate the catalytic activity. Method 1 involves homogenizing preliminary prepared AgNPs colloid solution and Norit NK followed by evaporation of the suspension. One-step route was used for Method 2, i.e. all components were mixed altogether and sonicated, resulting in the AgNPs formation directly on the surface and inside the pores of Norit NK. Additionally,some of the samples were thermally treated at 300°C for 1h under air and argon. The composites were characterized by X-ray diffraction (XRD), scanning electron microscopy with energy dispersive X-Ray analysis (SEM/EDX) and transmission electron microscopy (TEM). The catalytic activity of the obtained composites regarding oxygen reduction reaction (ORR) was investigated in AGDE using an aqueous 4M NaCl electrolyte. The thermally treated composite obtained via Method 2 appears to show improved electrochemical catalytic activity regarding ORR in comparison to the Method 1 samples.

Development of a smartphone-based colorimetric detection for quantification of vitamin C in dietary supplements and skin care products

This research project presents a development of an assay tool for quantification of vitamin C in dietary supplements and skin care products. The proposed method was developed based on decolorization of acidic potassium permanganate (KMnO4) by vitamin C through a redox reaction, with subsequent colorimetric detection by using digital imaging. The imaging was carried out using smartphone camera and free-downloaded RGB color detector application. To obtain optimal conditions, influential parameters such as light source position installed inside a 19 cm × 46 cm × 10 cm lightbox, reagent concentrations, and reaction time were studied. To the best conditions, good linearity (r2 &gt; 0.99) in the range 1–70 mg vitamin C/L was obtained. Relative standard deviation was less than 3.9% indicating high precision. The proposed method was validated by quantification of vitamin C content in 15 sample solutions using the proposed method in comparison with the reference iodometric titration method. The results obtained from those two methods were not significantly different using paired t-test at confidence level of 95% (texp=0.41, tcrit=2.14). The results indicated that utilizing smartphone camera with free-downloaded color detector application is possible as an alternative analysis tool for determination of vitamin C.