Reagent Addition Sequence Research Articles

Effect of Order of Reagents Addition on Optical and Structural Properties of CdS Quantum Dot Prepared by Chemical Bath Deposition Technique

Cadmium sulfide quantum dots were synthesized and deposited on glass substrates by chemical bath deposition (CBD) technique using cadmium sulfate and thiourea solutions in the presence of a 4,4’-(1,2-ethanediyldinitrilo)bis-(2-pentanone) (EDDBP) tetradentate ligand as a complexing agent. The order of reagents addition was varied to deposit films that were characterized for their surface morphological, optical, structural, and solid-state properties using a scanning electron microscope (SEM), a UV-visible spectrophotometer, an X-ray diffractometer (XRD), and Brunauer-Emmet-Teller (BET) analyses. The optimal condition for film deposition using the normal sequence of reagents addition was found at pH 8-12 and 298-353 ± 1K and gave films of 2.40-321.06 nm thickness, while the variation in the order of reagents addition gave improvements in the film properties. The optical properties and the observed direct band gaps (1.75-3.16 eV) of the films suggest usage in electroluminescent and solar cell devices since they have a first-order transition. The XRD patterns of the quantum dots indicated hexagonal wurzite structures, while the BET confirmed their mesoporous and nanonature.

A fluorescence nanoprobe of N-Acetyl-L-Cysteine capped CdTe QDs for sensitive detection of nitrofurazone

A method was established for detecting the content of nitrofurazone (NFZ) by fluorescence quenching of N-Acetyl-L-Cysteine (NAC) coated cadmium telluride quantum dots (CdTe QDs). By means of transmission electron microscopy (TEM) and multispectral methods such as fluorescence and ultraviolet visible spectra (UV–vis), the synthesized CdTe QDs were characterized. The quantum yield (φ) of CdTe QDs was measured as 0.33 by reference method. The CdTe QDs had a better stability, the RSD of fluorescence intensity was 1.51% in three months. NFZ quenching the emission light of CdTe QDs was observed. The analyses of Stern-Volmer and time-resolved fluorescence suggested the quenching was static. The binding constants (Ka) between NFZ and CdTe QDs were 1.14 × 104 (293 K), 0.74 × 104 (303 K) and 0.51 × 104 (313 K) L mol−1. The hydrogen bond or van der Waals force was the dominated binding force between NFZ and CdTe QDs. The interaction was further characterized by UV–vis absorption as well as Fourier transform infrared spectra (FT-IR). Using fluorescence quenching effect, a quantitative determination of NFZ was carried out. The optimal experimental conditions were studied and determined as following: pH was 7 and contact time was 10 min. The effects of reagent addition sequence, temperature and the foreign substances including some metals (Mg2+; Zn2+; Ca2+; K+; Cu2+), glucose, bovine serum albumin (BSA) and furazolidone on the determination were studied. There was a high correlation between the concentration of NFZ (0.40 – 39.63 μg mL−1) and F0/F with the standard curve F0/F = 0.0262c + 0.9910 (r = 0.9994). The detection limit (LOD) reached 0.04 μg mL−1 (3S0/S). The contents of NFZ in beef and bacteriostatic liquid were detected. The recovery of NFZ was 95.13% – 103.03% and RSD was 0.66% – 1.37% (n = 5).

Construction of fluorescence system of felodipine–tetracyanovinyl–2,2′-bipyridine complex

Abstract Felodipine (FEL)–tetracyanoethylene (TCNE)–2,2′-bipyridine (Bpy) complex was prepared with FEL, TCNE–Bpy and characterized by fluorescence, ultraviolet, and infrared. By exploring the concentration and dosage of Bpy, it was found that 1 mL 2 × 10−3 mol‧L−1 of Bpy had the best effect. The sequence of reagent addition was determined to be followed by FEL, then by TCNE, and then followed by Bpy. The concentration of FEL was 2.5 × 10−4 to 9.0 × 10−3 mol‧L−1, which had a good linear relationship with fluorescence intensity. The compound had good accuracy, precision, and specificity, and could be used for the determination of phelodipine content in FEL sustained-release tablets.

Protein encapsulation in mesoporous silica: Influence of the mesostructured and pore wall properties

The goal of this work is to study the influence of the structured mesoporous silica (SMS), used as scaffolds for tissue engineering, on the encapsulation and on the release of a model bone morphogenetic proteins (BMP), i.e. Soybean Trypsin Inhibitor (STI). First, SBA-15 silica samples were synthesized using tetraethyl orthosilicate (TEOS) as silica precursor in the presence of P123 as the surfactant in an acidic medium. Three homemade high-pressure stainless steel reactors (with smaller Teflon reactors inside), each equipped with a temperature probe, were used for the syntheses. In addition, a swelling agent was added to increase the pore size. Indeed, the common pore size for those mesostructured materials lies between 6 nm and 8 nm, while the STI has an average radius of 4 nm. The reagent addition sequence was also investigated, by playing on the time of addition of the swelling agent. It was observed that when the swelling agent was added with TEOS, an ordered mesoporous silica was produced. On the contrary, if the swelling agent was added during the surfactant dissolution step, it resulted in an unstructured yet still mesoporous silica. Because of the high affinity of STI for hydrophobic surfaces, SMS were also produced using silica precursors containing phenylene bridging groups (1,4-bis(triethoxysilyl)benzene, BTEB). The BTEB samples exhibited two 2D-hexagonal structures with different wall thicknesses. Synthesized materials were further characterized by infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), nitrogen sorption at 77 K, transmission electron microscopy (TEM), and small-angle X-ray scattering (SAXS). The influence of both the silica composition and structure on STI encapsulation/release was studied. For samples synthesized with TEOS, the unstructured sample showed a higher protein loading and a higher protein release, which could be explained by a difference in the pore interconnectivity within the sample. In fact, a fast release of STI was observed during the first 24 h. Afterwards, the STI release slowed down and seemed to reach a plateau. On the opposite, the structured sample showed a steady release over time. Finally, the sample synthesized with BTEB did not show a significant release over the same period of time. This led us to the conclusion that the hydrophobicity of the silica surface plays a major role on the protein encapsulation and its release rate.

Minimizing side reactions during amide formation using DIC and oxymapure in solid-phase peptide synthesis

N,N’-diisopropylcarbodiimide (DIC) and OxymaPure are the reagents of choice for the formation of peptide bonds in Solid-Phase Peptide Synthesis (SPPS). The combined use of DIC and OxymaPure in model cases can be accompanied by a serious side reaction with the ultimate formation of oxadiazole and HCN. Here we demonstrate, in a practical case, that the first step of the reaction (formation of an adduct) takes place with approximately 1% respect to the amount of OxymaPure. Furthermore, we found that the second part of the side-reaction (formation of oxadiazole and HCN) can be minimized and even suppressed with an appropriate protocol for the sequence of reagent addition. Thus, the best conditions are preactivation of the Fmoc-amino acid with only DIC for 2–5 min followed by addition of the resulting mixture to the peptide-resin. OxymaPure can be added to the resin before adding the preactivation mixture or after first adding the preactivation mixture, the latter approach giving the best results. Ultimately, in standard research conditions, the combined use of DIC and OxymaPure as coupling method in SPPS is safe.

Process Optimization of Silver Nanoparticle Synthesis and Its Application in Mercury Detection.

Silver nanoparticles (AgNPs) have stable reactivity and excellent optical absorption properties. They can be applied in various industries, such as environmental protection, biochemical engineering, and analyte monitoring. However, synthesizing AgNPs and determining their appropriate dosage as a coloring substance are difficult tasks. In this study, to optimize the process of AgNP synthesis and obtain a simple detection method for trace mercury in the environment, we evaluate several factors—including the reagent addition sequence, reaction temperature, reaction time, the pH of the solution, and reagent concentration—considering the color intensity and purity of AgNPs as the reaction optimization criteria. The optimal process for AgNP synthesis is as follows: Mix 10 mM of silver nitrate with trisodium citrate in a hot water bath for 10 min; then, add 10 mM of sodium borohydride to produce the AgNPs and keep stirring for 2 h; finally, adjust the pH to 12 to obtain the most stable products. For AgNP-based mercury detection, the calibration curve of mercury over the concentration range of 0.1–2 ppb exhibits good linearity (R2 > 0.99). This study provides a stable and excellent AgNP synthesis technique that can improve various applications involving AgNP-mediated reactions and has the potential to be developed as an alternative to using expensive detection equipment and to be applied for the detection of mercury in food.

Effect of Gold Nanoparticles Size on Detection of Methylphosphonic Acid Hydrolysis Product of Nerve Agent

Citrate reduction of gold (III) chloride trihydrate (HAuCl4) is commonly used method to synthesise citrate-capped gold nanoparticles (cit-AuNPs). In this study, the sequence of reagents addition was modified (“inverse” method) to synthesise smaller size of cit-AuNPs than the standard Turkevich method (“direct” method). Ultraviolet-visible spectroscopy (UV-vis) and field emission transmission electron microscopy (FETEM) confirmed the formation of cit-AuNPs. The cit-AuNPs synthesized using “inverse” method are smaller in size (14.0 ± 3.03 nm) with uniform spherical shape compared to “direct” method (23.5 ± 7.52 nm). Smaller particles size of cit-AuNPs provide higher efficiency and sensitivity for detection of methylphosphonic acid (MPA) via colorimetric incorporated with image processing with a linear range from 2.5 to 12.5 mM and a low detection limit of 6.28 mM at shorter detection period (24 to 30 s).

Differential flotation of pyrite and arsenopyrite: Effect of hydrogen peroxide and collector type

The present work investigates the role of hydrogen peroxide and collector type in differential flotation of pyrite and arsenopyrite model minerals without acid pretreatment. Ethylenediaminetetraacetic acid (EDTA) extraction and X-ray photoelectron spectroscopy (XPS) analysis were employed to determine the oxidation extent supplemented with zeta potential, UV–Vis and Time-of-Flight secondary ion mass spectrometry (TOF-SIMS) towards elucidating collector adsorption behaviour and surface species formation. The results showed higher extent of ferric hydroxide was generally observed for arsenopyrite compared to pyrite using EDTA extraction and XPS analysis. A 2 kg/t hydrogen peroxide addition and 120 g/t PAX collector concentration gave the best separation efficiency with 63.1% pyrite and 5.1% arsenopyrite recovery into the flotation concentrate. The addition of hydrogen peroxide (2 kg/t) had a minor effect on the mineral surface oxidation state according to XPS analysis. Thus, the oxidation of adsorbed xanthate ions into hydrophilic monothiocarbonate ion was the more apparent reason for remarkable arsenopyrite depression compared with pyrite. The observation was not affected with change in sequence of reagent addition and presents great opportunity in better, profitable processing of low-grade refractory auriferous sulphide ores.

Reagent addition sequence and equivalent in N‐heterocyclic carbene‐catalyzed nonpolar inversion enable conversion from aldimine to benzoxazole

AbstractThe umpolung reaction catalyzed by N‐heterocyclic carbenes (NHCs) has been widely studied and well recognized, but their role in the nonpolar inversion reaction under oxidative condition has been rarely reported. In this paper, the mechanism of the oxidative nonpolar inversion reaction catalyzed by NHCs to produce benzoxazole is investigated in detail. The reaction occurs through five processes. For oxidation in the second process, two successive tautomerizations followed by oxidation are energetically more favorable than the other two pathways. The rate‐determining step is the oxidation by 3,3′‐5,5′‐tetra‐tert‐butyl‐4,4′‐diphenoquinone. Mechanism calculations of the uncatalyzed reaction reveal that the very highly exothermic nature of the initial step is the main reason for the extremely high energy barrier in the following step. With the participation of NHC, this unfavorable transformation can be deftly prevented according to the specific sequence and equivalent of reagent addition, enabling the reaction to occur under mild conditions.

Effect of Solvent properties on Crystallinity and Morphology of Octavinyl-POSS: A Comparative Study

Polyhedral Oligomeric Silsesquioxanes (POSSs) are a class of hybrid structures synthesized through hydrolytic condensation (Sol-Gel method) of trifunctional silane monomers under specific conditions. Octavinyl silsesquioxane (OVS) nanostructures are comprised of a rigid inorganic silica core surrounded by vinyl functional groups with an under-developed synthesis procedure. Generally, POSS morphology, yield and crystallinity depend strongly on synthesis conditions such as solvent type, synthesis temperature, sequence of reagents addition, water/monomer molar ratio, etc. In this study, effect of solvent properties on the formation of OVS compounds, their morphology and crystallite size was studied under specific conditions. Finally, n-pentanol and butanol as the most efficient solvents were suggested according to solvent characteristics, theoretical background reported in previous studies and experimental results. Different characterization techniques such as XRD to investigate crystallinity and crystallite size, FE-SEM and TEM to determine the morphology, EDX to identify elemental and chemical composition, C-NMR and 1H-NMR to confirm the attachment of vinyl groups and FTIR to define chemical bonds, were employed to confirm the formation of the as-prepared structure. Based on the results, butanol and n-pentanol represent the best results regarding crystallinity and size by optimizing other influential parameters.

Determination of ultra trace amounts of metronidazole by 3-phenyl-N-[4-(10,15,20-triphenyl-porphyrin-5-yl)-phenyl]- acrylamide as the fluorescence spectral probe in CTAB microemulsion.

In this work, 3-Phenyl-N-[4-(10,15,20-triphenyl-porphyrin-5-yl)-phenyl]- acrylamide (TPPCA) was synthesized for the determination of metronidazole (MTZ). It was found that the type of fluorescence quenching was static quenching determined by Stern-Volmer plot and UV absorption spectroscopy, and thermodynamic related parameters were also obtained. Furthermore, the corresponding measurement conditions: the acidity of the system, the type of surfactant, the concentration of TPPCA and the sequence of reagent addition were optimized. Under the optimal experimental conditions, the linear range of MTZ was determined to be 0.01-0.20 μg mL-1, and the limit of detection (LOD) was 0.004 μg mL-1. Importantly, this report provides a simple, fast, and sensitive probe for the determination of MTZ in pharmaceutical practice.

Rapid Self-Assembly of Metal/Polymer Nanocomposite Particles as Nanoreactors and Their Kinetic Characterization.

Self-assembled metal nanoparticle-polymer nanocomposite particles as nanoreactors are a promising approach for performing liquid phase reactions using water as a bulk solvent. In this work, we demonstrate rapid, scalable self-assembly of metal nanoparticle catalyst-polymer nanocomposite particles via Flash NanoPrecipitation. The catalyst loading and size of the nanocomposite particles can be tuned independently. Using nanocomposite particles as nanoreactors and the reduction of 4-nitrophenol as a model reaction, we study the fundamental interplay of reaction and diffusion. The induction time is affected by the sequence of reagent addition, time between additions, and reagent concentration. Combined, our experiments indicate the induction time is most influenced by diffusion of sodium borohydride. Following the induction time, scaling analysis and effective diffusivity measured using NMR indicate that the observed reaction rate are reaction- rather than diffusion-limited. Furthermore, the intrinsic kinetics are comparable to ligand-free gold nanoparticles. This result indicates that the polymer microenvironment does not de-activate or block the catalyst active sites.

Elimination of the Adverse Effect of Calcium Ion on the Flotation Separation of Magnesite from Dolomite

The separation of magnesite from dolomite was studied by flotation tests, X-ray photoelectron spectroscopy (XPS), and zeta potential measurements in the presence of calcium ion (Ca2+) dissolved from dolomite. Sodium oleate (NaOL) was used as collector, and sodium carbonate (Na2CO3) and sodium hexametaphosphate (SH) were used as regulators. The results showed that SH had a good selective inhibition ability in pure mineral flotations of magnesite and dolomite. While in the presence of Ca2+ dissolved from dolomite, magnesite and dolomite were both inhibited by SH. The separation of magnesite from dolomite cannot be realized because Ca2+ can adsorb on the surface of magnesite in the form of CaCO3 and change the surface properties of magnesite. Thus, the magnesite flotation was depressed. When the sequence of reagent addition was changed to add SH prior to Na2CO3, a complex was made by Ca2+ reacting with SH, which avoided the adsorption of Ca2+ on the magnesite surface and prevented the changing of the magnesite’s surface properties. Then, after adjusting the solution pH with Na2CO3, the flotation separation of magnesite from dolomite could be achieved.

How does the size of gold nanoparticles depend on citrate to gold ratio in Turkevich synthesis? Final answer to a debated question

The dependence between the size of gold nanoparticle (AuNP) and the citrate to gold molar ratio (X) is still a matter of debate 65years after the seminal work by Turkevich et al. for high X values. We assume that this dispersion of results is due to the variation of certain parameters that are often not mentioned in the protocols, and to the use of a single characterization technique (dynamic light scattering (DLS) or transmission electron microscopy (TEM)). To adress definitely the question of this dependence, we have synthesized AuNPs with very precise protocols ensuring that the only parameters to be modified are X and the sequence of reagent addition. We have then studied, for the first time, the dependence of the size with X quantitatively with a multimodal approach (UV–Visible spectroscopy, DLS and TEM) for 2 synthetic routes differing only by the sequence of reagent addition. We show unambiguously that AuNPs’ size decay monotonically, with X whatever the order of reagent addition. It allows us to exclude the occurrence of a measurable discontinuity for a peculiar value of X that prompted some authors to postulate the existence of two different reaction pathways when the citrate to gold molar ratio is around this value. In contrast, our result is in line with one reaction pathway, likely a “seed-mediated” growth mechanism, which should leads to monotonic size decrease. Also, we note that our result agrees with the sole available theoretical prediction (Kumar et al., 2007) on the whole range of X. Despite this apparent agreement, we point some contradictions between recent experimental results and basal hypothesis of this model.

ChemInform Abstract: Ph3P‐I2 Mediated Aryl Esterification with a Mechanistic Insight.

Abstract In order to better understand the reaction mechanism and to obtain optimal conditions, the Ph 3 P-I 2 /Et 3 N mediated aryl esterification reaction was thoroughly investigated. Using a specific reagent addition sequence, the reaction proceeds remarkably well especially with acidic substrates. 31 P NMR studies revealed that the formation of an aryloxyphosphonium salt is crucial in governing the reaction path toward the formation of phenolic esters.

Ph3P-I2 mediated aryl esterification with a mechanistic insight

In order to better understand the reaction mechanism and to obtain optimal conditions, the Ph3P-I2/Et3N mediated aryl esterification reaction was thoroughly investigated. Using a specific reagent addition sequence, the reaction proceeds remarkably well especially with acidic substrates. 31P NMR studies revealed that the formation of an aryloxyphosphonium salt is crucial in governing the reaction path toward the formation of phenolic esters.

Metal-free amidation of carboxylic acids with tertiary amines

Combination of Ph3P and I2 with an appropriate reagent addition sequence could enable effective amidation of carboxylic acids with tertiary amines under mild conditions.

Investigating the Mechanism of Copper(0)-Mediated Living Radical Polymerization in Organic Media

Single electron transfer living radical polymerization (SET-LRP) is a versatile polymerization tool that allows for the synthesis of functional materials for a range of potential applications. An interesting scientific debate has dominated the literature during the past few years regarding the mechanism of Cu(0)-mediated polymerizations in both aqueous and organic media. This article is the first part of a mechanistic study regarding the role of Cu(0) and CuBr in these systems with the aim of offering some increased level of understanding of the mechanism to aid application. In this current contribution, disproportionation and comproportionation studies reveal significant variations in the thermodynamic and kinetic equilibria depending on the solvent composition, the nature of the monomer and the ligand concentration. Interestingly, the sequence of reagent addition significantly affects the disproportionation equilibrium, which is attributed to competitive complexation reactions between monomer, solvent, ligand, and copper species. The Cu(0) generated via the in situ disproportionation of [Cu(Me6TREN)]Br in DMSO prior to addition of monomer and initiator were demonstrated to contribute in different extents over the rate and control of the polymerization, depending on the equivalents of ligand employed. It was found that an increase in the concentration of the Cu(0) particles result in slower polymerization rates while when conditions that stabilize CuBr were employed, faster polymerization rates were observed. On the contrary, 5 cm of copper wire showed faster polymerization rates when compared with 9.4 mM of CuBr, highlighting that copper wire is essential for the efficient polymerization of acrylates in organic solvents.

Features of the synthesis of unsaturated sulfides proceeding from (2-chloroprop-2-en-1-yl)isothiouronium chloride

Procedure of synthesis of sulfides containing a chloropropenyl fragment sensitive to bases was modified. The change in the sequence of reagents addition ensuring a contact of isothiouronium salt with a minimal base quantity and the application of a mixture hydrazine hydrate-alkali allowed the preparation of target sulfides under mild conditions in up to 93% yields.

Significance of reagent addition sequence in the amidation of carboxylic acids mediated by PPh3 and I2

The outcome of the amidation reaction mediated by PPh3–I2 was found to be highly dependent on the addition sequence of the reagents.