Aqueous Alkaline Medium Research Articles

Synthesis and Characterization of Novel Isoxazole derivatives

Twenty five novel Isoxazole heterocycles are synthesized and characterized by IR, NMR and CHN analysis. Physico-chemical characteristics also notified. In the first step chalcones are synthesized by the reaction of aromatic aldehydes with aromatic ketones in aqueous alcoholic alkaline medium. These are made to react with hydroxylamine hydrochloride and sodium acetate to prepare title compounds. All synthesized compounds analyzed for obedience of Lipinsky’s rule. Six of the compounds showed slight violation to oral dosage form suitability. Most of the compounds were solid in nature and gave good yield.

Electrochemical Behavior and Shape Evolution of Structured Pd Nanoparticles in Alkaline Media─Influence of Electrochemically Absorbed Hydrogen.

We report on the electrochemical behavior and shape evolution of Pd nanocubes (Pd NCs) and Pd nanooctahedrons (Pd NOs) with an average size of 9.8 and 6.9 nm, respectively, in aqueous alkaline medium in the potential range of the underpotential deposition of H (UPD H) and H absorption. While the Pd NCs and Pd NOs remain stable in the potential region of the UPD H, H absorption and desorption of absorbed H (Habs) induce structural changes to the Pd NPs, as indicated by the results of electrochemical measurements and identical location-transmission electron microscopy (IL-TEM) analyses. Because both Pd NCs and Pd NOs are known to be stable in the potential region of H absorption and Habs desorption in acidic medium and maintain their structure, the irreversible structural changes are attributed to their interfacial interaction with the aqueous alkaline medium. In the alkaline medium, the nanoparticle surface/electrolyte interfacial structure plays an essential role in the mechanism of Habs desorption that is observed at higher potentials than that in the acidic medium. Hydrogen desorption is substantially hindered due to the structure of the water network adjacent to the Pd nanoparticles or the interaction between hydrated cations and adsorbed OH on the nanoparticle surface, resulting in the trapping of a small amount of H (incomplete Habs desorption). It is proposed that H trapping and associated structural strain lead to the deformation of the Pd nanoparticles and the loss of their initial structure.

A New Approach for Increasing the Chelating Capacity of the Tartrate Ion in the Extraction of Copper from Ores

The role of the tartrate ion in the extraction of copper from oxidized ore in aqueous alkaline medium is first reported. This was demonstrated by a sequential evaluation of the following: (i) The formation of an ionic complex resulting from the interaction of copper salts (CuSO4, Cu(NO3)2) with an alkaline aqueous solution of tartrate ions. (ii) The treatment of metallic copper with hydrogen peroxide. (iii) Spectrophotometric and potentiometric studies of malaquite. These studies demonstrated that the Cu(II)–tartrate interaction is only possible due to the chelating activity of tartrate ion leading to the formation of the [Cu(OH)2C4H4O6]2− anion complex and the lixiviation of the oxidized mineral is controlled by the chelating agent. The advantage of this approach relative to previous ones is discussed. Final conclusions are given.

Exceptionally water-soluble [CuII2] complexes for investigating monosaccharide-metal ion interactions

The design, synthesis and characterization of two new dinuclear copper(II) complexes [Cu2(phpda)(µ-Cl)]·2H2O (1) and [Cu2(phpda)(µ-NO3)]·2H2O (2) (H3phpda = N,N′ -bis[2-pyridylmethyl]-2‑hydroxy-1,3-propanediamine-N,N′-dipropionic acid) as carbohydrate binding models have been reported. The FTIR, UV–Vis, ESI-MS, microanalysis and molar conductance data have been utilized to characterize the synthesized complexes. The structures of 1 and 2 have been established by density functional theory (DFT) calculations that exhibit a self-aggregated closely packed arrangement with average inter-metallic Cu···Cu separation of 3.2484 Å. In aqueous alkaline media, both complexes have been studied for their binding interactions with biologically important monosaccharides, d-glucose and d-glucosamine by employing UV–Vis spectroscopy and DFT calculations. The binding-assisted steady decrease of absorbances of 1 and 2 accompanied by a significant red/blue shift of absorption maxima of the complexes upon UV–Vis titration of 1 and 2 with d-glucose and d-glucosamine has been observed, suggesting 1:1 complex/monosaccharide interactions. Evaluation of binding constant values of monosaccharide-bound copper(II) complexes has been accomplished by utilizing UV–Vis titration data, and the values are found to be 2.145 × 103 M−1, 2.652 × 103 M−1, 1.388 × 103 M−1 and 1.793 × 103 M−1 for 1/D-glucose, 1/D-glucosamine, 2/D-glucose and 2/D-glucosamine assemblies, respectively. Fukui functions (fk+) on the copper sites, including HOMO and LUMO in both complexes have been obtained from DFT calculations to understand the likely copper sites involved in the binding events with monosaccharides. However, a comparative assessment of their binding constant values showed that d-glucosamine interacts with 1 and 2 more preferentially than d-glucose.

Synthesis and Molecular Docking Studies of Novel Biheterocyclic Propanamides as Antidiabetic Agents Having Mild Cytotoxicity.

The aim of this work was to bring forth some new hybrid molecules having pharmacologically potent indole and 1,3,4-oxadiazole heterocyclic moieties unified with a propanamide entity. The synthetic methodology was initiated by esterification of 2-(1H-indol-3-yl)acetic acid (1) in a catalytic amount of sulfuric acid and ethanol in excess, to form ethyl 2-(1H-indol-3-yl)acetate (2), which was converted to 2-(1H-indol-3-yl)acetohydrazide (3) and further transformed to 5-(1H-indole-3-yl-methyl)-1,3,4-oxadiazole-2-thiol (4). 3-Bromopropanoyl chloride (5) was reacted with various amines (6a-s) in aqueous alkaline medium to generate a series of electrophiles, 3-bromo-N-(substituted)propanamides (7a-s), and these were further reacted with nucleophile 4 in DMF and NaH base to yield the targeted N-(substituted)-3-{(5-(1H-indol-3-ylmethyl)-1,3,4-oxadiazol-2-yl)sulfanyl}propanamides (8a-s). The chemical structures of these biheterocyclic propanamides were confirmed by IR, 1H NMR, 13C NMR, and EI-MS spectral techniques. These compounds were evaluated for their enzyme inhibitory potentials against the α-glucosidase enzyme, where the compound 8l showed promising enzyme inhibitory potential with an IC50 value less than that of the standard acarbose. Molecular docking results of these molecules were coherent with the results of their enzyme inhibitory potentials. Cytotoxicity was assessed by the percentage of hemolytic activity method, and these compounds generally exhibited very low values as compared to the reference standard, Triton-X. Hence, some of these biheterocyclic propanamides might be considered as salient therapeutic agents in further stages of antidiabetic drug development.

Complexation between chitosan and carboxymethyl cellulose in weakly acidic, neutral, and weakly alcaline media

The interaction between carboxymethyl cellulose and partially reacetylated chitosan soluble in acidic and alkaline aqueous media is studied by light scattering and isothermal titration calorimetry in a wide pH range. It is shown that the formation of polyelectrolyte complexes (PEC) can occur in the pH range of 6–8, while this pair of polyelectrolytes loses the ability to complexation upon transition to a more alkaline medium. The revealed dependence of the observed enthalpy of interaction on the ionization enthalpy of the buffer indicates the participation of proton transfer from the buffer substance to chitosan and its additional ionization in the binding process. This phenomenon is first observed in a mixture of a weak polybase chitosan and a weak polyacid. The possibility to obtain soluble nonstoichiometric PEC by a direct mixing of the components in a weakly alkaline medium is shown. The resulting PECs are polymolecular particles in shape close to homogeneous spheres with a radius of about 100 nm. The obtained results are promising for creating of biocompatible and biodegradable drug delivery systems.

One-Pot Synthesis of Colloidal Hybrid Au (Ag)/ZnO Nanostructures with the Participation of Maleic Acid Copolymers.

One-pot synthesis of colloidal Au/ZnO and Ag/ZnO nanohybrid structures was carried out. The copolymers of maleic acid-poly(N-vinyl-2-pyrrolidone-alt-maleic acid), poly(ethylene-alt-maleic acid), or poly(styrene-alt-maleic acid) were used as templates for the sorption of cations of metals-precursors and stabilization of the resulting nanoheterostructures. Simultaneous production of two types of nanoparticles has been implemented under mild conditions in an aqueous alkaline medium and without additional reagents. Equimolar ratios of the metal cations and appropriate load on all copolymers were used: molar ratio of maleic acid monomeric units of copolymer/gold (silver)cations/zinc cations was 1/0.15/0.23 (1/0.3/0.15). The process of obtaining the heterostructures was studied using UV-Vis spectroscopy. The kinetics of the formation of heterostructures was influenced by the nature of the maleic acid copolymer and noble metal cations used. A high reaction rate was observed in the case of using zinc and gold cations-precursors and a copolymer of maleic acid with N-vinylpyrrolidone as a stabilizer of nanoparticles. The structure of the synthesized polymer-stabilized heterostructures was studied using instrumental methods of analysis-XPS, FTIR, PXRD, and TEM. Under the conditions used, stable colloidal solutions of heterodimers were obtained, and such structure can be converted to a solid state and back without loss of properties.

Nickel selenide nano-cubes anchored on cadmium selenide nanoparticles: First-ever designed as electrode material for advanced hybrid energy storage applications

The rational design and impressive performance of the desired electrode material are one of the top priorities in the field of the supercapacitor era. Chalcogenides are functional materials that attracted tremendous research due to their great electrochemical activity, non-toxicity, high theoretical capacities, low cost, high environmental safety, and tunable electronic configurations. Combining two different materials (compositing strategy) is a popular route to develop novel, robust, and highly efficient electrodes for high capacity, energy, and power delivery with good durability. Herein, for the first time, a high-performance hybrid supercapacitor is developed based on NiSe2, and CdSe and their composites, e.g., NiSe2/CdSe (denoted as CN-1, CN-2, and CN-3) via hydrothermal via ex-situ wet-chemical method. By changing the stoichiometry of the host compounds (e.g., NiSe2, CdSe), various nanocomposites take birth, such as; CN-1, CN-2, and CN-3. Notably, their capacitive performance was measured and compared in an aqueous alkaline media in KOH with three milli molar concentration. Subsequently, the CN-2 electrode displayed a good electrochemical energy storage performance of 358C/g capacity and lower overall resistance, which promotes the fast diffusion of electrolyte kinetics; hence, optimized electrochemical properties prove its importance for the fabrication of full cell development. More strikingly, the CN-2//AC hybrid supercapacitor revealed a high capacitance of 90 F/g, 40.5 Wh/kg energy density, and a maximum power of 7161.2 W/kg coupled with a high stability of 87.6 % (20 A/g) when repeatedly tested for long-term 15,000 cycling. The proposed method portrays a cost-effective and appealing runner for high-energy hybrid supercapacitors in future energy storage applications.

Preliminary study on the blending of citrus fruit pulp under vacuum to extract cellulose nanofibers

In this study, agricultural waste-derived cellulose nanofiber (CNF) was extracted from parenchyma cells of citrus fruit residue by chemical pulping and fibrillation by a kitchen blender. By changing the pulp blending conditions such as carrying under negative pressure and alkaline aqueous medium, it was possible to obtain CNF morphology at an affordable cost and in a relatively short time.

Ruthenium-Catalyzed Transformation of Ethylene Glycol for Selective Hydrogen Gas Production in Water

We developed an efficient process for producing hydrogen gas from aqueous ethylene glycol (EG) at 90–160 °C over a ruthenium catalyst. We achieved a high yield of hydrogen gas (up to 3.0 n(H2)/n(EG)) and formic acid (85% yield) from ethylene glycol in aqueous alkaline medium at 110 °C, where the role of reaction temperature and base concentration was found to be critical in achieving a high yield of H2. The chemical and morphological properties of the synthesized ruthenium catalyst were established using P-XRD, TEM, XPS, and other techniques. Advantageously, the ruthenium catalyst exhibited appreciably high long-term stability for over 70 h, generating ca. 290 L of H2 per gram of Ru with a yield of 1035 L of H2 per L of ethylene glycol.

Glucose as an eco-friendly reducing agent for a one-pot multicomponent synthesis of quinoxalines

An efficient and scalable one-pot multicomponent process is developed for the synthesis of quinoxalines by using D-glucose as a clean, renewable and an eco-friendly reductant in an alkaline aqueous medium. This protocol eliminates the nitro reduction by using pyrophoric metal catalysts like Pd, Ni, Zn, etc., and cyclization as separate steps for the synthesis of quinoxalines. Gram scale experiments and further substrate scope of the reaction have also been well demonstrated.

Synthesis and catalytic activity of Cu (II) complex with 4-phenyl 2, 6-di (thiazol-2-yl) pyridine in the oxidation of para-aminophenol

In the present work the synthesis of 4-phenyl-2, 6-di (thiazol-2-yl) pyridine copper chloride (abbreviated as Cu-DTPy) complex using copper (II) chloride and 2, 6-di (thiazol-2-yl) pyridine has been carried out. The complex has been specified by UV-Vis, FT-IR, CHNS and ESI-MS methods of analysis. The synthesized copper complex has been used as catalyst in the oxidation of p-aminophenol using hexacyanoferrate (III) ions as an oxidant in aqueous alkaline medium by kinetic-spectrophotometric method. This experimental work was carried out at optimum pH 11.0 and temperature 25ºC. The variation of effect of concentration of p-aminophenol (abbreviated as PAP), hexacyanoferrate (III) ions, and Cu-DTPy catalyst on reaction rate has been studied. Thermodynamic parameters such as free energy of activation, activation energy, enthalpy and frequency factor have been evaluated with the change in rate of the reaction at four disparate temperatures i.e. 25-40ᵒC. The oxidation products have been identified by FT-IR and ESI-MS spectroscopic analytical techniques. The major product of this reaction is NN’-bis-(p-hydroxyphenyl)-2-hydroxy-5-amino-1,4-benzoquinone di-imine. Thus, this method is highly efficient and environmentally safe to remove PAP from polluted water resources.

Photocatalytic degradation of PET microfibers and hydrogen evolution by Ni5P4/TiO2/C NFs

The degradation of PET microfibers to organic compounds and hydrogen precipitation by Ni5P4/TiO2/C NFs photocatalysts in alkaline aqueous medium.

A quinary high entropy metal oxide exhibiting robust and efficient bidirectional O2 reduction and water oxidation

The O2/H2O couple-based transformation between renewable energy and electricity has emerged as a key step in implementing a carbon-neutral energy infrastructure. Therefore, an inexpensive and efficient electrocatalyst driving both O2 reduction and O2 evolution reaction in water becomes critical that can be directly applied in a unitized regenerative fuel cell in both electrolyzer or fuel cell mode. Here, we have crafted a high entropy metal oxide (HEO) containing readily abundant first-row transition metals (Fe, Cr, Co, Mn, Ni) via a metal-organic framework intermediate followed by regulated annealing at 750 °C. This material exhibited bidirectional ORR and OER activity in alkaline aqueous media (pH 14.0) with excellent energy efficiency on either side, showcasing a difference of 0.79 V (while achieving 10 mA cm−2 current density) and ∼90% Faradaic efficiency. The in-depth electrochemical and surface analysis pointed out the key formation of the Ni–OOH layer on the HEO particle and the optimal porosity for maximized electrochemical surface area generation as pivotal factors behind its superior reactivity. An alkaline electrolyzer was assembled with this HEO (anode) and Ni-foam (cathode), which demonstrated concurrent production of O2 and H2 over 6 h with minimal alterations in the anodic material. Therefore, this robust, inexpensive, and scalable HEO material can boost the progress in developing sustainable electrolyzer/fuel cell assemblies.

Facile preparation of water-dispersible carboxylated polyaniline

Polyaniline (PANI), containing carboxylic groups, was prepared by covalent modification of PANI base, using various amounts of thiolactic acid (TLA). It was found that using the excess of TLA, compared to the stoichiometric amount required for modification of emeraldine form of PANI, did not lead to increase of substitution degree. Elemental analysis showed that in all studied conditions ≈6.5 wt% of carboxylic groups were introduced into PANI backbone. Change of PANI chemical structure as a result of modification by TLA was studied by electronic, vibrational and photoelectron spectroscopy. It was shown that TLA is covalently bound to PANI without significant amount of free TLA and the initial PANI base also becomes partially protonated. Conductivity of PANI-TLA materials (≈5 ×10–7 S cm–1) increased by 4 orders of magnitude, compared to PANI base (5 ×10–11 S cm–1). Due to the presence of carboxylic groups, TLA-modified PANI is dispersible in alkaline aqueous medium, which can enable eco-friendly ways of PANI deposition for the applications in sensors and anticorrosive coatings.

A flow-drop electrochemiluminescent design for portable detection of soil and skin 2,4,6-trinitrotoluene

An automatic miniaturized flow-drop electrochemiluminescence (ECL) technique was established by utilizing a coalescing drop as a wall-less electrolytic cell, a self-driven mixer, and a µL scale reactor. Cost-effective ECL detection of 2,4,6-trinitrotoluene (TNT) was proposed, by virtue of the finding of the enhancement on luminol ECL by trace TNT in alkaline aqueous medium. The mechanism of TNT intensifying luminol ECL was suggested as that the one-electron reduction of TNT yielded TNT anion radical converts dissolved oxygen into superoxide anion radical, which subsequently reacted with luminol to produce luminol anion radical, finally resulting in the acceleration of luminol oxidation. By optimizing all the experimental conditions, the intensified ECL was found to be linear to TNT concentration over the 5–100 nM range, with a limit of detection of 0.5 nM. The method’s precision and accuracy were examined via F and t tests. The feasibility of this portable ECL method was validated by determining unknown TNT contents in real soil and finger skin samples via parallel official method. All results support the technique as a robust alternative for on-site TNT detection for environmental and forensic purposes.

Polymer materials based on metal-free hydroxy- and aminophenyl porphyrin as potential catalysts: Preparation and properties

Hydroxy- and aminophenylporphyrin polymer films have been obtained by a superoxide-assisted electrochemical deposition method. This paper demonstrates the effect of the porphyrin structure on the film morphology and electrocatalytic properties of the prepared materials. A catalytic activity series of the synthesized metal-free electropolymers has been defined for the oxygen electroreduction reaction in an aqueous alkaline medium. It is shown that the samples prepared from 2H-5,10,15,20-tetrakis(3-aminophenyl)porphyrin possess the highest catalytic activity.

Advances in enrichment and separation of cis-diol-containing compounds by porous organic frameworks

The design and synthesis of boronate affinity materials that show high efficiency, high selectivity, and high enrichment performance have gained significant attention. The principle of boronate affinity relies on the reversible covalent reactions, including the formation of stable five-membered or six-membered cyclic esters with cis-diol-containing compounds in alkaline aqueous media and dissociation of cyclic esters in an acidic surrounding to release cis-diol-containing compounds. Recently, various boronate affinity materials have been synthesized and utilized for selective enrichment of these compounds. Metal organic frameworks (MOFs) and covalent organic frameworks (COFs) have been widely used in chromatographic separation and sample pretreatment because of their adjustable pore size, high porosity, high specific surface area, tunable skeleton structure, and favorable chemical and thermal stability. To promote the enrichment selectivity of MOFs and COFs for cis-diol-containing compounds, boronic acid-functionalized MOFs and COFs with various structures and categories have been synthesized. This review summarizes more than 80 investigations into the categories, synthetic strategies, and applications of boronic acid-functionalized MOFs and COFs from the Science Citation Index. These synthesis methods include metal ligand-fragment co-assembly, post-synthetic modification, and bottom-up modification of boronic acid-functionalized porous materials. Although two modification strategies (post-synthetic and metal ligand-fragment co-assembly) have been introduced for the preparation of boronic acid-functionalized MOFs, the latter is more commonly adopted as it improves the enrichment selectivity and enrichment efficiency of MOFs. The common limitations of MOFs such as aggregation and aperture issues were also resolved. Boron affinity MOFs possessing favorable properties according to the characteristics of cis-diol-containing compounds, have also been synthesized. Furthermore, to facilitate enrichment and separation, many boronic acid-functionalized magnetic material MOFs have been developed for the enrichment and analysis of cis-diol-containing compounds. Additionally, the luminescent properties of Ln-MOFs have been used in combination with boronic acid affinity for the enrichment, separation, and subsequent detection of cis-diol-containing compounds. Post-synthetic modification and the bottom-up strategy are the primary methods for the preparation of boronic acid-functionalized COFs. Boronic acid-functionalized COFs are less investigated than boronic acid-functionalized MOFs, likely due to the greater complexity of COF synthesis. This work aims to summarize the research advances, synthesis ideas, and synthesis methods related to boric acid-functionalized porous organic frameworks, which will provide theoretical guidance and technical support for its applications while accelerating the commercialization of such organic frameworks.

The green synthesis of oligo(azomethine)s based on p-anisidine and o-anisidine: reaction conditions, electrochemical and thermal properties

Schiff bases and their conjugated oligo(azomethine)s have been synthesized via condensation and oxidative polycondensation of o-anisidine (OA) with 2-hydroxy-1-naphthaldehyde (2-HNA) and p-anisidine (PA) with 4-hydroxy benzaldehyde (4-HBA), respectively. The oxidative polycondensation reaction conditions of 1-[(2-methoxyphenylimino)methyl]naphthalen-2-ol (1,2-MPIMN) and 4-[(4-methoxyphenylimino)methyl]phenol (4,4-MPIMP) were studied by oxidants such as air and aqueous solutions of H2O2 and NaOCl in different concentrations in an aqueous alkaline medium between 50 °C and 90 °C at different reaction times. The structures of polymers were confirmed by FT-IR, UV-Vis and 1H-13C-NMR measurements. The molecular weights and surface morphologies of oligomers were determined by size exclusion chromatography (SEC) and scanning electron microscopy (SEM), respectively. Electrochemical and thermal features of compounds were studied using UV-Vis spectroscopies, cycling voltammetry (CV), and TG-DTA. The mass losses values ​​of the 1,2-MPIMN, oligo(1,2-MPIMN), 4,4-MPIMP, and oligo(4,4-MPIMP) were calculated from the thermogravimetric curves as 98.00%, 53.52%, 69.00%, and 58.70%, respectively, at 1000 °C. The HOMO, LUMO levels, electrochemical (E’ g ), and optical band gap energies (Eg ) values of the compounds were calculated from CV and UV-Vis data. The E’ g values of 1,2-MPIMN, oligo(1,2-MPIMN), 4,4-MPIMP, and oligo(4,4-MPIMP) were found to be 2.64, 1.54, 2.31, and 2.16 eV, respectively. The electrical properties of monomers and oligomers were determined at room temperature.

Ruthenium(III) catalyzed oxidation of paracetamol by chloramine‐T in aqueous alkaline medium – A kinetic and mechanistic pathway

AbstractThe kinetic study of ruthenium(III) chloride catalyzed oxidation of paracetamol by N‐chloro‐p‐toluene sulfonamide (chloramine‐T) in the alkaline medium has been performed. The reaction exhibits second order nature and the effect of the catalyst indicates the occurrence of uncatalyzed reaction simultaneously. Rate is decelerated by hydroxide ions. A plausible reaction mechanism has been suggested and the rate law is derived to account for such experiential observations. The activation parameters have been calculated. No evidence of the participation of free radicals is observed.