Ethanol-water Medium Research Articles

Potentiometric Determination of Stability Constants of Sulphathiazole and Glycine-Metal Complexes

Binary and ternary complexes of (Fe(III), Pb(II), Co(II), Al(III), La(III), Sr(II), Cr(III), Ti(II) and Zr(II)) with sulphathiazole (as primary ligand) and amino acid glycine (as secondary ligand) have been studied potentiometrically at 25°C ± 0.1°C and I = 0.1 M NaClO4 in 25% (v/v) pure ethanol-water medium. Although there are many methods available to study the stability of metal-ligand complexes, pH-metry is most frequently used. In extension of our study on solution equilibria, we used Calvin-Bjerrum method for the calculation of stability constants. Stoichiometries and stability constants of binary systems containing the above metal ions in a 1:1 and 1:2 and/or 1:3 ratios were also determined to compare the effect of the secondary ligand on (1:1) Metal:Sulphathiazole system. The protonation constants of the complexes were evaluated for the system M:Sulphathiazole:Glycine = 1:1:1. The order of stability of the binary and ternary complexes was examined. It was found that glycine adds preferably [M-Sulfathiazole] rather than to the aqueous complexes of metal ions. In all cases 1:1:1 complex was formed.

Temperature effect on the structure and characteristics of ZnS-based quantum dots

The synthesis of zinc sulfide (ZnS) quantum dots (QDs) by microwave heating in a water-ethanol medium is proposed. The effect of the synthesis temperature (80 °C, 100 °C, 120 °C, and 150 °C) on the QD characteristics is examined. Based on the analysis of X-ray diffraction profiles the conclusion is drawn that the hexagonal ZnS phase of wurtzite type with an average nanocrystal size of 2.6-3.7 nm forms in the synthesized QDs. The nanocrystallite size is found to increase with the QD synthesis heating temperature. The analysis of X-ray absorption spectra (XANES) at the zinc K-edge indicates a higher crystallinity of the QD samples prepared at higher synthesis temperatures. The combined analysis of X-ray diffraction profiles, optical diffuse reflectance spectra, and X-ray absorption spectra implies the following possible QD structure: the pure hexagonal ZnS phase of wurtzite type in the bulk of nanoparticles and the amorphous ZnO phase in the surface layer of nanoparticles.

X-ray spectroscopic diagnostics of the structure of quantum dots based on zinc and manganese sulfides and oxides

The microwave synthesis of quantum dots (QDs) based on zinc and manganese sulfides and oxides in a water-ethanol medium is proposed. The sample synthesized is characterized by X-ray diffraction (XRD), photoluminescence, X-ray absorption near edge structure (XANES), and extended X-ray absorption fine structure (EXAFS) spectroscopy. The XRD analysis shows the presence of the hexagonal ZnS phase of wurtzite type with an average nanocrystal size of 4.5 nm and manganese oxide Mn3O4 (hausmannite phase) with an average particle size of 12.5 nm in the sample under study, but does not provide the unambiguous conclusion about the doping of ZnS nanoparticles with Mn atoms. Although the analysis of the zinc and manganese K-edge XANES spectra suggests that the synthesized QD sample is a ZnMnS solid solution (~11%), a significant amount of a by-product (manganese oxide Mn3O4 of the hausmannite phase, ~89%) is formed.

Electrochemical oxidation of quercetin in aqueous and ethanol-water media with the use of graphite/chemically modified silica ceramic electrode

A mixture of silica chemically modified with 1-n-propyl-3-methylimidazolium chloride and graphite was used to fabricate a ceramic working electrode. The conventional three-electrode cell that included the prepared electrode has been used to investigate the electrochemical behavior of quercetin in aqueous and ethanol-water media by methods of cyclic voltammetry and chronoamperometry. The procedures for the quercetin determination in aqueous and ethanol-water media have been developed. The limits of detection are 0.05 μmol L−1 in aqueous medium and 3–6 μmol L−1 in ethanol solution and ethanol-water mixtures. The applicability of the electrode and the developed procedure has been verified by the analysis of real pharmaceutical. Therefore, the proposed procedures can be implemented in the drug quality control. The mechanisms of the quercetin oxidation depend on the medium. Oxidation at ~ 150 mV occurs according to the well-known mechanism that involves the removal of two electrons and two hydrogen ions from the quercetin molecule. The oxidation of quercetin in ethanol-water media takes place also at ~ 550 mV. The plausible mechanism of this process derived from the electrochemical data and confirmed by the quantum-chemical calculations includes firstly formation of the 7,4′-biradical structure which then transforms into the 7,4′-dione compound.

A kinetics study of dipolar protic solvent in alkaline hydrolysis of ethyl Nicotinate in water-ethanol media- A Solvent effect

A kinetics study of dipolar protic solvent in alkaline hydrolysis of ethyl Nicotinate in water-ethanol media- A Solvent effect

Photo-physical and structural studies of some synthesized arylazoquinoline dyes

This study presents the spectral and structure characteristics of seven azoquinoline dyes with different substituents and their new methylated counterparts for the first time, where some compounds are newly synthesized. The solvatochromic, tautomeric, halochromic, and dichroic behavior of the compounds were studied by electronic spectroscopy in various media. The different types of media were ordinary, multifunctional, and ordered liquids. The experiments were extended to include under acidic or basic conditions. The orientational behavior of the azo dye-doped liquid crystals was studied, and it was established that the azo form is the main species in high polar anisotropic media. The multi-parameter polarity scales were used to correlate the spectral data. Influence of acid and base on the absorption spectra of the dyes was also examined. Ionization constants for these dyes were determined in ethanol-water media. As a result, at the high dye concentrations, the intermolecular hydrogen bonding is more stable than the intra-molecular hydrogen bond, and therefore, the azo form is the main species in concentrated solutions. In order to provide more details, time-dependent density functional theory (TD-DFT) calculations were carried out for the representative models.

Refractometry Study of Some Substituted Isoxazoline in 70 % EthanolWater Medium at Different Temperature

Refractometry Study of Some Substituted Isoxazoline in 70 % EthanolWater Medium at Different Temperature

Chemicals from Biomass: Synthesis of Biologically Active Furanochalcones by Claisen–Schmidt Condensation of Biomass-Derived 5-hydroxymethylfurfural (HMF) with Acetophenones

Furanochalcones have been synthesized trough the Claisen–Schmidt condensation of acetophenones and 5-hydroxymethylfurfural (HMF) using different solid base catalysts such as MgO, Al/Mg mixed oxide (HTc) with Lewis basic sites, and a hydrated Al/Mg mixed oxide (HTr) with Bronsted basic sites. The three catalysts provide high selectivity in absence of solvent or in the presence of polar solvents such as ethanol or acetonitrile, however catalysts become rapidly deactivated due to the strong adsorption of HMF and the furanochalcone obtained on the catalyst surface. A further increase in solvent polarity by using a mixture ethanol–water allows obtaining high conversion and high selectivity to furanochalcone using HTc and HTr as catalysts. However, MgO becomes rapidly deactivated which was mainly attributed to structural changes on MgO that is in situ rehydrated into Mg(OH)2 with low activity for aldol condensations. When the reaction was performed using the homogeneous NaOH catalyst, it was found that their activity is higher than that of the solid catalyst, but the selectivity of the later is clearly better. The results indicate that the active phase of the HTc in the ethanol–water medium corresponds to a partially restored hydrotalcite with basic hydroxyl groups. The HTc sample could be applied to the synthesis of a variety of furanochalcones with excellent success, while the catalyst could be reused several reaction cycles without loss of activity.

Fabrication of Lignosulfonate Vesicular Reverse Micelles to Immobilize Horseradish Peroxidase

Sodium lignosulfonate reverse micelles (SLRMs) with vesicular structure were prepared by self-assembling in ethanol–water media and applied to encapsulate horseradish peroxidase (HRP). Results showed that sodium lignosulfonate (SL) could not form SLRMs until the ethanol content reached 63% when its initial concentration was 7.5 g L–1. Owing to strong electrostatic repulsion, solid spherical SLRMs gradually swelled to stable vesicular structures with an average size of 240 nm. The shell of the SLRM thickened when NaCl was added to screen the electrostatic interaction. HRP can be effectively encapsulated while retaining its activity in the hydrophilic core of a SLRM. When hydrogen peroxide was added to initiate the catalytic activity of HRP, SL molecules would be polymerized and the structure of SLRMs would be fixed. Furthermore, HRP immobilized in polymerized SLRMs showed high activity at a more acidic pH of 4 and at a lower optimal temperature decrease of 35 °C compared to free HRP. SLRM allows enzymes su...

Effect of Temperature and Solvent Composition on the Acid Dissociation Constants of 2-Pyrrol and 2-Thiophene Aldehyde Phenyl Sulphonyl Hydrazones

Acid dissociation constants, pKa, of 2-pyrrolaldehyde phenylsulphonyl hydrazone, 1, and 2-thiophenealdehyde phenylsulphonyl hydrazone, 2, have been determined spectrophotometrically in ethanol-water media of various compositions over the temperature range 25℃ - 45℃. The obtained results were used in the calculation of the enthalpy, △H°, and the entropy, △S°, of the ionization processes. The slight variations observed in the pKa values of the thiophene compound compared to the pyrrol analogue revealed that neither of the two hetero atoms in the pyrrol or thiophene rings, of the two compounds, is involved in a hydrogen bond chelation. This conclusion was also confirmed through measurements of the dipole moment, IR and NMR spectra.

Exploring the interactions between polyethyleneimine modified fluorescent carbon dots and bovine serum albumin by spectroscopic methods

Firstly polyethyleneimine modified fluorescent carbon dots (PEI-CDs) were successfully fabricated in water–ethanol medium using ascorbic acid as carbon source. It was found that the prepared PEI-CDs were approximately spherical and monodispersed with an average diameter of 10nm and the corresponding photoluminescence (PL) intensity was greatly enhanced compared to the bare CDs. And then the interactions between the obtained PEI-CDs and bovine serum albumin (BSA) were investigated by fluorescence quenching, UV–vis absorption and circular dichroism (CD) spectroscopies under the simulative physiological conditions. The analysis of BSA fluorescence quenching spectra at 300K revealed that the probable quenching mechanism of BSA fluorescence by PEI-CDs was a static quenching process via forming a 1:1 complex with a binding constant of 1.773×104M−1. In addition, the displacement experiments confirmed that the binding of PEI-CDs primarily occurred in site I of BSA. And the binding distance r was calculated to be 5.3nm, indicating that the non-radiation energy transfer from BSA to PEI-CDs took place. Finally, the synchronous fluorescence and CD spectra of BSA were used to examine whether the binding of PEI-CDs disturbed the microenviroment around amino acid residues and the secondary structure of BSA.

Enaminone-Based Three-Component Reactions for the Diastereoselective Synthesis of Fused Tetrahydropyridines

An environmentally benign multicomponent synthetic method has been realized for the diastereoselective construction of fused tetrahydropyridines. Structurally diverse products have been acquired with generally good yields via the assembly of simple starting materials, enaminones or nitroenamines, o-aminophenols, and cinnamaldehydes, in the presence of lactic acid in water–ethanol media.

Acidity and complex formation studies of 3-(adenine-9-yl)-propionic and 3-(thymine-1-yl)-propionic acids in ethanol–water media

The ligands 3-(adenine-9-yl)propionic acid (AA) and 3-(thymine-1-yl)propionic acid (TA) were prepared by N9-alkylation of adenine and N1-alkylation of thymine with ethylacrylate in presence of a base catalyst, followed by acid hydrolysis of the formed ethyl esters to give the corresponding propionic acid derivatives. The products were characterized by spectral methods (FTIR, 1H NMR and 13C NMR), which confirm their structures. The dissociation constants of ligands, were potentiometrically determined in 0.3M KCl at 20–50°C temperature range. The work was extended to study complexation behavior of AA and TA with various biologically important divalent metal ions (Co2+, Ni2+, Cu2+, Zn2+, Cd2+, Mn2+ and Pb2+) in 50% v/v water–ethanol medium at four different temperatures, keeping ionic strength constant (0.3M KCl). The order of the stability constants of the formed complexes decreases in the sequence Cu2+>Pb2+>Zn2+>Ni2+>Co2+>Mn2+>Cd2+ for both ligands. The effect of temperature was also studied and the corresponding thermodynamic functions (ΔG, ΔH, ΔS) were derived and discussed. The formation of metal complexes has been found to be spontaneous, and the stability constants were dependant markedly on the basicity of the ligands.

Evaluation of poly(pyrrole-2-carboxylic acid) particles synthesized by enzymatic catalysis

In this study an environmentally friendly synthesis of poly(pyrrole-2-carboxylic acid) (PCPy) particles dispersed in water–ethanol medium using enzymatic catalysis is proposed.

6-Butyl-4-hydroxyquinolin-2-(1H)-one as an enol type coupling component for the synthesis of some new azo disperse dyes

6-Butyl-4-hydroxyquinolin-2-(1H)-one (II) was synthesized by heating N, N′-bis (4-butylphenyl) malonamide (I) in polyphosphoric acid at 150–160°C. This compound was then coupled with ten diazotized p-substituted aniline derivatives to synthesize the corresponding azo disperse dyes 1–10 in satisfactory yields. The dyes were characterized by FT-IR, 1H NMR, UV–vis spectroscopic techniques and elemental analysis. The solvatochromism of the dyes was evaluated with respect to wavelength of maximum absorption (λmax) in six polar solvents: acetic acid, ethanol, chloroform, acetonitrile, dimethyl sulfoxide and dimethyl formamide. The effects of acid and base on the visible absorption spectra of the dyes were also reported. Spectrophotometric absorption method was used to determine ionization constants, pKa, for these dyes in 80vol.% ethanol–water medium at room temperature and the values were correlated with the substituent constant, σx, on the benzene ring.

Reductive de-polymerization of kraft lignin for chemicals and fuels using formic acid as an in-situ hydrogen source

In this study, formic acid (FA) was employed as an in-situ hydrogen donor for the reductive de-polymerization of kraft lignin (KL). Under the optimum operating conditions, i.e., 300°C, 1h, 18.6wt.% substrate concentration, 50/50 (v/v) water–ethanol medium with FA at a FA-to-lignin mass ratio of 0.7, KL (Mw∼10,000g/mol) was effectively de-polymerized, producing de-polymerized lignin (DL, Mw 1270g/mol) at a yield of ∼90wt.% and <1wt.% yield of solid residue (SR). The MW of the DL products decreased with increasing reaction temperature, time and FA-to-lignin mass ratio. The sulfur contents of all DL products were remarkably lower than that in the original KL. It was also demonstrated that FA is a more reactive hydrogen source than external hydrogen for reductive de-polymerization of KL.

Direct determination of antibacterial norfloxacin in urine by isopotential fluorimetry

A novel and simple method is presented for the determination of norfloxacin in human urine by matrix isopotential synchronous fluorescence spectrometry (MISF). This method is useful for the determination of compounds in samples with unknown background fluorescence, such as norfloxacin in urine, without the need for tedious sample pre-treatment. The method was performed in ethanol-water medium (10% v/v), at an apparent pH of 4.8 provided by adding sodium acetate-acetic acid buffer solution. In the determination of norfloxacin in urine the fluorescent intensity varied linearly with its concentration from 20 to 200 ng/mL. An exhaustive statistical analysis has been developed to all calibration graphs, this treatment includes robust regression such as least median of squares, which also detects outliers and leverage points. The overall least-squares regression has been applied to find the more exact straight line that fits the experimental data. The error propagation has been considered to calculate the detection limit and the repeatability of the method. The method shows very low detection limits with acceptable recoveries and precisions. The applicability of the proposed method was illustrated in the determination of norfloxacin in human urine sample without sample pre-treatment.

Solid-state characterization and solubility of a genistein–caffeine cocrystal

Combination of genistein and caffeine leads to a 1:1 cocrystalline phase, which was identified by means of a solvent-drop grinding experiment and isolated afterwards in a solution-evaporation approach. Obtained cocrystal was characterized by X-ray single-crystal and powder diffraction as well as investigated in terms of thermal stability and Hirshfeld surfaces. A scale-up procedure was provided by slurry technique, enabling solubility determination. Neutral forms of both compounds cocrystallize in a common P21/c space group of the monoclinic crystal system. Analysis of packing and interactions in the crystal lattice reveals formation of molecular layers, formed by O–H⋯O, O–H⋯N and C–H⋯O-type contacts between genistein and caffeine molecules, whereas stabilization of the three-dimensional crystal lattice is provided by π⋯π interactions. Dissolution studies in a 50:50 v/v ethanol–water medium revealed that the maximum solubility of the cocrystalline phase reached 0.861mg/mL after 8h, revealing some degree of enhancement as compared to parent genistein, maximum solubility of which was also reached after 8h and equalled 0.588mg/mL.

A complex of ceftriaxone with Pb(II): synthesis, characterization, and antibacterial activity study

A Pb(II) complex with ceftriaxone (H2Ceftria) antibiotic was synthesized by reaction of ceftriaxone disodium salt (hemi)heptahydrate with lead nitrate in water–ethanol medium. The complex was characterized on the basis of complexometric titration, spectrophotometric and thermogravimetric analyses, capillary electrophoresis, IR, Raman and UV–vis spectroscopies, and density functional theory calculations. Pb(II) is five-coordinate with distorted square pyramidal geometry. The coordination of Ceftria2− to Pb(II) occurs through N and O of the triazine, lactam carbonyl, carboxylate, and amine groups. The antibacterial activity study showed that Klebsiella pneumoniae is resistant to [Pb(Ceftria)]·3H2O. The antibacterial activity of [Pb(Ceftria)]·3H2O against Staphylococcus aureus is reduced compared with ceftriaxone. In contrast, the antibacterial activity of [Pb(Ceftria)]·3H2O against Escherichia coli is 28% higher than that of ceftriaxone antibiotic.

Fluorimetric Method for the Determination of Trace Amounts of Molybdenum Using 2-Hydroxy-1-Naphthaldehydene-p-Aminotoluene

A new fluorescent reagent, 2-hydroxy-1-naphthaldehydene-p-aminotoluene, was synthesized. The fluorescent reaction of this reagent with molybdenum was studied. Based on this chelation, a highly sensitive spectrofluorimetric method was developed for determination of trace amounts of molybdenum in a water-ethanol medium at pH 6.8. Under these conditions, the Mo-HNA complex has excitation and emission maxima at 300 and 380 nm, respectively. The linear range of the method is 0-2μg/L and the detection limit is 0.62μg/L. Interference of other ions was studied. It is necessary to remove the interfering cations through cation exchange. The procedure can be carried out easily and affords good precision and accuracy. This method has been successfully applied to the determination of molybdenum in pig liver and mussels.