Esomeprazole is the most effective of the proton-pump inhibitors for the acid-related diseases and at first was examined for the electroanalytical purposes. The drug standard and as a content of ...injection powder was investigated by cyclic voltammetry (CV) and quantitatively determined using square wave voltammetry (SWV) via its electrooxidation at Au electrode in 0.05M NaHCO3. SWV showed a linear dependency of the anodic peak currents vs. esomeprazole standard concentrations in the range from 3.0 to 500μgmL−1 with the values of limit of detection (LOD) and limit of quantification (LOQ): 1.4 and 4.6μgmL−1, respectively. Using the constructed and validated calibration curve, the values of unknown esomeprazole concentrations in injection powder and in human serum spiked with standard were determined. Before the electrochemical oxidation, it was shown by atomic force microscopy (AFM) that the small esomeprazole islands formed inside holes were visible and their diameter was about 200nm attributed to physico-chemical characteristics of esomeprazole. After the electrochemical oxidation, the morphology of esomeprazole standard on Au surface was completely changed and composed of spherical particles in a diameter between 200 and 600nm. With esomeprazole suspended in human serum, the process of crystallization partly occurred in the form of spherical grains with the average size of these grains was about 4μm. The analysis at the macro level done by the optical microscopy (OM) confirmed this opinion.
The study of esomeprazole degradation showed that at Au electrode, after 3h of cycling, a neglectable amount of the esomeprazole was changed. Using IrOx electrode under directed stress conditions, its almost complete degradation was realized after 3h confirmed by high performance liquid chromatography (HPLC). Total organic carbon (TOC) analysis showed that 95% of esomeprazole was mineralized. The HPLC and Liquid chromatography-mass spectrometry (LC-MS) study revealed the formation of 4-hydroxy omeprazole sulphide, 4-hydroxy omeprazole sulphone, esomeprazole sulphone and methylated esomeprazole.
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•SWV method for esomeprazole determination using Au electrode was developed.•Method was applied for esomeprazole determination in human serum/injection powder.•Morphology of Au electrode surface during study was characterized by AFM and OM.•Esomeprazole degradation at IrOx electrode led to 95% of its mineralization.•Several degradation products were detected by HPLC and LCMS analysis.
•Polyaniline in the form of base and salt was prepared chemically and electrochemically.•Corrosion of mild steel with different composite coatings were investigated.•Chemically prepared emeraldine ...salt posses good anticorrosion properties.•Anticorrosion properties were connected with the content of oligomers in the samples.•It was proposed that polyaniline acts as active barriers.
The protective abilities of composite coatings based on electrochemically and chemically formed polyaniline powder against the corrosion of mild steel were investigated. A polyaniline powder has been prepared in the form of an emeraldine base and benzoate salt through chemical dedoping and doping. The composite coatings using polyaniline powders, which were obtained through different routes, and base coatings, which were not corrosion-resistant, with different formulations were prepared and applied on mild steel samples. The corrosion was investigated using an electrochemical impedance technique in 3% NaCl, and the atmospheric corrosion was assessed in a humidity chamber. Emeraldine–benzoate salts, which are a chemically synthesized polyaniline, offer the best protection with an optimal polyaniline concentration of approximately 5wt%. The different corrosion behaviors were assessed relative to the presence of aniline oligomers in the samples after characterization using UV–vis spectrophotometry. Upon comparison between the corrosion behavior in 3% NaCl with commercial primer paint for iron and that with a paint containing 5wt% PANI, the composite coating has superior anticorrosion characteristics. The mechanism for the protection of mild steel from corrosion through composite polyaniline coatings was also considered.
Submicron carbon spherical particles were obtained by polycondensation of resorcinol and formaldehyde in a solution and subsequent ultrasonic spray pyrolysis of the prepared sol. Microscopic ...characterization indicates the regular spherical shape of the obtained particles and sphere diameters in 200–700
nm range. The carbon spheres are amorphous as confirmed by electron diffraction, EELS, XRD and HREM characterization. Activation procedure was performed with H
2O in a nitrogen flow for 15 and 30
min at 800
°C. The activation procedure preserved the initial spherical shapes of the particles while the particle porosity and specific surface area were increased. The amount of surface oxygen functionalities was also increased by activation procedure as indicated by FTIR analysis.
Ultraviolet absorption spectra of three isomeric pyridinecarboxylic acids (picolinic, nicotinic, and isonicotinic acids) were measured in 18 various solvents, in the wavelength range from 200 to ...400 nm. In order to analyze the solvent effect on the obtained absorption maxima, the ultraviolet absorption frequencies of the electronic transitions in the carbonyl group of the examined acids were correlated using a total solvatochromic equation in the forms ν
max
= ν
0
+
s
π
*
+ aα +
b
β and ν
max
= ν
0
+
s
π
*
+
b
β, where ν
max
is the absorption frequency (1/ν
max
), π
*
is a measure of the solvent polarity, α represents a scale of the solvent hydrogen bond donor acidity, and β represents a scale of the solvent hydrogen bond acceptor basicity. Correlation of the spectroscopic data was carried out by means of multiple linear regression analysis. The effects of two different solvent types on the ultraviolet absorption maxima of the examined acids were compared and discussed.
Alkoxy-derived cordierite gels were synthesized from tetraethylorthosilicate (TEOS), aluminum isopropoxide (Al(OPri)3), and magnesium ethoxide (Mg(OEt)2). TEOS was partially hydrolyzed at molar ...ratios H2O/TEOS = 1.2, in the presence of hydrochloric acid as a catalyst, HCl/TEOS = 0.1. Aluminum and magnesium alkoxides were added successively or as a double alkoxide. Phase transformations occurring in the gel were studied by differential thermal analysis, x-ray diffractometry, and Fourier-transform infrared spectroscopy. In all cases, μ-cordierite crystallized at similar temperatures (950–1000°C) with small amounts of spinel, which confirms dominant influence of the optimal conditions for partial hydrolysis of TEOS on the gels homogeneity. The transformation of μ- into α-cordierite began at about 1100°C. Broadening of diffraction peaks and appearance of new bands in the FT IR spectra confirmed the transformation of α- into modulated β-cordierite at temperatures above 1300°C. Differential thermal analysis under nonisothermal conditions also proved homogeneous nucleation with constant rate and three-dimensional crystallite growth during μ-cordierite crystallization. The overall activation energy of the crystallization of μ-cordierite is 580 ± 81 kJ/mol.
In numerous cases, metals and alloys traditionally used as structural materials in the process equipment can now be successfully replaced by nonmetallic composite materials. We study the influence of ...service solutions on the state of stress and tensile properties of glass-polyester pipes in the longitudinal and circumferential directions. These analyses are of great importance for the use of examined pipes in chemical industry. The pipes were produced by “Poliester” Corporation (Priboj). The influence of two solutions, methanol and ammonia, was studied. The samples were treated in solutions for three, seven and ten days. After this, the samples were subjected to tensile testing by the standard procedure. The stresses and strengths were determined both in the longitudinal direction (testing on flat test specimens) and in the circumferential direction (ring tests). The analysis of test results, according to the type of solution and the period of holding, was realized in comparison with the results obtained by testing intact pipes (not subjected to the influence of the solution). The micromechanical analysis of broken samples helped to determine the influence of the solution on the structure of composite pipes and determine the models and mechanisms responsible for the decrease in strength.
Mesoporous titania with well-crystallized anatase phase was synthesized by nonhydrolytic sol–gel process combined with solvothermal treatment. Titanium-isopropoxide, titanium-tetrachloride, and ...carbon-tetrachloride were used for synthesis under nitrogen atmosphere in a glove box. The obtained mixture was heated in an autoclave at 140
∘C for 3 h and 30 h. XRD analysis showed that dry gels contained anatase phase with low crystallinity, while powders obtained by calcination of dry gels at 500
∘C for 3 h consisted of pure anatase with high crystallinity. SEM analysis of dried gels and powders shows agglomerates of spherical particles of the size ∼300 nm. The TEM micrographs confirmed the nanoscale size of the titania powders, with the primary particle size of about 20 nm. Titania powders exhibit maximum pore diameter of 13.2 nm and 9.5 nm for gelation time 3 h and 30 h, respectively. The photocatalytic activity of such synthesized titania is superior to that of commercial photocatalyst Degussa P-25.
The rate constants for the reactions of diazodiphenylmethane (DDM) with 2-substituted nicotinic acids in nine aprotic solvents at 30 degree C were determined. The obtained second order rate constants ...in aprotic solvents were correlated using the Kamlet-Taft solvatochromic equation in the complete form: log k = log k sub(0) + s capital pi * + a alpha + b beta . The correlations of the kinetic data were realized by means of multiple linear regression analysis. The obtained results were analyzed in terms of the initial and the transition state of the reaction and compared with previously determined kinetic data for nicotinic acid. The signs of the equation coefficients (s, a and b) are in agreement with the reaction mechanism and the influence of the solvent on the reaction rate is discussed based on the correlation results. The mode of the transmission of the sub-stituent effect is discussed in light of the contribution of solute-solvent interaction to the reactivity of the acid. The substituent effect was additionally analyzed by the Hammett equation, log k = rho sigma + log k sub(0).
The effects of protic and aprotic solvents on the reactivity of picolinic, nicotinic and isonicotinic acid, as well as of some substituted nicotinic acids, with diazodiphenylmethane (DDM) were ...investigated. In order to explain the kinetic results through solvent effects, the second-order rate constants for the reaction of the examined acids with DDM were correlated using the Camlet-Taft Solvatochromic Equation. The correlations of the kinetic data were realized by means of multiple linear regression analysis and the solvent effects on the reaction rates were analyzed in terms of the contributions of the initial and the transition state. The signs of the coefficients of the Equation support the already known reaction mechanism. Solvation models for all the investigated acids are suggested and related to their specific structure.
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