•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.
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.
Fourteen mono- and bis-carbohydrazone ligands have been synthesized and characterized. Antioxidant activity of the substances was investigated together with possible (E)/(Z) isomerization, and ...explained on the most active antioxidant compound a4 in various dimethylsulphoxide–water mixtures. The addition of water to the system was involved in the formation of hydrated molecules which was confirmed in NMR after the addition of D2O. The ligands were tested in vitro against Gram-positive and Gram-negative bacteria and fungis, and their activity was discussed in relation to the structure of investigated carbohydrazone.
The ratios of E/Z isomers of sixteen synthesized 1,3-dihydro-3-(substituted phenylimino)-2H-indol-2-one were studied using experimental and theoretical methodology. Linear solvation energy ...relationships (LSER) rationalized solvent influence of the solvent–solute interactions on the UV–Vis absorption maxima shifts (νmax) of both geometrical isomers using the Kamlet-Taft equation. Linear free energy relationships (LFER) in the form of single substituent parameter equation (SSP) was used to analyze substituent effect on pKa, NMR chemical shifts and νmax values. Electron charge density was obtained by the use of Quantum Theory of Atoms in Molecules, i.e. Bader's analysis. The substituent and solvent effect on intramolecular charge transfer (ICT) were interpreted with the aid of time-dependent density functional (TD-DFT) method. Additionally, the results of TD-DFT calculations quantified the efficiency of ICT from the calculated charge-transfer distance (DCT) and amount of transferred charge (QCT). The antimicrobial activity was evaluated using broth microdilution method. 3D QSAR modeling was used to demonstrate the influence of substituents effect as well as molecule geometry on antimicrobial activity.
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•Detail analysis of E/Z ratio in isatin Schiff bases were obtained from UV, NMR and TD-DFT data.•LSER and LFER analysis of pKa, UV and NMR data quantified solvent and substituent effects.•Electronic transition were analyzed by Bader's analysis and QCT/DCT aided TD-DFT study.•The 3D QSAR model point to most influential structural motifs to antimicrobial activity.
The esters of substituted 1,4-dihydropyirdines (1,4-DHP) are formed in the reaction of an appropriate aldehyde and ethyl acetoacetate in the presence of concentrated water solution of ammonia. The ...esters form the amides by the reaction with primary amines. The series of the amides has been synthesized with the aim to analyze their chemical characteristics, antioxidant and antimicrobial activity. The amine used in this research is 2-aminothiazole. The antioxidant activity is analysed by 2,2-diphenyl-1-picrylhydrazyl (DPPH) and 2,2'-Azino-bis(3-ethylbenzthiazoline-6-sulfonic acid) (ABTS) methods and the antimicrobial activity screening was performed by broth microdilution method, using different microbial strains. The characterization of the obtained amides was done by melting points, FTIR, NMR and elemental analysis. The possibilities for further research was suggested, which could lead to the application of selected compounds.
The derivatives of isatin have already been known to display a variety of biological activities. Therefore, the studies on their activity and its relation to structure have recently become a popular ...subject for investigation. The examined compounds were synthesized by the reaction of isatin and substituted primary amines and characterized by spectroscopic methods. The investigation of the antimicrobial and antioxidative activity of the synthesized compounds was performed by broth microdilution method. As for the characterization of the investigated isatin based Schiff bases, the linear solvation energy relationships (LSER) were used to analyze the solvent influence on the UV absorption maxima shifts (?max), using the well known Kamlet?Taft model and taking geometrical isomers into consideration when possible. Linear free energy relationships (LFER) were used to analyze substituent effect on pKa, as well as NMR chemical shifts and ?max values. The antimicrobial activity and characterization were related using both experimental and theoretical methods.
The isatin derivatives, Schiff bases, were synthesized by the reaction of isatin and various substituted primary AMines and characterized by several spectroscopic methods. Investigation of the ...antimicrobial activity of the syn thesized compounds was performed by the agar dilution method, against dif ferent strains of bacteria and one fungus. The antioxidative activity of the syn thesized compounds was also determined. Some of the compounds showed sig nificant activity against the selected strains of microorganisms and antioxi da tive activity.
The substituent and solvent effects on solvatochromism in 3-(4-substituted) phenylaminoisobenzofuran-1(3H)-ones were studied using experimental and theoretical methodologies. The effect of specific ...and non-specific solvent?solute interactions on the shifts of UV?Vis absorption maxima were evaluated using the Kamlet?Taft and Catal?n solvent parameter sets. The experimental results were studied by density functional theory (DT) and time-dependent density functional theory (TD-DFT). The HOMO/LUMO energies (EHOMO/ELUMO) and energy gap (Egap) values, as well as the mechanism of electronic excitations and the changes in the electron density distribution in both ground and excited states of the investigated molecules were studied by calculation in the gas phase. The electronic excitations were calculated by the TD-DFT method in the solvent methanol. It was found that both substituents and solvents influence the degree of ?-electron conjugation of the synthesized molecules and affect the intramolecular charge transfer character.
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