Fathi H. Assaleh

Solvent and structural effects in tautomeric 3-cyano-4-(substituted phenyl)-6-phenyl-2(1H)-pyridones: experimental and quantum chemical study

The tautomeric equilibria between 2-pyridone and 2-hydroxypyridine forms of methoxy, chloro, and nitro derivatives of 3-cyano-4-(2-, 3-, and 4-substituted phenyl)-6-phenyl-2(1H)-pyridones were evaluated from UV/Vis spectral data. Linear solvation energy relationships of Kamlet–Taft and Catalán-rationalized solvent have influence on tautomeric equilibria. Transmission of substituent effect was analyzed by the Hammett equation. Quantum chemical calculations were performed by density functional theory (B3LYP). The experimental data were interpreted with the aid of time-dependent density functional method. Electron density distribution was analyzed by Bader’s analysis. It was found that substituents of different electronic properties change the extent of conjugation, and affect intramolecular charge transfer character. Theoretical calculations and experimental results gave insight into the influence of the molecular conformation on the transmission of substituent effects, as well as on contribution of different solvent–solute interactions.

Solvatochromism of Thiouracil Azo Dyes

A series of sixteen synthesized thiouracil azo dyes was obtained by condensation of arylazo acetoacetic esters with thiourea. Purified products were characterized by UV–Vis, FT–IR, 1H and 13C NMR spectroscopy. The UV–Vis absorption spectra of all synthesized compounds were recorded in nineteen solvents of different properties. The study and analysis of the spectral data of azo dyes generally indicate that the tautomeric equilibrium is shifted to the hydrazone tautomeric form in the solid state. Linear solvation energy relationships describe solvent influence on solvatochromism of the hydrazone form with the use of the Catalán model. Linear free energy relationships were applied in the form of single substituent parameter model to analyze substituent electronic effects on the spectral behavior of the compounds by Hammett’s equation. The correlations obtained with aid of theoretical calculations give insight into the influence of molecular conformation on the transmission of substituent effects, as well as different solvent–solute interactions.

Detailed solvent, structural, quantum chemical study and antimicrobial activity of isatin Schiff base

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. Baders 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.

Multivariate assessment of azo dyes' biological activity parameters

Lipophilicity as key molecular descriptor of potential biological activity for selected derivatives of azo dyes was determined mathematically, by using relevant software packages and by reversed-phase thin-layer chromatography (RPTLC) on C18 and cyano modified carriers in mixtures of water/n-propanol and water/acetone. The obtained chromatographic parameters, RM0 and m, of the examined azo dyes were correlated with the standard measure of lipophilicity, log P, important pharmacokinetic predictors and selected toxicity parameters applying linear regression analysis. Thereby, good correlations for each applied system were obtained (average correlation coefficient, r, 0.944, 0.885 and 0.919). Also, the correlations between the studied parameters of azo dyes were examined applying two multivariate methods (Cluster Analysis and Principal Component Analysis). It was shown that the polarity of the substituent, and to a lesser extent its electronic effects has the greatest influence on the studied parameters of the azo dyes derivatives. Multivariate methods pointed out the similarity of the chromatographic retention constant, RM0, with the parameters of lipophilicity, unlike the chromatographic parameter m, which exhibits better agreement with the toxicity parameters.