Experimental and theoretical study of substituent effect on 13C NMR chemical shifts of 5-arylidene-2,4-thiazolidinediones

Assessing the potential of para-donor and para-acceptor substituted 5-benzylidenebarbituric acid derivatives as push-pull electronic systems: Experimental and quantum chemical study

Electronic interactions in donor-π-linker-acceptor systems with barbituric acid as an electron acceptor and possible electron donor were investigated to screen promising candidates with a push-pull character based on experimental and quantum chemical studies. The tautomeric properties of 5-benzylidenebarbituric acid derivatives were studied with NMR spectra, spectrophotometric determination of the pKa values, and quantum chemical calculations. Linear solvation energy relationships (LSER) and linear free energy relationships (LFER) were applied to the spectral data - UV frequencies and ¹³C NMR chemical shifts. The experimental studies of the nature of the ground and excited state of investigated compounds were successfully interpreted using a computational chemistry approach including ab initio MP2 geometry optimization and time-dependent DFT calculations of excited states. Quantification of the push-pull character of barbituric acid derivatives was performed by the ¹³CNMR chemical shift differences, Mayer π bond order analysis, hole-electron distribution analysis, and calculations of intramolecular charge transfer (ICT) indices. The results obtained show, that when coupled with a strong electron-donor, barbituric acid can act as the electron-acceptor in push-pull systems, and when coupled with a strong electron-acceptor, barbituric acid can act as the weak electron-donor.

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 (ν_max) 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 pK_a, NMR chemical shifts and ν_max 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 (D_CT) and amount of transferred charge (Q_CT). 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.

RP-HPTLC Data in Correlation Studies of a 5-Arylidene-2,4-Thiazolidinedione Derivatives

Thiazolidinediones show a large scale of biological activities as a result of ability to perform interactions with a variety of biological targets. Modeling properties of newly synthesized thiazolidinediones is important for both understanding their activity and predicting their interactions. In the paper the chromatographic retention data determined in various RP chromatographic systems (stationary phases RP-CN and RP-18; six aqueous binary mobile phases modified with acetonitrile, methanol, ethanol, propanol, acetone and dioxane) were considered for 13 new 5-arylidene-2,4-thiazolidinediones. In this article, three attempts to find suitable quantitative structure-retention relationship (QSRR) models that quantify retention as a function ofmolecular descriptors had been presented. Models built for RP-18 show generally better multiple R but are also mostly monoparametric with logP as the dominant descriptor. More informative from the standpoint of molecular interactions are QSRR models for RP-CN. The quality of those models depends of the mobile phase modifier (the best was obtained for acetone and the worst for propanol as modifier). Since all QSRR models use extrapolated retention as a property which is indirectly connected with plasma protein binding further assessment of plasma protein binding should be based on extrapolated retention on a RP-CN stationary phase instead of standard RP-18.

Solvent and structural effects in tautomeric 2(6)-hydroxy-4-methyl-6(2)-oxo-1-(substituted phenyl)-1,2(1,6)-dihydropyridine-3-carbonitriles: UV, NMR and quantum chemical study

The state of the tautomeric equilibria of 2(6)-hydroxy-4-methyl-6(2)-oxo-1-(substituted phenyl)-1,2(1,6)-dihydropyridine-3-carbonitriles, 2-PY/6-PY, was evaluated using experimental and theoretical methodology. The experimental data were interpreted with the aid of time-dependent density functional (TD-DFT) method. Electron charge density was obtained by the use of Quantum Theory of Atoms in Molecules, i.e. Bader's analysis. Linear solvation energy relationships (LSER) rationalized solvent influence on tautomeric equilibrium. Linear free energy relationships (LFERs) were applied to the substituent-induced NMR chemical shifts (SCS) using SSP (single substituent parameter) and DSP (dual substituent parameter) model. Theoretical calculations and obtained correlations gave insight into the influence of molecular conformation on the transmission of substituent electronic effects, as well as on different solvent-solute interactions, and the state of tautomeric equilibrium.

Preparation of Diversely Substituted Triarylmethyl Radicals by the Quenching of Tris(2,3,5,6-tetrathiaaryl)methyl Cations with C-, N-, P-, and S-Nucleophiles

C-, N-, P-, and S-nucleophiles reacted with symmetrical tris(2,3,5,6-tetrathiaaryl)methyl cations, generated from the corresponding triarylmethanols by strong acids, to give a variety of asymmetrical monosubstituted persistent triaryl-methyl (TAM) radicals as the major products. The only byproducts were symmetrical TAMs.