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

Abstract

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 (v(max)) of both geometrical isomers using the Kamlet-Taft equation. Linear free energy relationships (LEER) in the form of single substituent parameter equation (SSP) was used to analyze substituent effect on pK(a), NMR chemical shifts and v(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. (C) 2018 Elsevier B.V. All rights reserved.