Structural and computational exploration of zwitterionic and quinoidal forms in Schiff base compound

Abstract

The stable NH-form of the Schiff base compound, (Z)-6-(((4-chlorobenzyl) amino) methylene)-2-hydroxycyclohexa-2,4-dienone was synthesized and characterized by FTIR, SEM, EDAX anlysis and X-ray crystallographic analysis. Structural analysis was carried out to examine the NH-form of the halogen-based Schiff base compound. Additionally, an analysis of bond lengths, based on previously reported NH-forms of other Schiff bases, was conducted to distinguish between the zwitterion and quinoid structures. Further, Hirshfeld surface analysis was performed to visualize and quantify intermolecular interactions, supported by shape index, 2D fingerprint plots, and Enrichment ratio analyzes, highlighting the importance of these interactions. Energy frameworks were established to deepen the understanding of crystal packing through the computation of intermolecular interaction energies. QTAIM analysis was performed to visualize and quantify intramolecular interactions, while Density Functional Theory (DFT) studies elucidated molecular properties such as the HOMO-LUMO energy gap and its derivatives. Evaluation of antibacterial activity against S. aureus was conducted via the disc diffusion assay supplemented by molecular docking studies. This comprehensive approach provides valuable structural insights into the NH-form, as well as molecular and biological aspects of (Z)-6-(((4-chlorobenzyl) amino) methylene)-2-hydroxycyclohexa-2,4-dienone.