Effects of electron donating and withdrawing substituents on crystal structures, cytotoxicity and in silico DNA interactions of isatinoxime Schiff base ligands

Abstract

We report a new series of isatin-oxime-based Schiff base derivatives (p–H, p–Cl, p–CH₃). Structural analyses of the compounds were conducted through FTIR, ¹H NMR, UV–Vis, and elemental analyses. X-ray crystallography demonstrated that compounds 1 and 2 adopted an orthorhombic crystal system with a P bca space group. Hirshfeld surface (HS) analysis indicated that hydrogen bonding and van der Waals interactions were predominant in the crystal packing. The volumes of the crystal voids and the percentages of free spaces in the unit cells were calculated as 293.87 ų and 10.63% (for 1), 320.34 ų and 11.04% (for 2), respectively. The evaluations of energy frameworks showed that stabilization was dominated by electrostatic energy contributions in compounds. In silico investigations on the DNA binding activity showed that the binding activity of the compounds was mediated via intercalation. The anticancer activity of the compounds was also tested via an MTT assay using HepG2 (liver cancer), Caco-2 (colorectal adenocarcinoma), A549 (lung cancer) and HEK-293 (normal cell) cell lines. The MTT assay demonstrated significant cytotoxic activity of compound 1 across HepG2, Caco-2, A549, and HEK-293 cell lines, with IC₅₀ values of 5.07 µM, 5.19 µM, 4.01 µM, and 5.63 µM, respectively, after 24 h, surpassing cisplatin in efficacy at all tested time intervals. The data indicate that substituents play a significant role in modulating cytotoxicity, with compound 1 (p–H) demonstrating the highest activity. These findings demonstrate the high cytotoxicity and cancer cell selectivity of isatin-oxime-based Schiff base derivatives, especially compound 1, suggesting their potential as strong alternatives to traditional chemotherapy agents.