Nano-sized metal(II) hybrids of a tridentate Schiff's base ligand: Synthesis, spectroscopic, molecular modeling and biological studies

Abstract

The Schiff's base ligand 1-((2-hydroxybenzylidene)amino)quinolin-2(1H)-one (HL) that formed by condensation reaction of 1-aminoquinolin-2(1H)-one and 2-hydroxybenzaldehyde has been synthesized and characterized using elemental analysis, (1H, 13C and 15N) NMR, mass, and FT-IR as well as UV–Vis spectra. The nano-sized divalent Mn, Co, Ni, Cu, Zn and Hg hybrids of the synthesized Schiff's base ligand was prepared and inspected by various spectroscopic and analytical techniques. Elemental and thermal (TG) analyses denoted the formation of the nano-sized Mn(II), Co(II), Ni(II), Cu(II), Zn(II) and Hg(II) hybrids in the molar ratio 1 L: 1 M. The FT-IR spectral studies confirmed the coordination of the ligand to the metal ions through the phenolic hydroxy oxygen, azomethine nitrogen and carbonyl oxygen. The Schiff's base ligand acts as monobasic tridentate OON donor. The geometrical structures have been found to be octahedral and tetrahedral. The molar conductance measurements of the nano-sized hybrids in DMF and DMSO correspond to be nonelectrolytic nature for all nano-sized metal (II) hybrids. Thus these hybrids may be formulated as [MLCl(H2O)2]nH2O and [HgLCl]3H2O (M = Mn(II); n = 4, Co(II); n = 2, Ni(II); n = 3, Cu(II); n = 2 and Zn(II); n = 2). Electrochemical behavior of nano-sized metal (II) hybrids were determined by cyclic voltammetry. Degradation pattern of the ligand HL and its nano-sized hybrids is shown by thermal studies. The activation of thermodynamic parameters are calculated using Coast-Redfern (CR) and Horowitz-Metzger (HM) methods. The data obtained from XRD, SEM, TEM, and AFM images unequivocally asserted the nano-sized metal chelates. In molecular modeling the geometries of Schiff's base and its nano-sized Cu(II), Co(II) and Zn(II) hybrids were fully optimized with respect to the energy using the DFT method from DMOL3 calculations. The brine shrimp bioassay was also carried out to study the in vitro cytotoxicity properties for the ligand and its hybrids against Artemia salina. The interaction of the complexes with calf thymus DNA (CT‒DNA) has been investigated by UV absorption method, and the mode of CT‒DNA binding to the HL ligand and its nano-sized hybrids has been explored. Furthermore, the DNA cleavage activity by the HL ligand and its nano-sized hybrids was performed. The solid state dc electrical conductivity of the HL ligand and its nano-sized Co(II), Cu(II) and Zn(II) hybrids have been measured over 303–423 K, and the hybrids were found to be of semiconducting nature.