Synthesis, characterization, and biological activities of zinc(II), copper(II) and nickel(II) complexes of an aminoquinoline derivative

Abstract

Interest is increasingly focused on the use of transition metal complexes as biochemical, medical, analytical, pharmaceutical, agronomic, anticancer, and antibacterial agents. In this study, three complexes of [Zn(H2L)Cl] (1), [Cu(H2L)(H2O)(NO3)] (2) and [Ni(H2L)(NO3)].2H2O (3) were synthesized from a 2-chloroquinoline-3-carbaldehyde derived ligand [H3L = ((E)-2-(((2-((2-hydroxyethyl)amino)quinolin-3-yl)methylene)amino)ethanol. The compounds were characterized using physicochemical and spectroscopic methods. The results demonstrate that the free ligand behaves as a tridentate ligand with one oxygen and two nitrogen (ONN) donor atoms in 1:1 metal:ligand ratio. The formation constants of the complexes were found to be (KZn(II) = 2.3 × 106, KCu(II) = 2.9 × 106, and KNi(II) = 3.8 × 105). The thermodynamic parameters indicated that the reactions were spontaneous with exothermic nature of metal-ligand interaction energies. Based on the analyses of the experimental (EDX, FTIR, PXRD, MS and TGA) and DFT results, a distorted tetrahedral, a distorted square pyramidal and square planar geometry for Zn(II), Cu(II) and Ni(II) complexes, respectively, were proposed. The B3LYP calculated IR frequencies and TD-B3LYP calculated absorption spectra were found to be in good agreement with the corresponding experimental results. The powder XRD data confirmed that the Zn(II), Cu(II) and Ni(II) complexes have polycrystalline nature with average crystallite sizes of 27.86, 33.54, 37.40 Å, respectively. In vitro antibacterial activity analyses of the complexes were studied with disk diffusion method, in which the complexes showed better activity than the precursor ligand. Particularly the Cu(II) complex showed higher percent activity index (62, 90%), than both Zn(II) (54, 82%) and Ni(II) (41, 68%) complexes against both E. coli and P. aeruginosa, respectively. Using the DPPH assay, the complexes were further assessed for their antioxidant capacities. All metal complexes showed improved antioxidant activity than the free ligand. Zn(II) and Cu(II) complexes, which had IC50 values of 10.46 and 8.62 μg/ml, respectively, showed the best antioxidant activity. The calculated results of Lipinski’s rule of five also showed that the target complexes have drug-like molecular nature and similarly, the results of binding mode of action of these compounds against E. coli DNA gyrase B and P. aeruginosa LasR.DNA were found to be in good agreement with the in vitro biological activities.

Cytotoxicity and Antibacterial Potentials of Mixed Ligand Cu(II) and Zn(II) Complexes: A Combined Experimental and Computational Study

“…Thus, we reasonably concluded that the coordination of chrysin was via its carbonyl oxygen . There was little red shift (6 and 2 nm) in complex 2 , which could be due to the predominant electron transfer raised from interligands, absence of d → d transition, and higher band gap energy in the Zn­(II) complex as a result of d 10 electron configuration . Moreover, the absence of a peak above 400 nm for complex 2 could be due to nonexiting ligand-to-metal charge transfer bands in Zn­(II) metal-centered complexes (Figure ).…”

“…The quantum chemical descriptors of the free ligands and the corresponding metal complexes are presented in Figure and Table S2, whereas the wave function distributions are shown in Figures and S3. In our previous study, we reported that the band gap energy ( E g ) has a strong correlation with various biological activities: antibacterial, antioxidant, and cytotoxicity. ,, Moreover, band gap energy has been used as an important stability descriptor. A compound with large band gap energy is suggested to be stable and hard, whereas that with small band gap energy is less stable, giving the compound softness and enhanced biological importance .…”

“…48 There was little red shift (6 and 2 nm) in complex 2, which could be due to the predominant electron transfer raised from interligands, absence of d → d transition, and higher band gap energy in the Zn(II) complex as a result of d 10 electron configuration. 49 Moreover, the absence of a peak above 400 nm for complex 2 could be due to nonexiting ligand-to-metal charge transfer bands in Zn(II) metal-centered complexes (Figure 6). However, the resulting changes in the electronic The fragments for the coordinating ligands chrysin and 1,10-phenathroline in complex 1 were found to appear as peaks at 255.065 and 181.076, respectively.…”

Organic–inorganic hybrid salt and mixed ligand Cr(III) complexes containing the natural flavonoid chrysin: Synthesis, characterization, computational, and biological studies

“…The DPPH scavenging activities of the synthesized complexes (Cr1 and Cr2) were evaluated as we described previously, with minor modifications (Lemilemu et al, 2021;Alem et al, 2022;Damena et al, 2023). The percent DPPH free radical scavenging activities of the synthesized complexes and the standard were calculated using Equation (1).…”

“…The calculated absorption spectra were red-shifted by 30 nm for better comparison with the corresponding experimental spectra. Quantum chemical descriptors calculation, frontier molecular orbital (FMO) visualization, and associated data were conducted as we previously reported (Alem et al, 2022;Damena et al, 2023).…”