Abstract:
Despite the common use of salens and hydroxyquinolines as therapeutic and bioactive
agents, their metal complexes are still under development. Here, we report the synthesis of novel
mixed-ligand metal complexes (MSQ) comprising salen (S), derived from (2,20
-{1,2-ethanediylbis
[nitrilo(E) methylylidene]}diphenol, and 8-hydroxyquinoline (Q) with Co(II), Ni(II), Cd(II), Al(III),
and La(III). The structures and properties of these MSQ metal complexes were investigated using
molar conductivity, melting point, FTIR, 1H NMR, 13C NMR, UV–VIS, mass spectra, and thermal
analysis. Quantum calculation, analytical, and experimental measurements seem to suggest the
proposed structure of the compounds and its uncommon monobasic tridentate binding mode of salen
via phenolic oxygen, azomethine group, and the NH group. The general molecular formula of MSQ
metal complexes is [M(S)(Q)(H2O)] for M (II) = Co, Ni, and Cd or [M(S)(Q)(Cl)] and [M(S)(Q)(H2O)]Cl
for M(III) = La and Al, respectively. Importantly, all prepared metal complexes were evaluated for
their antimicrobial and anticancer activities. The metal complexes exhibited high cytotoxic potency
against human breast cancer (MDA-MB231) and liver cancer (Hep-G2) cell lines. Among all MSQ
metal complexes, CoSQ and LaSQ produced IC50 values (1.49 and 1.95 µM, respectively) that were
comparable to that of cisplatin (1.55 µM) against Hep-G2 cells, whereas CdSQ and LaSQ had best
potency against MDA-MB231 with IC50 values of 1.95 and 1.43 µM, respectively. Furthermore, the
metal complexes exhibited significant antimicrobial activities against a wide spectrum of both Gram-
positive and -negative bacterial and fungal strains. The antibacterial and antifungal efficacies for the
MSQ metal complexes, the free S and Q ligands, and the standard drugs gentamycin and ketoconazole
decreased in the order AlSQ > LaSQ > CdSQ > gentamycin > NiSQ > CoSQ > Q > S for antibacterial
activity, and for antifungal activity followed the trend of LaSQ > AlSQ > CdSQ > ketoconazole >
NiSQ > CoSQ > Q > S. Molecular docking studies were performed to investigate the binding of
the synthesized compounds with breast cancer oxidoreductase (PDB ID: 3HB5). According to the
data obtained, the most probable coordination geometry is octahedral for all the metal complexes.
The molecular and electronic structures of the metal complexes were optimized theoretically, and
their quantum chemical parameters were calculated. PXRD results for the Cd(II) and La(III) metal
complexes indicated that they were crystalline in nature.