Cobalt complexes with bidentate (NO) versus monodentate (N) salicylaldimine ligands: Syntheses, crystal structures, and comparison in bioactivity profile against bacterial, fungal, and cancer cells and activities on wheat germination indices

Abstract

Two complexes of cobalt (II) with monobasic bi‐coordinated {2‐((isopropylimino)methyl)phenol} and neutral mono‐coordinated {2‐((pyridin‐3‐ylimino)methyl)phenol} ligands were prepared. The ligands were not separated as solids, and the complexes, respectively, [Co(L 1 ) 2 ] C1 and [Co (HL 2 ) 2 Cl 2 ] C2 , were obtained from solutions containing cobalt (II) chloride, salicylaldehyde, and the respective amine. The crystallographic studies confirmed fourfold coordinated cobalt in complexes C1 and C2 via N 2 O 2 and N 2 Cl 2 donor atoms, respectively. Further, these complexes crystallized in the orthorhombic Pbca ( C1 ) and monoclinic I 2/a ( C2 ) space groups. Against two fungi, the complexes (20 mg/mL) in DMSO induced only inhibition zones of 11 and 15 mm diameters in Candida albicans strains, but amphotericin B inhibited this fungus by 21 mm. All complexes (20 mg/mL) in DMSO were tested against Bacillus subtilis , Staphylococcus aureus , Escherichia coli , and Pseudomonas aeruginosa strains. Complex C1 showed similar inhibition zones each with 12 mm diameter against these bacteria, but C2 gave inhibition zones with 17, 21, 19, and 16 mm diameters closer to those due to ampicillin which inhibited these strains by 26, 21, 25, and 26 mm. The complexes' C1 and C2 cytotoxicity was also evaluated in MCF‐7 cancer and baby hamster kidney normal cells, and they, respectively, gave IC 50 values of 29.1 and 18.1 μM in the cancer cells and of 35.5 and 17.5 μM in the normal ones. The reference, doxorubicin, induced cytotoxic effect with IC 50 = 9.66 and 36.42 μM on the MCF‐7 and baby hamster kidney cells, respectively. Both complexes and the control offered 100% germination for a drought‐resistive wheat cultivar, but complex C1 offered only 95% wheat germination under drought conditions. For a drought‐sensitive wheat cultivar, the control, complex C1 , and complex C2 offered 90%, 85%, and 90% germination under normal irrigation and 95%, 100%, and 95% germination under drought.