Temperature and salt effects of the kinetic reactions of substituted 2-pyridylmethylene-8-quinolyl iron (II) complexes as antimicrobial, anti-cancer, and antioxidant agents with cyanide ions

Abstract

Kinetics of substitution reaction of three high-spin pyridylmethylene-8-quinolyl iron (II) complexes by CN– ions were studied spectrophotometrically in various ratios of aqueous–methanol binary mixtures at 298 ± 0.2 K. Kinetics of the substitution reaction follow the rate law (k2[CN−][complex]) on applying of the conditions of the pseudo first order reaction. Reactivity of the reaction was investigated in terms of ligand moiety and solvent effects. The rate of the reaction increased as the co-solvent methanol ratio increased. This reactivity trend is predominantly due to increases in the activity coefficient of those hydrophobic complexes in the organic methanol co-solvent, depending upon the hydrophobicity of the substituent groups (R) in the coordinated ligand in the complexes. Reactivity trends of the prepared complexes in the presence of the inserted hydrophobic salts such as tetrabutylammonium bromide (TBAB), tetraethylammonium bromide (TEAB), and tetramethylammonium bromide (TMAB) or hydrophilic salt potassium bromide (KBr) were studied. The observed decrease in the rate constants with increasing salt concentration was due to the cationic character of the reacting complexes. In addition, the synthesized compounds were tested for antimicrobial activity against selected strains of microbes. The results showed that the order of reactivity of the investigated complexes against the selected microbes were as follows: ppaqFe > paaqFe > pmaqFe. In addition, the investigated ligands and their Fe(II) complexes were screened for anticancer activities against several cell lines of cancer. The ppaqFe complex showed the best cytotoxic efficiency against the selected cancer lines (IC50 = 8.75–21.50 µg/µl), whereas the pmaq ligand showed the lowest cytotoxic efficiency (IC50 = 58.25– 72.40). Furthermore, the antioxidant potential of the presented compounds was studied by applying DPPH assays and showed a potential activity compared with standard vitamin C. The excellent antimicrobial and anticancer activities of the investigated Fe(II) chelates compared with literature values are promising and deserve further study.