Mixed ligand complexation of some transition metal ions in solution and solid state: Spectral characterization, antimicrobial, antioxidant, DNA cleavage activities and molecular modeling

Equilibrium studies of Ni(II), Cu(II) and Zn(II) mixed ligand complexes involving a primary ligand 5-fluorouracil (5-FU; A) and imidazoles viz., imidazole (him), benzimidazole (bim), histamine (hist) and L–histidine (his) as co-ligands(B) were carried out pH-metrically in aqueous medium at 310 ± 0.1 K with I = 0.15 M (NaClO4). In solution state, the stoichiometry of MABH, MAB and MAB2 species have been detected. The primary ligand(A) binds the central M(II) ions in a monodentate manner whereas him, bim, hist and his co-ligands(B) bind in mono, mono, bi and tridentate modes respectively. The calculated Δ log K, log X and log X′ values indicate higher stability of the mixed ligand complexes in comparison to binary species. Stability of the mixed ligand complex equilibria follows the Irving-Williams order of stability. In vitro biological evaluations of the free ligand(A) and their metal complexes by well diffusion technique show moderate activities against common bacterial and fungal strains. Oxidative cleavage interaction of ligand(A) and their copper complexes with CT DNA is also studied by gel electrophoresis method in the presence of oxidant. In vitro antioxidant evaluations of the primary ligand(A), CuA and CuAB complexes by DPPH free radical scavenging model were carried out. In solid, the MAB type of M(II)5-FU(A)his(B) complexes were isolated and characterized by various physico-chemical and spectral techniques. Both the magnetic susceptibility and electronic spectral analysis suggest distorted octahedral geometry. Thermal studies on the synthesized mixed ligand complexes show loss of coordinated water molecule in the first step followed by decomposition of the organic residues subsequently. XRD and SEM analysis suggest that the microcrystalline nature and homogeneous morphology of MAB complexes. Further, the 3D molecular modeling and analysis for the mixed ligand MAB complexes have also been carried out.

Equilibrium studies of Ni(II), Cu(II) and Zn(II) mixed ligand complexes involving 5-fluorouracil (5-FU; A) and imidazoles(B) viz., imidazole (him), benzimidazole (bim), histamine (hist) and L–histidine (his) were carried out pH-metrically in aqueous medium at 310 ± 0.1 K with I = 0.15 M (NaClO4). In solution state, the stoichiometry of MABH, MAB and MAB2 species have been detected. Stability of the mixed ligand complex equilibria follows the Irving–Williams order of stability. The Ni(II)/Cu(II)/Zn(II)5-FU(A)his(B) complexes were isolated and characterized by various physico-chemical and spectral techniques. From the spectral studies, 5-FU(A) and his(B) form a stable 4, 5, 6 membered chelate rings with distorted octahedral environment. Subsequently, the title complexes are promising antimicrobial and antioxidant scavenging tools. SEM pictogram and X-ray diffractogram illustrate that the complexes have homogeneous morphology with microcrystalline nature. Further, the 3D molecular modeling analysis supports the proposed geometry of the mixed ligand complexes.Figure optionsDownload as PowerPoint slideHighlights
► Stability constant of the mixed ligand complexes have been investigated by means of pH-metric as well as spectroscopic manner.
► Halogen substituted pyrimidines act as vital role in many drug systems.
► Structural and physico-chemical properties of the mixed ligand complexes have been studied by spectral and molecular modeling techniques.
► The in vitro antimicrobial and antioxidant evaluations of the complexes show more potent activities.
► Synthesized complexes have higher ability to cleave CT DNA under aerobic conditions.