Abstract
In the current research, the complex formation equilibria of 2,2′-dipyridylamine (DPA) with the metal ions Cu(II), Ni(II), Co(II), Mn(II), and Zn(II) are investigated potentiometrically. The relation between the stability constants of the formed complexes and the properties of the central metal ions was investigated. In addition, the solvent effect on the protonation of DPA and Co-DPA complex formation was also investigated and discussed. The formation of the ternary complexes Co(DPA)L (L = some selected dicarboxylic acids) was studied in aqueous solutions at 25 °C and 0.1 mol dm−3 ionic strength. Stability constants and stoichiometry are reported for the complexes formed in solution. The results show that ternary complexes are formed by a simultaneous reaction mechanism. The speciation of all the complexes was resolved. The effect of chelate ring size of the dicarboxylic acid complexes on their stability constants was also examined. The concentration distribution of the complexes in solution was evaluated. The solid complexes [Co(DPA)L] (where L is oxalic, malonic, succinic or 1,1-cyclobutanedicarboxylic (CBDC) acid) have been synthesized and fully characterized with the help of elemental analyses, infrared spectra, magnetic and conductance measurements. Spectroscopic studies and magnetic measurements (Meff) suggest a tetrahedral geometry for Co(II)-complexes. The measured molar conductance values in DMSO indicate that the complexes are nonelectrolytic in nature. The isolated solid complexes have also been screened for their pharmacological activities against some selected bacteria and fungi. The activity data show that the complexes have a significant activity against Escherichia coli (gram negative) and Staphylococcus aureus (gram positive), as well as an antifungal activity against Aspergillus flavus and Candida albicans.
Highlights
Metals have an esteemed place within medical biochemistry, until recently this was restricted only to organic drugs
The cumulative formation constant βpqr of a species is defined on the basis of the following equilibrium: pM + pL + rH M pLqHr, (2)
On comparing the biological activity of the synthesized complexes with the standards tetracycline and amphotericin B, the following results are obtained: (a) using G− E. coli and G+ S. aureus, we discovered that the biological activity of the CBDC acid complex is higher than that of the malonate, oxalate, and succinate complexes and slightly lower than that of tetracycline standard; (b) all complexes were found to be more active against G+ than G− bacteria
Summary
Metals have an esteemed place within medical biochemistry, until recently this was restricted only to organic drugs. This study becomes of paramount importance especially for researchers in the field of bioinorganic and medicinal chemistry and can serve as a useful model for gaining understanding of enzyme-metal ion-drug complexes In this investigation and as a continuation of our research program directed to investigate binary and ternary metal complexes involving biologically relevant metal ions, amino acids, amides, and DNA units [14, 15, 16, 17, 18, 19, 20], we report in this paper a quantitative study of the formation equilibria of binary complexes of DPA with Cu(II), Ni(II), Co(II), Mn(II), and Zn(II). The isolated solid complexes were tested for their antimicrobial activities against some selected bacteria and fungi in the sense that testing the biological activities for such systems is needed for researchers working in various fields of biology, pharmacy, and medicine
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