Equilibria in Aqueous Cobalt(II)—Reduced Schiff Base N-(2-hydroxybenzyl)alanine System: Chemical Characterization, Kinetic Analysis, Antimicrobial and Cytotoxic Properties

Abstract

The present study describes the coordination properties of a reduced Schiff base, N-(2-hydroxybenzyl)alanine, towards cobalt(II) using potentiometric as well as spectroscopic (UV-Vis and ESI-MS) methods. The results indicate the formation of six mononuclear complexes showing high stability in aqueous solution. Coordination occurs in the {O−phenolic,N,O−carboxyl} and {N,O−carboxyl} chelation modes, depending on the degree of ligand deprotonation. Examination of the complexation equilibria at pH ca 7, which is important from a biological point of view, allowed to identify two species: [CoL] and [CoL2H]−. The kinetic analysis showed a structural change of those cobalt(II) complexes from octahedral to tetrahedral in accordance with a first-order time relationship. The antimicrobial properties of N-(2-hydroxybenzyl)alanine, cobalt(II) nitrate and of the Co(II) – ligand complexes were determined against Gram-positive bacteria (Enterococcus faecalis, Staphylococcus aureus, Staphylococcus epidermidis), Gram-negative bacteria (Pseudomonas aeruginosa, Escherichia coli, Helicobacter pylori) and a fungal strain (Candida). The results indicate that the complexes are more active for more strains than the ligand alone. Nevertheless, the complexes induce a higher decrease in the metabolic activity of cells but without damage to nuclei. Tetrahedral structures show stronger anti-cellular toxicity than octahedral complexes, which is most likely due to the higher accessibility of the cobalt(II) center.

Chemical Characterization and Biological Evaluation of New Cobalt(II) Complexes with Bioactive Ligands, 2-Picolinehydroxamic Acid and Reduced Schiff Base N-(2-Hydroxybenzyl)alanine, in Terms of DNA Binding and Antimicrobial Activity

“…Heteroligand complexes are formed as a result of the cobalt(II) ion coordination with deprotonated functional groups of PicHA and AlaSal. Dissociation of both ligands begins at pH below 2 [25,26]. However, only the binary complexes with PicHA are formed in the {Npyr,N − } chelation mode in these conditions (Figure 2).…”

“…Chelation affects a distinct change in the biological properties of the ligands and the metal moiety; their presence can cause a range of diseases, including cancer; however, they can also be used to treat them [1]. To obtain biologically active metal complexes, it was advisable to use ligands such as 2-picolinehydroxamic acid (PicHA) and N-(2-hydroxybenzyl)alanine (AlaSal), Figure 1, which are known to demonstrate antibacterial and antifungal properties [25,26].…”

“…The Schiff base is derived from an amino acid and a carbonyl compound (e.g., salicylaldehyde). The reduction of its C=N bond to a single amine bond confers greater conformational flexibility to the backbone, allowing the compound to form complexes with more stable molecules [26]. Moreover, aromatic Schiff bases are a more stable class of compounds than those with alkyl substituents, which are relatively unstable and readily polymerizable [30].…”

Performance of Schiff Bases Metal Complexes and their Ligand in Biological Activity: A Review

“…In 2009, Al-Masoudi N. and co-workers synthesized a metal complexes of 1, 2, 4-triazole Schiff base which was given antiviral properties against human immunodeficiency virus (1) and human immunodeficiency virus (2). Tetrazolium based on MTT assay (Tetrazolium dye 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) is a colorimetric ocean used to measure the activity of enzymes and to determine the cytotoxicity of the medical component or toxic substances [19], the assay was used the mammalian cell lines MT-4 cells for the detection of anti-HIV.…”

“…Schiff base compounds are prepared from the reaction of a primary amine with the carbonyl group of aldehyde (RHCO) or ketone (R 2 CO), Figure 1. Schiff bases have a functional group carbonnitrogen double bond (CN) called azomethine or imine, this imine group is very important for complex reaction and gives an important application in biological activity [1][2][3][4].…”