Equilibria in Aqueous Cobalt(II)-Reduced Schiff Base
N-(2-hydroxybenzyl)alanine System: Chemical Characterization, Kinetic Analysis, Antimicrobial and Cytotoxic Properties.
Molecules 2020;
25:molecules25153462. [PMID:
32751474 PMCID:
PMC7436002 DOI:
10.3390/molecules25153462]
[Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/08/2020] [Revised: 07/27/2020] [Accepted: 07/28/2020] [Indexed: 11/16/2022] Open
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.
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