Antibacterial activity and human cell cytotoxic of cobalt (III) complexes with 1,10-phenanthroline and carbohydrate ligands

Abstract

The mononuclear cobalt (III) complex derived from 1,10-phenanthroline with lactose [Co(phen)(2)lactose]Cl-2 center dot 3H(2)O (1) has been prepared and its properties have been compared with the sucrose complex [Co(phen)(2)sucrose]Cl-2 center dot 3H(2)O (2) and the complex without carbohydrate [Co(phen)(2)Cl-2]Cl center dot 3H(2)O (3).

The chemical structure of (1) was assigned by H-1-NMR, IR, CD and UV-Vis spectral data. The antibacterial activity of (1) - (3) was evaluated by disc-diffusion assays, using Gram-negative and positive bacteria. The minimum inhibitory concentration of the three complexes on the studied bacteria and their cytotoxicity on HEK293 human cells was determined. A colorimetric plate assay was used to distinguish bacteriostatic from bactericidal effect. Finally, the complexes uptake mechanism was evaluated using bacteria with mutated genes that encode for carbohydrate and siderophore receptors. The results indicate that complex (1) has an antibacterial activity similar to (3), while (2) presents a more restricted one. Moreover, all three complexes act by a bacteriostatic effect against bacterial cells and both (1) and (3) use a siderophore uptake mechanism to enter on bacterial cytoplasm. Cytotoxicity assays show that carbohydrate complexes are not cytotoxic to human cells, in contrast with complex (3), which is highly toxic. These results suggest that the use of the lactose ligand would maintain the antibacterial activity and uptake mechanism of the complex at reasonable levels, and would also reduce its toxicity against human cells. Thus, its strategic use would allow a decrease in toxicity of complexes used in eventual studies on eukaryotic systems.