The mononuclear cobalt(III) complex derived from 1,10-phenanthroline and maltose ([Co(phen) 2 maltose]Cl 2 •3H 2 O) (1) has been synthesized and characterized in aqueous solution. Its characterization was based on its optical and spectroscopic properties.The antimicrobial activity of this complex was screened in vitro against the microorganisms Escherichia coli DH5a, Salmonella enterica sv Enteritidis ISP/953, Klebsiella pneumoniae RYC492, Pseudomonas aeruginosa PAO1, Enterococcus faecalis ATCC 29212, Bacillus cereus GCA234, Micrococcus sp. Staphylococcus aureus ATCC25923.Complex (1) showed antibacterial activity with a bacteriostatic effect over Gram positive and negative bacteria. The cytotoxicity of complex (1) was tested in vitro on human embryonic kidney cells.Keywords: Carbohydrate-cobalt(III) complexes; circular dichroism; antibacterial activity.e-mail: jparada@ciq.uchile.cl INTRODUCTIONTransition metal complexes are of interest since they display a wide variety of application in fields ranging from materials science and catalysis to biological activity [1].From the biological point of view, several studies have shown that the complexes may have antibacterial, antifungal and antitumor activity [2].The biological activity of metal complexes is highly dependent on the nature of the metal ions and the donor sequence of the ligands because different ligands exhibit different biological properties [3].An interesting group of ligands are the carbohydrates [4], whose complexes have shown significant antimicrobial activity against Gram-positive and Gramnegative bacterial strains as well as a few fungal strains [5]. Poller and Parkin reported the synthesis of organometallic derivatives of sucrose (lead, tin and germanium). In that study organotin was found to exhibit higher biocidal activities than would be expected from the tin content [6].A few sugar-cobalt complexes with antibacterial activity have been reported. An important example is grafted PVA polymer with a derivative of erythro-ascorbic acid (pentulosono-lactone-2,3-enedianisoate) reported by Salih et al. It was evaluated for antimicrobial properties against four pathogenic bacteria (Escherichia coli, Klebsiella pneumonae, Staphylococcus aureus, Staphylococcus albus) and fungi (Aspergillus niger, yeast). This cobalt complex showed good activity against the various microbial isolates [7].1,10-Phenanthroline is also one of the biologically important ligands, and several studies show that this ligand and a number of its complexes are effective against various strains of microorganisms. Here the synthesis of the mixed ligand cobalt complex [Co(phen) 2 maltose] Cl 2 ·3H 2 O (1), as well as its spectral features and optical activity are reported.UV-visible absorption spectroscopy and circular dichroism spectroscopy allow us to assign a D configuration to complex (1).The complex was also screened for antibacterial activity against Gram positive and Gram-negative bacteria. We determined the antibacterial effects and evaluated their cytotoxic effect on h...
The mononuclear cobalt (III) complex derived from 1,10-phenanthroline with lactose [Co(phen) 2 lactose]Cl 2 •3H 2 O (1) has been prepared and its properties have been compared with the sucrose complex [Co(phen) 2 sucrose]Cl 2 •3H 2 O (2) and the complex without carbohydrate [Co(phen) 2 Cl 2 ]Cl•3H 2 O (3). The chemical structure of (1) was assigned by 1 H-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.
RESUMEN:Las bacteriocinas son péptidos antimicrobianos de síntesis ribosomal secretadas por bacterias. Dentro de estas destaca nisina que posee potenciales usos en terapias antibióticas, como biopreservante de alimentos y probióticos. También se ha descrito que nisina posee citotoxicidad sobre líneas celulares neoplásicas, pero existe poca información de su efecto sobre células tumorales sanguíneas. Debido al potencial uso que presenta nisina, es relevante determinar la toxicidad que presenta sobre líneas celulares tumorales del tipo sanguíneo. Para esto, se realizaron ensayos de actividad hemolítica sobre eritrocitos humanos y de toxicidad sobre células mononucleares de sangre periférica humanas, determinándose que nisina no posee efecto citotóxico sobre este tipo de células normales humanas sanguíneas. Se realizaron también, ensayos de citotoxicidad con líneas celulares tumorales (K562 y U937), con el fin de determinar dosis, tiempo de exposición y selectividad en el efecto tóxico de nisina sobre las células tumorales humanas. Estos ensayos muestran que nisina presenta actividad citotóxica sobre líneas celulares K562 y U937 a las 72 h de exposición, a una concentración de 40 µg/mL, que corresponde a 100 veces la concentración mínima inhibitoria (MIC) usada para su acción sobre bacterias. Al comparar el efecto de nisina sobre células mononucleares de sangre periférica humanas con las líneas tumorales linfoides y mieloides (K562 y U937 respectivamente), se observa un efecto selectivo de nisina sobre las células tumorales sanguíneas.
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