Background: The use of antimicrobial agents affecting several biological targets at a time is
one of the promising ways to fight multidrug-resistant bacterial strains, and hence it may serve to increase
the efficiency of chemotherapy. Among the potential antimicrobial agents acting in this manner
are redox-active complexes of transition metals with sterically hindered diphenols.
Method: We synthesized the redox-active complexes of cycloaminomethyl derivatives of sterically
hindered diphenols with Zn(II) ions and estimated the level of their antimicrobial activity against Gramnegative
bacteria (Escherichia coli, Pseudomonas aeruginosa, Serratia marcescens, Salmonella typhimurium),
Gram-positive bacteria (Bacillus subtilis, Sarcina lutea, Staphylococcus spp., Mycobacterium
smegmatis), moulds (Aspergillus niger, Fusarium spp., Mucor spp., Penicillium lividum, Alternaria
alternata) and yeasts (Candida spp.) as compared to some standard antimicrobials. The compounds
were characterized by means of physico-chemical and pharmacological screening methods.
Results: The coordination core of these complexes is a tetrahedral chromophore [ZnO2N2], the phenolic
ligands being coordinated in monoanionic form (phenolate). The MIC value (0.010-0.027 µmol·ml–1)
comparable to those of standard antibiotics (tetracycline, streptomycin, chloramphenicol) was achieved
by structural modification of the ligands and complexation with zinc ions. The derivatives of orthodiphenols
and their Zn(II) complexes were found to be able to reduce cytochrome c - one of the key
components of the respiratory chain of microorganisms (υ=0.3-1.8 nmol.min–1). The investigation of
SOD-like activity provided a means to reveal potential SOD mimics (IC50=1.1-20.5 µmol.l–1) among the
ortho-diphenols and their Zn(II) complexes synthesized, because IC50 for the native Cu, Zn-SOD is 0.1
Conclusion: The correlation between the antimicrobial activity of these compounds and their reducing
ability deserves particular attention since they possess both antioxidant and antimicrobial activities.