Introducing N‐Heteroaromatic Bases into Copper(II) Thiosemicarbazon Complexes: A Way to Change their Biological Activity

Three new copper(II) complexes, [Cu(1,10‐Phen)(L)] (1), [Cu(2,2′‐Bpy)(L)] (2) and [Cu(3,4‐Lut)(L)] (3), where H(2)L=2‐[(2,4‐dihydroxyphenyl)methylidene]‐N‐(prop‐2‐en‐1‐yl)hydrazine‐1‐carbothioamide, 1,10‐Phen=1,10‐phenanthroline, 2,2′‐Bpy=2,2′‐bipyridine, 3,4‐Lut=3,4‐lutidine, have been synthesized and characterized by elemental analysis, FTIR spectroscopy and single crystal X‐ray crystallography (1, 2). All compounds are mononuclear. The introduction of a monodentate N‐heteroaromatic base (3,4‐dimethylpyridine) has led to a significant increase of antimicrobial activity against Gram‐negative Escherichia coli and antifungal activity against Candida albicans compared to the pro‐ligand and the precursor complex [Cu(L)H(2)O]. The introduction of bidentate N‐heteroaromatic bases did not lead to such increase of antimicrobial and antifungal activities. Moreover, complex 3 surpasses the inhibitory activity of tetracycline toward Enterobacter cloacae and the inhibitory activity of fluconazole toward Candida parapsilosis and Cryptococcus neoformans. The study of antioxidant activity against cation radicals ABTS⋅(+) showed that complexes 1–3 are more active than Trolox, but only introduction of the monodentate N‐heteroaromatic base (3,4‐dimethylpyridine) led to the increase of antioxidant properties compared to the precursor complex.