Employment of pyridyl oximes and dioximes in zinc(II) chemistry: Synthesis, structural and spectroscopic characterization, and biological evaluation

The employment of pyridine-2-amidoxime (ampaoH), 2,6-diacetylpyridine dioxime (dapdoH2) and pyridine-2,6-diamidoxime (dampdoH2) in zinc(II) chemistry is reported. The syntheses, crystal structures, spectroscopic and physicochemical characterization, and biological evaluation are described of [Zn(O2CMe)2(ampaoH)2] (1), [Zn(O2CPh)2(ampaoH)2] (2), [Zn(dapdoH2)2](NO3)2 (3) and [Zn(dampdoH2)2](NO3)2 (4). The reactions between Zn(NO3)2·4H2O and two equivalents of either dapdoH2 or dampdoH2 in MeOH led to the mononuclear, cationic complexes 3 or 4, respectively. The ZnII center in 3 and 4 is coordinated by two N,N′,N″-tridentate chelating (η3) dapdoH2 or dampdoH2 ligands, and it thus possesses a distorted octahedral coordination geometry. Strong intermolecular hydrogen bonding interactions provide appreciable thermodynamic stability and interesting supramolecular chemistry for compounds 1–4. The characterization of all four complexes with 1H and 13C NMR, and positive ion electrospray mass spectroscopies confirmed their integrity in DMSO solutions. The biological evaluation of complex 3 showed the highest cytotoxic activity against LMS and MCF-7 cells, among the other three complexes (1, 2 and 4). Flow cytometry analysis revealed that all four complexes cause apoptosis to LMS cells, at a dose-dependent manner. The combined work demonstrates the ability of pyridyl monoxime and pyridyl dioxime chelates not only to lead to polynuclear 3d-metal complexes with impressive structural motifs and interesting magnetic and optical properties, but also to yield new, mononuclear transition metal complexes with biological implications.