Two copper complexes from two novel naphthalene-sulfonyl-triazole ligands: Different nuclearity and different DNA binding and cleavage capabilities

Abstract

Two novel naphthalene-sulfonyl-triazole ligands, 5-amino-N1-(naphthalen-3-ylsulfonyl)-1,2,4-triazole (anstrz) and 3,5-diamino-N1-(naphthalen-3-ylsulfonyl)-1,2,4-triazole (danstrz), purposely designed to interact with DNA, have been prepared for the first time and then fully characterized by 1H, 13C NMR, and IR spectroscopy, mass spectrometry and elemental analysis. The crystal structures of two copper complexes of these derivatives, i.e. [Cu(anstrz)4(NO3)2]∙4CH3OH (1), mononuclear, and [Cu(danstrz)(μ-OAc)2]2∙2(danstrz) (OAc=acetato) (2), dinuclear, have been determined by single-crystal X-ray diffraction. In both cases the ligand coordinates in a monodentate fashion via the N4 nitrogen atom of the triazole ring. Compound 2, an example of paddle wheel type copper acetate, presents a Cu⋯Cu′ distance of 2.667(1) Å. As a result of strong stacking interactions and intense H-bonds, the structure of 2 constitutes a MOF (metal–organic framework). Besides, this dinuclear compound exhibits a very strong antiferromagnetic coupling (J=−324cm−1) and a silent X-band EPR at room temperature. The affinity toward DNA of 1 and 2 has been examined by fluorescence emission spectroscopy, thermal denaturation and viscosimetry assays. The apparent binding constant (Kapp) values of 2.2×107M−1 for 1 and 2.6×107M−1 for 2 suggest important DNA interaction. The dinuclear compound (2) intercalates and produces a high change in the Tm. Both compounds promote DNA scission in the presence of H2O2/ascorbate (1) or ascorbate (2) through oxidative mechanism. The possible reasons for the higher DNA affinity and the more efficient DNA cleavage displayed by compound 2 in relation to compound 1 are discussed.