Modulating the DNA cleavage ability of copper() Schiff bases through ternary complex formation

Copper( ii ) complexes with the potentially tridentate Schiff bases N -[(3-ethoxy-2-hydroxyphenyl)methylidene]- N ′-tosylbenzene-1,2-diamine (H 2 L 1 ) and N -[(2-hydroxynaphthanyl)methylidene]- N ′-tosylbenzene-1,2-diamine (H 2 L 2 ) have been synthesized by electrochemical oxidation of the metal in an electrochemical cell containing a solution of the corresponding ligand in acetonitrile. Adducts of these compounds with 2,2′-bipyridine (2,2′-bpy), 4,4′-bipyridine (4,4′-bpy) or 1,10-phenanthroline (phen) were also obtained. The complexes have been characterized by microanalysis, mass spectrometry, EPR, IR and UV-Vis spectroscopies, as well as DFT calculations. The ligand H 2 L 1 and the compounds [CuL 1 (H 2 O)]·H 2 O ( 1 ), [Cu 2 L 1 2 (4,4′-bpy)] ( 3 ), [CuL 1 (phen)] ( 4) , [CuL 2 (2,2′-bpy)] ( 6 ), and [Cu 2 L 2 2 (4,4′-bpy) 3 ] ( 7 ) have also been characterized by X-ray diffraction. The copper compounds 1 , 4 and 6 are mononuclear with a square planar geometry around the metal for 1 and square pyramidal for 4 and 6 . However, 3 and 7 are dinuclear complexes with a 4,4′-bpy ligand bridging two copper atoms with square planar ( 3 ) or square pyramidal ( 7 ) coordination. The supramolecular structures were studied by means of Hirshfeld surface analysis. The adducts of phen and 2,2′-bpy exhibit enhanced DNA cleavage ability compared to the [CuL(H 2 O)] complexes (L = L 1 or L 2 ), while the binuclear entities formed by 4,4′-bpy coordination present reduced nuclease efficiency. Copper( ii ) Schiff-bases were electrochemically synthesized and characterized. The presence of co-ligands such as 2,2′-bpy or phen in the metal coordination environment increases the DNA cleavage efficiency.