Studies on DNA binding, electrochemical activation, DNA photocleavage, and biopotency of N and O donor bidentate ligands with Cu(II), Co(II), and Zn(II)

Three Schiff-base ligands, namely 2-(3,4-dimethoxybenzylideneamino)phenol (HL1), 2-(3-hydroxy-4-nitrobenzylidene-amino)phenol (HL2), and 2-(3-methoxy-4-hydroxy-benzylideneamino)phenol (HL3) and their Cu(II), Co(II), and Zn(II) complexes were synthesized and characterized by spectroanalytical techniques. The UV-Vis and magnetic moment data revealed square-planar Cu(II) and tetrahedral Co(II) and Zn(II). Conductivity data showed the non-electrolytic nature of the complexes. Absorption and viscometric titration as well as cyclic voltammetry studies revealed the complexes as avid binders of calf thymus (CT) DNA through intercalation. A profound effect of substituents on the Schiff base was observed on binding of complexes to CT-DNA and in cleavage of supercoiled pBR322 DNA. All the complexes showed DNA cleavage in the presence of mercaptopropionic acid (MPA) except HL1 complexes. The cleavage activity increased with longer exposure time of irradiation at 365 nm and higher complex concentration. The cleavage reactions in the presence of MPA involve hydroxyl radical. The synthesized Schiff bases and their metal complexes were also tested for antibacterial and antifungal activities. The metal complexes exhibited higher antibacterial and antifungal activities than the parent ligands and their biopotency is discussed.