Synthesis, Crystal Structure, Antioxidant, Antimicrobial, and Mutagenic Activities and DNA Interaction Studies of Ni(II) Schiff Base 4-Methoxy-3-benzyloxybenzaldehyde Thiosemicarbazide Complexes

Three new Ni(II) square planar complexes of 4-methoxy-3-benzyloxybenzaldehyde thiosemicarbazide(4m3BTSC) having polypyridyl bases of general formulation [ML2] (1) and [MLB] (2, 3), where L = 4m3BTSC and B is N,N-donor heterocyclic bases, namely, 1,10-phenanthroline (phen, 2), 2,2′-bipyridine (bpy, 3), are synthesized and characterized. The free radical scavenging assay results showed that complex 1 possesses significant activity when compared to complexes 2 and 3. The biological studies showed that the ligand and its complexes exhibited significant and different biological activities and also the prepared compounds are nonmutagenic. They may be potential commercial antioxidants because of their nonmutagenic and nontoxic nature. The DNA interaction of the new complexes is evaluated by absorption, emission, and melting temperature methods, and the results suggested that the binding affinity of the complexes increases with the presence of planar ligand in the molecule. The nickel (II) complexes with planar phenanthroline bases show moderate DNA binding and cleavage ability. 1. Introduction Schiff bases have great importance in coordination chemistry due to their ability to form a range of complexes with applications in different fields [1]. Thiosemicarbazones have variable bonding modes, ability to form stable chelates with metal ions, and structural diversity [2]. The sulfur, oxygen, and nitrogen may be involved in coordination providing a useful model for bioinorganic processes [3]. These thiosemicarbazide ligands have good complexing ability, and their activity increases on complexation with transition metal ions [4]. These compounds are also of interest due to their biological activities including enzyme inhibition [5] and antifungal and pharmacological applications [6, 7]. The toxicological importance of the –N–C=S moiety has been well established in antifungal, antibacterial agents and pesticidal activities [8, 9]. It has been suggested that the azomethine linkage in Schiff bases is responsible for the biological activities such as antitumor, antibacterial, antifungal, and herbicidal activities [10]. The biological activities of thiosemicarbazones often showed a high dependence on their substituents. Minor modifications in the structure of thiosemicarbazones can lead to widely different biological activities. The biological properties of thiosemicarbazones are often modulated by metal coordination. In some cases, the highest biological activity is associated with a metal, and some side effects may decrease upon complexation [11]. Nickel(II) complexes