Ternary Copper(II) and Nickel(II) chelates of 2,2′-Bipyridyl and glycine: X-ray structures, kinetics, DNA binding and cleavage activities

Abstract

Ternary copper(II) and nickel(II) chelates of 2,2′-bipyridyl and glycine ligands with the formula of [Cu(BPy)(Gly)Cl] 1, [Cu(BPy)(Gly)(H2O)]NO32 and [Ni(BPy)(Gly)(H2O)2]Cl·H2O 3 were synthesized and structurally characterized by using X-ray crystallography. Copper(II) compounds 1 and 2 form slightly distorted square-pyramidal coordination geometries of CuN3ClO and CuN3O2, respectively. Whereas, nickel(II) compound 3 shows an octahedral coordination geometry of NiN3O3. Kinetic measurements have been made with the objective of correlating the influence of geometry. The thiourea substitution reaction of 1 in water is a monophasic process that involves the subsequent displacement of chloride ligand with k2300 = 21.1 ± 0.8 M−1s−1. The activation parameters, ΔH# = 79.2 ± 2.5 kJ mol−1 and ΔS# = 68.4 ± 8.7 J K−1 mol−1, for the chloride substitution reactions indicate that the reaction follows a dissociative mechanism. The interactions of compounds 2 and 3 towards DNA were examined with the help of absorption spectroscopic technique. The binding constants (Kb) of 2 and 3 to DNA were found to be 4.7 × 105 and 2.4 × 105 M−1, respectively, indicating that both compounds show good binding activity to calf thymus DNA. The nuclease mimic activity of both 2 and 3 was also assessed by its ability to cleave super coiled plasmid DNA to nicked and linear forms in the absence of any external additives. On the other hand, the quasi-reversible CuII/CuI redox couple slightly improves its reversibility with a considerable decrease in current intensity. All the experimental results indicated that the bipyridyl mixed copper(II) complex 2 intercalates more effectively into the DNA base pairs.