Synthesis and characterization of glucose-bis(pyrazole)-Cu(II)/Ni(II) complexes and their in vitro DNA binding...

The D-glucose-bis pyrazolyl complexes of Cu(II) 1 and Ni(II) 2 were synthesized and characterized by elemental analysis, molar conductance measurements and spectroscopic methods. The solution structures of the complex have been assessed to square pyramidal using electronic absorption and electronic paramagnetic resonance (EPR) spectroscopy. The interaction of 1 and 2 with calf thymus DNA (CT DNA) has been carried out by absorption, emission, viscometric and electrochemical methods. The intrinsic binding constant K(b) was determined as 13.4x10(5) M(-1), 4.5x10(5) M(-1) for 1 and 2, respectively suggestive of strong binding of complexes with DNA. Furthermore, higher value of K(b) for 1 implies that this complex interacts more strongly with CT DNA in comparison to 2. The quenching constant "K" of 1 and 2 obtained from emission spectral methods was 1.33, 0.55, respectively. Complex 1 hydrolytically cleaved pBR322 supercoiled DNA in absence of an activating agent. The enhanced cleavage of pBR322 DNA was observed in presence of ascorbic acid as a reducing agent, 1 also displays efficient photonuclease activity through double strand DNA breaks when irradiated at 365 nm through mechanistic pathway involving hydroxyl radicals. In addition to the above binding studies, an in vitro binding study of complex 1 with protein human serum albumin (HSA), tyrptophan and mixtures of HSA, L-tryptophan with CT DNA was carried out. The in vitro "binding study" also supports that 1 shows higher binding affinity towards CT DNA.