Synthesis and characterisations of copper(II) complexes of 5-methoxyisatin thiosemicarbazones: Effect of N-terminal substitution on DNA/protein binding and biological activities

The newly synthesized ligands (HL1-HL3) of 5-methoxyisatin thiosemicarbazone with different N-terminal substituents and their copper(II) complexes 1-3 respectively were exposed to spectral and structural characterization. The spectral studies reveal that the ligands show a tridentate mode of binding (ONS donor) with Cu (II) to form square planar complexes. The crystal structure of the ligand HL1 and complex 1 were confirmed by single crystal XRD. The compounds were subjected to DNA/BSA interaction studies using electronic and fluorescence spectroscopic techniques. The binding studies showed that, the complexes (1-3) were able to bind with DNA/BSA macromolecules with good binding constant. In which 1 (K-b = 0.83 x 10(5) M-1) shows good interaction with the DNA while 3 shows better interaction with BSA (K-b = 2.4 x 10(5) M-1). The complexes (1-3) were also tested for antimicrobial activity, radical scavenging activity and in vitro anti-proliferative activity. Complex 3 have shown potent efficacy with broad spectrum antimicrobial activity against the microorganisms, whereas the complex 1 has shown decent scavenging properties compared to the reference drug (ascorbic acid) with an IC50 value of 19.23 +/- 1.05 mu M. Further the, anti-proliferative activity study revealed that, the complex 1 has exhibited broad spectrum activity against MCF-7, A549 and HeLa with IC50 values 14.83 +/- 0.45 mu M, 17.88 +/- 0.16 mu M and 6.89 +/- 0.42 mu M, respectively compared to standard drug Doxorubicin.