Synthesis and the characterization of Schiff-base copper complexes: Reactivity with DNA, 4-NPP and BNPP

• We have synthesized new Schiff-base copper complexes.
• Crystal structures for the complexes have been determined.
• Reactivity of the complexes with CT-DNA and plasmid pBR322 DNA has been observed.
• Cleavage of phosphate ester bonds of BNPP and 4-NPP has been demonstrated.

Two new copper Schiff-base complexes have been synthesized and characterized by use of spectroscopic techniques. The Schiff-base ligands, (E)-N-((1-methyl-1H-imidazol-2-yl)methylene)quinolin-8-amine, MICQ and (E)-1-((quinolin-8-ylimino)methyl)naphthalen-2-ol, TL1 were obtained from the reaction of 8-aminoquinoline with 1-methyl-2-imidazolecarboxaldehyde and 2-hydroxy-1-napthaldehyde respectively. The reaction of MICQ with copper(II) chloride produced complex 1, [Cu(MICQ)Cl](PF6), whereas the reaction of TL1 with copper(II) acetate resulted in complex 2, Cu(TL1)(OAc)·CH3OH. The single crystal X-ray structure determination of both complexes show distorted square planar geometries around the copper center. The reactivity of the complexes with calf thymus DNA, CT-DNA and plasmid DNA have been studied using ethidium bromide displacement fluorescence emission, electronic absorption spectroscopy and agarose gel electrophoresis analysis. From the fluorescence emission studies Ksv values of 3.70 × 103 M−1 and 7.82 × 103 M−1 were obtained for complexes 1 and 2, respectively. The absorption titration resulted in Kb values of 1.52 × 105 M−1 for complex 1 and 5.00 × 105 M−1 for complex 2. The results indicate that both complexes significantly interact with CT-DNA and also show cleavage of supercoiled DNA. In addition, complex 2 was found to hydrolyze the DNA model compounds bis(4-nitrophenyl) phosphate, BNPP and 4-nitrophenyl phosphate, 4-NPP.

Copper complexes containing 8-aminoquinoline moiety as part of tridentate ligands.Figure optionsDownload as PowerPoint slide