Cu(II), Mn(II) and Zn(II) Complexes of Anthracene-Affixed Carboxylate-Rich Tridentate Ligand: Synthesis, Structure, Spectroscopic Investigation and Their DNA Binding Profile

Anthracene-affixed carboxylate-rich tridentate ligand containing three new mononuclear complexes, [Cu(acpa)(H2O)(2)].H2O (1), [Mn(acpa)(H2O)(2)] (2) and [Zn(acpa)(H2O)(2)] (3) (H(2)acpa=3-(anthracene-9-ylmethyl-carboxymethyl-amino)-propionic acid), have been synthesized and characterized by various analytical and spectral methods. In methanol, complexes 1-3 have been prepared by carrying out reaction of the ligand H(2)acpa with stoichiometric amounts of CuSO4 . 5H(2)O, MnSO4.H2O and ZnSO4 . 7H(2)O respectively, in the presence of NaOH at ambient temperature. The X-ray crystal structure analysis reveals that complex 1 consists of a distorted square pyramidal copper center, coordinated to one acpa(2-) ligand in a tridentate manner (N,O,O) and two exogenous water molecules. On the other hand, the molecular structures of complexes 2 and 3, optimized by DFT method indicate that their core arrangements around the metal centers are similar to that of 1. In solution, the coordination phenomena of Cu((II), Mn(II) and Zn(II) ions with the ligand H(2)acpa and the structural features of the complexes have been authenticated by UV-Vis and fluorescence titration experiments. The composition of the M-II/acpa(2-) complexes (M=Cu, Mn, Zn) in 1-3 has been observed to be 1 : 1, based on the UV-Vis/fluorescence titration results which are further supported by X-ray crystallography and DFT calculation. Complexes 1-3 are investigated for their binding affinity towards Calf Thymus (CT) DNA in solution at pH similar to 7.5 by UV-Vis and fluorescence spectroscopic methods. From the electronic absorption spectral studies, it has been found that the DNA binding constants of 1-3 are (5.67 +/- 0.32)x10(4) M-1, (2.35 +/- 0.26)x10(4) M-1 and (2.49 +/- 0.33)x10(4) M-1, respectively, following the order 1>3>2. Measurements of viscosity of DNA in the absence and presence of the metal complexes suggest that all three complexes interact with DNA through partial intercalative mode.

Automated summary

Three new mononuclear complexes, [Cu(acpa)(H2O)(2)].H2O (1), [Mn(acpa)(H2O)(2)] (2) and [Zn(acpa)(H2O)(2)] (3), containing anthracene-affixed carboxylate-rich tridentate ligand have been synthesized and characterized. Their binding affinity with CT DNA was confirmed by UV-Vis and fluorescence experiments, indicating partial intercalative mode of interaction.