Lanthanide Complexes Of 2, 6-bis (Benzimidazol-2-yl) Pyridine, Spectroscopic Studies And DNA Binding Studies

In this paper, the meaning and future of transition metal complexes and polypyridyl transition metal complexes, the development of small complexes binding with DNA and the studying of 2,6-bis(benzimidazol-2-yl)pyridine (H2bzimpy) have been discussed.H₂bzimpy has been synthesized rapidly by microwave irradiation and characterized by single crystal X-ray diffraction. It crystallizes in the monoclinic system, with space group P2₁/c. The lattice parameters are: a =1.8840(3), b =1.8446(3), c=1.03400(18) nm, β=104.818(3) °, Z=4, V=3.4739(10)nm³.The luminescence intensity of H₂bzimpy exhibits an obvious enhancement when DNA is added in the solvent of DMF and methanol. However, the luminescence intensity decreases when DNA is added in the solvent of acetone and CH₃CN. The distance between both neighboring base plans decreases in acetone and CH3CN. And DNA shrinks further. Finally, the conformation of DNA historians formed from B form to A form. Although the conformation of DNA changes in organic solvents, it does not denatured or dehelix.The coordination compounds of Eu(â…¢) and Dy(â…¢) with 2,6-bis(benzimidazol-2-yl)pyridine were synthesized and characterized by NMR, infrared spectroscopy and elemental analysis etc. And the binding of Eu(â…¢) and Dy(â…¢) complexes with calf thymus DNA have also been investigated by absorption, luminescence titration and viscosity measurements. The Eu(â…¢) complex [Eu(H₂bzimpy)(Hbzimpy)(NO₃)] (NO₃), where H₂bzimpy is a planar ligand with an extended aromatic system, has been found to bind to DNA with an apparent binding constant of (2.08 ±0.02)×10⁴ mol^-1.L. The effect of [Eu(H₂bzimpy)(Hbzimpy)(NO3)](NO3) on the viscosity of DNA clearly shows that the Eu(III) complex partly intercalate into the DNA base pairs. The result of absorption titration indicates that the complex binds to DNA with moderate strength. Fluorescence study shows that the fluorescence intensity of the complex decreases with increasing concentrations of DNA, which is due to the photoelectron transfer. The salt effect of Eu(III) complex shows that it doesn't bind with DNA by surface banding. The experimental results show that Eu(III) complex could partly intercalates into DNA base pairs via the ligand H2bzimpy. To the Dy(III) complex, [Dy(Hbzimpy)2](NO3), absorption titration shows that the complex binds to DNA with an apparent binding constant of (3.74±0.02)X 104 mol'1 ? L. The experiment results of fluorescence study viscosity measurements and salt effects of Dy(III) complex indicate that this complex bind to DNA through a partial intercalative mode, which is the same with Eu(III) complex. In summary, the results show that Dy(III) complex also could partly intercalates into DNA base pairs via the ligand H2bzimpy.In addition, the UV spectra and fluorescence spectra of H2bzimpy and [Dy(Hbzimpy)2](NO3) are very sensitive to solution pH, especially for the complex of Dy (III). Since the complex acts as dibasic acids, in which N-H protons on benzimidazole moieties are responsible for a deprotonation site. Both reduction potentials are strongly dependent on the solution pH, which leads to the basis of a proton-induced molecular switch. In inverse, the deprotonation of N-H protons can influence the electric charge distribution, electrochemical behavior and spectra property.