Photoluminescence studies of a Terbium(III) complex as a fluorescent probe for DNA detection

The photoluminescence properties of a Tb(III) complex of the form [Tb(phen)2Cl3·OH2] (phen=1,10-phenanthroline) in different solvents are presented. It shows the characteristic luminescence of the corresponding Ln3+ ion in the visible region. The emission intensity of this complex in coordinating solvent is higher than non-coordinating one. The suggested mechanism for the energy transfer between the ligand and Tb3+ ion is the intramolecular energy transfer mechanism. The interactions of the Tb(III) complex with fish salmon DNA are studied by fluorescence spectroscopy, circular dichroism study and viscosity measurements. The results of fluorescence titration reveal that DNA strongly quenches the intrinsic fluorescence of the complex through a static quenching procedure. The binding constant (Kb) of the above metal complex at 25 °C is determined by the fluorescence titration method and it is found to be (8.06±0.01)×103 M−1. The thermodynamic parameters (ΔH0>0, ΔS0>0 and ΔG0<0) indicate that the hydrophobic interactions play a major role in DNA-Tb complex association. The results support the claim that the title complex bonds to FS-DNA by a groove mode.