LAUSR

Abstract The binding of the lanthanum(III) complex containing 1,10-phenanthroline (phen), [La(phen) 3 Cl 3 ·OH 2 ], to DNA is investigated by absorption and emission methods. This complex shows absorption decreasing in a charge transfer band, and fluorescence decrement when it binds to DNA. Electronic absorption spectroscopy (UV–Vis), fluorescence spectra, iodide quenching experiments, salt effect and viscosity measurements, ethidium bromide (EB) competition test, circular dichroism (CD) spectra as well as variable temperature experiments indicate that the La(III) complex binds to fish salmon (FS) DNA, presumably via groove binding mode. The binding constants (K b ) of the La(III) complex with DNA is (2.55 ± 0.02) × 10 6  M −1 . Furthermore, the binding site size, n, the Stern–Volmer constant K SV and thermodynamic parameters; enthalpy change (ΔH 0 ) and entropy change (ΔS 0 ) and Gibb's free energy (ΔG 0 ), are calculated according to relevant fluorescent data and the Van't Hoff equation. The La(III) complex has been screened for its antibacterial activities by the disc diffusion method. Also, in order to supplement the experimental findings, DFT computation and NBO analysis are carried out.