Lanthanide (Ln3+) complexes of bifunctional chelate: Synthesis, physicochemical study and interaction with human serum albumin (HSA)

Abstract

Bifunctional chelate EDTA-bis amide (N,N'-bis (tyramide)ethylenediamine-N,N'-diacetic acid) that has ability to mimic natural amino acids was synthesized and analyzed by various spectroscopic techniques. The physicochemical studies were performed to calculate the various thermodynamic and kinetic parameters for the synthesized poly-amino carboxylate ligand. The two protonation constant (pka's=3.460 and 6.722) of the prepared ligand and stability constants (log KML's=15.8, 18.1, 16.2, 18.4, 17.5, 18.9, 13.6 and 12.8) of the complexes formed with Ce3+, Sm3+, Eu3+, Gd3+, Tb3+, Lu3+, Zn2+ and Cu2+ were determined by potentiometric titration using 0.1M Me4NOH as non-aqueous base. The formation kinetics of [EuEDTA-TA2]+and [CeEDTA-TA2]+was studied and the rate constants were found to be 2.95×10-5s-1 and 4.414×10-5s-1respectively including the exchange reaction of [EuEDTA-TA2]+ with Zn2+ and Cu2+ spectrophotometrically. The Eu(III) complex of EDTA(TA)2 gives three emission bands at 480nm, 540nm and 610nm (λmax=270nm, excitation) which shows efficacy of the ligand as an optical imaging agent. Molecular docking studies with Human Serum Albumin (HSA: PDB 1E78) showed binding pattern with the residues Arg218, Arg222, Lys195 and Lys444 in sub domain II A of site I via hydrogen bond and identifies the ligand-HSA interaction and specific insight for transportation to the target sites. Subsequently, fluorescence spectroscopy was performed at λex=350nm binding constant for HSA was 5.847×104 M-1 which showed effective quenching effect.