Photophysical, DFT and molecular docking studies of Sm(III) and Eu(III) complexes of newly synthesized coumarin ligand

Herein, [M(HL)₂(H₂O)₂]NO₃·2H₂O (M = Sm (III) /or Eu (III); HL = 4-(2-hydroxy benzylidene acetohyrazide)-7-hydroxy coumarin) were synthesized and characterized using several spectroscopic methods. The complexes stoichiometry with molar ratio 2L:1M were confirmed by Job's method. Tridentate ligand (HL) was coordinated to the lanthanide ions Sm(III) or Eu(III) through azomethine nitrogen atom, phenolic oxygen of hydrazide, and ketonic oxygen of the amide group. The photophysical properties of the ligand and its complexes were studied in different organic solvents and their fluorescence quantum yields were determined as well. Strong fluorescence emissions to red shifts of europium complex were observed at 580, 593, 617, 653, 693, 704 nm which were attributed to Eu(III) emission of ⁵D₀→⁷F₀, ⁵D₀→⁷F₁, ⁵D₀→⁷F₂, ⁵D₀→⁷F₃, ⁵D₀→⁷F₄, and ⁵D₀→⁷F₅, respectively. First-principles DFT calculations were performed to evaluate the optimized structure and separation energies of the HL compound, using the B3LYP/6-311++g(d,p) basis set. Molecular docking studies were carried out to predict the binding modes between the HL compound and active site of the xanthine oxidase enzyme [EC# (1.17.3.2) PDB ID: 1FIQ] which produced from liver patients of hepatitis C. The observed activity of the HL gave rise to the conclusion that it might exert its action through inhibition of the xanthine oxidase enzyme.