Fluorescence enhancement of europium(III) perchlorate by benzoic acid on bis(benzylsulfinyl)methane complex and its binding characteristics with the bovine serum albumin (BSA)

Abstract

A novel ligand with double sulfinyl groups, bis(benzylsulfinyl)methane L, was synthesized by a new method. Its novel ternary complex, EuL2.5⋅L′·(ClO4)2⋅5H2O, has been synthesized [using L as the first ligand, and benzoic acid L′ as the second ligand], and characterized by elemental analysis, molar conductivity, coordination titration analysis, FTIR, TG–DSC, 1H NMR and UV–vis. In order to study the effect of the second ligand on the fluorescence properties of rare-earth sulfoxide complex, a novel binary complex EuL2.5·(ClO4)3·3H2O has been synthesized. Photoluminescent measurement showed that the first ligand L could efficiently transfer the energy to Eu3+ ions in the complex. Furthermore, the detailed luminescence analyses on the rare earth complexes indicated that the ternary Eu (III) complex manifested stronger fluorescence intensities, longer lifetimes, and higher fluorescence quantum efficiencies than the binary Eu (III) materials. After introducing the second ligand L′, the fluorescence emission intensities and fluorescence lifetimes of the ternary complex enhanced more obviously than the binary complex. This illustrated that the presence of both the first ligand L and the second ligand L′ could sensitize fluorescence intensities of Eu (III) ions. The fluorescence spectra, fluorescence lifetime and phosphorescence spectra were also discussed. To explore the potential biological value of Eu (III) complexes, the binding interaction among Eu (III) complexes and bovine serum albumin (BSA) was studied by fluorescence spectrum. The result indicated that the reaction between Eu (III) complexes and BSA was a static quenching procedure. The binding site number, n, of 0.60 and 0.78, and binding constant, Ka, of 0.499 and 4.46 were calculated according to the double logarithm regression equation, respectively for EuL2.5⋅L′⋅(ClO4)2⋅5H2O and EuL2.5⋅(ClO4)3⋅3H2O systems.