A Theoretical and Experimental Analysis of the Luminescent Properties of Europium(III) Complex Sensitized by Tryptophan

Basic luminescent and intramolecular energy transfer properties of the Trp-Eu(III) complex in water at different concentrations are reported. Theoretical and experimental results are described and compared, showing good agreement between them, demonstrating that the modeling proposed in this work is appropriate to describe its behavior at the molecular level. The emission spectrum of the Eu(III) ion in water has a very high intensity for the D-5(0) -> (7) F-1 transition, which is hypersensitive to the environment in which it is found. So that the excitation of the Trp at low concentrations at lambda & nbsp;= 295 nm intensifies the signal of this transition through energy transfer from the ligand (Trp) to the Eu(III) ion. In contrast, at high concentrations of Trp, that is 1 and 10 mM, the luminescence of the Eu(III) ion is quenched. The methods use the TD-DFT and (INDO/S-CIS) approximations, working at a non-relativistic quantum chemistry level. The B3LYP functional was selected in the first method and the second, the SPARKLE/RM1 model. Both yield complementary information on the absorption and emission processes. This calculation allows a more detailed analysis of the experimental results based on the molecular orbitals involved in electronic transitions and the possible energy transfer paths. This work contributes to the understanding of the behavior of Eu(III) ion as a probe to study the fluorescence of proteins constituted by biologically important molecules such as Trp in aqueous media.