Influence of Lanthanide(III) Ions on the Reaction System Tryptophan—H2O2–Fe(II)

Abstract

Chemiluminescence (CL) studies were carried out with luminescent lanthanide ions as probes to a tryptophan-oxidation reaction at pH∼6. The redox system consisted of tryptophan, hydrogen peroxide, and Fe(II) ions (catalysts ofH2O2decomposition). The luminescent lanthanide(III) ions used were Eu(III), Tb(III), Gd(III), and Dy(III). In the case of the reaction system with the Tb(III) ion a significant increase in the chemiluminescence intensity and its duration was observed over the other Ln(III) ions. The CL spectrum registered for this system shows emission bands typical of Tb(III) ions with maxima atλ∼490 and 550 nm, corresponding to the electronic transitions of5D4→7F6and5D4→7F5, respectively. The presence of emission bands characteristic of the Ln(III) ions was also observed in the systems containing Eu(III) and Dy(III) ions. These studies revealed a strong influence of the chemiluminescence intensity associated with the tryptophan oxidation, on the concentration of Ln(III) ions. On the basis of the results obtained, a possible mechanism is proposed for reaction of the systemml: Ln(III)—tryptophan—H2O2–Fe(II), taking into consideration an energy transfer process from the tryptophan oxidation products to the Tb(III), Dy(III), or Eu(III) ions.