Interaction between the buffer Tris and the eu(III) ion: Luminescence and potentiometric investigation

Abstract

AbstractThe interaction between the buffer 2‐amino‐2‐(hydroxymethyl)propane‐1,3‐diol (Tris) and the Eu(III) ion has been studied by luminescence spectroscopy in D2O. Emission and excitation spectra (5D0←7F0 transition) indicate an interaction with both [TrisH]+ and neutral Tris species. The former is weak and probably of the outer‐sphere type. The latter is of inner‐sphere type and corresponds to the formation of the [Eu(Tris)]3+ species (estimated logK1 = 2.3 ± 0.3). Buffer Tris is also demonstrated to prevent the formation of an Eu‐hydroxo species in the pD range of 7–8. Potentiometric measurements in H2O allowed a more precise calculation of the stability constant: logK1 = 2.44 ± 0.07. Comparison with the data for aliphatic amines and other metal ions lead to the conclusion that the Eu/Tris interaction is mainly achieved through the amino group. 1H‐NMR spectra in presence of Tb(III) ions confirmed both this assumption and the presence of a weak interaction with TrisH+. Quantitative determinations of association constants between lanthanide ions and macromolecules of biological interest performed in presence of Tris should, therefore, be corrected for the Eu/Tris interaction.