Complex formation of curium(III) with amino acids of different functionalities: L-Threonine and O-Phospho-L-Threonine.

The speciation of curium(III) with L-Threonine and O-Phospho-L-Threonine was determined by time-resolved laser-induced fluorescence spectroscopy (TRLFS) at trace Cm(III) concentrations (3x10-7 M).
Curium species of the type MpHqLr were identified in the L-Threonine- and O-Phospho-L-Threonine system. These complexes are characterized by their individual luminescence spectra and luminescence lifetimes. The following formation constants were determined a) for L-Threonine: log β101 = 6.72 ± 0.07, log β102 = 10.22 ± 0.09, and log β1-22 = -(7.22 ± 0.19) at ionic strength I = 0.5 M and b) for O-Phospho-L-Threonine: log β121 = 18.03 ± 0.13 and log β111 = 14.17 ± 0.09 at ionic strength I = 0.154 M. Possible structures of the identified curium species will be discussed on the basis of the luminescence lifetime measurements and the magnitude of the formation constants.