Complexation of Curium(III) with Hydroxamic Acids Investigated by Time-Resolved Laser-Induced Fluorescence Spectroscopy

The unknown complex formation of Cm(III) with two hydroxamic acids, salicylhydroxamic (SHA) and benzohydroxamic acid (BHA) was studied by time-resolved laser-induced fluorescence spectroscopy (TRLFS). Hydroxamate containing chelating substances have the potential to enhance the solubility and mobility of metals and radionuclides by forming complexes. We explored the fluorescence properties, lifetimes and individual fluorescence emission spectra of the formed Cm(III) hydroxamate species. In both Cm(III)-hydroxamic acid systems a 1: 1 and a 1:2 complex of the type MpLqHr could be identified from the fluorescence emission spectra having peak maxima at 600 and 609 nm, respectively. An indirect excitation mechanism of the Cm(III) fluorescence was observed in the presence of the hydroxamic acids. Consistent stability constants were determined by using either indirect or direct excitation mode of the Cm(III) fluorescence. In the Cm(III)-SHA system, the stability constants are log β111 = 16.52 0.14 and log β121 = 24.09 0.62. The complex formation constants of the Cm(III)-BHA species results to log β110 = 6.52 0.19 and log β120 = 11.60 0.50. The stability constants were compared to those of natural pyoverdins.