Stoichiometry of An(III)–DMDOHEMA complexes formed during solvent extraction

N,N’-Dimethyl,N,N’-dioctylhexylethoxymalonamide (DMDOHEMA) is used to separate An(III) and Ln(III) from fission products in several liquid–liquid extraction processes that aim at recycling actinides. The stoichiometry of the extracted complexes is important for a complete understanding of the processes. The presented work focuses on the complexation of Cm(III) with DMDOHEMA studied by TRLFS in mono- and biphasic (solvent extraction) systems. The formation of [Cm(DMDOHEMA)n]3+ (n = 1–3) in 1-octanol containing 1.7 mol L−1 of water with log β’1 = 2.6 ± 0.3, log β’2 = 4.0 ± 0.5, log β’3 = 4.3 ± 0.5 was confirmed. In addition, fluorescence lifetime measurements indicated the formation of a 1 : 4 complex. Furthermore, solvent extraction experiments were performed, varying the proton and nitrate concentrations. TRLFS measurements of organic phases confirmed the existence of two species, [Cm(DMDOHEMA)3(NO3) (H2O)1–2]2+ (dominant at high proton and nitrate concentrations) and [Cm(DMDOHEMA)4(H2O)]3+ (dominant at low proton and nitrate concentrations). To support the proposed stoichiometries, vibronic sideband spectroscopy (VSBS) was employed, allowing the observation of vibrations of functional groups coordinated to the probed metal ion. Clear differences between the vibronic side bands of the 1 : 3 and 1 : 4 complex in the range of 900–1300 cm−1 were observed. Vibrational spectra calculated by DFT complimented the experimental data and confirmed the proposed stoichiometries. They revealed a monodentate coordination mode of the nitrate and two water molecules in the 1 : 3 complex

Influence of carbonate on the complexation of Cm(III) with human serum transferrin studied by time-resolved laser fluorescence spectroscopy (TRLFS)

The complexation of Cm(III) with transferrin is investigated in the pH range from 3.5 to 11.0 in the absence of carbonate and at c(carbonate)tot = 25 mM. In the absence of carbonate two Cm(III) transferrin species I and II are formed depending on pH. An increase of the total carbonate concentration favors the formation of the Cm(III) transferrin species II with Cm(III) bound at the Fe(III) binding site of transferrin at significantly lower pH values. The spectroscopic results directly prove that carbonate acts as a synergistic anion for Cm(III) complexation at the binding site of transferrin. At c(carbonate)tot = 25 mM the formation of the nonspecific Cm(III) transferrin species I is suppressed completely. Instead, three Cm(III) carbonate species Cm(CO3)+, Cm(CO3)2- and Cm(CO3)33- are formed successively with increasing pH. The formation of Cm(III) carbonate species results in a decreased fraction of the Cm(III) transferrin species II at pH [greater-than-or-equal] 7.4 which indicates that carbonate complexation is an important competition reaction for Cm(III) transferrin complexation at physiological carbonate concentration

Interaction of Cm(iii) and Am(iii) with human serum transferrin studied by time-resolved laser fluorescence and EXAFS spectroscopy

The complexation of Cm(iii) with human serum transferrin was investigated in a pH range from 3.5 to 11.0 using time-resolved laser fluorescence spectroscopy (TRLFS). At pH [greater-than-or-equal] 7.4 Cm(iii) is incorporated at the Fe(iii) binding site of transferrin whereas at lower pH a partially bound Cm(iii) transferrin species is formed. At physiological temperature (310 K) at pH 7.4{,} about 70% of the partially bound and 30% of the incorporated Cm(iii) transferrin species are present in solution. The Cm(iii) results obtained by TRLFS are in very good agreement with Am(iii) EXAFS results{,} confirming the incorporation of Am(iii) at the Fe(iii) binding site at pH 8.5