In vitro study of the interaction between neptunium ions and aposerumtransferrin by absorption spectrophotometry and ultrafiltration: the case of Np(V)

Abstract

Abstract The interaction between Np(V) and human aposerumtransferrin (apoTf) was studied in vitro under physiological conditions (37°C, pH 7.4, [NaCl]=0.15 M, [HEPES]=5×10-2 M) by UV-visible and near-IR absorption spectrophotometry and by ultrafiltration. It was found that Np(V) was bound in small fraction (<12%) to apoTf, and that the role of carbonate and citrate anions in binding is more competitive than synergistic. The complexes NpO2CO3 - and NpO2Cit2- tend to form rather than the Np(V)-apoTf complex. Np(V) binding on apoTf appears to be pH-dependent and reversible. Displacement experiments with FeIIINTA showed non-specific binding, suggesting a weak interaction between Np(V) and apoTf different from the reactions involving transferrin-specific sites with other metallic ions, such as Fe(III). The low overall charge, the size and the geometry of the linear di-oxocation NpO2 + could account for the weak interaction between Np(V) and human transferrin.