Publikationsrepositorium - Helmholtz-Zentrum Dresden-Rossendorf

The aerobic soil bacterium Pseudomonas fluorescens (CCUG 32456 A) isolated from the aquifers at the Äspö Hard Rock Laboratory, Sweden secretes pyoverdin-type siderophores. These unique bioligands have a high potential to bind uranium(VI) and curium(III) mainly due to their hydroxamate and catecholate functionalities [1, 2]. However, the interaction of neptunium(V) with pyoverdin-type siderophores is still unknown. In general, Np(V) interactions with natural bioligands are poorly understood. To address this lack, we thus present findings regarding the speciation of the neptunyl cation with pyoverdins in aqueous solution using near-infrared (NIR) absorption spectroscopy over a wide pH range. Np(V)-pyoverdin species of the type MxLyHz could be identified from the spectrophotometric titrations. Remarkable was that the influence of neptunium(V)-pyoverdin species could already be detected under equimolar conditions. The stability constants of these strong neptunyl(V)-bioligand complexes and their individual spectroscopic properties are reported. NIR absorption spectroscopy shows that the Np(V)-pyoverdin species cause a strong red shift of the characteristic NpO2+ absorption band at 980 to 1000 nm. The findings of our Np(V) speciation study with pyoverdins and selected model compounds indicate a stronger affinity of Np(V) to the catechol functionality of the pyoverdin molecules in contrast to for instance their hydroxamate groups.

[1] H. Moll, M. Glorius, G. Bernhard, A. Johnsson, K. Pedersen, M. Schäfer, H. Budzikiewicz, Geomicrobiol. J. 25, 157-166 (2008).
[2] H. Moll, A. Johnsson, M. Schäfer, K. Pedersen, H. Budzikiewicz, G. Bernhard, BioMetals 21, 219-228 (2008).