Research Group for Bioactinide
Group Leader : Toshihiko Ohnuki
Members : Naofumi Kozai, Fuminori Sakamoto, Shinya Yamasaki, Mingyu Jiang, Shousuke Igarashi

Group Activities

The research objectives of Bioactinides Chemistry Researchgroup are elucidate chemical states change of actinides andlanthanides including nano-particles formation in the biologicalreaction environments. In the year of 2011, chemical stateschange of lanthanides by the transfer of phosphorous ions andelectron from the cells to lanthanides has been studied.

Formation of phosphate nano-particles in the biologicalreaction environmentsPhosphate minerals containing heavy elements of lanthanides
and U are known to be hardly soluble in the aqueous solution
in the environments. Phosphorous is an essential element ofmicroorganisms. The microorganisms store P in their cells.
We have found that yeast, Saccharomyces cerevisiae releases
P in solution containing Ce(III), followed by the formation ofcerium phosphate mineral of monazite [1]. However, not only
mechanism of the formation of REE phosphate mineral, but roleof microorganisms for the formation have not been elucidated.
When the yeast cells are exposed to the solution containing
1.44 × 10 -4 mol/L Yb(III) (heavy REE) for 2-120 h, andtwo months at 25 ± 1 °C at an initial pH of 3, 4, or 5, Yb
concentrations in solutions decreased as a function of exposure
time [2]. Field-emission scanning electron microscopy equippedwith energy-dispersive X-ray spectroscopy (FESEM), andtransmission electron microscopy (TEM) analyses revealed
that nano-sized blocky Yb phosphate with an amorphous phaseformed on the yeast cells surfaces in the solutions with Yb.
These nano-sized precipitates that formed on the cell surfaces
remained stable without changing their size even after twomonths of exposure at 25 ± 1 °C around neutral pHs.
The synchrotron-based extended X-ray absorption finestructure (EXAFS) analysis revealed that the chemical stateof the accumulated Yb on the cell surfaces changed from theadsorption on both phosphate and carboxyl sites at 30 min
to Yb phosphate precipitates at 5 days, indicating the Ybphosphate precipitation as a major post-adsorption process. Inaddition, the precipitation of Yb phosphate occurred on cellsurfaces during 7 days of exposure in Yb-free solution after 2 hof exposure (short-term Yb adsorption) in Yb solution. Theseresults suggest the transformation of the adsorbed Yb to Yb
phosphate precipitates on cell surfaces, even though no P wasadded to the exposure solution. In an abiotic system, the EXAFS
data showed that the speciation of sorbed Yb on the referencematerials, carboxymethyl cellulose and Ln resin, did not changeeven when the Yb was exposed to P solution, without forming
Yb phosphate species. This result strongly suggests that thecell surface of the yeast plays an important role in the Ybphosphate precipitation process, not only as a carrier of thefunctional groups but also as a substrate inducing the nucleationof phosphate nanoparticles.
These results indicate that light and heavy REEs behave
different manner at the biological reaction environments. This
fact stimulates us to investigate the behaviour of series of REEs
at the biological reaction environment. We have a plan to study
on the behavior of series of REEs by yeast.

17 ASRC

Chemical states change of REEs - desferrioxamine B
complexes by Pseudomonas fluorescens and γ-Al2O3
Biological materials possess functional groups able tocomplex with metal cations. Siderophores are microbial
chelating agents produced to solubilize Fe(III). Desferrioxamine(DFO) B is a trihydroxamate siderophore ubiquitously found in
the environment and its interaction with various metal cations
has been studied. We found that at pH 7 negative adsorption
anomaly of Ce on P. fluorescens cells and γ-Al2O3 compared to
the neighbouring REEs(III), La(III) and Pr(III); this was because
the oxidization of Ce(III) to Ce(IV) during complexiation withDFO and the higher stability of the Ce(IV)-DFO complex thanthat of the Ce(III)-DFO complex and the La(III)- and Pr(III)DFO complexes [3].
In this study, we have studied the interactions of REEs (La,Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er) - DFO complexes
with P. fluorescens cells and with γ-Al2O3, at pH 4 – 9. The
higher percent adsorption of REEs was obtained at lower pHs
on P. fluorescens cells and at higher pHs on γ-Al2O3. Degreeof negative anomaly of Ce compared to its neighbouring
REEs, La(III) and Pr(III) decreased with increasing pH. XAFS
analysis showed that Ce exists as the Ce(IV)-DFO complex
in higher pH than 6. Thus, the pH dependence of Ce anomaly
is predominantly dependent on the stability of Ce(IV)-DFOcomplex.

Fig. 1 Degrees of Ce anomaly and Kd(Sm) on P. fluorescens
cells and γ-Al2O3 as a function of pH.The degree of Ce
anomaly for the Kd(REE) patterns was expressed by:
DA = logKd(Ce)-[logKd(La) + logKd(Pr)]/2.
References[1] M. Jiang et al., Chemical Geology, 277, 61(2010).
[2] M. Jiang, Thesis Kyushu Univ. (2012).
[3] T. Ohnuki, T. Yoshida, Chemistry Letters, 41, 98(2011) .