NMR-spectroscopic investigation of inorganic and organic lanthanide, actinide and selenium containing complexes found in the environment or in nuclear waste disposals
Radioactive elements can be emitted to the environment for several reasons. There are natural uranium and thorium compounds (and there decay products) in rock formations, which can be released by geologic alteration or mining processes. As a consequence of energy production in nuclear power plants over the last decades, huge amounts of nuclear waste were produced. If this waste is not stored adequately, radionuclides can enter the geo- or biosphere. Studying the transport behaviour of these radioactive elements and their fission products is the key aspect of our research. Here, rocks and natural mineral phases as well as organic molecules as potential binding sites are objects of investigation.
The elements of preferential interest are the actinides (from thorium to americium) as well as the metalloid selenium, a fission product of the uranium-234 decay. The former ones are metals and thus mostly found as cations, whereas the latter one mainly occurs as anions. All these elements possess a high radio- and chemotoxicity. Particularly, uranium and selenium show distinctive redox properties. Lanthanides can easily be used as inactive analogues for trivalent actinides, especially americium can be replaced by the isoelectronic europium.
Both, NMR spectroscopic structure elucidation of environmentally relevant complexes of lanthanides, actinides and selenium as well as the verification of results obtained by other techniques in former studies, are the aims of this work.
The study of large biomolecules such as proteins or humic acids is rather complicated. Therefore, compounds which are themselves potential complexing agents or at least possess structural similarities to larger molecules, are used as model substances, for instance glutathione (a tripeptide) or citrate.
Different one- and twodimensional solution and solid state NMR methods will be applied to dedicated systems, supplied by TRLFS, ATR FT-IR and EXAFS. Where possible, the radionuclides are supposed to be replaced by inactive analogues or isotopes. In the case of selenium, the spin ½ nucleus of Se-77 is well suited to be directly observed by NMR spectroscopy.