Lanthanide induced linkage of phosphorylated organic acids

Lanthanides have become a useful tool in NMR spectroscopy within the last 40 years. Due to their paramagnetic properties they can be utilized as probes to determine the binding sites of biologically or environmentally relevant organic molecules as they cause significant line broadenings and / or paramagnetic induced shifts.
In our former and actual research we investigate the interactions between actinides and biomolecules, revealing the structure as well as thermodynamic and kinetic behaviour. Lanthanides can easily be used as inactive analogues for trivalent actinides in consequence of their similar chemistry.
We found out that lanthanide ions are able to act as linkers to build up polymeric structures of bifunctional organic acids such as phosphorylated amino acids. For instance, in the case of O-phospho-L-serine the lanthanide ions can serve as a bridge between the carboxylate and the phosphate group of two amino acid molecules to form macromolecules with repetitive units. Solid state NMR spectroscopy was the most feasible tool for structure elucidation, proving that both the phosphate and the carboxylic group are involved in the complexation. By means of 1D and 2D methods it was confirmed that both functional groups lose their protons and, thus, must be the binding sites for the lanthanides, whereas the protons of the amino group are unaffected.
The interactions between the lanthanides (Eu3+, La3+) and the phosphorylated acids can be monitored by solution 31P-NMR spectroscopy and confirmed by dynamic light scattering. After mixing the reactants, colloids are formed immediately. After some minutes up to hours the formed aggregates precipitate. Different temperature, pH and ionic strength conditions may be object of further investigations.