Complexation of bisphosphonates with ytterbium(III): Application of phosphate and ATP detection assay based on Yb-pyrocatechol violet

The coordination chemistry of bisphosphonates with Yb³⁺ was investigated to evaluate the potential of the UV-vis based detection method using the Yb³⁺-pyrocatechol complexation reaction as a sensor for bisphosphonates. The complexation chemistry of Yb³⁺ with phosphate and ATP analogs was previously described (E. Gaidamauskas, K. Saejueng, A.A. Holder, S. Bharuah, B.A. Kashemirov, D.C. Crans, C.E. McKenna, J. Biol. Inorg. Chem. 13 (2008) 1291-1299), and we here studied the complexation chemistry of bisphosphonates in this system. The spectrophotometric assay yields direct evidence for formation of a 4:3 metal to ligand complex at neutral pH. Direct evidence for Yb³⁺:methylenebis(phosphonate) complexes with 1:1 and 1:2 stoichiometry was also obtained by potentiometry at acidic and basic pH. Direct evidence for complex formation was obtained using ¹H NMR spectroscopy although the stoichiometry was not accessed at neutral pH. Our results suggest that the spectroscopic observation of the YbPV complex can be used to conveniently measure concentrations of bisphosphonates down to 2-3 μM.