A cationic lanthanide complex binds selectively to phosphorylated tyrosine sites, aiding NMR analysis of the phosphorylated insulin receptor peptide fragment.

The binding of two cationic europium complexes to a differentially phosphorylated insulin receptor peptide has been studied by emission spectroscopy and (31)P NMR and (1)H NMR TOCSY methods. Analysis of the europium emission and NMR spectral data was consistent with the presence of species in slow exchange on the NMR and emission timescales, in agreement with selective binding of the lanthanide ion to the phospho-tyrosine site, allowing such complexes to be considered as prototypical chemoselective paramagnetic derivatising agents.