Luminescence of a novel Eu(diketonato)–epoxiphenanthroline complex and covalent coupling to peptidesvia the epoxigroup

Abstract

The application of rare earth complexes in several techniques and technologies requires their strong, i.e. preferably covalent, fixation to a substrate. The particularly useful luminescence properties of – readily available – rare earth β-diketonate complexes can widely be maintained on co-ligation with an epoxi-functionalised 1,10-phenanthroline. The linkage of epoxidised 1,10-phenanthroline to common peptides and proteins proceeds to free –SH and –NH₂ groups, with a clear preference for –SH. Subsequent luminescence activation with Eu(ttfa)₃ yields strongly emissive species, in which the Eu(ttfa)₃ coordinates to the N-bidentate phenanthroline protruding from the peptide. Luminescence, FTIR, ESI-MS, NMR and life time measurements provide the evidence for successful anchoring of the marker to the peptides. Additionally, the optical properties have been evaluated against analogous Eu complexes in polymer matrices and solution. The procedure described holds the promise of a facile method for the detection of free –SH groups in biological entities and their discrimination from oxidised –S–S– bridges.