Stable Europium(III) Complexes with Short Linkers for Site‐Specific Labeling of Biomolecules

摘要

In this study, two new terpyridine‐based Eu^III complexes were synthesized, the structures of which were optimized for luminescence resonance energy‐transfer (LRET) experiments. The complexes showed high quantum yields (32 %); a single long lifetime (1.25 ms), which was not influenced by coupling to protein; very high stability in the presence of chelators such as ethylenediamine‐N,N,N′,N′‐tetraacetate and ethylene glycol‐bis(2‐aminoethylether)‐N,N,N′,N′‐tetraacetic acid; and no interaction with cofactors such as adenosine triphosphate and guanosine triphosphate. A special feature is the short length of the linker between the Eu^III ion and the maleimide or hydrazide function, which allows for site‐specific coupling of cysteine mutants or unnatural keto amino acids. As a consequence, the new complexes appear particularly suited for accurate distance measurements in biomolecules by LRET.