Luminescence Resonance Energy Transfer in Heterodinuclear LnIII Complexes for Sensing Biologically Relevant Anions

Abstract

AbstractDinuclear lanthanide(III) complexes of the macrocycles 1,4‐bis[1‐4,7,10‐ tris(carbamoylmethyl)‐1,4,7,10‐tetraazacyclododecane]‐m‐xylene (1) and 1,3‐bis[1‐4,7,10‐tris(carbamoylmethyl)‐1,4,7,10‐tetraazacyclododecane]‐p‐xylene (2) with LnIII = EuIII, TbIII were prepared. Studies using direct excitation (7F0 → 5D0) europium(III) luminescence spectroscopy show that several anions including phosphate, methylphosphate, double‐stranded DNA, a DNA hairpin loop, and fluoride bind to both EuIII centers in Eu2(1) in solutions at pH 7.0, 0.100 M NaNO3. Recovered luminescence lifetime data is consistent with replacement of water ligands by these anions. There are distinct changes in the relative intensities of EuIII emission peaks for complexes of Eu2(1) and Eu2(2) with phosphate, fluoride, carbonate, and phosphate ester ligands. This suggests that the EuIII dinuclear complexes show promise as ratiometric sensors for these anions. In contrast, the emission peak ratios for the Tb2(1) and Tb2(2) complex show a lower response upon binding of each anionic ligand. Luminescence resonance energy transfer (LRET) studies with mixed EuIII/NdIII complexes show that the phosphate complexes of Ln2(1) or Ln2(2) both have LnIII–LnIII internuclear distances of 7.7 ± 0.9 Å and the methylphosphate complexes of Ln2(1) and Ln2(2) have internuclear distances of 7.8 ± 0.6 and 8.0 ± 0.7 Å, respectively. LRET experiments also show the two lanthanide ion centers in Ln2(2) are 8.4 ± 0.5 Å apart when bound to GC rich duplex DNA. None of the other anions (carbonate, fluoride, DNA hairpins) form complexes that show measurable energy transfer between the lanthanide ions, which is consistent with intranuclear distances >8 Å.