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Lanthanide Complexes with Heteroditopic Ligands as Fluorescent Zinc Sensors
Author(s) -
Roger Mélissa,
RegueiroFigueroa Martín,
Ben Azzeddine Chams,
Patinec Véronique,
Bonnet Célia S.,
PlatasIglesias Carlos,
Tripier Raphaël
Publication year - 2014
Publication title -
european journal of inorganic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.667
H-Index - 136
eISSN - 1099-0682
pISSN - 1434-1948
DOI - 10.1002/ejic.201301426
Subject(s) - chemistry , lanthanide , molecule , fluorescence , zinc , moiety , luminescence , spectroscopy , metal , coordination sphere , absorption (acoustics) , crystallography , metal ions in aqueous solution , ion , absorption spectroscopy , ligand (biochemistry) , stereochemistry , organic chemistry , materials science , biochemistry , physics , receptor , optoelectronics , quantum mechanics , composite material
We report the synthesis of two ligands containing a DO3A unit (H 3 DO3A = 1,4,7,10‐tetraazacyclododecane‐1,4,7‐triacetic acid) linked to a triazacyclononane (TACN) moiety by a 2,6‐dimethylpyridine spacer designed to form stable Ln 3+ complexes in solution that respond to the presence of Zn 2+ ions. The Eu 3+ and Gd 3+ complexes have been characterized by using a combination of experimental and theoretical techniques that include absorption and emission electronic spectroscopy, NMR spectroscopy, 1 H relaxometry, and DFT calculations. The Ln 3+ ions are eight‐coordinated by the ligand, which binds to the metal ion through the seven donor atoms of the DO3A unit and the nitrogen atom of the pyridyl linker. Luminescence lifetime measurements recorded from solutions of the Eu 3+ complexes in H 2 O and D 2 O and relaxometric measurements point to the absence of inner‐sphere water molecules. The addition of Zn 2+ causes important changes in the absorption spectra of the complexes that evidence the formation of both 1:1 and 2:1 (Ln 3+ /Zn 2+ ) complex species. However, the emission lifetimes of the Eu 3+ complexes and relaxivity experience weak changes, thus indicating that Zn 2+ addition does not significantly affect the number of coordinated water molecules. The Gd 3+ complexes show a weak emission band at 325 nm, the intensity of which dramatically increases in the presence of Zn 2+ . However, the “turn‐on” behaviour induced by Zn 2+ is not observed for other metal cations such as Ca 2+ , Mg 2+ or Cu 2+ . DFT calculations indicate that a photoinduced electron‐transfer (PET) process is responsible for the quenching of the luminescence in the absence of Zn 2+ .