Lanthanide Complexes with Heteroditopic Ligands as Fluorescent Zinc Sensors

Abstract

International audienceWe report the synthesis of two ligands containing a DO3A unit (H3DO3A = 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 Ln3+ complexes in solution that respond to the presence of Zn2+ ions. The Eu3+ and Gd3+ complexes have been characterized by using a combination of experimental and theoretical techniques that include absorption and emission electronic spectroscopy, NMR spectroscopy, 1H relaxometry, and DFT calculations. The Ln3+ 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 Eu3+ complexes in H2O and D2O and relaxometric measurements point to the absence of inner-sphere water molecules. The addition of Zn2+ causes important changes in the absorption spectra of the complexes that evidence the formation of both 1:1 and 2:1 (Ln3+/Zn2+) complex species. However, the emission lifetimes of the Eu3+ complexes and relaxivity experience weak changes, thus indicating that Zn2+ addition does not significantly affect the number of coordinated water molecules. The Gd3+ complexes show a weak emission band at 325 nm, the intensity of which dramatically increases in the presence of Zn2+. However, the “turn-on” behaviour induced by Zn2+ is not observed for other metal cations such as Ca2+, Mg2+ or Cu2+. DFT calculations indicate that a photoinduced electron-transfer (PET) process is responsible for the quenching of the luminescence in the absence of Zn2+

Responsive, Water‐Soluble Europium(III) Luminescent Probes

“…An attempt to design a more selective zinc probe was made by Tripier, based on a 9--N3 core as a binding site for Zn 2+ . [16] This Zn--binding site tends to favour a distorted tetrahedral coordination environment, disfavouring the binding of square--planar copper (II), in the case of [Eu.2] and [Eu.3] [16] . No change in the Eu hydration state occurred on zinc binding, and only [Eu.2] showed a variation in the ΔJ = 2/ΔJ = 1 emission intensity ratio.…”

The design of TACN-based molecular systems for different supramolecular functions

“…Presumably, the 1:1 complex formed between 12 and Zn 2+ , with the divalent metal ion bound to the iminodiacetate moiety, allows for the binding of the oxo-anions to the Eu 3+ centre in a common coordination mode and the consequent modulation of the emission spectrum. A spectral form of the total emission spectrum similar to the case of inorganic phosphate was observed following the addition of phosphorylated serine (Ser), thyrosine (Tyr) and threonine (Thr) (stability constant for binding each O-P-aminoacid was evaluated to be log K = 4.80) to a H2O/MeOH (1: An interesting use of lanthanide complexes of TACN derivatives as chemosensors for metal cations has been reported by Platas-Iglesias, Tripier and co-workers [30]. They have synthesized the two heteroditopic ligands H3L8 and H3L9 featuring a DO3A unit (H3DO3A = 1,4,7,10-tetraazacyclododecane-1,4,7-triacetic acid) linked to a TACN moiety by a 2,6dimethylpyridine spacer.…”

Detection of Copper(II) in Water by Methylene Blue Derivatives

“…A large variety of fluorimetric and colorimetric chemosensors and chemodosimeters for transition metal ions and particularly for copper(II) have been described in the last decades [38–43] . They are often characterized (at least in principle) by cost‐effectiveness and easy handling in addition to sensitivity and selectivity.…”