Bioinspired Luminescent Europium-Based Probe Capable of Discrimination between Ag+ and Cu. Inorg Chem 2021;60:10791-10798. [PMID: 34236828 DOI: 10.1021/acs.inorgchem.1c01486]

Luminescent lanthanide probes for cations and anions: Promises, compromises, and caveats

The long luminescence lifetimes and sharp emission bands of luminescent lanthanide complexes have long been recognized as invaluable strengths for sensing and imaging in complex aqueous biological or environmental media. Herein we discuss the recent developments of these probes for sensing metal ions and, increasingly, anions. Underappreciated in the field, buffers and metal hydrolysis influence the response of many responsive lanthanide probes. The inherent complexities arising from these interactions are further discussed.

Versatile Macrocyclic Platform for the Complexation of [natY/90Y]Yttrium and Lanthanide Ions

We report a macrocyclic ligand (H₃L⁶) based on a 3,6,10,13-tetraaza-1,8(2,6)-dipyridinacyclotetradecaphane platform containing three acetate pendant arms and a benzyl group attached to the fourth nitrogen atom of the macrocycle. The X-ray structures of the YL⁶ and TbL⁶ complexes reveal nine coordination of the ligand to the metal ions through the six nitrogen atoms of the macrocycle and three oxygen atoms of the carboxylate pendants. A combination of NMR spectroscopic studies (¹H, ¹³C, and ⁸⁹Y) and DFT calculations indicated that the structure of the YL⁶ complex in the solid state is maintained in an aqueous solution. The detailed study of the emission spectra of the EuL⁶ and TbL⁶ complexes revealed Ln³⁺-centered emission with quantum yields of 7.0 and 60%, respectively. Emission lifetime measurements indicate that the ligand offers good protection of the metal ions from surrounding water molecules, preventing the coordination of water molecules. The YL⁶ complex is remarkably inert with respect to complex dissociation, with a lifetime of 1.7 h in 1 M HCl. On the other hand, complex formation is fast (∼1 min at pH 5.4, 2 × 10^–5 M). Studies using the ⁹⁰Y-nuclide confirmed fast radiolabeling since [⁹⁰Y]YL⁶ is nearly quantitatively formed (radiochemical yield (RCY) > 95) in a short time over a broad range of pH values from ca. 2.4 to 9.0. Challenging experiments in the presence of excess ethylenediaminetetraacetic acid (EDTA) and in human serum revealed good stability of the [⁹⁰Y]YL⁶ complex. All of these experiments combined suggest the potential application of H₃L⁶ derivatives as Y-based radiopharmaceuticals.

A new versatile asymmetric ligand based on an 18-membered macrocycle possessing three acetate pendant arms and a benzyl moiety provides fast complexation with both ^natY(III) and ⁹⁰Y(III), as well as slow dissociation kinetics. A detailed structural study in the solid state and in solution evidences nona coordination of the metal ion by the ligand, offering good protection from solvent water molecules. These favorable properties make this ligand an attractive candidate to develop yttrium-based radiopharmaceuticals.

Ratiometric Luminescence Detection of Copper(I) by a Resonant System Comprising Two Antenna/Lanthanide Pairs

Selective and sensitive detection of Cu(I) is an ongoing challenge due to its important role in biological systems, for example. Herein, we describe a photoluminescent molecular chemosensor integrating two lanthanide ions (Tb³⁺ and Eu³⁺) and respective tryptophan and naphthalene antennas onto a polypeptide backbone. The latter was structurally inspired from copper-regulating biomacromolecules in Gram-negative bacteria and was found to bind Cu⁺ effectively under pseudobiological conditions (log K_Cu⁺ = 9.7 ± 0.2). Ion regulated modulation of lanthanide luminescence in terms of intensity and long, millisecond lifetime offers perspectives in terms of ratiometric and time-gated detection of Cu⁺. The role of the bound ion in determining the photophysical properties is discussed with the aid of additional model compounds.