Simultaneous Quantification of Lanthanoid Ions in Solution by Magnetic Anisotropy-Assisted 19F NMR

Abstract

Lanthanoid are indispensable for modern technologies including high-performance magnets, electronics, renewable energy, and medical imaging. However, their similar ionic radii and chemical properties make it inherently challenging for existing chemical, biochemical, and optical probes to distinguish individual Ln³⁺ ions in mixtures. It is even more difficult to simultaneously quantify multiple Ln³⁺ ions in solution. Due to their distinct magnetic anisotropy, Ln³⁺ ions and their complexes exhibit a wide range of magnetic anisotropies (except for La³⁺, Gd³⁺, and Lu³⁺) and exert differential effects on the NMR signals of nuclear spins surrounding the metal center. Designing high-performance probes for Ln³⁺ ion binding and discrimination is a great challenge because of their high coordination numbers and their tendency to form multiple conformations. Here, we designed and synthesized two chemical-magnetic probes (CF₃-TDA and F-TDA), each containing a ¹⁹F reporter and metal chelating moiety, for simultaneous discrimination and quantification of Ln³⁺ ions in solution thanks to the distinct magnetic anisotropy of Ln³⁺ ions. These probes form stable lanthanoid complexes, generating well-resolved ¹⁹F NMR chemical shifts induced by the distinct magnetic anisotropy of Ln³⁺. This strategy enables the simultaneous identification and quantification of individual Ln³⁺ in mixtures, even in the presence of competing common metal ions. This approach combines the metal-chelating property and distinct magnetic anisotropy for lanthanoid ion quantification by NMR. It provides a conceptually innovative and broadly applicable platform for precise lanthanoid assays, facilitating the monitoring of critical elements in industrial and strategic contexts.