Phosphoryl-containing derivatives of 8-hydroxyquinoline for the selective detection of uranyl cations†

Designing selective ligands for the effective and rapid detection of uranyl cations is a critical problem for nuclear power, environmental, biological, and medical science, and toxicology. It is known that 8-hydroxyquinoline (8-HQ) and phosphoryl-containing ligands effectively bind various metal ions, including the uranyl ion. Due to the effectiveness of 8-HQ and the phosphoryl group, the synthesis of phosphoryl-containing derivatives of 8-HQ and the study of their selectivity towards uranyl ions are of interest. For the first time, phosphoryl-containing derivatives of 8-HQ diphenyl((8-oxyquinolyl)methyl)phosphine oxide (L¹) and bis((8-oxyquinolyl)methyl) phosphinic acid (L²) were synthesized. The crystal structure of L¹ was determined by X-ray analysis. The complexation between the uranyl cation and ligands L¹, L² was studied. The complexes [UO₂(NO₃)₂L¹] (I) and [UO₂(NO₃)₃HL²]·HNO₃·H₂O (II) were synthesized and characterized by elemental analysis, IR and NMR spectroscopy, as well as X-ray analysis. The stability constants of the UO₂²⁺L¹, UO₂²⁺L² and Lu³⁺L¹ complexes in ethanol were determined using spectrophotometric titration. The stability constant of UO₂²⁺L¹ significantly exceeds those of UO₂²⁺L² and Lu³⁺L¹. L¹ shows high selectivity towards UO₂²⁺. A potentiometric sensor based on L¹ was developed for the selective detection of uranyl cations in water with a low measured detection limit of 8.1 × 10⁻⁶ mol L⁻¹. This provides a basis for the effective, rapid, and low-cost detection of UO₂²⁺ ions.