The separation of f-elements from alkaline high-level nuclear waste remains a significant challenge due to the need to reduce waste volume and mobility. Fluorescence sensing offers a promising approach for monitoring these elements during extraction. Previous work from our group demonstrated that o-sulfonamidophenol ligands can both extract and sense Ln(III). These ligands show strong binding and “turn-on” fluorescence sensing. We synthesized a dansyl sulfonamide that detected trace Sm(III) in NaOH/CH₃CN, showing a threefold increase in fluorescence due to chelation-enhanced fluorescence (CHEF). To further this study, we prepared additional ligands using the o-sulfonamidophenol framework, including the organic-soluble dabsyl o-sulfonamidophenol, N-(5-(tert-butyl)-2-hydroxyphenyl)-4-[[4-(dimethylamino)phenyl]diazenyl]benzenesulfonamide. UV-Visible titrations were carried out at constant ligand and NaOH concentrations, with sole variable the concentration of the Ln(III). Upon addition of Ln(III) nitrate salts (5.0 x 10^-4M) to the dabsyl sulfonamide (1.0 x 10^-5M) in acetonitrile containing 2.2 eq. of NaOH spectroscopic changes were observed for Eu(III), La(III) and Nd(III). Binding constants were obtained from the binding data by non-linear regression analysis using the HypSpec® program. Fluorescent changes were observed upon titrating Eu(NO₃)₃(4.0 x 10^-3 M) with the dabsyl sulfonamide (8.0 x 10^-3 M) in CH₃CN with 2.2 eq. of NaOH. Furthermore, a water-soluble dansyl o-sulfonamidophenol ligand containing sulfonate groups was also synthesized and characterized. The binding and sensing properties of the synthesized ligands were studied by UV-Vis and fluorescence titrations. Non-linear regression analysis of the binding data and Job plots provided insight into Ln(III) binding affinities and complexation stoichiometry.

Anthony DeSimone

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