Dual-ligand-functionalized dodeca-nuclear lanthanide–tungsten-cluster incorporated selenotungstates and fluorescence detection of dipicolinic acid (an anthrax biomarker)

Abstract

A series of rigid–flexible-ligand functionalized dodeca-nuclear lanthanide–tungsten heterometal cluster incorporated ring-shaped selenotungstates [H₂N(CH₃)₂]₁₆Na₂[Ln₄(H₂O)₆(HPZDA)₂(HFMA)₂W₈O₂₁][B-α-SeW₉O₃₃]₄·29H₂O [Ln = Ce³⁺ (1), Pr³⁺ (2), Nd³⁺ (3); H₂PZDA = 2,3-pyrazine dicarboxylic acid, H₂FMA = fumaric acid] and [H₂N(CH₃)₂]₁₄Cs₂Na₂[Eu₄(H₂O)₆(HPZDA)₂(HFMA)₂W₈O₂₁][B-α-SeW₉O₃₃]₄·30H₂O (4) were prepared by a cooperative strategy of rigid and flexible ligands. The polyanion skeletons of 1–4 comprise an inorganic–organic hybrid dodeca-nuclear [Ln₄(H₂O)₆(HPZDA)₂(HFMA)₂W₈O₂₁]¹⁴⁺ heterometallic cluster surrounded by four trivacant Keggin [B-α-SeW₉O₃₃]⁸⁻ subunits in a rectangle-like arrangement. Based on its fluorescence properties, 4 was used as a fluorescent probe for detecting an anthrax biomarker dipicolinic acid (DPA) with a low limit of detection, and excellent selectivity and anti-interference. The possible fluorescence enhancement mechanism of 4 in the process of detecting DPA may stem from energy transfer from DPA to Eu³⁺ ions in 4, which can be confirmed by decay lifetime measurements of 4 in H₂O and D₂O with and without DPA, and a positive signal of the partial substitution of H₂O ligands on Eu³⁺ ions by DPA ligands. This work proposes a feasible cooperative strategy of rigid and flexible ligands for constructing new structural types of polyoxometalate hybrids, and also provides some meaningful insights into efficient biomolecule detection by utilizing polyoxometalate-based luminescence materials.