Triazole appending ruthenium(ii) polypyridine complex for selective sensing of phosphate anions through C–H–anion interaction and copper(ii) ions via cancer cells

Abstract

A new ruthenium(II) polypyridine-based complex, [Ru^II(bpy)₂(Btb)] 2PF₆⁻ (Rbtb) {bpy = 2,2′-bipyridine and Btb = 2-((1-([2,2′-bipyridin]-4-yl)-1H-1,2,3-triazol-4-yl)methoxy)-1,3-benzothiazole}, was constructed using a 1,2,3-triazole linker holding a benzothiazole moiety. The complex was confirmed by FT-IR, ¹H NMR, ¹³C NMR, and mass spectroscopy. The detection properties were thoroughly checked with various anions and cations. The emission spectrum revealed that luminescence is enhanced by H₂PO₄⁻/H₂P₂O₇²⁻ anions by ∼2.3/1.9-fold in CH₃CN and quenched (nearly 80%) by Cu²⁺ ions in CH₃CN/10 mM HEPES buffer (pH = 7.4; 9/1 v/v). The ¹H NMR titration result exhibits basic H₂PO₄⁻/H₂P₂O₇²⁻ anions interacting with acidic triazole C–H, as observed from the downfield shift. The increase and decrease of lifetime obeys the emission result, along with disturbance of the probe structural motif upon binding with anions (mainly by C–H⋯anion interaction) and cations (photoinduced electron transfer), respectively. Better detection limit and binding constant values were obtained for Rbtb upon treatment with H₂PO₄⁻/H₂P₂O₇²⁻ anions (0.22/0.31 μM and 7.7/4.2 × 10⁴ M⁻¹) and Cu²⁺ ions (0.7 μM and 5.11 × 10⁴ M⁻¹). The generation of a new separate redox couple was noticed at 0.94 V and 0.45 V due to the interaction of H₂PO₄⁻/H₂P₂O₇²⁻ anions and Cu²⁺ ions, respectively. The 1 : 1 binding ratio of Cu²⁺ ion with Rbtb was established by mass spectrum, and square-based geometry of Rbtb–Cu²⁺ was identified according to the EPR spectrum (g_‖ > g_⊥ > 2.0023 and A_‖ = 134 × 10⁻⁴ cm⁻¹). Consequently, the luminescence intensity of Ru(bpy)₃ core is further tuned even with the disturbance of the acidic C–H proton of 1,2,3-triazole by H₂PO₄⁻/H₂P₂O₇²⁻ anions. Here, 1,2,3-triazole could not coordinate primarily to ruthenium(II), but bonded directly to the 4th position of 2,2′-bipyridine in the primary ruthenium complex core. Rbtb exhibited low cytotoxicity against MCF-7 cell lines and was used for live-cell imaging of Cu²⁺ ion. The biological study shows that the complex stained the cytoplasm and nuclear membrane of the cells and specifically binds with the metal ion.