Thienopyrimidine-derived multifunctional fluorescence sensor for the detection of Cu2+, Fe3+, and PPi in different solvents

Abstract

Hydrazine substituted thienopyrimidine, a new fluorophore, was used to synthesize a novel Schiff base R1 as a chemosensor via the condensation with p-formyltriphenylamine, and the structure was confirmed using nuclear magnetic resonance spectroscopy (NMR) and mass spectrometry (MS) analysis. When treated with Cu²⁺ in dimethylsulfoxide (DMSO)/H₂O buffer, R1 showed a phenomenon of fluorescence quenching, which was reversible with the action of ethylenediaminetetraacetic acid (EDTA). When treated with Fe³⁺ in dimethylformamide (DMF)/H₂O buffer, R1 exhibited the same phenomenon, but fluorescence was recovered with inorganic pyrophosphate (PPi) quantitatively. The complexation ratios for R1-Cu²⁺ and R1-Fe³⁺ were both 1:2, which were manifested by MS titrations and corresponding Job's plots. The limits of detection of R1 for Cu²⁺ and Fe³⁺ were 3.11 × 10^-8 and 1.24 × 10^-7 M, respectively. The sensing mechanism of R1 toward Cu²⁺ and Fe³⁺ was confirmed using density functional theory calculations and electrostatic potential analysis. Test strips of R1 were fabricated successfully for on-site detection of Cu²⁺ and Fe³⁺. In addition, R1 was applied to recognize Cu²⁺ and Fe³⁺ in actual water samples with satisfactory recovery.

Keywords: Schiff base; fluorescence probe; thienopyrimidine; transition metal.