A highly fluorescent zinc complex of a dipodal N-acyl hydrazone as a selective sensor for H2PO4− ions and application in living cells

Abstract

A dipodal N-acyl hydrazone receptor (R1) was synthesized in a single step, and utilized as a test probe for the selective sensing of metal ions as well as anions. Upon the exposure to various metal ions, R1 displays rapid colorimetric and absorption changes in the presence of Co²⁺, Ni²⁺, Cu²⁺ and Zn²⁺ ions. However, R1 shows a selective fluorescence response only in the presence of Zn²⁺ ions and no other metal ions showed obvious changes. In particular, zinc acetate showed higher sensitivity over other zinc sources. Upon the binding of Zn²⁺ ions with R1, the colorless solution changed into fluorescent yellow color accompanied by the conversion of the non-fluorescence nature into the highly fluorescence nature. The in situ formed R1–Zn²⁺ complex was further explored for the reversible recognition of H₂PO₄⁻ ions selectively over other anions such as F⁻, Cl⁻, Br⁻, AcO⁻, CN⁻, HSO₄⁻ and NO₃⁻ ions. A strong and enhanced emission at 502 nm and 534 nm corresponding to the R1–Zn²⁺ complex was quenched completely in the presence of H₂PO₄⁻ ions. Relay recognition of different phosphates such as mono, di and tri basic phosphate ions was also tested. Furthermore, R1 has good cell permeability and could serve as a bioprobe in living cells for the intracellular uptake of Zn²⁺ and H₂PO₄⁻ ions. Time dependent density functional (TDDFT) calculation has been performed to demonstrate the binding of Zn²⁺ ions with R1.