Copper(II) Driven Fluorescence switch-on Detection of Ovalbumin and GSH Using a Pyridoxal 5'-phosphate Derived Tetradentate Schiff Base and its Applications

Abstract

The facile detection of glutathione (GSH) and ovalbumin (OVA) is of great importance in biological research. Herein, a tetradentate Schiff base N, N'-bis(pyridoxal-5-phosphate)-o-phenylenediamine (L) obtained by condensing two moles of pyridoxal 5'-phosphate (PLP) with one mole of 1,2-phenylenediamine was employed for the fluorescence switch-on detection of GSH and OVA. When excited at 389 nm, receptor L showed a weak emission at 454 nm in an aqueous medium. The addition of GSH to the solution of L caused a significant fluorescence enhancement at 454 nm. Amino acids (leucine, glycine, serine, tryptophan, homocysteine, alanine, methionine, arginine and proline) and albumins (bovine serum albumin and OVA) failed to alter the fluorescence profile of L. Receptor L can be applied to detect GSH down to 1.16 µM. However, the fluorescence emission of L was quenched upon the formation of the L-Cu²⁺ complex. The addition of GSH and OVA to the in-situ formed L-Cu²⁺ complex restored not only the fluorescence emission of L but also a noticeable fluorescence enhancement observed at 454 nm. The decomplexation of L-Cu²⁺, along with the interaction of L with GSH and OVA is expected to suppress the conformational flexibility of L that enhanced the fluorescent intensity at 454 nm. Using L-Cu²⁺ complex, the concentration of OVA and GSH can be detected down to 0.31 µM and 0.20 µM, respectively. Molecular docking and dynamics simulation were performed to analyze the binding mode, conformational flexibility and dynamic stability of the L-Cu²⁺-OVA complex. Finally, the analytical novelty of L-Cu²⁺ was examined by detecting GSH/OVA in real biological samples, such as human blood serum, urine, and egg white.

Keywords: Fluorescent Chemosensor; Glutathione; Molecular Dynamics Simulation; Ovalbumin.