Anion-induced deprotonation as a simple strategy to improve analytical performance of an amphiphilic probe at mesoscopic interface

Abstract

A systematic improvement in the metal ion binding ability of a pyrene functionalized oxidized bisindolyl compound was investigated in the aqueous medium. In water, a color-changing response from orange to red was observed upon the addition of Hg2+ ion. However, in this condition, the compound suffered issues like poor selectivity (interference from Cu2+, Cd2+, and Zn2+) and low sensitivity (∼1.6-fold increment in absorbance). Incorporating nonionic surfactant as solubilizing agent alters the protonation equilibrium of the compound and improves its analytical performance to some extent (∼2.5-fold increment in absorbance by Hg2+ and minor interference from Cu2+ and Zn2+ ions). However, an excellent selectivity (no interference) towards Hg2+ ion was achieved when the probe molecules were undergone anion-induced deprotonation reaction before the interaction with metal ions. Also, the deprotonated receptor demonstrated superior sensitivity for Hg2+ (yellow to red color change, ∼5.2-fold increment in absorbance). Thus, in this work, we have developed anion-triggered deprotonation as an alternative strategy for improving the analytical performance of an oxidized bisindolyl probe.

Keywords

• Surfactant assembly
• Heavy metal pollutants
• Bisindolyl probe
• Naked-eye sensing
• Protonation equilibrium