Single molecular probe for multiple analyte sensing: Efficient and selective detection of mercury and fluoride ions

A molecular probe based on the newly exploited aldoxime chemistry was designed for the dual sensing of Hg2+ and F− ions. Aldoxime-derived azobenzene-containing probe, (E)-4-((E)-(4-(bis(2-hydroxyethyl)amino)phenyl)diazenyl)benzaldehyde oxime (Azo-2), was synthesized and characterized. Azo-2 exhibited excellent sensitivity and selectivity toward mercury ions through a Hg2+ ion-catalyzed dehydration reaction at pH = 5 in a DMSO/H2O mixture (0.5/9.5, v/v). The probe exhibited a 70 nm red shift in its absorption maximum upon the addition of Hg2+ ions, which was accompanied by a change in the color of the solution from pale yellow to dark violet. Interestingly, Azo-2 also exhibited high sensitivity and selectivity toward F− ions in a DMSO solution, which was achieved by the F− ion-induced deprotonation of oxime-OH and the subsequent formation of an energetically favored HF2− species. A change in the color of the solution from pale yellow to dark red helped detect F− ion visibly. The oxime-fluoride interaction and HF2− formation were confirmed by 1H and 19F nuclear magnetic resonance (NMR) spectroscopy. The oxime anion generated by F− in a DMSO solution was reacted with water molecules to return to the original protonated oxime, proving that the entire process is reversible.

Aldoxime-functionalized azobenzene-based molecular probe was designed and synthesized for the dual sensing of Hg2+ and F− ions.Figure optionsDownload as PowerPoint slide