Reduced texaphyrin: A ratiometric optical sensor for heavy metals in aqueous solution

Area of Science:

• Analytical Chemistry
• Materials Science
• Supramolecular Chemistry

Background:

• Expanded porphyrins, such as texaphyrins, are known for their use in organic synthesis.
• Metal complexation with texaphyrins typically involves changes in redox state and color in organic solvents.
• Sensing applications in aqueous media are less explored for these systems.

Purpose of the Study:

• To develop a water-soluble sensor system for metal cation detection using texaphyrin.
• To investigate the colorimetric and fluorescent responses of texaphyrin upon metal ion complexation in aqueous solutions.
• To assess the selectivity and sensitivity of the texaphyrin sensor for various metal cations.

Main Methods:

• Utilized an expanded porphyrin, texaphyrin, as the core sensing element.
• Investigated colorimetric changes (red to green) upon metal cation binding in aqueous media.
• Employed techniques including UV-Vis absorption, fluorescence spectroscopy, and HPLC for confirmation.

Main Results:

• Demonstrated naked-eye detectable colorimetric sensing of In(III), Hg(II), Cd(II), Mn(II), Bi(III), Co(II), and Pb(II) within 10 minutes.
• Achieved selective sensing for Hg(II) in competitive analysis scenarios.
• Observed unique ratiometric fluorescence changes with In(III) complexation.

Conclusions:

• Texaphyrin can function as a water-soluble sensor for specific metal cations, exhibiting distinct visual and fluorescent signals.
• The complexation-driven redox behavior of texaphyrin is effective for colorimetric sensing in aqueous environments.
• This system offers a novel approach for detecting less-common metal ions with high selectivity, particularly for Hg(II).