Colorimetric sensing of environmental fluoride contaminants using chemically-reactive triamidoborane ligands

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Project Period: 
Project Investigator(s): 
S. Daly, Department of Chemistry, The University of Iowa

Developing molecular sensors that can accurately detect elevated fluoride concentrations in groundwater is an important, but challenging goal. Fluorosis – a health condition that stems from chronic consumption of excess fluoride from mineral deposits and industrial pollution – results in severely debilitating bone deformations and other life-threatening ailments in many parts of the world. Optical sensors that change color in response to aqueous fluoride would offer an inexpensive method to detect high fluoride levels in drinking water, but there are two challenges that have yet to be fully addressed: (1) selectivity for fluoride over competing analytes, and (2) high binding affinity for fluoride in water. Previous research demonstrated that metal-bound triamidoborane ligands (TBDPhos) can selectively bind fluoride while bound to transition metals. Here we propose to chemically modify our colorless TBDPhos ligands to produce an optical change in response to fluoride binding so they can be used in fluoride sensing applications.

Project Results: 

The research aimed to provide colorimetric sensors that rapidly and selectively detect environmental contaminants in groundwater in Iowa and beyond. Current research funded by CHEEC is focused on detecting excessive fluoride contamination in water stemming from industrial run-off and natural fluoride deposits because excessive fluoride intake can lead to severely debilitating bone deformations and other life-threatening ailments (i.e. fluorosis). While fluoride was the primary focus, it should be emphasized that this research laid the foundation for selectivity detecting other toxic contaminants such as cyanide.

Primary findings made in support of this goal:

  1. Developed new fluorescent metal complexes that bind fluoride. The fluorescence of the metal complexes are quenched upon fluoride binding, yielding an optical response for potential sensing applications.
  2. Prepared new fluoride binding ligands that impart aqueous solubility to metal complexes so they can be used for aqueous detection.
  3. Researchers also gained a better understanding of the role of ligand protonation on fluoride binding, and have computed how ligand protonation and ligand variations affect the free energy of fluoride binding.