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1. The fluoride transporter FLUORIDE EXPORTER (FEX) is the major mechanism of tolerance to fluoride toxicity in plants1

   https://doi.org/10.1093/plphys/kiab131  

   Tausta, S. Lori; Berbasova, Tanya; Peverelli, Martin; Strobel, Scott A (March 2021, Plant Physiology)

   Abstract Fluoride is everywhere in the environment, yet it is toxic to living things. How biological organisms detoxify fluoride has been unknown until recently. Fluoride-specific ion transporters in both prokaryotes (Fluoride channel; Fluc) and fungi (Fluoride Exporter; FEX) efficiently export fluoride to the extracellular environment. FEX homologs have been identified throughout the plant kingdom. Understanding the function of FEX in a multicellular organism will reveal valuable knowledge about reducing toxic effects caused by fluoride. Here, we demonstrate the conserved role of plant FEX (FLUORIDE EXPORTER) in conferring fluoride tolerance. Plant FEX facilitates the efflux of toxic fluoride ions from yeast cells and is required for fluoride tolerance in plants. A CRISPR/Cas9-generated mutation in Arabidopsis thaliana FEX renders the plant vulnerable to low concentrations (100-µM) of fluoride at every stage of development. Pollen is particularly affected, failing to develop even at extremely low levels of fluoride in the growth medium. The action of the FEX membrane transport protein is the major fluoride defense mechanism in plants. 

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2. Distiboranes based on ortho -phenylene backbones as bidentate Lewis acids for fluoride anion chelation

   https://doi.org/10.1039/D1OB00536G  

   You, Di; Zhou, Benyu; Hirai, Masato; Gabbaï, François P. (June 2021, Organic & Biomolecular Chemistry)

   null (Ed.)

   As part of our efforts in the chemistry of main group platforms that support anion sensing and transport, we are now reporting the synthesis of anitmony-based bidentate Lewis acids featuring the o -C 6 F 4 backbone. These compounds can be easily accessed by reaction of the newly synthesized o -C 6 F 4 (SbPh 2 ) 2 ( 5 ) with o -chloranil or octafluorophenanthra-9,10-quinone, affording the corresponding distiboranes 6 and 7 of general formula o -C 6 F 4 (SbPh 2 (diolate)) 2 with diolate = tetrachlorocatecholate for 6 and octafluorophenanthrene-9,10-diolate for 7 , respectively. While 6 is very poorly soluble, its octafluorophenanthrene-9,10-diolate analog 7 readily dissolves in CH 2 Cl 2 and undergoes swift conversion into the corresponding fluoride chelate complex [ 7 -μ 2 -F] − which has been isolated as a [ n Bu 4 N] + salt. The o -C 6 H 4 analog of 7 , referred to as 8 , has also been prepared. Although less Lewis acidic than 7 , 8 also forms a very stable fluoride chelate complex ([ 8 -μ 2 -F] − ). Altogether, our experiental results, coupled with computational analyses and fluoride anion affinity calculations, show that 7 and 8 are some of the strongest antimony-based fluoride anion chelators prepared to date. Another notable aspect of this work concerns the use of the octafluorophenanthrene-9,10-diolate ligand and its ablity to impart advantageous solubility and Lewis acidity properties. 

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3. Fluoride: Good in Toothpaste, Bad for Plants

   https://doi.org/10.3389/frym.2023.853533  

   Tausta, S. Lori; Auslender, Alysha; Strobel, Scott A.; Hiller, David A. (March 2023, Frontiers for Young Minds)

   Fluorine is the 13th-most abundant element on earth, found most often bound to other elements in its negatively charged form, fluoride. Fluoride compounds are used to improve dental health, to make steel, and to make useful materials like Teflon. Fluoride is also emitted into the environment as a byproduct of both natural and industrial processes. Fluoride even contaminates the fertilizer used to help plants grow. In high amounts, fluoride can be toxic. Single-celled organisms like bacteria protect themselves by making a transporter that specifically removes fluoride from the cell. Yeast have a similar transporter called FEX (fluoride exporter). Bacteria and yeast without these transporters die in the presence of the small amount of fluoride found in tap water. Plants are more complicated, but they also use FEX to keep fluoride from building up inside themselves. Plants without FEX can not make new seeds when grown in normal soil. 

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4. High-throughput discovery of fluoride-ion conductors via a decoupled, dynamic, and iterative (DDI) framework

   https://doi.org/10.1038/s41524-022-00786-8  

   Sundberg, Jack D.; Druffel, Daniel L.; McRae, Lauren M.; Lanetti, Matthew G.; Pawlik, Jacob T.; Warren, Scott C. (May 2022, npj Computational Materials)

   Abstract Fluoride–ion batteries are a promising alternative to lithium–ion batteries with higher theoretical capacities and working voltages, but they have experienced limited success due to the poor ionic conductivities of known electrolytes and electrodes. Here, we report a high-throughput computational screening of 9747 fluoride-containing materials in search of fluoride-ion conductors. Via a combination of empirical, lightweight DFT, and nudged elastic band (NEB) calculations, we identified >10 crystal systems with high fluoride mobility. We applied a search strategy where calculations are performed in any order (decoupled), computational resources are reassigned based on need (dynamic), and predictive models are repeatedly updated (iterative). Unlike hierarchical searches, our decoupled, dynamic, and iterative framework (DDI) began by calculating high-quality barrier heights for fluoride-ion mobility in a large and diverse group of materials. This high-quality dataset provided a benchmark against which a rapid calculation method could be refined. This accurate method was then used to measure the barrier heights for 6797 fluoride–ion pathways. The final dataset has allowed us to discover many fascinating, high-performance conductors and to derive the design rules that govern their performance. These materials will accelerate experimental research into fluoride–ion batteries, while the design rules will provide an improved foundation for understanding ionic conduction. 

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5. Phosphonium Boranes for the Selective Transport of Fluoride Anions across Artificial Phospholipid Membranes

   https://doi.org/10.1002/anie.201914958  

   Park, Gyeongjin; Gabbaï, François P. (February 2020, Angewandte Chemie International Edition)

   Abstract With the view of developing selective transmembrane anion transporters, a series of phosphonium boranes of general formula [p‐RPh₂P(C₆H₄)BMes₂]⁺have been synthesized and evaluated. The results demonstrate that variation of the R group appended to the phosphorus atom informs the lipophilicity of these compounds, their Lewis acidity, as well as their transport activity. Anion transport experiments in POPC‐based large unilamellar vesicles show that these main‐group cations are highly selective for the fluoride anion, which is transported more than 20 times faster than the chloride anion. Finally, this work shows that the anion transport properties of these compounds are extremely sensitive to the steric crowding about the boron atom, pointing to the crucial involvement of the Group 13 element as the anion binding site. 

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