With the aim of developing selective transmembrane anion transporters, we have revisited the properties of a family of phosphonium boranes of general formula [p-RPh2P(C6H4)BMes2]+ (R = alkyl or aryl group) which we developed several years ago as water compatible fluoride anion sensors. In this new effort, we have synthesized additional examples of such boranes and have systematically varied the size of the R group as a way to modulate their lipophilicity and membrane insertion properties. These synthetic efforts have been coupled with anion transport experiments carried out in phospholipid vesicles. These experiments reveal that the above mentioned phosphonium boranes are highly selective fluoride anion transporters providing that the lipophilicity of the phosphonium unit does not become excessive. Indeed, the most lipophilic derivatives are also the most Lewis acidic and are thus prone to neutralization by hydroxide anions in water at neutral pH, impairing their ability to interact with other anions. These observations open a new chapter in the chemistry of organoboranes as anion transporters.

Phosphonium boranes for the selective transport of fluoride anions across artificial phospholipid membranes

ACS Fall 2021

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