Biotin[6]uril Esters: Chloride-Selective Transmembrane Anion Carriers Employing C-H···Anion Interactions.

Biotin[6]uril hexaesters represent a new class of anionophores which operate solely through C-H···anion interactions. The use of soft H-bond donors favors the transport of less hydrophilic anions (e.g., Cl(-), NO3(-)) over hard, stongly hydrated anions (e.g., HCO3(-) and SO4(2-)). Especially relevant is the selectivity between chloride and bicarbonate, the major inorganic anions in biological systems.