Tunable Pnictogen Bonding at the Service of Hydroxide Transport across Phospholipid Bilayers.

Our growing interest in the design of pnictogen-based strategies for anion transport has prompted an investigation into the properties of three simple triarylcatecholatostiboranes ( 1 - 3 ) of the general formula ( o -C 6 Cl 4 O 2 )SbAr 3 with Ar = Ph ( 1 ), o -tolyl ( 2 ), and o -xylyl ( 3 ) for the complexation and transport of hydroxide across phospholipid bilayers. A modified hydroxypyrene-1,3,6-trisulfonic acid (HPTS) assay carried out in artificial liposomes shows that 1 and 2 are potent hydroxide transporters while 3 is inactive. These results indicate that the steric hindrance imposed by the three o -xylyl groups prevents access by the hydroxide anion to the antimony center. Supporting this interpretation, 1 and 2 quickly react with TBAOH·30 H 2 O ([TBA] + = [ n Bu 4 N] + ) to form the corresponding hydroxoantimonate salts [ n Bu 4 N][ 1 -OH] and [ n Bu 4 N][ 2 -OH], whereas 3 resists hydroxide coordination and remains unperturbed. Moreover, the hydroxide transport activities of 1 and 2 are correlated to the +V oxidation state of the antimony atom as the parent trivalent stibines show no hydroxide transport activity.