A Dimeric Bis(melamine)-Substituted Bispidine for Efficient Transmembrane H+ /Cl- Cotransport.

A 3,7-diazabicyclo[3.3.1]nonane linking to two melamines is a unique transmembrane H+ /Cl- carrier. In the solid state, the V-shaped compound forms a HCl-bound zig-zag network through cooperative protonation and hydrogen bond interactions. In the lipid membrane, the receptor forms a dimeric self-assembly involving multiple H+ and Cl- leading to the efficient transport of the acid. The pH-dependent Cl- efflux observed for the compound was rationalized based on a gradual protonation model that confers an active transmembrane carrier at physiological pH.