Quantification of nitrate-π interactions and selective transport of nitrate using calix[4]pyrroles with two aromatic walls.

Herein we disclose the results of our investigations regarding the interactions between the biologically relevant nitrate oxoanion and several "two-wall" aryl-extended calix[4]pyrroles. There exists a clear relationship between the electronic nature of the aromatic walls of the calix[4]pyrroles and the stability of the nitrate⊂calix[4]pyrrole complex. This suggests that NO3(-)-π interactions have an important electrostatic component. We provide energetic estimates for the interaction of nitrate with several phenyl derivatives. Additionally, we report solid-state evidence for a preferred binding geometry of the nitrate anion included in the calix[4]pyrroles. Finally, the "two-wall" aryl-extended calix[4]pyrroles show excellent activity in ion transport through lipid-based lamellar membranes. Notably the best anion transporters are highly selective for transport of nitrate over other anions.