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.