Molecular Design of a "Molecular Syringe" Mimic for Metal Cations Using a 1,3-Alternate Calix[4]arene Cavity

The chemically switchable actions well imitate the function of a "molecular syringe," has been studied in theory using the 1,3-alternate calix [4]arene bearing a nitrogen-containing crown cap at one side and a bis(ethoxyethoxy) group at another side by the pi-basic calixtube as a pipette mid the crown ring as a rubber cap The model is characterized by geometry optimization using density functional theory (DFT) at B3LYP/6-31G level The obtained optimized structures are used to perform natural bond orbital (NBO) and frequency analysis The electron-donating heteroatoms O and N offer Ione pair electrons to the contacting RY* (1-center Rydberg) or LP* (1-center valence antibond Ione pair) orbitals of K+, Ag+ The results indicate that when the nitiogen atom in the crown ring is protonated. K+ and Ag+ will be pushed out to the bis(ethoxyethoxy) side through a pi-basic calixtube When the nitrogen H+ in the crown ring is deprotonated. K+ and Ag+ are sucked back to the crown-capped side again In the course of the coordination, both the intermolecular electrostatic interactions and the cation-pi interactions between the metal ion and pi-orbitals of the two parts facing inverted benzene rings play a significant role It is believed that this prototype of a "molecular syringe" is a novel molecular architectuie for the action of metal cations (C) 2010 Wiley Periodicals. Inc. J Comput Chem 31 2143-2156. 2010