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

A 1,3-alternate calix[4]arene bearing a nitrogen-containing crown cap at one side and a bis(ethoxyethoxy) group at another side has been synthesized. 1 H NMR spectroscopic studies showed that Ag + is bound to the crown-capped side (log K ass. = 9.78: CD 2 Cl 2:CD 3 OD = 4:1 v/v, 30 °C), and the dissociation of Ag + from this cavity is very slow. When the nitrogen atom in the crown ring is protonated with trifluoroacetic acid, Ag + is pushed out to the bis(ethoxyethoxy) side through a π-basic tube of the 1,3-alternate calix[4]arene. The dissociation of the complex from the bis(ethoxyethoxy) side occurs relatively fast. On the other hand, when the nitrogen·H + in the crown ring is deprotonated with Li 2 CO 3 and diazabicycloundecene, Ag + is sucked back to the crown-capped side through the π-basic tube. These chemically-switchable actions well imitate the function of a “syringe”, using the π-basic tube as a pipette and the crown ring as a rubber cap. We believe that this prototype of a “molecular syringe” is a novel molecular architecture for the action of metal cations.