A 1,3-alternate calixarene bearing a nitrogen-containing crown cap at one side and a bis(ethoxyethoxy) group at another side has been synthesized. 1H NMR spectroscopic studies showed that Ag+ is bound to the crown-capped side (log Kass = 9.78: CD2Cl2:CD3OD = 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 calixarene. 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 Li2CO3 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.
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