Simple Molecular Architecture Using Alkylamines, α-cyclodextrin and 18-crown-6 in Aqueous Solution

Abstract

Alkylamines are able to form complexes with α-cyclodextrin and crown ethers. In the case of complex formation with cyclodextrins, the alkyl group is located inside the cavity of the cyclodextrins, whereas the polar group is positioned outside the cavity in contact with water molecules. Crown ether complexes with alkylammonium ions are formed by ion-dipole interactions between the charged nitrogen atom and the oxygen donor atoms of the crown ether. Formation of 1:1:1 complexes between the alkylammonium ions, 18-crown-6, and α-cyclodextrin is therefore observed. Using calorimetric and potentiometric titrations, each individual reaction step can be measured. The experimental results for each individual reaction step are validated using a thermodynamic cycle. The reactions under study typify the self organization of three different species in solution.