Amplified Recognition of Basic Anions Induced by Cooperative Interaction of Ureido-Binding Sites Preorganized by Azacalix[4]arene Skeleton

High Resolution Image Download MS PowerPoint Slide The reaction of tetranitropolyamino carriers with 4- tert -butylphenyl isocyanate gives rise to ureido-based receptors. These receptors vary in the acidity of their bridging N H groups on supporting skeletons, significantly affecting their complexation ability. While introducing nonbasic anions leads to the independent action of ureido-binding sites, accomplished with low binding efficiency for all studied compounds, the results for basic anions depend on the system used. Here, due to a different electron density distribution on supporting skeletons, the interaction with basic anions may cause unwanted deprotonation (acyclic systems 5 ) or lead to anion complexation (macrocycles 6 and 7 ). Moreover, in the case of tetraureido azacalix[4]arene 6, the addition of carboxylates and phosphate induces system cooperativity, which changes the complex stoichiometry from 1:4 to a 1:2 ratio (receptor: anion) and positively improves binding efficiency.