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

## TL;DR

This paper explores how ureido-based receptors interact with anions, showing that certain structures can enhance binding efficiency through cooperative interactions.

## Contribution

The study reveals how preorganized azacalix[4]arene skeletons enable cooperative anion recognition with improved binding efficiency.

## Key findings

- Tetraureido azacalix[4]arene 6 shows improved binding efficiency for carboxylates and phosphate through system cooperativity.
- The complex stoichiometry changes from 1:4 to 1:2 for basic anions in macrocyclic systems.
- Unwanted deprotonation occurs in acyclic systems when interacting with basic anions.

## Abstract

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 NH 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.