The bisureas demonstrated interesting differences in complexation: the meta,meta and para,para isomers preferred 2 : 1 complexes, while the analogous meta,para isomer formed a 1 : 1 complex.

The repetition of urea-based binding units within the receptor structure does not only lead to monomer properties multiplication. As confirmed by spectroscopic studies, UV-Vis and ¹H-NMR in classical or competitive titration mode, the attachment to a carrier allocates the active moieties to mutual positions predetermining the function of the whole receptor molecule. Bivalent receptors form self-aggregates. Dendritic receptors with low dihydrogen phosphate loadings offer a cooperative complexation mode associated with a positive dendritic effect. In higher dihydrogen phosphate concentrations, the dendritic branches act independently and the binding mode changes to 1:1 anion: complexation site. Despite the anchoring, the dendritic receptors retain the superior efficiency and selectivity of a monomer, paving the way to recyclable receptors, desirable for economic and ecological reasons.

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.