Experimental and theoretical study of novel polyamine bis(nitrophenylureylbenzamide) receptors with anion and cation interaction capacity

In this work the interaction of three new heterotopic polyamine bis(nitrophenylureylbenzamide) receptors (R = 3A-3C) with anions (A) and cations (M) was analyzed by UV-Vis spectroscopy and theoretical calculations. These receptors are highly pre-organized and form supramolecular complexes R-A at different ratios depending on the anion characteristics (1:1, 2:1, 3:1 and 4:3). The calculated log K values based on UV-Vis absorbance profiles and the structural information obtained from geometry optimizations using Density Functional Theory indicate strong stability in these complexes due to multiple intermolecular interactions between both species. Changes in the absorption band of receptors evidence the interaction with metallic ions forming complexes R-M (1:1) and the theoretical calculations predict the coordination with polyamine and amide groups adopting an aza-crown type conformation surrounding the Cu or Zn atoms. The subsequent formation of ternary complexes R-M-A with acetate showed different spectral changes for R-Cu and R-Zn ligands. The spectral changes with R-Cu ligands allowed to identified and calculated log K values for R-Cu-A and R-Cu-A2 complexes. Moreover, the optimized structures for R-Cu-A and R-Cu-A2 complexes show the coordination of one acetate ion with the metal center and a subsequent interaction of a second acetate with the urea groups in agreement with the experimental results.