Pillar[5]arenes Bearing Amide and Carboxylic Groups as Synthetic Receptors for Alkali Metal Ions

Pillar[5]arenes bearing amide and carboxylic groups have demonstrated recognition performance for some representative alkali metal ions including Li+, Na+, K+ and Cs+ in series cations of s- and d-metals compared to pillar[5]arenes with hydroxyl, methoxy and acetone fragments. Their complexation abilities toward these cations were evaluated by UV-Vis technique. The complexation results revealed that pillar[5]arene, containing glicylglicyne groups, were the most efficient cation receptors for Li+, Na+, K+ and Cs+ over other synthesized and studied pillar[5]arenes. Introduction of long glycylglycide fragments into macrocycle structure allowed to increase the association constant logarithm in the case of L-i+ by 2 orders. In addition, in the set of macrocycles, incorporation of the additional amide fragments and carboxyl group into macrocycle structure leads to increasing the binding efficiency with alkali metal cations.