Transition metal anion complexation agenst: sensors, molecular carriers and acids-base titrants.

Studies on the noncovalent coordination of anions may be considered to have started in 1968, with early contributions by Park and Simmons, later developed in particular by Schmidtchen and Lehn. After this pioneering start, there was extensive diffusion in 1990s. Since then, design and development of new anion receptors has become a more and more attractive aim. In fact, a full understanding of the reversible intermolecular interaction between a receptor and its complementary anion paves the way toward the availability of high-sensitivity anion sensors, which is particularly interesting for anionic species that are the cause of serious environmental problems. In such cases, stable and reversible receptor–anion complexes could function as carriers of a pollutant anion and thus to remove it from blood, cells, soil, water, and so on. Furthermore, anion transport by receptor–anion carriers through a lipid bilayer membrane by a receptor that can function as a mobile carrier or may form a channel, could find application in biology and medicine.