Heteroditopic Chiral Uranyl-Salen Receptor for Molecular Recognition of Amino Acid Ammonium Salts

A new heteroditopic chiral uranyl-salen complex incorporating two pyrenyl groups was designed and synthesized for the recognition of ammonium salts, tetrabutylammonium (TBA) and tetramethylammonium (TMA) amino acids. UV/Vis measurements indicate the formation of 1:1 host-guest complexes with high association constants and an excellent enantiomeric discrimination between the two enantiomers of phenylalanine-TMA. T-ROESY NMR experiments confirm cation-pi and CH-pi interactions between the TBA and TMA cations and the two pyrenyl arms, leading to the strong stability of the complexes. This is the first report of a uranyl receptor able to recognize chiral carboxylate guests.