Two selective fluorescent chemosensors for cadmium ions in 99% aqueous solution: the end group effect on the selectivity, DFT calculations and biological applications

Abstract

Two fluorescent chemosensors for cadmium ions, 2-(2-formylquinolin-8-yloxy)-N,N-diisopropylacetamide (FQDIPA) and 2-(2-formylquinolin-8-yloxy)-N,N-diphenylacetamide (FQDPA), were first assessed in 99% aqueous solutions. The sensor FQDIPA with an end group of an aliphatic amine can recognize Cd²⁺ from other metal ions more selectively and sensitively than FQDPA with that of aromatic amines, which was further demonstrated by DFT calculations that were comparable to the experimental results. It is indeed the distinction between the end groups of these chemosensors that results in the variation of the energy difference between the LUMOs and HOMOs and the interaction energies of FQDIPA·Cd²⁺ and FQDPA·Cd²⁺. Furthermore, the living cell image experiment could also indicate that the FQDIPA is more suitable than the FQDPA in the practical applications in biological systems.