New amino acid-based thiosemicarbazones and hydrazones: synthesis and evaluation as fluorimetric chemosensors in aqueous mixtures

Abstract

A series of new phenylalanine derivatives bearing thiosemicarbazone and hydrazone units at the side chain were synthesised and evaluated as fluorimetric chemosensors for ions. They were tested for the recognition of organic and inorganic anions, (such as AcO-, F-, Cl-, Br-, I-, ClO4-, CN-, NO3-, BzO-, OH-, H2PO4- and HSO4-) and of alkaline, alkaline-earth, and transition metal cations, (such as Na+, K+, Cs+, Ag+, Cu+, Cu2+, Ca2+, Cd2+, Co2+, Pb2+, Pd2+, Ni2+, Hg2+, Zn2+, Fe2+, Fe3+ and Cr3+) in acetonitrile and its aqueous mixtures in varying ratio through spectrofluorimetric titrations. The results indicate that there is a strong interaction through the donor N, O and S atoms at the side chain of the various phenylalanines, with higher sensitivity for Cu2+, Fe3+ and F- in a 1:2 ligand-ion stoichiometry. The photophysical and metal ion sensing properties of these phenylalanines suggest that they can be suitable for incorporation into peptidic chemosensory frameworks.