Fluorescence switch-on sensor for Cu2+ by an amide linked lower rim 1,3-bis(2-picolyl)amine derivative of calix[4]arene in aqueous methanol

A highly selective fluorescence switch on sensor, L for detecting Cu2+ has been synthesized by introducing a bis-(2-picolyl)amine moiety at the lower rim of a calix[4]arene platform via amide linkage. Binding properties of L toward ten different biologically relevant Mn+ ions have been studied by fluorescence and absorption spectroscopy in methanol and aqueous methanol. L was found to detect Cu2+ selectively down to a concentration of 196 and 341 ppb, respectively, in methanol and 1:1 aqueous methanol even in the presence of other metal ions. The composition of the complex has been found to be 1:1 based on the Job plot and is further confirmed by ESI MS. The role of calix[4]arene platform as well as the pre-organized binding core in the selective recognition of Cu2+ has been demonstrated by studying appropriate reference molecules. The possible modes of binding of L with Cu2+ have been modeled by computational calculations. L and its Cu2+ complex could very well be differentiated based on the nano-structural features observed in SEM and AFM.

Graphical abstractA highly selective fluorescence switch on sensor, L for detecting Cu2+ has been synthesized, characterized, and studied for its metal ion binding properties toward ten different biologically relevant Mn+. L was able to detect Cu2+ selectively, down to a concentration of 196 ppb, even in the presence of other ions and forms a 1:1 complex as proven based on absorption and ESI MS. Based on computations, a highly distorted Cu2+ center bound to four pyridyl nitrogens was observed in the complex. L and its Cu2+ complex could very well be differentiated based on the nano-structural features observed in SEM and AFM.Download full-size image