Selective recognition of Cu²⁺ by di-O-picolyl derivative of 1,1'-methylene-bis(2-naphthol)

Abstract

Di-derivatives of 1,1'-methylene-bis(2-naphthol) (L₁) possessing ester (L₂), carboxylic acid (L₃) or picolyl (L₄) as end groups of the pendants have been synthesized and characterized. Titration of these derivatives for their recognition towards M²⁺ (where M = Mg, Ca, Mn, Fe, Co, Ni, Cu, Zn) were performed by following the fluorescence emission intensities in methanol solution. The picolyl derivative (L₄) has been found to be well suited for Cu²⁺ recognition (=630 ppb) via the formation of 1:1 complex that was further proven based on absorption as well as ESI MS studies. On the other hand, L₁ and L₂ were mainly insensitive towards M²⁺, where as the carboxylic derivative (L₃) shows fluorescence changes with almost all the metal ions and hence none of the L₁, L₂ and L₃ are suited for any M²⁺ recognition. The studies clearly suggested that the chemical nature of the functional groups and the coordination preferences of the metal ion seem to play important role in the selective recognition of the metal ion.