Structure of a di-zinc complex of a bis-calix[4]arene conjugate and its sensing of cysteine among the amino acids

Abstract

A triethylene glycol di-imine locked triazole linked bis-calix[4]arene conjugate (L) and its Zn2+ complex [Zn2L], were synthesised, characterised and the three-dimentional (3-D) structure of the complex was established by single crystal XRD. In this complex, the Zn2+ centre exhibits distorted tetrahedral geometry with N2O2 binding core. The complex showed selectivity towards cysteine (Cys) with greater sensitivity followed by histidine (His) among the naturally occurring amino acids studied based on fluorescence and absorption spectroscopy. The fluorescence quenching of the complex is much greater with Cys as compared to that of His. The detection limit of Cys is 650 ppb. Release of Zn2+ from its complex [Zn2L] followed by its capture by –SH containing molecules was shown based on absorption and emission spectroscopy. This was also shown in one case by 1H NMR spectroscopy.