Triazole-linked-thiophene conjugate of calix[4]arene: its selective recognition of Zn²⁺ and as Biomimetic model in supporting the events of the metal detoxification and oxidative stress involving metallothionein

Abstract

Supramolecular calix[4]arene conjugate (L) has been developed as a sensitive and selective sensor for Zn²⁺ in HEPES buffer among the 12 metal ion by using fluorescence, absorption and ESI MS and also by visual fluorescent color. The structural, electronic, and emission properties of the calix[4]arene conjugates L and its zinc complex, [ZnL], have been demonstrated using ab initio density functional theory (DFT) combined with time-dependent density functional theory (TDDFT) calculations. The TDDFT calculations reveal the switch on fluorescence behavior of L is mainly due to the utilization of the lone pair of electrons on imine moiety by the Zn²⁺. The resultant fluorescent complex, [ZnL], has been used as a secondary sensing chemo-ensemble for the detection of -SH containing molecules by removing Zn²⁺ from [ZnL] and forming {Cys/DTT·Zn} adducts as equivalent to those present in metallothioneins. The displacement followed by the release of the coordinated zinc from its Cys/DTT complex by heavy metal ion (viz. Cd²⁺ and Hg²⁺), as in the metal detoxification process or by ROS (such as H₂O₂) as in the oxidative stress, has been well demonstrated using the conjugate L through the fluorescence intensity retrieval wherein the fluorescence intensity is the same as that observed with [ZnL], which in turn mimics the zinc sensing element (MTF) in biology.