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 Zn(2+) 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 Zn(2+). The resultant fluorescent complex, [ZnL], has been used as a secondary sensing chemo-ensemble for the detection of -SH containing molecules by removing Zn(2+) 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. Cd(2+) and Hg(2+)), as in the metal detoxification process or by ROS (such as H(2)O(2)) 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.

Zn2+‐Ion Sensing by Fluorescent Schiff Base Calix[4]arene Macrocycles

“…The fluorescencei ntensity was found to be linear between 1 10 À6 and 6 10 À8 m Zn 2 + (Figure 4), the LOD value being 0.147 (6) ppb. The fluorescencei ntensity was found to be linear between 1 10 À6 and 6 10 À8 m Zn 2 + (Figure 4), the LOD value being 0.147 (6) ppb.…”

“…[1] In the past few years, effective fluorescent Zn 2 + chemosensors based on salicylidene chromophores have been reported. [6][7][8] Rao et. [3] The p-tert-butyl-calix[4]arenes [4,5] have turned out to be versatile building blocks for the synthesiso fm etal-ion selectivec hemosensors.…”

“…[2] Compared to open chain compounds, macrocyclic sensors display severali mportant advantages.T hus, macrocyclic structures are more rigid than their acyclicc ounterparts, reducing the loss of energy by radiation-lessp rocesses and in turn vibrational relaxation, and can increaset he binding efficiency and recognition selectivity for specific analytes. [6][7][8] Rao et. [6][7][8] Rao et.…”

Synthesis, Complexation and DFT Computational Studies of Bis(naphthyl)methane‐“Capped” Triazole‐Linked Calix[4]arenes as Fe3+ Fluorescent Chemosensors

“…The precursors 3 a , 3 b , and 4 b were all synthesized according to published literature procedures, but a modified literature procedure was used to synthesize 4 a . The 1,1‐bis(azidomethyl)‐2,3‐dimethoxynaphthalene 2 which has not previously been reported was synthesized via the corresponding bromomethyl precursor 1 .…”

Calixarene‐Based Chemosensors by Means of Click Chemistry

“…Rao and co-workers designed and synthesized a triazole-linked imino-thiophenyl calixarene 13. [30] First, the selectivity of 13 towards Zn 2 + ions in the presence of 12 metal ions was studied. In a 1:2 4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid (HEPES) buffer/ethanol mixture at pH 7.4, only the addition of Zn 2 + ions to 13 enhanced the fluorescence intensity, whereas no significant enhancement was observed in the case of other ions as shown in Figure 3.…”