Abstract
Herein, a novel N-(4-(tert-butyl)-phenyl)-2-chloroacetamide functionalized thiacalix[4]arene architecture, viz TCAN2PA has been synthesized and the sensing behaviour towards metal ions were explored. The probe, TCAN2PA displayed "turn-on" fluorescence response towards Hg(II) ions in acetonitrile over a series of competing common metal ions. A bathochromic shift in absorption band along with a significant "Turn-On" fluorescence behaviour of TCAN2PA was observed upon interaction with Hg(II) ions. The lower rim modification of thiacalixarene with N-(4-(tert-butyl)-phenyl)-2-chloroacetamide actively contributes toward the fluorescence property due to the presence of strong electron-donating aryl amido substituent. Fluorescence titration experiments were conducted to find out the limit of detection and to understand binding stoichiometry as well. The electron transfer interactions between the electron rich TCAN2PA host with Hg(II) ions have been postulated which is also supported by computational modelling insights.
Highlights
In recent years, there has been a curiosity in the invention of fluorescent sensors for detection of various heavy metal ions concerning its toxicity and negative environmental impact[1,2]
Mercury can be determined by various methods i.e. spectrophotometry[7], neutron activation analysis[8], anodic stripping voltammetry[9], X-ray fluorescence spectrometry[10], electrothermal atomic absorption spectrometry[11], atomic fluorescence spectrometry[12], atomic absorption spectrometry (AAS)[13,14,15], potentiometric ion-selective electrodes[16], inductively coupled plasma mass spectrometry (ICP-MS), capillary electrophoresis and high-performance liquid chromatography (HPLC) and inductively plasma-atomic emission spectroscopy (ICP-AES)[17]
Cation binding by fluorescent sensors occurs through the mechanisms like photo-induced charge transfer (PCT), photo-induced electron transfer (PET)[18,19,20,21], formation of monomer/excimer and recently most of fluorescence resonance energy transfer (FRET)[22]
Summary
There has been a curiosity in the invention of fluorescent sensors for detection of various heavy metal ions concerning its toxicity and negative environmental impact[1,2]. Fluorescence-based measurements are mostly used due to their high sensitivity and simplicity, which converts molecular recognition into actual fluorescence signals. The thiacalix[4]arene assembly has an inherent hydrophobic cavity that allows recognition of various cationic, anionic, and neutral guests[28,29,30,31,32,33]. The selectivity to bind any particular guest or metal ion by thiacalix[4]arene can be controlled by functionalizing with several binding units as amides, acids, imines, esters, amines and thioethers. The thiacalix[4]arene scaffold exhibits many interesting binding features as a chemosensor for metal ions[34]. N-(4-(tert-butyl)phenyl)-2chloroacetamide moiety has been functionalized to the lower rim of the parent thiacalix[4]arene and photochemical measurements including absorption and emission techniques were introduced to investigate its selectivity and sensitivity toward Hg(II) ions. Molecular docking calculation helps to find the bind interaction between TCAN2PA and Hg (II) ions
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