Highly selective colorimetric sensor for Zn 2+ based on hetarylazo derivative Paramjit Kaur a, * , Sandeep Kaur a , Aman Mahajan b , Kamaljit Singh b, * a Department of Chemistry, Guru Nanak Dev University, Amritsar 143 005, India b Organic Synthesis Laboratory, Department of Applied Chemical Sciences and Technology, Guru Nanak Dev University, Amritsar 143 005, India Received 19 December 2007; accepted 19 February 2008 Available online 26 February 2008 Abstract An intensely colored hetarylazo derivative 1 possessing thiadiazole derivative as diazo component and m-aminoacetanilide based cou- pling component has been synthesized and demonstrates a highly selective color change from red to faint orange upon sensing of Zn 2+ . Other cations of the same group; Cd 2+ did not interfere in the sensing process; however, Hg 2+ interfered only at very high concentrations but depicted interesting sensing behaviour of its own. Other commonly occurring cations such as Ca 2+ , Mg 2+ and Cu 2+ did not respond to the sensing event. The pH stability of the azo derivative offers additional advantage in the sensing process. Ó 2008 Elsevier B.V. All rights reserved. Keywords: Hetarylazo dye; Colorimetric sensing; Chemosensor; Cation sensing; Zinc sensing The development of new chemosensors for metal ions is an important area of investigation in supramolecular chemistry due to their fundamental roles in medical diag- nostics, physiology and environmental applications [1].A number of examples of sensors based on mass changes, [2a] electrochemical devices, [2b] biosensors, [2c] chromo- genic [2d] and fluorescent [2e,2f] chemosensors have been reported over the past few years. Colorimetric sensing events have gained more importance owing to the ease in monitoring of the process without resorting to sophisti- cated techniques. A great effort has been invested in devel- oping simple-to-make and use naked-eye diagnostic tools for sensing of metal ions. Zinc is a divalent cation exhibiting important role in health and disease as evidenced by the functional capacity of more than 300 metalloenzymes where the cellular Zn 2+ is tightly bound by the protein, [3] the relatively loosely bound histochemically observable zinc exists in several tis- sues, including the pancreas [4] and brain [5]. Zinc ions function as signalling agents to mediate processes such as gene expression, [6] neurotransmission [5] and apoptosis [7]. In addition to maintain the structure of nucleic acid protein, cell membrane, zinc exerts a vital role in various physiological processes such as cell growth and division. Whereas much is known about the structural chemistry of zinc, [8] the description of the spatial and temporal dis- tribution patterns of this vital metal ion during biological events has only recently begun and remains poorly under- stood [9]. This can be associated, at least in part, to the lack of techniques for determining Zn 2+ in biological systems. This has led to the emergence of some zinc specific chemo- sensors for imaging biological Zn 2+ [10]. The first genera- tion of successful chemosensors, though not ideal but having convincingly established their utility to probe a number of zinc related biological events constitute amino- quinoline derivatives [11,12]. This was chased by some bright bathochromic but not very efficient chromophores represented by Zinpyr and Zinspy families. They show only weak fluorescence enhancements upon zinc binding and were based on rhodamine conjugated with picolylamines, aminocarboxylates and cyclen chelating groups [13]. Thus there is a strong need for the continued improvement in 1387-7003/$ - see front matter Ó 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.inoche.2008.02.025 * Corresponding authors: Tel.: +91 183 2258853; fax: +91 183 2258819. E-mail addresses: paramjit19in@yahoo.co.in (P. Kaur), kamaljit19i- n@yahoo.co.in (K. Singh). www.elsevier.com/locate/inoche Available online at www.sciencedirect.com Inorganic Chemistry Communications 11 (2008) 626–629