Coumarin Based Highly Sensitive and Selective Ratiometric Fluorescence Sensor for Chromium Ions in Aqueous Media

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International Journal of Research and Scientific Innovation (IJRSI) | Volume IV, Issue X, October 2017 | ISSN 2321–2705 

Coumarin Based Highly Sensitive and Selective Ratiometric Fluorescence Sensor for Chromium Ions in Aqueous Media

Subarna Guha
Central Institute of Plastic Engineering and Technology, Haldia, West Bengal, India

IJRISS Call for paper

Abstract: – A fluorescent sensor, 6-(bis((1H-benzo[d]imidazol-2- yl)methyl)amino)-2H-chromen-2-one (BIC), based on 2- chloromethyl benzimidazole with 6-amino coumarin as receptor, was synthesized. Both BIC and its Cr(III) complex are well characterized by different spectroscopic techniques like 1HNMR, QTOF–MS ES+ , FTIR and elemental analysis as well. BIC exhibits fluorescence enhancement upon binding Cr(III) in aqueous (water: methanol =7:3, v/v) solutions. Detection limit of the method is 1 x10-7 M. Binding constant is estimated with the Benesi-Hildebrand method and the value 1.39 x105 indicates a fairly strong interaction between BIC and Cr(III) . There has no fluorescence response seen towards other competing cations. BIC a water soluble off-on type ratiometric Cr(III) selective fluorescent probe and used for biological applications like living cell imaging at physiological pH using a confocal microscope. The fluorescence enhancement can be ascribed to the CHEF effect associated with better rigidity and planarity of the sensor molecules induced by chelation of Cr(III). The design strategy and remarkable photophysical properties of sensor BIC help to extend the development of fluorescent sensors for metal ions.

Keywords: Coumarin, 2-chloromethyl benzimidazole, Turn-on fluorescent probe, Cr(III), living cells.


Chromium is the new entry, after lead, cadmium and mercury in the major toxic metal series. Chromium exists in the environment mainly in two stable oxidation states, Cr(III) and Cr(VI). This two species differ in charge, physicochemical properties and in chemical and biological reactivity. Trivalent chromium is relatively immobile and less toxic because its compounds are usually weakly soluble in aquatic media and it also forms stable complex with soil minerals. Cr(III) is an essential micro nutrient for maintenance of ―glucose tolerance factor‖ whereas excess Cr(III) is harmful to human health [1]. The National Research Council has recommended 50–200 μg d−1 as the safe and proper quantity of Cr(III) .On the other hand, Cr(VI) is extremely toxic and potentially carcinogenic [2]. WHO states that the guideline values of 50 μg L−1 Cr(VI) are considered to be too high compared with its genotoxicity [3]. Higher oxidation potential and relatively smaller size of Cr(VI) enables it to penetrate biological cell membranes.