Talanta 91 (2012) 18–25 Contents lists available at SciVerse ScienceDirect Talanta jo u r n al hom epage: www.elsevier.com/locate/talanta Thiophene anchored coumarin derivative as a turn-on fluorescent probe for Cr 3+ : Cell imaging and speciation studies Subarna Guha a , Sisir Lohar a , Arnab Banerjee a , Animesh Sahana a , Ipsit Hauli b , Subhra Kanti Mukherjee b , Jesús Sanmartín Matalobos c,∗∗ , Debasis Das a,∗ a Department of Chemistry, The University of Burdwan, Burdwan, West Bengal, India b Department of Microbiology, The University of Burdwan, Burdwan, West Bengal, India c Departamento de Química Inorgánica, Facultade de Química, Avda. Das Ciencias s/n, 15782 Santiago de Compostela, Spain a r t i c l e i n f o Article history: Received 27 September 2011 Received in revised form 3 December 2011 Accepted 5 December 2011 Available online 8 December 2011 Keywords: Thiophene–coumarin X-ray structure Fluorescence enhancement Cr 3+ Speciation Cell imaging a b s t r a c t A thiophene–coumarin hybrid molecule, (6E)-6-((thiophen-2-yl)methyleneamino)-2H-chromen-2-one (TMC) has been prepared and its single crystal X-ray structure is reported. TMC can selectively detect Cr 3+ in presence of other common cations. Both TMC and its Cr 3+ complex are well characterized by different spectroscopic techniques like 1 H NMR, QTOF-MS ES + , FTIR and elemental analysis as well. TMC exhibits fluorescence enhancement upon binding Cr 3+ in CH 3 CN–HEPES buffer (0.02 M, pH 7.4) (4:6, v/v) medium. Detection limit of the method is 1 × 10 -6 M. Binding constant is estimated with the Benesi–Hildebrand method and the value 8 × 10 4 indicates a fairly strong interaction between TMC and Cr 3+ . Speciation studies have been performed in a fast and environment friendly way using least sample volume, less hazardous chemicals and solvents. Cr 3+ assisted restricted rotation around the imine bond and inhib- ited photo-induced electron transfer from the N,S-donor sites to the coumarin unit are responsible for fluorescence enhancement. TMC is capable to detect intracellular Cr 3+ in living cells. © 2011 Elsevier B.V. All rights reserved. 1. Introduction Cr 3+ is an essential micro nutrient for maintenance of “glu- cose tolerance factor” whereas excess Cr 3+ is harmful to human health [1]. On the other hand, Cr(VI) is extremely toxic and potentially carcinogenic [2,3]. Higher oxidation potential and rel- atively smaller size of Cr(VI) enables it to penetrate biological cell membranes. It causes skin lesions [4], dental erosion, lung cancer and other forms of cancer [5]. Chromium compounds are used in wood preservatives and as an anti-corrosion agent [6]. General methods for measuring chromium include titrimetry [7], potentiometry [8], spectrophotometry [9–11], fluorimetry [12,13], chromatography [14], solid-phase spectrophotometry coupled to anion exchange membrane [15], flame atomic absorption spec- trometry [16,17], graphite furnace atomic absorption spectrometry [18,19], inductively coupled plasma atomic emission spectroscopy [20], X-ray fluorescence spectrometry [21] and electrochemical methods [22,23]. Fluorescence method has more advantages over all the other mentioned methods due to its operational simplicity, high ∗ Corresponding author. Tel.: +91 342 2533913; fax: +91 342 2530452. ∗∗ Corresponding author. E-mail address: ddas100in@yahoo.com (D. Das). selectivity, sensitivity, rapidity, nondestructive methodology, enhanced sensitivity, high sampling frequency and low cost of equipment and direct visual perception [24]. For an efficient flu- orescent sensor, in addition to high selectivity towards the target ion, a significant change in the fluorescence intensity and/or a spec- tral change of the probe are essential upon its interaction with the specific analyte [25]. Very few of the reported Cr 3+ selective fluo- rescent sensors [26] have been used for trace level speciation and estimation [27]. We [28] have recently reported trace level determi- nation and speciation of chromium using 9-acridone-4-carboxylic acid as a Cr 3+ selective fluorescent probe. Paramagnetic nature of Cr 3+ limits the development of its turn- on fluorescent sensor and consequently fluorescence monitoring of intracellular Cr 3+ in living cells remains underdeveloped. Sarkar et al. [29] reported di-(2-ethylsulfanylethyl)amine as a Cr 3+ selec- tive receptor in tetrahydrofuran. Mao et al. [30] reported two fluorescent sensors capable of discriminating Fe 3+ and Cr 3+ . 8- hydroxyquinoline containing rhodamine B derivative [31] is used for bio-imaging of Cr 3+ in contaminated cells. Zhou et al. [32] reported a ratiometric FRET-based fluorescent probe for imaging chromium (III) in living cells. A Dansyl-based Cr 3+ selective fluo- rescent chemosensor is reported by Wu et al. [33]. On the other hand, coumarin and its derivatives are widely used as anti-coagulants [34], antibacterial agents [35], antifungal agents [36], biological inhibitors [37], chemotherapeutics [38] 0039-9140/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.talanta.2011.12.014