Quinoline Driven Fluorescence Turn On 1,3-Bis-calix[4]arene Conjugate-Based Receptor to Discriminate Fe 3+ from Fe 2+ Rakesh Kumar Pathak, † Jayaraman Dessingou, † Vijaya Kumar Hinge, ‡ Atul Gajanan Thawari, † Santanu Kumar Basu, § and Chebrolu Pulla Rao* ,†,‡ † Department of Chemistry, ‡ Department of Biosciences & Bioengineering, and § Department of Chemical Engineering, Indian Institute of Technology Bombay, Powai, Mumbai 400076, India * S Supporting Information ABSTRACT: The synthesis and characterization of a triazole linked quinoline appended calix[4]arene conjugate, L, and its fluorescence turn on receptor property for Fe 3+ have been demonstrated. The selective and sensitive discrimination of Fe 3+ has been shown using fluorescence and absorption titration experiments. The Fe 3+ binding to L has been further shown by ITC and ESI MS. The mode of binding of Fe 3+ by calix[4]arene conjugate has been shown by absorption, 1 H NMR and visual color change and the species were modeled based on DFT computations. The {L + Fe 3+ } has been shown to label cells with fluorescence imaging. Moreover the utility of this conjugate has been demonstrated by the combination logic gate system. I ron is one of the most widely distributed and crucial elements of human life. 1 In biological systems, it plays a vital role by being present as a cofactor in various proteins, owing to its easy redox reaction between Fe 2+ and Fe 3+ . Iron is involved in the stimulation of reactive oxygen species, which induces the lipid peroxidation, mitochondrial dysfunction, and DNA fragmentation to degrade the cellular contents and thereby causes cell death. 2 Thus, the discrimination between +2 and +3 is important in order to understand the biological functions regulated by iron. Imbalance in the homeostasis of this can cause various diseases and severe infections and thus can also be used for the diagnosis of a particular disease related to iron. Thus, the detection and discrimination of Fe 3+ from other ions including Fe 2+ at lower concentration has potential applications in the environment as well as in biological systems in order to decipher several correlated events. 3 A number of molecular receptors reported in the literature suffer from one or more of the following three major aspects, viz., quenching of fluorescence, interference by other metal ions such as Cu 2+ , and higher concentration being the detection limit. 4 The rhodamine-based systems sense Fe 3+ by ring cleavage and not by binding. 5 Therefore, the development of an organic molecular system that can selectively recognize Fe 3+ through exhibiting fluorescence enhancement is challenging to synthetic chemists and to molecular recognition scientists. Herein, for the first time, we report a quinoline-appended triazole linked calix[4]arene conjugate (L) as a fluorescence turn on as well as a visually detectable receptor for Fe 3+ among the different metal ions studied, including Fe 2+ . The role of the quinoline moiety has been delineated by a comparison of the results obtained from a control molecular system that possesses a pyridyl moiety in place of the quinoline moiety. On the other hand, the role of the calix[4]arene platform has been addressed by making a noncalix[4]arene-based analog of this. The present system has also been developed to exhibit molecular logic gate properties. Materials and Methods. 1 H and 13 C NMR spectra were measured on a Varian Mercury NMR spectrometer working at 400 MHz. The mass spectra were recorded on a Q-TOF micromass (YA-105), using an electrospray ionization method. Steady-state fluorescence spectra were measured on a Perkin- Elmer LS55 spectrofluorimeter. The absorption spectra were measured on a Varian Cary 100 Bio instrument. All the solvents used were of HPLC grade and were dried by routine procedures immediately before use. All the metal salts, viz. NaClO 4 ·H 2 O, KClO 4 , Ca(ClO 4 ) 2 ·4H 2 O, Mg(ClO 4 ) 2 ·6H 2 O, Mn(ClO 4 ) 2 ·6H 2 O, Fe(ClO 4 ) 2 ·xH 2 O, Fe(ClO 4 ) 3 ·xH 2 O, Co- (ClO 4 ) 2 ·6H 2 O, Ni(ClO 4 ) 2 · 6H 2 O, Cu(ClO 4 ) 2 ·6H 2 O, Hg- (ClO 4 ) 2 ·4H 2 O, Zn(ClO 4 ) 2 ·6H 2 O Cd(ClO 4 ) 2 ·H 2 O, Cr(OAc) 3 , Al 2 (SO 4 ) 3 ·18H 2 O, tert-butyl hydroperoxide (TBH), and dithiothreitol (DTT), were purchased from Sigma Chem. Company. All the fluorescence titrations were carried out in a 1 cm quartz cell by using 30 μL of calix[4]arene conjugate (L) (10 -4 M), and the total volume in each measurement was made to 3 mL to give a final concentration of the ligand as 1 μM. During the titration, the concentration of the metal ion has been varied accordingly to result in requisite mole ratios of metal ion to L, and the total volume of the solution was maintained at 3 mL in each case by the addition of acetonitrile. Received: January 8, 2013 Accepted: February 26, 2013 Published: February 26, 2013 Article pubs.acs.org/ac © 2013 American Chemical Society 3707 dx.doi.org/10.1021/ac400059w | Anal. Chem. 2013, 85, 3707-3714