Fluorescent Sensing and Selective Pb(II) Extraction by a Dansylamide Ion-Exchanger

Abstract

Lead poisoning, which is especially prevalent in children, is still the most common environmentally caused disease nationally and worldwide. 1 Development of extractants and fluorescent chemosensors 2 for Pb(II) is of importance for monitoring EPA mandated levels and for a variety of applications related to lead toxicity, biodistribution, and removal. For such applications, it is essential to achieve high selectivity for Pb(II) against both alkaline earth and other common metal ions present in biological systems, such as Cu(II) and Zn(II). 3 Exploiting the unique coordination properties of Pb(II) 3,4 provides opportunities for the design of selective sensors 5 and extractants. 6 Successful fluorescent Pb(II) sensor designs are based on complexation by peptides, 7 ionizable chelates, 8 DNAzymes, 9 or macrocycles 10 with covalently linked fluorophores. Macrocycles can be tedious to synthesize and typically exhibit a wide variety of polydentate Pb(II) coordination patterns. On the other hand, ion exchange extraction from water to an organic solvent by simpler chelates can lead to improved selectivity by taking advantage of the unique preference of Pb(II) for low-coordinate hemidirected 3 geometries with a stereochemically expressed lone pair. Moreover, simpler chelates tend to be easier to synthesize, an advantage that could potentially be exploited for sensor discovery by using rapid screening methods. 11 As part of our effort to design low-coordinate Pb(II) extractants and sensors, we now wish to report efficient and selective ion-exchange extraction of Pb(II) from water into 1,2-dichloroethane (DCE) with concurrent fluorescence quenching using as an ion-exchanger, the sulfonamide fluorophore 1. This simple system does not require a secondary co-ligand in order to extract Pb and shows remarkable extraction selectivity against other metals with D Pb > 130 D Cu and D Pb > 1400 D Zn .Sulfonamide 1 is available in good yields from o-phenylenediamine and 1-(dimethylamino)-5-naphthalene sulfonyl chloride (dansyl chloride). 12 The dansyl group is a well-known E-mail: kavallie@fiu.edu. † Florida International University. ‡ University of Miami.Supporting Information Available: Synthesis, procedures, extraction plots, and X-ray crystallographic details of 1. This material is available free of charge via the Internet at http://pubs.acs.org. (Figure 1). Neither Ca(II) nor Na(I) were extracted to any appreciable extent. We ascribe the observed selectivity to the formation of the low-coordinate complex 3, which is apparently disfavored for other competing metals. The crystal structure of the binary Pb complex of the analogous bis-(phenylsulfonyl) derivative of phenylenediamine, which is insoluble in DCE, has showed the formation of a coordination polymer via S=O-Pb axial coordination and a stereochemically active lone pair. 15 The fact that the dansyl complex 3 is soluble in DCE indicates that the S=O-Pb axial coordination is no longer significant and is most likely replaced by weak coordination from solvent molecules or wate...

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Pyridoxal Based Fluorescent Chemosensor for Detection of Copper(II) in Solution With Moderate Selectivity and Live Cell Imaging

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A new fluorescent sensor selective for Pb2+ in water capable of two-photon-induced fluorescence measurement

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