Anion-binding properties of ureidoquinoline and its turn-on fluorescence in the presence of fluoride anionsTetrahedron Letters

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Authors
Sathish Kurapati, Yunhee Jo, Jung-Ho Hong, Tae-Hyun Kim, Dong-Gyu Cho
Year
2015
DOI
10.1016/j.tetlet.2015.05.038
Subject
Organic Chemistry / Biochemistry / Drug Discovery

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Accepted Manuscript

Anion-binding properties of ureidoquinoline and its turn-on fluorescence in the presence of fluoride anions

Sathish Kurapati, Yunhee Jo, Jung-Ho Hong, Tae-Hyun Kim, Dong-Gyu Cho

PII: S0040-4039(15)00847-3

DOI: http://dx.doi.org/10.1016/j.tetlet.2015.05.038

Reference: TETL 46310

To appear in: Tetrahedron Letters

Received Date: 31 March 2015

Revised Date: 30 April 2015

Accepted Date: 11 May 2015

Please cite this article as: Kurapati, S., Jo, Y., Hong, J-H., Kim, T-H., Cho, D-G., Anion-binding properties of ureidoquinoline and its turn-on fluorescence in the presence of fluoride anions, Tetrahedron Letters (2015), doi: http://dx.doi.org/10.1016/j.tetlet.2015.05.038

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Tetrahedron Letters jo urn al h om e pa ge: w w w.els evi er . com

Anion-binding properties of ureidoquinoline and its turn-on fluorescence in the presence of fluoride anions

Sathish Kurapati,a, b Yunhee Jo,a Jung-Ho Hong,a Tae-Hyun Kimb, * and Dong-Gyu Choa, ∗ aDepartment of Chemistry, Inha University, Inharo 100, Namgu, Incheon 402-751, Republic of Korea bDepartment of Chemistry, Incheon National University, 119 Academy-ro, Yeonsu-gu, Incheon 406-772, Republic of Korea ——— ∗

Corresponding authors. E-mail addresses: dgcho@inha.ac.kr (D.-G. Cho) and tkim@inu.ac.kr (T.-H. Kim)

In supramolecular chemistry, new receptors that recognize both neutral and charged species have drawn the attention of researchers. Of particular interest are colorimetric or fluorescent sensors that detect target species and can provide qualitative (or quantitative) analytic information simply by analyzing the changes in their optical signals.1 These sensors often afford rapid and convenient analysis techniques for the target species compared to methods based on instrumental analysis. Generally, fluorescent sensors are preferred over colorimetric sensors because of their superior sensitivity. Thus, there have been many efforts to develop new fluorophores that possess selective characteristics for analytes.1, 2 To date, many chromophores have been developed, and each chromophore has its own merits.

However, 8-hydroxyquinoline-based chromophores have been relatively less explored, but they have been modified to be sensors for anions3 and cations4, and materials5 for organic lightemitting diodes (OLEDs). Recently, our group reported that bisureidoquinoline (3) exhibits turn-on fluorescence in the presence of F−, which occurs via the NH groups of bis-ureidoquinoline hydrogen bonding to F− (Scheme 1).3a, 6 In the previous study, bis-ureidoquinoline (3) was synthesized from two molecules of ureidoquinoline (2), which was in turn obtained from 1 as shown in Scheme 1. We also recognized and partly understood the anion-binding properties of 2. However, they were not reported because the binding properties of 2 were quite different from that of 3. Thus, we report the detailed anion-binding properties of ureidoquinoline here. The unique anion-binding behavior of 2 is attributed to the phenolic OH of 2. Specifically, while bisureidoquinoline 3 selectively binds to F−, 2 binds to H2PO4− and

BzO−. However, F− deprotonates the phenolic OH group of 2 in the presence of more than 2 equiv. of F−. Moreover, by itself, 2 exhibits very weak fluorescence, but it emits intense fluorescence in the presence of more than 2 equiv. of F−.

Scheme 1. Syntheses of ureidoquinoline (2) and bis-ureidoquinoline (3).

To evaluate the anion-binding properties of 2, it was titrated with various anions in the form of tetrabutylammonium (TBA) salts. In the absence of F−, 2 shows a sharp UV absorption band

ARTIC LE INFO ABSTRACT

Article history:

Received

Received in revised form

Accepted

Available online 2009 Elsevier Ltd. All rights reserved.

The anion-binding properties of ureidoquinoline, a derivative of 8-hydroxyquinoline, were investigated. In the presence of anions, ureidoquinoline exhibits turn-on fluorescence rather than its fluorescence being quenched or shifted. These properties are rare for phenol-based sensors. In particular, ureidoquinoline binds to H2PO4− and BzO−, while F− binds to ureidoquinoline via its hydrogen bonds when less than 2 equiv. of F− are present. With more than 2 equiv. of F−, the phenolic OH group of ureidoquinoline is deprotonated. Under such conditions, ureidoquinoline emits intense fluorescence. Under the condition, ureidoquinoline can be used for the detection of fluoride anions under illumination from a laboratory hand-held UV lamp or using a spectrofluorometer.

Keywords:

Anion binding

Quinoline

H2PO4−

F− induced deprotonation

Tetrahedron 2 at 263 nm and a very broad band at 356 nm when dissolved in

CH3CN containing 0.2% water. The sharp band of 2 ([H] = 2.0 × 10−5 M) was red-shifted (∆λ263 = 15 nm) and the intensities of the two bands at 366 and 436 nm increased as the concentration of F− increased (Figure 1). However, no noticeable changes were seen in the UV-Vis spectrum of 2 upon the addition of other anions (see the Supporting Information). The binding properties of 3 were also examined in CH3CN containing 0.2% water. By using the same conditions, this allows us to compare the properties of 2 and 3.

To see the possibility that fluorescent changes could be enlarged for certain anions, fluorescence titrations were performed. We carefully chose a range of concentration that fluorescence intensities of the receptor are directly proportional to their concentrations. (Figure S1 in the Supporting Information). Thus, the fluorescence spectra of 2 were recorded during the anion titrations, and spectral changes were clearly seen for most of the anions tested. Except for the addition of I− (possibly due to its well-known fluorescence quenching ability), the fluorescence band of 2 at 460 nm increased when irradiated at 264 nm (see the