- Email: [email protected]
A rapid response colorimetric and ratiometric fluorescent sensor for detecting fluoride ion, and its application in real sample analysis
Tetrahedron Letters 57 (2016) 5846–5849
Contents lists available at ScienceDirect
Tetrahedron Letters journal homepage: www.elsevier.com/locate/tetlet
A rapid response colorimetric and ratiometric fluorescent sensor for detecting fluoride ion, and its application in real sample analysis Xujun Zheng a,d, Wencheng Zhu b,c,d, Hua Ai b,⇑, Yan Huang a, Zhiyun Lu a,⇑ a
Key Laboratory of Green Chemistry and Technology (Ministry of Education), College of Chemistry, Sichuan University, Chengdu 610064, PR China National Engineering Research Center for Biomaterials, Sichuan University, Chengdu 610064, PR China c Institute of Biochemistry and Cell Biology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai 200031, PR China b
a r t i c l e
i n f o
Article history: Received 28 October 2016 Accepted 7 November 2016 Available online 9 November 2016 Keywords: Chemosensor Fluoride ion Rapid response Dual-channel Real sample
a b s t r a c t A novel naphthalimide-based fluorescent sensor, namely NIMS, is designed and synthesized for fluoride ion detection. NIMS undergoes a desilylation reaction upon addition of F ion, thereby shows a colorimetric/fluorometric dual-channel spectral response, i.e., a huge ratiometric absorption value of 229 nm together with distinct colour change from yellow to blue, and drastically quenched fluorescence as well. Additionally, NIMS shows high selectivity, good sensitivity and rapid response toward F ion, and could be used in qualitative detection of F ion in the solid state and quantitative detection F ion in toothpaste samples. Ó 2016 Published by Elsevier Ltd.
Introduction Owing to their high selectivity, sensitivity and handy operational process, fluorescent probes have been considered as a powerful and versatile tool in environmental monitoring (e.g., neutral1–4 or ionic5–7 species), cell biology (e.g., lysosome8,9 or mitochondrion10,11 tracking and labeling) and molecular biology (e.g., enzyme activity detection12,13). Fluoride ion, the smallest anion, has unique chemical properties due to the high electronegativity and strong basicity. Although the beneficial roles of fluoride ions in dental health and treatment of osteoporosis14,15 have been well-established, its excessive ingestion may lead to fluorosis, urolithiasis, and even cancer,16,17 hence enormous research efforts have been devoted to the exploitation of optical probes showing high selectivity, sensitivity and rapid response toward F ion.18–21 As far as the molecular design strategy is concerned, most of the reported F probes fall into the following three signaling mechanisms: 1) F -induced deprotonation through H-bonding18,20; 2) F -caused complexation through B–F interactions18; and 3) F -promoted desilylation of Si–O/Si–C bonds.21 For probes based on the first mechanism, they generally suffer from unsatisfactory selectivity due the interference from alkaline anions like H2PO4 , AcO and CN .20,22 For probes based on a B–F complexation mech-
⇑ Corresponding authors. d
E-mail addresses: [email protected] (H. Ai), [email protected] (Z. Lu). These authors contributed equally to this work.
http://dx.doi.org/10.1016/j.tetlet.2016.11.032 0040-4039/Ó 2016 Published by Elsevier Ltd.
anism, their high cytotoxicity and chemical instability will severely limit their biological applications.23 Although these disadvantages could be overcome by probes constructed on the last strategy, fluoride ion probes based on a desilylation mechanism often suffer from the need of much excessive F ions (in some cases, even 1400 equiv.24) as well as unsatisfactory response time (often > 60 s),19,25 which should be ascribed to the relatively slow reaction rates. Besides, for a perspective optical probe, the following features are also necessary: 1) capable of ‘‘naked eye” detection22,26,27; 2) showing a huge ratiometric value (>200 nm) to provide more precise built-in correction with minimized environmental effects28,29; 3) being practically applicable in real samples.30–32 Consequently, the development of high-performance optical F probes remains a challenge. Due to their good photo-, thermo-, and chemical stability, 1,8naphthalimides derivatives have been considered to be perspective candidates as laser dyes, chemo/biosensors,33 and electroluminescent (EL) materials.34–36 Recently, we reported a naphthalimidebased fluoride ion sensor which undergoes deprotonation through hydrogen bonding.31 Here, we developed a novel fluorescent sensor, [(E)-6-(4-((tert-butyldiphenylsilyl)oxy)styryl)-2-(2-(dimethylamino)ethyl)-1H-benzo[de]isoquinoline-1,3(2H)-dione] (NIMS, molecular structure shown in Scheme 1). It could act as a high-performance F ion probe with satisfactory selectivity, sensitivity and response time through colorimetric/fluorometric dual-channel. Moreover, upon addition of F , their maximum absorption wavelengths were both red-shifted to the deep red region, resulting in
X. Zheng et al. / Tetrahedron Letters 57 (2016) 5846–5849
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Scheme 1. Molecular structure of NIMS.
a huge ratiometric value of about 230 nm in absorption maximum (kab max), and drastically quenched fluorescence as well. In addition, NIMS could be used to fabricate solid films for detection of F ion, and could also be used to detect the fluoride concentration in commercial toothpaste.
Fig. 1. (a) UV–vis absorption spectra of NIMS (20 lM in DMSO) upon titration of TBAF (40 equiv.); (b) Photoluminescence (PL) spectra of NIMS (20 lM in DMSO, kex = 430 nm) upon titration of TBAF (30 equiv.). Insets: photographs indicating optical changes of NIMS upon addition of F ion.
Results and discussion Uv–vis and fluorescence spectral changes of NIMS toward F ion titration In dilute DMSO solution (20 lM), the kab max of NIMS is 421 nm (shown in Fig. 1a). Upon addition of tetrabutylammonium fluoride (TBAF), this absorption band is weakened gradually together with a slight blue-shift, and a new band with kab max of 650 nm emerges and is intensified progressively, leading to a distinct colour change from yellow to blue together with a huge ratiometric value of 230 nm in kab max. Moreover, the addition of F ion will trigger significant quenched yellow fluorescence of NIMS (kem max = 550 nm, vide Fig. 1b). Therefore, NIMS is a colorimetric/fluorometric dual-channel ‘‘naked eye” indicator for fluoride ion. Limit of detection (LOD) of NIMS toward F ion The ratiometric values of A650 nm/A421 nm of NIMS show linear correlation with the F concentrations in the range of 0 160 lM, and the slope k was calculated to be 310 (R2 = 0.995) (vide Fig. S1). As the standard deviation (S. D.) of our Uv–vis spectrophotometer was calculated to be 5.45 10 4 through 7-time measurements on the absorption intensity of NIMS solution in the absence of F ion, the detection limit (LOD) of NIMS toward F was determined to be 5.27 lM according to the equation LOD = 3 S. D./k. Note that this LOD value is much lower than that of the enforceable drinking water standard for F (210 lM) set by the United States Environmental Protection Agency (EPA). It should be pointed out that although desilylation-mechanismed F probes generally suffer from the need of much excessive analyte to saturate their optical signals (even 1400 equiv.24), in the case of NIMS, however, both its signals at A650 nm and I550 nm could reach their saturation points at a low F concentration of 40 equiv., indicative of the high sensitivity of NIMS toward F ion.
Fig. 2. (a) Kinetics of absorbance enhancement profile of NIMS (20 lM in DMSO) at 650 nm in the presence of F (40 equiv.); (b) Kinetics of fluorescence decrease profile of NIMS (20 lM in DMSO, kex = 430 nm) at 550 nm in the presence of F (30 equiv.).
Selectivity of NIMS toward F ion To investigate the specificity of NIMS toward F , various anion species including Cl , Br , I , NO3 , H2PO4 , AcO , F (TBAF), F (KF), SO24 , BF4 and CN were examined in parallel to F under similar conditions. As shown in Fig. 3, among all these anionic species, only F can trigger distinct spectral and visual changes of NIMS, indicating that NIMS exhibits high selectivity toward F ion, hence could be used to differentiate F from other anions by ‘‘naked eye”.
Probing mechanism of NIMS toward F ion To confirm if the spectral changes of NIMS toward F ion arise from the F -promoted desilylation of the Si–O bond of NIMS, 1H NMR spectra of NIMS in the presence of 0 4.0 equiv. of F ion were recorded. As shown in Fig. 4, with increasing concentrations of F ion, the 1H NMR signals of the Ha, Hb, Hc and Hd protons of NIMS were all found to be upfield-shifted obviously. These observations are consistent with the proposed F -promoted desilylation
Response time of NIMS toward F ion Generally, F probes constructed on a desilylation mechanism will suffer from a slow response time due to their relatively low reaction rates, which will limit their practical applications.37 However, in the case of NIMS, kinetic studies on both enhancement profile of its A650 nm (40 equiv.) and quenching profile of its I550 nm (30 equiv.) (vide Fig. 2) indicate that its response time toward F is as short as 50 s, which is a rather satisfactory response time in comparison with the F probes based on a desilylation mechanism reported so far.25,38–40
Fig. 3. (a) Absorption response (A650 nm) of NIMS (20 lM in DMSO) toward various anions (40 equiv., 800 lM); (b) Fluorescence response (I550 nm) of NIMS (20 lM in DMSO, kex = 430 nm) toward various anions (30 equiv., 600 lM). Insets: photographs of NIMS solutions upon addition of various anions. 1, free; 2, Cl ; 3, Br ; 4, I ; 5, NO3 ; 6, H2PO4 ; 7, AcO ; 8, F (TBAF); 9, F (KF); 10, SO24 ; 11, BF4 ; 12, CN .
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X. Zheng et al. / Tetrahedron Letters 57 (2016) 5846–5849
a b Si O
d c
O N
N
O
NIMS
F
-
-
O
a' b'
d' c'
O N
N
+
Si F
O Phenolate Anion
Fig. 6. Photographs of 0.2 wt% NIMS-doped PMMA sheets before (left) and after (right) being manually written the letters ‘‘F ” with 1 M TBAF solution in MeCN/ H2O (v/v, 95/5) (right). (a): Photos taken in the ambient light conditions; (b): Photos taken under UV irradiation at 365 nm.
Fig. 4. Partial 1H NMR spectral changes of NIMS in DMSO-d6 in the presence of TBAF (0 4.0 equiv.).
mechanism of NIMS, since the resulted phenolate anion will possess stronger electron-donating capability than the silyl ether subunit of NIMS. Further ESI-HRMS experimental results indicated that upon addition of F , an m/z signal at 385.1560 was discernable, which could be assigned to the phenolate anion species derived from the desilylation reaction of NIMS (Fig. S2). Consequently, the optical response of NIMS toward F ion should be attributed to a desilylation mechanism.
Practical applications of NIMS To validate if NIMS could be used to detect fluoride ion in practical applications, the response of NIMS toward two different toothpaste samples, i.e., F -containing Colgate and F -free Saky, was studied. As illustrated in Fig. 5, the addition of the two pretreated solutions of analyte samples into the DMSO solution of NIMS would indeed trigger different spectral response: significant spectral and colour changes (yellow ? blue) could be observed in
the Colgate sample, but no distinct changes were discernable in the F -free Saky sample. Since the signaling in solid state is also crucial to realize portable detection, we prepared a NIMS-doped (0.2 wt%) film sample using poly(methyl methacrylate) as the doping matrix. As shown in Fig. 6, upon addition of TBAF solution (1 M) on the NIMS-based film, the colour or PL intensity of F -exposed regions of the films changed significantly, implying that NIMS could also be used to detect F ion in solid state. Conclusions In summary, a naphthalimide-based fluorescent sensor for detecting fluoride ion, namely NIMS, has been demonstrated. It shows high selectivity, good sensitivity and rapid response time through colorimetric/fluorometric dual optical channels, and the signaling mechanism lies in the F -induced desilylation reaction of NIMS at the Si–O bond. In addition, NIMS could be used to fabricate solid films for detection of F ion, and it could also be used in the detection of fluoride ions in commercial toothpastes, which demonstrate its great potential for practical applications. Experimental section Apparatus and reagents
Fig. 5. UV–vis absorption and fluorescence spectra (kex = 430 nm) of NIMS (20 lM in DMSO) upon titration of water soluble components (30 equiv., 600 lM) of Saky toothpaste sample (a, b), and Colgate toothpaste sample (c, d). Insets: photographs illustrating the optical changes upon addition of analyte under visible light (a, c) and UV lamp of 365 nm (b, d).
All the chemicals commercially available were used directly without further purification unless otherwise stated. All the solvents were of analytical grade and freshly distilled prior to use. All the photophysical experiments were conducted in a nitrogen atmosphere to exclude the interference of oxygen at 298 K. Solutions containing the following anion species [Cl , Br , I , NO3 , H2PO4 , AcO , F (TBAF), F (KF), SO24 , BF4 , and CN ] were prepared by dissolving their corresponding salts in DMSO/H2O (90/10, v/v). 1H NMR and 13C NMR spectra were measured using a Bruker Avance AV II-400 MHz spectrometer, and the chemical shifts were recorded in units of ppm with TMS as the internal standard. Coupling constants (J) were reported in Hertz. FT-IR spectrum was recorded on a Perkin-Elmer 2000 infrared spectrometer with KBr pellets under an ambient atmosphere. High resolution MS spectrum was measured with a Q-TOF Premier ESI mass spectrometer (Micromass, Manchester, UK). UV–vis absorption spectra in solution were measured on a Perkin–Elmer Lambda 950 scanning spectrophotometer. PL spectra were recorded on a Perkin-Elmer LS55 fluorescence spectrophotometer at 298 K. Melting point was determined on a X-6 microscopic melting point apparatus.
X. Zheng et al. / Tetrahedron Letters 57 (2016) 5846–5849
Pre-treatment of toothpaste samples 2 g of commercially available toothpaste sample (Saky or Colgate) was added into 40 mL of double-distilled water. The mixture was stirred at 100 °C for 3 h, then filtered. The cake was washed with double-distilled water for three times, and the filtrate was concentrated in vacuum. The residue was then diluted with 4.5 mL of double-distilled water to afford the solution of analyte. Acknowledgements We acknowledge the financial support for this work by the National Natural Science Foundation of China (project No. 21372168, 21190031, 51173117, 51573108 and 21432005) and National Key Basic Research Program of China (2013CB933903). We are grateful to the Analytical & Testing Center of Sichuan University for providing NMR data for the intermediates and objective molecules. A. Supplementary data Supplementary data associated with this article can be found, in the online version, at http://dx.doi.org/10.1016/j.tetlet.2016.11. 032. References 1. 2. 3. 4. 5.
Zhang G, Palmer GM, Dewhirst MW, Fraser CL. Nat Mater. 2009;8:747. Xu Q, Lee S, Cho Y, Kim MH, Bouffard J, Yoon J. J Am Chem Soc. 2013;135:17751. Mosca L, Karimi Behzad S, Anzenbacher Jr P. J Am Chem Soc. 2015;137:7967. Yin J, Kwon Y, Kim D, et al. J Am Chem Soc. 2014;136:5351. Roy A, Kand D, Saha T, Talukdar P. Chem Commun. 2014;50:5510.
6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19. 20. 21. 22. 23. 24. 25. 26. 27. 28. 29. 30. 31. 32. 33. 34. 35. 36. 37. 38. 39. 40.
5849
Ding J, Li H, Wang C, et al. ACS Appl Mater Interfaces. 2015;7:11369. Barba-Bon A, Costero AM, Gil S, et al. Chem Commun. 2012;48:3000. Fan F, Nie S, Yang D, Luo M, Shi H, Zhang YH. Bioconjug Chem. 2012;23:1309. Chen L, Wu J, Schmuck C, Tian H. Chem Commun. 2014;50:6443. Leung CW, Hong Y, Chen S, Zhao E, Lam JW, Tang BZ. J Am Chem Soc. 2013;135:62. Hu Q, Gao M, Feng G, Liu B. Angew Chem. 2014;53:14225. Leung KH, He HZ, Ma VP, et al. Chem Commun. 2013;49:5630. Leung KH, He HZ, Wang W, et al. ACS Appl Mater Interfaces. 2013;5:12249. Rakita PE. J Chem Educ. 2004;81:677. Kleerekoper M. Endocrinol Metab Clin North Am. 1998;27:441. Ayoob S, Gupta AK. Crit Rev Environ Sci Technol. 2006;36:433. Singh PP, Barjatiya MK, Dhing S, Bhatnagar R, Kothari S, Dhar V. Urol Res. 2001;29:238. Zhou Y, Zhang JF, Yoon J. Chem Rev. 2014;114:5511. Jiao Y, Zhu B, Chen J, Duan X. Theranostics. 2015;5:173. Cametti M, Rissanen K. Chem Commun. 2009;2809. Gai L, Mack J, Lu H, et al. Coord Chem Rev. 2015;285:24. Hu R, Feng J, Hu D, et al. Angew Chem. 2010;49:4915. Kim D, Singha S, Wang T, et al. Chem Commun. 2012;48:10243. Kim SY, Hong JI. Org Lett. 2007;9:3109. Yang XF, Qi H, Wang L, Su Z, Wang G. Talanta. 2009;80:92. Cheng X, Li S, Xu G, Li C, Qin J, Li Z. ChemPlusChem. 2012;77:908. Liu CX, Xu J, Yang F, et al. Sensor Actuat B-Chem. 2015;212:364. Lin W, Long L, Yuan L, Cao Z, Chen B, Tan W. Org Lett. 2008;10:5577. Gai L, Chen H, Zou B, et al. Chem Commun. 2012;48:10721. Udhayakumari D, Velmathi S. Sensor Actuat B-Chem. 2015;209:462. Zheng X, Zhu W, Liu D, Ai H, Huang Y, Lu Z. ACS Appl Mater Interfaces. 2014;6:7996. Suganya S, Park JS, Velmathi S. Sensor Actuat B-Chem. 2014;190:679. Duke RM, Veale EB, Pfeffer FM, Kruger PE, Gunnlaugsson T. Chem Soc Rev. 2010;39:3936. Wang Y, Zhou J, Wang X, et al. Dyes Pigments. 2014;100:87. Zhou J, Chen P, Wang X, et al. Chem Commun. 2014;50:7586. Zheng X, Peng Q, Lin J, et al. J Mater Chem C. 2015;3:6970. Xiong L, Feng J, Hu R, et al. Anal Chem. 2013;85:4113. Zheng FY, Zeng F, Yu CM, Hou XF, Wu SZ. Chem-Eur J. 2013;19:936. Hou P, Chen S, Wang H, Wang J, Voitchovsky K, Song X. Chem Commun. 2014;50:320. Ke B, Chen W, Ni N, et al. Chem Commun. 2013;49:2494.
Contents lists available at ScienceDirect
Tetrahedron Letters journal homepage: www.elsevier.com/locate/tetlet
A rapid response colorimetric and ratiometric fluorescent sensor for detecting fluoride ion, and its application in real sample analysis Xujun Zheng a,d, Wencheng Zhu b,c,d, Hua Ai b,⇑, Yan Huang a, Zhiyun Lu a,⇑ a
Key Laboratory of Green Chemistry and Technology (Ministry of Education), College of Chemistry, Sichuan University, Chengdu 610064, PR China National Engineering Research Center for Biomaterials, Sichuan University, Chengdu 610064, PR China c Institute of Biochemistry and Cell Biology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai 200031, PR China b
a r t i c l e
i n f o
Article history: Received 28 October 2016 Accepted 7 November 2016 Available online 9 November 2016 Keywords: Chemosensor Fluoride ion Rapid response Dual-channel Real sample
a b s t r a c t A novel naphthalimide-based fluorescent sensor, namely NIMS, is designed and synthesized for fluoride ion detection. NIMS undergoes a desilylation reaction upon addition of F ion, thereby shows a colorimetric/fluorometric dual-channel spectral response, i.e., a huge ratiometric absorption value of 229 nm together with distinct colour change from yellow to blue, and drastically quenched fluorescence as well. Additionally, NIMS shows high selectivity, good sensitivity and rapid response toward F ion, and could be used in qualitative detection of F ion in the solid state and quantitative detection F ion in toothpaste samples. Ó 2016 Published by Elsevier Ltd.
Introduction Owing to their high selectivity, sensitivity and handy operational process, fluorescent probes have been considered as a powerful and versatile tool in environmental monitoring (e.g., neutral1–4 or ionic5–7 species), cell biology (e.g., lysosome8,9 or mitochondrion10,11 tracking and labeling) and molecular biology (e.g., enzyme activity detection12,13). Fluoride ion, the smallest anion, has unique chemical properties due to the high electronegativity and strong basicity. Although the beneficial roles of fluoride ions in dental health and treatment of osteoporosis14,15 have been well-established, its excessive ingestion may lead to fluorosis, urolithiasis, and even cancer,16,17 hence enormous research efforts have been devoted to the exploitation of optical probes showing high selectivity, sensitivity and rapid response toward F ion.18–21 As far as the molecular design strategy is concerned, most of the reported F probes fall into the following three signaling mechanisms: 1) F -induced deprotonation through H-bonding18,20; 2) F -caused complexation through B–F interactions18; and 3) F -promoted desilylation of Si–O/Si–C bonds.21 For probes based on the first mechanism, they generally suffer from unsatisfactory selectivity due the interference from alkaline anions like H2PO4 , AcO and CN .20,22 For probes based on a B–F complexation mech-
⇑ Corresponding authors. d
E-mail addresses: [email protected] (H. Ai), [email protected] (Z. Lu). These authors contributed equally to this work.
http://dx.doi.org/10.1016/j.tetlet.2016.11.032 0040-4039/Ó 2016 Published by Elsevier Ltd.
anism, their high cytotoxicity and chemical instability will severely limit their biological applications.23 Although these disadvantages could be overcome by probes constructed on the last strategy, fluoride ion probes based on a desilylation mechanism often suffer from the need of much excessive F ions (in some cases, even 1400 equiv.24) as well as unsatisfactory response time (often > 60 s),19,25 which should be ascribed to the relatively slow reaction rates. Besides, for a perspective optical probe, the following features are also necessary: 1) capable of ‘‘naked eye” detection22,26,27; 2) showing a huge ratiometric value (>200 nm) to provide more precise built-in correction with minimized environmental effects28,29; 3) being practically applicable in real samples.30–32 Consequently, the development of high-performance optical F probes remains a challenge. Due to their good photo-, thermo-, and chemical stability, 1,8naphthalimides derivatives have been considered to be perspective candidates as laser dyes, chemo/biosensors,33 and electroluminescent (EL) materials.34–36 Recently, we reported a naphthalimidebased fluoride ion sensor which undergoes deprotonation through hydrogen bonding.31 Here, we developed a novel fluorescent sensor, [(E)-6-(4-((tert-butyldiphenylsilyl)oxy)styryl)-2-(2-(dimethylamino)ethyl)-1H-benzo[de]isoquinoline-1,3(2H)-dione] (NIMS, molecular structure shown in Scheme 1). It could act as a high-performance F ion probe with satisfactory selectivity, sensitivity and response time through colorimetric/fluorometric dual-channel. Moreover, upon addition of F , their maximum absorption wavelengths were both red-shifted to the deep red region, resulting in
X. Zheng et al. / Tetrahedron Letters 57 (2016) 5846–5849
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Scheme 1. Molecular structure of NIMS.
a huge ratiometric value of about 230 nm in absorption maximum (kab max), and drastically quenched fluorescence as well. In addition, NIMS could be used to fabricate solid films for detection of F ion, and could also be used to detect the fluoride concentration in commercial toothpaste.
Fig. 1. (a) UV–vis absorption spectra of NIMS (20 lM in DMSO) upon titration of TBAF (40 equiv.); (b) Photoluminescence (PL) spectra of NIMS (20 lM in DMSO, kex = 430 nm) upon titration of TBAF (30 equiv.). Insets: photographs indicating optical changes of NIMS upon addition of F ion.
Results and discussion Uv–vis and fluorescence spectral changes of NIMS toward F ion titration In dilute DMSO solution (20 lM), the kab max of NIMS is 421 nm (shown in Fig. 1a). Upon addition of tetrabutylammonium fluoride (TBAF), this absorption band is weakened gradually together with a slight blue-shift, and a new band with kab max of 650 nm emerges and is intensified progressively, leading to a distinct colour change from yellow to blue together with a huge ratiometric value of 230 nm in kab max. Moreover, the addition of F ion will trigger significant quenched yellow fluorescence of NIMS (kem max = 550 nm, vide Fig. 1b). Therefore, NIMS is a colorimetric/fluorometric dual-channel ‘‘naked eye” indicator for fluoride ion. Limit of detection (LOD) of NIMS toward F ion The ratiometric values of A650 nm/A421 nm of NIMS show linear correlation with the F concentrations in the range of 0 160 lM, and the slope k was calculated to be 310 (R2 = 0.995) (vide Fig. S1). As the standard deviation (S. D.) of our Uv–vis spectrophotometer was calculated to be 5.45 10 4 through 7-time measurements on the absorption intensity of NIMS solution in the absence of F ion, the detection limit (LOD) of NIMS toward F was determined to be 5.27 lM according to the equation LOD = 3 S. D./k. Note that this LOD value is much lower than that of the enforceable drinking water standard for F (210 lM) set by the United States Environmental Protection Agency (EPA). It should be pointed out that although desilylation-mechanismed F probes generally suffer from the need of much excessive analyte to saturate their optical signals (even 1400 equiv.24), in the case of NIMS, however, both its signals at A650 nm and I550 nm could reach their saturation points at a low F concentration of 40 equiv., indicative of the high sensitivity of NIMS toward F ion.
Fig. 2. (a) Kinetics of absorbance enhancement profile of NIMS (20 lM in DMSO) at 650 nm in the presence of F (40 equiv.); (b) Kinetics of fluorescence decrease profile of NIMS (20 lM in DMSO, kex = 430 nm) at 550 nm in the presence of F (30 equiv.).
Selectivity of NIMS toward F ion To investigate the specificity of NIMS toward F , various anion species including Cl , Br , I , NO3 , H2PO4 , AcO , F (TBAF), F (KF), SO24 , BF4 and CN were examined in parallel to F under similar conditions. As shown in Fig. 3, among all these anionic species, only F can trigger distinct spectral and visual changes of NIMS, indicating that NIMS exhibits high selectivity toward F ion, hence could be used to differentiate F from other anions by ‘‘naked eye”.
Probing mechanism of NIMS toward F ion To confirm if the spectral changes of NIMS toward F ion arise from the F -promoted desilylation of the Si–O bond of NIMS, 1H NMR spectra of NIMS in the presence of 0 4.0 equiv. of F ion were recorded. As shown in Fig. 4, with increasing concentrations of F ion, the 1H NMR signals of the Ha, Hb, Hc and Hd protons of NIMS were all found to be upfield-shifted obviously. These observations are consistent with the proposed F -promoted desilylation
Response time of NIMS toward F ion Generally, F probes constructed on a desilylation mechanism will suffer from a slow response time due to their relatively low reaction rates, which will limit their practical applications.37 However, in the case of NIMS, kinetic studies on both enhancement profile of its A650 nm (40 equiv.) and quenching profile of its I550 nm (30 equiv.) (vide Fig. 2) indicate that its response time toward F is as short as 50 s, which is a rather satisfactory response time in comparison with the F probes based on a desilylation mechanism reported so far.25,38–40
Fig. 3. (a) Absorption response (A650 nm) of NIMS (20 lM in DMSO) toward various anions (40 equiv., 800 lM); (b) Fluorescence response (I550 nm) of NIMS (20 lM in DMSO, kex = 430 nm) toward various anions (30 equiv., 600 lM). Insets: photographs of NIMS solutions upon addition of various anions. 1, free; 2, Cl ; 3, Br ; 4, I ; 5, NO3 ; 6, H2PO4 ; 7, AcO ; 8, F (TBAF); 9, F (KF); 10, SO24 ; 11, BF4 ; 12, CN .
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X. Zheng et al. / Tetrahedron Letters 57 (2016) 5846–5849
a b Si O
d c
O N
N
O
NIMS
F
-
-
O
a' b'
d' c'
O N
N
+
Si F
O Phenolate Anion
Fig. 6. Photographs of 0.2 wt% NIMS-doped PMMA sheets before (left) and after (right) being manually written the letters ‘‘F ” with 1 M TBAF solution in MeCN/ H2O (v/v, 95/5) (right). (a): Photos taken in the ambient light conditions; (b): Photos taken under UV irradiation at 365 nm.
Fig. 4. Partial 1H NMR spectral changes of NIMS in DMSO-d6 in the presence of TBAF (0 4.0 equiv.).
mechanism of NIMS, since the resulted phenolate anion will possess stronger electron-donating capability than the silyl ether subunit of NIMS. Further ESI-HRMS experimental results indicated that upon addition of F , an m/z signal at 385.1560 was discernable, which could be assigned to the phenolate anion species derived from the desilylation reaction of NIMS (Fig. S2). Consequently, the optical response of NIMS toward F ion should be attributed to a desilylation mechanism.
Practical applications of NIMS To validate if NIMS could be used to detect fluoride ion in practical applications, the response of NIMS toward two different toothpaste samples, i.e., F -containing Colgate and F -free Saky, was studied. As illustrated in Fig. 5, the addition of the two pretreated solutions of analyte samples into the DMSO solution of NIMS would indeed trigger different spectral response: significant spectral and colour changes (yellow ? blue) could be observed in
the Colgate sample, but no distinct changes were discernable in the F -free Saky sample. Since the signaling in solid state is also crucial to realize portable detection, we prepared a NIMS-doped (0.2 wt%) film sample using poly(methyl methacrylate) as the doping matrix. As shown in Fig. 6, upon addition of TBAF solution (1 M) on the NIMS-based film, the colour or PL intensity of F -exposed regions of the films changed significantly, implying that NIMS could also be used to detect F ion in solid state. Conclusions In summary, a naphthalimide-based fluorescent sensor for detecting fluoride ion, namely NIMS, has been demonstrated. It shows high selectivity, good sensitivity and rapid response time through colorimetric/fluorometric dual optical channels, and the signaling mechanism lies in the F -induced desilylation reaction of NIMS at the Si–O bond. In addition, NIMS could be used to fabricate solid films for detection of F ion, and it could also be used in the detection of fluoride ions in commercial toothpastes, which demonstrate its great potential for practical applications. Experimental section Apparatus and reagents
Fig. 5. UV–vis absorption and fluorescence spectra (kex = 430 nm) of NIMS (20 lM in DMSO) upon titration of water soluble components (30 equiv., 600 lM) of Saky toothpaste sample (a, b), and Colgate toothpaste sample (c, d). Insets: photographs illustrating the optical changes upon addition of analyte under visible light (a, c) and UV lamp of 365 nm (b, d).
All the chemicals commercially available were used directly without further purification unless otherwise stated. All the solvents were of analytical grade and freshly distilled prior to use. All the photophysical experiments were conducted in a nitrogen atmosphere to exclude the interference of oxygen at 298 K. Solutions containing the following anion species [Cl , Br , I , NO3 , H2PO4 , AcO , F (TBAF), F (KF), SO24 , BF4 , and CN ] were prepared by dissolving their corresponding salts in DMSO/H2O (90/10, v/v). 1H NMR and 13C NMR spectra were measured using a Bruker Avance AV II-400 MHz spectrometer, and the chemical shifts were recorded in units of ppm with TMS as the internal standard. Coupling constants (J) were reported in Hertz. FT-IR spectrum was recorded on a Perkin-Elmer 2000 infrared spectrometer with KBr pellets under an ambient atmosphere. High resolution MS spectrum was measured with a Q-TOF Premier ESI mass spectrometer (Micromass, Manchester, UK). UV–vis absorption spectra in solution were measured on a Perkin–Elmer Lambda 950 scanning spectrophotometer. PL spectra were recorded on a Perkin-Elmer LS55 fluorescence spectrophotometer at 298 K. Melting point was determined on a X-6 microscopic melting point apparatus.
X. Zheng et al. / Tetrahedron Letters 57 (2016) 5846–5849
Pre-treatment of toothpaste samples 2 g of commercially available toothpaste sample (Saky or Colgate) was added into 40 mL of double-distilled water. The mixture was stirred at 100 °C for 3 h, then filtered. The cake was washed with double-distilled water for three times, and the filtrate was concentrated in vacuum. The residue was then diluted with 4.5 mL of double-distilled water to afford the solution of analyte. Acknowledgements We acknowledge the financial support for this work by the National Natural Science Foundation of China (project No. 21372168, 21190031, 51173117, 51573108 and 21432005) and National Key Basic Research Program of China (2013CB933903). We are grateful to the Analytical & Testing Center of Sichuan University for providing NMR data for the intermediates and objective molecules. A. Supplementary data Supplementary data associated with this article can be found, in the online version, at http://dx.doi.org/10.1016/j.tetlet.2016.11. 032. References 1. 2. 3. 4. 5.
Zhang G, Palmer GM, Dewhirst MW, Fraser CL. Nat Mater. 2009;8:747. Xu Q, Lee S, Cho Y, Kim MH, Bouffard J, Yoon J. J Am Chem Soc. 2013;135:17751. Mosca L, Karimi Behzad S, Anzenbacher Jr P. J Am Chem Soc. 2015;137:7967. Yin J, Kwon Y, Kim D, et al. J Am Chem Soc. 2014;136:5351. Roy A, Kand D, Saha T, Talukdar P. Chem Commun. 2014;50:5510.
6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19. 20. 21. 22. 23. 24. 25. 26. 27. 28. 29. 30. 31. 32. 33. 34. 35. 36. 37. 38. 39. 40.
5849
Ding J, Li H, Wang C, et al. ACS Appl Mater Interfaces. 2015;7:11369. Barba-Bon A, Costero AM, Gil S, et al. Chem Commun. 2012;48:3000. Fan F, Nie S, Yang D, Luo M, Shi H, Zhang YH. Bioconjug Chem. 2012;23:1309. Chen L, Wu J, Schmuck C, Tian H. Chem Commun. 2014;50:6443. Leung CW, Hong Y, Chen S, Zhao E, Lam JW, Tang BZ. J Am Chem Soc. 2013;135:62. Hu Q, Gao M, Feng G, Liu B. Angew Chem. 2014;53:14225. Leung KH, He HZ, Ma VP, et al. Chem Commun. 2013;49:5630. Leung KH, He HZ, Wang W, et al. ACS Appl Mater Interfaces. 2013;5:12249. Rakita PE. J Chem Educ. 2004;81:677. Kleerekoper M. Endocrinol Metab Clin North Am. 1998;27:441. Ayoob S, Gupta AK. Crit Rev Environ Sci Technol. 2006;36:433. Singh PP, Barjatiya MK, Dhing S, Bhatnagar R, Kothari S, Dhar V. Urol Res. 2001;29:238. Zhou Y, Zhang JF, Yoon J. Chem Rev. 2014;114:5511. Jiao Y, Zhu B, Chen J, Duan X. Theranostics. 2015;5:173. Cametti M, Rissanen K. Chem Commun. 2009;2809. Gai L, Mack J, Lu H, et al. Coord Chem Rev. 2015;285:24. Hu R, Feng J, Hu D, et al. Angew Chem. 2010;49:4915. Kim D, Singha S, Wang T, et al. Chem Commun. 2012;48:10243. Kim SY, Hong JI. Org Lett. 2007;9:3109. Yang XF, Qi H, Wang L, Su Z, Wang G. Talanta. 2009;80:92. Cheng X, Li S, Xu G, Li C, Qin J, Li Z. ChemPlusChem. 2012;77:908. Liu CX, Xu J, Yang F, et al. Sensor Actuat B-Chem. 2015;212:364. Lin W, Long L, Yuan L, Cao Z, Chen B, Tan W. Org Lett. 2008;10:5577. Gai L, Chen H, Zou B, et al. Chem Commun. 2012;48:10721. Udhayakumari D, Velmathi S. Sensor Actuat B-Chem. 2015;209:462. Zheng X, Zhu W, Liu D, Ai H, Huang Y, Lu Z. ACS Appl Mater Interfaces. 2014;6:7996. Suganya S, Park JS, Velmathi S. Sensor Actuat B-Chem. 2014;190:679. Duke RM, Veale EB, Pfeffer FM, Kruger PE, Gunnlaugsson T. Chem Soc Rev. 2010;39:3936. Wang Y, Zhou J, Wang X, et al. Dyes Pigments. 2014;100:87. Zhou J, Chen P, Wang X, et al. Chem Commun. 2014;50:7586. Zheng X, Peng Q, Lin J, et al. J Mater Chem C. 2015;3:6970. Xiong L, Feng J, Hu R, et al. Anal Chem. 2013;85:4113. Zheng FY, Zeng F, Yu CM, Hou XF, Wu SZ. Chem-Eur J. 2013;19:936. Hou P, Chen S, Wang H, Wang J, Voitchovsky K, Song X. Chem Commun. 2014;50:320. Ke B, Chen W, Ni N, et al. Chem Commun. 2013;49:2494.