Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 137 (2015) 1055–1060
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Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy journal homepage: www.elsevier.com/locate/saa
A new diketopyrrolopyrrole-based probe for sensitive and selective detection of sulfite in aqueous solution Xiaofeng Yang ⇑, Yu Cui, Yexin Li, Luyi Zheng, Lijun Xie, Rui Ning, Zheng Liu, Junling Lu, Gege Zhang, Chunxiang Liu, Guangyou Zhang ⇑ Key Laboratory of Chemical Sensing & Analysis in Universities of Shandong, School of Chemistry and Chemical Engineering, University of Jinan, No. 336, West Road of Nan Xinzhuang, Jinan 250022, Shandong, China
h i g h l i g h t s
g r a p h i c a l a b s t r a c t
The novel diketopyrrolopyrrole-
derived probe 1 was simple to synthesize. Probe 1 exhibited selectivity and sensitivity for SO32 within 20 min. The detection limit of probe 1 for SO32 was 0.1 mM.
a r t i c l e
i n f o
Article history: Received 21 May 2014 Received in revised form 28 August 2014 Accepted 31 August 2014
Keywords: Diketopyrrolopyrrole Fluorescence Sulfite anion detection Aqueous solution
a b s t r a c t A new probe was synthesized by incorporating an a,b -unsaturated ketone to a diketopyrrolopyrrole fluorophore. The probe had exhibited a selective and sensitive response to the sulfite against other thirteen anions and biothiols (Cys, Hcy and GSH), through the nucleophilic addition of sulfite to the alkene of probe with the detection limit of 0.1 lM in HEPES (10 mM, pH 7.4) THF/H2O (1:1, v/v). Meanwhile, it could be easily observed that the probe for sulfite changed from pink to colorless by the naked eye, and from pink to blue under UV lamp after the sulfite was added for 20 min. The NMR and Mass spectral analysis demonstrated the expected addition of sulfite to the C@C bonds. Ó 2014 Elsevier B.V. All rights reserved.
Introduction Anions play an important role in biological, industrial, and environmental processes [1–4]. In the environment, anionic species can be either essential to sustain growth or act as harmful pollutants [5–10]. Among various anions, sulfite is widely used as a preservative in food and beverages (e.g. beer and wine) to prevent oxidation and bacterial growth and inhibit the development of either enzymatic or nonenzymatic browning during production and storage [11]. However, sulfite is toxic in high doses, and some people are extremely sensitive to even low levels of sulfite, as it is associated
⇑ Corresponding authors. Tel.: +86 531 82765407; fax: +86 531 82765475. E-mail addresses: [email protected] (X. Yang), [email protected] (G. Zhang). http://dx.doi.org/10.1016/j.saa.2014.08.144 1386-1425/Ó 2014 Elsevier B.V. All rights reserved.
with allergic reaction and food intolerance symptoms, such as mild to severe skin allergy, asthma, or gastrointestinal diseases [12,13]. Due to the harmful effects of sulfite, the sulfite content in food products has been the subject of legislation [14]. On the other hand, sulfur dioxide (SO2) is a common air pollutant, and human exposure to SO2 has become increasingly widespread due to the combustion of fossil fuels. Inhaled SO2 is easily hydrated in the respiratory tract and subsequently forms its derivatives sulfite (SO2 3 ) and bisulfite (HSO3 ) (when the pH is close to neutrality (around 7.0), bisulfite (or hydrogen sulfite) ions exist in the form of sulfite ions), and the toxicity of SO2 is mainly affected by the two derivatives. Epidemiological studies implied that SO2 exposure not only induces many respiratory responses [15], but is also linked to lung cancer, cardiovascular diseases, and many neurological disorders [16]. As for the applications in food quality control,
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Scheme 1. The synthesis procedure of probe 1.
Scheme 2. The structure of probe 1 and the proposed recognition mechanism for sulfite.
environmental pollution monitoring and biological assays, it would be highly desirable that the sensors are of low toxicity and operable in aqueous media. Conventional sulfite detection methods were usually time consuming and need sample pretreatment and/or expensive equipments [17–22]. Therefore, to develop analytic methods for sensitive and selective determination of sulfite in foods and environmental samples was of great interest. Recently, several fluorescent probes for sulfite measurement had been designed, such as colorimetric or fluorescence OFF–ON probes [23–37], and small number of ratiometric and colorimetric fluorescent probes [38,39]. Diketopyrrolopyrrole (DPP) was a robust chromophore [40–46] and had been widely used in electromaterials such as organic semiconductors [47], photovoltaics [48–52], and two photon absorption materials [53,54], but its application in fluorescent molecular probes was very rare [55–62]. In the present work, probe 1 for sulfite was designed and synthesized (Scheme 1), in which DPP was used as the fluorophore and an a,b-unsaturated ketone moiety was introduced as the sulfite receptor (Scheme 2).
Results indicated that probe 1 had a sensitivity, selectivity and good competition for sulfite over other some anions and biothiols with color changes. Experimental Reagents and chemicals Unless otherwise stated, reagents were commercially obtained and used without further purification. All solvents were freshly distilled: THF from Na/benzophenone. Ultra-pure water was prepared through Sartorius Arium611DI system. Reactions were monitored by TLC. Flash chromatography separations were carried out using silica gel (200–300 mesh). Apparatus 1
H NMR and 13C NMR spectra were collected on a Bruker Avance II 400 MHz spectrometer at 400 MHz spectrometer.
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Fig. 1. (a) Time-dependent absorption of probe 1 (20 lM) in the presence of 20 equiv. of sulfite in HEPES (10 mM, pH 7.4) THF/H2O (1:1, v/v). The inset showed the visible color change of the probe with 20 equiv. sulfite for 20 min, 30 °C. (b) Time-dependent emission spectra (kex = 356 nm) of probe 1 (10 lM) in the presence of 20 equiv. of sulfite in HEPES (10 mM, pH 7.4) THF/H2O (1:1, v/v) system. The insets showed the visual fluorescence color changes of the probe with 20 equiv. sulfite for 20 min, 30 °C. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)
Fig. 2. The It/I0 or At/A0 plots of probe 1 as a function of time in the presence of 20 equiv. of sulfite in HEPES (10 mM, pH 7.4) THF/H2O (1:1, v/v) system. (a) Probe 1 (10 lM), It and I0 were the fluorescence intensity at 610 nm at t and 0 time, 30 °C. (b) Probe 1 (20 lM), At and A0 were the absorbance at 487 nm at t and 0 time, 30 °C.
Scheme 1. Their structures were conformed by 1H NMR and NMR (Figs. S1–S7, Supporting information).
13
C
Synthesis of probe 1
Fig. 3. Partial 1H NMR spectra of probe 1 (in CDCl3) and 1-SO3H (in CD3OD).
Infrared spectra were recorded using a Bruker Vertex 70 FT-IR spectrometer with KBr pellets. UV–vis spectra were recorded on a Shimadzu 3100 spectrometer. Fluorescence measurements were carried out using an Edinburgh Instruments Ltd-FLS920 fluorescence spectrophotometer. Synthesis of 5 Compound 5 was prepared according to the reference [63]. The synthetic detail for synthesis of this compound was shown in
Probe 1 could be easily obtained through the reaction between 5 and 1-(2-hydroxyphenyl)ethanone (Scheme 2). Compound 2 (130 mg, 0.2848 mmol), 1-(2-hydroxyphenyl)ethanone (140 mg, 1.0253 mmol) and five drops of pyrrolidine were added to 10 mL of CH2Cl2/EtOH (1:1, v/v). The resulting clear wine red solution was stirred at room temperature for additional 24 h to afford purple precipitates, which were filtered. Further purification by recrystallization in CH2Cl2 gave desired probe 1 as purple crystals (83 mg, 42%). 1H NMR (CDCl3, 400 MHz) d (ppm) 12.75 (s, 2H), 8.05–7.93 (m, 8H), 7.85–7.74 (m, 6H), 7.53 (t, J = 7.6 Hz, 2H), 7.05 (d, J = 8.4 Hz, 2H), 6.98 (t, J = 7.6 Hz, 2H), 3.81 (t, J = 7.6 Hz, 4H), 1.66–1.60 (m, 4H), 1.33–1.25 (m, 4H), 0.88 (t, J = 7.2 Hz, 6H). 13C NMR (CDCl3, 100 MHz) d (ppm) 193.4, 163.7, 162.6, 147.7, 143.7, 137.3, 136.7, 130.1, 129.6, 129.3, 129.0, 122.1, 120.0, 119.0, 118.8, 110.7, 41.9, 31.6, 20.0, 13.6; IR (KBr): 3434, 2971, 2924, 2873, 2852, 1663, 1639, 1601, 1583, 1547, 1504, 1490, 1467, 1454, 1442, 1417, 1384, 1371, 1343, 1307, 1266, 1237, 1207, 1158, 1123, 1092, 1051, 1025, 982, 880, 839, 825, 794, 749, 737, 614. ESI: m/z 693.2909(M + H)+, calculated 693.2886 for (M + H)+;
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diluted with HEPES (2-[4-(2-hydroxyethyl)-1-piperazinyl]ethanesulfonic acid) (10 mM, pH 7.4) buffer solution to obtain 2 105 or 1 105 M aqueous solution. Stock solution of common anions 3 4 2 (SO2 3 , PO4 , I , P2O7 , S2O3 , CH3COO , HCO3 , SCN , NO3 , NO2 , Cl, F, Br, SO2 ), cysteine (Cys), homocysteine (Hcy) and gluta4 thione (GSH) solutions were prepared in HEPES (10 mM, pH 7.4) buffer solution to obtain 3 102 M.
Preparation for UV–vis kinetic study Test solutions were prepared by placing 3 mL of 2 105 M probe 1 aqueous solution into a test tube, adding an appropriate volume of 3 102 M freshly prepared anion-HEPES or amino acid-HEPES. The UV–vis spectral changes were set to be monitored at 30 °C.
Preparation for fluorescence study Fig. 4. The pH-dependent fluorescence intensity (kex/kem = 356/610 nm) for probe 1 (10 lM) and 1-SO3H (10 lM) measured in various pH values at 30 °C.
Element analysis (%): C 76.20, H 5.89, N 4.14, calculated C 76.28, H 5.82, N 4.04 (Figs. S8–S10, Supporting information). Synthesis of 1-SO3H A solution of Na2SO3 (10 mg, 0.0940 mmol) in 4 mL H2O was added dropwise to a solution of 1 (28 mg, 0.0404 mmol) in 10 mL THF. After stirring at room temperature for 1 h, the solvent was evaporated under vacuum. Crude was washed with acetone and CH2Cl2 in turn, to give an orange solid (31 mg, 85%). 1H NMR (CD3OD, 400 MHz) d (ppm) 8.56 (s, 2H), 7.78–7.71 (m, 6H), 7.55–7.48 (m, 6H), 6.99–6.88 (m, 4H), 4.76 (q, J = 7.6 Hz, 2H), 3.98 (t, J = 7.2 Hz, 2H), 3.88–3.82 (m, 6H), 1.77–1.69 (m, 4H), 1.48–1.41 (m, 4H), 0.77 (t, J = 7.2 Hz, 6H). 13C NMR (CD3OD , 100 MHz) d (ppm) 209.0, 162.0, 161.0, 143.74, 136.1, 132.7, 130.9, 130.5, 130.3, 129.8, 129.0, 128.5, 128.2, 126.5, 119.6, 118.8, 117.6, 109.1, 62.9, 41.1, 40.9, 32.0, 22.3, 13.0. ESI: m/z 855.2314 (M H), calculated 855.2336 for (M H). (Figs. S11–S13, Supporting information). Sample preparation The accurately weighted amount of probe 1 was dissolved in THF to obtain 1 104 M stock solution. The stock solution was
Test solutions were prepared by placing 3 mL of 1 105 M probe 1 aqueous solution into a test tube, adding an appropriate volume of 3 102 M freshly prepared anion-HEPES or amino acid-HEPES. Normally, excitation at 356 nm. Both the excitation and emission slit widths were 5 nm 5 nm. Fluorescence spectra were monitored 20 min after addition of anions or amino acids at 30 °C.
pH titrations Probe 1 and its addition product 1-SO3H were dissolved in HEPES (10 mM, pH 7.4) THF/H2O (1:1, v/v) directly. The pHs of these solution were adjusted with HCl or NaOH aqueous solution.
Determination of the detection limit The detection limit was calculated based on the fluorescence titration. Probe 1 was employed at 1 105 M. To determine the S/N ratio, the emission intensity of probe 1 without Na2SO3 was measured by 10 times and the standard deviation of blank measurements was determined. The detection limit was then calculated with the equation: detection limit = 3rbi/m, where rbi was the standard deviation of blank measurements, m was the slope between intensity difference versus sample concentration.
Fig. 5. (a) Fluorescence spectra (kex = 356 nm) of 1 (10 lM) with SO2 3 in HEPES (10 mM, pH 7.4) THF/H2O (1:1, v/v) from 0 to 0.4 mM for 20 min at 30 °C. (b) The plot of fluorescence intensity difference (kex/kem = 356/610 nm) with probe 1 (10 lM) against varied concentration of SO2 3 in HEPES (10 mM, pH 7.4) THF/H2O (1:1, v/v) from 0 to 0.4 mM for 20 min at 30 °C.
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Fig. 6. (a) The fluorescence spectra (kex = 356 nm) of probe 1 (10 lM) in the presence of 20 equiv. of various additives in HEPES (pH = 7.4) for 20 min. (b) Fluorescence intensities (kex/kem = 356/610 nm) of probe 1 (10 lM) in the presence of 20 equiv. of various additives in HEPES (10 mM, pH 7.4) THF/H2O (1:1, v/v) for 20 min.
Results and discussion
Sensitivity and detection limit
The photophysical responses of probe 1 toward sulfite in HEPES
To investigate the possibility of precise quantitative detection of sulfite, probe 1 was treated with different concentration of sulfite in HEPES. Fig. 5a showed the SO2 3 concentration-dependent emission fluorescence spectra of probe 1 (10 lM). When excited at 356 nm, the emission fluorescence intensity at 610 nm decreased about 6-fold upon increasing the concentration of SO2 3 from 0 to 0.4 mM. A satisfactory linear relationship between fluorescence intensity difference and SO2 concentration (0–0.4 mM) was 3 observed with a correlation coefficient as high as 0.99929 (Fig. 5b). According to fluorometric method, the detection limit of probe 1 for SO2 3 was determined as 0.1 lM. This result was better than the reported fluorescent probes, while comparable to those data reported previously [24–32,34–39]. Meanwhile, the UV–vis spectrum absorption titration experiment was performed under the same conditions (Fig. S15, Supporting information), which was accordance with the fluorescent changes.
Fig. 1 showed the time-dependent absorbance and the fluorescence of probe 1 in the presence of sulfite at 30 °C in HEPES (10 mM, pH 7.4). As the reaction progressed, absorption peaks of 1 centered at 487 nm and 325 nm decreased steadily accompanied with the solution color changing from pink to colorless (Fig. 1a). At the same time, emission bands at 610 nm and 536 nm decreased steadily. Correspondingly, the emission color of the solution changed from pink to blue (Fig. 1b). From the dynamic reaction curve (Fig. 2), it could be seen that about 97% of the probe 1 was transformed to the addition product after 20 min (t1/2 3 min). Therefore, the assay time of 20 min was used in the evaluation of the selectivity and sensitivity of probe 1 toward sulfite. Mechanism
Selectivity
To confirm the formation of the addition product 1-SO3H, probe 1 was treated with Na2SO3, and the reaction product was isolated. The partial 1H NMR of 1 and the isolated 1-SO3H were shown in Fig. 3. The resonance signal corresponding to the vinylic protons (Hb and Ha at d 7.96, 7.75 ppm) of 1 disappeared with the concomitant appearance of new peaks around 4.76 ppm (quartet) assigned to the proton at Cb0 and around 3.98 and 3.85 ppm assigned to the proton at Ca0 , which indicated that the reaction took place through the Michael reaction. On the other hand, 13C resonance peaks of Ca and Cb respectively shifting from 122.06 ppm and 147.66 ppm to 40.88 ppm and 62.91 ppm (Fig. S14, Supporting information) also confirmed the addition of sulfite to the double bond. Mass spectral analysis of the resulting mixture had shown a corroborative evidence for the product 1-SO3H formation at m/z obsd 855.2314 (M H) (calcd 855.2336 for (M H)) (Fig. S13, Supporting information).
To evaluate the selectivity of probe 1, thirteen typical anions 4 2 (PO3 4 , I , P2O7 , S2O3 , CH3COO , HCO3 , SCN , NO3 , NO2 , Cl , F , 2 Br , SO4 ) and biothiols (Cys, Hcy and GSH) were investigated in parallel under the same test conditions (probe 1 as Blank). As shown in Fig. 6a, only SO2 3 generated a significant change in fluorescence intensity at about 610 nm, which was accompanied by a visual fluorescence color change from pink1 to blue, while the other anions did not show this behavior. Cys, GSH and Hcy led to fluorescence weaker at 610 nm but to much smaller extents. Adding SO2 3 into other anion solution, respectively, presented the similar emission spectra (Fig. S16, Supporting information) and fluorescence intensity (Fig. 6b) as that of the solo SO2 3 ion. The result demonstrated that probe 1 could be used to detect SO2 3 with high selectivity over other biologically relevant anions.
Effect of pH
Conclusions
The changes of fluorescence intensity under various pH values were investigated (Fig. 4). It was found that probe 1 itself was stable at pH values of 4–10 in the absence of SO2 3 , whereas the best pH value for 1-SO3H detection system was determined at pH 4–8. Considering the potential biological application, all the measurements were carried out under simulated physiological condition of pH 7.4 HEPES.
In this study, we had developed a new fluorescent probe 1 for 2 SO2 3 . The probe exhibited sensitivity and selectivity for SO3 with detection limit as low as 0.1 lM to be achieved visually within 20 min. 1 For interpretation of color in Fig. 6, the reader is referred to the web version of this article.
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Acknowledgements The authors are grateful for the support from the foundation of University of Jinan (No. XBS0923), Scientific Research Foundation for Returned Overseas Chinese Scholars, State Education Ministry (No. SQT1101), Scientific Research Foundation of University of Jinan (XKY1416) and University Young Key Teacher Home Visit by the Ministry of Education of Shandong Province. Appendix A. Supplementary material Supplementary material associated with this article can be found, in the online version, at http://dx.doi.org/10.1016/ j.saa.2014.08.144. References [1] V. Amendola, D. Esteban-Gómez, L. Fabbrizzi, M. Licchelli, Acc. Chem. Res. 39 (2006) 343–353. [2] X. Cheng, H. Jia, T. Long, J. Feng, J. Qin, Z. Li, Chem. Commun. 47 (2011) (1980) 11978–11980. [3] F. Zapata, A. Caballero, N.G. White, T.D.W. Claridge, P.J. Costa, V. Félix, P.D. Beer, J. Am. Chem. Soc. 134 (2012) 11533–11541. [4] P. Kaur, H. Kaur, K. Singh, Analyst 138 (2013) 425–428. [5] T. Noipa, T. Tuntulani, W. Ngeontae, Talanta 105 (2013) 320–326. [6] Y.-L. Duan, Y.-S. Zheng, Talanta 107 (2013) 332–337. [7] N. Pourreza, H. Golmohammadi, Talanta 119 (2014) 181–186. [8] J.-T. Hou, B.-Y. Liu, K. Li, K.-K. Yu, M.-B. Wu, X.-Q. Yu, Talanta 116 (2013) 434– 440. [9] P.A. Gale, Chem. Soc. Rev. 39 (2010) 3746–3771. [10] R. Martínez-Máñez, F. Sancenón, Chem. Rev. 103 (2003) 4419–4476. [11] B.L. Wedzicha, Chemistry of Sulphur Dioxide in Foods, Elsevier Applied Science Publishers, New York, 1984, pp. 275–311. [12] H. Vally, N.L.A. Misso, V. Madan, Clin. Exp. Allergy 39 (2009) 1643–1651. [13] R.C. Claudia, J.C. Francisco, Food Chem. 112 (2009) 487–493. [14] M. Koch, R. Köppen, D. Siegel, A. Witt, I. Nehls, J. Agric. Food Chem. 58 (2010) 9463–9467. [15] S. Iwasawa, Y. Kikuchi, Y. Nishiwaki, M. Nakano, T. Michikawa, T. Tsuboi, S. Tanaka, T. Uemura, A. Ishiqami, H. Nakashima, T. Takebayashi, M. Adachi, A. Morikawa, K. Maruyama, S. Kudo, I. Uchiyama, K. Omae, J. Occup. Health 51 (2009) 38–47. [16] N. Sang, Y. Yun, H. Li, L. Hou, M. Han, G. Li, Toxicol. Sci. 114 (2010) 226–236. [17] J.M. Vahl, J.E. Converse, J. Assoc. Off. Anal. Chem. 63 (1980) 194–199. [18] D.R. Migneault, Anal. Chem. 61 (1989) 272–275. [19] N. Ekkad, C.O. Huber, Anal. Chim. Acta 332 (1996) 155–160. [20] R. Spricigo, R. Dronov, F. Lisdat, S. Leimkühler, F.W. Scheller, U. Wollenberger, Anal. Bioanal. Chem. 393 (2009) 225–233. [21] S. Sasaki, K. Ikebukuro, Y. Arikawa, M. Shimomura, I. Karube, Anal. Commun. 34 (1997) 299–302. [22] G. Brychkova, D. Yarmolinsky, R. Fluhr, M. Sagi, Plant Sci. 190 (2012) 123–130. [23] S.S.M. Hassan, M.S.A. Hamza, A.H.K. Mohamed, Anal. Chim. Acta 570 (2006) 232–239. [24] M.G. Choi, J. Hwang, S. Eor, S.-K. Chang, Org. Lett. 12 (2010) 5624–5627. [25] S. Chen, P. Hou, J. Wang, X. Song, RSC Adv. 2 (2012) 10869–10873.
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Contents lists available at ScienceDirect
Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy journal homepage: www.elsevier.com/locate/saa
A new diketopyrrolopyrrole-based probe for sensitive and selective detection of sulfite in aqueous solution Xiaofeng Yang ⇑, Yu Cui, Yexin Li, Luyi Zheng, Lijun Xie, Rui Ning, Zheng Liu, Junling Lu, Gege Zhang, Chunxiang Liu, Guangyou Zhang ⇑ Key Laboratory of Chemical Sensing & Analysis in Universities of Shandong, School of Chemistry and Chemical Engineering, University of Jinan, No. 336, West Road of Nan Xinzhuang, Jinan 250022, Shandong, China
h i g h l i g h t s
g r a p h i c a l a b s t r a c t
The novel diketopyrrolopyrrole-
derived probe 1 was simple to synthesize. Probe 1 exhibited selectivity and sensitivity for SO32 within 20 min. The detection limit of probe 1 for SO32 was 0.1 mM.
a r t i c l e
i n f o
Article history: Received 21 May 2014 Received in revised form 28 August 2014 Accepted 31 August 2014
Keywords: Diketopyrrolopyrrole Fluorescence Sulfite anion detection Aqueous solution
a b s t r a c t A new probe was synthesized by incorporating an a,b -unsaturated ketone to a diketopyrrolopyrrole fluorophore. The probe had exhibited a selective and sensitive response to the sulfite against other thirteen anions and biothiols (Cys, Hcy and GSH), through the nucleophilic addition of sulfite to the alkene of probe with the detection limit of 0.1 lM in HEPES (10 mM, pH 7.4) THF/H2O (1:1, v/v). Meanwhile, it could be easily observed that the probe for sulfite changed from pink to colorless by the naked eye, and from pink to blue under UV lamp after the sulfite was added for 20 min. The NMR and Mass spectral analysis demonstrated the expected addition of sulfite to the C@C bonds. Ó 2014 Elsevier B.V. All rights reserved.
Introduction Anions play an important role in biological, industrial, and environmental processes [1–4]. In the environment, anionic species can be either essential to sustain growth or act as harmful pollutants [5–10]. Among various anions, sulfite is widely used as a preservative in food and beverages (e.g. beer and wine) to prevent oxidation and bacterial growth and inhibit the development of either enzymatic or nonenzymatic browning during production and storage [11]. However, sulfite is toxic in high doses, and some people are extremely sensitive to even low levels of sulfite, as it is associated
⇑ Corresponding authors. Tel.: +86 531 82765407; fax: +86 531 82765475. E-mail addresses: [email protected] (X. Yang), [email protected] (G. Zhang). http://dx.doi.org/10.1016/j.saa.2014.08.144 1386-1425/Ó 2014 Elsevier B.V. All rights reserved.
with allergic reaction and food intolerance symptoms, such as mild to severe skin allergy, asthma, or gastrointestinal diseases [12,13]. Due to the harmful effects of sulfite, the sulfite content in food products has been the subject of legislation [14]. On the other hand, sulfur dioxide (SO2) is a common air pollutant, and human exposure to SO2 has become increasingly widespread due to the combustion of fossil fuels. Inhaled SO2 is easily hydrated in the respiratory tract and subsequently forms its derivatives sulfite (SO2 3 ) and bisulfite (HSO3 ) (when the pH is close to neutrality (around 7.0), bisulfite (or hydrogen sulfite) ions exist in the form of sulfite ions), and the toxicity of SO2 is mainly affected by the two derivatives. Epidemiological studies implied that SO2 exposure not only induces many respiratory responses [15], but is also linked to lung cancer, cardiovascular diseases, and many neurological disorders [16]. As for the applications in food quality control,
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Scheme 1. The synthesis procedure of probe 1.
Scheme 2. The structure of probe 1 and the proposed recognition mechanism for sulfite.
environmental pollution monitoring and biological assays, it would be highly desirable that the sensors are of low toxicity and operable in aqueous media. Conventional sulfite detection methods were usually time consuming and need sample pretreatment and/or expensive equipments [17–22]. Therefore, to develop analytic methods for sensitive and selective determination of sulfite in foods and environmental samples was of great interest. Recently, several fluorescent probes for sulfite measurement had been designed, such as colorimetric or fluorescence OFF–ON probes [23–37], and small number of ratiometric and colorimetric fluorescent probes [38,39]. Diketopyrrolopyrrole (DPP) was a robust chromophore [40–46] and had been widely used in electromaterials such as organic semiconductors [47], photovoltaics [48–52], and two photon absorption materials [53,54], but its application in fluorescent molecular probes was very rare [55–62]. In the present work, probe 1 for sulfite was designed and synthesized (Scheme 1), in which DPP was used as the fluorophore and an a,b-unsaturated ketone moiety was introduced as the sulfite receptor (Scheme 2).
Results indicated that probe 1 had a sensitivity, selectivity and good competition for sulfite over other some anions and biothiols with color changes. Experimental Reagents and chemicals Unless otherwise stated, reagents were commercially obtained and used without further purification. All solvents were freshly distilled: THF from Na/benzophenone. Ultra-pure water was prepared through Sartorius Arium611DI system. Reactions were monitored by TLC. Flash chromatography separations were carried out using silica gel (200–300 mesh). Apparatus 1
H NMR and 13C NMR spectra were collected on a Bruker Avance II 400 MHz spectrometer at 400 MHz spectrometer.
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Fig. 1. (a) Time-dependent absorption of probe 1 (20 lM) in the presence of 20 equiv. of sulfite in HEPES (10 mM, pH 7.4) THF/H2O (1:1, v/v). The inset showed the visible color change of the probe with 20 equiv. sulfite for 20 min, 30 °C. (b) Time-dependent emission spectra (kex = 356 nm) of probe 1 (10 lM) in the presence of 20 equiv. of sulfite in HEPES (10 mM, pH 7.4) THF/H2O (1:1, v/v) system. The insets showed the visual fluorescence color changes of the probe with 20 equiv. sulfite for 20 min, 30 °C. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)
Fig. 2. The It/I0 or At/A0 plots of probe 1 as a function of time in the presence of 20 equiv. of sulfite in HEPES (10 mM, pH 7.4) THF/H2O (1:1, v/v) system. (a) Probe 1 (10 lM), It and I0 were the fluorescence intensity at 610 nm at t and 0 time, 30 °C. (b) Probe 1 (20 lM), At and A0 were the absorbance at 487 nm at t and 0 time, 30 °C.
Scheme 1. Their structures were conformed by 1H NMR and NMR (Figs. S1–S7, Supporting information).
13
C
Synthesis of probe 1
Fig. 3. Partial 1H NMR spectra of probe 1 (in CDCl3) and 1-SO3H (in CD3OD).
Infrared spectra were recorded using a Bruker Vertex 70 FT-IR spectrometer with KBr pellets. UV–vis spectra were recorded on a Shimadzu 3100 spectrometer. Fluorescence measurements were carried out using an Edinburgh Instruments Ltd-FLS920 fluorescence spectrophotometer. Synthesis of 5 Compound 5 was prepared according to the reference [63]. The synthetic detail for synthesis of this compound was shown in
Probe 1 could be easily obtained through the reaction between 5 and 1-(2-hydroxyphenyl)ethanone (Scheme 2). Compound 2 (130 mg, 0.2848 mmol), 1-(2-hydroxyphenyl)ethanone (140 mg, 1.0253 mmol) and five drops of pyrrolidine were added to 10 mL of CH2Cl2/EtOH (1:1, v/v). The resulting clear wine red solution was stirred at room temperature for additional 24 h to afford purple precipitates, which were filtered. Further purification by recrystallization in CH2Cl2 gave desired probe 1 as purple crystals (83 mg, 42%). 1H NMR (CDCl3, 400 MHz) d (ppm) 12.75 (s, 2H), 8.05–7.93 (m, 8H), 7.85–7.74 (m, 6H), 7.53 (t, J = 7.6 Hz, 2H), 7.05 (d, J = 8.4 Hz, 2H), 6.98 (t, J = 7.6 Hz, 2H), 3.81 (t, J = 7.6 Hz, 4H), 1.66–1.60 (m, 4H), 1.33–1.25 (m, 4H), 0.88 (t, J = 7.2 Hz, 6H). 13C NMR (CDCl3, 100 MHz) d (ppm) 193.4, 163.7, 162.6, 147.7, 143.7, 137.3, 136.7, 130.1, 129.6, 129.3, 129.0, 122.1, 120.0, 119.0, 118.8, 110.7, 41.9, 31.6, 20.0, 13.6; IR (KBr): 3434, 2971, 2924, 2873, 2852, 1663, 1639, 1601, 1583, 1547, 1504, 1490, 1467, 1454, 1442, 1417, 1384, 1371, 1343, 1307, 1266, 1237, 1207, 1158, 1123, 1092, 1051, 1025, 982, 880, 839, 825, 794, 749, 737, 614. ESI: m/z 693.2909(M + H)+, calculated 693.2886 for (M + H)+;
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diluted with HEPES (2-[4-(2-hydroxyethyl)-1-piperazinyl]ethanesulfonic acid) (10 mM, pH 7.4) buffer solution to obtain 2 105 or 1 105 M aqueous solution. Stock solution of common anions 3 4 2 (SO2 3 , PO4 , I , P2O7 , S2O3 , CH3COO , HCO3 , SCN , NO3 , NO2 , Cl, F, Br, SO2 ), cysteine (Cys), homocysteine (Hcy) and gluta4 thione (GSH) solutions were prepared in HEPES (10 mM, pH 7.4) buffer solution to obtain 3 102 M.
Preparation for UV–vis kinetic study Test solutions were prepared by placing 3 mL of 2 105 M probe 1 aqueous solution into a test tube, adding an appropriate volume of 3 102 M freshly prepared anion-HEPES or amino acid-HEPES. The UV–vis spectral changes were set to be monitored at 30 °C.
Preparation for fluorescence study Fig. 4. The pH-dependent fluorescence intensity (kex/kem = 356/610 nm) for probe 1 (10 lM) and 1-SO3H (10 lM) measured in various pH values at 30 °C.
Element analysis (%): C 76.20, H 5.89, N 4.14, calculated C 76.28, H 5.82, N 4.04 (Figs. S8–S10, Supporting information). Synthesis of 1-SO3H A solution of Na2SO3 (10 mg, 0.0940 mmol) in 4 mL H2O was added dropwise to a solution of 1 (28 mg, 0.0404 mmol) in 10 mL THF. After stirring at room temperature for 1 h, the solvent was evaporated under vacuum. Crude was washed with acetone and CH2Cl2 in turn, to give an orange solid (31 mg, 85%). 1H NMR (CD3OD, 400 MHz) d (ppm) 8.56 (s, 2H), 7.78–7.71 (m, 6H), 7.55–7.48 (m, 6H), 6.99–6.88 (m, 4H), 4.76 (q, J = 7.6 Hz, 2H), 3.98 (t, J = 7.2 Hz, 2H), 3.88–3.82 (m, 6H), 1.77–1.69 (m, 4H), 1.48–1.41 (m, 4H), 0.77 (t, J = 7.2 Hz, 6H). 13C NMR (CD3OD , 100 MHz) d (ppm) 209.0, 162.0, 161.0, 143.74, 136.1, 132.7, 130.9, 130.5, 130.3, 129.8, 129.0, 128.5, 128.2, 126.5, 119.6, 118.8, 117.6, 109.1, 62.9, 41.1, 40.9, 32.0, 22.3, 13.0. ESI: m/z 855.2314 (M H), calculated 855.2336 for (M H). (Figs. S11–S13, Supporting information). Sample preparation The accurately weighted amount of probe 1 was dissolved in THF to obtain 1 104 M stock solution. The stock solution was
Test solutions were prepared by placing 3 mL of 1 105 M probe 1 aqueous solution into a test tube, adding an appropriate volume of 3 102 M freshly prepared anion-HEPES or amino acid-HEPES. Normally, excitation at 356 nm. Both the excitation and emission slit widths were 5 nm 5 nm. Fluorescence spectra were monitored 20 min after addition of anions or amino acids at 30 °C.
pH titrations Probe 1 and its addition product 1-SO3H were dissolved in HEPES (10 mM, pH 7.4) THF/H2O (1:1, v/v) directly. The pHs of these solution were adjusted with HCl or NaOH aqueous solution.
Determination of the detection limit The detection limit was calculated based on the fluorescence titration. Probe 1 was employed at 1 105 M. To determine the S/N ratio, the emission intensity of probe 1 without Na2SO3 was measured by 10 times and the standard deviation of blank measurements was determined. The detection limit was then calculated with the equation: detection limit = 3rbi/m, where rbi was the standard deviation of blank measurements, m was the slope between intensity difference versus sample concentration.
Fig. 5. (a) Fluorescence spectra (kex = 356 nm) of 1 (10 lM) with SO2 3 in HEPES (10 mM, pH 7.4) THF/H2O (1:1, v/v) from 0 to 0.4 mM for 20 min at 30 °C. (b) The plot of fluorescence intensity difference (kex/kem = 356/610 nm) with probe 1 (10 lM) against varied concentration of SO2 3 in HEPES (10 mM, pH 7.4) THF/H2O (1:1, v/v) from 0 to 0.4 mM for 20 min at 30 °C.
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Fig. 6. (a) The fluorescence spectra (kex = 356 nm) of probe 1 (10 lM) in the presence of 20 equiv. of various additives in HEPES (pH = 7.4) for 20 min. (b) Fluorescence intensities (kex/kem = 356/610 nm) of probe 1 (10 lM) in the presence of 20 equiv. of various additives in HEPES (10 mM, pH 7.4) THF/H2O (1:1, v/v) for 20 min.
Results and discussion
Sensitivity and detection limit
The photophysical responses of probe 1 toward sulfite in HEPES
To investigate the possibility of precise quantitative detection of sulfite, probe 1 was treated with different concentration of sulfite in HEPES. Fig. 5a showed the SO2 3 concentration-dependent emission fluorescence spectra of probe 1 (10 lM). When excited at 356 nm, the emission fluorescence intensity at 610 nm decreased about 6-fold upon increasing the concentration of SO2 3 from 0 to 0.4 mM. A satisfactory linear relationship between fluorescence intensity difference and SO2 concentration (0–0.4 mM) was 3 observed with a correlation coefficient as high as 0.99929 (Fig. 5b). According to fluorometric method, the detection limit of probe 1 for SO2 3 was determined as 0.1 lM. This result was better than the reported fluorescent probes, while comparable to those data reported previously [24–32,34–39]. Meanwhile, the UV–vis spectrum absorption titration experiment was performed under the same conditions (Fig. S15, Supporting information), which was accordance with the fluorescent changes.
Fig. 1 showed the time-dependent absorbance and the fluorescence of probe 1 in the presence of sulfite at 30 °C in HEPES (10 mM, pH 7.4). As the reaction progressed, absorption peaks of 1 centered at 487 nm and 325 nm decreased steadily accompanied with the solution color changing from pink to colorless (Fig. 1a). At the same time, emission bands at 610 nm and 536 nm decreased steadily. Correspondingly, the emission color of the solution changed from pink to blue (Fig. 1b). From the dynamic reaction curve (Fig. 2), it could be seen that about 97% of the probe 1 was transformed to the addition product after 20 min (t1/2 3 min). Therefore, the assay time of 20 min was used in the evaluation of the selectivity and sensitivity of probe 1 toward sulfite. Mechanism
Selectivity
To confirm the formation of the addition product 1-SO3H, probe 1 was treated with Na2SO3, and the reaction product was isolated. The partial 1H NMR of 1 and the isolated 1-SO3H were shown in Fig. 3. The resonance signal corresponding to the vinylic protons (Hb and Ha at d 7.96, 7.75 ppm) of 1 disappeared with the concomitant appearance of new peaks around 4.76 ppm (quartet) assigned to the proton at Cb0 and around 3.98 and 3.85 ppm assigned to the proton at Ca0 , which indicated that the reaction took place through the Michael reaction. On the other hand, 13C resonance peaks of Ca and Cb respectively shifting from 122.06 ppm and 147.66 ppm to 40.88 ppm and 62.91 ppm (Fig. S14, Supporting information) also confirmed the addition of sulfite to the double bond. Mass spectral analysis of the resulting mixture had shown a corroborative evidence for the product 1-SO3H formation at m/z obsd 855.2314 (M H) (calcd 855.2336 for (M H)) (Fig. S13, Supporting information).
To evaluate the selectivity of probe 1, thirteen typical anions 4 2 (PO3 4 , I , P2O7 , S2O3 , CH3COO , HCO3 , SCN , NO3 , NO2 , Cl , F , 2 Br , SO4 ) and biothiols (Cys, Hcy and GSH) were investigated in parallel under the same test conditions (probe 1 as Blank). As shown in Fig. 6a, only SO2 3 generated a significant change in fluorescence intensity at about 610 nm, which was accompanied by a visual fluorescence color change from pink1 to blue, while the other anions did not show this behavior. Cys, GSH and Hcy led to fluorescence weaker at 610 nm but to much smaller extents. Adding SO2 3 into other anion solution, respectively, presented the similar emission spectra (Fig. S16, Supporting information) and fluorescence intensity (Fig. 6b) as that of the solo SO2 3 ion. The result demonstrated that probe 1 could be used to detect SO2 3 with high selectivity over other biologically relevant anions.
Effect of pH
Conclusions
The changes of fluorescence intensity under various pH values were investigated (Fig. 4). It was found that probe 1 itself was stable at pH values of 4–10 in the absence of SO2 3 , whereas the best pH value for 1-SO3H detection system was determined at pH 4–8. Considering the potential biological application, all the measurements were carried out under simulated physiological condition of pH 7.4 HEPES.
In this study, we had developed a new fluorescent probe 1 for 2 SO2 3 . The probe exhibited sensitivity and selectivity for SO3 with detection limit as low as 0.1 lM to be achieved visually within 20 min. 1 For interpretation of color in Fig. 6, the reader is referred to the web version of this article.
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Acknowledgements The authors are grateful for the support from the foundation of University of Jinan (No. XBS0923), Scientific Research Foundation for Returned Overseas Chinese Scholars, State Education Ministry (No. SQT1101), Scientific Research Foundation of University of Jinan (XKY1416) and University Young Key Teacher Home Visit by the Ministry of Education of Shandong Province. Appendix A. Supplementary material Supplementary material associated with this article can be found, in the online version, at http://dx.doi.org/10.1016/ j.saa.2014.08.144. References [1] V. Amendola, D. Esteban-Gómez, L. Fabbrizzi, M. Licchelli, Acc. Chem. Res. 39 (2006) 343–353. [2] X. Cheng, H. Jia, T. Long, J. Feng, J. Qin, Z. Li, Chem. Commun. 47 (2011) (1980) 11978–11980. [3] F. Zapata, A. Caballero, N.G. White, T.D.W. Claridge, P.J. Costa, V. Félix, P.D. Beer, J. Am. Chem. Soc. 134 (2012) 11533–11541. [4] P. Kaur, H. Kaur, K. Singh, Analyst 138 (2013) 425–428. [5] T. Noipa, T. Tuntulani, W. Ngeontae, Talanta 105 (2013) 320–326. [6] Y.-L. Duan, Y.-S. Zheng, Talanta 107 (2013) 332–337. [7] N. Pourreza, H. Golmohammadi, Talanta 119 (2014) 181–186. [8] J.-T. Hou, B.-Y. Liu, K. Li, K.-K. Yu, M.-B. Wu, X.-Q. Yu, Talanta 116 (2013) 434– 440. [9] P.A. Gale, Chem. Soc. Rev. 39 (2010) 3746–3771. [10] R. Martínez-Máñez, F. Sancenón, Chem. Rev. 103 (2003) 4419–4476. [11] B.L. Wedzicha, Chemistry of Sulphur Dioxide in Foods, Elsevier Applied Science Publishers, New York, 1984, pp. 275–311. [12] H. Vally, N.L.A. Misso, V. Madan, Clin. Exp. Allergy 39 (2009) 1643–1651. [13] R.C. Claudia, J.C. Francisco, Food Chem. 112 (2009) 487–493. [14] M. Koch, R. Köppen, D. Siegel, A. Witt, I. Nehls, J. Agric. Food Chem. 58 (2010) 9463–9467. [15] S. Iwasawa, Y. Kikuchi, Y. Nishiwaki, M. Nakano, T. Michikawa, T. Tsuboi, S. Tanaka, T. Uemura, A. Ishiqami, H. Nakashima, T. Takebayashi, M. Adachi, A. Morikawa, K. Maruyama, S. Kudo, I. Uchiyama, K. Omae, J. Occup. Health 51 (2009) 38–47. [16] N. Sang, Y. Yun, H. Li, L. Hou, M. Han, G. Li, Toxicol. Sci. 114 (2010) 226–236. [17] J.M. Vahl, J.E. Converse, J. Assoc. Off. Anal. Chem. 63 (1980) 194–199. [18] D.R. Migneault, Anal. Chem. 61 (1989) 272–275. [19] N. Ekkad, C.O. Huber, Anal. Chim. Acta 332 (1996) 155–160. [20] R. Spricigo, R. Dronov, F. Lisdat, S. Leimkühler, F.W. Scheller, U. Wollenberger, Anal. Bioanal. Chem. 393 (2009) 225–233. [21] S. Sasaki, K. Ikebukuro, Y. Arikawa, M. Shimomura, I. Karube, Anal. Commun. 34 (1997) 299–302. [22] G. Brychkova, D. Yarmolinsky, R. Fluhr, M. Sagi, Plant Sci. 190 (2012) 123–130. [23] S.S.M. Hassan, M.S.A. Hamza, A.H.K. Mohamed, Anal. Chim. Acta 570 (2006) 232–239. [24] M.G. Choi, J. Hwang, S. Eor, S.-K. Chang, Org. Lett. 12 (2010) 5624–5627. [25] S. Chen, P. Hou, J. Wang, X. Song, RSC Adv. 2 (2012) 10869–10873.
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