A ready-to-use multifunctional coordinative system, 2,2’-dihydroxyazobenzene –aluminum (III) (DHAB–Al3+), was created to recognize several anions effectively through three channels, namely colorimetric detection, UV-Vis spectroscopy, and fluorescence spectroscopy. Under naked eye visualization, the H2PO−4 can be readily distinguished from the other anions by the DHAB–Al3+ system through a change in color from reddish-orange to light yellow.
Turk J Chem (2015) 39: 905 916 ă ITAK ˙ c TUB ⃝ Turkish Journal of Chemistry http://journals.tubitak.gov.tr/chem/ doi:10.3906/kim-1412-37 Research Article Effective recognition of multiple anions by an azobenzene–Al 3+ system Ye ZHANG, Ping JIA, Zhangfa TONG, Hai-Bo LIU, Jing WANG∗ Guangxi Key Laboratory of Petrochemical Resource Processing and Process Intensification Technology, School of Chemistry and Chemical Engineering, Guangxi University, Nanning, P.R China Received: 15.12.2014 • Accepted/Published Online: 18.03.2015 • Printed: 30.10.2015 Abstract: A ready-to-use multifunctional coordinative system, 2,2’-dihydroxyazobenzene –aluminum (III) (DHAB– Al 3+ ) , was created to recognize several anions effectively through three channels, namely colorimetric detection, UV-Vis spectroscopy, and fluorescence spectroscopy Under naked eye visualization, the H PO − can be readily distinguished from the other anions by the DHAB–Al 3+ system through a change in color from reddish-orange to light yellow H PO − 2− − was qualitatively detected by using UV-Vis and fluorescence spectra Differentiating SO 2− , HPO , and HCO anions 2− 2− − colorimetrically is difficult; thus, CO 2− , SO , HPO , and HCO were discriminated by adopting distinct changes 2− − in the UV-Vis spectra CO 2− , HPO , and HCO were accurately quantified using fluorescence spectra The DHAB– 2− Al 3+ system responded to H PO − via a sensing mechanism based on a displacement approach By contrast, and CO 2− − the system responded to SO 2− , HPO , and HCO based on a binding site–signaling subunit approach The DHAB– 2− 2− 2− Al 3+ system can determine the concentration ranges of H PO − with the naked eye and quantify CO , SO , HPO , and HCO − through UV-Vis spectra Key words: Multifunctional, colorimetrically, DHAB–Al 3+ system, anions Introduction Anions serve important functions in chemical and physiological systems and in the environment For example, 2− phosphates (e.g., H PO − and HPO ) are associated with a variety of fundamental processes, such as genetic information storage, energy transduction, signal processing, and membrane transport Sulfite (SO 2− ) contents should be strictly limited in foods and beverages because of the potential toxic and harmful effects of sulfur on hypersensitive people Carbonate (CO 2− ) is only slightly toxic, but large doses of the anion are corrosive to the gastrointestinal tract, causing severe abdominal pain, vomiting, diarrhea, collapse, and possible death Hydrogen carbonate (HCO − ), a substrate in photosynthesis generated during cellular respiration from carbon dioxide, maintains the pH of biological fluids Among the various methods for detecting anions, optical methods (fluorescence or UV-Vis spectroscopy) are the most prominent because of their high sensitivity and operational simplicity, while colorimetric assays are the most desirable because they are inexpensive and allow naked-eye detection Colorimetric and optical detections of anions have attracted much attention in recent years 6−11 Researchers have designed and developed various single-ion responsive organic or hybrid systems; 12,13 however, the construction of multi-ion recognition systems with differential response modes remains challenging 14−17 To ∗ Correspondence: wjwyj82@gxu.edu.cn 905 ZHANG et al./Turk J Chem the best of our knowledge, a single method that can discriminate between more than two anions using a single probe has remained elusive so far 18,19 Thus, we aimed to design a single system that can differentiate multiple anions via differential responses Azobenzene, one of the most common and frequently used chromophores, has been widely used as a signal group in designing colorimetric sensors 20,21 However, applications of the azobenzene group acting as the recognition group have been rarely studied in the sensor field 22 The azobenzene derivative 2,2’-dihydroxyazobenzene (DHAB), which features hydroxyl groups at the ortho position, is an important organic complexing reagent 23 DHAB can coordinate with a variety of metal ions, such as Cu 2+ , Zn 2+ , and Al 3+ , but the optical properties of DHAB-related systems, especially their applicability in sensors, have not been widely studied 24,25 In our previous work, we found that high selectivity of DHAB derivatives for metal ions could be achieved by tuning the substitution groups, 26 and highly selective and sensitive anion sensors could be obtained by combining DHAB ligands and metal ions DHAB–metal systems provide a unique function compared with individual DHAB or metal ions For example, we reported a DHAB–Cu 2+ system used for detecting CN − , 27 and the 28 DHAB–Zn 2+ system can detect H PO − Similar to most sensor designs, however, the DHAB–Cu 2+ and DHAB–Zn 2+ systems are restricted to measuring one specific anion Therefore, developing a DHAB–metal system with multifunctional capabilities that can identify more than two anions is an important undertaking The responsiveness of DHAB–metal systems toward anions can be tuned by varying the metal ions in the complex DHAB, a fluorogenic ligand of aluminum(III) (Al 3+ ), has been used to quantify Al 3+ by fluorometry 29−32 In spite of these studies, however, no fluorescence response of the DHAB–Al 3+ system in the presence of anions was investigated before In the present work, we examined the responses of DHAB–Al 3+ to − 2− 2− 2− − − 3+ seven anions, i.e SO 2− , NO , CO , SO , HPO , H PO , and HCO We report that the DHAB–Al 2− 2− − − system can differentiate five anions, SO 2− , CO , HPO , H PO , and HCO , through changes in color and absorption and fluorescence spectra The concentration range of the anions may be determined with the naked eye or through distinct variations in UV-Vis spectra, which is useful for future applications Results and discussion 2.1 Interaction between DHAB and Al 3+ DHAB can chelate with Al 3+ with 1:1 and 2:1 stoichiometry The 1:1 aluminium(III) chelate is fluorescent, whereas the 2:1 chelate is not fluorescent 31 It was found in earlier studies 29−32 that the pH can control the composition of DHAB and Al 3+ In order to obtain the fluorescent 1:1 DHAB-Al 3+ complex, the interaction between DHAB and Al 3+ was examined, through UV-Vis and fluorescence spectroscopy, in EtOH-(0.1 M piperazine-N,N-bis(2-ethanesulfonic acid) (PIPES)-KOH) buffer (1:1, v/v) at pH 6.5 Figure 1a depicts the absorption spectra of DHAB in the presence of various concentrations of Al 3+ Free DHAB exhibits two absorption bands at 325 nm and 395 nm, corresponding to its azo (Scheme a) and hydrazone forms (Scheme b), respectively 33 Upon addition of increasing amounts of Al 3+ , the band at 395 nm gradually decreased (Figure 1b) The band at 325 nm slightly decreased and exhibited a bathochromic shift to a new band at 330 nm, along with the simultaneous emergence of a new absorption at 480 nm 29−32 A well-defined isosbestic point was noted at 425 nm, which suggests the formation of a complex between DHAB and Al 3+ (DHAB–Al 3+ ) Azo–hydrazone tautomerism occurs after Al 3+ complexation, and DHAB in the DHAB–Al 3+ complex exists in azo form 34 906 ZHANG et al./Turk J Chem (a) 0.2 0.3 0.4 0.5 0.6 0.8 0.9 1.0 2.0 3.0 4.0 5.0 10.0 20.0 0.3 Absorbance (a.u.) 0.40 Concentration of Al 3+ (10 -5 M) 0.2 0.1 0.0 (b) 0.35 0.30 Absorbance (a.u.) 0.4 0.25 0.20 0.15 0.10 480 nm 395 nm 325 nm 0.05 0.00 300 400 500 600 Wavelength (nm) 10 Concentration of Al 15 3+ 20 -5 (10 M) Figure (a) UV-Vis spectra of DHAB (2.0 × 10 −5 M) upon gradual addition of Al 3+ (0–2.0 × 10 −4 M) and (b) effect of Al 3+ (0–2.0 × 10 −4 M) on the change in the UV-Vis spectra of DHAB (2.0 × 10 −5 M) at 325 nm, 395 nm, and 480 nm in EtOH-(0.1 M PIPES-KOH) buffer (1:1, v/v) at pH 6.5 O OH N N N H N OH OH (a) (b) Scheme Two tautomeric forms of 2,2’-dihydroxyazobenzene (DHAB): (a) azo form and (b) hydrazone form We conducted fluorescence titration experiments of DHAB in the presence of Al 3+ under the same conditions Figure 2a shows that DHAB exhibits almost no fluorescence as a typical azo dye 33 even though the hydroxyl group at the ortho position of DHAB can prevent trans-to-cis isomerization to some extent Upon treatment with increasing concentrations of Al 3+ , a new peak at approximately 575 nm appeared and gradually increased before reaching saturation when the amount of Al 3+ exceeded equiv (Figure 2b) The strong fluorescence of DHAB in the presence of Al 3+ may be due to blockage of the cis–trans transformation of azobenzene as well as abolishment of intramolecular hydrogen bonding upon coordination of Al 3+ with DHAB 34 The Job’s plot revealed a 1:1 stoichiometry for the binding between DHAB and Al 3+ (Figures 3a, 3b, and S1 (on the journal’s website)), the association constant (K ass ) of which was determined from the fluorescence titration curve to be about 6.5 × 10 M −1 (Figure S2) 2.2 Responses of the DHAB–Al 3+ system to various anions − 2− 2− The responses of the DHAB–Al 3+ (2.0 × 10 −5 M/4.0 × 10 −5 M) system to SO 2− , NO , CO , SO , − − −3 HPO 2− M) were investigated by monitoring changes in solution color as , H PO , and HCO (4.0 × 10 well as absorption and emission spectra in EtOH-(0.1 M PIPES-KOH) buffer (1:1, v/v) at pH 6.5 907 ZHANG et al./Turk J Chem 400 Fluorescence intensity (a.u.) Concentration of Al 3+ (10 -5 M) 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 2.0 3.0 4.0 5.0 10.0 20.0 300 200 100 500 600 700 Fluorescence intensity at 575 nm (a.u.) 400 (a) (b) 300 200 100 800 10 15 20 Concentration of Al 3+ (10 -5 M) Wavelength (nm) Figure (a) Fluorescence spectra of DHAB (2.0 × 10 −5 M) upon gradual addition of Al 3+ (0–2.0 × 10 −4 M) and (b) effect of Al 3+ (0–2.0 × 10 −4 M) on the change in the fluorescence spectra of DHAB (2.0 × 10 −5 M) at 575 nm in EtOH-(0.1 M PIPES-KOH) buffer (1:1, v/v) at pH 6.5 λex = 330 nm 700 700 (a) Mole fraction of Al 3+ 0.1 0.2 0.3 0.325 0.35 0.375 0.4 0.5 0.6 0.625 0.65 0.675 0.7 0.8 0.9 1.0 500 400 300 200 100 Fluorescence intensity at 575 nm (a.u.) Flurorescence intensity (a.u.) 600 (b) 600 500 400 300 200 100 0 500 600 700 800 0.0 0.2 Wavelength (nm) Figure (a) and (b) Job’s plot of DHAB and Al and Al 3+ 0.4 0.6 Mole fraction of Al 3+ 0.8 1.0 3+ , λex = 330 nm, λem = 575 nm The total concentration of DHAB ion is 0.1 mM, in EtOH-(0.1 M PIPES-KOH) buffer (1:1, v/v) at pH 6.5 We first examined color changes of the DHAB–Al 3+ and DHAB system in the presence of anions (4.0 × 10 −3 M) (Figures 4a and 4b) Figure 4a shows that the reddish-orange DHAB–Al 3+ solution turns light yellow 2− − when H PO is added to it Anions such as SO 2− , HPO , and HCO induced dramatic color changes from 2− − reddish-orange to red under identical conditions; however, discriminating between SO 2− , HPO , and HCO with the naked eye was difficult The color of the DHAB–Al 3+ system showed no or nearly no change in the 2− 2− presence of NO − , CO , and SO DHAB–Al 3+ displays two main peaks centered at 330 nm and 480 nm as illustrated in Figure Upon treatment with H PO − , the band at 480 nm disappeared, and the band at 330 nm showed hypsochromic ( ∆λ = nm) and hyperchromic (1.25-fold) shifts with concomitant development of a new absorption band at 395 nm When CO 2− was added to the DHAB–Al 3+ system, the intensity of the absorption band at 480 nm decreased with the concomitant formation of a new blue-shifted band at approximately 325 nm and the appearance of a 908 ZHANG et al./Turk J Chem new shoulder band at approximately 600 nm The absorbance of DHAB–Al 3+ at 480 nm red-shifted to about 2− − 2− 2− 505 nm by addition of SO 2− , HPO , and HCO ; however, recognizing 100 equiv of SO , HPO , and − 2− HCO − through UV-Vis spectroscopy was difficult In the presence of NO and SO , the position of the 2− absorption peak was maintained with increases (NO − ) or decreases (SO ) in the absorbance of the DHAB– Al 3+ system at 480 nm The emission of the DHAB–Al 3+ system at 575 nm was completely quenched by all 2− of the investigated anions except for NO − (Figure 6) and SO SO 32- NO 2- CO 32- SO 42- HPO 42- H 2PO 4- HCO 3- DHAB-Al 3+ (a) SO 32- NO 2- CO 32- SO 42- HPO 42- H 2PO 4- HCO 3- DHAB (b) Figure Colorimetric changes in (a) DHAB–Al 3+ (2.0 × 10 −5 M/4.0 × 10 −5 M) and (b) DHAB (2.0 × 10 −5 M) when different anions are added (4.0 × 10 −3 M, 100 equiv of Al 3+ , 200 equiv of DHAB) in EtOH-(0.1 M PIPES-KOH) − 2− 2− 2− − − buffer (1:1, v/v) at pH 6.5 Anions from left to right: SO 2− , NO , CO , SO , HPO , H PO , HCO , and blank 0.4 400 DHAB-Al 3+ SO 32- 0.3 CO 2- Fluorescence intensity (a u.) Absorbance (a.u.) DHAB-Al SO 2NO 2CO 2SO 2HPO H2 PO HCO NO SO 42HPO 2- H2 PO 0.2 HCO - - 0.1 0.0 300 200 3+ 100 300 400 500 500 600 Wavelength (nm) Figure UV-Vis spectra of DHAB–Al 3+ (2.0 × 10 −5 700 800 Figure Fluorescence spectra of DHAB–Al 3+ (2.0 × −3 10 −5 M/4.0 × 10 −5 M) in the presence of anions (4.0 M, 100 equiv of Al 3+ ) in EtOH-(0.1 M PIPES-KOH) × 10 −3 M, 100 equiv of Al 3+ ) in EtOH-(0.1 M PIPES- buffer (1:1, v/v) at pH 6.5 KOH) buffer (1:1, v/v) at pH 6.5 λex = 330 nm M/4.0 × 10 −5 600 Wavelength (nm) M) in the presence of anions (4.0 × 10 These results indicate that the DHAB–Al 3+ system might exhibit specific colorimetric selectivity for − 2− H PO − in the UV-Vis channel We thus hypothesized that the and could recognize H PO and CO 2− − DHAB–Al 3+ system responds to SO 2− , HPO , and HCO with differential modes even though 100 equiv 2− − of SO 2− , HPO , and HCO cannot be discriminated visually or optically We conducted detailed titration experiments to demonstrate the above assumption and explored the possible mechanisms 909 ZHANG et al./Turk J Chem 2.3 Sensitivity of the DHAB–Al 3+ system to anions and mechanism studies Changes in the color and UV-Vis and fluorescence spectra of the DHAB (2.0 × 10 −5 M) and DHAB–Al 3+ (2.0 × 10 −5 M/4.0 × 10 −5 M) system upon titration of anions are shown in Figures 7–10 and Figures S3–S9 Among the seven anions investigated, the DHAB–Al 3+ system displayed no or almost no response to SO 2− (Figure S8) and NO − (Figure S9) 0.30 0.25 DHAB SO3 2NO2 - Absorbance (a.u.) 0.20 CO3 2SO4 2- 0.15 HPO4 2H2PO4 HCO3 - 0.10 0.05 0.00 300 400 500 600 Wavelength (nm) Figure UV-Vis spectra of DHAB (2.0 × 10 −5 M) in the presence of anions (4.0 × 10 −3 M, 200 equiv of DHAB) in EtOH-(0.1 M PIPES-KOH) buffer (1:1, v/v) at pH 6.5 SO 32- NO 2- CO 32- SO 42- HPO 42- H 2PO HCO DHAB-Al 3+ - - × 10-3 M × 10-3 M × 10-4 M × 10-4 M × 10-4 M × 10-4 M × 10-5 M × 10-5 M Figure Photographs showing the color change of the DHAB–Al 3+ system (2 × 10 −5 M/4 × 10 −5 M) in the presence of different concentrations of anions (from 0.5 equiv to 50 equiv of Al 3+ ) in EtOH-(0.1 M PIPES-KOH) buffer (1:1, v/v) at pH 6.5 910 ZHANG et al./Turk J Chem 0.4 0.4 (a) (b) - Concentration of CO32- (10 -5M) -5 Concentration of H 2PO4 (10 M) 1.0 2.0 5.0 8.0 10.0 20.0 40.0 80.0 100.0 200.0 0.2 0.1 0.3 Absorbance (a u.) Absorbance (a u.) 0.3 0.1 0.2 0.5 0.8 1.0 2.0 5.0 8.0 10.0 20.0 40.0 80.0 100.0 200.0 0.2 0.1 0.0 0.0 300 400 500 600 300 400 500 Wavelength (nm) 600 Wavelength (nm) Absorption spectra of DHAB–Al 3+ (2.0 × 10 −5 M/4.0 × 10 −5 M) upon progressive addition of (a) Figure −3 H PO − M, 0–50 equiv of Al 3+ ) and (b) CO 2− (0–2.0 × 10 −3 M, 0–50 equiv of Al 3+ ) in EtOH-(0.1 (0–2.0 × 10 M PIPES-KOH) buffer (1:1, v/v, at pH 6.5) 0.4 0.4 (a) Concentration of SO 32- (10 -5 M) Absorbance (a.u.) 0.3 0.2 0.1 Concentration of HPO42- (10 -5 M) 0.1 0.2 0.5 0.8 1.0 2.0 5.0 8.0 10.0 20.0 40.0 80.0 100.0 200.0 0.2 0.1 0.0 0.0 300 (b) 0.3 Absorbance (a.u.) 0.1 0.2 0.5 0.8 1.0 2.0 5.0 8.0 10.0 20.0 40.0 80.0 100.0 200.0 400 500 Wavelength (nm) 600 300 400 500 Wavelength (nm) 600 0.4 (c) Concentration of HCO3- (10 -5 M) 0.1 0.2 0.5 0.8 1.0 2.0 5.0 8.0 10.0 20.0 40.0 80.0 100.0 200.0 Absorbance (a.u.) 0.3 0.2 0.1 0.0 300 400 500 600 Wavelength (nm) Figure 10 Absorption spectra of DHAB–Al 3+ (2.0 × 10 −5 M/4.0 × 10 −5 M) upon progressive addition of (a) SO 2− (0–2.0 × 10 −3 M, 0–50 equiv of Al 3+ ) , (b) HPO 2− (0–2.0 × 10 −3 M, 0–50 equiv of Al 3+ ) and (c) HCO − (0–2.0 × 10 −3 M, 0–50 equiv of Al 3+ ) in EtOH-(0.1 M PIPES-KOH) buffer (1:1, v/v, at pH 6.5) 911 ZHANG et al./Turk J Chem 2− 2.3.1 Displacement approach: H PO − and CO 2.3.1.1 Detection of H PO − DHAB, which features absorption peaks at 325 nm and 395 nm, showed no response to H PO − (Figures 4b and 7) The DHAB and DHAB–Al 3+ system exhibited light yellow (Figure 4b) and reddish-orange (Figures 4a and 8) coloration, respectively The color, absorption, and emission spectra of DHAB gradually recovered 3+ upon titrating H PO − (2.0 × 10 −5 M/4.0 × 10 −5 M) system with the DHAB–Al −5 M, the color of the DHAB–Al 3+ system changed At H PO − concentrations at or above 5.0 × 10 from reddish-orange to light yellow (Figure 8) When H PO − was added to this system, the intensity of the absorption and emission bands of the DHAB–Al 3+ system at λmax,abs = 480 nm (Figure 9a) and λem = 575 nm (Figure S3a) rapidly and significantly decreased A new absorption band at 395 nm also appeared and gradually increased, and moderate hypsochromic ( ∆λ = nm) and hypochromic shifts were observed for the band centered at 330 nm DHAB recovery was attributed to the larger association constant 35 between 3+ 36 3+ , i.e H PO − from the Al 3+ and H PO − bonded with the Al than that of the complex of DHAB–Al DHAB–Al 3+ system, DHAB-Al 3+ dissociated, and DHAB was released from the system −5 Various concentration ranges of H PO − M, 2.0 × 10 −5 –5.0 × 10 −5 M, and above (0–2.0 × 10 5.0 × 10 −5 M) could be determined with the naked eye by utilizing the DHAB–Al 3+ system (Figure 8) The fluorescence intensity at 575 nm also showed a linear relationship (R = 0.997, Figure S4a) with H PO − concentration, which indicates that the DHAB–Al 3+ system is particularly sensitive to the detection of H PO − 2.3.1.2 Detection of CO 2− When 200 equiv of CO 2− was added to the DHAB solution, the absorption of DHAB at 325 nm decreased as the peak at 395 nm disappeared, as illustrated in Figure A new peak at 485 nm and a shoulder-like absorption peak at about 600 nm appeared, with the solution color changing from light yellow to reddish-orange (Figure 4b) The UV-Vis and fluorescence spectra of the DHAB–Al 3+ system exhibited almost no change in the presence of 0–2.0 × 10 −5 M CO 2− , as shown in Figures 9b and S3b In the concentration range of 5.0 × 10 −5 –4.0 × 10 −4 M, the absorbance of the DHAB–Al 3+ system at 480 nm decreased and gradually redshifted to 502 nm The fluorescence at 575 nm gradually decreased, which may be caused by equilibration 2− among DHAB, Al 3+ , and CO 2− concentration was above 8.0 × 10 −4 M, a new absorption When the CO peak at approximately 600 nm appeared and the absorption peak at 330 nm blue-shifted by nm (325 nm) and decreased The absorption peak at 480 nm red-shifted by nm (485 nm) (Figure 9b) and fluorescence at 575 nm was completely quenched (Figure S3b); these results are attributed to the interaction between DHAB and CO 2− (Figure 7) The concentration range of CO 2− cannot be determined by color changes (Figure 8) and 3 must instead by monitored via changes in UV-Vis spectra (Figure 9b) The fluorescence at 575 nm showed an interesting “turn-off” optical response when 5.0 × 10 −5 –8.0 × 10 −4 M of CO 2− was added, as shown in Figure S3b Varying the concentrations of CO 2− resulted in a 3 particularly linear response (R = 0.992) over the concentration range of 5.0 × 10 −5 –1.0 × 10 −4 M (Figure S4b) 912 ZHANG et al./Turk J Chem 2− − 2.3.2 Binding site–signaling subunit approach: detection of SO 2− , HPO , and HCO 2− − The responses of the DHAB–Al 3+ system to SO 2− , HPO , and HCO are shown in Figures 8, 10, and S5–S9 2− − When the concentration of the three anions was in the range of 0–1.0 × 10 −4 M, SO 2− , HPO , and HCO could be discriminated by the naked eye (Figure 8) The DHAB–Al 3+ system did not exhibit color changes −5 for SO 2− M) to light yellow The system underwent three color changes: from reddish orange (2.0 × 10 (5.0 × 10 −5 M)-light red (1.0 × 10 −4 M) upon coordination with HPO 2− , and from reddish orange (0–5.0 2− 2− × 10 −4 M) to red (1.0 × 10 −4 M) upon addition of HCO − Selective visual recognition of SO , HPO , −4 and HCO − M UV-Vis spectra and fluorescence (Figure 8) was difficult at concentrations above 2.0 × 10 spectra were measured in detailed titration experiments to further investigate the selectivity and sensitivity of 2− − the DHAB–Al 3+ system to SO 2− , HPO , and HCO Detection of SO 2− : The absorption (Figure 10a) and fluorescence spectra (Figure S5) of the DHAB– Al 3+ system did not initially exhibit any detectable change in the presence of 0–1.0 × 10 −4 M SO 2− When SO 2− concentrations at or above 2.0 × 10 −4 M were added to the system, however, the absorption spectra displayed an nm red-shift with a new peak appearing at approximately 505 nm (Figure 10a) The fluorescence intensity at 575 nm was significantly quenched (Figure S5), which was attributed to the interaction between SO 2− and Al 3+ in the DHAB–Al 3+ system because DHAB is unreactive to SO 2− (Figures 4b and 7) The 3 DHAB–Al 3+ –SO 2− system exhibited nearly constant absorbance at 480 nm (0–1.0 × 10 −4 M) and 505 nm 2− (above 2.0 × 10 −4 M of SO 2− can be qualitatively recognized but not quantitated using the ) Thus, SO proposed DHAB–Al 3+ system Detection of HPO 2− : The typical absorption peak centered at 480 nm decreased slightly after 0–5.0 × 10 −5 M of HPO 2− was added to the DHAB–Al 3+ system (Figure 10b) The absorption spectra of the DHAB–Al 3+ system underwent a blue-shift from 480 nm to 474 nm when the concentration of HPO 2− was 5.0 × 10 −5 –1.0 × 10 −4 M and a red-shift from 474 nm to 500 nm when the concentration of HPO 2− was 1.0 × 10 −4 –4.0 × 10 −4 M After HPO 2− concentrations of up to 4.0 × 10 −4 M were added to the system, the absorbance at 500 nm decreased with the appearance of a new band at approximately 395 nm and generation of an isosbestic point at 425 nm, which indicates equilibrium between DHAB and DHAB–HPO 2− (Figure 7) The fluorescence intensity of the DHAB–Al 3+ system at 575 nm gradually decreased (Figure S6a) Data analysis showed that a linear relationship exists between normalized fluorescence intensities at 575 nm and HPO 2− concentrations in the range of 2.0 × 10 −5 –1.0 × 10 −4 M (Figure S6b) Regrettably, consecutive blue (5.0 × 10 −5 –1.0 × 10 −4 M) and red shifts (1.0 × 10 −4 –4.0 × 10 −4 M) in absorbance depending on the concentrations of HPO 2− were unclear at this stage 3+ Detection of HCO − system showed equilibration when less than 1.0 × 10 −4 M : The DHAB–Al − of HCO − was added to it, as shown in Figures 10c and S7a As the amount of HCO increased to 2.0 × 10 −4 M, the absorbance red-shifted to 490 nm and the fluorescence at 575 nm decreased significantly In the range of 2.0 × 10 −4 –2.0 × 10 −3 M, the absorbance at 490 nm increased and gradually red-shifted to 504 nm when the concentration of HCO − was increased (Figure 10c) The fluorescence at 575 nm was also drastically 3+ quenched during titration (Figure S7a) because of the interaction between HCO − in DHAB–Al 3+ and Al 913 ZHANG et al./Turk J Chem given that DHAB does not respond to HCO − , as shown in Figures 4b and A relationship with R = 0.993 (linear range: 5.0 × 10 −5 –2.0 × 10 −4 M) allows quantification of HCO − (Figure S7b) 2− 2− − − The DHAB–Al 3+ system allowed differentiation of SO 2− , CO , HPO , H PO , and HCO using − − 2− dual channels via colorimetric determination and UV-Vis spectra CO 2− , HPO , H PO , and HCO could be sensitively detected by detecting changes in the fluorescence spectra of the DHAB–Al 3+ system Conclusions A three-channel system, including colorimetric, ultraviolet, and fluorescent systems, based on DHAB–Al 3+ has 2− 2− − − 2− been presented to identify SO 2− (5.0 , CO , HPO , H PO , and HCO qualitatively and detect CO − −5 × 10 −5 –1.0 × 10 −4 M), HPO 2− (2.0 × 10 −5 –1.0 × 10 −4 M), H PO − –1.0 × 4 , and HCO (2.0 × 10 2− 10 −4 M) quantitatively H PO − were detected using the displacement approach, while effective and CO 2− − detection of SO 2− , HPO , and HCO was achieved using the binding site–signaling subunit approach 2− 2− The DHAB–Al 3+ system allowed determination of the concentration ranges of SO 2− , HPO , CO , − H PO − , and HCO with the naked eye (colorimetric detection) or through the UV-Vis spectra The DHAB– 2− − 2− − 2− Al 3+ system can discriminate SO 2− , CO , and H PO from SO , HCO , and HPO , respectively, with the naked eye or by UV-Vis spectroscopy in EtOH-(0.1 M PIPES-KOH) buffer (1:1, v/v) at pH 6.5 Experimental 4.1 Materials and instrumentations All the chemicals used were of analytical reagent grade and purchased from Sigma-Aldrich Chemical Company UV-Vis absorption spectra were recorded using a TU-1900 spectrophotometer Fluorescence spectra measurements were performed on a 960 MC fluorescence spectrophotometer The excitation and emission slit width was kept constant at nm 4.2 Preparation of stock solutions First, 0.0214 g of DHAB (4.0 × 10 −4 M) and 0.0240 g of AlCl (2.0 × 10 −3 M) were dissolved in 250.0 mL and 50.0 mL EtOH-(0.1 M PIPES-KOH) buffer (1:1, v/v), respectively A total of 0.0126 g of Na SO (2.0 × 10 −3 M), 0.0069 g of NaNO (2.0 × 10 −3 M), 0.0106 g of Na CO (2.0 × 10 −3 M), 0.0084 g of NaHCO (2.0 × 10 −3 M), 0.0142 g of Na SO (2.0 × 10 −3 M), 0.0358 g of Na HPO (2.0 × 10 −3 M), and 0.0156 g of NaH PO (2.0 × 10 −3 M) were separately dissolved in 50.0 mL of EtOH-(0.1 M PIPES-KOH) buffer (1:1, v/v) 4.3 Preparation of anion titration solutions A stock solution of the DHAB–Al 3+ (4.0 × 10 −5 M/8.0 × 10 −5 M) system was obtained by adding AlCl (1.6 × 10 −4 M, 50 mL) to the solution of DHAB (8.0 × 10 −5 M, 50 mL) in EtOH-(0.1 M PIPES-KOH) buffer (1:1, v/v) Test solutions were prepared by placing 2.0 mL of the DHAB–Al 3+ stock solution in a test tube, adding an appropriate aliquot of each anion stock, and diluting the solution to 4.0 mL with EtOH-(0.1 M PIPES-KOH) buffer (1:1, v/v) Excitation was performed at 330 nm for all measurements Both excitation and emission slit widths were nm 914 ZHANG et al./Turk J Chem Acknowledgments This work was financially supported by National Natural Science Foundation of China (Grant No 31360020), Scientific Research Foundation of Guangxi University (Grant No XGZ130080 and XGZ130081), Scientific Research Foundation for the Returned Overseas Chinese Scholars, State Education Ministry ([2014]1985), and grants funded by Opening Project of Guangxi Key Laboratory of Petrochemical Resource Processing and Process Intensification Technology (No 2013K002) as well as the Foundation for Fostering Talents of Department of Chemistry & Chemical Engineering, Guangxi University (Grant No 2013102) Supplementary Material Supplementary data associated with this 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575 –4 –3 8.0 × 10 M–2.0 × 10 M 325, 485, 600 ― 0–1.0 × 10–4 M 330, 480 575 2.0 × 10–4 M–2.0 × 10–3 M 330, 505 ― 330, 480 575 5.0 × 10 M–1.0 × 10 M 330, 474 575 1.0 × 10–4 M–4.0 × 10–4 M 330, 500 575 325, 395, 500 ― 330, 480 575 330, 490 575 330, 504 ― 5.0 × 10 M–4.0 × 10 M –5 –4 –3 4.0 × 10 M–2.0 × 10 M –4 0–1.0 × 10 M HCO3 575 330, 480 –4 – 330, 480 –4 0–5.0 × 10 M HPO4 λmax,ems/nm –5 –5 2– λmax,abs/nm 1.0 × 10–4 M–2.0 × 10–4 M –4 –3 2.0 × 10 M–2.0 × 10 M 2– 0–2.0 × 10 M 330, 480 575 NO2– 0–2.0 × 10–3 M 330, 480 575 SO4 –3 2.0 Mole fraction of Al3+ 0.1 0.2 0.3 0.325 0.35 0.375 0.4 0.5 0.6 0.625 0.65 0.675 0.7 0.8 0.9 1.0 Absorbance (a u.) 1.5 1.0 0.5 0.0 300 400 500 600 Wavelength (nm) Figure S1 Job’s plot of DHAB and Al3+, the total concentration of DHAB and Al3+ ion is 0.1 mM, pH 6.5 0.14 0.12 0.10 I0 / I-I0 0.08 0.06 0.04 0.02 0.00 -0.02 1.0 1.5 2.0 2.5 3.0 3.5 / [Al3+] (105 M-1) Figure S2 Estimation of association constant for DHAB and Al3+ The plot was calculated based on 1:1 binding model (R2 = 0.992) I and I0 are the fluorescence of DHAB at 575 nm in the presence and absence of Al3+, respectively 400 500 (a) (b) Concentration of CO32- (10-5 M) 300 Fluorescence intensity (a u.) Fluorescence intensity (a u.) Concentration of H2PO4- (10-5 M) 1.0 2.0 5.0 8.0 10.0 20.0 40.0 80.0 100.0 200.0 200 100 400 0.1 0.2 0.5 0.8 1.0 2.0 5.0 8.0 10.0 20.0 40.0 80.0 100.0 200.0 300 200 100 0 500 550 600 650 700 750 800 500 550 600 Wavelength (nm) 650 700 750 800 Wavelength (nm) Figure S3 Fluorescence spectra of DHAB–Al3+ (2.0 × 10–5 M/4.0 × 10–5 M) upon progressive addition of (a) H2PO4– (0–2.0 × 10–3 M) and (b) CO32– (0–2.0 × 10–3 M) in EtOH-(0.1 M PIPES-KOH) buffer (1:1, v/v, at pH 6.5) 500 (a) Fluorescence intensity at 575 nm Fluorescence intensity at 575 nm 400 350 300 250 200 150 100 (b) 400 300 200 100 -100 50 100 150 200 Concentration of H2PO4- (10-5 M) 250 10 12 Concentration of CO32- (10-5 M) Figure S4 Plot of fluorescence intensity of DHAB–Al3+ (2.0 × 10–5 M/4.0 × 10–5 M) at 575 nm versus the concentrations of (a) H2PO4– (0–2.0 × 10–3 M) and (b) CO32– (0, 5.0 × 10–5 M–1.0 × 10–4 M) 500 Fluorenscence intensity (a u.) Concentration of SO32- (10-5M) 400 0.1 0.2 0.5 0.8 1.0 2.0 5.0 8.0 10.0 20.0 40.0 80.0 100.0 200.0 300 200 100 500 550 600 650 700 750 800 Wavelength (nm) Figure S5 Fluorescence spectra of DHAB–Al3+ (2.0 × 10–5 M/4.0 × 10–5 M) upon progressive addition of SO32– (0–2.0 × 10–3 M) in EtOH-(0.1 M PIPES-KOH) buffer (1:1, v/v, at pH 6.5) 500 (a) 2- -5 Fluorescence intensity (a u.) Concentration of HPO4 (10 M) 400 0.1 0.2 0.5 0.8 1.0 2.0 5.0 8.0 10.0 20.0 40.0 80.0 100.0 200.0 300 200 100 Fluorescence intensity at 575 nm 500 (b) 400 300 200 100 0 500 550 600 650 Wavelength (nm) 700 750 800 10 12 Concentration of HPO42- (10-5 M) Figure S6 (a) Fluorescence spectra of DHAB–Al3+ (2.0 × 10–5 M / 4.0 × 10–5 M) upon progressive addition of HPO42– (0–2.0 × 10–3 M) in EtOH-(0.1 M PIPES-KOH) buffer (1:1, v/v, at pH 6.5); (b) plot of fluorescence intensity at 575 nm versus the concentrations of HPO42– (0, 2.0 × 10–5 M–1.0 × 10–4 M) 500 (a) Concentration of HCO3- (10-5 M) 0.1 0.2 0.5 0.8 1.0 2.0 5.0 8.0 10.0 20.0 40.0 80.0 100.0 200.0 300 200 100 Fluorescence intensity at 575 nm Fluorescence intensity (a u.) 400 (b) 400 300 200 100 500 550 600 650 700 750 800 10 12 14 16 18 20 22 Concentration of HCO3- (10-5 M) Wavelength (nm) Figure S7 (a) Fluorescence spectra of DHAB–Al3+ (2.0 × 10–5 M / 4.0 × 10–5 M) upon progressive addition of HCO3– (0–2.0 × 10–3 M) in EtOH-(0.1 M PIPES-KOH) buffer (1:1, v/v, at pH 6.5); (b) plot of fluorescence intensity at 575 nm versus the concentrations of HCO3– (5.0 × 10–5 M–2.0 × 10–4 M) 400 (a) Concentration of SO42- (10-5M) 0.1 0.2 0.5 0.8 1.0 2.0 5.0 8.0 10.0 20.0 40.0 80.0 100.0 200.0 Absorbance (a u.) (b) Concentration of SO42- (10-5 M) 0.1 0.2 0.5 0.8 1.0 2.0 5.0 8.0 10.0 20.0 40.0 80.0 100.0 200.0 300 200 100 0.0 300 Fluorescence intensity (a u.) 400 500 600 Wavelength (nm) 500 550 600 650 700 750 800 Wavelength (nm) Figure S8 Absorption spectra (a) and fluorescence spectra (b) of DHAB–Al3+ (2.0 × 10–5 M/4.0 × 10–5 M) upon progressive addition of SO42– (0–2.0 × 10–3 M) in EtOH-(0.1 M PIPES-KOH) buffer (1:1, v/v, at pH 6.5) 500 (a) Concentration of 0.1 0.2 0.5 0.8 1.0 2.0 5.0 8.0 10.0 20.0 40.0 80.0 100.0 200.0 0.3 Absorbance (a u.) NO2- (10-5 M) 0.2 0.1 0.0 300 (b) Concentration of NO2- (10-5 M) Fluorescence intensity (a u.) 0.4 400 0.1 0.2 0.5 0.8 1.0 2.0 5.0 8.0 10.0 20.0 40.0 80.0 100.0 200.0 300 200 100 400 500 600 Wavelength (nm) 500 550 600 650 700 750 800 Wavelength (nm) Figure S9 Absorption spectra (a) and fluorescence spectra (b) of DHAB–Al3+ (2.0 × 10–5 M/4.0 × 10–5 M) upon progressive addition of NO2– (0–2.0 × 10–3 M) in EtOH-(0.1 M PIPES-KOH) buffer (1:1, v/v, at pH 6.5) ... assumption and explored the possible mechanisms 909 ZHANG et al./Turk J Chem 2.3 Sensitivity of the DHAB–Al 3+ system to anions and mechanism studies Changes in the color and UV-Vis and fluorescence... DHAB–Al 3+ system, the intensity of the absorption band at 480 nm decreased with the concomitant formation of a new blue-shifted band at approximately 325 nm and the appearance of a 908 ZHANG et... 6.5 We first examined color changes of the DHAB–Al 3+ and DHAB system in the presence of anions (4.0 × 10 −3 M) (Figures 4a and 4b) Figure 4a shows that the reddish-orange DHAB–Al 3+ solution turns