sensors Article
Theoretical and Experimental: The Synthetic and Anion-Binding Properties of Tripodal Salicylaldehyde Derivatives Zhong-Jie Xu 1,2 and Li-Rong Zhang 1, * 1 2
*
School of Basic Medicine, Zhengzhou University, Zhengzhou 450052, China;
[email protected] Life Science and Technology College, Xinxiang Medical University, Xinxiang 453003, China Correspondence:
[email protected]; Tel.: +86-373-383-1301; Fax: +86-373-383-1048
Academic Editors: Jong Seung Kim and Min Hee Lee Received: 2 March 2016; Accepted: 12 May 2016; Published: 19 May 2016
Abstract: A series of colorimetric anion probes 1–6 containing OH and NO2 groups were synthesized, and their recognition properties toward various anions were investigated by visual observation, ultraviolet–visible spectroscopy, fluorescence, 1 H nuclear magnetic resonance titration spectra and theoretical investigation. Nanomaterials of three compounds 2–4 were prepared successfully. Four compounds 3–6 that contain electron-withdrawing substituents showed a high binding ability for AcO´ . The host–guest complex formed through a 1:1 binding ratio, and color changes were detectable during the recognition process. Theoretical investigation analysis revealed that an intramolecular hydrogen bond existed in the structures of compounds and the roles of molecular frontier orbitals in molecular interplay. These studies suggested that this series of compounds could be used as colorimetric probes to detect of AcO´ . Keywords: molecular probe; tripodal compound; theoretical investigation; colorimetric binding; nano-material
1. Introduction Investigations of synthetic anion receptors have attracted considerable attention in the field of host-guest chemistry because of the important roles of anions in biomedicinal and chemical processes [1–12]. The design of these receptors has focused on the ability to recognize and sense the biologically important anions selectively. Water-soluble anions such as fluoride, chloride, bromide and phosphate are critical in a range of biological phenomena and are implicated in many disease states [13]. Acetate anions have unique chemical properties and can form the strongest hydrogen-bond interaction with hydrogen-bond donors because of the trigonal geometry and the high basicity. Much literature is available on selective receptor molecules for acetate anions [14–16]. Phosphorylated species play critical roles in a variety of fundamental processes and exist in many chemotherapeutic and antiviral drugs [17–20]. Phosphate that originates from the overuse of agricultural fertilizers can also lead to eutrophication in inland waterways [21]. To recognize and sense oxy-anions and phosphorylated biomolecules will become more important than other biologically functional anions [22–24]. In many cases, a colorimetric receptor for special anionic species is of particular interest because of its simplicity and high sensitivity [25,26]. In particular, colorimetric-based sensing is especially attractive because it allows visible detection of analytes without requiring expensive equipment [27,28]. In general, these chemosensors are constructed according to a general receptor-chromophore general binomial, which involves the binding of a special anion substrate with receptor sites and a chromophore responsible for translating the receptor-anion association into an optical signal [29–31]. Color variation occurs when a charge-transfer complex is formed [32]. Therefore, it is necessary to develop a
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colorimetric receptor with high sensitivity and selectivity. reasoned thathigh a simple colorimetric Therefore, itanion is necessary to develop a colorimetric anion We receptor with sensitivity and anion receptor would be obtained by coupling the phenol group as a recognition site with a nitro selectivity. We reasoned that a simple colorimetric anion receptor would be obtained by coupling chromophore as a signal group. Therefore, we asynthesized a series ofas tripodal compounds that contain the phenol group as a recognition site with nitro chromophore a signal group. Therefore, we NO and a phenol group (Scheme 1). As expected, this series of compounds showed a strong binding synthesized a series of tripodal compounds that contain NO 2 and a phenol group (Scheme 1). As 2 ability for oxy-anions and a color change from yellow to orange occurred during the host–guest expected, this series of compounds showed a strong binding ability for oxy-anions and a color interaction. also studied theoccurred effect of different substituents o,p-Br, change fromWe yellow to orange during the host–guest(o-OCH interaction. alsoo-NO studied thep-NO effect 3 , o-Br,We 2 and 2) to and selectivity. of sensitivity different substituents (o-OCH3, o-Br, o,p-Br, o-NO2 and p-NO2) to sensitivity and selectivity.
Scheme 1. 1. Synthesis 1–6. Scheme Synthesis of of compounds compounds 1–6.
2. Experimental 2. ExperimentalSection Section 2.1. Materials
were obtained commercially and and all reagents and solvents used Most of of the thestarting startingmaterials materials were obtained commercially all reagents and solvents were of analytical grade. All anions, the form tetrabutylammonium salts (such assalts (n-C(such 4H9)4NF, used were of analytical grade. Allinanions, in of the form of tetrabutylammonium as (n-C44H99))44NCl, (n-C 4 H 9 ) 4 NBr, (n-C 4 H 9 ) 4 NI, (n-C 4 H 9 ) 4 NAcO, (n-C 4 H 9 ) 4 NH 2 PO 4 ), were purchased from NF, (n-C4 H9 )4 NCl, (n-C4 9 )4 NBr, (n-C4 H9 )4 NI, (n-C4 H9 )4 NAcO, (n-C4 H9 )4 NH2 PO4 ), were Sigma-Aldrich Co. (Shanghai, China), and were stored inand a desiccator under that purchased fromChemical Sigma-Aldrich Chemical Co. (Shanghai, China), were stored in vacuum a desiccator contained self-indicating silica, and were used without any further purification. under vacuum that contained self-indicating silica, and were used without any further purification. Tetra-n-butylammonium salts salts were weredried driedfor for24 24hhin invacuum vacuumwith withPP22O O55 at 333 K. Dimethyl sulfoxide Tetra-n-butylammonium after being being dried dried with with CaH CaH22. (DMSO) was distilled in vacuo after 2.2. Apparatus Melting points were determined on a XT-4 binocular microscope (Beijing (Beijing Tech Instrument Co., Co., 11H nuclear magnetic Beijing, China). C, H and N elemental analysis was achieved using Vanio-EL elemental using Vanio-EL resonance (NMR) (Bruker, Karlsruhe, Germany), and spectra were recorded on a Varian UNITY Plus-400 MHz (Agilent, PaloPalo Alto, Alto, CA, USA). was performed with a MARINER MHzSpectrometer Spectrometer (Agilent, CA, ESI-MS USA). ESI-MS was performed with a apparatus Palo Alto, CA, USA). Ultraviolet (UV)–visible spectroscopy were MARINER(Agilent, apparatus (Agilent, Palo Alto, CA, USA). Ultraviolet(vis) (UV)–visible (vis)titrations spectroscopy made using a Shimadzu UV2550 spectrophotometer (Shimadzu, Kyoto, Japan) atKyoto, 298 K. Fluorometric titrations were made using a Shimadzu UV2550 spectrophotometer (Shimadzu, Japan) at 298 titrations were performed an Eclipse fluorescence spectrophotometer Palo Alto, CA, USA) K. Fluorometric titrationson were performed on an Eclipse fluorescence (Agilent, spectrophotometer (Agilent, at 298Alto, K. Scanning electron microscopy (SEM) imagesmicroscopy were obtained by Quanta FEI with Au Palo CA, USA) at 298 K. Scanning electron (SEM) imagesTM450 were obtained by coating USA). Optimized compound geometries were obtained used density functional Quanta (Hillsboro, TM450 FEIOR, with Au coating (Hillsboro, OR, USA). Optimized compound geometries were theory at the B3LYP/3-21G level with theory Gaussian03 program (Pittsburgh, PA,with USA).Gaussian03 The affinity program constant, obtained used density functional at the B3LYP/3-21G level K the non-linear leastconstant, squares calculation methodby for the datanon-linear fitting. (Pittsburgh, PA, by USA). The affinity Ks, was obtained least squares s , was obtained calculation method for data fitting.
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2.3. Synthesis Compounds 1–6 were synthesized according to the route shown in Scheme 1. 5-Nitro-1,3-dialdehydebenzene [33] 1, 3-Dialdehydebenzene (8.35 g, 35 mmol) was dissolved in sulfuric acid (28 mL). The solution was cooled to 1 ˝ C and 100% HNO3 (4.5 mL, 0.11 mol) was added dropwise with stirring. The temperature did not exceed 1 ˝ C. After the mixture had reacted for 4 h, the suspension was poured into ice water. The precipitate was filtered and recrystallized from ethanol. Yield: 89%. 1 H-NMR (DMSO-d6 ): δ 10.12 (s, 2H, -CHO), 9.61 (s, 2H, ph-H), 9.05 (s, 1H, ph-H). Elemental analysis calcd. for C8 H5 NO4 : C, 53.64; H, 2.81; N, 7.82; found: C, 53.90; H, 2.66; N, 8.17. 5-Nitro-1,3-dimethylenehydrazine-benzene 5-Nitro-1,3-dialdehydebenzene (1 mmol, 180 mg) in dry ethanol (15 mL) was added to an ethanol (30 mL) solution containing hydrazine hydrate (80%, 0.5 mL) under stirring. Then, the mixture was heated under refluxing for 8 h and the yellow precipitate was separated by filtration. The solid was washed with diethyl ether and dried under vacuum. Yield: 84%. 1 H-NMR (400 MHz, DMSO-d6 , 298 K) δ 9.96 (s, 4H, NH2 ), 9.74 (s, 2H, ph-H), 9.18 (s, 1H, ph-H). Elemental analysis: calc. for C8 H9 N5 O2 : C, 46.38; H, 4.38; N, 33.80; found: C, 46.59; H, 4.26; N, 33.63. Six compounds 1–6 were synthesized according to the following method. 5-Nitro-1,3-dimethylenehydrazine-benzene (1 mmol, 207 mg) was dissolved in dry ethanol (30 mL) and substituent salicylaldehyde (2 mmol) in dry ethanol (15 mL) was added to the solution under stirring. Then, the mixture was heated under refluxing for 8 h and the precipitate was separated by filtration. The solid was washed with diethyl ether, recrystallized with ethanol, and dried under vacuum. Compound 1: Yield: 73%. 1 H-NMR (400 MHz, DMSO-d6 , 298 K) δ 11.12 (s, 2H), 9.01 (s, 2H), 7.71–7.69 (dd, 2H), 7.57–7.54(dd, 4H) 7.41–7.40 (m, 4H), 6.97–6.70 (m, 3H). Elemental analysis: calc. for C22 H17 N5 O4 : C, 63.61; H, 4.12; N, 16.86; found: C, 63.38; H, 4.54; N, 16.63. ESI-MS (m/z): 414.2 [M ´ H]´ . Compound 2: Yield: 77%. 1 H-NMR (400 MHz, DMSO-d6 , 298 K) δ 10.90 (s, 2H), 9.06–8.99 (m, 3H), 8.80 (d, 2H), 7.34–7.28(dd, 2H), 7.17–7.12(t, 2H), 6.94–6.89(dd, 2H), 3.83(s, 3H). Elemental analysis: calc. for C24 H21 N5 O6 : C, 60.63; H, 4.45; N, 14.73; found: C, 60.99; H, 4.31; N, 14.47. ESI-MS (m/z): 474.4 [M ´ H]´ . Compound 3: Yield: 82%. 1 H-NMR (400 MHz, DMSO-d6 , 298 K) δ 11.21 (s, 1H), 11.14 (s, 1H), 9.03–8.94 (m, 5H), 8.83–8.79 (dd, 2H), 7.95–7.90 (dd, 2H), 7.55–7.53 (dd, 2H), 6.99–6.94 (dd, 2H). Elemental analysis: calc. for C22 H15 Br2 N5 O4 : C, 46.10; H, 2.64; N, 12.22; found: C, 46.74; H, 2.28; N, 12.56. ESI-MS (m/z): 569.7 [M ´ H]´ . Compound 4: Yield: 89%. 1 H-NMR (400 MHz, DMSO-d6 , 298 K) δ 12.31 (s, 2H), 9.13–9.05 (dd, 2H), 8.79 (d, 2H), 7.99–7.87 (m, 5H), 6.99–6.94 (dd, 2H). Elemental analysis: calc. for C22 H13 Br4 N5 O4 : C, 36.15; H, 1.79; N, 9.58; found: C, 36.41; H, 1.68; N, 9.95. ESI-MS (m/z): 725.5 [M ´ H]´ . Compound 5: Yield: 79%. 1 H-NMR (400 MHz, DMSO-d6 , 298 K) δ 12.37 (s, 2H), 9.22 (s, 2H), 9.18 (s, 1H), 9.14 (s, 1H), 8.82 (d, 2H), 8.15–8.05 (dd, 4H), 7.22–7.18 (t, 3H). Elemental analysis: calc. for C22 H15 N7 O8 : C, 52.28; H, 2.99; N, 19.40; found: C, 52.73; H, 3.15; N, 19.02. ESI-MS (m/z): 504.0 [M ´ H]´ . Compound 6: Yield: 84%. 1 H-NMR (400 MHz, DMSO-d6 , 298 K) δ 12.19 (s, 2H), 9.06 (s, 2H), 9.01 (dd, 2H), 8.73 (s, 1H), 8.67 (d, 4H), 8.25–8.22 (dd, 2H), 7.15–7.12 (d, 2H). Elemental analysis: calc. for C22 H15 N7 O8 : C, 52.28; H, 2.99; N, 19.40; found: C, 52.73; H, 3.15; N, 19.02. ESI-MS (m/z): 504.3 [M ´ H]´ . 2.4. Preparation of Nanomaterials Nanomaterials were prepared by reprecipitation method [34,35]. The DMSO and the aqueous solution of hexadecyl trimethyl ammonium bromide (CTAB) were a good solvent and a poor solvent, respectively. The good compound-containing solvent (0.35 mL, 4 mmol¨ L´1 ) was poured into the
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poor solvent that contained CTAB (100 mL, 3 mmol¨ L´1 ). The mixture was centrifuged after 24 h. solvent,solid respectively. The good (0.35 mL, 4 mmol·L−1) was poured The resultant was washed withcompound-containing water and dried insolvent vacuum. into the poor solvent that contained CTAB (100 mL, 3 mmol·L−1). The mixture was centrifuged after Sensors 2016, 16, 733
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24 h.and The Discussion resultant solid was washed with water and dried in vacuum. 3. Results
solvent, respectively. The good compound-containing solvent (0.35 mL, 4 mmol·L−1) was poured
3. Images Results of and Discussion 3.1. SEM Nanomaterials into the poor solvent that contained CTAB (100 mL, 3 mmol·L−1). The mixture was centrifuged after 24 h. TheImages resultant solid was washed with water and dried in vacuum.2–4) were prepared successfully. 3.1. SEM of Nanomaterials Only three of the attempted six nanomaterials (compound The SEM were usingsix Quanta TM450 (compound FEI with Au coating (Hillsboro, OR, USA) and Only and three ofobtained the attempted nanomaterials 2–4) were prepared successfully. 3. images Results Discussion were shown in Figure Compound 2 was formed intoFEIa sheet. 3 could assembled The SEM images 1. were obtained using Quanta TM450 with AuCompound coating (Hillsboro, OR,beUSA) 3.1.platelets SEM of Nanomaterials and wereImages shown in Compound 2The was flakiness formed into sheet. Compound 3according could be to the into oval over theFigure entire1. compound. wasa nanometer-wide assembled into oval platelets overtwo thebromine entire compound. The the flakiness was were nanometer-wide scale. For compound platelets stacked together Only three 4ofthat the contained attempted six nanomaterialssubstituents, (compound 2–4) were prepared successfully. according to the scale. For compound 4 that contained two bromine substituents, the platelets ´ were The SEMshape. images Although were obtained using Quanta TM450 FEI with the Au coating (Hillsboro, OR, in a flower-like compounds 3 and 4 contained same substituent (Br USA) ), the SEM stacked together in a flower-like shape. Although compounds 3 and 4 contained the same and were shown in Figure 1. Compound 2 was formed into a groups. sheet. Compound 3 the could be images were different because of the different numbers of bromine Therefore, SEM substituent (Br−), the SEM images were different because of the different numbers of bromine images assembled into oval platelets over the entire compound. The flakiness was nanometer-wide were related with space the configuration. groups. Therefore, SEM images were related with space configuration. according to the scale. For compound 4 that contained two bromine substituents, the platelets were stacked together in a flower-like shape. Although compounds 3 and 4 contained the same substituent (Br−), the SEM images were different because of the different numbers of bromine groups. Therefore, the SEM images were related with space configuration.
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Figure 1. SEM images of compounds. (a) Compound 2; (b) Compound 3; (c) Compound 4.
Figure 1. SEM images of compounds. (a) Compound 2; (b) Compound 3; (c) Compound 4. 3.2. UV-Vis Titration(a)
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3.2. UV-Vis Titration
The binding abilities of six compounds to acetate anion were Figure 1. SEM images of compounds. (a) Compound 2; (b) Compound 3; (c)investigated Compound 4.using UV-Vis absorption spectra in DMSO at 298 K. The UV-Vis spectral changes of the sixusing compounds The binding abilities of six compounds to acetate anion were investigated UV-Viswere absorption 3.2. UV-Vis Titration2 during the titration with acetate anion. In the absence of acetate anion, shown in Figure spectra in DMSO at 298 −5K. The−1 UV-Vis spectral changes of the six compounds were shown in compound 1 (4.0 × 10 mol·L in DMSO) exhibited two obvious peaks centered at ~300 and 350 nm. The binding abilities with of sixacetate compounds to acetate were of investigated using UV-Vis Figure 2With during the titration anion. In theanion absence acetate anion, compound 1 an increase in acetate concentration, the intensity of the above two absorption peaks absorption spectra in DMSO at 298 K. The UV-Vis spectral changes of the six compounds were ´ 5 ´ 1 (4.0 ˆ 10strengthened mol¨ L and in weakened, DMSO) exhibited two obvious peaks centered at ~300 and 350 respectively. One new peak appeared centered at 475 nm. As a nm. result,With an shown in Figure 2 during the titration with acetate anion. In the absence of acetate anion, increasethe inred-shift acetate phenomenon concentration, the intensity of the1above twowith absorption peaks and occurred after compound interacted acetate anion and strengthened the solution compound 1 (4.0 × 10−5 mol·L−1 in DMSO) exhibited two obvious peaks centered at ~300 and 350 nm. colorrespectively. changed from colorless to yellowish (Figure 3). Two isosbestic points appeared at 310 and weakened, One new peak appeared centered at 475 nm. As a result, the red-shift With an increase in acetate concentration, the intensity of the above two absorption peaks −). Analogous investigations 310 nm,occurred which indicated the formation of stable complexation (1-AcO phenomenon compound 1 interacted anion and at the solution changed strengthened andafter weakened, respectively. One newwith peakacetate appeared centered 475 nm. As acolor result, were carried out on the other anions. The additions of H2PO4− and F− to compound 1 induced similar the red-shift phenomenon occurred compound 1 interacted acetate at anion the310 solution from colorless to yellowish (Figure 3).after Two isosbestic points with appeared 310and and nm, which spectral change, which indicated that compound 1 also´interacted with the above anions. However, color changed fromofcolorless to yellowish (Figure 3). Two isosbestic points appeared at 310 carried and indicated the formation stable complexation (1-AcO ). Analogous investigations were out − − − Cl , Br and I additions did not induce any spectral response, which −indicated that compound 1 310 nm, which indicated the formation of´stable complexation (1-AcO ). Analogous investigations ´ to compound 1 induced similar spectral change, on the other anions. The additions of H PO and F 4 these anions and the binding ability could be ignored. showed a very weak binding ability 2toward were carried out on the other anions. The additions of H2PO4− and F− to compound 1 induced´similar which indicated that compound 1 also interacted with the above anions. However, Cl , Br´ and I´ spectral change, which indicated that compound 1 also interacted with the above anions. However, additions any spectral response, compound 1 showed a very Cl−did , Br−not andinduce I− additions did not induce any which spectralindicated response, that which indicated that compound 1 weak bindingshowed ability atoward these anions andtoward the binding ability be ignored. very weak binding ability these anions andcould the binding ability could be ignored.
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Figure 2. Cont.
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(d)
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Figure 2. UV-Vis spectral changes of six compounds with acetate anion addition. [compound] = 4.0 ×
Figure 102.−5 mol·LUV-Vis changes of −1six compounds acetate anion addition. −1; [acetatespectral anion] = 0–1.6 × 10−3 mol·L . Arrows indicate the with direction of increasing anion ´5 mol¨ L´1 ; [acetate anion] ´3 mol¨ L´1 . (f)Arrows indicate (d) (e) [compound] = 4.0 ˆ 10 = 0–1.6 ˆ 10 concentration. (a) Compound 1; (b) Compound 2; (c) Compound 3; (d) Compound 4; (e) Compound 5; (f) Compound 6.of six compounds the direction increasing anion concentration. (a) Compound (b) Compound 2; (c) Compound 3; Figure 2. of UV-Vis spectral changes with acetate 1; anion addition. [compound] = 4.0 × (d) Compound (e) Compound 5; (f)×Compound 10−5 mol·L−1;4;[acetate anion] = 0–1.6 10−3 mol·L−1. 6. Arrows indicate the direction of increasing anion
The acidity of this kind of compounds can be tuned by changing the electron property of the concentration. (a) Compound 1; (b) Compound 2; (c) Compound 3; (d) Compound 4; substituent on the ortho-, meta- or para-position according to resonance structure and the (e) Compound 5; (f)kind Compound 6. Thecorresponding acidity of this of compounds changing the [36]. electron property of anion binding ability can can also be be tuned changedbycorrespondingly Therefore, the substituent the ortho-, metaor2)para-position according to to resonance 2 (o-OCH3),on 3 (o-Br), 4 (o, p-Br), 5 (o-NO and 6 (p-NO2) were synthesized investigatestructure the effect ofand the The acidity of this kind of compounds can be tuned by changing the electron property of the electron properties of the substituent on the host–guestcorrespondingly interaction. As expected, the absorption corresponding binding be changed [36]. structure Therefore, 2 (o-OCH substituentanion on the ortho-,ability meta-can or also para-position according to resonance and the 3 ), spectra of 2, 3, 4, 5 and 6 indeed exhibited various changes with an increase in acetate anion 3 (o-Br), 4 (o, p-Br), 5 (o-NO ) and 6 (p-NO ) were synthesized to investigate the effect of electron 2 2 corresponding anion binding ability can also be changed correspondingly [36]. Therefore, concentration (Figure 2) and were accompanied by color changes (Figure 3). Red-shift phenomena properties of the on the host–guest interaction. Assynthesized expected, the absorption of 2, 3, 2 (o-OCH 3), 3substituent (o-Br), 4 (o, p-Br), 5 (o-NO 2) and 6 (p-NO2) were to investigate thespectra effect of occurred to different degrees and one clear isosbestic point also appeared, which indicated that five electron properties of the substituent on the host–guest interaction. expected, the absorption 4, 5 and 6 indeed exhibited various changes with an increase in acetateAs1anion (Figure 2) compounds all interacted with acetate anion. Compared with compounds and 2,concentration the red-shift effect spectra of 2, 3, 4, 5by 6contained indeed exhibited various changes with an increase intoacetate and were color changes (Figure 3). Red-shift phenomena occurred different of accompanied compounds 3 to 6and that electron-withdrawing groups was remarkably, which relatedanion todegrees concentration (Figure 2) and were accompanied by color changes (Figure 3). Red-shift phenomena the substituent effect. In addition, compound 5 contained one nitro group, as well as compound 6. and one clear isosbestic point also appeared, which indicated that five compounds all interacted occurred to different degrees and one clear isosbestic point also appeared, which indicated that five3 to 6 However, the spectra of free compound and the host–guest complex were clear differently. The with acetate anion. Compared with compounds 1 and 2, the red-shift effect of compounds compounds allbe interacted withsite acetate anion. compounds 1 and 2, thethe red-shift effect reason may the different of the nitro Compared group. Thewith above results indicated that interacted that contained electron-withdrawing groups was remarkably, which related to the substituent effect. of compounds 3 to 6were thatrelated contained mode and ability withelectron-withdrawing the geometry structure.groups was remarkably, which related to
In addition, compound 5 contained one nitro group, as well as compound 6. However, the spectra of the substituent effect. In addition, compound 5 contained one nitro group, as well as compound 6. free compound andspectra the host–guest complex and werethe clear differently. The reason maydifferently. be the different However, the of free compound host–guest complex were clear The site of thereason nitro group. The above results indicated that the interacted mode and ability were related may be the different site of the nitro group. The above results indicated that the interacted with the geometry mode andstructure. ability were related with the geometry structure.
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Figure 3. Color changes of six compounds with addition of various anions. (A) Blank; (B) F−; (C) Cl−; (D) Br−; (E) I−; (F) AcO−; (G) H2PO4−. (a) Compound 1, 3 and 5; (b) Compound 2, 4 and 6.
3.3. Fluorescence
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The photo physical responses of six compounds toward the additions of various anions tested −; (C) Cl−; Figure 3. investigated Color changesinof DMSO six compounds with addition of various Blank; (B) Fintensity were solution. shown of invarious Figure anions. 4, the (A) fluorescence Figure 3.also Color changes of six compounds withAs addition anions. (A) Blank; (B) F´ ; (C)of Cl´ ; − − − − ; (E) I ; (F) AcO ; (G) H 2PO4 . (a) Compound 1, 3 and 5; (b) Compound 2, 4 and 6. (D) Br ´ ´ ´ ´ the stepwise addition of acetate anion. Two possible mechanisms (D)compounds Br ; (E) I ;1–4 (F) increased AcO ; (G)with H2 PO 4 . (a) Compound 1, 3 and 5; (b) Compound 2, 4 and 6. may explain the fluorescence enhancement: (1) inhibition of photo-induced electronic transfer (PET) 3.3.[37] Fluorescence and (2) the guest binding-induced rigidity of the host molecule [38,39]. The oxygen atom of 3.3. Fluorescence -OH an responses intramolecular bond withthe near-hydrogen atoms (proven by Thecould photo form physical of sixhydrogen compounds toward additions of various anions tested theoretical investigation), which led to a PET and a decrease in fluorescence. However, the werephoto also investigated in DMSO solution. As shown in the Figure 4, the of fluorescence intensity of were The physical responses of six compounds toward additions various anions tested interaction1–4 between compounds the acetate anionofresulted in an inhibition of PET and an compounds increased with theand stepwise acetate anion. Two possible mechanisms also investigated in DMSO solution. As shownaddition in Figure 4, the fluorescence intensity of compounds enhancement in fluorescent spectra intensity after acetate anion addition to a transfer solution (PET) of may explain the fluorescence enhancement: (1) inhibition of photo-induced electronic
1–4 increased with the stepwise addition of acetate anion. Two possible mechanisms may explain the [37] and (2) the guest binding-induced rigidity of the host molecule [38,39]. The oxygen atom of fluorescence enhancement: (1) inhibition of photo-induced electronic transfer (PET) [37] and (2) the -OH could form an intramolecular hydrogen bond with near-hydrogen atoms (proven by guest binding-induced rigidity of the host molecule [38,39]. The oxygen atom of -OH could form an theoretical investigation), which led to a PET and a decrease in fluorescence. However, the intramolecular hydrogen bond with near-hydrogen atoms (proven by theoretical investigation), which interaction between compounds and the acetate anion resulted in an inhibition of PET and an led toenhancement a PET and aindecrease in fluorescence. However, interaction betweentocompounds fluorescent spectra intensity after the acetate anion addition a solution and of the acetate anion resulted in an inhibition of PET and an enhancement in fluorescent spectra intensity after acetate anion addition to a solution of compounds 1–4. For two compounds 5 and 6, the fluorescence
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compounds 1–4. For after two compounds 5 and the fluorescence intensity was quenched acetate intensity was quenched acetate anion was6,added. The reason may be related to theafter strong electron anion waseffect. added. Theelectron reason may be related toofthe strong electron withdrawing withdrawing The delocalization two compounds 5 and 6 was effect. strongThe andelectron the rigidity delocalization of two compounds and 6 was strong and theeffect rigidity stableTherefore, because of free structure was stable because of the5electron-withdrawing ofstructure the nitrowas group. the electron-withdrawing effect of the nitro group. Therefore, free compounds 5 and 6 showed a compounds 5 and 6 showed a strong fluorescence response before the acetate anion was added. After strong fluorescence response before the acetate anion was added. After acetate anion addition, the acetate anion addition, the strong rigidity structure was broken and the fluorescence intensity was strong rigidity structure was broken and the fluorescence intensity was decreased. Similar decreased. Similar fluorescence spectral responses compounds 1–6the were induced by theanions additions fluorescence spectral responses of compounds 1–6ofwere induced by additions of other ´ and F´ . Nevertheless, their fluorescence emission was insensitive to of other anions such as H PO − − 4 such as H2PO4 and F .2Nevertheless, their fluorescence emission was insensitive to the additions of ´ , Br´ and I´ ), which indicated that the host-guest − and (Cl the additions of largeofquantities of other anions large quantities other anions (Cl−, Br I−), which indicated that the host-guest interactions interactions were very and binding the anion binding could be ignored. were very weak andweak the anion ability couldability be ignored.
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Figure 4. Fluorescence response of six compounds (4.0 × 10−5 mol·L−1) with acetate anion addition
Figure 4. Fluorescence response of six compounds (4.0 ˆ 10´5 mol¨ L´1 ) with acetate anion (0–2.0 × 10−3 mol·L−1). Arrows indicate the increase in direction of acetate concentration. ´3 addition (0–2.0 ˆ 101; (b) mol¨Compound L´1 ). Arrows the increase in direction4;of(e) acetate concentration. (a) Compound 2; (c)indicate Compound 3; (d) Compound Compound 5; (a) Compound 1; (b) Compound 2; (c) Compound 3; (d) Compound 4; (e) Compound 5; (f) Compound 6. (f) Compound 6.
3.4. Binding Constant 3.4. Binding Constant Six compounds interactedwith withvarious various anions according to the job–plot analysis. Six compounds interacted anionsininaa1:1 1:1ratio ratio according to the job–plot analysis. By the method of non-linear least squares calculation, the binding constants could be obtained and By the method of non-linear least squares calculation, the binding constants could be obtained and were listed in Table 1 based on the UV-Vis data [40–42]. From Table 1, four compounds that were listed in Table 1 based on the UV-Vis data [40–42]. From Table 1, four compounds that −contained contained electron-withdrawing groups (3–6) all showed the strongest binding ability for´AcO and electron-withdrawing groups all H showed the strongest binding ability for AcO and a certain 2PO4− among the anions tested. However, two compounds a certain binding ability for(3–6) F− and ´ and H PO ´ among the anions tested. However, two compounds (1 and 2) that binding ability for F 2 4 (1 and 2) that contained electron-donating groups showed a strong binding ability for F−. The above contained showed a strongIn binding ability for F´ . Theallabove results may be resultselectron-donating may be related to groups the space configuration. addition, six compounds showed a very related to the space configuration. In addition, compounds all showed a very weak binding ability I− could besix ignored. π-π stacking may have existed between five weak binding ability for Cl−, Br− and ´ ´ ´ nanomaterials and anions. For the acetate anion, the binding ability followed the order of: for Cl , Br and I could be ignored. π-π stacking may have existed between five nanomaterials and 6 >For 5 > the 4 > 3acetate > 1 > 2.anion, This order agreed with thefollowed ability ofthe theorder electron-withdrawing and theorder anions. the binding ability of: 6 > 5 > 4 > 3 group > 1 > 2. This acidity of the six compounds. Compound 6 that contained an m-NO 2 group showed the strongest agreed with the ability of the electron-withdrawing group and the acidity of the six compounds. binding ability for acetate anion among the six compounds. The anion binding ability of Compound 6 that contained an m-NO2 group showed the strongest binding ability for acetate anion compound 5 that contained o-NO2 was weaker than that of compound 6 because of steric hindrance. among the six compounds. The anion binding ability of compound 5 that contained o-NO2 was weaker In general, this series of compounds could be used as sensors to detect acetate anion. than that of compound 6 because of steric hindrance. In general, this series of compounds could be used as sensors to detect acetate anion.
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Table 1. Binding constants of compounds with various anions. Table 1. Binding constants of compounds with various anions.
Anions a AnionsKas (1) Ks (1)Ks (2) Ks (2)Ks (3) Ks (3)Ks (4) Ks (4)Ks (5) Ks (5) Ks (6)
AcO− ´ × 103 (9.56AcO ± 0.05) (1.28˘±0.05) 0.06)ˆ×1010 3 3 (9.56 3 4 (2.76˘±0.06) 0.03)ˆ×1010 (1.28 4 4 (2.76 (5.65˘±0.03) 0.08)ˆ×1010 4 (5.65 (6.48˘±0.08) 0.11)ˆ×10104 4 (6.48 4 (8.49˘±0.11) 0.19)ˆ×1010 4
H2PO4− F− Cl− (Br−, I−) 2 4 ´ ´ (4.11 ± 0.14) (2.31 ± 0.03) F× 10 NDClb´ (Br´ , I´ ) H2 PO×4 10 3 4 (1.18 ± 0.01) × 10 ± 0.04) × 10 ˆ 104 ND ND b (4.11 ˘ 0.14) ˆ 102(2.45 (2.31 ˘ 0.03) 3 3(1.60 ± 0.04) × 104 (2.33 ± 0.02) × 10 (1.18 ˘ 0.01) ˆ 10 (2.45 ˘ 0.04) ˆ 104 ND ND 3 4 (2.33 ˘ 0.02) ˆ 10 (4.10 (1.60 ˘ 0.04) (4.35 ± 0.02) × 10 ± 0.10) × 104ˆ 104 ND ND 4 4 (4.35 ˘ 0.02) ˆ 410 (3.35 (4.10 ˘ 0.10) (5.67 ± 0.08) × 10 ± 0.05) × 104ˆ 10 ND ND 4 4 (5.67 ˘ 0.08) ˆ 410 (4.69 (3.35 ˘ 0.05) (6.07 ± 0.07) × 10 ± 0.12) × 104ˆ 104 ND ND 4
Ks (6) ND (8.49 ˘ 0.19) ˆ 10 (6.07 ˘ 0.07) ˆ 10 (4.69 ˘ 0.12) ˆ 10 All anions were added in the form of tetra-n-butylammonium (TBA) salts; b The binding constant a All anions were added in the form of tetra-n-butylammonium (TBA) salts; b The binding constant could not could not be determined. be determined. a
1 3.5. 3.5. 1HNMR HNMR Titration Titration To explain the the interaction interaction between between the the six six compounds compounds and and the the anions, anions, as as an an example, example, 11H-NMR To explain H-NMR − spectral were investigated investigated upon upon AcO AcO´ addition spectral changes changes were addition as as its its tetrabutylammonium tetrabutylammonium salt salt to to the the DMSO-d6 solution of compound 6 (1 × 10´−22 mol·L−1´).1 Figure 5 showed that the peak at 12.19 ppm, DMSO-d6 solution of compound 6 (1 ˆ 10 mol¨ L ). Figure 5 showed that the peak at 12.19 ppm, which was assigned assigned to to ´OH, −OH, broadened which was broadened and and thoroughly thoroughly disappeared disappeared upon upon the the addition addition of of different different −, which indicated that the strong hydrogen-bonding interactions occurred equivalents of AcO ´ equivalents of AcO , which indicated that the strong hydrogen-bonding interactions occurred between between compound 6 and the AcO− ion [43]. In the nitro-phenol moiety, the protons compound 6 and the AcO´ ion [43]. In the nitro-phenol moiety, the protons (H2: 7.15–7.12 ppm; (H2: 7.15–7.12 ppm; H3: 8.25–8.22 ppm) were overlapped when the anion was absent. With increase H3: 8.25–8.22 ppm) were overlapped when the anion was absent. With increase in AcO´ ion, the in AcO− ion, the proton peaks of phenol all split and shifted in the upfield direction because of the proton peaks of phenol all split and shifted in the upfield direction because of the deshielding effect deshielding effect on the nitrophenol moiety. When the AcO− ion was added, the binding site (–OH on the nitrophenol moiety. When the AcO´ ion was added, the binding site (–OH group) interacted − group) interacted with AcO to form a shielding effect. Therefore, the proton peak of phenol moved with AcO´ to form a shielding effect. Therefore, the proton peak of phenol moved downfield and downfield and disappeared. The non-interacted site experienced a deshielding effect and shifted in disappeared. The non-interacted site experienced a deshielding effect and shifted in the upfield the upfield direction. The above results indicated that the synthesized compounds interacted with direction. The above results indicated that the synthesized compounds interacted with acetate anion acetate anion through hydrogen-bonding, which was reversible in the host-guest interaction. through hydrogen-bonding, which was reversible in the host-guest interaction.
1 ´2 −1) )with Figure 5. L´1 withaddition addition of of molar 6 6(1(1ˆ×10 Figure 5. 1H-NMR spectra spectra of of compound compound66ininDMSO-d DMSO-d 10−2 mol¨ mol·L ´ − equivalent of of AcO AcO . . equivalent
3.6. Theoretical Investigation the the relationship between the structures and the photo-physical properties, To further furtherunderstand understand relationship between the structures and the photo-physical the geometries six compounds were optimized 6) using density functional theory at the properties, the of geometries of six compounds were(Figure optimized (Figure 6) using density functional B3LYP/3-21G level with thelevel Gaussian03 [44]. program As shown[44]. in Figure 6, theinsix compounds all theory at the B3LYP/3-21G with theprogram Gaussian03 As shown Figure 6, the six showed tripodal geometries. A different form of bond existed between the compounds all showed tripodal geometries. A intramolecular different formhydrogen of intramolecular hydrogen bond oxygen atom of ´OH the near-hydrogen for six compounds. The difference in intramolecular existed between the and oxygen atom of −OH atom and the near-hydrogen atom for six compounds. The
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hydrogen bond a different red-shift effect in the UV-Vis spectra and different difference in induced intramolecular hydrogen bond induced a different red-shift effect in the UV-Visfluorescence spectra difference in host-guest. intramolecular hydrogen induced a different red-shift effect in the UV-Vis spectra and different fluorescence responses ofbond the host-guest. responses of the and different fluorescence responses of the host-guest.
(a) (a)
(b) (b)
(c) (c)
(d) (d)
(e) (e)
(f) (f)
Figure 6. Optimized structures of six compounds. (a) Compound 1; (b) Compound 2;
Figure 6. Optimized structures of six compounds. (a) Compound 1;6.(b) Compound 2; (c) Compound 3; Figure 6. Optimized structures six compounds. (a) Compound 1; (b) Compound 2; (c) Compound 3; (d) Compound 4; (e)ofCompound 5; (f) Compound (d) Compound 4; (e) Compound 5; (f) Compound 6. (c) Compound 3; (d) Compound 4; (e) Compound 5; (f) Compound 6.
Figure 7. Selected HOMO (a) and LUMO (b) distributions of 1–6. (1a,b) Compound 1; (2a,b) Compound Figure Selected HOMO (a) and (b) distributions of 1–6. (2a,b) Compound 2; (3a,b) 3; (4a,b) Compound 4; (5a,b) Compound 5; (1a,b) (6a,b)Compound Compound Figure 7. 7.Compound Selected HOMO (a)LUMO and LUMO (b) distributions of 1–6. 1;6. (1a,b) Compound 1; 2; (3a,b) Compound 3; (4a,b) Compound 4; (5a,b) Compound 5; (6a,b) Compound 6. (2a,b) Compound 2; (3a,b) Compound 3; (4a,b) Compound 4; (5a,b) Compound 5; (6a,b) Compound 6.
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The selected frontier orbitals for six compounds 1–6 were shown in Figure 7. The molecular frontier orbital was introduced in order to explain the UV-Vis absorption spectra in the host–guest interacted process by electron transition of the frontier orbital. Orbital analysis revealed that the highest occupied molecular orbital (HOMO) density in compounds 1–6 was localized mainly on the phenol moiety or on the whole molecule, whereas the lowest unoccupied molecular orbital (LUMO) density was localized on the nitrophenyl moiety. The electron transition of the lowest LUMO caused the red-shift phenomenon in the UV-Vis spectra. 4. Conclusions Six tripodal compounds were synthesized and demonstrated a highly sensitive and selective absorption assay for oxy-anions. Nanomaterials of three compounds 2, 3, 4 were developed and the SEM images were related to the space configuration. Although two compounds 3 and 4 had the same substituent (-Br), SEM images were significantly different because of the different numbers of bromine groups. Compound 6 that contained m-NO2 exhibited the strongest binding ability for AcO´ ions among the six compounds. The host–guest interaction accompanied by color changes may be used as a colorimetric probe for the AcO´ ion detection. This understanding of the AcO´ sensing mechanism helps to determine possible structural modifications and achieve new nanomaterials that have an acetate sensing capacity in aqueous solution. The results are useful in expanded applications of tripodal structure derivatives. Author Contributions: Z.J.X. conducted the experiment and wrote the paper. The ideas of this manuscript came from L.R.Z., who also revised the above manuscript. Conflicts of Interest: The authors declare no conflict of interest.
References 1.
2.
3.
4. 5. 6.
7.
8.
9.
González Mdel, C.; Otón, F.; Espinosa, A.; Tárraga, A.; Molina, P. Tris (triazole) tripodal receptors as selective probes for citrate anion recognition and multichannel transition and heavy metal cation sensing. Org. Biomol. Chem. 2015, 13, 1429–1438. [CrossRef] [PubMed] Velu, R.; Ramakrishnan, V.T.; Ramamurthy, P. Selective fluoride ion recognition by a thiourea based receptor linked acridinedione functionalized gold nanoparticles. J. Photoch. Photobiolo. A Chem. 2011, 217, 313–320. [CrossRef] Kim, S.-H.; Hwang, I.-J.; Gwon, S.-Y.; Burkinshaw, S.M.; Son, Y.-A. An anion sensor based on the displacement of 2,6-dichlorophenol-indo-o-cresol sodium salt from a water-soluble tetrasulfonated calix[4]arene. Dyes Pigment. 2011, 88, 84–87. [CrossRef] Yang, C.; Wu, B.; Chen, Y.; Zhang, K. Gels based on anion recognition between triurea receptor and phosphate anion. Macromol. Rapid Commun. 2015, 36, 750–754. [CrossRef] [PubMed] Cametti, M.; Rissanen, K. Highlights on contemporary recognition and sensing of fluoride anion in solution and in the solid state. Chem. Soc. Rev. 2013, 42, 2016–2038. [CrossRef] [PubMed] Bodo, E.; Ciavardini, A.; Dalla Cort, A.; Giannicchi, I.; Yafteh Mihan, F.; Fornarini, S.; Vasile, S.; Scuderi, D.; Piccirillo, S. Anion recognition by uranyl-salophen derivatives as probed by infrared multiple photon dissociation spectroscopy and ab initio modeling. Chemistry 2014, 20, 11783–11792. [CrossRef] [PubMed] Shang, X.F.; Wang, Y.L.; Wei, X.F.; Fu, Z.Y.; Zhang, J.L.; Xu, X.F. Synthesis and binding ability of molecular probes based on a phenanthroline derivative: Theory and experiment. Molecules 2013, 18, 14840–14848. [CrossRef] [PubMed] Lin, Q.; Cai, Y.; Li, Q.; Shi, B.B.; Yao, H.; Zhang, Y.M.; Wei, T.B. Fluorescent “turn-on” detecting CN´ by nucleophilic addition induced schiff-base hydrolysis. Spectrochim. Acta A Mol. Biomol. Spectrosc. 2015, 141, 113–118. [CrossRef] [PubMed] Cornes, S.P.; Davies, C.H.; Blyghton, D.; Sambrook, M.R.; Beer, P.D. Contrasting anion recognition behaviour exhibited by halogen and hydrogen bonding rotaxane hosts. Org. Biomol. Chem. 2015, 13, 2582–2587. [CrossRef] [PubMed]
Sensors 2016, 16, 733
10. 11.
12. 13.
14.
15. 16.
17. 18.
19.
20.
21. 22. 23. 24.
25.
26. 27. 28. 29. 30. 31.
10 of 11
Gale, P.A. Anion and ion-pair receptor chemistry: highlights from 2000 to 2001. Coord. Chem. Rev. 2003, 240, 191–221. [CrossRef] Robinson, S.W.; Mustoe, C.L.; White, N.G.; Brown, A.; Thompson, A.L.; Kennepohl, P.; Beer, P.D. Evidence for halogen bond covalency in acyclic and interlocked halogen-bonding receptor anion recognition. J. Am. Chem. Soc. 2015, 137, 499–507. [CrossRef] [PubMed] Xu, Z.; Kim, S.K.; Yoon, J. Revisit to imidazolium receptors for the recognition of anions: Highlighted research during 2006–2009. Chem. Soc. Rev. 2010, 39, 1457–1466. [CrossRef] [PubMed] Tomich, J.M.; Wallace, D.; Henderson, K.; Mitchell, K.E.; Radke, G.; Brandt, T.; Amber, C.A.; Scott, A.; Ganthan, J.; Sullivan, L.; et al. Aqueous solubilization of transmembrane peptide sequences with retention of membrane insertion and function. Biophys. J. 1998, 74, 256–267. [CrossRef] Hossain, M.A.; Llinares, J.M.; Powell, D.; Bowman-James, K. Multiple hydrogen bond stabilization of a sandwich complex of sulfate between two macrocyclic tetraamides. Inorg. Chem. 2001, 40, 2936–2937. [CrossRef] [PubMed] Szumna, A.; Jurczak, J. A new macrocyclic polylactam-type neutral receptor for anions—Structural aspects of anion recognition. Eur. J. Org. Chem. 2001, 21, 4031–4039. [CrossRef] Beer, P.D.; Szemes, F.; Balzani, V.; Salà, C.M.; Drew, M.G.B.; Dent, S.W.; Maestri, M. Anion selective recognition and sensing by novel macrocyclic rransition metal receptor systems. 1 H-NMR, electrochemical, and photophysical investigations. J. Am. Chem. Soc. 1997, 119, 11864–11875. [CrossRef] Sessler, J.L.; Cho, D.G.; Lynch, V. Diindolylquinoxalines: Effective indole-based receptors for phosphate anion. J. Am. Chem. Soc. 2006, 128, 16518–16519. [CrossRef] [PubMed] Furman, P.A.; Fyfe, J.A.; Clair St, M.H.; Weinhold, K.; Rideout, J.L.; Freeman, G.A. Phosphorylation of 3’-azido-3’-deoxythymidine and selective interaction of the 5’-triphosphate with human immunodeficiency virus reverse transcriptase. Proc. Natl. Acad. Sci. USA 1986, 83, 8333–8337. [CrossRef] [PubMed] Král, V.; Sessler, J.L. Molecular recognition via base-pairing and phosphate chelation. Ditopic and tritopic sapphyrin-based receptors for the recognition and transport of nucleotide monophosphates. Tetrahedron 1995, 51, 539–554. [CrossRef] Ojida, A.; Mito-oka, Y.; Sada, K.; Hamachi, I. Molecular recognition and fluorescence sensing of monophosphorylated peptides in aqueous solution by bis (zinc (II)-dipicolylamine)-based artificial receptors. J. Am. Chem. Soc. 2004, 126, 2454–2463. [CrossRef] [PubMed] Gale, P.A. A phenylhydrazone-based indole receptor for sensing acetate. Chem. Commun. 2005, 30, 3761–3772. Lee, G.W.; Singh, N.; Jang, D.O. Benzimidazole and thiourea conjugated fluorescent hybrid receptor for selective recognition of PO4 3´ . Tetrahedron Lett. 2008, 49, 1952–1956. [CrossRef] Shao, J.; Lin, H.; Shang, X.F.; Chen, H.M.; Lin, H.K. A novel neutral receptor for selective recognition of H2 PO4 ´ . J. Incl. Phenom. Macrocycl. Chem. 2007, 59, 371–375. [CrossRef] Jimenez Blanco, J.L.; Bootello, P.; Benito, J.M.; Ortiz Mellet, C.; Garcia Fernandez, J.M. Urea-, thiourea-, and guanidine-linked glycooligomers as phosphate binders in water. J. Org. Chem. 2006, 71, 5136–5143. [CrossRef] [PubMed] Gunnlaugsson, T.; Glynn, M.; Tocci, G.M.; Kruger, P.E.; Pfeffer, F.M. Anion recognition and sensing in organic and aqueous media using luminescent and colorimetric sensors. Coord. Chem. Rev. 2006, 250, 3094–3117. [CrossRef] Feng, C.; Dai, S.; Wang, L. Optical aptasensors for quantitative detection of small biomolecules: A review. Biosens. Bioelectron. 2014, 59, 64–74. [CrossRef] [PubMed] Amendola, V.; Esteban-Gomez, D.; Fabbrizzi, L.; Licchelli, M. What anions do to NH-containing receptors. Acc. Chem. Res. 2006, 39, 343–353. [CrossRef] [PubMed] Jung, H.S.; Chen, X.; Kim, J.S.; Yoon, J. Recent progress in luminescent and colorimetric chemosensors for detection of thiols. Chem. Soc. Rev. 2013, 42, 6019–6031. [CrossRef] [PubMed] Nishiyabu, R.; Anzenbacher, P. 1,3-Indane-based chromogenic calixpyrroles with push-pull chromophores: Synthesis and anion sensing. Org. Lett. 2006, 8, 359–362. [CrossRef] [PubMed] Wang, Y.H.; Lin, H.; Shao, J.; Cai, Z.S.; Lin, H.K. A phenylhydrazone-based indole receptor for sensing acetate. Talanta 2008, 74, 1122–1125. [CrossRef] [PubMed] Liu, Z.Q.; Shi, M.; Li, F.Y.; Fang, Q.; Yi, T.; Huang, C.H. Highly selective two-photon chemosensors for fluoride derived from organic boranes. Org. Lett. 2005, 7, 5481–5484. [CrossRef] [PubMed]
Sensors 2016, 16, 733
32. 33.
34. 35. 36. 37. 38. 39.
40. 41.
42. 43.
44.
11 of 11
Lin, Z.H.; Ou, S.J.; Duan, C.Y.; Zhang, B.G.; Bai, Z.P. Naked-eye detection of fluoride ion in water: A remarkably selective easy-to-prepare test paper. Chem. Commun. 2006, 6, 624–626. [CrossRef] [PubMed] Lin, Z.H.; Zhao, Y.G.; Duan, C.Y.; Zhang, B.G.; Bai, Z.P. A highly selective chromo- and fluorogenic dual responding fluoride sensor: Naked-eye detection of F´ ion in natural water via a test paper. Dalton Trans. 2006, 30, 3678–3684. [CrossRef] [PubMed] Xu, Z.; Kim, S.; Lee, K.H.; Yoon, J. A highly selective fluorescent chemosensor for dihydrogen phosphate via unique excimer formation and PET mechanism. Tetrahedron Lett. 2007, 48, 3797–3800. [CrossRef] Kumar, G.S.; Neckers, D.C. Photochemistry of azobenzene-containing polymers. Chem. Rev. 1989, 89, 1915–1925. [CrossRef] Harada, J.; Fujiwara, T.; Ogawa, K. Crucial role of fluorescence in the solid-state thermochromism of salicylideneanilines. J. Am. Chem. Soc. 2007, 129, 16216–16221. [CrossRef] [PubMed] Liu, Y.; Han, B.H.; Zhang, H.Y. Spectroscopic studies on molecular recognition of modified cyclodextrins. Curr. Org. Chem. 2004, 8, 35–46. [CrossRef] Liu, Y.; You, C.C.; Zhang, H.Y. Supramolecular Chemistry; Nankai University Publication: Tianjin, China, 2001. Bourson, J.; Pouget, J.; Valeur, B. Ion-responsive fluorescent compounds. 4. Effect of cation binding on the photophysical properties of a coumarin linked to monoaza-and diaza-crown ethers. J. Phys. Chem. 1993, 97, 4552–4557. [CrossRef] Bonizzoni, M.; Fabbrizzi, L.; Taglietti, A.; Tiengo, F. (Benzylideneamino) thioureas—Chromogenic interactions with anions and N-H deprotonation. Eur. J. Org. Chem. 2006, 16, 3567–3574. [CrossRef] Frisch, M.J.; Trucks, G.W.; Schlegel, H.B.; Frisch, M.J.; Trucks, G.W.; Schlegel, H.B.; Scuseria, G.E.; Robb, M.A.; Cheeseman, J.R.; Montgomery, J.A., Jr. Software for Computational Chemistry; Gaussian, Inc.: Pittsburgh, PA, USA, 2003. Smith, K.; Musson, A.; De Boos, G. Superior methodology for the nitrate ion of simple aromatic compounds. Chem. Soc. Chem. Commun. 1996, 469–470. [CrossRef] Zhang, X.; Zhang, X.; Zou, K.; Lee, C.S.; Lee, S.T. Single-crystal nanoribbons, nanotubes, and nanowires from intramolecular charge-transfer organic molecules. J. Am. Chem. Soc. 2007, 129, 3527–3532. [CrossRef] [PubMed] Hu, D.H.; Yu, J.; Padmanadan, G.; Ramakrishanan, S.; Barbara, P.F. Spatial confinement of excition transfer and the role of conformational order in organic nanoparticles. Nano Lett. 2002, 2, 1121–1124. [CrossRef] © 2016 by the authors; licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC-BY) license (http://creativecommons.org/licenses/by/4.0/).
