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Journal of Macromolecular Science, Part A
Pure and Applied Chemistry
ISSN: 1060-1325 (Print) 1520-5738 (Online) Journal homepage: https://www.tandfonline.com/loi/lmsa20
Macrocyclic anthracene-anchored calix[4]arene as
a sensitive and selective fluorescent chemosensor
for ytterbium ions
Bahar Yilmaz & Mevlut Bayrakci
To cite this article: Bahar Yilmaz & Mevlut Bayrakci (2018) Macrocyclic anthracene-anchored calix[4]arene as a sensitive and selective fluorescent chemosensor for ytterbium ions, Journal of Macromolecular Science, Part A, 55:7, 513-518, DOI: 10.1080/10601325.2018.1476822
To link to this article: https://doi.org/10.1080/10601325.2018.1476822
Published online: 31 May 2018.
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Macrocyclic anthracene-anchored calix[4]arene as a sensitive and selective fluorescent
chemosensor for ytterbium ions
Bahar Yilmaz and Mevlut Bayrakci
Karamanoglu Mehmetbey University, Department of Bioengineering, Karaman, Turkey
ARTICLE HISTORY
Received February 2018 Revised April 2018 Accepted May 2018
ABSTRACT
A novel anthracene anchored cone calix[4]arene pyridine amide receptor C4PA was synthesized and characterized by combination of spectroscopic and spectrophotometric techniques. Ion binding properties of C4PA towards a series of metal cations were investigated by UV andfluorescence spectra. A remarkable increase for receptor C4PA influorescence intensity in the presence of trace amounts of Yb3C was observed. C4PA showed“turn on” type fluorescence response toward Yb3Cwith high selectivity and C4PA also retained its selectivity toward Yb3Cin the presence of most competing metal ions.
KEYWORDS
Calixarene; anthracene; ytterbium;fluorescent; chemosensor
1. Introduction
In recent years, the development offluorescent chemosensors for the selective and sensitive detection of heavy metal ions has attracted considerable attention worldwide because these metals play important roles in living systems and have a toxic impact on the environment.[1,2]Accumulation of heavy metal ions as ytter-bium in the bodies of humans and animals can lead to serious ill-nesses even in low concentration.[3] Although ytterbium is substantially stable rare-earth element, it should be stored in closed containers to protect it from air and moisture. Ytterbium compounds are known to cause skin and eye irritation and may be teratogenic. Furthermore, metallic ytterbium dust poses afire and explosion hazard.[4]As a result, the design of selective and sensitive sensors for the low-level determination of Yb3Cis of con-siderable importance for the prevention of environmental pollu-tion and the protecpollu-tion of human health. Today, different types of fluorescent receptors are known for the sensing of rare-earth metals.[5–7] However, they often show fluorescence quenching (turn-off) response.[4]Systems with turn-onfluorescence response especially for Yb3Care still rare.[8]Calixarene-based chemosensors have been widely studied as a highly selective and sensitive detec-tion technology. Compared to other molecular systems, calixar-enes have some advantages such as a hydrophobic cavity and easy functionalization at the upper or lower rims. Calixarenes are cyclic oligomeric structures and regarded as the third generation of host molecules because of their inclusion complexation ability with cat-ions, ancat-ions, and neutral molecules.[9,10]Calix[4]arenes can be eas-ily functionalized both at lower and upper rims.[11] Calixarenes have become important receptors in synthesis and applications as supramolecular platforms for molecular recognition, drug discov-ery, self-assembly, catalysis, nanotechnology and sensing.[12–14] Calixarene molecules generally exist in four main conformations such as cone, partial cone, 1,2-alternate and 1,3-alternate.
Compared these conformers, the cone is the most powerful con-formation for construction of useful and stable calixarene struc-tures. This conformation has less polarity than the other conformations cone (i.e. partial cone and 1,2-alternate).[15] In addition, it provides excellent topological advantages because it affords excellent cavities on same side of the calix[4]arene frame-work composed of the phenolic oxygen donor atoms and aro-matic moieties.[16] Although preparation of bulky calixarene chemosensor in cone conformation is rare, its synthetic strategy is quite interesting. However, to the best of our knowledge, calixar-ene chemosensor in cone conformation, especially with turn-on fluorescence response for Yb3C, have not been reported yet. Thus, development of a new calixarene receptor capable of recognizing Yb3Chas attracted our interest.
2. Materials and methods 2.1. Materials and apparatus 1
H and13C NMR spectra were obtained using Agilent Premium Compact spectrometer operating at 600 MHz. IR spectra were recorded on a Perkin-Elmer spectrum 100 FTIR spectrometer (ATR). UV-vis. Absorbance spectra were collected by a Perkin Elmer Lambda 25 UV-vis spectrophotometer using quartz cells of 1.0 cm path length. Fluorescence measurements are carried out by using a Perkin Elmer LS 55 spectrofluorimeter. All the chemicals used were of analytical grade, and they were used as received. Aque-ous solutions were prepared with deionized water that had been passed through a Millipore Milli-Q Plus water purification system.
2.2. Synthesis
Starting calixarene compounds 5,11,17,23-Tetra-tert-butyl-25,26,27,28-tetrahydroxycalix[4]arene (1),
5,11,17,23-Tetra-tert-CONTACT Mevlut Bayrakci mevlutbayrakci@gmail.com Department of Bioengineering, Faculty of Engineering, Karamanoglu Mehmetbey University, Karaman, Turkey.
Color versions of one or more of thefigures in the article can be found online atwww.tandfonline.com/lmsa
© 2018 Taylor & Francis Group, LLC
https://doi.org/10.1080/10601325.2018.1476822 2018, VOL. 55, NO. 7, 513–518
butyl-25,27,-di-(methoxycarbonylmethoxy)-26,28-dihydroxycalix [4]arene (2) and 5,11,17,23-Tetra-tert-butyl-25,27-bis-(2-amino-methyl-pyridinecarbonylmethoxy)-26,28-dihydroxycalix[4]arene (3) were synthesized according to literature procedures.[9,16,17]
Final product C4PA has been synthesized for thefirst time according to the following procedure:
Synthesis of C4PA:
To a stirred suspension of compound3 (1.62 mmol) and Na2CO3
(16.2 mmol) in 200 mL dry acetone was added 9-(Chloromethyl) anthracene (16.2 mmol) in the presence of NaI (16.2 mmol); the reaction mixture was stirred under reflux for 72 h under nitrogen atmosphere. The solvent was removed under reduced pressure and the residue was treated with CH2Cl2(40 mL) and water (30 mL).
The organic phase was washed twice with water (2£ 25 mL), dried over MgSO4, and the solvent was evaporated. Column
chromatog-raphy on silica gel eluting with hexane and ethyl acetate gave the pale yellow solidproduct C4PA in 55% yield.1H NMR (400 MHz CDCl3): d 0.62 (s, 18H, tBu), 1.19 (s, 18H, tBu), 2.29–2.31 (d, J D
13.2 Hz, 4H, ArCH2Ar), 4.03–4.05 (d, 4H, J D 13.2 Hz, ArCH2Ar),
4.77 (s, 4H, OCH2CO), 5.17–518 (d, 4H, ArCH2NH), 5.80 (s, 4H,
OCH2-Antr), 6.04 (s, 4H, ArH), 6.80 (s, 4H, ArH), 7.13–7.15 (m, J
D 6.2 Hz, 2H, PyH), 7.33–7.34 (m, 8H,Anth-H), 7.54–7.55 (d, 2H, J D 7.8 Hz, PyH), 7.69–7.70 (m, 2H, PyH), 7.84–7.85 (d, 4H, J D 8.4 Hz, Anth-H), 7.91–7.92 (d, 4H, J D 7.2 Hz,Anth-H), 8.42 (s, 2H, Anth-H), 8.56–8.57 (d, 2H, J D 5.7 Hz, PyH), 9.16–9.18 (t, J D 6.0 Hz, 2H, NH).13C NMR (CDCl 3): 171.2, 158.5, 154.5, 149.7, 149.5, 145.4, 145.2, 136.8, 133.9, 131.9, 131.8, 130.8, 128.7, 128.6, 126.9, 126.4, 126.0, 124.8, 124.4, 123.8, 122.1, 121.8, 74.6, 69.0, 45.2, 33.9, 33.3, 31.4, 31.2, 30.9. Anal. calcd. For C90H94O6N4: C, 81.41;
H, 7.14; N, 4.22. Found: C, 81.31; H, 7.13; N, 4.14%.
2.3. UV–vis and fluorescence studies
The anthracene anchored calix[4]arene pyridine amide recep-tor (C4PA) and the metal nitrates were dissolved in CHCl3and CH3OH, respectively, and all the stock solutions were prepared to be 1 mM concentration. All the measurements have been made in 1 cm quartz cells and maintained afinal receptor con-centration of 10 mM and the concon-centration of metal nitrates were varied with respect to the corresponding mole ratios of metal ion to the receptor. During the titration of the receptor with metal nitrates, the total volume of the solution was main-tained constant (3 mL).
3. Results and discussion
3.1. Synthesis and characterization
The synthesis of targeted molecule C4PA is illustrated inScheme 1. The ester derivative of p-tert-butylcalix[4]arene (2) reacted with 2-(aminomethyl) pyridine to gain bis-picolyl amide substituted calix [4]arene (3).[17]
Further alkylation of 3 with 9-(chloromethyl) anthracene in the presence of Na2CO3afforded cone calix[4]arene pyridine amide receptor containing anthracene units (C4PA) as a pale yellow solid in good yield.1H NMR spectra for C4PA have indicated that the calix[4]arene skeleton is fully substituted due to the absence of any singlet signal assigned to the phenolic hydroxyl groups (Figure 1). The1H NMR spectra of C4PA have a typical AX pattern for the methylene bridge proton (ArCH2Ar) of the calixar-ene moiety, respectively, around 2.30 (JAB: 13.2 Hz) and 4.05 ppm (JAB: 13.2 Hz), which demonstrated that the compound C4PA existed in the cone conformation. In addition to above signals,
ionophore C4PA also showed one singlet peak around 5.80 ppm corresponding to the -OCH2protons of anthracene fragments. Fur-thermore, new signals attributable aromatic protons of anthracene units appeared around 7.33–8.42 ppm for C4PA as singlet, doublet or multiplet. In the13C NMR spectra of compound C4PA, it was obvious that C4PA was symmetrical and therefore the number of signals observed in the13C NMR was lesser than the number of C atoms in the related compound C4PA (Figure 1). Thirty carbon sig-nals in13C NMR spectra were observed due to symmetrical struc-ture of compound C4PA while it was ninety carbon atoms.
3.2. Spectroscopic studies
With an objective to evaluate the potential use of probe C4PA as a chemosensor, the selectivity of C4PA towards different nitrate salts of metal ions (Cu2C, Hg2C, Cr3C, Co2C, AgC, Tb3C, Zn2C, Cd2C, Ni2C, Ga3C, Mn3C, Yb3C and Gd3C) in MeOH/ CHCl3(1:3) solvent system wasfirstly examined by UV/Vis and fluorescence spectroscopy at room temperature. C4PA exhibits typical anthracene-based absorption bands at 348 nm, 365 nm and 385 nm, respectively. These absorption bands may be attributable to p- p transition of the aromatic moieties.[18] Upon addition of metal ions, probe C4PA only shows sensing behavior toward Yb3C, with the increasing of anthracene-based absorption bands of C4PA, and the low energy band red shift (Figure 2). When compound C4PA is complexed with Yb3C, the original peak at 280 nm is increased and the intense absorp-tion band of anthracene conjugated system around 350– 380 nm is given a slightly bathochromic shift in presence of Yb3C.[19]The conjugation between receptor and metal ions is caused to charge transfer from the p-system to metal ion that the changes in the absorption band may be due to expansion of p-conjugated system by addition of Yb3C and occurrence of donor-acceptor charge transfer (CT) in the large p conjugate system owing to the presence of the anthracene units.[20]The recognition abilities of C4PA towards selected metal ions are then investigated by the detection of emission. The receptor
Scheme 1.Synthetic route of preparation of anthracene anchored calix[4]arene pyridine amide receptor (C4PA) (i) NaOH, formaldehyde (37%), Diphenylether; (ii) Dry acetone, K2CO3, Bromomethyl acetate, 48h, reflux under N2; (iii) 2-picolin-amine, toluene-methanol, 36 h, reflux under N2; (iv) 9-(Chloromethyl)anthracene, dry acetone, Na2CO3, NaI, 72 h, reflux under N2.
C4PA is not show any remarkable emission alone when the excitation wavelength is at 320 nm. Upon addition of metal cat-ions to solutcat-ions of compound C4PA, a large increase and shift of the maximum emission of receptor C4PA around 420 and 480 nm is observed for Yb3C excited at 320 nm, indicating strong complex formation with this cation. Compared to other ions and Yb3C, any appreciable increase is not observed for other ions.
Either in the absorption spectra (Figure 2) or in the emission spectra (Figure 2), when receptor C4PA is bound the Yb3C, it exhibits a spectrum having features very similar to the spec-trum of anthracene units. All this variation indicates the role of the lone pair of two pyridine amide groups on calixarene skele-ton in increasing thefluorescence by the metal ion binding that utilizes the lone pair. The emission results reveal that Yb3Cis sensitive to C4PA. Therefore, the calix[4]arene pyridine amide containing anthracene units could act as an antenna unit, capa-ble of light harvesting (by the binding of analyte). The target (C4PA-Yb3C) caused these changes in the emission spectra. Binding of Yb3C metal ion at the amide center reduces the
effect of lone pair present on nitrogen atom that is responsible for the conjugation and thereby enhances the intensity of fluo-rescence. In addition, upon complexation with Yb3C, the nitro-gen atom of imine group donates its lone pair electrons to the empty orbital of the Yb3C, and in this way a large chelation enhancedfluorescence (CHEF) is observed because the chela-tion terminates the photoinduced electron transfer (PET) which is known an excited state electron transfer process from donor to acceptor. Furthermore, this effect can be related to the blocking of the carbonyl groups of two amide bridges by metal ion complexation. Because, in the literature it is well-known that trivalent cations as Yb3Care effectively bound by the amide groups.[18,21]Owing to the large lability and high coordination number properties of the lanthanide ions, the multi-dentate chelating agents containing anionic groups, amides, carboxy-lates, and/or O and N donor atoms are preferred for the com-plexation via ion-dipole interactions with little covalent character.[22]
Figure 4 shows the changes in both fluorescence and UV spectra of C4PA upon titration with Yb3C(0–20eq). The
fluorescence titration of C4PA with Yb3Cwas performed with an excitation at 320 nm for the quantitative study. The fluores-cence intensity of C4PA increase gradually with increasing
amount of Yb3Cions stepwise. When 20 eq of Yb3Cis added, maximum increase for the fluorescence intensity of C4PA is observed. Consequently, the titration curves demonstrate a clear color change from yellow to brighter yellow under UV lamp. Therefore, C4PA can be used as a turn onfluorescence sensor for Yb3C detection. Furthermore, the competing ion studies are performed for C4PA in the presence of Yb3Cmixed with the tested metal cations such as Cu2C, Hg2C, Cr3C, Co2C, AgC, Tb3C, Zn2C, Cd2C, Ni2C, Ga3C, Mn3Cand Gd3C.
InFigure 5, I0and I are the emission intensities of C4PA in the absence and presence of metal cations, respectively. 1 mM of receptor C4PA is treated with 20 mM of Yb3Cin the pres-ence of other metal ions (20 mM). In general, considerable change is not observed in the fluorescence intensity with respect to Yb3Csensing after addition of competing metal ons. Hence, the presence of most of the studied competing cati-ons does not affect the selectivity of C4PA for Yb3C; while the presence of Hg2Cions slightly decreases the emission intensity of C4PA-Yb3Cmixture.
The effect of response time on the fluorescence intensity of C4PA is investigated at 480 nm. The change in thefluorescence intensity of C4PA is specified for different selected time intervals in the range 0– 20 min. As it can be seen inFigure 6, the fluores-cence intensity gradually increases until the 6th min, and then remains almost unchanged upon further increments in response time from 6 to 20 min. Moreover, no obvious emission intensity variation for receptor C4PA is observed even for prolonged response times up to 30 minutes. Thus, it is concluded that com-plex formation between C4PA and Yb3Creaches an equilibration state within thefirst six minutes. Since long response time periods are not preferable for manyfluorescent sensors, which record for the receptor C4PA is evaluated as reasonably good. Furthermore, the structure of the receptor that bears pyridine amide units is understood to be stable under the studied conditions.
To understand the binding stoichiometry of complex forma-tion of C4PA with Yb3C, the Job’s plot analysis is carried out. In
Figure 7, the emission intensity at 480 nm is plotted against the molar fraction of Yb3C. Maximum emission intensity is measured for a molar fraction of 0.5, indicating a 1:1 complex formation between C4PA and Yb3C. Also, this theory can be supported by the modified Hildebrand-Benesi Equation if a linear relationship gained from the reciprocal plot of 1/F-F0vs. 1/[Q].[23]Reciprocal plots helping the determination of the stoichiometry ratio for the
Figure 2.Absorption spectra of receptor C4PA (1£ 10–6 M) and its complexes (Cu2C, Hg2C, Cr3C, Co2C, AgC, Tb3C, Zn2C, Cd2C, Ni2C, Ga3C, Mn3C, Yb3C and Gd3C) in MeOH/CHCl3.
Figure 3.Fluorescence spectra of the receptor C4PA in the absence and presence of various metal cations. Added cation ion concentrations were 10 mM. Excitation: 320 nm.
Figure 4.(a) Emission and (b) absorption titration curves of receptor C4PA with Yb3C in MeOH/CHCl3 at emission of 480 nm in ?ex D 320 nm. The concentration of Yb3Cwas varied with 0–20 equiv.
complex formation are given inFigure 7. From curve fitting of probe C4PAfluorescence intensity against the reciprocal of the Yb3C concentration, Benesi–Hildebrand equation plot shows a linearfit. This linearity evidenced the 1:1 complexation behavior of C4PA with Yb3Cand the value of the stability constant is also calculated as 3.3¢104
M¡1. Furthermore, to clarify the possible interaction mechanism between C4PA and Yb3C, we tried to per-form1H NMR titration experiments. However, we did not obtain considerable NMR data for the formed complex structure during the addition of the metal ions to the deuterated solution of C4PA. However, FT-IR spectra of the free C4PA and its Yb3Ccomplex is
used to investigate the possible binding mechanism between ligand and metal cation. The FT-IR spectra of the FT-IR spectra of the free C4PA and its Yb3Care given inFigure 8. The character-istic band at around 1671 cm¡1is attributed to the NHCO stretch-ing of the amide group of C4PA. This band disappears and shifts downward to 1648 cm¡1 in the C4PA-Yb3Ccomplex structure which suggests that the coordinate bonds form between oxygen atom of carbonyl group and Yb3C. In addition, the free isolated C D N group at around 1590 cm¡1as reported in literature[24]
also shifts to lower wavenumber at 1560. These shifts and decreases in the IR signals of C4PA prove that a coordination between N atoms of imine group and Yb3Cis taken place. All data supports that the possible interaction between C4PA and Yb3Cis occurred by two amide linkages on calixarene skeleton.
Figure 5.Fluorescence responses of the receptor C4PA forYb3C in the presence or absence of competing metal ions.
Figure 6.The effect of response time for the complex formation between receptor C4PA and Yb3C.
Figure 7.Job’s plot analysis with possible interaction mechanism and Benesi–Hildebrand plot for the complex formation between receptor C4PA and Yb3C at emission of 480 nm in MeOH/CHCl3, ?exD 320 nm.
4. Conclusion
Typical behavior of a new fluorescent chemosensor based on calix[4]arene pyridine amide containing anthracene units (C4PA) for ytterbium ions has been studied, and the developed receptor is proposed as a sensitive and selective chemosensor for Yb3C. The efficiency of C4PA for the recognition of Yb3Cwas confirmed in presence of several competing ions such as Cu2C, Hg2C, Cr3C, Co2C, AgC, Tb3C, Zn2C, Cd2C, Ni2C, Ga3C, Mn3C, Yb3C and Gd3C. The receptor C4PA is proposed as a selective “turn-on” type fluorescent chemosensor for the determination of Yb3C. This design and methodology will contribute to extending the development of useful calixarene basedfluorescent chemo-sensors for Yb3C. Andfinally, the concept is believed to be an important contribution to development of selective, sensitive, rapid, facile, and inexpensive sensing technologies.
Acknowledgments
We thank Karamanoglu Mehmetbey University Research Foundation
(Project No: 25-M-15) and The Scientific and Technological Research Application Center (BILTEM) for thefinancial and technical supports.
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