Tripodal synthetic receptors based on cyclotriphosphazene scaffold for highly selective and sensitive spectrofluorimetric determination of iron(III) in water samples

Journal of Photochemistry & Photobiology A: Chemistry 372 (2019) 156–167

Contents lists available at ScienceDirect

Journal of Photochemistry & Photobiology A: Chemistry journal homepage: www.elsevier.com/locate/jphotochem

Tripodal synthetic receptors based on cyclotriphosphazene scaffold for highly selective and sensitive spectrofluorimetric determination of iron(III) in water samples Süreyya Oğuz Tümay, Serkan Yeşilot

T

⁎

Department of Chemistry, Gebze Technical University, Gebze, 41400, Kocaeli, Turkey

A R T I C LE I N FO

A B S T R A C T

Keywords: Tripodal receptor Cyclotriphosphazene Spectrofluorimetric determination Water samples Iron

Two novel tripodal synthetic receptors based on cyclotriphosphazene scaffolds were prepared for spectrofluorimetric quantification of iron ions in environmental water samples. The receptors were designed by using the planar structure of cyclotriphosphazene which were modified by metal ion detecting naphtalene or anthracene-triazole groups above the plane and water solubility interacting triethylene glycol monomethyl ether (TEGME) groups below. All compounds were characterized by standard spectroscopic techniques such as 1H, 13 C, 31P NMR and mass spectrometry (MALDI-TOF). The new developed methods based selective and sensitive complexation of CBTSRs with iron prior to spectrofluorimetric determination without any preconcentration processes. The experimental conditions such as pH, buffer and buffer concentration, initial CBTSRs concentration and time before measurement were optimized for selective complexation, which provided submicromolar spectrofluorimetric determination of iron under optimized conditions. The obtained results demonstrated that CBTSRs led to develop sensitive (LODs, 0.54 and 0.44 μM), selective and time-saving spectrofluorimetric methods for quantification of iron ions in environmental water samples under the optimized conditions (pH, 7.0; initial CBTSRs concentration, 10 μM and 5 μM; solvent, aqueous ethanol, (3:1 v/v and 9:1 v/v); buffer and buffer concentration, 0.1 M Britton-Robinson buffer; time before measurement, 20 and 25 s).

1. Introduction In recent years, there has been considerable interest in the study of the selective and sensitive determination of metal ions by synthetic receptors due to their potential applications in various areas such as environmental and biological analyzes [1,2]. Among these metal ions, iron is the most abundant transition metal in the human body and vital element for almost all living organisms due to catalysis of enzyme, synthesis and repair of DNA/RNA, in the structure of hemoglobin for oxygen carrier and cofactor in many enzymatic reactions [3,4]. On the other hand, while, excessive intake of iron can cause substantial diseases such as Alzheimer’s diseases, Perkinson and cancer, deficiency of iron leads diabetes, breathing problems and anemia which can harms or even kill organs because lack of oxygen [5,6]. Although, there are innumerable instrumental analysis methods were presently used for iron determination, these methods generally require expert users/analysts to quantification because of sophisticated equipment’s and precontentration treatment which led to use excessive adsorbents and eluents [7,8]. Recently, sensitive detection and determination of iron with using

⁎

spectrofluorimetry has been attractive analytical method, which provided quick response, high selectivity/sensitivity, easy operation for determination of iron in organic, aqueous or mixed aqueous media [9–11]. The design of synthetic receptors for selective and sensitive determination of iron is still challenging research area because these receptors can be used for the development of new analytical methods by using fluorescent signals to determine the amount of iron in environmental samples [12]. Until now, there were numerous reports existed in literature about detection of iron in model solution via fluorescent signal changing of receptor [13–16], but real sample application for determination of iron by spectrofluorimetry is rarely studied [17,18]. Consequently, development of new spectrofluorimetric method for determination of iron levels by synthetic receptors in environmental or biological water samples still required and vital research area. Various strategies have been applied for designing and developing synthetic receptors with high selectivity towards targeted metal ions via wide range of properties of synthetic receptor that should be adjusted to size or shape of target component. Consequently, arranged topology of

Corresponding author at: Department of Chemistry, Gebze Technical University, P.O.Box: 141, Gebze, 41400, Kocaeli, Turkey. E-mail address: [email protected] (S. Yeşilot).

https://doi.org/10.1016/j.jphotochem.2018.12.012 Received 17 November 2018; Received in revised form 7 December 2018; Accepted 8 December 2018 Available online 14 December 2018 1010-6030/ © 2018 Elsevier B.V. All rights reserved.

Journal of Photochemistry & Photobiology A: Chemistry 372 (2019) 156–167

S.O. Tümay, S. Yeşilot

2. Experimental

synthetic receptor becomes an important for determination of the target component with receptor-ion interaction/complexation. The tripodal receptors, which are one of the best important acyclic ionophore class, were coordinated to analyte by multiarmed ligands and these arms consist a special functional group according to morphology or chemical properties of analyte [19,20]. Up to now, tripodal receptors for recognition of target components have been used as an optical sensor [21–23] owing to these kind of molecular platforms include three arms, which are modified to interact with the analyte [24]. In addition, molecular design for tripodal receptors allows the control of binding process such as selectivity, sensitivity and complex stability through rigidity of arms and their cavity size [25,26]. It is well known that tripodal-based synthetic receptors have a various advantages over dipodal or monopodal receptors, for instance, tripodal-based receptors generally interact to metal ions very vigorously owing to the improved chelating properties and the bulkiness of tripodal-based receptors that can be arranged for controlling of metal binding reactivity [19]. Therefore, the designing and developing of new synthetic tripodal receptor systems are an attractive research area for not only in supramolecular chemistry but also in analytical chemistry [19,27]. Although numerous synthetic receptor, which based on the change of the fluorescence signal for detection of metal ions, are in the literature, only a few tripodal-based synthetic receptor have been reported for application via fluorescence signal changing [28–30]. Also, best our knowledge, only very few of tripodal-based synthetic receptor mainly focused on determination of iron ions in environmental samples [31,32]. 1,2,3-triazoles have been widely used by researchers in synthetic receptor due to significant binding properties and as a linker part between ionophore and fluophore in receptor system. In addition, it can be easily obtained by Cu(I)-catalyzed azide–alkyne cycloaddition reaction [33] In recent years, polyaromatic hydrocarbons such as anthracene, naphtalene and their derivates can be used for make new fluorophores [34,35] because of their unique properties, commercial availability, easy processability, thermal and electrochemical stability [36,37]. Another signicant feature of naphtalene and anthracene is that its ring is easily functionalized according to desired application such as artificial light activatable protein cleaving agents, organic light emitting devices and fluorescence sensor [38,39]. Owing to optical inactivity of hexachlorocyclotriphosphazene ring, N3P3Cl6, which means it does not absorb any radiation in the UV/Vis absorption region and additionally, optical behaviours of cyclotriphosphazene based molecular systems can be customized according to target application [40,41]. Also, N3P3Cl6 can be derivatized with various groups according to the side of planarity which make this ring suitable platform for design and develop excellent synthetic receptors for metal detection [32,41]. Therefore, by taking these advantages of N3P3Cl6, considerable interest in preparation of synthetic receptors has been carried out for a few years [42,43]. In this paper, we have designed and developed highly selective and sensitive spectrofluorimetric methods for determination of iron in environmental water samples without preconcentration processes using two novel cyclotriphosphazene based tripodal synthetic receptors (CBTSRs) which were formed by three naphtalene-triazole (CBTSR-1) and/or anthracene-triazole moities (CBTSR-2) at the above the planar structure of cyclotriphosphazene as fluoroionophores and water solubility interacting triethylene glycol monomethyl ether (TEGME) moities below the plane as solubility agents. The structural characterization of CBTSRs were done by 1H, 31P, 13C NMR and MALDI-MS as standard spectroscopic techniques. Optimization of experimental conditions for developed spectrofluorimetric determination methods (CBTSRs-FL) were carried out and validation has been performed by ICP-OES analysis and spike/recovery test. According to obtained results, CBTSRs can be used in environmental water samples as a selective, sensitive, simple, rapid, time friendly and low cost complexation procedures for spectrofluorimetric determination of iron under optimized conditions.

2.1. Reagents and equipment All the chemicals were obtained from commercial suppliers. Cyclohexane, sodium azide, dichloromethane, n-hexane, ethanol, acetonitrile, triethylene glycol monomethyl ether, THF-d8, dimethyl sulfoxide-d6 and chloroform-d1 were purchased from Merck. Hexachlorocyclotriphosphazene, 2-naphthol, 2-bromoethanol, 9-anthracenemethanol, diethyl ether, sodium hydride, N,N,N’,N’’,N’’-pentamethyldiethylenetriamine (PMDTA), copper(I) bromide and tetrahydrofuran purchased from Sigma-Aldrich. MALDI matrix (2,5dihydroxybenzoic acid) purchased from Fluka. To purify sodium hydride (> 60%) from mineral oil, it was washed with n-hexane. Tetrahydrofuran was distilled with sodium/potassium alloy at inert atmosphere. Fractional crystallization was used for purification of hexachlorocyclotriphosphazene (trimer). All synthetic processes were performed in dry argon atmosphere. Silica gel (Merck, Kieselgel 60, 70–230 mesh) was used for column chromatography and thin layer chromatography (TLC) was performed with using silica gel plates with F254 indicator (Merck, Kieselgel 60, 0.25 mm thickness). 2.2. Equipment UV/Vis absorption studies were performed by Shimadzu 2101 UV spectrophotometer. Varian Eclipse spectrofluorometer was used for fluorescence emission experiments. Pathlenght of cuvette was 1 cm and slit widths were 5 nm in all fluorescence emission experiments which were carried out at room temperature. Fluoro Hub-B Single Photon Counting Controller equipped Horiba- Jobin-Yvon-SPEX Fluorolog 32iHR was used for the fluorescence lifetimes measurements. Signal obtaining of measurements was performed by TCSPC module and an excitation wavelength was selected as 310 nm. Mass spectra of newly synthesized compounds were obtained with Bruker Daltonics Microflex MALDI-TOF mass spectrometer. Varian INOVA 500 MHz spectrometer were used for 31P, 1H and 13C NMR spectra with deuterated solvents (THF-d8, DMSO-d6, CDCl3-d1). In addition, 1H and 13C NMR measurements were performed with using internal reference (trimethylsilane) and 31P NMR measurements were carried out with using external reference (85% H3PO4). Fluorescence titration data was fitted with the appropriate non-linear regression analyses using Sigma-Plot 14.0 (Systat Software Inc., Point Richmond, CA). 2.3. Synthesis 2-(prop-2-yn-1-yloxy)naphthalene, 2-azido-1-ethanol, 9-((prop-2yn-1-yloxy)methyl)anthracene and compound 1 were synthesized and purified according to the literature [44–47]. In addition, compound 2 were synthesized according to our previous report [32]. Newly synthesized compounds (3, 4, CBTSR-1 and CBTSR-2) were characterized by 1H, 31P, 13C NMR and MALDI-MS spectra and all the results, which were given in supplementary material (Figs. S1–S4) consistent with structures of compounds. 2.3.1. Synthesis of 2-(4-((naphthalen-2-yloxy)methyl)-1H-1,2,3-triazol-1yl)ethan-1-ol (3) 2-(prop-2-yn-1-yloxy)naphthalene (200.0 mg, 1.097 mmol), Cu(I)Br (263.0 mg, 1.834 mmol), PMDTA (318.0 mg, 1.834 mmol) and 2-azido1-ethanol (79.7 mg, 0.914 mmol) were dissolved in dry dichlorometane (10 mL) under inert atmosphere. The resulting mixture was vigorously mixed with magnetic stirrer for six hours at 25 °C and when the reaction was finished, extraction with dichloromethane/H2O were performed and the organic phase was dried over Na2SO4. Organic solvent was removed by rotary evaporator and column chromatography was performed to purify the crude product. Silica gel and n-hexane:THF (2:1, v/v) were used as stationary and mobil phase, respectively. Compund 3, 157

Journal of Photochemistry & Photobiology A: Chemistry 372 (2019) 156–167

S.O. Tümay, S. Yeşilot

white solid, yield: 233.0 mg, 94.8%. 1H NMR (CDCl3-d1), 298 K, δ (ppm); 7.77 (s, 1 H), 7.74 (d, J = 8.8 Hz, 4 H), 7.44 (t, J = 7.4 Hz, 1 H), 7.35 (t, J = 7.4 Hz, 1 H), 7.17 (d, J = 8.8 Hz, 1 H), 5.30 (d, J = 5.8 Hz, 2 H), 4.48 (t, J = 4.6 Hz, 2 H), 4.08 (t, J = 4.6 Hz, 2 H); 13C NMR (CDCl3-d1), 298 K, δ (s, ppm); 156.04, 134.39, 129.59, 129.19, 127.63, 126.90, 126.50, 124.10, 123.95, 118.7, 107.23, 61.83, 61.06, 52.83; [M]+: 269,173 m/z (calc. [M]+: 269,300).

12 H), 5.47 (s, 6 H), 4.77 (s, 6 H), 4.55 (t, J = 7.3 Hz, 6 H), 4.10 (t, J = 7.2 Hz, 6 H), 3.73 (t, J = 6.5 Hz, 6 H), 3.41-3.36 (m, 30 H), 3.18 (s, 9 H); 13C NMR (CDCl3-d1), 298 K, δ (s, ppm); 147.25, 131.34, 128.95, 128.45, 126.36, 125.71, 125.02, 124.66, 124.30, 123.05, 120.02, 71.87, 70.49, 70.44, 67.52, 66.44, 64.73, 64.02, 62.10, 58.97, 51.99; 31 P NMR (CDCl3-d1) δ = 17.04 (s, 3 P); [M]+: 1621.018 m/z (calc. [M]+: 1621.670).

2.3.2. 2-(4-((anthracen-9-ylmethoxy)methyl)-1H-1,2,3-triazol-1-yl)ethan1-ol (4) 9-((prop-2-yn-1-yloxy)methyl)anthracene (60.0 mg, 0.244 mmol), Cu(I)Br (58.2 mg, 0.406 mmol), PMDTA (70.4 mg, 0.406 mmol) and 2azido-1-ethanol (17.7 mg, 0.203 mmol) were dissolved in dry dichlorometane (10 mL) under inert atmosphere. The resulting mixture was vigorously mixed with magnetic stirrer for six hours at 25 °C and when the reaction was finished, extraction with dichloromethane/H2O were performed and the organic phase was dried over Na2SO4. Organic solvent was removed by rotary evaporator and column chromatography was performed to purify the crude product. Silica gel and n-hexane:THF (2:1, v/v) were used as stationary and mobil phase, respectively. Compund 4, yellow solid, yield: 65.5 mg, 96.7%. 1H NMR (THF-d8), 298 K, δ (ppm); 8.48-8.40 (m, 3 H), 8.00 (d, J = 8.3 Hz, 2 H), 7.79 (s, 1 H), 7.50-7.41 (m, 4 H), 6.91 (s, 1 H), 5.55 (s, 2 H), 4.80 (s, 2 H), 4.39 (t, J = 4.8 Hz, 2 H), 3.85 (t, J = 4.9 Hz, 2 H); 13C NMR (THF-d8), 298 K, δ (s, ppm); 145.47, 137.90, 132.31, 131.82, 130.08, 129.36, 128.60, 126.42, 125.66, 124.04, 64.64, 61.45, 53.15, 47.49; [M]+: 333.142 m/ z (calc. [M]+: 333.390).

2.4. Samples Three different types of environmental water samples were collected from Gebze/Kocaeli and İkitelli/İstanbul in Turkey. Blue band filter paper was used to filter the samples, after filtration process, all water samples were acidified with HNO3 (70%) and they stored at 4 °C prior to analysis. 2.5. Developed spectrofluorimetric determination methods (CBTSRs-FL) for iron in environmental water samples The developed CBTSRs-FL methods are based on selective complexation of CBTSRs with iron prior to spectrofluorimetric determination without any preconcentration processes (Fig. 1). The fluorescence emission signals of CBTSRs were originated from blue emission of naphthalene or anthracene, which nearly completely quenched with complexation of iron. Fe2+ ions contained in environmental water samples were oxidized to Fe3+ by the acidic medium which was used in storage. Therefore, developed methods were based on spectrofluorimetric determination of Fe3+. The iron content of environmental water samples was determined by calibration curves for both methods and generated with different quantity of Fe3+ of water samples which was calculated according to (1);

2.3.3. cis-2,4,6-tris(methyltriglycol)-tris(2-(4-((naphthalen-2-yloxy) methyl)-1,2,3-triazol-1-yl)ethoxy)cyclotriphosphazene (CBTSR-1) 2-(prop-2-yn-1-yloxy)naphthalene (555.0 mg, 3.050 mmol), Cu(I)Br (525.0 mg, 3.660 mmol), PMDTA (634.0 mg, 3.660 mmol) and compound 2 (539.0 mg, 0.610 mmol) were dissolved in dry dichlorometane (10 mL) under inert atmosphere. The resulting mixture was vigorously mixed with magnetic stirrer for six hours at 25 °C and when the reaction was finished, extraction with dichloromethane/H2O were performed and the organic phase was dried over Na2SO4. Organic solvent was removed by rotary evaporator and column chromatography was performed to purify the crude product. Silica gel and n-hexane:THF (6:1, v/v) were used as stationary and mobil phase, respectively. CBTSR-1, viscous liquid, yield: 803.0 mg, 92.1%. 1H NMR (DMSO-d6), 298 K, δ (ppm); 8.11 (s, 3 H), 7.65 (dd, J = 8.1, 4.8 Hz, 9 H), 7.34 (d, J = 2.0 Hz, 3 H), 7.30 (t, J = 7.5 Hz, 3 H), 7.12 (t, J = 7.5 Hz, 3 H), 7.02 (dd, J = 8.9, 2.4 Hz, 3 H), 5.10 (s, 6 H), 4.51 (t, J = 4.7 Hz, 6 H), 4.05 (t, J = 4.7 Hz, 6 H), 3.68 (t, J = 5.3 Hz, 6 H), 3.37-3.35 (m, 24 H), 3.253.23 (m, 6 H), 3.05 (s, 9 H); 13C NMR (CDCl3-d1), 298 K, δ (s, ppm); 156.15, 134.42, 129.57, 129.12, 127.6, 126.93, 126.48, 123.88, 118.6, 107.20, 71.88, 70.56, 70.48, 65.42, 64.12, 61.82, 58.96, 50.08, 46.51; 31 P NMR (CDCl3-d1) δ = 17.28 (s, 3 P); [M+H]+: 1429,753 m/z (calc. [M]+: 1429.410).

CFe3 + =

[(F0 − F )/ F0] − n m

(1)

where F0, F, (F0-F)/F0 and CFe represent fluorescence emission response of CBTSRs in the absence of Fe3+, fluorescence emission response of CBTSRs - Fe3+ complexes, relative fluorescence intensity changing and iron quantity of the water sample at μM levels. Also, m is the slope of the calibration curves and n is the intercept (line crosses the axis). The emission signals of CBTSRs were originated from blue emission of naphthalene or anthracene which were quenched with increasing amount of Fe3+. These gradual quenching were proportional up to 400 μM of Fe3+ and 350 μM of Fe3+ for CBTSR-1 and CBTSR-2, respectively, which were applicable for quantitative analysis of Fe3+ in environmental water samples. For quantitative analysis of iron amount in water samples with CBTSRs, 0.250 mL of CBTSR-1 and 0.100 mL of CBTSR-2 were added to individual volumetric flask (10 mL) from stock solution of CBTSR-1 (4 × 10−4 M) and CBTSR-2 (1 × 10-3 M) and then, 7.250 mL of ethanol for CBTSR-1 and 8.9 mL of ethanol for CBTSR-2 were added to their own volumetric flask. After, (pH 7.0) 0.5 mL of Britton–Robinson buffer and 0.4 mL of environmental water samples were added to volumetric flasks (10 mL) and they were filled up to mark of volumetric flasks with deionized water. Then, obtained mixtures were vigorously shaken during 20 and 25 s for CBTSR-1 and CBTSR-2, respectively. For determination and optimization studies, relative fluorescence intensity for CBTSRs-Fe3+ complexes were calculated and recorded at 351 nm (for CBTSR-1) and 412 nm (for CBTSR2). Before spectrofluorimetric analysis, the accuracy of (CBTSRs-FL) methods were evaluated with ICP-OES analysis and spike/recovery measurements under optimum conditions. 3+

2.3.4. cis-2,4,6-tris(methyltriglycol)-tris(2-(4-((anthracen-9-ylmethoxy) methyl)-1H-1,2,3-triazol-1-yl)ethoxy) cyclotriphosphazene (CBTSR-2) 9-((prop-2-yn-1-yloxy)methyl)anthracene (87.0 mg, 0.353 mmol), Cu(I)Br (61.0 mg, 0.421 mmol), PMDTA (73.0 mg, 0.421 mmol) and compound 2 (62.0 mg, 0.070 mmol) were dissolved in dry dichlorometane (10 mL) under inert atmosphere. The resulting mixture was vigorously mixed with magnetic stirrer for six hours at 25 °C and when the reaction was finished, extraction with dichloromethane/H2O were performed and the organic phase was dried over Na2SO4. Organic solvent was removed by rotary evaporator and column chromatography was performed to purify the crude product. Silica gel and n-hexane:THF (6:1, v/v) were used as stationary and mobil phase, respectively. CBTSR-2, yellow viscous liquid, yield: 103.0 mg, 90.8%). 1H NMR (DMSO-d6), 298 K, δ (ppm); 8.59 (s, 3 H), 8.34 (d, J = 8.4 Hz, 6 H), 8.06 (d, J = 8.2 Hz, 6 H), 8.04 (s, 3 H), 7.51 (dt, J = 13.6, 6.2 Hz,

2.6. Photophysical calculations In order to evaluate of the photophysical properties of CBTSRs, fluorescence quantum yields (ΦF) were determined by the comparative method (Eq. (2)) [48]. 158

Journal of Photochemistry & Photobiology A: Chemistry 372 (2019) 156–167

S.O. Tümay, S. Yeşilot

Fig. 1. Schematic presentation of developed CBTSRs-FL methods for iron determination.

∅F = ∅FStd

F . AStd . n2 2 FStd . A. nStd

90.8%) by “click reaction” of compound 2 with 2-(prop-2-yn-1-yloxy) naphthalene (for CBTSR-1) and 9-((prop-2-yn-1-yloxy)methyl)anthracene (for CBTSR-2). To understand the contributions of cyclotriphosphazene platform about complexation properties of CBTSRs for determination, precursors of target molecules which namely compounds 3 and 4 were synthesized with high yield (94.8% and 96.7%) by “click reaction” of 2-(prop-2-yn-1-yloxy)naphthalene and 9-((prop-2-yn-1yloxy)methyl)anthracene with 2-azido-1-ethanol. After, purification of novel compounds by column chromatography, structural characterization was performed with using mass, 1H, 13C and 31P NMR spectroscopies. All characterization results given in supplementary material (Figs. S1–S4) were compatible with the estimated structures of compounds Scheme 1. For instance, the 1H NMR of 3, 4 and CBTSRs were given at Fig. S1. The chemical shifts and integration of the methylene/methyl group signals and aromatic proton signals in the 1H NMR of 3, 4 and CBTSRs consistent with proposed structures (Fig. S1). Also, in 31P NMR spectra, singlet peak was observed at 17.28 ppm for CBTSR-1 and 17.04 ppm for CBTSR-2 (Fig. S4).This situation means that CBTSRs showed A3 spin system and is important evidence of non-geminal-cis-tris-formations [50]. According to 31P NMR spectroscopy, it was understood that the same organic groups attached same side of planar structure of cyclotriphosphazene scaffold. Therefore, “tripodal” structures of the target receptor were achieved by the three-fluoionophore groups positioned at the above of cyclotriphosphazene plane when the three-solubility agent positioned in below of plane.

(2)

where F and FStd represented the areas under the fluorescence bands of the CBTSRs and the standard. A and AStd demonstrate absorbance of CBTSRs and the standard at the excitation wavelengths. Fluorescence quantum yield of standard and CBTSRs were examined in different solvents so that the refractive indices (n) of the solvents were used for fluorescence quantum yield calculations. Quinine sulfate (in 0.1 M H2SO4) (ΦF = 0.54) [49] was used as the standard. 10 μM and 5 μM concentration was chosen for calculations at the excitation wavelength for CBTSR-1 and CBTDR-2, respectively. Also, fluorescence lifetimes of the CBTSRs and CBTSRs - Fe3+ complexes were directly measured and determined with mono exponential calculations. 3. Results and discussions 3.1. Synthesis/structural characterization We have previously discussed the synthesis of the tripodal cyclotriphosphazene core which can be carried out in two different synthetic routes [32]. With the experience that we have gained from this study, we preferred to synthesize CBTSRs with the “click reaction” that applied in the last step of reactions, which had higher reaction yield and easier purification process. Firstly, synthesis and characterization processes of non-geminal-cis-tris-TEGME appended cyclotriphosphazene (1) were performed in accordance with literature procedure to increase the solubility of target molecules [44]. Then, in order to synthesized compound (2) which is required for “click reaction” as a core, 3 mol of 2-azido-1-ethanol and 1 mol of compound 1 were reacted in presence of NaH at room temperature in THF [32]. After prepared cyclotriphosphazene core, we synthesized 2-(prop-2-yn-1-yloxy)naphthalene and 9-((prop-2-yn-1-yloxy)methyl)anthracene according to literature [46,47]. Then, CBTSRs were synthesized with high yields (92.1% and

3.2. Photophysical properties of CBTSRs Photophysical properties of CBTSRs were investigated by UV/Vis and fluorescence spectrophotometers at 25 °C with spectroscopic cuvette. Different solvents were used to evaluate electronic absorption and fluorescence spectra of 10 μM CBTSR-1 and 5 μM CBTSR-2 such as 1,4159

Journal of Photochemistry & Photobiology A: Chemistry 372 (2019) 156–167

S.O. Tümay, S. Yeşilot

Scheme 1. The synthetic pathways for preparation of CBTSRs, reagents and conditions: (i) propargyl bromide, DMF, K2CO3, 60 °C for 30 min. then reflux for 3 h; (ii) THF, TEGME, NaH, -60 C; (iii) 2-azido-1-ethanol, NaH, THF, RT; (iv) propargyl bromide, dry THF, t-BuLi, RT; (v) PMDTA, Cu(I)Br, CH2Cl2, 2-azido-1-ethanol; (vi) PMDTA, Cu(I)Br, CH2Cl2, 2-(prop-2-yn-1-yloxy)naphthalene for CBTSR-1, 9-((prop-2-yn-1-yloxy)methyl)anthracene for CBTSR-2.

with the monomer emissions shown by CBTSRs [53]. Fluorescence quantum yields of 10 μM CBTSR-1 and 5 μM CBTSR-2 in ethanol solution were calculated as 0.11 and 0.08, respectively by comparing with the quinine sulfate (in 0.1 M H2SO4) (ΦF = 0.54) [49] with same concentration.

dioxane, acetonitrile, aqueous ethanol (EtOH:water), cyclohexane, dichloromethane, ethanol (EtOH), THF, toluene and water. As can be seen at Fig. S5, electronic absorption maxima of CBTSR-1 and CBTSR-2 were observed at 274 nm and 366 nm, respectively. These absorption characteristic of CBTSR-1 and CBTSR-2 were exactly same with naphthalene and anthracene moities and they were attributed to π–π* transition [46,51]. This situation was expected because cyclotriphosphazenes does not have any optical properties in UV/Vis region as we mentioned previously published papers [42]. In addition, fluorescence emission properties of CBTSRs were investigated at same solvent systems (Fig. S5c-d) and fluorescence maxima were observed at 351 nm and 412 nm for CBTSR-1 and CBTSR-2, respectively, which were also same with monomeric fluorescence emissions of naphthalene and anthracene. According to obtained results (Fig. S5a-d), optic properties of CBTSRs were consistent and did not affected by the change of solvent systems. The appropriate fluorescence signals for spectrofluorimetric determination of iron in environmental water samples were obtained in aqueous ethanol systems (3:1 and 9:1 v/v for CBTSR-1 and CBTSR-2, respectively) as shown Fig. S6. It is well known that fluorescence properties of fluorophores importantly depends on the applied concentration [52]. Therefore, different concentration from 10 μM to 1 μM of CBTSRs were prepared to investigate and determine of optimum fluorescence signals for determination studies in aqueous ethanol. According to Fig. S7, fluorescence emission intensity of CBTSRs were gradually decreased without any red- or blue shift when concentrations of solution were diluted from 10 μM to 1 μM, which indicated that there were no inter- or intramolecular interactions existed among the attached fluorophore groups on CBTSRs. Also, these experimental results were in accordance

3.3. Optimization of CBTSRs procedures To get quantitative recovery with highest selectivity and sensitivity in complexation procedures with CBTSRs for iron, experimental conditions such as effect of competitive ions, pH, buffer and buffer concentration, initial CBTSRs concentration and time before measurement were optimized with using UV/Vis and fluorescence spectroscopy. 3.3.1. Effect of competitive metal cations and anions Selectivity of CBTSRs were examined with using UV/Vis absorption and fluorescence emission spectroscopies. All experimental measurements were carried out at room temperature with spectroscopic quartz cuvette and final volume of solution was arranged to 2 mL by micropipette. Stock solutions of metal ions (as a chloride salts, except for Pb2+/ Ag+) and anions (as a sodium salts) were prepared in water while the CBTSRs were prepared in ethanol. UV/Vis electronic absorption and fluorescence emission signals of 10 μM CBTSR-1 in buffered aqueous ethanol (3:1 v/v, λex = 290 nm, pH 7.0) and 5 μM CBTSR-2 in buffered aqueous ethanol (9:1 v/v, λex = 345 nm, pH 7.0) were investigated with addition of various metal ions such as Ag+, K+, Na+, Li+, Cs+, Ba2+, Ni2+, Cu2+, Pb2+, Ca2+, Fe2+, Zn2+, Cd2+, Co2+, Hg2+, Mn2+, Mg2+, Fe3+, Al3+, Cr3+ and their concentrations were 400 μM and 350 μM for CBTSR-1 and CBTSR-2, respectively. As 160

Journal of Photochemistry & Photobiology A: Chemistry 372 (2019) 156–167

S.O. Tümay, S. Yeşilot

Fig. 2. UV–vis absorption (a, b) and naked-eye color changes (c, d) of 10 μM CBTSR-1 in EtOH:water (3:1 v/v, pH 7.0) and 5 μM CBTSR-2 in EtOH:water (9:1 v/v, pH 7.0) upon addition 400 μM (for CBTSR-1) and 350 μM (for CBTSR-2) of various metal ions.

Fig. 3. Fluorescence emission (a, b) and fluorescence color changes (c, d) of 10 μM CBTSR-1 in EtOH:water (3:1 v/v, pH 7.0, λex = 290 nm) and 5 μM CBTSR-2 in EtOH:water (9:1 v/v, pH 7.0, λex = 345 nm) upon addition 400 μM (for CBTSR-1) and 350 μM (for CBTSR-2) of various metal ions.

used for investigated of selectivity of CBTSRs with the same experimental conditions with UV/Vis spectroscopy. It was clearly seen at Fig. 3, fluorescence emission signals of CBTSRs were fully quenched with addition of 400 μM and 350 μM of Fe3+, accompanied by the fluorescence color change from blue to brownish (Fig. 3c-d). Fluorescence quenching of fluorophore with addition of paramagnetic metal ions such as Fe3+, Fe2+ was commonly explicated with chelation enhanced fluorescent quenching (CHEQ) mechanism [55]. The selectivity of CBTSRs towards to cations and anions (Ag+, K+, + Na , Li+, Cs+, Ba2+, Ni2+, Cu2+, Pb2+, Ca2+, Fe2+, Zn2+, Cd2+,

shown at Fig. 2a-b, UV/Vis electronic absorption of CBTSR-1 and CBTSR-2 were significantly increased (∼ 4 fold) with addition of Fe3+ when other tested various metal cations did not affect electronic absorption spectra upon addition of various metal cations. These changes in UV/Vis electronic spectra of CBTSRs might be attributed to electron reorganization with addition of Fe3+, which were caused by formation of CBTSRs - Fe3+ complexes [54]. Moreover, the addition of Fe3+ to aqueous ethanol solution of CBTSRs caused important color change while other various metal ions induced no significant solution color change at daylight (Fig. 2c and d). Fluorescence spectroscopy was also 161

Journal of Photochemistry & Photobiology A: Chemistry 372 (2019) 156–167

S.O. Tümay, S. Yeşilot

Fig. 4. Fluorescence responses of 10 μM CBTSR-1 in EtOH:water (3:1 v/v, pH 7.0, λex = 290 nm) and 5 μM CBTSR-2 in EtOH:water (9:1 v/v, pH 7.0, λex = 345 nm) upon addition 400 μM (for CBTSR-1) and 350 μM (for CBTSR-2) of various competitive cations and anions.

Co2+, Hg2+, Mn2+, Mg2+, Fe3+, Al3+, Cr3+, H2PO4−, HSO4−, Cl−, F−, NO3−, I−, CN−, CO32-, SO42-) were demonstrated at Fig. 4 with relative fluorescence emission intensity change. Importantly, relative fluorescence emission intensity of CBTSRs did not change with addition of iron-free metal mixture when fully changed with iron-containing metal mixture, which clearly demonstrated selectivity of CBTSRs towards Fe3+. The precursors of CBTSRs were also synthesized (3 and 4) for investigated the effect and contribution of “tripodal” structured cyclotriphosphazene core to complexation properties. Fluorescence signal change of precursors (3 and 4) were examined under same analytical conditions with their “tripodal” structured cyclotriphosphazene forms. Fluorescence signals of precursors did not affect with addition competitive cations included Fe3+ which clearly indicated, interaction of Fe3+ can be form via “tripodal” conformation of cyclotriphosphazene core (Fig. S8). Consequently, development of highly sensitive and selective spectrofluorimetric determination methods for Fe3+ with these fluoroionophores, there is a necessity to “tripodal” structured cyclotriphosphazene core.

observed at 5 μM and then it had almost unchanged with increasing concentration. On the other hand, the maximum relative fluorescence intensity for CBTSR-1 were observed at 10 μM. According to obtained results, optimum initial concentration of CBTSR-1 and CBTSR-2 for complexation with Fe3+ were determined as 10 μM and 5 μM, respectively, for the determination processes in real samples when consider relative fluorescence response and stability of complexes. 3.3.4. Effect of buffer solutions and buffer concentration In order to obtain stable CBTSRs - Fe3+ complexes, determination of proper buffer to adjust the pH of medium is important [56]. Therefore, the effect of different buffer systems besides BeR buffer such as Tris-HCl and phosphate buffer solution on relative fluorescence intensity of CBTSRs - Fe3+ were investigated at pH 7.0. For that optimization, 400 μM and 350 μM Fe3+ were used for 10 μM CBTSR-1 and 5 μM CBTSR-2 with 0.1 M of buffer solution when other experimental conditions kept constant. According to results (Fig. S11), maximum relative fluorescence intensity for CBTSRs-Fe3+ were obtained at BeR buffer solution where other buffer solutions had lower relative fluorescence intensity changes, accordingly BeR buffer was used for iron determination studies. After the buffer solution was selected, effect of the buffer solution’s concentration on the complexation of CBTSRs and Fe3+ should be evaluated. Therefore, various concentration from 0.4 M to 0.1 M of BeR buffer solutions at pH 7.0 were used with 400 μM and 350 μM Fe3+ for 10 μM CBTSR-1 and 5 μM CBTSR-2 when other experimental conditions kept constant. As depicted at Fig. S12, the maximum relative fluorescence intensity of CBTSRs-Fe3+ complexes were obtained at 0.1 M BeR solution when higher concentrations of BeR solution were decreased to signal intensities. Therefore, 0.1 M BeR buffer solution would be enough to complexation.

3.3.2. Effect of pH The pH of solution is very important for quantitative recovery because pH can be affect the chemical structure of CBTSRs and consequently complexation with Fe3+. Therefore, relative fluorescence signal of CBTSRs - Fe3+ complexes were evaluated with different pH values (6.0–10.0). For that purpose, 400 μM Fe3+ with 10 μM CBTSR-1 and 350 μM Fe3+ with 5 μM CBTSR-2 were used at different pH values (6.0–10.0) when other experimental conditions were kept constant. pH values of CBTSR-1 and CBTSR-2 in buffered aqueous ethanol (3:1 v/v and 9:1 v/v, respectively) were adjust with Britton-Robinson (B–R, 0.1 M) buffer. As can be seen in Fig. S9, maximum relative intensities were observed at 7.0 for CBTSRs - Fe3+ complexes. When complex formation and stability were considered, developed spectrofluorimetric analysis processes for environmental water samples were performed at pH 7.0.

3.3.5. Effect of time before measurement The effect of the time on the complexation of CBTSRs with Fe3+ was studied in the range of 0–60 seconds with using 400 μM Fe3+ for 10 μM CBTSR-1 and 350 μM Fe3+ for 5 μM CBTSR-2 when other experimental conditions kept constant. The pH of the aqueous ethanol solutions, which were containing 10 μM CBTSR-1 and 5 μM CBTSR-2 were adjusted 7.0 with 0.1 M B–R buffer and then 400 μM and 350 μM Fe3+ were added respectively to buffered aqueous solutions of CBTSRs. The fluorescence measurements were carried out after mixed strongly from 0 to 60 s and plotted against the time (Fig. S13). The results showed that, 20 and 25 s would be enough to complexations with Fe3+ for CBTSR-1 and CBTSR-2, respectively. Because after these times, fluorescence intensities kept nearly constant. Accordingly, when consider complexation with Fe3+ and stability of complexes, 20 and 25 s were used for the determination processes in real samples.

3.3.3. Effect of initial CBTSRs concentration To determined optimum initial concentration of CBTSRs for complexation with Fe3+, different concentration from 10 μM to 1 μM of CBTSRs were prepared in aqueous ethanol and investigated by relative fluorescence intensity change with addition of Fe3+ (400 μM for CBTSR-1 and 350 μM for CBTSR-2, respectively) when other experimental conditions kept constant for complexation. As can be seen from Fig. S10, relative fluorescence intensity of CBTSR-1 and CBTSR-2 were sharply changed when their concentration increased from 1 μM to 5 μM. The maximum relative fluorescence intensities of CBTSR-2 was 162

Journal of Photochemistry & Photobiology A: Chemistry 372 (2019) 156–167

S.O. Tümay, S. Yeşilot

7.0) aqueous ethanol solutions of 10 μM CBTSR-1 and 5 μM CBTSR-2. Then, solutions mixed strongly for 20 and 25 s, respectively, and the fluorescence measurements were carried out from 0 to 60 min in daylight. The photostability of CBTSRs and CBTSRs - Fe3+ complexes were demonstrated by plotting relative florescence intensities of CBTSRsFe3+ complexes against the time (Fig. S15) which indicated that not only CBTSRs but also CBTSRs-Fe3+ complexes were highly photostable. The reversibility of CBTSRs towards Fe3+ ions was evaluated by further addition of EDTA to CBTSRs + Fe3+ complexes. As shown in Fig. S16, quenched fluorescence signals of CBTSRs with addition Fe3+ were restored by addition of EDTA (50.0 equiv.) which demonstrating that the Fe3+ recognition is a complexing and reversible process. It is well known that static and dynamic quenching processes are very different from each other and two different ways for fluorescence quenching. Although, static quenching process is originated from nonfluorescent complex, which is occurred by complexation of fluorophore and quencher in ground state, dynamic quenching which is diffusioncontrolled process is based on collision of the excited state molecules of the fluorophore and the quencher [52]. Therefore, fluorescence lifetime of fluorophore is not affected in static quenching process when it must reduce in dynamic quenching process. In addition, the dependency of fluorescence intensity to the increasing concentration of quencher can shed light into quenching mechanism. In order to investigate the quenching mechanisms of CBTSRs with Fe3+, Stern-Volmer equation were used (Eq. (3)) [60].

Fig. 5. Continuous variation (Job’s) plots of 10 μM CBTSR-1 in EtOH:water (3:1 v/v, pH 7.0, λex = 290 nm) and 5 μM CBTSR-2 in EtOH:water (9:1 v/v, pH 7.0, λex = 345 nm) for Fe3+.

3.4. Complex formation and quenching mechanism of CBTSRs with Fe3+ Chemical stoichiometry of CBTSRs - Fe3+ complexes were determined by continuous variation (Job’s) plots in buffered aqueous ethanol (pH 7.0) and non-linear curve fitting analyses [57–59]. 10 μM CBTSR-1 and 5 μM CBTSR-2 were used and mole fraction of Fe3+ ions in complexes gradually increased to perform the continuous variation (Job’s) method (Fig. 5). As can be seen at Fig. 5, fluorescence signal of complexes reached maximum at 0.33, which means that stoichiometry of CBTSRs - Fe3+ complexes were 2:1 (ligand:metal). In addition, plots of increasing relative fluorescence intensity with addition of Fe3+ to CBTSRs demonstrated an inflection point where the stoichiometric ratio of Fe3+ to CBTSRs were determined to be 2:1 (ligand:metal) according to non-linear curve fitting analyses (Fig. S14). The obtained results from continuous variation (Job’s) method and non-linear curve fitting analyses, the proposed binding mechanisms for CBTSRs - Fe3+ complexes represented in Scheme 2. For spectrofluorimetric determination applications, receptors and complexes should be photostable to get higher precision and accurate results. In order to evaluate photostability of CBTSRs and CBTSRs Fe3+ complexes, 400 μM and 350 μM Fe3+ were added to buffered (pH

I0 = K SV [Q] + 1 I

(3)

where, Ksv, Stern-Volmer constant, I0, initial fluorescence intensity of CBTSRs, I, final fluorescence intensity of CBTSRs with addition of Fe3+ and Q, concentration (molar) of Fe3+. In static quenching, the graph of the I0/I against [Q] give linear line and y-axis intercept of that line is 1 according to Stern-Volmer equation. On the other hand, the observed positive deviation when the concentration increases demonstrates that not only static quenching but also dynamic quenching were effective in the system [61]. Stern-Volmer graphs of CBTSRs + Fe3+ complexes were given at Fig. S17. According to results, the I0/I linearly increased until 200 μM of Fe3+ and after this concentration, the positive deviations were observed for CBTSRs-Fe3+ complexes which demonstrated that fluorescence signal quenching processes of CBTSRs were affected both static and dynamic quenching. As we mentioned, fluorescence lifetimes are an alternative way to get information about quenching

Scheme 2. Proposed binding mechanism for CBTSRs with Fe3+. 163

Journal of Photochemistry & Photobiology A: Chemistry 372 (2019) 156–167

S.O. Tümay, S. Yeşilot

Fig. 6. Fluorescence titration spectra of a) 10 μM CBTSR-1 in EtOH:water (3:1 v/v, pH 7.0, λex = 290 nm) and b) 5 μM CBTSR-2 in EtOH:water (9:1 v/v, pH 7.0, λex = 345 nm) with gradually increased amount of Fe3+.

mechanism. Therefore, to get deeper information about fluorescence signal quenching processes, fluorescence lifetime of CBTSRs and CBTSRs - Fe3+ complexes were measured. The fluorescence lifetimes of CBTSR-1 (τ01), CBTSR-2 (τ02), CBTSR-1 - Fe3+ (τ1) and CBTSR-2 Fe3+ (τ2) were calculated as 8.387 ± 0.020 (τ01), 1.379 ± 0.039 ns (τ02), 8.120 ± 0.031 ns (τ1) and 1.403 ± 0.011 ns (τ2), respectively. According to Fig. S18, fluorescence lifetime of CBTSRs and τ0/τ values nearly did not change with addition of 400 μM and 350 μM Fe3+ which were demonstrated that the non-fluorescent ground-state complexes of CBTSRs and Fe3+ caused to quenching and static quenching was dominant in these processes [52].

conditions, photophysical properties of CBTSR-1 and CBTSR-2 were evaluated by fluorescence titration experiments and calibration curves at same solvent condition (9:1 v/v EtOH:water) towards Fe3+. According to Fig. S19, sensitivity and fluorescence response of CBTSRs towards Fe3+ were nearly unchanged in same solvent system (9:1 v/v EtOH:water) and different solvent systems (3:1 v/v and 9:1 v/v EtOH:water). Limit of detection (LOD), which defined as 3σ/K, where σ is the standard deviation of the blank sample, K is slope of calibration curve were calculated for developed CBTSRs-FL methods as 0.54 μM and 0.44 μM for CBTSR-1 and CBTSR-2, respectively. In addition, limit of quantification (LOQ) were found as 1.32 μM and 1.00 μM for CBTSR-1 and CBTSR-2, respectively. The precision of the determination method is an important for consistent results. For this reason, precisions of developed CBTSRs-FL methods should be identified. The precisions of methods found as 2.28% and 3.19% for CBTSR-1 and CBTSR-2, respectively under optimized conditions (N = 10) which indicated a high selectivity and sensitivity of the CBTSRs-FL methods. In order to evaluate performance of developed CBTSRs-FL methods for Fe3+ determination in environmental water samples, spike and recovery tests were carried out. Environmental water samples were spiked in the range of 0–40 μM with Fe3+ and developed CBTSRs-FL methods were applied. Relative fluorescence signal changes of CBTSRs with spiked environmental water samples were measured spectrofluorimetrically, after then obtained recoveries were calculated and summarized at Table S1, quantitative recoveries were obtained with low RSD% and the results were consistent with spiked and recovered amounts of analyte. After evaluate the accuracy, iron content of environmental water

3.5. Analytical parameters and real sample applications Dynamic range of developed CBTSRs-FL methods under optimized conditions were determined by fluorescence titration experiments which were performed by gradually increased amount of Fe3+ (Fig. 6). At Fig. 6, fluorescence intensities of CBTSRs at 351 and 412 nm were gradually quenched with increased amount of Fe3+ and when concentration of Fe3+ reached 400 μM and 350 μM, fluorescence signal of CBTSRs were nearly completely quenched. Calibration curves of developed CBTSRs-FL methods for determination of Fe3+ were demonstrated at Fig. 7. According to Fig. 7, calibration curves of CBTSRs were linear in the range of 0.5–400 μM and 0.4–350 μM for CBTSR-1 and CBTSR-2, respectively. In addition, linear regression equations of methods are (F0-F)/F0 = 0.0025[Fe3+] + 0.0083 and (F0-F)/F0 = 0.0026[Fe3+] + 0.0054 with correlation coefficients of 0.9984 and 0.9981 for CBTSR-1 and CBTSR-2, respectively. After performed photophysical experiments under optimized

Fig. 7. Calibration curves of 10 μM CBTSR-1 in EtOH:water (3:1 v/v, pH 7.0, λex = 290 nm) and 5 μM CBTSR-2 in EtOH:water (9:1 v/v, pH 7.0, λex = 345 nm) for Fe3+. Insets: Photographs of showing the change in color of fluorescence emissions. 164

Journal of Photochemistry & Photobiology A: Chemistry 372 (2019) 156–167 [65] [66]

[69]

[67]

[68]

PW

No interference

No interference

No interference

No interference

100

0.54 (CBTSR1) 0.44 (CBTSR2)

1-100,000

0.5-400 (CBTSR-1) 0.4-350 (CBTSR-2)

4.0–6.0

7.0 SFL

PM

alloys and pharmaceutical samples water samples

3.5-40000 4.5-6.5 PM

water samples and iron tablets

1 - 10000 4.0 - 8.8 PM

water samples

1.79 5.26 1.790 − 71.626 10-150 5.0 5.0–10.0

extraction of the complex to chloroform for 2 min (preconcentration before measurement, PF: NR) water sample, sensor solutions, metal ions were added into a 5 mL volumetric flask, and then diluting the solution to 5 mL with methanol. Electrote modified with synthesized ionophore and potentiometric analysis performed after waiting < 20 s to get steady signal Electrote modified with synthesized ionophore and potentiometric analysis performed after waiting < 15 s to get steady signal Electrote modified with synthesized ionophore and potentiometric analysis performed after waiting 30 s to get steady signal waiting only 20 and 25 seconds for complexation before measurements water samples water samples FAAS SFL

samples was determinated by developed CBTSRs-FL methods without any preconcentration process and obtained results were summarized at Table S1. In order to confirm the accuracy and precision of developed CBTSRs-FL methods, ICP-OES as a reference method was used for analyze environmental water samples (Table S1). According to obtained results, RSD% and recoveries for determination of iron with developed CBTSRs-FL methods demonstrated high precision and accuracy in environmental water samples. 3.6. Comparison of CBTSRs-FL methods with reported iron determination methods The analytical parameters of developed CBTSRs-FL methods were compared with some other iron determination methods includingspectrofluorimetric, spectrophotometric and potantiometric methods which previously reported in the literature [60,62–66]. As seen from Table 1, developed CBTSRs-FL methods have larger linear ranges, lower LODs and higher sensitivity than given spectrofluorimetric and spectrophotometric determination methods which can be attribute to selective, simple and time-saving complexation procedures of CBTSRs with iron at natural pH [64,63–66]. Although, some determination methods have a lower LOD than developed CBTSRs-FL methods, these methods include interfering ions or preconcentration steps which are time-consuming and requires extra reagents such as adsorbents and eluents [60,62,63]. In addition, the comparison of developed CBTSRs-FL methods with some of potentiometric methods indicated that CBTSRs-FL methods have lower LODs than given potansiometric determination methods without interfering at natural pH [67–69]. This comparison showed that when consider obtained results such as recoveries, RSDs%, linear range, response time and LODs, developed CBTSRs-FL methods are powerful and accessible alternative for the determination of iron in environmental water samples.

FAAS, flame atomic absorption spectrometry; SFL, spectrofluorimetry; PM, potentiometry; PF, preconcentration factor; NR, not reported; PW, present work.

[64]

Interering ions masking with KF No interference No interference 3.00 5.013 − 10.027 SFL

bovine liver

NR

2.50

[63] Cu2+ and Cd2+ 0.30 0.5-5.0 SFL

3.2

0.63

[60] [62] Co2+, Sm3+ and Y3+ No interference 1-10 0.716 − 17.906 8.5 2.5

waiting 10 min for fluorescence stability extraction with modified octadecyl silica membrane, EDTA solution was used for stripping iron(III) from the disk (preconcentration before measurement, PF: 166) water samples were mixed with KI solution and stored in a dark place for 10 min. Then, fluorescence receptor was added and the final solution was kept in a dark place for 10 min. waiting 20 min for fluorescence stability SFL FAAS

water samples water samples and powdered milk water samples

0.05 0.05

Ref. Method*

Table 1 The comparison of developed CBTSRs-FL methods with some previously reported determination methods for iron in real samples.

Linear Range (μM) pH Procedures Before Measurement Sample

LOD (μM)

Interference

S.O. Tümay, S. Yeşilot

4. Conclusion To summarize, two novel cyclotriphosphazene based tripodal synthetic receptors (CBTSRs) were designed and synthesized which were used for selective and sensitive spectrofluorimetric determination of iron in environmental water sample after validation of methods without preconcentration processes. The tripodal structures of CBTSRs were formed by three naphtalene-triazole (CBTSR-1) and anthracene-triazole moities (CBTSR-2) at the above of cyclotriphosphazene plane as fluoroionophores and TEGME moities at the below of plane as solubility agents. In order to develop selectivity and sensitivity of complexation procedures over competitive species, experimental conditions such as pH, buffer and buffer concentration, initial CBTSRs concentration, and time before measurement were optimized before spectrofluorimetric determination. The obtained results showed that selective and sensitive complexation of CBTSRs with iron provided submicromolar level spectrofluorimetric determination under optimized conditions without preconcentration processes and interferences, which may be due to the conformational properties of tripodal planar structure cyclotriphosphazene core. The spike and recovery tests and ICP-OES analyses demonstrated that complexation of CBTSRs with iron led to a selective, sensitive, precise, time-saving, simple and accurate methods for the spectrofluorimetric determination of iron. In addition, comparison of analytical parameters with other determination methods include spectrofluorimetric, spectrophotometric and potantiometric methods for iron determination analysis demonstrated that developed CBTSRs-FL methods ensured better ability in terms of sensitivity, RSDs%, cost, simplicity, response time, LODs and accuracy in environmental water samples. Appendix A. Supplementary data Supplementary material related to this article can be found, in the 165

Journal of Photochemistry & Photobiology A: Chemistry 372 (2019) 156–167

S.O. Tümay, S. Yeşilot

online version, at doi:https://doi.org/10.1016/j.jphotochem.2018.12. 012.

[30] S. Goswami, A.K. Das, K. Aich, A. Manna, S. Maity, K. Khanra, N. Bhattacharyya, Ratiometric and absolute water-soluble fluorescent tripodal zinc sensor and its application in killing human lung cancer cells, Analyst 138 (2013) 4593–4598. [31] T. Palanché, F. Marmolle, M.A. Abdallah, A. Shanzer, A.-M. Albrecht-Gary, Fluorescent siderophore-based chemosensors: iron(III) quantitative determinations, JBIC J. Biol. Inorg. Chem. 4 (1999) 188–198. [32] S.O. Tümay, S.Y. Sarıkaya, S. Yeşilot, Novel iron(III) selective fluorescent probe based on synergistic effect of pyrene-triazole units on a cyclotriphosphazene scaffold and its utility in real samples, J. Lumin. 196 (2018) 126–135. [33] Y.H. Lau, P.J. Rutledge, M. Watkinson, M.H. Todd, Chemical sensors that incorporate click-derived triazoles, Chem. Soc. Rev. 40 (2011) 2848–2866. [34] H. Li, M. Fang, T. Xu, Y. Hou, R. Tang, J. Chen, L. Liu, H. Han, T. Peng, Q. Li, Z. Li, New anthracene-based organic dyes: the flexible position of the anthracene moiety bearing isolation groups in the conjugated bridge and the adjustable cell performance, Org. Chem. Front. 3 (2016) 233–242. [35] S.-S. Li, K.-J. Jiang, C.-C. Yu, J.-H. Huang, L.-M. Yang, Y.-L. Song, A 2,7-pyrenebased dye for solar cell application, New J. Chem. 38 (2014) 4404–4408. [36] J. Xiao, Z. Yin, B. Yang, Y. Liu, L. Ji, J. Guo, L. Huang, X. Liu, Q. Yan, H. Zhang, Q. Zhang, Preparation, characterization, physical properties, and photoconducting behaviour of anthracene derivative nanowires, Nanoscale 3 (2011) 4720–4723. [37] S.H. Kim, I. Cho, M.K. Sim, S. Park, S.Y. Park, Highly efficient deep-blue emitting organic light emitting diode based on the multifunctional fluorescent molecule comprising covalently bonded carbazole and anthracene moieties, J. Mater. Chem. 21 (2011) 9139–9148. [38] A. Sahana, A. Banerjee, S. Das, S. Lohar, D. Karak, B. Sarkar, S. Kanti Mukhopadhyay, A.K. Mukherjee, D. Das, A naphthalene-based Al3+ selective fluorescent sensor for living cell imaging, Org. Biomol. Chem. 9 (2011) 5523–5529. [39] M. Aydemir, G. Haykır, A. Battal, V. Jankus, S.K. Sugunan, F.B. Dias, H. Al-Attar, F. Türksoy, M. Tavaslı, A.P. Monkman, High efficiency OLEDs based on anthracene derivatives: the impact of electron donating and withdrawing group on the performance of OLED, Org. Electron. 30 (2016) 149–157. [40] H.A. Alidağı, F. Hacıvelioğlu, S.O. Tümay, B. Çoşut, S. Yeşilot, Synthesis and spectral properties of fluorene substituted cyclic and polymeric phosphazenes, Inorg. Chim. Acta 457 (2017) 95–102. [41] A. Uslu, S.O. Tümay, A. Şenocak, F. Yuksel, E. Özcan, S. Yeşilot, Imidazole/benzimidazole-modified cyclotriphosphazenes as highly selective fluorescent probes for Cu2+: synthesis, configurational isomers, and crystal structures, Dalton Trans. 46 (2017) 9140–9156. [42] H.A. Alidağı, S.O. Tümay, A. Şenocak, S. Yeşilot, Pyrene functionalized cyclotriphosphazene-based dyes: synthesis, intramolecular excimer formation, and fluorescence receptor for the detection of nitro-aromatic compounds, Dyes Pigm. 153 (2018) 172–181. [43] S.O. Tümay, A. Uslu, H. Ardıç Alidağı, H.H. Kazan, C. Bayraktar, T. Yolaçan, M. Durmuş, S. Yeşilot, A systematic series of fluorescence chemosensors with multiple binding sites for Hg(ii) based on pyrenyl-functionalized cyclotriphosphazenes and their application in live cell imaging, New J. Chem. 42 (2018) 14219–14228. [44] A. Uslu, S. Guvenaltn, The investigation of structural and thermosensitive properties of new phosphazene derivatives bearing glycol and amino acid, Dalton Trans. 39 (2010) 10685–10691. [45] Y. Li, J. Yang, B.C. Benicewicz, Well-controlled polymerization of 2-azidoethyl methacrylate at near room temperature and click functionalization, J. Polym. Sci., Part A: Polym. Chem. 45 (2007) 4300–4308. [46] N. Guven, P. Camurlu, Electrosyntheses of anthracene clicked poly(thienylpyrrole)s and investigation of their electrochromic properties, Polymer 73 (2015) 122–130. [47] S. Balabadra, M. Kotni, V. Manga, A.D. Allanki, R. Prasad, P.S. Sijwali, Synthesis and evaluation of naphthyl bearing 1,2,3-triazole analogs as antiplasmodial agents, cytotoxicity and docking studies, Bioorg. Med. Chem. 25 (2017) 221–232. [48] S. Fery-Forgues, D. Lavabre, Are fluorescence quantum yields so tricky to measure? A demonstration using familiar stationery products, J. Chem. Educ. 76 (1999) 1260. [49] W.H. Melhuish, Quantum efficiencies of fluorescence of organic substances: effect of solvent and concentration of the fluorescent solute1, J. Phys. Chem. 65 (1961) 229–235. [50] A. Uslu, S. Yeşilot, Chiral configurations in cyclophosphazene chemistry, Coord. Chem. Rev. 291 (2015) 28–67. [51] K. Mondal, S. Bhattacharyya, A. Sharma, Photocatalytic degradation of naphthalene by electrospun mesoporous carbon-doped anatase TiO2 nanofiber mats, Ind. Eng. Chem. Res. 53 (2014) 18900–18909. [52] J.R. Lakowicz, Principles of Fluorescence Spectroscopy, third ed., Springer, Singapore, 2006. [53] S. Yesilot, B. Cosut, H.A. Alidag, F. Hacvelioglu, G.A. Ozpnar, A. Klc, Intramolecular excimer formation in hexakis(pyrenyloxy)cyclotriphosphazene: photophysical properties, crystal structure, and theoretical investigation, Dalton Trans. 43 (2014) 3428–3433. [54] T. Senthilkumar, N. Parekh, S.B. Nikam, S.K. Asha, Orientation effect induced selective chelation of Fe2+ to a glutamic acid appended conjugated polymer for sensing and live cell imaging, J. Mater. Chem. B 4 (2016) 299–308. [55] Y. Zheng, J. Orbulescu, X. Ji, F.M. Andreopoulos, S.M. Pham, R.M. Leblanc, Development of fluorescent film sensors for the detection of divalent copper, J. Am. Chem. Soc. 125 (2003) 2680–2686. [56] N. Pourreza, H. Golmohammadi, Hemoglobin detection using curcumin nanoparticles as a colorimetric chemosensor, RSC Adv. 5 (2015) 1712–1717. [57] A.E. Brummett, N.J. Schnicker, A. Crider, J.D. Todd, M. Dey, Biochemical, kinetic, and spectroscopic characterization of ruegeria pomeroyi DddW–a mononuclear iron-dependent DMSP lyase, PloS One 10 (2015) e0127288-e0127288. [58] S.C. Chai, Q.-Z. Ye, Analysis of the stoichiometric metal activation of methionine

References [1] D. Diamond, K. Nolan, Peer reviewed: calixarenes: designer ligands for chemical sensors, Anal. Chem. 73 (2001) 22A–29A. [2] L.P. Ramteke, P.R. Gogate, Treatment of water containing heavy metals using a novel approach of immobilized modified sludge biomass based adsorbents, Sep. Purif. Technol. 163 (2016) 215–227. [3] A. Aroun, J.L. Zhong, R.M. Tyrrell, C. Pourzand, Iron, oxidative stress and the example of solar ultraviolet a radiation, Photochem. Photobiol. Sci. 11 (2012) 118–134. [4] A.M. Şenol, Y. Onganer, K. Meral, An unusual “off-on” fluorescence sensor for iron (III) detection based on fluorescein–reduced graphene oxide functionalized with polyethyleneimine, Sens. Actuators, B 239 (2017) 343–351. [5] G. Papanikolaou, K. Pantopoulos, Iron metabolism and toxicity, Toxicol. Appl. Pharmacol. 202 (2005) 199–211. [6] P.J. Aggett, Iron. In. Present Knowledge in Nutrition, 10th ed., ed., Wiley-Blackwell, Washington, 2012. [7] M. Grotti, M.L. Abelmoschi, F. Soggia, R. Frache, Determination of ultratrace elements in natural waters by solid-phase extraction and atomic spectrometry methods, Anal. Bioanal. Chem. 375 (2003) 242–247. [8] A. Bobrowski, K. Nowak, J. Zarębski, Application of a bismuth film electrode to the voltammetric determination of trace iron using a Fe(III)–TEA–BrO3−catalytic system, Anal. Bioanal. Chem. 382 (2005) 1691–1697. [9] A. Asan, M. Andac, I. Isildak, Flow injection spectrofluorimetric determination of iron(III) in water using salicylic acid, Chem. Papers 64 (2010) 424–428. [10] J. Mao, Q. He, W. Liu, An rhodamine-based fluorescence probe for iron(III) ion determination in aqueous solution, Talanta 80 (2010) 2093–2098. [11] L. Dong, ChongWu, X. Zeng, L. Mu, S.-F. Xue, Z. Tao, J.-X. Zhang, The synthesis of a rhodamine B schiff-base chemosensor and recognition properties for Fe3+ in neutral ethanol aqueous solution, Sens. Actuators, B 145 (2010) 433–437. [12] J. Janata, Principles of Chemical Sensors, 2nd ed., Springer, Amsterdam, 2009. [13] H. Zhang, Y. Huang, X. Lin, F. Lu, Z. Zhang, Z. Hu, Lanthanum loaded graphitic carbon nitride nanosheets for highly sensitive and selective fluorescent detection of iron ions, Sens. Actuators, B 255 (2018) 2218–2222. [14] G.J. Park, G.R. You, Y.W. Choi, C. Kim, A naked-eye chemosensor for simultaneous detection of iron and copper ions and its copper complex for colorimetric/fluorescent sensing of cyanide, Sens. Actuators, B 229 (2016) 257–271. [15] Y. Fang, J. Tan, H. Choi, S. Lim, D.-H. Kim, Highly sensitive naked eye detection of iron (III) and H2O2 using poly-(tannic acid) (PTA) coated Au nanocomposite, Sens. Actuators, B 259 (2018) 155–161. [16] L. Tang, S. Mo, S.G. Liu, L.L. Liao, N.B. Li, H.Q. Luo, Synthesis of fluorescent polydopamine nanoparticles by michael addition reaction as an analysis platform to detect iron ions and pyrophosphate efficiently and construction of an IMPLICATION logic gate, Sens. Actuators, B 255 (2018) 754–762. [17] H.E.M. Sayour, T.M.A. Razek, K.F. Fadel, Flow injection spectrofluorimetric determination of iron in industrial effluents based on fluorescence quenching of 1naphthol-2- sulfonate, J. Fluorescence 21 (2011) 1385–1391. [18] G.W. Aodeng, W.Y. Bai, Z.Q. Duan, Determination of iron(II) in the Chinese herbal medicine based on the fluorescence quenching of phenanthroline, Guang pu xue yu guang pu fen xi = Guang pu 21 (2001) 846–848. [19] M.J. Berrocal, A. Cruz, I.H.A. Badr, L.G. Bachas, Tripodal ionophore with sulfate recognition properties for anion-selective electrodes, Anal. Chem. 72 (2000) 5295–5299. [20] A. Metzger, V.M. Lynch, E.V. Anslyn, A synthetic receptor selective for citrate, Angew. Chem. Int. Ed. English 36 (1997) 862–865. [21] C. Schmuck, M. Schwegmann, A naked-eye sensing ensemble for the selective detection of citrate-but not tartrate or malate-in water based on a tris-cationic receptor, Organic & Biomolecular Chemistry 4 (2006) 836–838. [22] S.L. Wiskur, H. Ait-Haddou, J.J. Lavigne, E.V. Anslyn, Teaching Old indicators New tricks, Acc. Chem. Res. 34 (2001) 963–972. [23] R. Kumar, S. Sandhu, P. Singh, G. Hundal, M.S. Hundal, S. Kumar, Tripodal fluorescent sensor for encapsulation-based detection of picric acid in Water, Asian J. Org. Chem. 3 (2014) 805–813. [24] K. Sato, S. Arai, T. Yamagishi, A new tripodal anion receptor with C□h···x− hydrogen bonding, Tetrahedron Lett. 40 (1999) 5219–5222. [25] P. Ballester, A. Costa, P.M. Deyà, M. Vega, J. Morey, G. Deslongchamps, Influence of remote intramolecular hydrogen bonds on the thermodynamics of molecular recognition of cis-1,3,5-cyclohexanetricar□ylic acid, Tetrahedron Lett. 40 (1999) 171–174. [26] H.M. Chawla, M. Shahid, L.S. Arora, B. Uttam, Synthesis and evaluation of a triarmed molecular receptor for recognition of mercury and cyanide toxicants, Supramol. Chem. 29 (2017) 111–119. [27] M.M. Reinoso-García, A. Dijkman, W. Verboom, D.N. Reinhoudt, E. Malinowska, D. Wojciechowska, M. Pietrzak, P. Selucky, Metal complexation by tripodal N-acyl (thio)urea and picolin(thio)amide compounds: Synthesis/Extraction and potentiometric studies, Eur. J. Org. Chem. 2005 (2005) 2131–2138. [28] M.B. Jones, C.E. MacBeth, Tripodal phenylamine-based ligands and their CoII complexes, Inorg. Chem. 46 (2007) 8117–8119. [29] X. Zeng, C. Wu, L. Dong, L. Mu, S. Xue, Z. Tao, A new tripodal rhodamine B derivative as a highly selective and sensitive fluorescence chemosensor for copper(II), Sci. China Series B: Chem. 52 (2009) 523–528.

166

Journal of Photochemistry & Photobiology A: Chemistry 372 (2019) 156–167

S.O. Tümay, S. Yeşilot

liver with 4-hydroxyquinoline, Il Farmaco 53 (1998) 611–616. [65] S. Tautkus, L. Steponeniene, R. Kazlauskas, Determination of iron in natural and mineral waters by flame atomic absorption spectrometry, J. Serb. Chem. Soc. (2004). [66] W. Lin, L. Long, L. Yuan, Z. Cao, J. Feng, A novel ratiometric fluorescent Fe3+ sensor based on a phenanthroimidazole chromophore, Anal. Chim. Acta 634 (2009) 262–266. [67] M.H. Mashhadizadeh, I.S. Shoaei, N. Monadi, A novel ion selective membrane potentiometric sensor for direct determination of Fe(III) in the presence of Fe(II), Talanta 64 (2004) 1048–1052. [68] G. Ekmekci, D. Uzun, G. Somer, Ş. Kalaycı, A novel iron(III) selective membrane electrode based on benzo-18-crown-6 crown ether and its applications, J. Membr. Sci. 288 (2007) 36–40. [69] D. Ersin, K. Barıs, B. Olcay, Y.A.-E. Hassan, A novel iron(III)-selective membrane potentiometric sensor based on 5-chloro-3-[4-(trifluoromethoxy) phenylimino] indolin-2-one, Current Anal. Chem. 11 (2015) 29–35.

aminopeptidase, BMC Biochem. 10 (2009) 32-32. [59] S.C. Chai, J.-P. Lu, Q.-Z. Ye, Determination of binding affinity of metal cofactor to the active site of methionine aminopeptidase based on quantitation of functional enzyme, Anal. Biochem. 395 (2009) 263–264. [60] K.-W. Cha, K.-W. Park, Determination of iron(III) with salicylic acid by the fluorescence quenching method, Talanta 46 (1998) 1567–1571. [61] P.K. Behera, T. Mukherjee, A.K. Mishra, Simultaneous presence of static and dynamic component in the fluorescence quenching for substituted naphthalene—CCl4 system, J. Lumin. 65 (1995) 131–136. [62] S.H.G. Khayatian, F. Nasiri, A. Zolali, Preconcentration, determination and speciation of iron by solid-phase extraction using dimethyl (E)-2-[(Z)-1-acetyl)-2-hydroxy-1-propenyl]-2-butenedioate, Química Nova 35 (2012) 535–540. [63] Y. Du, M. Chen, Y. Zhang, F. Luo, C. He, M. Li, X. Chen, Determination of iron(III) based on the fluorescence quenching of rhodamine B derivative, Talanta 106 (2013) 261–265. [64] G.C. Ragos, M.A. Demertzis, P.B. Issopoulos, *A high-sensitive spectrofluorimetric method for the determination of micromolar concentrations of iron(III) in bovine

167