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

Article abstract of DOI:10.1016/j.jphotochem.2018.12.012

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, ¹³C, 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).

Full text of DOI:10.1016/j.jphotochem.2018.12.012

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
Department of Chemistry, Gebze Technical University, Gebze, 41400, Kocaeli, Turkey
A R T I C L E I N F O
A B S T R A C T
Keywords:
Two novel tripodal synthetic receptors based on cyclotriphosphazene scaffolds were prepared for spectro-
fluorimetric 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 an-
Tripodal receptor
Cyclotriphosphazene
Spectrofluorimetric determination
Water samples
thracene-triazole groups above the plane and water solubility interacting triethylene glycol monomethyl ether
1
(
TEGME) groups below. All compounds were characterized by standard spectroscopic techniques such as H,
Iron
1
3
31
C, P 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 con-
centration and time before measurement were optimized for selective complexation, which provided sub-
micromolar spectrofluorimetric determination of iron under optimized conditions. The obtained results de-
monstrated 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
spectrofluorimetry has been attractive analytical method, which pro-
vided quick response, high selectivity/sensitivity, easy operation for
In recent years, there has been considerable interest in the study of
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 en-
vironmental 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 ap-
plication for determination of iron by spectrofluorimetry is rarely stu-
died [17,18]. Consequently, development of new spectrofluorimetric
method for determination of iron levels by synthetic receptors in en-
vironmental or biological water samples still required and vital research
area.
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 dis-
eases 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 in-
numerable instrumental analysis methods were presently used for iron
determination, these methods generally require expert users/analysts to
quantification because of sophisticated equipment’s and precontentra-
tion treatment which led to use excessive adsorbents and eluents [7,8].
Recently, sensitive detection and determination of iron with using
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: yesil@gtu.edu.tr (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.

S.O. Tümay, S. Yeşilot
Journal of Photochemistry & Photobiology A: Chemistry 372 (2019) 156–167
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 re-
cognition of target components have been used as an optical sensor
2. Experimental
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-d
8
, dimethyl
[
21–23] owing to these kind of molecular platforms include three arms,
sulfoxide-d and chloroform-d were purchased from Merck.
6
1
which are modified to interact with the analyte [24]. In addition, mo-
lecular design for tripodal receptors allows the control of binding pro-
cess such as selectivity, sensitivity and complex stability through ri-
gidity of arms and their cavity size [25,26]. It is well known that
tripodal-based synthetic receptors have a various advantages over di-
podal 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 re-
ceptor systems are an attractive research area for not only in supra-
molecular chemistry but also in analytical chemistry [19,27]. Although
numerous synthetic receptor, which based on the change of the fluor-
escence signal for detection of metal ions, are in the literature, only a
few tripodal-based synthetic receptor have been reported for applica-
tion via fluorescence signal changing [28–30]. Also, best our knowl-
edge, only very few of tripodal-based synthetic receptor mainly focused
on determination of iron ions in environmental samples [31,32].
Hexachlorocyclotriphosphazene, 2-naphthol, 2-bromoethanol, 9-an-
thracenemethanol, diethyl ether, sodium hydride, N,N,N’,N’’,N’’-pen-
tamethyldiethylenetriamine (PMDTA), copper(I) bromide and tetra-
hydrofuran purchased from Sigma-Aldrich. MALDI matrix (2,5-
dihydroxybenzoic acid) purchased from Fluka. To purify sodium hy-
dride (> 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 3-
2iHR 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
1,2,3-triazoles have been widely used by researchers in synthetic
receptor due to significant binding properties and as a linker part be-
tween ionophore and fluophore in receptor system. In addition, it can
be easily obtained by Cu(I)-catalyzed azide–alkyne cycloaddition re-
action [33] In recent years, polyaromatic hydrocarbons such as an-
thracene, 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
were used for 31P, H and C NMR spectra with deuterated solvents
1
13
its ring is easily functionalized according to desired application such as
artificial light activatable protein cleaving agents, organic light emit-
ting devices and fluorescence sensor [38,39]. Owing to optical in-
8 6 3 1
(THF-d , DMSO-d , CDCl -d
). In addition, 1H and C NMR measure-
13
ments were performed with using internal reference (trimethylsilane)
and 31P NMR measurements were carried out with using external re-
3 3 6
activity of hexachlorocyclotriphosphazene ring, N P Cl , which means
it does not absorb any radiation in the UV/Vis absorption region and
additionally, optical behaviours of cyclotriphosphazene based mole-
cular systems can be customized according to target application
3 4
ference (85% H PO ). Fluorescence titration data was fitted with the
appropriate non-linear regression analyses using Sigma-Plot 14.0
(Systat Software Inc., Point Richmond, CA).
[
3 3 6
40,41]. Also, N P Cl can be derivatized with various groups ac-
cording to the side of planarity which make this ring suitable platform
for design and develop excellent synthetic receptors for metal detection
2.3. Synthesis
[
32,41]. Therefore, by taking these advantages of N
3
P
3
Cl
6
, considerable
2-(prop-2-yn-1-yloxy)naphthalene, 2-azido-1-ethanol, 9-((prop-2-
yn-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 syn-
thesized compounds (3, 4, CBTSR-1 and CBTSR-2) were characterized
by H, P, C NMR and MALDI-MS spectra and all the results, which
were given in supplementary material (Figs. S1–S4) consistent with
structures of compounds.
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 en-
vironmental water samples without preconcentration processes using
two novel cyclotriphosphazene based tripodal synthetic receptors
1
31
13
(
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 solu-
bility interacting triethylene glycol monomethyl ether (TEGME) moities
below the plane as solubility agents. The structural characterization of
CBTSRs were done by H, P, C 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 ana-
lysis 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.
2.3.1. Synthesis of 2-(4-((naphthalen-2-yloxy)methyl)-1H-1,2,3-triazol-1-
yl)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-azido-
1-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
1
31
13
was finished, extraction with dichloromethane/H
2
O were performed
and the organic phase was dried over Na SO . Organic solvent was
2
4
removed by rotary evaporator and column chromatography was per-
formed 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

S.O. Tümay, S. Yeşilot
Journal of Photochemistry & Photobiology A: Chemistry 372 (2019) 156–167
white solid, yield: 233.0 mg, 94.8%. 1H NMR (CDCl
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,
3
1
-d ), 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
2
.35 (t, J = 7.4 Hz, 1 H), 7.17 (d, J = 8.8 Hz, 1 H), 5.30 (d, J = 5.8 Hz,
9 H); 13C NMR (CDCl
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;
3 1
-d ), 298 K, δ (s, ppm); 147.25, 131.34, 128.95,
1
3
H), 4.48 (t, J = 4.6 Hz, 2 H), 4.08 (t, J = 4.6 Hz, 2 H); C NMR
-d ), 298 K, δ (s, ppm); 156.04, 134.39, 129.59, 129.19, 127.63,
26.90, 126.50, 124.10, 123.95, 118.7, 107.23, 61.83, 61.06, 52.83;
(
CDCl
3
1
31
+
1
P NMR (CDCl
[M] : 1621.670).
3
-d
1
) δ = 17.04 (s, 3 P); [M] : 1621.018 m/z (calc.
+
+
+
[
M] : 269,173 m/z (calc. [M] : 269,300).
2
1
.3.2. 2-(4-((anthracen-9-ylmethoxy)methyl)-1H-1,2,3-triazol-1-yl)ethan-
-ol (4)
2.4. Samples
9
-((prop-2-yn-1-yloxy)methyl)anthracene (60.0 mg, 0.244 mmol),
Three different types of environmental water samples were col-
lected from Gebze/Kocaeli and İkitelli/İstanbul in Turkey. Blue band
filter paper was used to filter the samples, after filtration process, all
Cu(I)Br (58.2 mg, 0.406 mmol), PMDTA (70.4 mg, 0.406 mmol) and 2-
azido-1-ethanol (17.7 mg, 0.203 mmol) were dissolved in dry di-
chlorometane (10 mL) under inert atmosphere. The resulting mixture
was vigorously mixed with magnetic stirrer for six hours at 25 °C and
water samples were acidified with HNO (70%) and they stored at 4 °C
3
prior to analysis.
when the reaction was finished, extraction with dichloromethane/H
2
O
were performed and the organic phase was dried over Na SO . Organic
2
4
2.5. Developed spectrofluorimetric determination methods (CBTSRs-FL) for
solvent was removed by rotary evaporator and column chromatography
was performed to purify the crude product. Silica gel and n-hexane:THF
iron in environmental water samples
(
2:1, v/v) were used as stationary and mobil phase, respectively.
The developed CBTSRs-FL methods are based on selective com-
plexation of CBTSRs with iron prior to spectrofluorimetric determina-
tion 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
1
Compund 4, yellow solid, yield: 65.5 mg, 96.7%. H NMR (THF-d
2
1
8
),
98 K, δ (ppm); 8.48-8.40 (m, 3 H), 8.00 (d, J = 8.3 Hz, 2 H), 7.79 (s,
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
1
3
(
t, J = 4.8 Hz, 2 H), 3.85 (t, J = 4.9 Hz, 2 H); C NMR (THF-d
8
), 298 K,
δ (s, ppm); 145.47, 137.90, 132.31, 131.82, 130.08, 129.36, 128.60,
1
z (calc. [M] : 333.390).
+
3+
26.42, 125.66, 124.04, 64.64, 61.45, 53.15, 47.49; [M] : 333.142 m/
samples were oxidized to Fe by the acidic medium which was used in
+
storage. Therefore, developed3 methods were based on spectro-
+
fluorimetric determination of Fe . The iron content of environmental
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)
-(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 com-
pound 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/H O were performed
and the organic phase was dried over Na SO . Organic solvent was
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
(
[
(F0 − F)/F0] − n
CFe3+
=
m
(1)
(
where F
0
, F, (F
0
-F)/F
0
and CFe3+ represent fluorescence emission re-
3
+
sponse of CBTSRs in the absence of Fe , fluorescence emission re-
sponse 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 in-
creasing amount of Fe . These gradual quenching were proportional
up to 400 μM of Fe and 350 μM of Fe for CBTSR-1 and CBTSR-2,
respectively, which were applicable for quantitative analysis of Fe 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
2
2
4
removed by rotary evaporator and column chromatography was per-
formed 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,
1
viscous liquid, yield: 803.0 mg, 92.1%. H NMR (DMSO-d
6
), 298 K, δ
3+
(
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+
3+
3
H), 7.30 (t, J = 7.5 Hz, 3 H), 7.12 (t, J = 7.5 Hz, 3 H), 7.02 (dd,
3+
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), 3.25-
1
3
3
1
1
3 1
.23 (m, 6 H), 3.05 (s, 9 H); C NMR (CDCl -d ), 298 K, δ (s, ppm);
56.15, 134.42, 129.57, 129.12, 127.6, 126.93, 126.48, 123.88, 118.6,
−
4
-3
07.20, 71.88, 70.56, 70.48, 65.42, 64.12, 61.82, 58.96, 50.08, 46.51;
solution of CBTSR-1 (4 × 10
M) and CBTSR-2 (1 × 10 M) and
3
1
+
P NMR (CDCl
3
-d
1
) δ = 17.28 (s, 3 P); [M+H] : 1429,753 m/z (calc.
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)
+
[
M] : 1429.410).
0.5 mL of Britton–Robinson buffer and 0.4 mL of environmental water
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)
-((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 (62.0 mg, 0.070 mmol) were dissolved in dry di-
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 cal-
culated and recorded at 351 nm (for CBTSR-1) and 412 nm (for CBTSR-
2). Before spectrofluorimetric analysis, the accuracy of (CBTSRs-FL)
methods were evaluated with ICP-OES analysis and spike/recovery
measurements under optimum conditions.
9
2
chlorometane (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/H
2
O
were performed and the organic phase was dried over Na SO . Organic
2
4
solvent was removed by rotary evaporator and column chromatography
was performed to purify the crude product. Silica gel and n-hexane:THF
2.6. Photophysical calculations
(
6:1, v/v) were used as stationary and mobil phase, respectively.
1
CBTSR-2, yellow viscous liquid, yield: 103.0 mg, 90.8%). H NMR
DMSO-d ), 298 K, δ (ppm); 8.59 (s, 3 H), 8.34 (d, J = 8.4 Hz, 6 H),
.06 (d, J = 8.2 Hz, 6 H), 8.04 (s, 3 H), 7.51 (dt, J = 13.6, 6.2 Hz,
In order to evaluate of the photophysical properties of CBTSRs,
fluorescence quantum yields (ΦF) were determined by the comparative
method (Eq. (2)) [48].
(
8
6
158

S.O. Tümay, S. Yeşilot
Journal of Photochemistry & Photobiology A: Chemistry 372 (2019) 156–167
Fig. 1. Schematic presentation of developed CBTSRs-FL methods for iron determination.
F. AStd . n2
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)anthra-
cene (for CBTSR-2). To understand the contributions of cyclotripho-
sphazene platform about complexation properties of CBTSRs for de-
termination, 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-1-
yloxy)methyl)anthracene with 2-azido-1-ethanol. After, purification of
novel compounds by column chromatography, structural characteriza-
∅
F = ∅FStd
F
Std. A. n2
(2)
Std
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
) (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 - Fe complexes were directly measured and
H
2
SO
4
tion was performed with using mass, 1H, C and P NMR spectro-
13
31
scopies. All characterization results given in supplementary material
(
Figs. S1–S4) were compatible with the estimated structures of com-
3
+
pounds Scheme 1.
determined with mono exponential calculations.
1
For instance, the H NMR of 3, 4 and CBTSRs were given at Fig. S1.
The chemical shifts and integration of the methylene/methyl group
3
. Results and discussions
1
signals and aromatic proton signals in the H NMR of 3, 4 and CBTSRs
consistent with proposed structures (Fig. S1). Also, in 31P NMR spectra,
3.1. Synthesis/structural characterization
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 A
3
spin
We have previously discussed the synthesis of the tripodal cyclo-
system and is important evidence of non-geminal-cis-tris-formations
triphosphazene 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 ap-
plied in the last step of reactions, which had higher reaction yield and
easier purification process. Firstly, synthesis and characterization pro-
cesses of non-geminal-cis-tris-TEGME appended cyclotriphosphazene
31
[
50]. According to P NMR spectroscopy, it was understood that the
same organic groups attached same side of planar structure of cyclo-
triphosphazene 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.
(
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
3.2. Photophysical properties of CBTSRs
2-azido-1-ethanol and 1 mol of compound 1 were reacted in presence of
NaH at room temperature in THF [32]. After prepared cyclotripho-
sphazene core, we synthesized 2-(prop-2-yn-1-yloxy)naphthalene and
Photophysical properties of CBTSRs were investigated by UV/Vis
and fluorescence spectrophotometers at 25 °C with spectroscopic cuv-
ette. Different solvents were used to evaluate electronic absorption and
fluorescence spectra of 10 μM CBTSR-1 and 5 μM CBTSR-2 such as 1,4-
9-((prop-2-yn-1-yloxy)methyl)anthracene according to literature
[
46,47]. Then, CBTSRs were synthesized with high yields (92.1% and
159

S.O. Tümay, S. Yeşilot
Journal of Photochemistry & Photobiology A: Chemistry 372 (2019) 156–167
Scheme 1. The synthetic pathways for preparation of CBTSRs, reagents and conditions: (i) propargyl bromide, DMF, K
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, CH
PMDTA, Cu(I)Br, CH Cl , 2-(prop-2-yn-1-yloxy)naphthalene for CBTSR-1, 9-((prop-2-yn-1-yloxy)methyl)anthracene for CBTSR-2.
2
CO
3
, 60 °C for 30 min. then reflux for 3 h; (ii)
2
Cl , 2-azido-1-ethanol; (vi)
2
2
2
dioxane, acetonitrile, aqueous ethanol (EtOH:water), cyclohexane, di-
chloromethane, 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 cyclotripho-
sphazenes 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 sys-
tems (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 an-
thracene. 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.
with the monomer emissions shown by CBTSRs [53]. Fluorescence
quantum yields of 10 μM CBTSR-1 and 5 μM CBTSR-2 in ethanol so-
lution were calculated as 0.11 and 0.08, respectively by comparing with
2 4
the quinine sulfate (in 0.1 M H SO ) (ΦF = 0.54) [49] with same con-
centration.
3.3. Optimization of CBTSRs procedures
To get quantitative recovery with highest selectivity and sensitivity
in complexation procedures with CBTSRs for iron, experimental con-
ditions such as effect of competitive ions, pH, buffer and buffer con-
centration, 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 measure-
ments were carried out at room temperature with spectroscopic quartz
cuvette and final volume of solution was arranged to 2 mL by micro-
pipette. Stock solutions of metal ions (as a chloride salts, except for
It is well known that fluorescence properties of fluorophores im-
portantly depends on the applied concentration [52]. Therefore, dif-
ferent concentration from 10 μM to 1 μM of CBTSRs were prepared to
investigate and determine of optimum fluorescence signals for de-
termination studies in aqueous ethanol. According to Fig. S7, fluores-
cence emission intensity of CBTSRs were gradually decreased without
any red- or blue shift when concentrations of solution were diluted from
2+
+
Pb / Ag ) and anions (as a sodium salts) were prepared in water
while the CBTSRs were prepared in ethanol. UV/Vis electronic ab-
sorption and fluorescence emission signals of 10 μM CBTSR-1 in buf-
fered 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
,
,
1
0 μM to 1 μM, which indicated that there were no inter- or in-
+
+
+
2+
2+
2+
2+
2+
2+
2+
2+
Na , Li , Cs , Ba , Ni , Cu , Pb , Ca , Fe , Zn , Cd
tramolecular interactions existed among the attached fluorophore
groups on CBTSRs. Also, these experimental results were in accordance
Co , Hg2+, Mn2+, Mg2+, Fe , Al , Cr3+ and their concentrations
2+
3+
3+
were 400 μM and 350 μM for CBTSR-1 and CBTSR-2, respectively. As
160

S.O. Tümay, S. Yeşilot
Journal of Photochemistry & Photobiology A: Chemistry 372 (2019) 156–167
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.
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 ab-
sorption spectra upon addition of various metal cations. These changes
in UV/Vis electronic spectra of CBTSRs might be attributed to electron
used for investigated of selectivity of CBTSRs with the same experi-
mental conditions with UV/Vis spectroscopy. It was clearly seen at
Fig. 3, fluorescence emission signals of CBTSRs were fully quenched
3+
with addition of 400 μM and 350 μM of Fe , accompanied by the
fluorescence color change from blue to brownish (Fig. 3c-d). Fluores-
cence quenching of fluorophore with addition of paramagnetic metal
3
+
reorganization with addition of Fe , which were caused by formation
3
+
3+
3+
2+
of CBTSRs - Fe
complexes [54]. Moreover, the addition of Fe
to
ions such as Fe , Fe
was commonly explicated with chelation en-
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
hanced fluorescent quenching (CHEQ) mechanism [55].
The selectivity of CBTSRs towards to cations and anions (Ag+, K
+
,
,
Na+, Li , Cs , Ba , Ni , Cu , Pb , Ca , Fe , Zn , Cd
+
+
2+
2+
2+
2+
2+
2+
2+
2+
161

S.O. Tümay, S. Yeşilot
Journal of Photochemistry & Photobiology A: Chemistry 372 (2019) 156–167
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+, Hg , Mn , Mg2+, Fe3+, Al3+, Cr3+, H
F
2+
2+
−
, HSO
−
, Cl
−
,
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, re-
spectively, for the determination processes in real samples when con-
sider relative fluorescence response and stability of complexes.
2
PO
4
4
−
−
−
−
2-
2-
, NO , I , CN , CO , SO ) were demonstrated at Fig. 4 with
3 3 4
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 to-
3
+
wards Fe
.
The precursors of CBTSRs were also synthesized (3 and 4) for in-
vestigated the effect and contribution of “tripodal” structured cyclo-
triphosphazene 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 compe-
3
.3.4. Effect of buffer solutions and buffer concentration
3+
In order to obtain stable CBTSRs - Fe
complexes, determination
of proper buffer to adjust the pH of medium is important [56]. There-
fore, the effect of different buffer systems besides BeR buffer such as
Tris-HCl and phosphate buffer solution on relative fluorescence in-
tensity of CBTSRs - Fe
mization, 400 μM and 350 μM Fe were used for 10 μM CBTSR-1 and
5
conditions kept constant. According to results (Fig. S11), maximum
relative fluorescence intensity for CBTSRs-Fe were obtained at BeR
buffer solution where other buffer solutions had lower relative fluor-
escence 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
3
+
titive cations included Fe
which clearly indicated, interaction of
can be form via “tripodal” conformation of cyclotriphosphazene
core (Fig. S8). Consequently, development of highly sensitive and se-
3+
were investigated at pH 7.0. For that opti-
3
+
Fe
3+
μM CBTSR-2 with 0.1 M of buffer solution when other experimental
3
+
lective spectrofluorimetric determination methods for Fe
with these
fluoroionophores, there is a necessity to “tripodal” structured cyclo-
triphosphazene core.
3+
3.3.2. Effect of pH
The pH of solution is very important for quantitative recovery be-
3+
cause pH can be affect the chemical structure of CBTSRs and conse-
Fe should be evaluated. Therefore, various concentration from 0.4 M
3
+
quently complexation with Fe . Therefore, relative fluorescence signal
to 0.1 M of BeR buffer solutions at pH 7.0 were used with 400 μM and
3
+
3+
of CBTSRs - Fe
complexes were evaluated with different pH values
350 μM Fe
for 10 μM CBTSR-1 and 5 μM CBTSR-2 when other ex-
3
+
(
3
6.0–10.0). For that purpose, 400 μM Fe
with 10 μM CBTSR-1 and
perimental conditions kept constant. As depicted at Fig. S12, the
3
+
3+
50 μM Fe
with 5 μM CBTSR-2 were used at different pH values
maximum relative fluorescence intensity of CBTSRs-Fe
complexes
(
6.0–10.0) when other experimental conditions were kept constant. pH
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.
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
3
+
were observed at 7.0 for CBTSRs - Fe
complexes. When complex
3
.3.5. Effect of time before measurement
The effect of the time on the complexation of CBTSRs with Fe
formation and stability were considered, developed spectrofluorimetric
analysis processes for environmental water samples were performed at
pH 7.0.
3+
3+
was studied in the range of 0–60 seconds with using 400 μM Fe for 10
3+
μM CBTSR-1 and 350 μM Fe
for 5 μM CBTSR-2 when other experi-
mental conditions kept constant. The pH of the aqueous ethanol solu-
3
.3.3. Effect of initial CBTSRs concentration
tions, which were containing 10 μM CBTSR-1 and 5 μM CBTSR-2 were
3
+
To determined optimum initial concentration of CBTSRs for com-
adjusted 7.0 with 0.1 M B–R buffer and then 400 μM and 350 μM Fe
3
+
plexation with Fe , 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 experi-
mental 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
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
3
+
that, 20 and 25 s would be enough to complexations with Fe
for
CBTSR-1 and CBTSR-2, respectively. Because after these times, fluor-
escence 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.
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Journal of Photochemistry & Photobiology A: Chemistry 372 (2019) 156–167
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 day-
light. The photostability of CBTSRs and CBTSRs - Fe3+ complexes were
demonstrated by plotting relative florescence intensities of CBTSRs-
3
+
Fe
complexes against the time (Fig. S15) which indicated that not
3+
only CBTSRs but also CBTSRs-Fe
complexes were highly photo-
3+
stable. The reversibility of CBTSRs towards Fe ions was evaluated by
further addition of EDTA to CBTSRs + Fe3+ complexes. As shown in
3
+
Fig. S16, quenched fluorescence signals of CBTSRs with addition Fe
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 non-
fluorescent complex, which is occurred by complexation of fluorophore
and quencher in ground state, dynamic quenching which is diffusion-
controlled 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,
3
+
λ
ex = 345 nm) for Fe
.
3
.4. Complex formation and quenching mechanism of CBTSRs with Fe3+
Chemical stoichiometry of CBTSRs - Fe3+ complexes were de-
termined by continuous variation (Job’s) plots in buffered aqueous
ethanol (pH 7.0) and non-linear curve fitting analyses [57–59]. 10 μM
I
I
0
3+
= K [Q] + 1
SV
CBTSR-1 and 5 μM CBTSR-2 were used and mole fraction of Fe ions
(3)
in complexes gradually increased to perform the continuous variation
(
Job’s) method (Fig. 5). As can be seen at Fig. 5, fluorescence signal of
where, K , Stern-Volmer constant, I , initial fluorescence intensity of
CBTSRs, I, final fluorescence intensity of CBTSRs with addition of Fe
and Q, concentration (molar) of Fe . In static quenching, the graph of
sv
0
3
+
complexes reached maximum at 0.33, which means that stoichiometry
3
+
3+
of CBTSRs - Fe 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
the I /I against [Q] give linear line and y-axis intercept of that line is 1
0
according to Stern-Volmer equation. On the other hand, the observed
3
+
ratio of Fe
to CBTSRs were determined to be 2:1 (ligand:metal) ac-
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
cording 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.
+
were given at Fig. S17. According to results, the I /I linearly increased
0
3+
until 200 μM of Fe
and after this concentration, the positive devia-
tions 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
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 -
3
+
3+
Fe complexes, 400 μM and 350 μM Fe were added to buffered (pH
Scheme 2. Proposed binding mechanism for CBTSRs with Fe3+
.
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Journal of Photochemistry & Photobiology A: Chemistry 372 (2019) 156–167
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,
ex = 345 nm) with gradually increased amount of Fe3+
λ
.
mechanism. Therefore, to get deeper information about fluorescence
signal quenching processes, fluorescence lifetime of CBTSRs and
CBTSRs - Fe complexes were measured. The fluorescence lifetimes of
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 Fe . Ac-
3
+
3+
3
+
CBTSR-1 (τ01), CBTSR-2 (τ02), CBTSR-1 - Fe
(τ
) were calculated as 8.387 ± 0.020 (τ01), 1.379 ± 0.039 ns
02), 8.120 ± 0.031 ns (τ ) and 1.403 ± 0.011 ns (τ ), respectively.
According to Fig. S18, fluorescence lifetime of CBTSRs and τ /τ values
1
) and CBTSR-2 -
cording to Fig. S19, sensitivity and fluorescence response of CBTSRs
3
+
3+
Fe
(τ
2
towards Fe
were nearly unchanged in same solvent system (9:1 v/v
(
τ
1
2
EtOH:water) and different solvent systems (3:1 v/v and 9:1 v/v
EtOH:water).
0
3
+
nearly did not change with addition of 400 μM and 350 μM Fe which
were demonstrated that the non-fluorescent ground-state complexes of
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, re-
spectively under optimized conditions (N = 10) which indicated a high
selectivity and sensitivity of the CBTSRs-FL methods.
3
+
CBTSRs and Fe
caused to quenching and static quenching was
dominant in these processes [52].
3.5. Analytical parameters and real sample applications
Dynamic range of developed CBTSRs-FL methods under optimized
conditions were determined by fluorescence titration experiments
3
+
which were performed by gradually increased amount of Fe (Fig. 6).
At Fig. 6, fluorescence intensities of CBTSRs at 351 and 412 nm were
3
+
In order to evaluate performance of developed CBTSRs-FL methods
for Fe3+ determination in environmental water samples, spike and re-
covery tests were carried out. Environmental water samples were
gradually quenched with increased amount of Fe
and when con-
3
+
centration of Fe reached 400 μM and 350 μM, fluorescence signal of
CBTSRs were nearly completely quenched.
3+
spiked in the range of 0–40 μM with Fe
and developed CBTSRs-FL
Calibration curves of developed CBTSRs-FL methods for determi-
3
+
methods were applied. Relative fluorescence signal changes of CBTSRs
with spiked environmental water samples were measured spectro-
fluorimetrically, 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.
nation of Fe
bration curves of CBTSRs were linear in the range of 0.5–400 μM and
.4–350 μM for CBTSR-1 and CBTSR-2, respectively. In addition, linear
were demonstrated at Fig. 7. According to Fig. 7, cali-
0
= 0.0025[Fe3+] +
regression equations of methods are (F -F)/F
= 0.0026[Fe ] + 0.0054 with correlation
0
0
3
+
0
0 0
.0083 and (F -F)/F
coefficients of 0.9984 and 0.9981 for CBTSR-1 and CBTSR-2, respec-
tively. After performed photophysical experiments under optimized
After evaluate the accuracy, iron content of environmental water
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
3+
Fe . Insets: Photographs of showing the change in color of fluorescence emissions.
164

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Journal of Photochemistry & Photobiology A: Chemistry 372 (2019) 156–167
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 ob-
tained results, RSD% and recoveries for determination of iron with
developed CBTSRs-FL methods demonstrated high precision and ac-
curacy 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 in-
cludingspectrofluorimetric, 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 spectro-
fluorimetric and spectrophotometric determination methods which can
be attribute to selective, simple and time-saving complexation proce-
dures 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 de-
veloped CBTSRs-FL methods with some of potentiometric methods
indicated that CBTSRs-FL methods have lower LODs than given po-
tansiometric 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, de-
veloped CBTSRs-FL methods are powerful and accessible alternative for
the determination of iron in environmental water samples.
4. Conclusion
To summarize, two novel cyclotriphosphazene based tripodal syn-
thetic 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 cyclotripho-
sphazene core. The spike and recovery tests and ICP-OES analyses de-
monstrated 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 spec-
trofluorimetric, 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

S.O. Tümay, S. Yeşilot
Journal of Photochemistry & Photobiology A: Chemistry 372 (2019) 156–167
online version, at doi:https://doi.org/10.1016/j.jphotochem.2018.12.
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