A novel flavone-based fluorescent probe for relay recognition of HSO3- and Al3+

Article abstract of DOI:10.1016/j.saa.2015.04.072

In this work, a new flavone-based fluorescent probe 3-hydroxy-3′-formylflavone (3HFF) was designed to achieve highly selective relay recognition of HSO₃^- and Al³⁺ in DMSO-H₂O (2:8, v/v) solution. 3HFF displayed a highly selective response to HSO₃^- with a green fluorescence appearing at 524 nm. Moreover, the in situ generated 3HFF + HSO₃^- system demonstrated eminent relay recognition capability for Al³⁺ with a blue fluorescence appearing at 453 nm by the formation of a 1:1 complex between 3HFF and Al³⁺ in DMSO-H₂O (2:8, v/v) solution. However, only slight change was observed in emission intensity with addition of Al³⁺ to 3HFF, and indicated HSO₃^- was essential for the sensing of Al³⁺. This work achieves the detection of HSO₃^- and Al³⁺ by only one probe and provides another example for this rare combination (anion/metal).

Full text of DOI:10.1016/j.saa.2015.04.072

Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 149 (2015) 208–215
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Spectrochimica Acta Part A: Molecular and
Biomolecular Spectroscopy
journal homepage: www.elsevier.com/locate/saa
A novel flavone-based fluorescent probe for relay recognition of HSO3ꢀ
and Al3+
⇑
Shuai Xu, Ruiren Tang , Zhen Wang, Yin Zhou, Rui Yan
School of Chemistry and Chemical Engineering, Central South University, Changsha 410083, China
h i g h l i g h t s
g r a p h i c a l a b s t r a c t
ꢁ
ꢁ
ꢁ
ꢁ
A novel flavone-based fluorescent
sensor (3HFF) for HSOꢀ3 was
developed.
The in situ generated 3HFF + HSOꢀ3
system demonstrated nice relay
recognition capability for Al3+
.
A blue-shifted emission band is
observed after the addition of Al3+ to
3HFF + HSOꢀ3 system.
A novel relay recognition probe has
realized sensing of HSOꢀ3 and Al3+
with sequence specificity.
a r t i c l e i n f o
a b s t r a c t
In this work, a new flavone-based fluorescent probe 3-hydroxy-30-formylflavone (3HFF) was designed to
achieve highly selective relay recognition of HSOꢀ3 and Al3+ in DMSO–H2O (2:8, v/v) solution. 3HFF dis-
played a highly selective response to HSOꢀ3 with a green fluorescence appearing at 524 nm. Moreover,
the in situ generated 3HFF + HSOꢀ3 system demonstrated eminent relay recognition capability for Al3+
with a blue fluorescence appearing at 453 nm by the formation of a 1:1 complex between 3HFF and
Al3+ in DMSO–H2O (2:8, v/v) solution. However, only slight change was observed in emission intensity
with addition of Al3+ to 3HFF, and indicated HSOꢀ3 was essential for the sensing of Al3+. This work achieves
the detection of HSO3ꢀ and Al3+ by only one probe and provides another example for this rare combination
(anion/metal).
Article history:
Received 8 November 2014
Received in revised form 20 April 2015
Accepted 22 April 2015
Available online 29 April 2015
Keywords:
Fluorescent probe
3-Hydroxyflavone
3-Hydroxy-30-formylflavone
Relay recognition
Bisulfite anion
Ó 2015 Elsevier B.V. All rights reserved.
Aluminum ion
Introduction
tract, and gastrointestine [8,9]. On the other hand, metal ions, as
essential elements present in human body, play critical roles in
Most of life forms have a great requirement for anions and met-
als, as they play critical roles in various physical activities [1,2].
Among the biologically important anions, hydrogen sulfite is
extensively used as antimicrobial agent, enzyme inhibitor and
antioxidant for foods and beverages to preserve their freshness
and shelf life [3–7]. However, it has been discovered that a certain
concentration of hydrogen sulfite is harmful to skin, respiratory
many biological processes. Aluminum is the third most abundant
metal in the earth’s crust, and is found to distribute to all tissues
in the body as well as natural waters everywhere [10]. However,
aluminum may deposit in various organs and be harmful to
humans [11]. Owing to the diversity of their functions mentioned
above, the sensing of HSOꢀ3 and Al3+ is crucial in controlling their
concentration levels in the environmental monitoring and their
direct impact on human health [12]. Fluorescent probes are
broadly used as powerful tools to spy on ionic species owing to
their low cost, high selectivity, versatility and easy monitoring
⇑
Corresponding author. Tel.: +86 731 88836961.
E-mail address: trr@csu.edu.cn (R. Tang).
http://dx.doi.org/10.1016/j.saa.2015.04.072
1386-1425/Ó 2015 Elsevier B.V. All rights reserved.

S. Xu et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 149 (2015) 208–215
209
Scheme 1. Synthesis of 3HFF.
selective recognition probes bearing an aldehyde group have been
designed to detect HSOꢀ3 [21–23]. However, the function of these
probes is unitary and has not been further studied. The adduct sub-
unit generated from the detection of HSOꢀ3 was deconjugated from
the electron rich moiety. If another binding site for metal ion is
existed in the electron rich moiety, optical properties for specific
metal may be different between the probe and the adduct gener-
ated from the detection of HSOꢀ3 .
In order to detect these two biologically and environmentally
important ions relying on only one probe, we designed a new com-
pound, 3-hydroxy-30-formylflavone (3HFF), which demonstrated
highly selective and successive recognition of HSOꢀ3 and Al3+ in
DMSO–H2O (2:8, v/v) solution. To the best of our knowledge, this
is the first report about aldehyde-based fluorescent probe to sense
both HSOꢀ3 and Al3+, although many Al3+ sensors have been
reported [24–28]. Meanwhile, another compound, 3-hydrox-
yflavone (3HF), as an Al3+ probe based on the former research
[29] was prepared as a reference substance to discuss the process
of sequential recognition.
Fig. 1. Fluorescence emission spectra of 3HFF (10 l
M) with the addition of HSO3ꢀ
(0–40 equiv) in DMSO–H2O (2:8, v/v, pH = 5) solution (kex = 345 nm).
Experimental section
[13]. Some of selective recognition probes based on the hydrogen
bonding, electrostatic interactions or coordination with suitable
metal ions have been exploited to detect anions [14–17]. Among
these examples, the reaction-based probes, which adopt special
chemical reactions triggered by target analytes, provide us multi-
ple methods for investigating extensive analytes [18,19].
Aldehyde is known to react with hydrogen sulfite by forming an
aldehyde–hydrogen sulfite adduct which can bring about changes
in the electron acceptor strength [20]. Based on this process, many
General information
The chemicals used were of analytical reagent grade and used
without further purification, if not stated. Deionized water was
used throughout the experiments. All reactions were carried out
on the magnetic stirrers and their reaction processes were moni-
tored on thin layer chromatography (TLC). Absorption and fluores-
cence spectra were taken on
a
Shimadzu UV-2450
Fig. 2. Fluorometric traces for the reaction of 3HFF (10
lM) with 40 equiv and 15
Fig. 3. Emission spectra of 3HFF (10
anions in DMSO–H2O (2:8, v/v, pH = 5) solution with an excitation of 345 nm.
lM) in the absence and presence of 40 equiv
equiv HSOꢀ3 in DMSO–H2O (2:8, v/v, pH = 5).

210
S. Xu et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 149 (2015) 208–215
1483.83, 1471.62, 1275.97, 799.59 and 753.35. 1H NMR (DMSO-
d6, 400 MHz): d 10.13 (s, 1H), 9.95 (s, 1H), 8.76 (t, J = 1.2 Hz, 1H),
8.54 (dt, J = 6.4 Hz, 1.2 Hz, 1H), 8.15 (dd, J = 6.4 Hz, 1.2 Hz, 1H),
8.05 (m, 1H), 7.81–7.87 (m, 3H), 7.49–7.52 (m, 1H). 13C NMR
(DMSO-d6, 100 MHz): d 193.4, 173.6, 155.1, 144.4, 140.1, 136.9,
134.4, 133.5, 132.8, 131.2, 130.0, 128.8, 125.3, 125.2, 121.8,
118.9. Anal. Calcd for C16H10O4 (266.06): C, 72.16; H, 3.78%.
Found: C, 71.63; H, 3.52%.
Results and discussion
General information
A standard procedure was used to prepared the intermediate 2,
3-(diethoxymethyl)benzaldehyde, which was reacted with 1-(2-
hydroxyphenyl)ethanone in ethanol solution by one pot method
at room temperature to afford 3HFF in modest yield (Scheme 1).
3HFF was characterized by IR, 1H NMR, 13C NMR, and Elemental
analysis (Figs. S1–S3). The photo-physical properties of 3HFF with
several anions in DMSO–H2O (2:8, v/v) solution were investigated
by UV–vis and fluorescence measurements. After that, the spectral
characteristics of the 3HFF + HSOꢀ3 system with various metal ions
were also further studied.
Fig. 4. Competitive selectivity of 3HFF (10 l
M) (labeled as L1) toward HSO3ꢀ
(400 lM) in the presence of various anions (0.2 mM).
spectrophotometer and a Hitachi F-7000 fluorescence spectrome-
ter, respectively. IR spectra were measured on KBr pellets on a
Nicolet NEXUS 670 FT-IR spectrophotometer. Melting points were
recorded on an X-4 digital melting-point apparatus. 1H NMR and
13C NMR measurements were performed on a Bruker-400 MHz
nuclear magnetic resonance spectrometer with DMSO as solvent
and TMS as internal reference. All pH measurements were made
with a pH-10C digital pH meter.
Sensing properties of 3HFF toward HSO3ꢀ
The fluorescence spectra of 3HFF containing different concen-
tration of HSOꢀ3 solution were recorded at 370–600 nm upon exci-
tation at 345 nm in DMSO–H2O (2:8, v/v, pH = 5) (Fig. 1). As we can
see, 3HFF alone exhibits weak dual emission maximum at 407 nm
and 524 nm. The reason is that 3HFF transforms from a normal iso-
mer (N) in the ground state to the tautomer (T⁄) through the
excited-state intramolecular proton transfer (ESIPT) process upon
photoexcitation [32,33]. In this process, blue (407 nm) and green
(524 nm) fluorescence occur from N⁄ and T⁄, respectively. There
0.2 mol Lꢀ1 Na2HPO4 citric acid buffers were prepared in deion-
ized water. Stock solutions of the anions (1 ꢂ 10ꢀ3 mol Lꢀ1) and
metal ions (2 ꢂ 10ꢀ3 mol Lꢀ1) were prepared from their sodium
salts and chloride salts in deionized water, respectively. All the
measurements were performed at room temperature. For fluores-
cence measurements, both the excitation and emission slit widths
were 5.0 nm, and the PMT voltage was 700 V.
was a low fluorescence quantum yield (
U = 0.0009) using cou-
marin 1 (
U = 0.50 in ethanol) as standard [34]. Upon addition of
increased amounts of HSOꢀ3 , the initial fluorescence intensities at
407 nm and 524 nm were gradually increased with a relatively
Synthesis
higher fluorescence quantum yield (
U = 0.0065) and accompanied
Synthesis of 1,3-bis(diethoxymethyl)benzene (1), 3-
by a visual fluorescence color change from colorless to green.
Fig. S4 is the calibration graph for HSOꢀ3 and the graph is linear
(diethoxymethyl)benzaldehyde (2) and 3-hydroxyflavone (3HF)
In the process of synthesis of 3-hydroxy-30-formylflavone, 1,3-
bis(diethoxymethyl)benzene (1) and 3-(diethoxymethyl)benzalde-
hyde (2) were also used. The 3HF [30], compound 1 and compound
2 [31] were synthesized according to reported procedures.
for the hydrogen sulfite concentration between 4 and 60
R = 0.99014. According to IUPAC, the detection limit is calculated
as 1.97 M based on the 3 /slope where is the standard devia-
tion of the blank solution.
lM,
l
a
a
Response time is a very important point in sensing for most
reaction-based probes. We then proceeded to investigate the time
required for the reaction of 3HFF and HSOꢀ3 at 25 °C. As shown in
Fig. 2, when 40 equiv and 15 equiv HSOꢀ3 were added to 3HFF solu-
tions, the fluorescence intensities at 524 nm increased with reac-
tion time and then levels off at reaction time greater than about
8 min. It showed that 3HFF could use to detect HSOꢀ3 with a rapid
analytical method.
Selectivity is a very important parameter to evaluate the perfor-
mance of a new fluorescent probe. Emission spectra of 3HFF
exposed to 40 equiv of various anions such as SO24ꢀ, CO32ꢀ, HCO3ꢀ,
PO34ꢀ, HPO24ꢀ, AcOꢀ, Clꢀ, Brꢀ, Iꢀ, Fꢀ, ClOꢀ3 , S2O28ꢀ, S2O23ꢀ, HSOꢀ3 were
investigated at the same test condition in order to validate the
specific affinity of 3HFF towards hydrogen sulfite (Fig. 3). There
was a clear fluorescence enhancement (14-fold) at 524 nm with
addition of HSOꢀ3 to 3HFF, but little fluorescence intensity changes
were observed with other anions, indicating the probe could be
utilized to selectively detect HSOꢀ3 without interference from other
anions.
Synthesis of 3-hydroxy-30-formylflavone (3HFF)
3HFF was synthesized by one pot method. KOH (5.6 g, 10 mmol)
was added to a ethanolic solution (10 mL) of 20-hydroxyacetophe-
none (0.15 g, 1.1 mmol). The obtained solution was cooled to room
temperature. Compound 2 (0.18 g, 1 mmol) was added and the
reaction mixture was stirred for 12 h. Then, the solvent was evap-
orated under reduced pressure. Deionized water (2 mL) and
methanol (6 mL) were added to the reaction mixture. The reaction
mixture was placed in an ice-water bath and 1 mL of 30% H2O2
solution was slowly added, and then stirred at room temperature
for another 5 h. After this period, concentrated HCl (37%) was
added until pH = 2 and then the reaction mixture was stirred for
another 30 min. Then the precipitate was collected by filtration,
washed with cold ethanol, and dried in vacuum. The crude product
was purified by chromatography on silica gel (dichloromethane/
petroleum ether = 1:6, v/v) to afford 3HFF as a colorless powder
in 30.1% yield (0.08 g); m.p. 224–226 °C. IR (cmꢀ1, KBr): 3178.97,
2956.39, 2870.66, 1691.84, 1633.11, 1623.85, 1597.19, 1573.5,

S. Xu et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 149 (2015) 208–215
211
Fig. 5. 1H NMR spectra of 3HFF without (top) and with (40 equiv) HSOꢀ3 (base) in 2/3DMSO ꢀ d6 + 1/3D2O.
Fig. 6. Fluorescence emission spectra of 3HFF (10
3HFF + HSOꢀ3 (10
M + 400 M) with various metal ions (500
(2:8, v/v) solution (kex = 345 nm).
l
M) with Al3+ (500
M) in DMSO–H2O
l
M) and
Fig. 7. Fluorescence emission spectra of 3HFF (10
(10 M + 400 M) and 3HF (10
H2O (2:8, v/v) solution (kex = 345 nm).
l
M), 3HFF + HSOꢀ3
l
l
l
l
l
l lM) in DMSO–
M) in the presence of Al3+ (500
Furthermore, competition experiments were conducted in
order to examine practical applicability of this sensor. As shown
in Fig. 4, the presence of other anions resulted in almost no distur-
bance with the determination of hydrogen sulfite in DMSO–H2O
(2:8, v/v) solution which indicated that 3HFF was feasible for
practical.
To exam the effect of pH on the fluorescence properties, the flu-
orimetric titration in the absence and presence of hydrogen sulfite

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Fig. 8. The interaction mechanism between 3HFF and Al3+
.
Fig. 9. The absorption responses of 3HFF (10
l
M) with relay recognition of HSO3ꢀ
Fig. 10. UV–vis spectral changes of 3HFF + HSOꢀ3 system (10
lM + 400 lM) as a
(400 l lM) in DMSO–H2O (2:8, v/v) solution.
M) and Al3+ (500
function of Al3+ in DMSO–H2O (2:8, v/v) solution.
was investigated in different pH solutions. As shown in Fig. S5, the
fluorescence signals of 3HFF at 524 nm were quite weak and the
changes were minor in the pH range from 2 to 10. Meanwhile,
the fluorescence intensity of the 3HFF + HSOꢀ3 system increased
sharply from pH 2.0 to 4.0 and decreased at pH values above 7.0,
but maintained relatively invariable from 4.0 to 7.0. Considering
practical application, a pH 7.0 solution was selected for the analyt-
ical system in subsequent experiments.
HSOꢀ3 . The proton signals of the phenol group at 7.47–8.72 were
shifted to 7.24–8.24. These results are attributed to the nucle-
ophilic addition of the probe’s formyl group to the bisulfate ion.
Now, 3HFF and the 3HFF + HSOꢀ3 system would be expected to
serve as a probe for the sensing of some metal ions because several
binding sites exist for coordination. With this in mind, a series of
metal ions including Na+, Ca2+, Cu2+, Mg2+, Al3+, Ba2+, Zn2+, Cd2+
,
Co2+, Mn2+, Ag+, Fe3+, Pb2+, K+ and Ni2+ were added to the 3HFF
and 3HFF + HSO3ꢀ system, respectively. To our surprise, the addi-
tion of Al3+ to 3HFF + HSOꢀ3 system leaded to a dramatic enhance-
ment of fluorescence intensity at about 453 nm and other metal
ions induced almost no fluorescence increase. However, only a
slight change was observed with the addition of Al3+ to 3HFF solu-
tion (Fig. 6).
The increase of fluorescence at 407 nm and 524 nm is also
explained. The fluorescence quenching due to a possible charge
transfer from the flavonol HOMO to the aldehyde carbonyl LUMO
in 3HFF is depressed in the 3HFF + HSOꢀ3 system, where the sp2
hybrid carbonyl is transformed to an sp3 hybrid carbon owing to
the addition reaction of aldehyde.
To further analyze the reaction pathway, 1H NMR titrations
were carried out in 2/3DMSO-d6 + 1/3D2O. 1H NMR spectra of
3HFF before and after treatment with 40 equiv of HSOꢀ3 are shown
in Fig. 5. The proton signal of d 10.08 could be assigned to the alde-
hyde proton and the signal was shifted to 5.25 after the addition of
In order to explain the difference in emission spectrum caused
by Al3+, 3-hydroxyflavone (3HF) was synthesized and the fluores-
cence spectrum response to Al3+ was examined in DMSO–H2O
(2:8, v/v) solution. The results show that 3HF has a similar

S. Xu et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 149 (2015) 208–215
213
a high fluorescence quantum yield (
U
= 0.34407). The linear
response range cover a concentration range of Al3+ ions from 5 to
100
of 3HFF + HSOꢀ3 system for Al3+ is calculated as 0.521
relative standard deviation is 8.11 for 3HFF + HSOꢀ3 system
lM, R = 0.991 (Fig. S6). According to IUPAC, the detection limit
l
M and the
(10 lM + 400 l
M). The possible binding mode of 3HFF + HSOꢀ3 sys-
tem and Al3+ is also presented in Scheme 2.
Time course for the change in the fluorescence intensities of
3HFF + HSOꢀ3 system in the presence of 50 equiv and 15 equiv of
Al3+ was also studied in the neutral aqueous conditions (Fig. 12).
Before the tests, 40 equiv of HSOꢀ3 was added to 3HFF and the mix-
ture was shook for 10 min. As we can see, the fluorescence inten-
sity reaches the maximum value within 8 min. It reveals that
3HFF + HSOꢀ3 system detect Al3+ rapidly and can be used to monitor
Al3+ in real time.
To further check the practical applicability of this sensor, the
competition experiments were also measured by addition of 50
equiv of Al3+ to 3HFF + HSOꢀ3 system in the presence of 250 equiv
of other cations. As shown in Fig. 13, the fluorescence enhance-
Fig. 11. Fluorescence titration spectra of 3HFF + HSOꢀ3 (10
lM + 400 lM) upon the
addition of 0–50 equiv of Al3+ in DMSO–H2O (2:8, v/v) solution (kex = 345 nm) Inset:
the relationship between the concentration of Al3+ and emission intensity at
453 nm.
ment caused by Al3+ is not disturbed by Co2+, Ni2+, Zn2+, Cd2+
,
Na+, K+, Mg2+, Ca2+, Ag+, Cr3+ and Pb2+ except Cu2+, Mn2+ which
response with 3HFF + HSO3ꢀ system towards Al3+ (Fig. 7). The fluo-
rescence intensity of 3HF appearing at about 453 nm can be attrib-
uted to the formation of the complex with Al3+ [29], which blocks
the ESIPT process and results in quenching of the T emission.
However, the aldehyde group which functions as an electron
acceptor in 3HFF may cause electron transfer from the Al3+ com-
plex and lead to the slight change in fluorescence intensity. The
interaction mechanism between 3HFF and Al3+ was also studied
by performing 1H NMR titration (Fig. 8). When HSOꢀ3 was added
to 3HFF, the aldehyde group was deconjugated from the flavonol
moiety and a significant enhancement in fluorescence emission
intensity at about 453 nm was observed after the further addition
of Al3+ to 3HFF + HSOꢀ3 system. The absorption responses of 3HFF
with relay recognition of HSOꢀ3 and Al3+ were also carried out
(Fig. 9). All these data indicate that 3HFF can be served as a specific
probe to detect HSOꢀ3 and Al3+ with sequence specificity in the
same media.
Sensing properties of 3HFF + HSOꢀ3 system toward Al3+
Spectroscopic investigations of 3HFF + HSOꢀ3 system and 3HF
with Al3+ were carried out in DMSO–H2O (2:8, v/v) solution.
The UV–vis titration of 3HFF + HSOꢀ3 system in the presence of
different concentration of Al3+ was recorded (Fig. 10). Upon intro-
duction of Al3+ to the solution, the absorbance bands at about
345 nm gradually decrease and shift to 400 nm. Meanwhile, one
isosbestic point at 368 nm is observed which prove the existence
of only two absorbing species in equilibrium.
Fig. 12. Fluorometric traces for the reaction of 3HFF + HSOꢀ3 system with 50 equiv
and 15 equiv Al3+ in DMSO–H2O (2:8, v/v, pH = 7).
In order to study the fluorescence-sensing behavior of
3HFF + HSOꢀ3 system with Al3+, a quantitative investigation was
carried out by fluorescence titration in DMSO–H2O (2:8, v/v) solu-
tion (Fig. 11). Upon addition of Al3+, the fluorescence intensity of
3HFF + HSOꢀ3 system at about 453 nm is increased 177-fold with
Fig. 13. Competitive selectivity of 3HFF + HSOꢀ3 system (10
as L2) toward Al3+ (500
M) in the presence of various anions (0.25 mM).
lM + 400 lM) (labeled
Scheme 2. Proposed binding model of 3HFF + HSOꢀ3 system with Al3+
.
l

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S. Xu et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 149 (2015) 208–215
Fig. 16. Fluorescence emission spectra of 3HF (10 lM) in the presence of various
metal ions (500 lM) in DMSO–H2O (2:8, v/v) solution (kex = 345 nm).
Fig. 14. UV–vis spectral changes of 3HF (10 l
M) as a function of Al3+ in DMSO–H2O
(2:8, v/v) solution.
l lM)
M) (labeled as L3) toward Al3+ (400
Fig. 15. Fluorescence titration spectra of 3HF (10 lM) upon the addition of 0–50
Fig. 17. Competitive selectivity of 3HF (10
in the presence of various anions (0.2 mM).
equiv of Al3+ in DMSO–H2O (2:8, v/v) solution (kex = 345 nm).
To study the fluorescence-sensing behavior of 3HF, a quantita-
tive fluorescent titration of 3HF with Al3+ was also carried out
(Fig. 15). Upon an enhancement in the concentration of Al3+, the
emission intensity is gradually increased at about 453 nm, which
somewhat inhibit the interaction between the 3HFF + HSOꢀ3 system
and Al3+
.
contributes to the formation of the complex between 3HF and Al3+
.
Detection of HSOꢀ3 and Al3+ in water sample
Moreover, the selectivity of 3HF for various metal ions was
investigated in DMSO–H2O (2:8, v/v) solution. As shown in
Fig. 16, a clear fluorescence enhancement is observed with addi-
As already indicated, it is necessary to monitor the level of HSO3ꢀ
and Al3+ in water samples as they may contaminate water sources.
3HFF was employed to determine HSOꢀ3 and Al3+ concentrations in
water samples from Xiang River and YueLu spring (Tables S1 and
S2). The results show that HSOꢀ3 and Al3+ can be detected with good
recovery in the water samples. It also means that the relay recog-
nition concept from HSO3ꢀ to Al3+ is feasible in water samples.
tion of Al3+, but other metal ions such as Fe3+, Zn2+, Cu2+, Co2+
,
Ca2+, Mn2+, Mg2+, Ag+, Na+, Cu2+ and K+ produce little fluorescence
intensity changes, indicating 3HF can be served as a selective fluo-
rescent chemosensor for Al3+ without interference from other
metal ions.
To further test the feasibility of 3HF as a specific sensor for Al3+
,
competition experiments were carried out. As shown in Fig. 17,
except Fe3+ and Cu2+, other metal ions exhibit no interference with
the detection of Al3+. Thus, 3HF can be used as a selective fluores-
cent sensor for Al3+ in the presence of other competing metal ions.
Absorption and fluorescence studies of 3HF toward Al3+
The UV–vis titration of 3HF was recorded upon the addition of
different concentrations of Al3+ in DMSO–H2O (2:8, v/v) solution
(Fig. 14). With the increase of Al3+, the absorption peak at
Conclusion
346 nm gradually decreases while
a new peak appears at
413 nm, which is consistent with the work of pioneer contributors
[29].
In summary, anion to cation relay recognition has been pre-
sented and further displayed in the highly selective sensing of

S. Xu et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 149 (2015) 208–215
215
HSOꢀ3 and Al3+. There is a clear fluorescence enhancement (14-fold)
at about 524 nm with addition of HSOꢀ3 to 3HFF. Then, a blue-
shifted emission band is observed from 524 nm to 453 nm with
addition of Al3+ to 3HFF + HSOꢀ3 system. The corresponding detec-
[14] A.P. Davis, Anion binding and transport by steroid-based receptors, Coord.
Chem. Rev. 250 (2006) 2939–2951.
[15] V. Amendola, L. Fabbrizzi, Anion receptors that contain metals as structural
units, Chem. Commun. (2009) 513–531.
[16] S. Erdemir, S. Malkondu, A simple triazole-based ‘‘turn on’’ fluorescent sensor
for Al3+ ion in MeCN–H2O and Fꢀ ion in MeCN, J. Lumin. 158 (2015) 401–406.
[17] J. Yoon, S.K. Kim, N.J. Singh, K.S. Kim, Imidazolium receptors for the recognition
of anions, Chem. Soc. Rev. 35 (2006) 355–360.
[18] M. Eun Jun, B. Roy, K. Han Ahn, ‘‘Turn-on’’ fluorescent sensing with ‘‘reactive’’
probes, Chem. Commun. 47 (2011) 7583–7601.
tion limits are 1.97 lM and 0.521 lM, respectively. In the course of
our research, 3HF was also successfully used as a reference sub-
stance to prove the process of relay recognition. A novel relay
recognition probe has realized sensing of HSOꢀ3 and Al3+ with
sequence specificity and more applications of this efficient strategy
might be found based on this concept.
[19] X. Qian, Y. Xiao, Y. Xu, X. Guo, J. Qian, W. Zhu, ‘‘Alive’’ dyes as fluorescent
sensors: fluorophore, mechanism, receptor and images in living cells, Chem.
Commun. 46 (2010) 6418–6436.
[20] D.P. Kjell, B.J. Slattery, M.J. Semo,
A novel, nonaqueous method for
regeneration of aldehydes from bisulfite adducts, J. Org. Chem. 64 (1999)
5722–5724.
Appendix A. Supplementary data
[21] X.-F. Yang, M. Zhao, G. Wang, A rhodamine-based fluorescent probe selective
for bisulfite anion in aqueous ethanol media, Sens. Actuators, B 152 (2011) 8–
13.
Supplementary data associated with this article can be found, in
the online version, at http://dx.doi.org/10.1016/j.saa.2015.04.072.
[22] G.J. Mohr, A chromoreactand for the selective detection of HSOꢀ3 based on the
reversible bisulfite addition reaction in polymer membranes, Chem. Commun.
(2002) 2646–2647.
References
[23] C. Yu, M. Luo, F. Zeng, S. Wu, A fast-responding fluorescent turn-on sensor for
sensitive and selective detection of sulfite anions, Anal Methods 4 (2012)
2638–2640.
[24] X. Fang, S. Zhang, G. Zhao, W. Zhang, J. Xu, A. Ren, C. Wu, W. Yang, The solvent-
dependent binding modes of a rhodamine-azacrown based fluorescent probe
for Al3+ and Fe3+, Dyes Pigm. 101 (2014) 58–66.
[25] Y.-Y. Guo, L.-Z. Yang, J.-X. Ru, X. Yao, J. Wu, W. Dou, W.-W. Qin, G.-L. Zhang, X.-
L. Tang, W.-S. Liu, An, ‘‘OFF–ON’’ fluorescent chemosensor for highly selective
and sensitive detection of Al (III) in aqueous solution, Dyes Pigm. 99 (2013)
693–698.
[1] K.P. Carter, A.M. Young, A.E. Palmer, Fluorescent sensors for measuring metal
ions in living systems, Chem. Rev. 114 (2014) 4564–4601.
[2] J.-m. An, M.-h. Yan, Z.-y. Yang, T.-r. Li, Q.-x. Zhou, A turn-on fluorescent sensor
for Zn(II) based on fluorescein-coumarin conjugate, Dyes Pigm. 99 (2013) 1–5.
[3] L.C. de Azevedo, M.M. Reis, L.F. Motta, GOd Rocha, L.A. Silva, J.B. de Andrade,
Evaluation of the formation and stability of hydroxyalkylsulfonic acids in
wines, J. Agric. Food Chem. 55 (2007) 8670–8680.
[4] L. Decnop-Weever, J. Kraak, Determination of sulphite in wines by gas-
diffusion flow injection analysis utilizing spectrophotometric pH-detection,
Anal. Chim. Acta 337 (1997) 125–131.
[26] Y.K. Jang, U.C. Nam, H.L. Kwon, I.H. Hwang, C. Kim, A selective colorimetric and
fluorescent chemosensor based-on naphthol for detection of Al3+ and Cu2+
Dyes Pigm. 99 (2013) 6–13.
,
[5] A. Isaac, A.J. Wain, R.G. Compton, C. Livingstone, J. Davis,
A novel
electroreduction strategy for the determination of sulfite, Analyst 130 (2005)
1343–1344.
[27] S. Malkondu,
A highly selective and sensitive perylenebisimide-based
fluorescent PET sensor for Al3+ determination in MeCN, Tetrahedron 70
(2014) 5580–5584.
[6] S.K. Verma, M.K. Deb, Single-drop and nanogram level determination of sulfite
(SO23ꢀ
) in alcoholic and nonalcoholic beverage samples based on diffuse
[28] J.Y. Noh, S. Kim, I.H. Hwang, G.Y. Lee, J. Kang, S.H. Kim, J. Min, S. Park, C. Kim, J.
Kim, Solvent-dependent selective fluorescence assay of aluminum and gallium
ions using julolidine-based probe, Dyes Pigm. 99 (2013) 1016–1021.
[29] Y.A. Davila, M.I. Sancho, M.C. Almandoz, S.E. Blanco, Structural and
spectroscopic study of Al(III)–3-hydroxyflavone complex: determination of
the stability constants in water–methanol mixtures, Spectrochim. Acta Part A
Mol. Biomol. Spectrosc. 95 (2012) 1–7.
reflectance fourier transform infrared spectroscopic (DRS-FTIR) analysis on KBr
matrix, J. Agric. Food Chem. 55 (2007) 8319–8324.
[7] X.-F. Yang, X.-Q. Guo, Y.-B. Zhao, Novel spectrofluorimetric method for the
determination of sulfite with rhodamine B hydrazide in a micellar medium,
Anal. Chim. Acta 456 (2002) 121–128.
[8] Y.-Q. Sun, P. Wang, J. Liu, J. Zhang, W. Guo, A fluorescent turn-on probe for
bisulfite based on hydrogen bond-inhibited C=N isomerization mechanism,
Analyst 137 (2012) 3430–3433.
[9] D. áBrynn Hibbert, J. áJustin Gooding, A sulfite biosensor fabricated using
electrodeposited polytyramine: application to wine analysis, in: Analyst 124
(1999) 1775–1779.
[10] J. Lee, H. Kim, S. Kim, J.Y. Noh, E.J. Song, C. Kim, et al., Fluorescent dye
containing phenol-pyridyl for selective detection of aluminum ions, Dyes
Pigm. 96 (2013) 590–594.
[30] A. Kurzwernhart, W. Kandioller, S. Bächler, C. Bartel, S. Martic, M. Buczkowska,
et al., Structure-activity relationships of targeted RuII(g6-p-Cymene)
anticancer complexes with flavonol-derived ligands, J. Med. Chem. 55 (2012)
10512–10522.
[31] A. Hachem, Y. Le Floc’h, R. Gree, Y. Rolland, S. Simonet, T. Verbeuren, Synthesis
of novel aromatic analogues of 12-HETE, Tetrahedron Lett. 43 (2002) 5217–
5219.
[32] P.K. Mandal, A. Samanta, Evidence of ground-state proton-transfer reaction of
3-hydroxyflavone in neutral alcoholic solvents, J. Phys. Chem. A 107 (2003)
6334–6339.
[33] P.K. Sengupta, M. Kasha, Excited state proton-transfer spectroscopy of 3-
hytdroxyflavone and quercetin, Chem. Phys. Lett. 68 (1979) 382–385.
[34] G.A. Reynolds, K.H. Drexhage, New coumarin dyes with rigidized structure for
flashlamp-pumped dye lasers, Opt. Commun. 13 (1975) 222–225.
[11] S.V. Verstraeten, L. Aimo, P.I. Oteiza, Aluminium and lead: molecular
mechanisms of brain toxicity, Arch. Toxicol. 82 (2008) 789–802.
[12] Z.-C. Liao, Z.-Y. Yang, Y. Li, B.-D. Wang, Q.-X. Zhou,
A simple structure
fluorescent chemosensor for high selectivity and sensitivity of aluminum ions,
Dyes Pigm. 97 (2013) 124–128.
[13] X. Cheng, H. Jia, J. Feng, J. Qin, Z. Li, ‘‘Reactive’’ probe for hydrogen sulfite: Good
ratiometric response and bioimaging application, Sens. Actuators,
(2013) 274–280.
B 184