A fluorescence turn-on chemosensor for hydrogen sulfate anion based on quinoline and naphthalimide

Article abstract of DOI:10.1016/j.saa.2016.06.022

A new fluorescence turn-on chemosensor 1 based on quinoline and naphthalimide was prepared and its anion sensing toward various anions behavior was explored in this paper. Sensor 1 exhibited a highly selective fluorescent response toward HSO₄^- with an 8-fold fluorescence intensity enhancement in the presence of 10 equiv. of HSO₄^- in DMSO-H₂O (1/1, v/v) solution. The sensor also displayed high sensitivity to hydrogen sulfate and the detection limit was calculated to be 7.79 × 10^{- 7} M. The sensing mechanism has been suggested to proceed via a hydrolysis process of the Schiff base group. The hydrolysis product has been isolated and further identified by ¹H NMR and MS.

Full text of DOI:10.1016/j.saa.2016.06.022

Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 169 (2016) 38–44
Contents lists available at ScienceDirect
Spectrochimica Acta Part A: Molecular and Biomolecular
Spectroscopy
journal homepage: www.elsevier.com/locate/saa
A fluorescence turn-on chemosensor for hydrogen sulfate anion based on
quinoline and naphthalimide
⁎
Zaoli Luo, Kai Yin, Zhu Yu, Mengxue Chen, Yan Li, Jun Ren
Hubei Collaborative Innovation Center for Advanced Organic Chemical Materials & Key Laboratory for the Synthesis and Application of Organic Functional Molecules, Ministry of Education & Col-
lege of Chemistry & Chemical Engineering, Hubei University, Wuhan 430062, PR China
a r t i c l e i n f o
a b s t r a c t
Article history:
A new fluorescence turn-on chemosensor 1 based on quinoline and naphthalimide was prepared and its anion
sensing toward various anions behavior was explored in this paper. Sensor 1 exhibited a highly selective fluores-
cent response toward HSO−4 with an 8-fold fluorescence intensity enhancement in the presence of 10 equiv. of
HSO−4 in DMSO-H2O (1/1, v/v) solution. The sensor also displayed high sensitivity to hydrogen sulfate and the de-
tection limit was calculated to be 7.79 × 10−7 M. The sensing mechanism has been suggested to proceed via a
hydrolysis process of the Schiff base group. The hydrolysis product has been isolated and further identified by
1H NMR and MS.
Received 25 August 2015
Received in revised form 18 May 2016
Accepted 14 June 2016
Available online 15 June 2016
Keywords:
Fluorescent chemosensor
Quinoline
© 2016 Elsevier B.V. All rights reserved.
Naphthalimide
Hydrogen sulfate
Hydrolysis
1. Introduction
HSO−4 selective “turn-on” chemosensors based on a Schiff base platform
via a hydrolysis mechanism are still scarce [32–34].
The design and development of new chemosensors for biologically
and environmentally important anions have attracted considerable at-
tention [1–11]. Among various important anions, hydrogen sulfate
(HSO−4 ) is of particular interest owing to its established role in biological
system and industrial areas. This amphiphilic anion eventually dissoci-
ates at high pH to generate toxic sulfate anion (SO24−), causing irritation
of skin and eyes and even respiratory paralysis [12–13]. Therefore, reli-
able and efficient ways of detecting and sensing the HSO−4 anion are
necessary.
Herein, we report a new turn-on type chemosensor 1 based on Schiff
base, which was synthesized by the simple linkage of 8-hydroxy-2-
quinolinecarbaldehyde 2 and N-amido-4-butyl-1,8-naphthalimide 4
(Scheme 1). More importantly, sensor 1 not only displayed obvious
fluorescence enhancement in the presence of HSO−4 anion but also ex-
hibited high selectivity and sensitivity to hydrogen sulfate anion over
other competitive anions in DMSO-H2O solution.
2. Experimental
In recent years, many efforts have been devoted to designing and de-
veloping various sensors for HSO−4 anions detection [14–23]. Among
those chemosensors, fluorescence chemosensors become increasingly
popular due to their high sensitivity. In terms of sensitivity, the “Off-
On” fluorescent sensors are favored over “On-Off” fluorescent sensors.
However, designing and developing novel fluorescence turn-on recep-
tors for anion detection is still a challenging issue since anions in general
act as fluorescence quenchers [24–27].
Up to now, many of the reported chemosensors based on the hydro-
gen bonding (O\\H or N\\H) mechanism between the receptors with
HSO−4 anion were designed, which have displayed poor selectivity in
aqueous media [28–31]. Chemosenors based on Schiff bases for HSO4−
anion have proven attractive because they could easily hydrolyze in
the presence of HSO−4 in aqueous solution. However, the examples of
2.1. Materials and apparatus
All reagents were purchased from commercial suppliers and were
used without further purification. Double distilled water was used
throughout the experiment. The solution of anions was prepared from
the form of tetrabutylammonium (TBA) salts. Fluorescence detections
were performed on a RF5301 fluorescence spectrometer. The 1H NMR
spectroscopy study was conducted with a Varian INOVA-400 spectrom-
eter using tetramethylsilane (TMS; δ = 0 ppm) as an internal standard.
MS were carried out on LCMS-QP2010 (Shimadzu).
2.2. Synthesis
2.2.1. Synthesis of 8-hydroxy-2-quinolinecarbaldehyde (2) [35]
8-hydroxy-2-methylquinoline (2.00 g, 12.5 mmol), selenium diox-
ide (1.74 g, 15.6 mmol) and 50 mL of 1,4-dioxane were mixed and
⁎
Corresponding author.
E-mail address: renjun@hubu.edu.cn (J. Ren).
http://dx.doi.org/10.1016/j.saa.2016.06.022
1386-1425/© 2016 Elsevier B.V. All rights reserved.

Z. Luo et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 169 (2016) 38–44
39
yield). M.p.: 138–140 °C. 1H NMR (400 MHz, DMSO-d6): δ 10.16 (s,
1H), 8.90 (s, 1H), 8.78 (d, 1H, J = 7.2 Hz), 8.51 (d, 2H, J = 9.0 Hz),
8.32 (t, 2H, J = 7.0 Hz), 7.94–7.91 (m, 1H), 7.73 (t, 1H, J = 7.8 Hz),
7.57 (t, 1H, J = 7.9 Hz), 7.51 (d, 1H, J = 7.9 Hz), 7.19 (d, 1H, J =
7.1 Hz), 6.84 (d, 1H, J = 8.8 Hz), 3.43–3.35 (m, 2H), 1.74–1.67 (m,
2H), 1.49–1.40 (m, 2H), 0.96 (t, 3H, J = 7.3 Hz). 13C NMR (150 MHz,
DMSO-d6): δ 169.4, 159.9, 159.3, 153.5, 150.6, 149.3, 137.8, 136.6,
134.4, 130.7, 129.2, 129.0, 128.5, 128.4, 123.8, 121.5, 119.7, 117.8,
117.4, 112.0, 106.6, 103.5, 42.1, 29.4, 19.4, 13.3 ppm. HRMS-ESI: Calcd.
for C26H22N4O3 [M + H]+: 439.1770. Found: 439.1761.
2.3. General procedure for fluorescence experiment
The solution of sensor 1 (5.0 × 10−6 mol L−1) in DMSO-H2O (1/1, v/
v) was prepared and stored in dry atmosphere. The solution was used
for all spectroscopic studies after appropriate dilution. The solution of
5.0 × 10−5 mol L−1 TBA salts of the respective anions (F−, Cl−, Br−
,
I
−, SO24−, ClO−4 , AcO−, H2PO4−, CN−, CO23–, HCO–3, SO23−, HSO3−, S2−
,
NO−3 , PO−4 , SCN− and HSO−4 ) was prepared in double distilled water.
The fluorescence spectra were obtained by excitation at 467 nm and
emission at 542 nm. The excitation and emission slit widths were both
set at 3 nm.
3. Results and discussion
3.1. Selectivity studies
Scheme 1. The synthetic route of sensor 1.
The selectivity properties of sensor 1 for anions (F−, Cl−, Br−, I−
,
SO24−, ClO−4 , AcO−, H2PO−4 , CN−, CO32–, HCO3–, SO23−, HSO3−, S2−, NO−3
,
PO−4 , SCN− and HSO−4 ) were studied using tetrabutylammonium as a
counter in DMSO-H2O (1/1, v/v) solution. The absorption spectra of sen-
sor 1 was conducted with the common anions (10 equiv.), the results
show that the UV–vis absorbance has no change in the presence of dif-
ferent anions (Fig. 1).
stirred in a 100 mL round bottom flask. The resulting solution was
refluxed for 24 h. The reaction was monitored until completion by TLC
method. The reaction mixture was then filtered off and the selenium
metal was washed with dichloromethane. The combined filtrates were
evaporated off under reduced pressure. The crude product was purified
by column chromatography on silica gel to give pure 2 as a yellow nee-
dle crystal (1.30 g, 59.9% yield). 1H NMR (400 MHz, CDCl3): δ 10.17 (s,
1H), 8.28 (d, 1H, J = 8.3 Hz), 8.11 (s, 1H), 8.01 (d, 1H, J = 8.3 Hz),
7.58 (t, 1H, J = 7.7 Hz), 7.39 (d, 1H, J = 7.9 Hz), 7.24 (d, 1H, J = 8.0 Hz).
Besides, the fluorescent spectrum of sensor 1 was characterized by a
strong emission at 542 nm. Among the common anions (10 equiv.), the
fluorescence were greatly enhanced only in the presence of HSO−4 (Fig.
2). The results suggest that sensor 1 has a high selectivity for the hydro-
gen sulfate anion over the common anions.
3.2. Fluorescence titration experiment
2.2.2. Synthesis of N-amido-4-bromine-1,8-naphthalimide (5) [36]
1,8-naphthalimide (2.77 g, 10 mmol) was dissolved in absolute eth-
anol (50 mL). An excess of hydrazine hydrate (85% w/w, 1.18 g, 20 ml)
was added. After refluxing for 4 h, the mixture was cooled and the pre-
cipitate was filtered and recrystallized from ethanol to give 5 as a yellow
solid (2.48 g, 84.9% yield). 1H NMR (400 MHz, CDCl3): δ 8.68 (d, 1H, J =
7.3 Hz), 8.60 (d, 1H, J = 8.3 Hz), 8.43 (d, 1H, J = 7.8 Hz), 8.05 (d, 1H, J =
7.9 Hz), 7.86 (t, 1H, J = 7.9 Hz), 5.52 (s, 2H).
To gain deeper insight into the fluorescent properties, the fluores-
cence titration of sensor 1 toward HSO−4 was investigated. Upon the ad-
dition of various equivalents of HSO−4 , fluorescence intensity gradually
2.2.3. Synthesis of N-amido-4-butyl-1,8-naphthalimide (4) [37]
Compound 5 (1.46 g, 5 mmol) and 10 mL n-butylamine were added
into 30 mL of methoxyethanol and refluxed for 3 h. After cooled to room
temperature, the mixture was poured into 100 mL water. The precipi-
tate was filtered, dried in vacuum to give 4 as a yellow solid (1.35 g,
95.6% yield). 1H NMR(400 MHz, CDCl3): δ 8.57 (d, 1H, J = 6.8 Hz),
8.44 (d, 1H, J = 8.8 Hz), 8.10 (d, 1H, J = 8.2 Hz), 7.61 (t, 1H, J =
7.9 Hz), 6.69 (d, 1H, J = 8.5 Hz), 5.51 (s, 2H), 5.38 (s, 1H), 3.43–3.38
(m, 2H), 1.84–1.76 (m, 2H), 1.56–1.51 (m, 2H), 1.02 (t, 3H, J = 7.3 Hz).
2.2.4. Synthesis of sensor 1 [37]
Compound 2 (0.69 g, 3.9 mmol) was dissolved in 30 mL hot ethanol,
then compound 4 (1.00 g, 3.5 mmol) was added to the solution. The
mixture was refluxed for 3 h and the solid was precipitated. After filtra-
tion, the solid was collected, washed successively with ethanol and
dried in vacuum to give compound 1 as an orange solid (1.40 g, 90.8%
Fig. 1. The absorption spectra of sensor 1 (5.0 μM) in the presence of 10 eq. of different
anions (as TBA salts) in DMSO-H2O (1/1, v/v) solution.

40
Z. Luo et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 169 (2016) 38–44
Fig. 4. Fluorescence intensity of 1 vs HSO−4 concentrations. [1] =5 μM. The concentrations
of HSO−4 in the range of 5 μM to 50 μM.
Fig. 2. Fluorescent emission spectra of sensor 1 (5.0 μM) in the presence of 10 eq. of
different anions (as TBA salts) in DMSO-H2O (1/1, v/v) solution. The excitation
wavelength was 467 nm.
Where σ is the standard deviation of the blank solution; S is the
slope of the calibration curve. The detection limit was sufficiently low
to detect a submicromolar concentration of HSO−4 , which indicates
this chemosensor may have a high potential for the determination of
hydrogen sulfate anion in biological and environmental science. More-
over, the detection limit of the sensor 1 is compared with representative
reported sensors (Table 1).
increased. When the concentration of hydrogen sulfate anions in-
creased to 10 equiv., the fluorescence intensity reached maximum
with 8-fold enhancement (Fig. 3). Fig. 3 (inset) also shows that there
was a good linearity between the fluorescence intensity (542 nm) and
concentrations of HSO−4 in the range from 5 μM to 50 μM, indicating
that sensor 1 can detect quantitatively relevant concentrations of
HSO−4 . The linear equation was found to be y = 10.72× + 254.62
(R2 = 0.9986) (Fig. 4), where y is the fluorescence intensity at 542 nm
measured at a given HSO−4 concentration and x represents the concen-
tration of HSO−4 added. Therefore, the detection limit (DL) of fluorescent
spectra of sensor 1 for HSO4− was 7.79 × 10−7 M according to the Stern-
Volmer plot [38]:
3.3. Interference experiments
It is a matter of necessity for a good chemosensor to have high selec-
tivity. To further certify the excellent selectivity of sensor 1, the interfer-
ence experiments were also carried out by the addition of 10 equiv. of
anions such as F−, Cl−, Br−, I−, SO42−, ClO4−, AcO−, H2PO−4 , CN−, CO23–
,
DL ¼ 3σ=S ¼ 7:79 ꢀ 10−7
M
HCO–3, SO32−, HSO3−, S2−, NO3−, PO4− and SCN− to a DMSO-H2O (1/1, v/v)
Fig. 3. Fluorescent emission spectra of sensor 1 (5.0 μM) in the presence of different equiv. of HSO−4 in DMSO-H2O (1/1, v/v) solution. The excitation wavelength was 467 nm.

Z. Luo et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 169 (2016) 38–44
41
Table 1
The comparison of the sensor 1 with other representative reported chemosensors for hydrogen sulfate anion.
Number
Fluorophore
Detection methods
DL (M)
Mechanism
References
1
2
3
4
5
6
7
Azobenzene
Naphthalene
Triphenylamine
Diketopyrrolopyrrole
4-Amino-7-nitro-2,1,3-benzoxadiazole
BODIPY
Uv-vis absorption
2.00 × 10−6
2.91 × 10−6
1.00 × 10−8
6.45 × 10−9
2.40 × 10−7
6.45 × 10−8
7.79 × 10−7
Hydrogen bond
Hydrogen bond
Hydrogen bond
Hydrolysis
Hydrolysis
Hydrolysis
[14]
[24]
[39]
[32]
[33]
[23]
This work
Uv-vis absorption Fluorescence
Uv-vis absorption Fluorescence
Uv-vis absorption Flurescence
Uv-vis absorption Fluorescence
Uv-vis absorption Fluorescence
Fluorescence
Naphthalimide
Hydrolysis
Fig. 5. Results of the interference experiments in the presence of 10 eq. of different anions in DMSO-H2O (1/1, v/v) solution. The excitation wavelength was 467 nm.
solution of sensor 1 in the presence of 10 equiv. of HSO−4 . As shown in Fig.
5, all the competitive anions had no obvious interference with the detec-
tion of HSO−4 , indicating that the sensor 1 displayed an excellent selectiv-
ity toward HSO−4 .
3.4. Response time
The effect of reaction time on the fluorescent spectra of the detecting
system was studied. After adding 10 equiv. of HSO−4 to the solution of
Fig. 6. Time course for the fluorescence intensity changes of sensor 1 in the presence of
10 eq. of HSO−4 in DMSO-H2O (1/1, v/v) solution. The excitation wavelength was 467 nm.
Fig. 7. The effect of pH on the fluorescence intensity changes of sensor 1 with and without
HSO−4 (10 equiv.).

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Fig. 8. Partial 1H NMR spectra of sensor 1 in the presence of 0 eq. (a) and 10 eq. (b) of TBAHSO4 in DMSO-d6/D2O (10:1, v/v).
sensor 1, the fluorescent intensity at 542 nm of the system reached the
maximum at 3.5 min and remained stable with increasing time (Fig. 6).
Therefore, sensor 1 has a very short response time for HSO−4 .
products were identified by 1H NMR as compound 2 and compound 4.
Besides, the high resolution mass spectra of 1 was conducted in the ab-
sence or presence of HSO−4 anion (Fig. 9). When 10 equiv. HSO−4 was
added to the solution of sensor 1, the peak at m/z = 439.1761 disap-
peared, and the new peak at m/z = 174.0450 and 284.1262 appeared,
which corresponded to molecular ion peaks of the compound 2
(Calcd. for C10H8NO2 [M + H]+: 174.0555) and the compound 4
(Calcd. for C16H18N3O2 [M + H]+: 284.1399) separately. By the 1H
NMR and the ESI-HRMS experiments, the fluorescence enhancement
was caused by the HSO−4 -promoted hydrolysis of Schiff base, which
leads to the cleavage of the imine bond to generate fluorescent amine
and aldehyde (Scheme 2).
3.5. The effect of pH
As pH value affects the sensor 1 and may change its fluorescence
properties, we also evaluated the effect of pH on the fluorescence signal
response to sensor 1 in DMSO-H2O (1/1, v/v) solution. The fluorescence
intensity of sensor 1 with HSO−4 (10 equiv.) remained unaffected and no
emission band shifts occurred over a pH range from 6 to 8 (Fig. 7).
Therefore, sensor 1 could work over a pH span from 6 to 8 and has po-
tential for biological applications.
4. Conclusion
3.6. Mechanism studies for hydrogen sulfate recognition
In summary, we have designed and synthesized
a novel
To better understand the detailed reaction pathway of sensor 1 with
HSO−4 , 1H NMR experiment was carried out in DMSO-d6-D2O (10/1, v/
v). As was shown in Fig. 8, 1H NMR analysis of the product showed
that free 1 had a singlet at δ 8.90 ppm which was assigned to the
imino proton (–CH = N). After addition of 10 equiv. of HSO−4 , the singlet
at δ 8.90 ppm disappeared and a new singlet at δ 9.83 ppm correspond-
ing to the aldehyde proton (–CHO) appeared. After separation, the
chemosensor for hydrogen sulfate anion detection based on
naphthalimide and quinoline. Addition of hydrogen sulfate anion to a
DMSO-H2O solution of sensor 1 resulted in an obvious fluorescence en-
hancement in a short time, triggered by the hydrolysis of the C_N bond
to form corresponding aldehyde and amine. The chemosensor showed
fast response, good selectivity and high sensitivity toward hydrogen
sulfate anion over other competing anions. This chemosensor has a

Z. Luo et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 169 (2016) 38–44
43
Fig. 9. Mass spectrum of sensor 1 in the presence of 0 eq. (a) and 10 eq. (b) of TBAHSO4.
high potential for the determination of hydrogen sulfate anion in bio-
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