A naphthalene-quinoline based chemosensor for fluorescent “turn-on” and absorbance-ratiometric detection of Al3+ and its application in cells imaging

Article abstract of DOI:10.1016/j.saa.2018.07.039

A new naphthalene-quinoline based chemosensor L was prepared and structurally characterized. L exhibited excellent selectivity and sensitivity to Al³⁺ through distinct fluorescence enhancement (335-fold) and ratiometric detection in DMF/H₂O (v/v, 1/9) based on the combined mechanisms of ESIPT and CHEF. The recognizing behavior of L toward Al³⁺ had been investigated in detail through Job's Plot, FT-IR, HNMR, and HRMS analysis. The limit of detection (LOD) for Al³⁺ was as low as and 3.67 × 10^?8 M. L was successfully applied in real sample detection and construction of molecular logic gate. Moreover, L was verified to be of low cytotoxicity and good imaging characteristics for the detection of Al³⁺ in cells HSC.

Full text of DOI:10.1016/j.saa.2018.07.039

Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 205 (2018) 276–286
Contents lists available at ScienceDirect
Spectrochimica Acta Part A: Molecular and Biomolecular
Spectroscopy
journal homepage: www.elsevier.com/locate/saa
A naphthalene-quinoline based chemosensor for fluorescent “turn-on”
3
+
and absorbance-ratiometric detection of Al and its application in
cells imaging
Shuang Zeng a,1, Shi-Jie Li b,1, Xue-Jiao Sun , Ming-Qiang Li , Yu-Qing Ma , Zhi-Yong Xing ⁎, Jin-Long Li
a
a
a
a,
c
a
Department of Applied Chemistry, College of Science, Northeast Agricultural University, Harbin 150030, PR China
College of Animal Science and Technology, Northeast Agricultural University, Harbin 150030, PR China
School of Chemistry and Chemical Engineering, Qiqihar University, Qiqihar 161006, PR China
b
c
a r t i c l e i n f o
a b s t r a c t
Article history:
A new naphthalene-quinoline based chemosensor L was prepared and structurally characterized. L exhibited ex-
cellent selectivity and sensitivity to Al through distinct fluorescence enhancement (335-fold) and ratiometric
Received 12 April 2018
Received in revised form 11 July 2018
Accepted 12 July 2018
Available online xxxx
3+
2
detection in DMF/H O (v/v, 1/9) based on the combined mechanisms of ESIPT and CHEF. The recognizing behav-
3+
ior of L toward Al had been investigated in detail through Job's Plot, FT-IR, HNMR, and HRMS analysis. The limit
of detection (LOD) for Al3+ was as low as and 3.67 × 10 M. L was successfully applied in real sample detection
and construction of molecular logic gate. Moreover, L was verified to be of low cytotoxicity and good imaging
characteristics for the detection of Al3+ in cells HSC.
−8
Keywords:
Naphthalene
Quinoline
© 2018 Elsevier B.V. All rights reserved.
Chemosensor
Ratiometric
Cells HSC
1
. Introduction
Aluminum, the third most abundant metal in the earth's crust (ap-
methods mentioned above, fluorescence detection method has drawn
special attention of the researchers attribute to its simple and conve-
nient operation, high selectivity and sensitivity, rapidity, non-
destructive and naked-eye recognition [12,19–22]. However, it is still
difficult to design a sensitive and selective fluorescent chemosensor
for Al3 due to its drawbacks such as lack of spectroscopic characteris-
tics, poor coordination and strong hydration ability [23]. Moreover,
compared with the intensity-based probes [12,24–28], ratiometric sens-
ing of an analyte is gaining more and more attention because the ratio of
two intensities of absorption or emission wavelength reduces the error
(s) which could have been arising from the physical and chemical
method. A number of ratiometric Al3 sensors based on various
fluorophores and sensing mechanisms have been developed [29–36],
but some of them still suffer from the shortcomings such as complicated
synthesis, insolubility in water, or interfered by other trivalent metal ion
proximately 8% of total mineral components) [1–4], is closely related
to people's lives due to its widely use in food additives, cooking utensils,
paper and packing materials, textile, clinical drugs and water treatment
+
[5–7]. However, as non-essential element for human, accumulation of
3
+
excessive amount of Al
Parkinson's disease, Alzheimer's disease, amyotrophic lateral sclerosis,
anemia, liver damages and hemochromatosis [8–11]. Furthermore,
high concentration of Al can hamper plant growth and kill fish in
aquatic ecosystems [12,13]. According to the recommendation of
world health organization (WHO), average human intake capacity of
aluminum is 3–10 mg/day and the permitted level of Al3 in drinking
water is 7.4 μM [14]. Thus, the design of chemosensors for detecting
can cause a number of diseases such as
3
+
+
+
3+
3+
3+
Al in aqueous medium is of great significance.
such as Fe and Cr and lack practical applicability in real samples.
Moreover, to our best knowledge, there were few papers concerning
Over the past few decades, many modern techniques were
employed for the detection of Al3 , such as classical atomic absorption
spectrometry, inductively coupled plasma mass spectroscopy, electro-
chemical methods, hydride generation-atomic, neutron activation anal-
ysis and ion chromatography [15–18]. Compared with those detection
+
3+
the fluorogenic and ratiometric absorbance chemosensor for Al
based on naphthalene-quinoline [33]. In order to extend our research
on the development of Al3 chemosensor [37–39], as show in
Scheme 1, we designed and synthesized a novel naphthalene-
quinoline chemosensor L. L showed excellent selectivity and sensitivity
to Al3 through fluorescence enhancement (335-fold) and ratiometric
+
+
⁎
Corresponding author.
absorption detection in DMF/H
chemosensor L was successfully applied in detection of Al
water samples and the fluorescence signal of chemosensor L could be
2
O (v/v, 1/9). Furthermore, the
E-mail address: zyxing@neau.edu.cn (Z.-Y. Xing).
These authors contributed equally to this work and should be considered co-first
3+
1
in real
authors.
https://doi.org/10.1016/j.saa.2018.07.039
1386-1425/© 2018 Elsevier B.V. All rights reserved.

S. Zeng et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 205 (2018) 276–286
277
Scheme 1. Synthesis of sensor L. Reagents and conditions: (a) dichloromethane, chloracetyl chloride, triethylamine, reflux; (b) 1-boc-piperazine, K
2
CO
3
, acetonitrile, reflux;
2 3 3 3
(c) acetonitrile, K CO , HCl, Ethyl bromoacetate, reflux; (d) hydrazine hydrate, CH OH, reflux; (e) CH OH, 2-Hydroxy-1-naphthaldehyde, reflux.
used in the construction of molecular logic gate. We also found that the
application of L for the imaging of Al in human stromal cell (HSC) by
fluorescence changes was also achieved.
crude product was purified by column chromatography on silica gel
using dichloromethane as eluent to get white needle-like solid 1
(600 mg, yield: 68.1%); m.p.:148–149 °C. H NMR (600 MHz,
3+
1
6
DMSO d ) δ (ppm) 10.71 (s, 1H), 9.00–8.93 (m, 1H), 8.65 (d, J =
2
. Experimental
7.7 Hz, 1H), 8.45 (d, J = 8.3 Hz, 1H), 7.74 (d, J = 8.2 Hz, 1H), 7.68 (dd,
J = 8.2, 4.2 Hz, 1H), 7.63 (t, J = 8.0 Hz, 1H), 4.63 (s, 2H).
2
.1. Materials and Instruments
2.2.2. Synthesis of Intermediate Compound 2
Unless otherwise specified, all the solvents and reagents (analytical
2 3
The 1-boc-piperazine (450 mg, 2.4 mmol) and K CO (500 mg,
or spectroscopic grade) were obtained commercially and used without
further purification. H NMR spectra and C NMR spectra were re-
corded on a Bruck AV-600 spectrometer. Chemical shifts (δ) are re-
3.6 mmol) were added to a stirred solution of compound 1 (440 mg,
2 mmol) in acetonitrile (30 mL) and refluxed for 6 h. After the complete
consumption of the starting material monitored using TLC, the reaction
mixture was allowed to room temperature and the solvent was re-
moved under reduced pressure. The crude product was purified by col-
1
13
ported in ppm, relative to TMS (tetramethylsilane) and using DMSO d
6
as the solvent. UV–vis spectroscopy measurements were acquired on a
Pgeneral TU-1901 and absorption spectra were recorded at 25 °C. Fluo-
rescence measurements were measured on a Perkin Elmer LS55 fluores-
cence spectrometer. Mass spectra were measured on a Waters Xevo
UPLC/G2-SQ Tof MS spectrometer. The melting point was measured
on a Beijing XT4-100X microscopic melting point apparatus. The pH
measurements were made with a model PHS-3C meter (Shanghai,
China). Cell image were collected using laser confocal microscope
umn chromatography on silica gel using MeOH/CH
white solid 2 (520 mg, yield: 70.2%); m.p.:165–166 °C. H NMR
(600 MHz, DMSO d ) δ (ppm) 11.30 (s, 1H), 8.97–8.90 (m, 1H), 8.63
2 2
Cl (v/v, 1/20) to get
1
6
(d, J = 7.6 Hz, 1H), 8.39 (d, J = 8.3 Hz, 1H), 7.66 (d, J = 8.2 Hz, 1H),
7.62 (dd, J = 8.2, 4.2 Hz, 1H), 7.57 (t, J = 7.9 Hz, 1H), 3.48 (s, 4H),
3.27 (s, 2H), 2.54 (m, 4H), 1.40 (s, 9H).
(
Leica, TCS SP2 AOBS).
2.2.3. Synthesis of Intermediate Compound 3
The compound 2 (550 mg, 1.5 mmol) and hydrochloric acid (1 M,
3 mL) were dissolved in acetonitrile (20 mL), and the reaction mixture
was allowed to reflux for 2 h. After cooling to the room temperature,
2
.2. Synthesis
The intermediate compounds 1–4 were prepared according to the
2 3
ethyl bromoacetate (250 mg, 1.5 mmol) and K CO (1.38 g, 10 mmol)
reported procedure [39–41].
were directly added to the mixture and refluxed for 5 h. The reaction mix-
ture was cooled and solvent was evaporated under reduced pressure. The
crude product was purified by column chromatography on silica gel using
2
.2.1. Synthesis of Intermediate Compound 1
In a 100 mL round bottom flask equipped with dichloromethane
10 mL), 8-aminoquinoline (580 mg, 4 mmol) and TEA (0.3 mL) were
2 2
MeOH/CH Cl (v/v, 1/30) to get compound 3 as yellow oil liquid (336 mg,
yield: 63%). H NMR (600 MHz, DMSO d ) δ (ppm) 11.36 (s, 1H), 8.95 (dd,
6
1
(
added successively. Chloroacetyl chloride (0.15 mL) dissolved in dichlo-
romethane (10 mL) was slowly added to a round bottom flask with a
dropping funnel. The solution was stirred at room temperature for
J = 4.2, 1.6 Hz, 1H), 8.65 (dd, J = 7.6, 1.2 Hz, 1H), 8.41 (dd, J = 8.3, 1.6 Hz,
1H), 7.68–7.64 (m, 2H), 7.59 (t, J = 7.9 Hz, 1H), 4.13 (q, J = 7.1 Hz, 2H),
3.31 (s, 2H), 3.26 (s, 2H), 2.72 (s, 4H), 2.63 (s, 4H), 1.23 (t, J = 7.1 Hz, 3H).
2
4 h. After the complete consumption of the starting material moni-
tored using TLC, the mixture was extracted with hydrochloric acid
1 M, 20 mL) three times. The dichloromethane layers were dried
with anhydrous sodium sulfate and evaporated under vacuum. The
2.2.4. Synthesis of Intermediate Compound 4
The compound 3 (180 mg, 0.5 mmol) and hydrazine hydrate
(100 mg, 2 mmol) were dissolved in methanol (20 mL). Then the
(

278
S. Zeng et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 205 (2018) 276–286
mixture was refluxed for 2 h under stirring. After completion of reaction
as checked by TLC, the solvent was removed under reduced pressure.
The crude product was purified by column chromatography on silica
equiv.) were individually added into the L (10 μM) solution, the fluores-
cence and UV–vis absorption spectrum of each sample were measured,
respectively.
gel using MeOH/CH
0%); m.p.:194–196 °C. H NMR (600 MHz, DMSO d
s, 1H), 8.93 (d, J = 2.8 Hz, 1H), 8.90 (s, 1H), 8.62 (d, J = 7.3 Hz, 1H),
2 2
Cl (v/v, 1/20) to get white solid 4 (154 mg, yield:
1
9
(
6
) δ (ppm) 11.32
2.3.3. Fluorescence Competition Experiments
50 μL of each metal solution (10 mM) were taken and added into
10 mL of each L solution (10 μM) prepared above to make 5 equiv.
8
4
.39 (d, J = 8.2 Hz, 1H), 7.69–7.59 (m, 2H), 7.57 (t, J = 7.9 Hz, 1H),
.23 (s, 2H), 3.23 (s, 2H), 2.98 (s, 2H), 2.61 (s, 8H).
3+
Then, 50 μL of the Al solution (10 mM) were added into the mixed so-
lution of each metal ion and L to make 5 equiv. Fluorescence spectra
were taken at room temperature after mixing them.
2
.2.5. Synthesis of Sensor L
The compound
4 (102 mg, 0.3 mmol) and 2-hydroxy-1-
naphthaldehyde were dissolved in methanol (20 mL). The reaction mix-
ture was refluxed 2 h. After the complete consumption of the starting ma-
terial monitored using TLC, the reaction mixture was cooled to room
temperature. The precipitate was filtered and washed 5 times with etha-
2.3.4. Fluorescence and UV–Vis Absorption Titration Experiments
For fluorescence titration, increasing doses of Al3 (0–8 equiv.) were
added into L (10 μM) solution to give the samples that containing differ-
ent Al3 concentrations, then the fluorescence spectrum of each sample
was measured. For UV–vis absorption titration, a procedure similar to
that in fluorescence titration was adopted except that the Al3+ was
used from 0 to 2 equiv.
+
+
1
nol to get the yellow product L (100 mg, yield 69%); m.p.:262–263 °C. H
6
NMR (600 MHz, DMSO d ) (Fig. S1) δ (ppm) 12.74 (s, 1H), 11.49 (s, 1H),
1
8
7
1.38 (s, 1H), 9.45 (s, 1H), 8.95 (d, J = 1.5 Hz, 1H), 8.63 (d, J = 7.6 Hz, 1H),
.39 (d, J = 8.3 Hz, 1H), 8.22 (d, J = 8.7 Hz, 1H), 7.91 (d, J = 8.9 Hz, 1H),
.88 (d, J = 8.3 Hz, 1H), 7.65 (d, J = 8.2 Hz, 1H), 7.62–7.54 (m, 3H), 7.39
2.3.5. Job Plot Measurement
3+
(
t, J = 7.4 Hz, 1H), 7.21 (d, J = 8.9 Hz, 1H), 3.32 (s, 2H), 3.27 (s, 2H), 2.72
2
A series of DMF/H O solution (1/9, v/v) containing L and Al were
1
3+
6
(s, 8H). C NMR (151 MHz, DMSO d ) (Fig. S2) δ (ppm) 169.05, 165.96,
prepared so that the total concentration of Al and L was kept as 10
μM. The mole fraction of Al was varied from 0.1 to 0.9. Fluorescence
3+
1
1
6
C
58.33, 149.72, 147.03, 138.38, 136.98, 134.39, 133.01, 132.11, 129.35,
28.33, 128.24, 127.48, 122.67, 121.32, 119.36, 115.86, 108.97, 62.10,
spectra were taken at room temperature.
+
0.98, 53.66, 53.02. HRMS m/z (TOF MS ES ) (Fig. S3): calcd for
+
3+
28
H
29
N
6
O
3
: 497.2301[M + H] , found:497.2306.
2.4. Preparation of [L-Al
]
2
2
5
.3. General Procedures of Spectral Detection
The compound L (10 mg, 0.02 mmol) and Al(NO
.02 mmol) were dissolved in ethanol (10 mL). Then the mixture was
3 3 2
) ·9H O (7.5 mg,
0
.3.1. Preparation of Stock Solutions
Stock solution of L (0.1 mM) was prepared with pure DMF and
0 mL of L solution (0.1 mM) was diluted in 450 mL ultrapure water
refluxed for 2 h under stirring. The solution turned to deep yellow and
cooled to the temperature. After removing the solvent under reduced
pressure and drying under vacuum for 60 min, the L-Al3 complex (yel-
low solid) were obtained and directly used for spectrum measurement
without further purification.
+
to make the final concentration of 10 μM. Stock solutions of metal ions
(
(
10 mM) were prepared in ultrapure water using NaClO
ClO , Ba(ClO , Zn(ClO ·6H O, Cu(ClO ·6H O, AgNO
, Pb(NO , Co(NO ·6H O, Ni(NO ·6H O, Fe(ClO ·xH
NO ·4H O, Al(NO ·9H O, MnSO ·H O, HgCl , and FeCl ·4H
2
4
, KClO
, Cd(NO
O, Ca
O.
4
, Mg
)
4 2
)
4 2
)
4 2
2
4
)
2
2
3
3
)
2
3
)
2
3
)
2
2
3
)
2
2
4
)
3
2
2.5. Cell Culture and Staining
(
)
3 2
2
)
3 3
2
4
2
2
2
The human stromal cell line (HSC) purchased from ATCC (CRL-
4003) was routinely cultured in 1:1 mixture of DMEM medium
and F-12 medium supplemented with 10% heat-inactivated FBS,
100 U/mL penicillin, 100 μg/mL streptomycin, and 1 mM sodium py-
2
.3.2. Fluorescence and UV–Vis Absorption Selectivity Experiments
In the fluorescence and UV–vis absorption selectivity experiments,
+
+
2+
2+
2+
2+
+
2+
different metal ions (Na , K , Mg , Ba , Zn , Cu , Ag , Cd
,
Pb , Co , Ni , Fe , Fe , Ca2+, Al , Mn , Hg ) (each of 5
2
+
2+
2+
2+
3+
3+
2+
2+
2
ruvate at 37 °C, 5%CO for maintained. After plant HSC into 35 mm
2
Fig. 1. Fluorescence emission spectra (λex = 380 nm) of L (10 μM) in the presence of 5 equiv. of various metal ions in DMF/H O (1/9, v/v). Inset: the color changes of L (10 μM) in the
3
+
2
presence of Al ions (5 equiv.) in DMF/H O (1/9, v/v) under UV light of 365 nm.

S. Zeng et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 205 (2018) 276–286
279
Scheme 2. Probable one-way ESIPT of sensor L.
4
2
plates at concentration of 5 × 10 cells/cm , the media without FBS
or antibiotic, was used for culture cells and chemical treatment.
There were three L staining groups: A. normal group: HSC were
were also calculated from the emission spectrum [42]. The CIE system
is a two-dimensional space (XY plane), each point on the chromaticity
diagram represents a certain color. The CIE chromaticity coordinates
3+
not treated with Al(NO
incubated 1 h with 1 mL media added Al(NO
high concentration group: HSC were incubated 1 h with 1 mL
3
)
3
; B. low concentration group: HSC were
of L-Al complex was found to be x = 0.1459, y = 0.0777 at room tem-
perature. This indicates that the color coordinates shifts gradually from
navy blue to blue color region upon progressive addition of Al3 into the
solution of L (Fig. 2).
−
6
3
)
3
(5 × 10
M); C.
+
−
5
3 3
media added Al(NO ) (5 × 10 M). Then fibroblast cells of every
group were washed with PBS 3 times and were fixed by using a stan-
dard paraformaldehyde fixation protocol. After fixation, fibroblast
cells were rinsed with 4:6 mixture solution of DMF and water and
then stained by incubating for 2 h with L (1 × 10 M). Lastly, the
cells were mounted in standard mounting media and imaged by
laser confocal microscope, with an excitation wavelength of
Moreover, to further reveal the identification performance of L
to aluminum ions, the titration experiments of L with Al3+ were
done and the results were shown in Fig. 3. Upon the addition of
−
4
3+
Al (0–8equiv.) to L, the fluorescence intensity of L increases grad-
3
+
ually and almost do not change when the addition of Al is 4 equiv-
alents. The concentration of aluminum ions shows a good linear
relationship with the fluorescence intensity of L in the range of
4
05 nm and an emission wavelength of 440 nm.
0
.1–40 μM (Fig. S4), and the limit of detection (LOD) was calculated
−
7
3
. Results and Discussion
as1.92 × 10 M (based on 3σ/k, where σ is the standard deviation
of the blank measurements, and k is the slope of the intensity ratio
versus sample concentration plot) [43].
The chemosensor L was synthesized by the following steps depicted
1
in Scheme 1, and the structure of L was fully characterized by HNMR,
CNMR and HRMS analysis.
To further determine the selectivity of the probe to aluminum ions in
the presence of other cations, we also conducted the competitive
13
3
.1. Fluorescence Spectra Characteristics for Ions
The fluorescence responses of L to various cations were illus-
trated in Fig. 1. L (10 μM) alone exhibited very weak fluorescence-
emission (λem = 440 nm) in the solution of DMF/H O (1/9, v/v).
2
The weak emission of L could be attributed to the following two as-
pects. Firstly, the isomerization of C_N moiety, which can greatly
quench the fluorescence of L at the excited state. Secondly, the pos-
sible one-way ESIPT process of L at the excited state (Scheme 2),
which leads to nonradiative decay of the excited state and thus
caused fluorescence quenching [6,28–30]. However, upon the addi-
3
+
tion of Al , a 335-fold fluorescence enhancement was observed at
40 nm, and the solution of L showed a significant color change
4
from colorless to bright blue at the same time, which could easily
be detected by the naked-eye under UV light of 365 nm. This result
was due to chelating of the probe L with Al3 , which not only
inhibited the C_N isomerization and ESIPT processes, but also in-
creased the rigidity of the molecular assembly by restricting the
free rotations of the azomethine carbon linking to the naphthalene
ring resulting in a significant enhancement of the fluorescence inten-
sity, which is known as chelation–enhanced fluorescence (CHEF).
The fluorescent behavior of L (10 μM) upon addition of other metal
+
+
+
2+
2+
2+
2+
2+
2+
2+
2+
ions like Na , K , Ca , Mg , Pb , Cu , Co , Cd , Ni , Fe
,
Hg , Mn , Ag and Zn2+ (50 μM) in DMF/H
2
+
2
+
O (1/9, v/v) was also
2
studied but there was hardly any change in emission intensity of L.
This result shows that the probe L has a good selectivity for the iden-
3
+
tification of Al
.
To better understand the chromaticity changes in fluorescence spec-
tra of the probe L upon complexation, CIE chromaticity coordinates
Fig. 2. CIE diagram of the chemosensor L and L with Al3+ (5 equiv.) in DMF/H
2
O (1:9 v/v)
solution.

280
S. Zeng et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 205 (2018) 276–286
3+
3+
2
Fig. 3. Fluorescence spectra of L (10 μM) on addition of different amount of Al in DMF/H O (1/9, v/v). Inset: fluorescence intensity at 440 nm versus the number of equiv. of Al added.
3
+
experiment on the probe L (10 μM) for Al
(50 μM) mixed with
DMF/H
absorption spectrum of L (10 μM) exhibited two absorption bands
at 320 and 354 nm in DMF/H O (1/9, v/v) solution. However, upon
2
O (1/9, v/v) solution, respectively. As shown in Fig. 5, the
+
+
2+
2+
2+
2+
other tested metal ions such as Na , K , Ca , Mg , Pb , Cu
Co , Cd , Ni , Fe , Hg , Mn , Ag and Zn
show in Fig. 4, the fluorescence intensity of L-Al complexation is
almost unaffected except for Cu2 which almost completely
quenched the fluorescence due to the paramagnetic effect from
spin-orbit coupling of Cu2 induced the fluorescence quenching
,
2
+
2+
2+
2+
2+
2
+
2+
(50 μM). As
2
3
+
3+
addition of Al , the absorption band at 354 nm disappeared and a
new band at 400 nm was observed, indicated the formation of com-
+
3
+
plexation between L and Al . Moreover, the binding properties of L
+
3+
with Al were further studied by UV–vis titration experiments. On
3
+
3+
[
44]. Thus, the probe L has good selectivity for Al in the presence
the treatment of Al (0–1.2 equiv.) to the solution of L, as shown in
of most competing metal ions.
Fig. 6, the absorption band at 354 nm was gradually attenuated ac-
companied with a drastic increase in the peak at 400 nm. A well
isosbestic point was observed at 375 nm, indicating the formation
3+
3
.2. UV–Vis Studies of L Toward Al
3
+
of the L-Al adduct. And the absorbance intensity ratios of the re-
ceptor L at 400 nm and 354 nm (A400/A354) increased linearly with
According to the specific fluorescence responses of L to Al3+
among the tested cations, the UV–vis absorption of L (10 μM)
were measured in the absence and presence of Al3 (50 μM) in
the amount of Al3 in the range of 1–7 μM (Fig. S5), indicating a
+
+
3+
clear ratiometric absorbance response of the probe L toward Al
.
Fig. 4. Competition experiment of receptor L toward Al3+ in the presence of 5 equiv. of other cations. [L] = 10 μM, [Al ] = 50 μM, and [X ] = 50 μM in DMF/H
3+
n+
2
O (1/9, v/v). λex = 380 nm.

S. Zeng et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 205 (2018) 276–286
281
attributed to [L + H ] (calcd. m/z 497.2301) and [L - 2H + Al3+]
+
(
calcd. m/z 521.1882), respectively, suggesting a 1:1 L–Al3+ bind-
ing stoichiometry, which is consistent with the Job's plot analysis.
Based on the Job's plot and ESI-MS analysis, according to the
Benesi–Hildebrand plot, the association constant was calculated to
4
−1
be 6.6 × 10 M from nonlinear curve fitting of the absorbance ti-
tration data (Fig. S6).
3
+
The FT-IR spectra of L and L-Al
complexes were also mea-
sured, respectively (Fig. S7). Compared to the FT-IR spectra of L,
−
1
the characteristic OH absorption peak at 3346 cm
vanished in
the presence of Al3 , indicating the deprotonation of phenolic hy-
droxyl and the coordination of oxygen atom with the Al ion. The
+
3
+
characteristic imide absorption of linker \\C_N\\ shifted from
−
1
−1
1
593 cm
to 1373 cm , which is accordance with previous re-
ports [8]. This variation could be caused by the coordination of the
3
+
imide N atom to the Al ions.
1
6
H NMR experiments were carried out in DMSO d to understand
3
+
the exact binding mode of L-Al . As show in Fig. 9, upon the addi-
tion of Al3 , the protons of hydroxyl (H
+
) and of amide (H ) con-
a j
Fig. 5. UV–vis absorption spectra of L (10 μM) in the absence (black curve) and presence
3
nected with quinoline ring of L were all disappeared, indicated the
2
(red curve) of 5 equiv. of Al in DMF/H O (1/9, v/v). (For interpretation of the references
to color in this figure legend, the reader is referred to the web version of this article.)
occurrence of deprotonation during the process of coordination of
3
+
Al with oxygen atom of the hydroxyl and the nitrogen of amide.
In addition, the protons of methylene (H and H ) and the protons
(H and H ) of the piperazine moiety L were all obviously shifted
downfield to 3.39 ppm, indicating that the two nitrogen atoms of pi-
d
g
The detection limit was calculated as 3.67 × 10− M, which showed
that ratiometric detection was more sensitive than that one which
calculated from fluorescent titration experiments. The comparative
analysis of chemosensor L with previously reported sensors were
shown in Table 1.
8
e
f
perazine ring might coordinate to Al3
+
.
According to the analysis of Job's plot, ESI–MS, FT–IR spectra and
1
3+
H NMR, a possible bonding mode for L with Al
was proposed
(
Scheme 3).
3
.3. Binding Stoichiometry and Sensing Mechanism
In order to confirm the binding mechanism of L toward Al3+,
3.4. Effect of pH Toward the Fluorescence Intensity
Job's method for fluorescent titration was carried out (Fig. 7). The
maximum fluorescent intensity was reached at a molar fraction of
In order to evaluate the practical applicability, the effect of pH on
the emission intensity (λem = 440 nm) of L in the absence and pres-
ence of Al3 were measured, respectively (Fig. S8). The probe L has
almost no fluorescence emission in the wide pH range 2–12, but
upon addition of Al3 into L at different pH conditions, obvious
fluorescence enhancement was observed from pH 4 to 8, indicated
3
+
0
.5, which indicate a 1:1 ratio for the L-Al complex. Furthermore,
+
the ESI mass spectrum of L, which is regarded as the direct evidence
to study the binding mechanism between cations and the
chemosensor, were also measured in the absence and presence of
+
3
+
Al
(Fig. 8). The peaks at m/z 497.2292 and m/z 521.1888 were
Fig. 6. UV–vis absorption spectra of L (10 μM) in DMF/H
2
O (1/9, v/v) upon the addition of Al3+ (0–12 μM).

282
S. Zeng et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 205 (2018) 276–286
Table 1
Comparison of the characteristics of L with the previously reported Al3+ sensors.
Ref.
Methods of detections
Selectivity
Al3
Interfering metal ions
LOD
Binding constants
Recovery
NR
+
−7
−7
[
[
[
[
[
[
29]
30]
31]
32]
33]
34]
Ratiometric fluorescent
Ratiometric fluorescent
Fluorescent
Ratiometric fluorescent
Ratiometric fluorescent
Absorbance
Ratiometric fluorescent
Colorimetric and ratiometric fluorescent
Ratiometric fluorescent
Colorimetric and fluorescent
Colorimetric and fluorescent
Colorimetric and fluorescent
Ratiometric absorbance
Fluorescent
NR
2.9 × 10
2.9 × 10
4 × 10
2.4 × 10
2.3 × 10
M
M
NR
NR
3
3
3
3
+
+
+
+
2−
Al
Al
Al
None
EDTA
EDTA
2+
−6
3
−1
2−
Cu
M
4 × 10
M
−8
−5
5.6 × 10 M−1
4
None
None
None
M
M
NR
NR
NR
3+
3+
3+
3
−1
Al 、Fe 、Cr
Al 、Fe 、Cr
8.77 × 10
6.7 × 10
M
3+
3+
−8
4
-1⁎
7.79 × 10
M
M
M
M
M
M
2.71 × 10−
8
Al3
+
Ni2+ and Cu2+
None
5.21 × 10
8.06 × 10
1.59 × 10
6.9 × 10
7.4 × 10
−7
−8
−7
2.08 × 10
2.31 × 10
6.37 × 10
6
4
4
M
M
M
−2
−1
−1
NR
NR
EDTA
[
[
[
[
[
35]
36]
37]
38]
39]
3
3
3
3
3
+
+
+
+
+
Al
Al
Al
Al
Al
2−
None
2+
−6
4
−1
2−
Mn
M
M
7.6 × 10
M
EDTA
−9
4
−1
None
1.62 × 10
M
NR
EDTA
2+
−8
4
−1
2−
This work
Cu
3.67 × 10
M
M
6.6 × 10
M
1.92 × 10−
7
1.038 × 10 M−1
4
LOD: The limit of detection; NR: Not reported in the corresponding paper.
3
+
determination of Al3+ in real water samples collected from local re-
that L could be a good probe for Al detection in neutral to acidic
medium.
3
+
gion of campus. Water samples were spiked with standard Al ions
at different concentration levels, and then diluted within working
linear range and analyzed with the method proposed under opti-
mized conditions (Table 2). The results show that L has good recov-
erability and high accuracy for the practical application of aluminum
3+
3
.5. Reversibility of L for Al
Reversibility is another significant criterion for the development
of chemosensor in the facet of its practical application. The revers-
ibility of the recognition process of L was investigated by adding
2
Na EDTA which is a common binding agent for Al (Fig. S9–S10).
Upon the addition of Al , the absorption band of L at 354 nm disap-
peared and a new band at 400 nm emerged, and the dramatic
fluorescence enhancement at 440 nm also was observed in its fluo-
rescence spectrum. However, the addition of EDTA to the solutions
3
+
ions in water, indicated that L could be used in Al detection in en-
vironmental analysis.
3
+
3
+
3.7. Molecular Logic Gates
One major feature of information technology is the processing of
input signals by logic gates [45]. In today's era, molecular logic gates be-
come increasingly important in the field of molecular computing re-
3
+
of L-Al , the UV–Vis absorption spectra and fluorescence spectra
3+
3
+
search. Thus, based on the fluorescence responses of L with Al and
EDTA, one identical molecular logic gate has been designed, which is a
INHIBIT logic gate (Fig. 10).
of the solution of L-Al
were all nearly recovered to the original
state of L in the absence of Al , indicating the regeneration of the
L. Such reversibility and regeneration are significant for the manu-
3
+
We set Al3 and EDTA separately as inputs signals 1 and inputs sig-
nals 2 for the Set (S) and Reset I process, the fluorescence signal of the
chemosensor L at 440 nm as output. In truth table shown in Fig. 10,
the fluorescence intensity is low for Off (0) state and high for On
+
facture of devices to detect Al3
+
.
3+
3
.6. Application of L for Al Analysis in Water Samples
(
(
1) state. When neither input is on, the gate is off. When only input 1
Al ) is present, the chemosensor showed a significant fluorescence
In order to explore the practical application of L for the detection
of aluminum ions, detail experiments were carried out for the
3+
enhancement at 440 nm and indicating ON state of the system. When
only input 2 (EDTA) is present, the emission is low at this output indi-
cating OFF state. When both the inputs are present, the output is also
in the off condition. Based on the above basic logic gates, a sequential
logic circuit i.e. memory device which displays “write-read-erase-
read” sequences in the form of binary logic function can be constructed
[8]. Now the system writes the state “1” when the SET input is high at
4
40 nm and it is erased by RESET input resulting in state “0”. And this
form of setting can cause the entire process to be repeated several
times. However, according to the result of the competitive experiment,
this molecular logic gates has its limitation in that it is not able to con-
3+
firm whether the existence of Al in tested sample which had been
contaminated with Cu2
+
.
3.8. Cells Imaging
For evaluation of the potential of detecting Al3+ in cells with L, the
human stromal cell (HSC), this endometrium fibroblast cell line was de-
rived from the human stromal cells and immortalized with hTERT, has
been used as an in vetro model. Chemically defined serum-free and
antibiotic-free medium was used to incubate cells with chemical for
avoid non-specific fluorescence. As determined by laser confocal micro-
scope (Fig. 11), the cells without Al3 -loading gave no intracellular fluo-
rescence. After the cells was incubated with L in the presence of
+
Fig. 7. Job plot of Al complex formation. {[Al3+] / ([Al3+] + [L])} is the molar fraction of
Al ion.
3
+
3
+

S. Zeng et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 205 (2018) 276–286
283
3
+
3 2
Fig. 8. ESI–MS spectrum of L (50 μM) upon addition of 5 equiv. of Al in CH CH OH.
Fig. 9. 1H NMR spectra of L with Al3+ in DMSO d
.
6

284
S. Zeng et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 205 (2018) 276–286
λex = 380 nm
OH
O
N
N
N
Al3+
N
N
HN
N
O
O
Al3
+
N
O
N
O
NH
NH
N
λem = 440 nm
Scheme 3. Probable binding mode of sensor L with Al3+ ions.
Table 2
Determination of Al in water samples from different water sources.
3
+
4. Conclusion
Water samples studied Amount of
standard
Total Al3+ Recovery
found
RSD Relative
(%) error
(%)
In summary, we successfully designed and synthesized a highly
of Al3
+
3
+
selective and sensitive chemosensor L through distinct fluorescence en-
Al added
μmol/L)
(n = 3)
(μmol/L)
(n = 3)
added (%)
hancement (335-fold) and ratiometric detection Al3 in DMF/H
+
(
2
O (v/v,
1
/9) based on the combined mechanisms of ESIPT and CHEF. The bind-
Ultrapure water
3
5
6
3
5
6
2.96
4.84
6.15
2.96
5.21
6.16
98.67
96.80
102.50
98.67
104.20
102.67
1.02 −1.30
2.13 −3.20
4.54 2.50
0.90 −1.33
2.09 4.20
2.89 2.67
3+
ing phenomenon of L and Al was successfully studied by different
spectroscopic techniques, and the limit of detection for Al was deter-
mined as 3.67 × 10 M. Moreover, L was successfully applied for the
detection of Al in cells HSC confirming its low cytotoxicity and good
3+
−8
Tap water (Department
of Chemistry)
3+
imaging characteristics.
Acknowledgements
different amounts of Al3+ (5 and 50 μM), the cells showed a strong fluo-
rescent. These results suggest that the probe L have potential bio-
medical applications.
This work was supported by the Scientific Research Fund of Heilong-
jiang Provincial Education Department (No. 12531033).
3
+
Fig. 10. (a) INHIBIT logic gates based on L by monitoring of the emission spectral change at 440 nm in the presence of Al (5 equiv.) and EDTA (5 equiv.); (b) fluorescence intensity
changes of L at 440 nm upon alternate addition of Al3+ and EDTA for five cycles; (c) the logic circuit displaying memory unit with two inputs (In 1 and In 2) and one output, and
(d) corresponding truth table.

S. Zeng et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 205 (2018) 276–286
285
3+
3+
Fig. 11. (A) The cells was incubated 2 h with L (0.1 mM); (B) cells was incubated 5 μM of Al and 0.1 mM of L; (C) cells was incubated 50 μM of Al and 0.1 mM of L.
[
7] D. Don, K. Velmurugan, J. Prabhu, N. Bhuvanesh, A. Thamilselvan, R. Nandhakumar,
Appendix A. Supplementary data
A dual analyte fluorescent chemosensor based on a furan-pyrene conjugate for Al3
+
&
3
HSO , Spectrochim. Acta A 174 (2017) 62–69.
3
+
Supplementary data to this article can be found online at https://doi.
org/10.1016/j.saa.2018.07.039.
[8] A. Roy, S. Dey, P. Roy, A ratiometric chemosensor for Al based on naphthalene-
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9] B. Liu, P.F. Wang, J. Chai, X.Q. Hu, T. Gao, J.B. Chao, T.G. Chen, B.S. Yang, Naphthol-
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