‘Turn-on’ fluorescent chemosensors based on naphthaldehyde-2-pyridinehydrazone compounds for the detection of zinc ion in water at neutral pH

Article abstract of DOI:10.1002/bio.3368

A series of naphthaldehyde-2-pyridinehydrazone derivatives were discovered to display interesting ‘turn-on’ fluorescence response to Zn²⁺ in 99% water/DMSO (v/v) at pH?7.0. Mechanism study indicated that different substituent groups in the naphthaldehyde moiety exhibited significant influence on the detection of Zn²⁺. The electron rich group resulted in longer fluorescence wavelengths but smaller fluorescence enhancement for Zn²⁺. Among these compounds, 1 showed the highest fluorescence enhancement of 19-fold with the lowest detection limit of 0.17?μmol/L toward Zn²⁺. The corresponding linear range was at least from 0.6 to 6.0?μmol/L. Significantly, 1 showed an excellent selectivity toward Zn²⁺ over other metal ions including Cd²⁺.

Full text of DOI:10.1002/bio.3368

Received: 5 April 2017
DOI: 10.1002/bio.3368
Revised: 1 May 2017
Accepted: 18 May 2017
R E S E A R C H A R T I C L E
‘
2
Turn‐on’ fluorescent chemosensors based on naphthaldehyde‐
‐pyridinehydrazone compounds for the detection of zinc ion in
water at neutral pH
1
|
2,3
1
4
1
1
|
|
|
|
|
Yuanyuan Liu
Yuanyuan Li
Qi Feng
Na Li
Kai Li
Hongwei Hou
2
Bing Zhang
1
College of Chemistry and Molecular
Engineering, Zhengzhou University, Henan, P.
R. China
Abstract
A
series of naphthaldehyde‐2‐pyridinehydrazone derivatives were discovered to display
2+
2
School of Chemical Engineering and Energy,
interesting ‘turn‐on’ fluorescence response to Zn in 99% water/DMSO (v/v) at pH 7.0.
Zhengzhou University, Henan, P. R. China
Mechanism study indicated that different substituent groups in the naphthaldehyde moiety
2+
3
College of Chemistry, Chemical and
exhibited significant influence on the detection of Zn . The electron rich group resulted in longer
Environmental Engineering, Henan University
of Technology, Henan, P. R. China
2+
fluorescence wavelengths but smaller fluorescence enhancement for Zn . Among these
4
compounds, 1 showed the highest fluorescence enhancement of 19‐fold with the lowest
Department of Pharmacy, Women & Infants
2+
Hospital of Zhengzhou, Henan, P. R. China
detection limit of 0.17 μmol/L toward Zn . The corresponding linear range was at least from
2+
Correspondence
0.6 to 6.0 μmol/L. Significantly, 1 showed an excellent selectivity toward Zn over other metal
2+
Yuanyuan Li, School of Chemical engineering
and Energy, Zhengzhou University, Henan
ions including Cd
.
4
50001, P. R. China.
KEYWORDS
Email: yuanyuanli@haut.edu.cn
chemosensor, fluorescence, turn‐on, zinc ion
Kai Li, College of Chemistry and Molecular
Engineering, Zhengzhou University, Henan
4
50001, P. R. China.
Email: likai@zzu.edu.cn
Funding information
National Natural Science Foundation of China,
Grant/Award Number: 21371155, 21501150
and 51502079
[
11–14]
1
|
INTRODUCTION
being non‐destructive and celerity
. Up to now, numerous
fluorescent chemosensors based on different fluorogens have been
2
+ [15–20]
Zinc is one of the necessary microelements for human beings, which is
important and helpful for many biological activities such as gene code,
DNA recombination or recognition, neural signal transmission and
utilized for the detection of Zn
. Outstanding sensitivity and
2+
selectivity toward Zn have been achieved. However, most of these
reported fluorescent chemosensors worked in an environment
[
1–3]
cellular metabolism
physiological diseases
. Deficiency or surplus of zinc may cause
. Therefore, the measurement of zinc has
containing high contents of organic co‐solvents, which was not
[21,22]
[
4–6]
beneficial for the application in real samples
. Moreover, it is still
2
+
2+
significant values. Current analytical techniques such as flame atomic
absorption spectrometry (FAAS), surface enhanced Raman scattering
a challenge to distinguish Zn from Cd due to their similar coordina-
[
23,24]
tion modes and fluorescence responses
. Therefore, there is an
2
+
(
SERS), colorimetry and ion selective electrode (ISE) have been applied
urgent need to develop fluorescent chemosensors for Zn detection
to conquer the earlier mentioned challenges.
2
+ [7–10]
for the detection of Zn
. Among these methods, fluorescent
have been developed as a widely used
2
+
chemosensors for Zn
In this work, naphthaldehyde‐2‐pyridinehydrazone based
‘turn‐on’ fluorescent chemosensor of 1‐hydroxy‐2‐naphthaldehyde‐
technique because of the merits such as convenience, emission signals
2‐pyridinehydrazone (1) and its control compounds 1‐hydroxy‐4‐
chloro‐2‐naphthaldehyde‐2‐pyridinehydrazone (2) and 1‐hydroxy‐4‐
methoxy‐2‐naphthaldehyde‐2‐pyridinehydrazone (3) for detecting
Abbreviations used: CHEF, chelation‐enhanced fluorescence; DMSO, dimethyl
sulfoxide; ESI‐MS, electrospray ionization mass spectrometry.
Luminescence. 2017;1–5.
wileyonlinelibrary.com/journal/bio
Copyright © 2017 John Wiley & Sons, Ltd.
1

2
LIU ET AL.
SCHEME 1 Synthesis of 1–3
2
+
Zn in 99% water/dimethyl sulfoxide (DMSO) (v/v) at neutral pH
paraformaldehyde (84 mmol) in acetonitrile solution (50 mL). After
being stirred at 90°C for 24 h, water (50 ml) was used to dilute the
mixture and then extracted with ethyl acetate (300 ml). The organic
layer was washed with 1% aqueous HCl solution and dried over anhy-
drous sodium sulfate. All volatiles were took away under reduced
pressure and the products 1a–3a were isolated by flash chromatogra-
phy (EA/PE) on silica gel (yield of 41%, 36% and 31%, respectively).
were reported (Scheme 1). Enhancement of cyan fluorescence
2+
emission was detected with a UV lamp after mixing Zn with an
aqueous solution of 1 at neutral pH, enabling fluorescence ‘turn‐on’
2+
2+
detection of Zn . Compound 1 showed good sensitivity toward Zn
2+
with a detection limit of 0.17 μmol/L. In fact, 1 was a Zn ‐selective
fluorescent chemosensor, which could distinguish other metal ions
2+
2+
˗
including Cd from Zn
.
ESI‐MS spectrometry: m/z calc. For 1a: 171.1 ([M ‐ H] ), found:
1
1
1
70.8. H–NMR (CDCl
3
) δ (ppm): 7.28 (d, 1H, J = 8.0 Hz), 7.36 (d,
H, J = 8.0 Hz), 7.51 (t, 1H, J = 8.0 Hz), 7.62 (t, 1H, J = 8.0 Hz), 7.73
2
2
|
EXPERIMENTAL
Reagents
(
d, 1H, J = 8.0 Hz), 8.41 (d, 1H, J = 8.0 Hz), 9.88 (s, 1H), 12.68 (s,
13
1
3
H). C–NMR (CDCl ) δ (ppm): 114.23, 119.41, 124.27, 124.44,
.1
|
126.09, 126.42, 127.62, 130.55, 137.46, 161.77, 196.26.
˗
ESI‐MS spectrometry: m/z calc. For 2a: 205.0 ([M ‐ H] ), found:
All the materials utilized in this experiment were of analytical grade
unless otherwise noted. 1‐Naphthol, 4‐chloro‐1‐naphthol, hexamethy-
lenetetramine, trifluoroacetic acid were purchased from Energy Chem-
ical Co., Shanghai, China. 4‐Methoxy‐1‐naphthol, 2‐hydrazinopyridine
were ordered from J&K Chemical Co., Beijing, China. All the other
materials were purchased from Sinopharm Chemical Reagent Beijing
Co., Beijing, China. Deionized water (distilled) and DMSO were applied
throughout the experiments. All the metal ions solutions used in the
experiment were prepared from their nitrate salts or perchlorate salts.
Tris–HCl buffer solutions which possessed a wide pH range were
prepared by utilizing 10 mmol/L Tris and suitable amount of hydrogen
chloride (HCl) or sodium hydroxide (NaOH) modulated by a pH meter.
1
2
04.9. H–NMR (CDCl
3
)
δ
(ppm): 7.54 (s, 1H), 7.63 (t, 1H,
J = 4.0 Hz), 7.79 (t, 1H, J = 8.0 Hz), 8.18 (d, 1H, J = 12.0 Hz), 8.46 (d,
13
1
H, J = 12.0 Hz), 9.88 (s, 1H), 12.56 (s, 1H). C–NMR (CDCl
3
)
δ (ppm): 114.07, 122.44, 124.53, 124.74, 125.59, 125.65, 126.93,
1
31.61, 134.41, 160.73, 195.24.
˗
ESI‐MS spectrometry: m/z calc. For 3a: 201.1 ([M ‐ H] ), found:
1
2
1
00.9. H–NMR (CDCl
3
) δ (ppm): 4.02 (s, 3H), 6.75 (s, 1H), 7.63 (t,
H, J = 8.0 Hz), 7.72 (t, 1H, J = 8.0 Hz), 8.24 (d, 1H, J = 8.0 Hz), 8.45
13
(
d, 1H, J = 8.0 Hz), 9.94 (s, 1H), 12.40 (s, 1H). C–NMR (CDCl
3
)
δ (ppm): 55.74, 101.85, 113.07, 122.09, 124.27, 125.37, 126.80,
1
30.27, 130.30, 148.54, 156.72, 195.95.
The original files for the NMR spectrometry are provided in the
Supporting Information.
2
.2
|
Apparatus
Absorption spectra were determined on a JASCO V‐550 UV–vis
spectrophotometer. Fluorescence spectra were measured on a JASCO
FP‐8300 spectrofluorimeter equipped with an ETC‐815 peltier
thermostatted single cell holder. All pH tests were measured with a
MettlerToledo FE20/EL20 pH meter. NMR spectra were recorded
using a BRUKER400 spectrometer operated at 400 MHz. Mass spectra
2
.4
|
Synthesis of 1‐hydroxy‐2‐naphthaldehyde‐2‐
pyridinehydrazone derivatives (1–3)
Componds 1a–3a (1 mmol) and 2‐hydrazinopyridine (1 mmol) were
dissolved in 20 ml pure ethanol. The mixture were stirred for 3 h at
room temperature to form a precipitate. After being filtered, the
precipitate was washed with 30 ml absolute ethanol three times. The
precipitate was then dried under reduced pressure for a suitable time
to gain the products 1–3 (yield of 82%, 77% and 87%, respectively).
(
electrospray ionization mass spectrometry [ESI‐MS]) were measured
on a Bruker Esquire 3000 pius ion trap mass spectrometer.
+
ESI‐MS spectrometry: m/z calc. For 1: 264.1 ([M + H] ), found: 264.0.
2
.3
|
Synthesis of 1‐hydroxy‐2‐naphthaldehyde
1
6
H–NMR (DMSO‐d ) δ (ppm): 6.82 (t, 1H, J = 8.0 Hz), 7.00 (d, 1H,
derivatives (1a–3a)
J = 8.0 Hz), 7.43 (d, 1H, J = 8.0 Hz), 7.52 (m, 3H), 7.70 (t, 1H,
1
‐Hydroxy‐2‐naphthaldehyde derivatives were prepared as previous
J = 8.0 Hz), 7.84 (t, 1H, J = 8.0 Hz), 8.21 (d, 1H, J = 4.0 Hz), 8.31 (t, 1H,
13
[
25,26]
reported
.
Then anhydrous magnesium chloride (MgCl
N) (37.5 mmol) were added to the
mixture of 1‐hydroxy‐2‐naphthaldehyde derivatives (14 mmol) and
2
)
J = 4.0 Hz), 8.42 (s, 1H), 11.15 (s, 1H), 12.13 (s, 1H). C–NMR (DMSO‐
(
15 mmol) and triethylamine (Et
3
6
d ) δ (ppm): 106.63, 113.44, 115.80, 119.44, 122.71, 124.94, 126.00,
126.38, 127.58, 128.02, 134.27, 138.64, 142.38, 148.66, 153.30, 156.09.

LIU ET AL.
3
+
ESI‐MS spectrometry: m/z calc. For 2: 298.1 ([M + H] ), found:
(10 mmol/L Tris–HCl with desired pH). The final concentration of
20 μmol/L was obtained for further experiments. Metal ions dissolved
in water were added to the solution of 1 under the same conditions.
After being blended well, the solutions were allowed to stay at 25°C
for 1 min. Then absorption or fluorescence spectra were recorded.
1
2
97.9. H–NMR (DMSO‐d
6
) δ (ppm): 6.84 (dd, 1H, J = 8.0 Hz), 7.01
(
d, 1H, J = 8.0 Hz), 7.65 (m, 1H), 7.71 (m, 2H), 7.81 (s, 1H), 8.09 (d,
1
H, J = 8.0 Hz), 8.22 (t, 1H, J = 4.0 Hz), 8.35 (d, 1H, J = 8.0 Hz), 8.38
13
(
s, 1H), 11.24 (s, 1H), 12.14 (s, 1H). C–NMR (DMSO‐d
6
) δ (ppm):
1
1
06.97, 114.54, 116.00,121.22, 123.41, 124.17, 125.68, 126.31,
26.97, 128.90, 130.56, 138.64, 140.28, 148.64, 152.31, 155.94.
+
ESI‐MS spectrometry: m/z calc. For 3: 294.1 ([M + H] ), found:
3
3
|
RESULTS AND DISCUSSION
1
2
94.0. H–NMR (DMSO‐d
6
) δ (ppm): 3.96 (s, 3H), 6.83 (dd, 1H,
J = 8.0 Hz), 7.02 (s, 1H), 7.04 (d, 1H, J = 8.0 Hz), 7.56 (m, 2H), 7.70
t, 1H, J = 8.0 Hz), 8.10 (d, 1H, J = 8.0 Hz), 8.20 (d, 1H, J = 8.0 Hz),
.25 (d, 1H, J = 8.0 Hz), 8.41 (s, 1H), 11.14 (s, 1H), 11.33 (s, 1H).
2+
.1
|
Binding of 1 with Zn
(
2+
The binding properties of 1 with Zn were investigated by UV–vis
absorption and fluorescence spectroscopy in an aqueous solution buff-
ered by 10 mmol/L Tris–HCl at pH 7.0. As shown in Figure 1a, the
absorption bands of 1 originally appeared at 376 nm and 396 nm in
8
13
6
C–NMR (DMSO‐d ) δ (ppm): 56.14, 103.37, 105.61, 113.35,
1
1
15.70, 121.96, 122.75, 126.02, 126.12, 126.63, 127.00, 138.63,
41,71, 146,97, 148.34, 148.59, 156.32.
2+
2+
the absence of Zn . With the addition of Zn , these two absorption
bands decreased gradually and a new absorption band at 416 nm
appeared. The isosbestic point at 406 nm suggested the formation of
The original files for the NMR spectrometry are provided in the
Supporting Information.
1
–Zn complex. Under the same condition, the fluorescence spectra
2
.5
|
Absorption and fluorescence measurements
2+
showed obvious enhancement at 484 nm with the increase of Zn
.
2
+
The absorption and fluorescence spectra were recorded at 25°C. A stock
solution of 1 (2 mmol/L) was prepared in absolute DMSO. In 4 ml glass
tubes 0.03 ml of the stock solution was added to 2.97 ml buffer
When more than 1 equiv. Zn was added, the fluorescence intensity
reached to the maximum and varied very slightly (Figure 1b). A 19‐fold
2+
‘turn‐on’ fluorescence enhancement of 1 toward Zn could be observed.
2+
FIGURE 1 (a) absorption spectra and (c) fluorescence spectra of 1 (20 μmol/L) upon the addition of Zn (0–30 μmol/L). (b) the absorbance ratio
2+
(A416/A396) and (d) the fluorescence intensity (F484) as a function of Zn concentration. Inset: The photographss are 1 in the absence and presence
2+
of 1 equiv. Zn in a glass cuvette excited by (a) sun‐light and (c) UV light (365 nm). Conditions: 99% water/DMSO (v/v) at pH 7.0 buffered by
0 mmol/L Tris–HCl
1

4
LIU ET AL.
2
+
The non‐linear fitting of the titration curve indicated that the combina-
3.2
|
Selectivity of 1 to Zn over other metal ions
2+
tion of 1 and Zn was probably a 1:1 stoichiometry. The association con-
2+
To explore the selectivity of 1 to Zn , competition experiments in the
6
stant K
a
value was about 4.94 × 10 L/mol. Fluorescence emission
2+
presence of Zn mingled with other metal ions were carried out. As
2+
enhancement at 484 nm of 1 upon the addition of Zn is considered
2
+
shown in Figure 3, most of the metal cations, especially Cd , showed
to be on account of the generation of the 1–Zn complex, which is a
2
+
scarce interference when detecting Zn , suggesting that 1 possessed
[27]
typical chelation‐enhanced fluorescence (CHEF) process
. To further
2+
excellent selectivity for Zn detection. It should be noted that 1
2+
confirm the metal‐to‐ligand ratio, Job's plot of 1 and Zn was tested
from the fluorescence spectra with a whole concentration of 20 μmol/L
exhibited relatively poor detection selectivity in the presence of
2+
Cu , which is due to the paramagnetic metal ions leading to
(
Figure 2), which also suggested the formation of a 1:1 complex.
According to the reports, the introduction of electron rich groups
[
29]
fluorescence quenching
. Both 2 and 3 showed similar selectivity
2+
with 1 toward Zn as well as toward other metal ions under the same
will bathochromic the fluorescence wavelength of the CHEF
conditions. However, the fluorescence enhancements of 2 and 3 with
[
28]
process
. Therefore, control compounds 2 and 3 with electron rich
2+
Zn were not as good as 1 (Figures S4 and S5).
groups of chloric and methoxy were synthesized. Both of them exhib-
2+
ited fluorescence ‘turn‐on’ response to Zn (Supporting Information
3
.3
|
Optimizing the pH for fluorescent
Figure S1), which was similar to that of 1. Meanwhile, the metal‐
2
+
2+
determination of Zn
to‐ligand ratios of Zn to 2 and 3 were also 1:1 from Job's plots
in Figures S2 and S3, which suggested that they exhibited analogous
response mechanism as 1. As expected, both of the fluorescence
wavelengths of 2–Zn (490 nm) and 3–Zn (510 nm) were longer than
that of 1–Zn. Nevertheless, the fluorescence enhancements of the
two conpounds were only seven‐ and five‐fold, respectively, which
were due to their stronger fluorescence backgrounds than that of 1.
2+
The effect of pH on Zn detection was also investigated. As shown in
Figure 4, the fluorescence intensity of 1 was independent on the pH of
the solution, which was due to the protonation of 1 in its pyridine unit.
In contrast, for 1–Zn complex, the fluorescence intensity reached a
maximum at neutral pH. The reason could be explained as follows: in
FIGURE 2 Job's plot method for evaluating the stoichiometry of 1–Zn
FIGURE 4 Fluorescence intensity of 1 in the absence and presence of
2+
2+
2+
complex. [1] + [Zn ] = 20 μmol/L. conditions: 99% water/DMSO (v/v)
at pH 7.0 buffered by 10 mmol/L Tris–HCl. Excitation and emission
was at 395 nm and 484 nm, respectively
Zn at different pH. Conditions: [1] = 20 μmol/L, [Zn ] = 20 μmol/L,
99% water/DMSO (v/v) at different pH buffered by 10 mmol/L Tris–
HCl. Excitation and emission was at 395 nm and 484 nm, respectively
2
+
+
+
+
2+
2+
2+
FIGURE 3 Fluorescence intensity of 1 in the presence of different metal ions with or without Zn . Ions: Blank, Li , Na , K , Mg , Ca , Ba
,
2+
3+
2+
2+
2+
+
2+
2+
2+
3+
2+
Mn , Fe , Co , Ni , Cu , Ag , Cd , Hg , Pb , Cr . Conditions: [1] = 20 μmol/L, [M] = 20 μmol/L, [Zn ] = 20 μmol/L, 99% water/DMSO
v/v) at pH 7.0 buffered by 10 mmol/L Tris–HCl. Excitation and emission was at 395 nm and 484 nm, respectively
(

LIU ET AL.
5
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with Zn decreased the fluorescence of 1–Zn. For the sake of achiev-
[
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ing the highest signal‐to‐noise ratio, pH 7.0 was used for Zn detec-
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4
|
CONCLUSION
In conclusion, we have prepared a series of naphthaldehyde‐2‐
SUPPORTING INFORMATION
2+
pyridinehydrazone derivatives fluorescent chemosensors for Zn
Additional Supporting Information may be found online in the
supporting information tab for this article.
detection in aqueous solution at neutral pH. As a sensitive and
2+
selective fluorescent chemosensor for Zn , 1 displayed the detection
2+
limit of 0.17 μmol/L toward Zn with a linear range of 0.6 to
6
.0 μmol/L. Especially, when other physiological relevant metal ions
2+
2+
including Cd existed, 1 also showed excellent selectivity to Zn
.
How to cite this article: Liu Y, Li Y, Feng Q, et al. ‘Turn‐on’
fluorescent chemosensors based on naphthaldehyde‐2‐
pyridinehydrazone compounds for the detection of zinc ion in
water at neutral pH. Luminescence. 2017;1–5. https://doi.org/
10.1002/bio.3368
ACKNOWLEDGEMENT
The authors are very grateful for the financial support from the
National Natural Science Foundation of China (No. 51502079,
2
1501150, 21371155).