K. Wang et al.
Dyes and Pigments 194 (2021) 109587
Fig. 1. The selective detection of HZ for hydrazine.
hydrazine have been exploited [21–23]. These fluorescent probes con-
nected the fluorophores with the recognition groups, which was
commonly the nucleophilic reaction site. The reported recognition
groups of hydrazine mainly included acetyl [24–28], levulinate [29,30],
2. Experimental section
2.1. Materials and instruments
4
-bromo butyrate [31–33], phthalimide [34–36], aldehyde [37], cyano
The chemicals reagents were commercially acquired from Aladdin
Reagents. Chromatographic purification was performed using 300–400
mesh chromatography silica gel (Haiyang, Qingdao, P.R. China). All
amino acids were obtained from Sigma-Aldrich. The fluorescence
spectra were carried out on Hitachi F-7000 spectrophotometer. UV–vis
spectra recording was conducted on Shimadzu UV-2550 spectrometer.
The NMR spectra were acquired in Bruker DRX-600 and Advance III HD
spectrometer. The Mass spectra were obtained from AB SCIEX Triple-
TOF 4600. The pH detection was carried out with PHS-25 pH-meter
(Shanghai Geotechnical International Trading Co. Ltd., Shanghai, P.R.
China).
group [38,39], and so on. Nevertheless, most of the hydrazine fluores-
cent probes had some disadvantages, such as strong background signal,
negative selectivity, high cytotoxicity, and complex synthesis process.
These disadvantages limited the scope of applications of the probes
greatly, thus much attention has been paid to design fluorescence probes
with better selectivity and higher sensitivity for the detection of hy-
drazine. It is believed that with the continuous improvement of selec-
tivity and sensitivity in future research, the applications of hydrazine
probes in various fields will face new opportunities and challenges.
As far as we know, benzofuranone and its derivatives have attracted
much attention because of their excellent photo-physical properties,
high fluorescence quantum yield, and photo bleaching resistance among
many organic fluorophores. These favorable properties make benzo-
furanone become a powerful platform for the development of fluores-
cent probes for a variety of targets. Herein, we designed and synthesized
a novel fluorescent probe HZ based on benzofuranone for monitoring of
hydrazine (Fig. 1). Compared with other species, HZ had higher selec-
tivity for hydrazine, and it could be used for detecting hydrazine in a
variety of samples. With the addition of hydrazine, the 4-bromo butyrate
group of HZ was replaced by hydrazine nucleophilic substitution into
2.2. Synthesis of compound 1
To a solution of 6-hydroxybenzofuran-3(2H)-one (5 mmol, 0.74 g) in
dry ethanol (10 mL) was added benzaldehyde (5 mmol, 0.53 g) and
sodium hydroxide (10 mmol, 0.4 g). The mixture was refluxed for 5 h
until the starting compound was consumed, as determined by TLC [53,
54]. After completing the reaction, the solution was cooled to room
temperature and acidified to pH = 6.0 with acetic acid. To gain the
precipitate, the ice water was added slowly. Finally, the residue was
filtered, and the crude product was purified by silica gel column chro-
the corresponding hydrazone. Then the electron of the N atom attacked
–
1
the C positive ion in the C
–
O double bond, which affected the distri-
matography to acquire compound 1 (Yield: 0.83 g, 70%). H NMR (600
bution of intramolecular electron density. Finally, the fluorophore of
benzofuranone derivative was formed by cyclization and elimination
reaction. As a result, there were significant changes in the absorption
and fluorescence spectra of HZ. In Table S1, we listed the previously
reported probes for hydrazine and compared the properties including
response time, excitation/emission wavelength, detection limit, and
biological imaging capabilities [3,5,12,19,22–25,33,36,39–52].
Compared with some other hydrazine probes [49], the response time of
HZ was short (<7 min), which was conducive to the rapid detection. In
addition, because of the specificity of the recognition group 4-bromo
butyrate group, HZ had high selectivity for hydrazine among various
species than the ones with other reaction mechanisms [50]. Further-
more, HZ had smaller steric hindrance than other probes [33], so it was
easier to adjust the excitation and emission wavelength due to its flex-
ible structure.
MHz, DMSO‑d
6
) δ 11.26 (s, 1H), 7.96 (d, J = 7.4 Hz, 2H), 7.65 (d, J =
8.4 Hz, 1H), 7.51 (t, J = 7.5 Hz, 2H), 7.44 (t, J = 7.3 Hz, 1H), 6.82 (d, J
1
3
= 1.9 Hz, 1H), 6.81 (s, 1H), 6.74 (dd, J = 8.4, 1.9 Hz, 1H). C NMR
(151 MHz, DMSO) δ 181.94, 168.46, 167.09, 147.85, 132.55, 131.53,
130.12, 129.45, 126.49, 113.57, 113.20, 110.80, 99.12. HRMS (ESI--
TOF) m/z: [M+H]+ Calcd. for C15
10 3
H O 239.0663, Found 239.0699.
2.3. Synthesis of probe HZ
4-dimethylaminopyridine (DMAP) (40 mg, 0.32 mmol), 1-ethyl-3-(3-
dimethylaminopropyl) carbodiimide hydrochloride (EDC⋅HCl) (202 mg,
1.04 mmol) and 4-bromobutyric acid (120 mg, 0.72 mmol) were dis-
solved into 40 mL anhydrous DCM with compound 1 [33,49]. At room
temperature, the mixture was stirred for 16 h. After the reaction
completed, the solvent was removed, and the residue was purified by
In this work, the developed probe, HZ, had a large Stokes Shift
eluting with (PE/EA = 50/1, v/v) to afford probe HZ (Yield: 181 mg,
1
(
>110 nm) and a wide linear range (10–100
μ
M). Besides, HZ had a low
65%). H NMR (600 MHz, DMSO‑d
6
) δ 8.00 (d, J = 7.3 Hz, 2H), 7.87 (d,
proportion of DMSO (1% DMSO), which was more suitable for biological
applications. Meanwhile, the limit of detection (LOD) was determined to
J = 8.3 Hz, 1H), 7.55–7.50 (m, 3H), 7.48 (t, J = 7.3 Hz, 1H), 7.14 (dd, J
= 8.3, 1.9 Hz, 1H), 6.97 (s, 1H), 3.66 (t, J = 6.6 Hz, 2H), 2.82 (t, J = 7.3
1
3
be 0.75
μ
M. Given the above characteristics, we applied the probe to the
Hz, 2H), 2.25–2.17 (m, 2H). C NMR (151 MHz, DMSO) δ 182.90,
170.86, 166.58, 157.82, 147.21, 131.90, 130.67, 129.53, 125.86,
119.11, 118.82, 112.87, 107.83, 34.31, 32.71, 27.91. HRMS (ESI-TOF)
rapid measurement of hydrazine in environmental water samples. In
addition, HZ could penetrate living cells, which enabled us to use the
probe for confocal imaging of hydrazine in MCF-7 cells successfully.
m/z: [M+H]+ Calcd. for C19
4
H15BrO 387.0217, Found 387.0217.
2