Z. Ma et al.
Inorganic Chemistry Communications 130 (2021) 108753
microscope.
probe HgP1 in CH
3
OH/HEPES(10 mM, pH = 7.4, 1/1, v/v) solution
The solvents and reagents used in the experiment are analytically
system was weak between 400 nm and 700 nm, and the fluorescence
2
+
pure, purchased from commercial companies and used directly. The
metal ions used in the analysis experiment are corresponding chloride or
nitrate salts, dissolved in distilled water to prepare a 10 mM stock so-
lution. The probe HgP1 was dissolved in MeOH to prepare 1 mM stock
solution.
emission of the solution system was significantly enhanced when Hg
(10 eq.) was added. However, when 10 eq. of various common metal
+
+
+
2+
2+
2+
2+
2+
4+
2+
2+
ions (K , Na , Li , Ca , Mg , Ba , Zn , Sn , Sn , Fe , Mn ,
2
+
2+
2+
3+
3+
+
2+
2+
Pb , Cu , Co , Fe , Cr , Ag , Ni , Cd ) were added, the fluo-
rescence emission of the solution system did not change significantly.
The above experimental results showed that the probe has good selec-
tivity to Hg2
In order to test potential competition of probe HgP1 towards Hg
detection, the fluorescence emission spectra of the probe recognizes
+
.
2
.2. Synthesis
2
+
Compound QCHO was synthesized by referring to the known liter-
2
+
Hg were measured in the presence of common metal ions and anions.
As shown in Fig. 2, in the presence of other metal ions or anions, the
ature [30]. The detail synthetic steps of probe HgP1 are as follows:
Compound QCHO (352 mg, 1 mmol) and p-toluenesulfonic acid
2
+
fluorescence emission intensity (at 544 nm) of the probe for Hg
recognition is almost the same as that of Hg2 recognition alone. The
results showed that the probe can be used to identify Hg2 under com-
plex conditions, which improves the practical application value of the
probe.
(
17.2 mg, 0.10 mmol) were dissolved in 25 mL anhydrous dichloro-
+
methane solution, and ethyl mercaptan (497 mg, 8 mmol) was added to
the above solution. And the reaction solution was stirred at room tem-
+
2
perature for about 15 h under N atmosphere. After the reaction is
complete, 30 mL saturated NaCl solution was added to the above solu-
tion. Then the organic solvent was separated, and dried over anhydrous
Good detection limit is one of the criteria to check whether a probe
molecule has application value. Fluorescence spectrometer was used to
Na
2 4
SO . The crude product was purified by silica gel chromatography
determine the Hg2 detection limit in CH
+
OH/HEPES (10 mM, pH = 7.4,
M) ex-
OH/HEPES (10 mM, pH =
3
(
petroleum/ ethyl acetate = 15:1, v/v) to get probe HgP1 as a brown
1
1/1, v/v) solution. As shown in Fig. 3A, the single probe (10
hibits weak fluorescence emission in the CH
.4, 1/1, v/v) solution. With the continuous addition of Hg , the
μ
solid (343.5 mg, 75%). H NMR (CDCl
3
, 400 MHz) δ 1.15 (t, J = 7.0 Hz,
H), 2.62 (m, 4H), 5.01 (s, 1H), 7.67 (d, J = 7.6 Hz, 2H), 7.80 (s, 2H),
.12 (t, J = 9.2 Hz, 3H), 8.23 (t, J = 7.8 Hz, 2H), 8.32 (s, 1H), 11.28 (s,
3
6
8
1
1
1
1
2
+
7
1
3
fluorescence emission intensity of the solution system increases
H); C NMR (CDCl , 100 MHz) δ 185.19, 182.61, 156.19, 149.51,
3
continuously, indicating that probe HgP1 is a fluorescence “turn-on”
44.34, 134.48, 133.98, 133.81, 133.33, 133.18, 128.72, 128.67,
probe for the detection of Hg2 . It should be noted that the fluorescence
+
28.07, 127.62, 127.33, 126.52, 125.73, 122.06, 118.06, 52.16, 26.34,
+
+
emission intensity (at 544 nm) of the solution system has a good linear
4.32; HR-ESI-MS calcd for [M + H ] (C26
23 2 2 2
H N O S ): 459.1201,
2
2+
+
relationship (R = 0.990) with the concentration of Hg in the range of
–1.0 M (Fig. 3B). According to the calculation of IUPAC (3sd/k), the
detection limit of Hg by this probe is estimated to 8.2 nM [32], which
found 459.1188 [M + H ].
0
μ
2
+
3
. Results and analysis
2
+
can meet the national requirement of limiting the content of Hg in
food and water, indicating that this probe HgP1 has great application
value in the quality and safety of agricultural products [33].
Probe HgP1 was synthesized in a simple step, and its chemical
structure was verified by 1H NMR, C NMR and HRMS (Fig. S1-S3).
13
In order to further evaluate the effect of different pH of buffer so-
Probe HgP1 showed good solubility in common organic solvents. By
lution on the detection of Hg2 by probe HgP1, fluorescence titration
experiments of buffer solutions with different pH values were carried
out. As shown in the Fig. 4, the fluorescence emission intensity (at 544
+
referring to the previous experimental methods [31], the best recogni-
tion system for Hg2 is CH
+
3
OH/HEPES(10 mM, pH = 7.4, 1/1, v/v)
solution (Fig. S4).
nm) of the single probe (10
μ
M) is very low and stable between pH 4 and
M), the solution system exhibits strong
. In the presence of Hg2 (100
+
μ
9
3
.1. Fluorescence spectra
Specific selectivity is an important factor to evaluate the efficiency of
fluorescence emission at pH 4–8, indicating that the probe can be used to
identify Hg2 under physiological conditions. The result of kinetic ex-
periments shows that the fluorescence emission of the solution reaches
the maximum value in about 400 s (Fig. S5), which further indicates that
+
fluorescent probe molecules. Firstly, the selectivity of probe HgP1 to-
wards various metal ions was investigated by fluorescence spectrometer.
As shown in Fig. 1, the fluorescence emission intensity of the single
2+
the probe has a rapid recognition effect on Hg . Comparing with the
fluorescent probes based on desulfurization reaction mechanism for the
detection of Hg2 listed in Table S1, the probe HgP1 demonstrates
moderate advantages in the aspects of detection limit, recognition time,
recognition system and application field, which provides a new choice
+
for the detection of Hg2
+
.
3
.2. Mechanism
The above results showed that the probe HgP1 has good recognition
performance for Hg2 , and we further studied the mechanism of
+
detection. Based on the addition of EDTA, the reversible recognition
experiment of Hg2 was investigated (Fig. S6). When excess EDTA was
+
added to the HgP1-Hg2 solution, the fluorescence emission spectrum
+
2
+
was almost the same as the HgP1-Hg solution, which indicates that
the coordination of HgP1 with Hg2 is chemically nonreversible.
+
1
H
NMR titration experiment was conducted on probe HgP1 with different
amounts of Hg2 in DMSO‑d
ppm (H
) which assigned to the proton on the –CHO signal appeared
and increased, along with the amounts of Hg increasing. Meanwhile,
the peak at 5.30 ppm (H ), assigned to methine proton of the thioacetal
group in probe HgP1 were gradually decreased and finally disappeared.
+
(shown in Fig. S7). A new peak at 9.65
6
′
1
2
+
Fig. 1. The fluorescence emission spectra of probe HgP1 (10
μ
M) towards
different metal ions (100
μ
3
M) in CH OH/HEPES(10 mM, pH = 7.4, 1/1, v/v)
1
solution (λex = 390 nm).
2