2
W. Chen et al. / Journal of Molecular Structure 1207 (2020) 127822
Scheme 1. Synthetic strategy of probe NFOS.
and triethylamine (0.3 mL) were added in CH
ice-water bath. Then, a mixture of 2-thiophenecarbonyl chloride
2
Cl
2
(40 mL) under
The high specificity of the probe is an important parameter for
their potential applications in complex biological systems. The ef-
fects of common biologically relevant species, such as the repre-
(
0.963g, 6.6 mmol) and CH
2
Cl
2
(8 mL) was added drop-wise and
ꢀ
þ þ 2þ 2þ 2þ
sentative cations (Na , K , Ca , Mg , Zn , 100 mM), anions
stirred at 25 C for 4 h. After removing the solvents, the crude
ꢁ
ꢁ
ꢁ
ꢁ
ꢁ
ꢁ
ꢁ
2ꢁ
2ꢁ
2ꢁ ꢁ
4
, SCN , 100 mM),
product was refined by silica gel column chromatography (MeOH:
(HCO
3
, Cl , Br , I , CN , NO
3
, SO
3
, S , SO
2
O
3
1
ꢁ
CH
2
Cl
2
¼ 1:100) to obtain a yellow solid (1.516g, 77.51%).
H
ROS and RNS (H
2
O
2
, O
2
, OCl , NO, 100 mM) and biothiols (Cys, Lys,
NMR(Chloroform-d, 400 MHz):
d
(ppm) 6.96 (dd, J ¼ 8.7, 3.5 Hz,
1.00 mM, GSH, 10.0 mM), on fluorescence spectra/absorption
response of probe NFOS were assessed. As depicted in Fig. 3, a
significant fluorescence/absorption enhancement was observed
1
H), 7.18 (q, J ¼ 4.1 Hz, 4H), 7.25 (dt, J ¼ 12.4, 4.0 Hz, 1H), 7.55 (dd,
J ¼ 8.8, 3.5 Hz, 1H), 7.73 (m, 5H), 7.78 (dt, J ¼ 8.1, 3.6 Hz, 2H), 7.95 (t,
J ¼ 3.7 Hz, 3H), 8.11 (t, J ¼ 3.7 Hz, 1H), 8.18 (d, J ¼ 4.7 Hz, 1H), 8.88
2
only after incubation with H S. Other biologically relevant species
þ
(
C
dd, J ¼ 9.1, 3.5 Hz, 1H). MS (ESI) m/z ¼ 653.0673 [Mþ H] , calc. for
exhibited no notable influence on the fluorescence/absorption of
the solution of the probe at relevant concentrations. Therefore, the
experiment results corroborated that our proposed probe could
þ
28
H
20
N
2
O
6
H
¼ 653.065.
detect H
As shown in Fig. S2, the experimental results indicated that
probe NFOS (10.00 M) could effectively detect H S (20.00 M) in
2
S with excellent selectivity.
3
. Results and discussion
m
2
m
3.1. Optical response towards H
2
S
the pH range between 6.8 and 8.0, which implies its potential for
application in the physiological pH range (pH ¼ 7.4).
To evaluate the reaction between probe NFOS and NaHS (a
standard source of H S), fluorescenc/UVevis spectra were con-
2
ducted in a solution of DMSO-PBS (1/99, v/v, pH 7.4). Firstly, the
time-dependence of fluorescence and absorption response of probe
3.2. Proposed mechanism
NFOS were examined in the presence of 10.0
in Fig. S1, the fluorescence signal (680 nm)/absorbance signal
640 nm) reached a maximum within 10 min. Therefore, subse-
quent experiments were performed after a response time of 10 min.
As shown in Fig. 1, probe NFOS (10.0 M) displayed negligible
fluorescence ( S. After the addition of H
¼ 0.03) without H
30.0 M), 8.1-fold fluorescence enhancement at 680 nm (19.2-fold
enhancement at 640 nm) was observed and the solution emitted
strong red fluorescence with a quantum yield of 0.18. As expected in
Fig. 2, there was a good linearity between fluorescence intensity
2
mM of H S. As shown
The probe contained naphthofluorescein as the signal group and
thiophenecarboxylic ester as the recognition unit. The hydroxyl
group in probe NFOS which was protected by thiophenecarboxylic
ester resulted in weak fluorescence intensity and absorbance of
(
m
F
2
2
S
2
probe NFOS. Upon the treatment with excess H S for 10 min, the
(
m
phenolic hydroxyl group was released, resulting in the recovery of
naphthofluorescein structure, thus the significantly enhancement
of fluorescence/absorption was observed. In order to confirm this
reaction mechanism, the HRMS analysis of the product was
(
680 nm)/absorbance (640 nm) and the concentration of H
range of 2.00e10.0 M with a detection limit of 0.50 M/0.10
N ¼ 3). The regression equation is Y ¼ 20.7Xþ22.4; R ¼ 0.9954
2
S in the
investigated. After incubation of probe NFOS with excess H
2
S, a
m
m
mM (S/
new peak (Fig. S6) was appeared at m/z ¼ 431.1209 (m/z calcd for
2
þ
ꢁ
15 5
[M-H ] C28
H O : 431.0925), which was in accordance with the
2
(
fluorescence intensity)/Y ¼ 0.0553X-0.0171, R ¼ 0.9909 (absorp-
tion). These facts indicated that probe NFOS was able to quantify
S with excellent sensitivity.
exact mass of compound 3 (naphthofluorescein). The results
strongly supported the proposed sensing mechanism depicted in
Scheme 2.
H
2
Fig. 1. Fluorescence spectra/UVevis spectra of probe NFOS (10.0
mM) titrated by H
2
S from 0.0 to 3.0 equiv.
lex ¼ 600 nm.