Y.-P. Zhang et al.
Inorganic Chemistry Communications 130 (2021) 108735
heterocyclic compounds which has rigid flat structure but only an
unsaturation degree of two [40], has higher hole-transport efficiency,
good membrane permeability and low toxicity. Therefore, pyrazoline
derivatives have widely been used as whitening or brightening reagents
for synthetic fibers, hole-transport materials in the electrophotography
[41], electroluminescence fields and fluorescent chemosensors for
recognition of metal ions [42,43]. Moreover, the pyrazoline fluorescent
probe has practical application in cell imaging [44,45]. Herein, we
report a fluorescent probe that is based on pyrazoline, which could
function as a “turn-on” fluorescent chemosensor for Zn2+ and Cd2+ ions
in ethanol aqueous and successful applications to imaging in living cells.
Probe 1 was characterized by 1H NMR, 13C NMR and ESI-MS. The se-
lective chemosensor properties of probe 1 for different metal ions (Na+,
Ca2+, Al3+, Cu2+, Li+, Cd2+, Fe3+, Fe2+, Bi3+, Zn2+, Co2+, Ni2+, Ba2+
,
Ag+, Mn2+, Pb2+ and Hg2+ ions (15 equiv.). It was exciting to observe
that among the tested metal ions, Cu2+, Ag+, Zn2+, Cd2+, Hg2+ and Fe3+
induced certain characteristic changes in the absorbance spectra of
probe 1. In the case of Cu2+, Zn2+ and Cd2+ ions the addition of metal
ions caused a decrease of absorption intensity to some extent at 335 nm,
accompanied by a new absorption peak that appeared obvious at the
range of 380 nm. Furthermore, in the case of Fe3+, Ag+ and Hg2+ the
addition of metal ions caused a considerable change of absorption in-
tensity to some extent at 307 nm and 335 nm.
To investigate the binding property of probe 1 toward Zn2+ and
Cd2+, the absorption spectra titration experiment was further carried
out (Fig. 1). The absorbance of probe 1 at 335 nm gradually decreases
with an increasing concentration of Zn2+ ion. Moreover, a new ab-
sorption peak appears at the range of 358–430 nm and its absorption
intensity gradually increases with the addition of Zn2+ ion. Simulta-
neously, an isosbestic point was observed at 358 nm, which indicates the
formation of a coordination complex between 1–Zn2+. Similarly, upon
the addition of increasing concentration of Cd2+ to the buffered solution
of probe 1, absorbance at 335 nm gradually decreased and a new ab-
sorption band at 358–430 nm, its absorption intensity gradually in-
creases, which indicate a complex 1–Cd2+ formed. The absorption of
probe 1 at 395 nm increases with the increase of Zn2+ / Cd2+ concen-
tration. There is a good linear relationship between the absorption value
at 395 nm and the concentration of Zn2+ / Cd2+ (0–15 equiv.) (Fig. S3).
Mg2+, K+, Ca2+, Al3+, Cu2+, Li+, Cd2+, Fe3+, Fe2+, Bi3+, Zn2+, Co2+
Ni2+, Ba2+, Ag+, Mn2+, Pb2+ and Hg2+) were investigated in detail.
,
2. 2.Results and discussion
2.1. Synthesis of the probe 1
Synthesis of 5-(4-(dimethylamino)phenyl)-3-(2-hydroxyphenyl)-4,5-
dihydro-1H-pyrazole-1-carbothioamide (probe 1).
The general synthetic route of probe 1 is given in Scheme 1. Probe 1
was obtained in 76% yield by the reaction of chalcone 2 with thio-
semicarbazide 5 at reflux condition in the ethanol. The crude product
was filtrated and recrystallized with ethanol to afford probe 1.The
structure of probe 1 was confirmed by 1H NMR, 13C NMR,ESI-MS
(supporting information).
2.4. Selectivity studies
Selectivity is a very important parameter to detect the performance
of a new fluorescent probe. The optical properties of probe 1 induced by
metal ions were studied in EtOH-H2O solution (10.0 mM HEPES, pH 7.4,
EtOH-H2O = 1:1 (v/v)) at room temperature. Fig. 2 showed the fluo-
2.2. Spectral studies for the solvent effects toward 1 and 1-Zn2+/Cd2+
.
The solvents play significant roles in the optical properties of 1 and
its binding ability with different metal ions. Therefore, corresponding
fluorescence spectra tests for various solvents were conducted. As shown
in Fig. S1, take Zn2+ as an example, upon the addition of 15.0 equiv. In
addition to MeOH and DMF, Zn2+ ions created significant fluorescence
enhancement in EtOH, ACM, DMSO and THF solutions with a dramat-
ically bathochromic shift effect. However, the fluorescence intensity of
ethanol increased the highest and its toxicity was the lowest compared
with other solvents. Therefore, EtOH would be the suitable solvent for
the comprehension of the sensitive, selective and binding properties of
rescence spectra changes (excited at 380 nm) stimulated by Na+, Mg2+
K+, Ca2+, Al3+, Cu2+, Li+, Cd2+, Fe3+, Fe2+, Bi3+, Zn2+, Co2+, Ni2+
,
,
Ba2+, Ag+, Mn2+, Pb2+ and Hg2+ ions (15.0 equiv.). The probe showed a
weak emission at 441 nm when excited at 380 nm. However, unlike the
UV–Vis spectra, the fluorescence of probe 1 exhibited obvious changes
only induced by Cd2+ and Zn2+. When Zn2+ was added, the emission
intensity of probe 1 was enhanced obviously (10-fold) and the emission
peak red-shifted from 441 nm to 469 nm. Upon addition of Cd2+ to the
solution of probe 1, the fluorescence intensity was also enhanced
evidently (8-fold). Similarly, the emission peak is red-shifted from 441
nm to 469 nm. All above-mentioned changes may be attributed to the
formation of the 1-Zn2+ and 1-Cd2+ complexes. All these experiments
indicated that probe 1 could serve as a fluorescence probe to selectively
detect Cd2+ and Zn2+ from other metal ions in EtOH-H2O solution (10.0
mM HEPES, pH 7.4, EtOH-H2O = 1:1 (v/v)).
probe 1 with Zn2+ and Cd2+
.
2.3. UV–vis absorption studies
Selective detection of probe 1 was done by using UV– visible ab-
sorption spectrum in EtOH-H2O (10 mM HEPES, pH 7.4, EtOH-H2O =
1:1 (v/v)) solution. The absorption spectrum of probe 1 showed a strong
absorption at 335 nm and a small hump at 307 nm (Figure. S2). The
probe 1 was treated with various metal ions including Na+, Mg2+, K+,
To further understand the reason for these interesting red-shifted
fluorescence intensity enhancements, subsequent fluorescence titration
experiments with Zn2+ ions (Figure. S4a) and Cd2+ ions (Figure. S4b)
Scheme 1. Synthesis of probe 1.
2