Colorimetric and ratiometric sensors derivated from natural building blocks for fluoride ion detection

Article abstract of DOI:10.1016/j.tetlet.2019.151330

Three novel colorimetric and ratiometric probes (SH-1~3) for fluoride ion detection were designed and synthesized from nature small molecules. Obvious yellow-to-orange color change of these probes in the THF was achieved only in presence of F^?

Full text of DOI:10.1016/j.tetlet.2019.151330

Tetrahedron Letters xxx (xxxx) xxx
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Tetrahedron Letters
journal homepage: www.elsevier.com/locate/tetlet
Colorimetric and ratiometric sensors derivated from natural building
blocks for fluoride ion detection
Heng Shi a, Fengfei Zhao a, Xinghan Chen a, Shilong Yang b, Jieni Xing a, Hongjin Chen a, Rui Zhang a,c,
,
⇑
Jian Liu a,c,
*
a College of Chemical Engineering, Jiangsu Key Lab of Biomass-based Green Fuels and Chemicals, Nanjing Forestry University, Nanjing 210037, China
b Advanced Analysis and Testing Center, Nanjing Forestry University, Nanjing 210037, China
c Jiangsu Co-Innovation Center of Efficient Processing and Utilization of Forest Resources, Nanjing Forestry University, Nanjing 210037, China
a r t i c l e i n f o
a b s t r a c t
Article history:
Three novel colorimetric and ratiometric probes (SH-1~3) for fluoride ion detection were designed and
synthesized from nature small molecules. Obvious yellow-to-orange color change of these probes in
the THF was achieved only in presence of FÀ among the eight anions (FÀ, ClÀ, BrÀ, IÀ, H2PO4À, HSOÀ4 ,
CH3COO–, ClOÀ4 ), along with the emission shifting from green to orange red. These three probes are 1:1
complexed with fluoride ions, with complexation constant of around 0.1 Â 104 MÀ1. The detection limit
Received 16 September 2019
Revised 23 October 2019
Accepted 25 October 2019
Available online xxxx
of probes SH-1~3 reached as low as around 1 l
M. 1H NMR titration study suggested that the fluoride ion
Keywords:
induced deprotonation of the probe through hydrogen bonding interaction between amino group of
probe and fluoride ion.
Fluoride ion
Colorimetric
Deprotonation
Flavone
Ó 2019 Elsevier Ltd. All rights reserved.
Introduction
death [22–25]. So far, there are many types of molecular probes
with the recognition mechanisms have been developed, involving
The recognition and detection of ions have been received con-
tinuous attention due to their significance in biological and envi-
ronmental fields [1,2]. Recently, the visual molecular recognition
technology has been considered as a promising tool owing to its
high sensitivity, good selectivity and practical operation, of which
the concept is the change of the color and/or fluorescence of
molecular probe caused by the structure change upon ion sensing
[3,4]. The molecular design strategy of chemosensors should be
dependent on the nature of the target ions [5–8]. Generally, the
development of ratiometric sensors is crucial to improve the sensi-
tivity and selectivity, involving the variations in the ratio of the
intensities of the absorption or the emission peaks [9–18].
Fluoride is one of the essential trace elements in the human
body, which is widely existed in nature in the form of fluorine ions
[19–21]. Deficiency of fluoride in the human body can lead to den-
tal caries, and the lack of fluoride in the elderly can lead to osteo-
porosis. However, excessive intake of fluoride in the human body
can cause fluorosis and urolithiasis, and severe cases can lead to
FÀ-mediated desilylation of Si-O/Si-C bonds, B-F complexation,
FÀ-induced deprotonation through H-bonding, intramolecular
charge transfer, and so on [7,26–40]. Among them, molecular
probes with acylhydrazone skeleton have been demonstrated to
be promising due to their good sensitivity, high selectivity and a
rapid response during the FÀ-induced deprotonation process
[32,41–46].
Flavones are widely found in nature, which have been demon-
strated to be possessing good biocompatibility and received con-
siderable interest in pharmacological field [47,48]. However, only
few molecular sensor has been developed based on flavones [49–
51]. For example, Xu et al. designed a new flavone-based fluores-
cence probe for the detection of Al3+ and HSO3À [49]. Pina-Luis
et al. reported a new fluorescent sensor for Cu2+ detection based
on a flavone functional material [50]. On the other hand, nature
b-phenylacrylic acids, such as erucic acid, caffeic acid and cinnamic
acid, are also frequently used in the synthetic chemistry. We envis-
aged that the potential application of these nature molecules in
molecular engineering of novel ion probes. Herein, we developed
three novel highly selective naked-eye and fluorescent probe for
fluoride ion detection based on functional acylhydrazones, which
was constructed from nature molecules. Specially, b-phenylacrylic
acid derivates (erucic acid, caffeic acid and cinnamic acid) were
easily converted to corresponding acylhydrazines, which were fur-
⇑
Corresponding authors at: College of Chemical Engineering, Jiangsu Key Lab of
Biomass-based Green Fuels and Chemicals, Nanjing Forestry University, Nanjing
210037, China.
E-mail addresses: zhangrui@njfu.edu.cn (R. Zhang), liu.jian@njfu.edu.cn (J. Liu).
https://doi.org/10.1016/j.tetlet.2019.151330
0040-4039/Ó 2019 Elsevier Ltd. All rights reserved.
Please cite this article as: H. Shi, F. Zhao, X. Chen et al., Colorimetric and ratiometric sensors derivated from natural building blocks for fluoride ion detec-
tion, Tetrahedron Letters, https://doi.org/10.1016/j.tetlet.2019.151330

2
H. Shi et al. / Tetrahedron Letters xxx (xxxx) xxx
ther reacted with flavone to prepare the desired acylhydrazone-
type probes SH-1~3 in moderated yield, respectively (Scheme 1).
These novel probes realized fast naked eye recognition of fluoride
ion from yellow to orange in tetrahydrofuran with low detection
limits around 1 lM.
Results and discussion
Naked eye sensing and selectivity of probes SH-1~3
The interactions between probe SH-1~3 and other anions (FÀ,
ClÀ, BrÀ, IÀ, H2PO4À, HSO4À, CH3COO–, ClOÀ4 ) were firstly checked
by naked eye and UV–vis absorption upon the addition of 3 equiv
tetrabutyl salt solution (FÀ, ClÀ, BrÀ, IÀ, H2POÀ4 , HSO4À, CH3COO–,
ClOÀ4 ) in THF solutions. As shown in Figs. 1 and S31, with the addi-
tion of fluoride ion salt, the color of the solution of probes in THF
change from pale yellow to orange, along with the obvious
enhancement of the absorption intensity in the peak around
480 nm. However, upon adding same mole amount of the other
ions (ClÀ, BrÀ, IÀ, H2PO4À, HSO4À, CH3COO–, ClOÀ4 ), almost no color
change shown in the solution of probes in THF. The results indi-
cated that the present novel probes SH-1~3 exhibit naked-eye sen-
sitivity and good selectivity for fluoride ion detection.
Fig. 1. The intensity of the maximum absorption peak of probe SH-1 (1 Â 10À4 M)
in the presence of 3 equiv. of various anions in THF at room temperature. (Inset:
Color changes of probe SH-1 with the addition of 3 equiv of various anions under
ambient light.)
1.773 (Fig. 2b), which demonstrated that SH-1 can serve as a ratio-
metric sensor for FÀ [52]. Moreover, we also investigated the prop-
erties of compound SH-2 and SH-3 by the same way
(Figs. S32~S35). The results indicated that both SH-2 and SH-3 pos-
sessing similar sensing behavior for FÀ with SH-1, which revealed
that the successful design of probes from b -phenylacrylic acid
derivates and flavone.
UV–vis absorbance of probe SH-1 studies in THF
In order to further investigate the effect of fluoride ion concen-
tration on the absorption spectra of these probes SH-1~3 solution,
UV–vis absorption titration test was performed. As shown in
Fig. 2a, with the adding amount of fluoride ion increasing, the
intensity of the maximum absorbance peaks of pristine probe
SH-1 in the UV region around 370 nm decreased, while a new
absorption band in visible region around 480 nm appeared and
its intensity was enhanced gradually. When 3 equiv. of fluoride
ion was added, the intensity of new absorption peak in visible
region reached the maxima, which suggested that the absorbance
reached the saturated value (Fig. S32a). As a result, a naked-eye
color of the probe SH-1 in THF changed from yellow to dark orange
upon FÀ sensing, while a weak fluorescence from green to orange
was observed (Fig. S33) under 365 nm UV irradiation. When the
To determine the stoichiometric ratio of the present probes SH-
1~3 with fluoride ion, Job-plots of these probes with fluoride ion in
THF were calculated from the continuous variation of the intensity
of the absorption band during the titration process, respectively
(Figs. 3a and S36). The results showed the maxima at 0.5 of [FÀ]/
([FÀ] + [probes]), which suggested that the formation of a complex
with a 1:1 stoichiometric ratio between probe SH-1~3 and FÀ dur-
ing the initial stage of the reaction, respectively. We also calculated
Benesi-Hildebrand equations of these probes. As shown in Fig. 3b
and Fig. S37, the measured absorbance [1/(A À A0)] at 480 nm
showed
a
linear relationship with the concentration of FÀ
(R = 0.998 for SH-1, R = 0.998 for SH-2 and R = 0.990 for SH-3),
concentration of fluoride ion increased from 0 to 300
lmol/L, the
which further indicated the 1:1 stoichiometry between FÀ and
absorbance ratio (A480nm/A350nm) increased linearly from 0.008 to
Scheme 1. Synthetic route of probes SH-1~3.
Please cite this article as: H. Shi, F. Zhao, X. Chen et al., Colorimetric and ratiometric sensors derivated from natural building blocks for fluoride ion detec-
tion, Tetrahedron Letters, https://doi.org/10.1016/j.tetlet.2019.151330

H. Shi et al. / Tetrahedron Letters xxx (xxxx) xxx
3
Fig. 2. a) Absorbance spectra of probe SH-1 (10À4 M) in THF in the presence of different concentration of FÀ (0 ~ 3 eq); b) Plot of A480nm/A350nm versus [FÀ].
Fig. 3. a) Benesi-Hilderbrand plot of probe SH-1 with FÀ, b) UV–vis titration and calculation of banding constant of probe SH-1 for FÀ, c) Absorbance of probe SH-1 in the
presence of FÀ (from TBAF) at various concentrations in THF, d) The response time of probe SH-1.
these probes, respectively. The corresponding association con-
stants between probes and FÀ were 0.12 Â 104 MÀ1 for SH-1,
0.066 Â 104 MÀ1 for SH-2 and 0.18 Â 104 MÀ1 for SH-3, respec-
We also investigated the influence of the water content on the
sensing effect of these three probes. As shown in Figs. 4 and S41,
with increasing the content of water in THF, the intensity of the
absorption bands around 480 nm of probes SH-1~3 in the presence
of 3 eq TBAF decreased gradually, respectively. When the content
of water increased over 1%, the absorption bands around 480 nm
of these samples disappeared, which suggested that the present
sensors SH-1~3 are not effective for the FÀ detection under high
tively. The limit of detection was calculated to be 0.91
lM for
SH-1, 1.39 lM for SH-2 and 0.84 lM for SH-3, respectively
(Figs. 3c and S38). Furthermore, probes SH-1~3 possessed good sta-
bility in THF (Fig. S39) and exhibited transient response to FÀ sens-
ing (Figs. 3d and S40).
Please cite this article as: H. Shi, F. Zhao, X. Chen et al., Colorimetric and ratiometric sensors derivated from natural building blocks for fluoride ion detec-
tion, Tetrahedron Letters, https://doi.org/10.1016/j.tetlet.2019.151330

4
H. Shi et al. / Tetrahedron Letters xxx (xxxx) xxx
which implied that the probe SH-1 would be deprotonated at
higher fluoride ion concentration. Hence, the result of 1H NMR
titrations proposed a similar mechanism with those probes with
acylhydrazone backbone reported previously [44].
Conclusion
In summary, we have developed three novel new colorimetric
and ratiometric sensors based on natural small molecules for fluo-
ride ion detection. Probes SH-1, SH-2 and SH-3 showed good sen-
sitivity and high selectivity to FÀ with naked-eyes color change
from yellow to orange, as well as weak fluorescence from green
to orange under 365 nm irradiations. Moreover, all these three
probes possessed good stability in THF and showed transient
response to FÀ sensing, with low detection limit around 1
lM. This
work provide enlightenment for further molecular design of ion
probes by natural molecules. The biocompatibility of these probes
will be expected and studied systematically in our future work.
Fig. 4. Absorbance spectra of probe SH-1 in the presence of 3 eq FÀ in THF with
various content of water.
Declaration of interests
The authors declare that they have no known competing finan-
cial interests or personal relationships that could have appeared to
influence the work reported in this paper.
water content. The phenomena was similar with other acylhydra-
zone-type sensors reported previously [41].
1H NMR titration experiments
Acknowledgements
To gain further insight into the interaction between these
probes and FÀ, we carried out 1H NMR titration experiments in
THF-d8 solution with varied amount of FÀ anion (0, 0.1, 1 equiv)
by employing the sample of SH-1 with sufficient solubility. As
shown in Fig. 5, the signal peak of NAH proton at 11.04 ppm
decreased and broadened upon addition of 0.1 equiv of TBAF4,
which suggested the complexation between amino proton of SH-
1 and fluoride at low con centration, probably due to the hydrogen
bond interactions. With further increase the concentration of
TBAF4, the resonance signal of the NAH active proton disappeared,
This work was supported in part by the Natural Science Founda-
tion of Jiangsu Province (BK20191385), the National Natural
Science Foundation of China (201502088 and 21631006) and the
High Level Talent Project of Nanjing Forestry University
(GXL2018003).
Appendix A. Supplementary data
Supplementary data to this article can be found online at
https://doi.org/10.1016/j.tetlet.2019.151330.
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Please cite this article as: H. Shi, F. Zhao, X. Chen et al., Colorimetric and ratiometric sensors derivated from natural building blocks for fluoride ion detec-
tion, Tetrahedron Letters, https://doi.org/10.1016/j.tetlet.2019.151330