Mercaptooxazole-phenazine based blue fluorescent sensor for the ultra-sensitive detection of mercury(II) ions in aqueous solution

Article abstract of DOI:10.1039/c7ra07992c

Herein, a mercury(ii) ion fluorescent sensor (Z-3) with high sensitivity and immediate response is designed and synthesized. The sensor uses the phenazine group as a luminophore and sulfhydryl as a recognition moiety. The sensor is easily synthesized and it exhibits a remarkable blue shift with Hg²⁺. Correspondingly, its fluorescence color changes from yellow to blue. In addition, the low naked eye detection limit (10^-5) of the sensor allows the identification of concentration limits. Moreover, the sensor could detect mercury(ii) ions over a wide pH range (from 2 to 8), which indicates that the detection can be carried out in aqueous systems. In addition, test strips are fabricated, which could act as a convenient pathway for the recognition of Hg²⁺.

Full text of DOI:10.1039/c7ra07992c

RSC Advances
View Article Online
View Journal | View Issue
PAPER
Mercaptooxazole–phenazine based blue
fluorescent sensor for the ultra-sensitive detection
of mercury(II) ions in aqueous solution†
Cite this: RSC Adv., 2017, 7, 47547
Hai-Li Zhang, Wen-Ting Li, Wen-Juan Qu, Tai-Bao Wei, * Qi Lin,
You-Ming Zhang * and Hong Yao
*
Herein, a mercury(II) ion fluorescent sensor (Z-3) with high sensitivity and immediate response is designed
and synthesized. The sensor uses the phenazine group as a luminophore and sulfhydryl as a recognition
2+
moiety. The sensor is easily synthesized and it exhibits
a remarkable blue shift with Hg .
Correspondingly, its fluorescence color changes from yellow to blue. In addition, the low naked eye
Received 20th July 2017
Accepted 25th September 2017
ꢀ5
detection limit (10 ) of the sensor allows the identification of concentration limits. Moreover, the sensor
could detect mercury(II) ions over a wide pH range (from 2 to 8), which indicates that the detection can
DOI: 10.1039/c7ra07992c
be carried out in aqueous systems. In addition, test strips are fabricated, which could act as a convenient
2+
rsc.li/rsc-advances
pathway for the recognition of Hg .
Among the reported sensors, phenazine and its derivatives
have been widely employed in the design of uorescent sensors
Introduction
Mercury plays an important role in electrical and chemical due to their stable optical properties, easy synthesis, cheap raw
1
–3
30–32
applications. Its electrical applications include thermome- materials and large conjugate systems.
They act as an
ters, barometers, sphygmomanometers and other related important skeleton in uorescence sensors used to identify
33–35
instruments. In the chemical industry, mercury is used to amino acids, citrate and other ions.
electrolyze a salt for the preparation of high purity chlorine and
According to these superior properties and our goals, we
However, excessive consumption of mercury designed and synthesized phenazine derivative Z-3
can lead to irreversible damage to the environment and human (Scheme 1), which could rapidly select Hg in aqueous solu-
36
4–11
caustic soda.
a
2
+
1
2–15
body.
cause vital organ dysfunction such as DNA damage, mitosis sensor could detect Hg with blue uorescence in a wide pH
As a toxic metal, mercury and its compound could tions. Based on its deprotonation mechanism, the uorescent
2
+
16
ꢀ
9
17
18
impairment, and nervous system defects. The emission of range (from 2–8). It also exhibits high selectivity (2.14 ꢁ 10 M)
mercury ions has been increasing due to the full speed devel- and other common metal ions have nearly no inuence on its
19,20
opment of the mercury industry.
body through the food chain and accumulate gradually, which limits are 10 and 10 for solution and test strips, respec-
Mercury ions enter the sensing behavior. Moreover, its naked eye minimum detection
ꢀ
5
ꢀ4
directly affects the safety of human life. To date, many sensors tively, which greatly improve the practicality of this sensor.
2
+
have been reported for the detection of Hg . However, some Moreover, the test strips also can act as a reliable means for the
2
+
sensors are made by complex synthesis processes and expensive detection of Hg in real-time.
21–24
raw materials or are difficult to synthesize,
and thus their
Fluorescence spectra were measured with different metal
practical applications are limited in certain aspects. Due to their ions in DMSO/H
rapid testing, strong practicality and easy operation, colori- As shown in Fig. 1a, the addition of Hg induced a distinct
metric and uorescent sensors are the best choice for the
2
O (v/v, 3 : 2, buffered with HEPES, pH ¼ 7.20).
2+
detection of mercury(II) ions in physiological and environ-
25–29
mental samples.
Key Laboratory of Eco-Environment-Related Polymer Materials, Ministry of Education
of China, Key Laboratory of Polymer Materials of Gansu Province, College of Chemistry
and Chemical Engineering, Northwest Normal University, Lanzhou, Gansu, 730070, P.
R. China. E-mail: weitaibao@126.com; zhangnwnu@126.com
†
Electronic supplementary information (ESI) available: Experimental details,
synthesis of M2, NMR spectra, and other materials. See DOI: 10.1039/c7ra07992c
Scheme 1 Synthesis of compound Z-3.
This journal is © The Royal Society of Chemistry 2017
RSC Adv., 2017, 7, 47547–47551 | 47547

View Article Online
RSC Advances
Paper
Fig. 1 (a) Fluorescence spectra (lex ¼ 400 nm) of Z-3 (2 ꢁ 10–5 M)
3
+
2+
+
2+
2+
2+
2+
2+
with different metal ions: Fe , Hg , Ag , Ca , Cu , Co , Ni , Cd
,
2+
2+
3+
2+
Pb , Zn , Cr and Mg (10 equiv., respectively) in DMSO/H
: 2; buffered with HEPES, pH ¼ 7.20). (b) Visual fluorescence emis-
sion of the Z-3 sensor upon the addition of different metal ions.
2
O (v/v,
3

uorescence enhancement with an obvious blue-shi (from 544
to 496 nm). Moreover, the uorescence color of the solutions
changed from yellow to blue under illumination with a 365 nm Fig. 2 (a) Fluorescence spectra of Z-3 and Z-3 + Hg in the presence
O (v/v, 3 : 2; buffered with
2+
UV lamp (Fig. 1b). We speculated that the sensor complexed of 10 equiv. various metal ions in DMSO/H
2
2+
2
+
HEPES, pH ¼ 7.20) solutions; (b) error bar of Z-3 + Hg in the pres-
with Hg , which resulted in the uorescence colour change. All
ence of various cations.
these facts indicate that the sensor could be used for the
2
+
selective identication of Hg among other cations.
The most important aspect of selective recognition is that
the target analyte is detected over other possible interfering
metal ions, and thus a competition experiment was carried out.
In Fig. 2a and b, in the presence of other metal ions, such as
8
, while the uorescence intensity increases obviously at pH > 8,
which may result from the fact that too high pH will result in
a reaction between Hg and –OH to form the corresponding
metal hydroxides. This fact indicates that the sensor could be
used in a wide pH range from 2 to 8 for the detection of Hg .
2
+
3
+
+
2+
2+
2+
2+
2+
2+
2+
3+
2+
Fe , Ag , Ca , Cu , Co , Ni , Cd , Pb , Zn , Cr and Mg ,
there was no evident uorescence emission peak shi and color
change. Therefore, it is clear that the interference of other ions
2
+
2
+
is negligible during the detection of Hg . These results further
2
+
suggest that Z-3 has a strong ability to complex with Hg over
2
+
other metal ions and could be used as a sensor for Hg over
a wide range of cations.
We also performed a uorescence titration to verify the
recognition behavior sensitivity (Fig. 3). In the uorescence
2
+
spectrum, upon the addition of Hg to Z-3, the emission peak
gradually blue shied from 544 nm to 496 nm with a uores-
cence color change from yellow to blue. The detection of Z-3 for
2
+
Hg calculated on the basis of 3s/m for the uorescence spectra
ꢀ
9
37
(
Fig. S5†) is 2.14 ꢁ 10 M, which is lower than the EPA
38
guideline of 10 nM. This result also shows that Z-3 has higher
2
+
2+
sensitivity for Hg compared with other reported Hg sensors
Table 1).
In order to improve the actual operating performance of the
detection behavior, we studied the pH scope of Z-3 + Hg and
fabricated comparison test strips. As shown in Fig. 4, Z-3 with
(
Fig. 3 Fluorescence spectra of Z-3 with different concentrations of
2
+
2+
Hg in DMSO/H
solutions. Insert: plot of fluorescence intensity vs. concentration of
2
O (v/v, 3 : 2; buffered with HEPES, pH ¼ 7.20)
2
+
2+
Hg exhibits strong uorescence intensity in the pH range of 2– Hg in the range of 0 to 63.06 equiv. (lex ¼ 400 nm).
47548 | RSC Adv., 2017, 7, 47547–47551
This journal is © The Royal Society of Chemistry 2017

View Article Online
Paper
RSC Advances
2+
Table 1 A comparison of the detection limits for Hg
Method
Analyte
Solvent
Detection limit
2+
2+
2+
2+
2+
ꢀ8
ꢀ7
Ref. 39
Ref. 40
Ref. 41
Ref. 42
Our work
Hg
Hg
Hg
Hg
Hg
1-Propanol-cyclohexane
1.7 ꢁ 10
2.1 ꢁ 10
M
M
MeOH–H
THF-HEPES
CH CN–H
DMSO–HEPES
2
O
ꢀ8
ꢀ8
8 ꢁ 10
9 ꢁ 10
M
3
2
O
M
ꢀ8
2.14 ꢁ 10
M
Fig. 6 Naked-eyes detection limit under UV lamp at 365 nm.from left
2+
ꢀ1
ꢀ2
ꢀ3
ꢀ4
to right, the concentration of Hg is 10 M, 10 M, 10 M, 10 M,
ꢀ ꢀ6
5
1
0
M, 10 and 0 M.
–
SH. Based on these facts, we believe that Z-3 has two tautomers
of thioketone (]S) and thiols (–SH), and the structure of thione
1
(
]S) is the main form in solution. From the H NMR titration
(
Fig. 7), the peak at 14.41 ppm disappeared with the addition of
2
+
Hg , which suggests that the complexation occurred aer the
NH proton was fully deprotonated. Amazingly, the solution
–
precipitated solid on the addition of 0.2 equivalents of mercury
ions. We speculate that it may be from the perchlorate, and its
+
ꢀ
4
. In addition, we also
molecular formula may be [Z-3 + Hg] ClO
carried out an IR experiment on the solid of Z-3 and Z-3 + Hg .
Fig. 4 Fluorescence intensity (lex ¼ 400 nm and lem ¼ 496 nm) of the
2+
2+
Z-3 + Hg complex at various pH values in DMSO/H
2
O (v/v, 3 : 2;
ꢀ
1
As shown in Fig. S3,† the peak at 2675 cm , which was
recognized as the characteristic peak of –SH, disappeared upon
the addition of Hg . All these results indicate that the mercury
ions coordinated with the sulfur atom and nitrogen atom on the
oxazole ring aer the protonation of the sensor.
buffered with HEPES, pH ¼ 7.20) solution.
2
+
Test strips were prepared by immersing lter paper into
ꢀ
4
a DMSO solution of Z-3 (2 ꢁ 10 M) and then drying them in
2
+
air. The test strips containing Z-3 were utilized to sense Hg . As
shown in Fig. 5, with a decrease in the Hg concentration, the
Moreover, in order to clarify the stoichiometric relationship
between Hg and Z-3, the Job plot was obtained. As shown in
2
+
2+
test paper uorescence color gradually becomes yellow. The
Fig. 8, the uorescence intensity at 496 nm was plotted against
molar fraction of Z-3 sensor. The maximum emission intensity
was reached when the molar fraction was 0.4. This result
ꢀ
4
minimum identication limit of the test strips is 10
M.
Moreover, the test strips could act as a convenient method for
2
+
the detection of Hg in an aqueous solution. We also con-
ducted the experiments with the minimum detection limit with
respect to naked eyes. As shown in Fig. 6, when the concen-
2+
manifests a 1 : 1 ratio for the Z-3 + Hg complex.
Based on all these facts, we propose a reasonable mechanism
2+
for the detection of Hg by the sensor in an aqueous solution
2
+
ꢀ6
tration of Hg is 10 M, the uorescence color of the solution
is consistent with the sensor (Z-3). We thought that the lowest
(
Fig. 9). We hypothesize that the thiocarbonyl and secondary
2+
amine nitrogen of the oxazole motif coordinate with Hg , and
then the complex and perchloric acid form a salt and
precipitate.
2
+
ꢀ5
detection limit of Hg was 10 M.
In order to study the combination of mercury ions(II) with Z-
3
, we rst studied the isomerization of Z-3. As shown in Fig. S1,†
1
the peak at 14.41 ppm is ascribed to the –NH proton in the H
NMR spectrum. Moreover, we also observed a peak at 2675 cm
in the IR spectrum (Fig. S2†), which is the characteristic peak of
ꢀ1
2+
Fig. 5 Photographs of test strips (the concentration of Hg is 0 M,
ꢀ
1
ꢀ2
ꢀ3
ꢀ4
ꢀ5
1
3
0
6
M, 10 M, 10 M, 10 M, 10 M, both under an UV lamp at Fig. 7 Partial 1H NMR spectra of Z-3 in DMSO-d with different
2+
65 nm).
concentrations of Hg .
This journal is © The Royal Society of Chemistry 2017
RSC Adv., 2017, 7, 47547–47551 | 47549

View Article Online
RSC Advances
Paper
3
D. G. Streets, M. K. Devane, Z. Lu, T. C. Bond,
E. M. Sunderland and D. J. Jacob, Environ. Sci. Technol.,
2011, 45, 10485.
4
5
6
7
8
L. Wang, J. Jin, L. Zhao, H. Shen, C. Shen and P. Zhang,
Carbohydrate Research, 2016, 433, 41.
K. P. Carter, A. M. Young and A. E. Palmer, Chem. Rev., 2014,
114, 4564.
J. Kuchlyan, S. Basak, D. Dutta, A. K. Das and D. Ma, Chem.
Phys. Lett., 2017, 673, 84.
T. Yu, T. T. Zhang, W. Zhao, J. J. Xu and H. Y. Chen, Talanta,
2017, 165, 570.
N. Busschaert, C. Caltagirone, W. V. Rossom and P. A. Gale,
Chem. Rev., 2015, 115, 8038.
9 C. T. Driscoll, R. P. Mason, H. M. Chan, D. J. Jacob and
2+
Fig. 8 Job plot examining the relationship between Z-3 and Hg
.
N. Pirrone, Environ. Sci. Technol., 2013, 47, 4967.
10 H. H. Wang, L. Xue, C. L. Yu, Y. Y. Qian and H. Jiang, Dyes
Pigm., 2011, 91, 350.
1
1 (a) L. Campbell, D. G. Dixon and R. E. Hecky, J. Toxicol.
Environ. Health, Part B, 2003, 6, 325; (b) Q. Ye, F. Yan,
Y. Luo, Y. Wang, X. Zhou and L. Chen, Spectrochim. Acta,
Part A, 2017, 173, 854; (c) C. Jiang, Z. Guan, S. Y. Rachel
Lim, L. Polavarapu and Q. H. Xu, Nanoscale, 2011, 3, 3316;
(
d) Y. Chen, L. Wu, Y. Chen, N. Bi, X. Zheng, H. Qi and
M. Qin, Microchim. Acta, 2012, 177, 341.
2
+
Fig. 9 Possible binding mode of Z-3 with Hg
.
12 (a) Y. Li, H. Huang, Y. Li, X. Su, Y. Li, H. Huang, Y. Li and
X. Su, Sens. Actuators, B, 2013, 188, 772; (b) W. Ren, C. Zhu
and E. Wang, Nanoscale, 2012, 4, 5902; (c) E. O. Ganbold,
J. H. Park, K. S. Ock and S. W. Joo, Bull. Korean Chem. Soc.,
2011, 32, 519.
In conclusion, we obtained a uorescent sensor Z-3 via
2
+
a simple method for the detection of Hg , which displays high
selectivity and sensitivity in the recognition process. The sensor 13 C. Chen, R. Wang, L. Guo, N. Fu, H. Dong and Y. Yuan, Org.
exhibits an obvious uorescence colour change from yellow to
Lett., 2011, 13, 1162.
blue, and its detection behaviour operates in a wide pH range. 14 H. H. Harris, I. J. Pickering and G. N. George, Science, 2003,
Moreover, its test strips and naked-eyes minimum detection
301.
limit greatly improve the practicality of Z-3. Hence, this study 15 P. B. Tchounwou, W. K. Ayensu, N. Ninashvili and D. Sutton,
also implies that phenazine and its derivatives are potential
candidates for the detection of ions.
Environ. Toxicol., 2003, 18, 149.
16 C. Wu, J. Wang, J. Shen, C. Bi and H. Zhou, Sens. Actuators, B,
2017, 243, 678.
1
1
1
2
7 I. Samb, J. Bell, P. Y. Toullec, V. Michelet and I. Leray, Org.
Lett., 2011, 13, 1182.
8 Y. Ding, W. Zhu, Y. Xu and X. Qian, Sens. Actuators, B, 2015,
Conflicts of interest
There are no conicts to declare.
220, 762.
9 X. Ma, J. Wang, Q. L. Shan, Z. W. Tan, G. H. Wei, D. B. Wei
and Y. G. A. Du, Org. Lett., 2012, 14, 820.
Acknowledgements
0 (a) Z. S. Qian, X. Y. Shan, L. J. Chai, J. J. Ma, J. R. Chen and
H. Feng, ACS Appl. Mater. Interfaces, 2014, 6, 6797; (b)
P. F. Wei, D. B. Li, B. B. Shi, Q. Wang and F. Huang, Chem.
Commun., 2015, 51, 15169; (c) C. H. Yao, Y. H. Cao,
Q. Wang, Y. Pan, J. L. Jiang and L. Y. Wang, Chem.
Commun., 2016, 52, 8715; (d) C. Jin, M. Zhang, L. Wu,
Y. F. Guan, Y. Pan, J. L. Jiang, C. Lin and L. Y. Wang,
Chem. Commun., 2013, 49, 2015.
This study was supported by the National Natural Science
Foundation of China (NSFC) (No. 21662031; 21661028;
21574104; 21262032), the Natural Science Foundation of Gansu
Province (1506RJZA273) and the Program for Changjiang
Scholars and Innovative Research Team in University of
Ministry of Education of China (IRT 15R56).
21 X. F. Wu, Q. J. Ma, X. J. Wei, Y. M. Hou and X. Zhu, Sens.
Actuators, B, 2013, 183, 565.
Notes and references
22 Z. Chen, T. Lou, Q. Wu, K. Li, L. Tan and J. Sun, Sens.
Actuators, B, 2015, 221, 36.
1
2
C. Caltagirone and P. A. Gale, Chem. Soc. Rev., 2009, 38, 520.
R. Zare-Dorabei, R. Rahimi, A. Koohi and S. Zargari, RSC
Adv., 2015, 5, 93310.
47550 | RSC Adv., 2017, 7, 47547–47551
This journal is © The Royal Society of Chemistry 2017

View Article Online
Paper
RSC Advances
23 P.
Jarujamrus,
M.
Amatatongchai,
A.
Thima, 32 (a) F. J. Huo, J. Su, Y. Q. Sun, C. X. Yin, J and B. Chao, Chem.
T. Khongrangdee and C. Mongkontong, Spectrochim. Acta,
Part A, 2015, 142, 86.
4 M. Taki, K. Akaoka, S. Iyoshi and Y. Yamamoto, Inorg. Chem.,
Lett., 2010, 39, 738; (b) Y. A. Son, Y. M. Park, S. Y. Park,
C. J. Shin and S. H. Kim, Dyes Pigm., 2007, 73, 76; (c) J. Xu,
S. B. Sun, Q. Li, Y. Yue, Y. D. Li and S. J. Shao, Anal. Chim.
Acta, 2014, 849, 36; (d) F. J. Huo, C. X. Yin, Y. T. Yang,
J. Su, J. B. Chao and D. S. Liu, Anal. Chem., 2012, 84, 2219;
(e) S. Erdemir and O. Kocyigit, Sens. Actuators, B, 2015, 221,
900; (f) C. J. Gao, X. J. Jin, X. H. Yan, P. An, Y. Zhang,
L. L. Liu, H. Tian, W. S. Liu, X. J. Yao and Y. Tang, Sens.
Actuators, B, 2013, 176, 775.
2
2
2
012, 51, 13075.
5 (a) L. Y. Wang, L. H. Zhu and D. Cao, New J. Chem., 2015, 39,
211; (b) X. Y. Hu, X. Wu, Q. Duan, T. Xiao, C. Lin and
7
L. Wang, Org. Lett., 2012, 14, 4826; (c) M. Xue, Y. Yang,
X. Chi, Z. Zhang and F. Huang, Acc. Chem. Res., 2012, 45,
1
2
294; (d) L. Y. Wang, X. G. Chen and D. Cao, RSC Adv.,
016, 6, 96676.
33 X. Zhang, Y. Yan, Y. Hang, J. Wang, J. Hua and H. Tian,
Chem. Commun., 2017, 53, 5760.
2
6 (a) W. Ren, Y. Zhang, H. G. Chen, H. Z. F. Gao, N. B. Li and
H. Q. Luo, Anal. Chem., 2016, 88, 1385; (b) K. Johari, 34 Y. Gao, G. Huang, Z. Ou, Z. Wang, B. Ju, Y. Li, X. Wang and
N. Saman, S. T. Song, S. C. Cheu, H. Kong and H. Mat, S. Yin, New J. Chem., 2015, 39, 8948.
Chemosphere, 2016, 156, 56; (c) S. Sun, X. Y. Hu, D. Chen, 35 (a) P. Y. Gu, Z. Wang and Q. Zhang, J. Mater. Chem., 2016, 4,
J. Shi, Y. Dong, C. Lin, Y. Pan and L. Wang, Polym. Chem.,
013, 4, 2224; (d) Y. Chen, M. He, B. Li, L. Wang, H. Meier
and D. Cao, RSC Adv., 2013, 3, 21405.
7 E. M. Nolan and S. J. Lippard, Chem. Rev., 2008, 108, 3443.
8 D. T. Quang and J. S. Kim, Chem. Rev., 2010, 110, 6280.
7060; (b) J. Li, J. Gao, W. W. Xiong, P. Z. Li, H. Zhang, Y. Zhao
and Q. Zhang, Chem.–Asian J., 2014, 9, 121; (c) J. F. Zhao,
Y. Liu, J. B. Soh, Y. X. Li, R. Ganguly, K. Q. Ye, F. Huo,
L. Huang, A. I. Y. Tok, J. S. C. Loo and Q. Zhang,
Tetrahedron Lett., 2012, 53, 6044.
2
2
2
2
9 C. Zhu, L. Li, F. Fang, J. Chen and Y. Wu, Chem. Lett., 2005, 36 (a) W. T. Li, G. Y. Wu, W. J. Qu, Q. Li, J. C. Lou, Q. Lin, H. Yao,
3
4, 898.
Y. M. Zhang and T. B. Wei, Sens. Actuators, B, 2017, 239, 671;
(b) H. L. Zhang, T. B. Wei, W. T. Li, W. J. Qu, Y. L. Leng,
J. H. Zhang, Q. Lin, Y. M. Zhang and H. Yao, Spectrochim.
Acta, Part A, 2017, 175, 117.
3
0 (a) D. C. Lee, B. Cao, K. Jang and P. M. Forster, J. Mater.
Chem., 2010, 20, 867; (b) V. S. S. Mosali, G. A. Bowmaker,
M. Gerard, P. A. Kilmartin, J. T. Sejdicb and Z. D. Zujovicb,
Polym. Int., 2015, 64, 1135; (c) S. Biradar, Y. Shigemitsu, 37 Analytical Methods Committee, Analyst 1987, 112, 199.
Y. Kubota, K. Funabiki, H. Satoc and M. Matsui, RSC Adv., 38 H. F. Wang and S. P. Wu, Tetrahedron, 2013, 69, 1965.
2
014, 4, 59387; (d) J. F. Zhao, Y. Liu, J. B. Soh, Y. X. Li, 39 N. A. Bumagina, E. V. Antina and D. I. Sozonov, J. Lumin.,
R. Ganguly, K. Q. Ye, F. Huo, L. Huang, A. I. Y. Tok, 2017, 183, 315.
J. S. C. Loo and Q. Zhang, Tetrahedron Lett., 2012, 53, 6044; 40 Y. Lei, H. Li, X. Huang, J. Chen, M. Liu, W. Gao, J. Ding,
(
e) J. Zhao, G. Li, C. Wang, W. Chen, S. C. J. Loo and
D. Lin and H. Wu, Tetrahedron, 2015, 71, 3453.
Q. Zhang, RSC Adv., 2013, 3, 9653.
41 M. Kaur, M. J. Cho and D. H. Choi, Dyes Pigm., 2016, 125, 1.
31 C. J. Tonzola, M. M. Alam, W. Kaminsky and S. A. Jenekhe, J. 42 I. Samb, J. Bell, P. Y. Toullec, V. Michelet and I. Leray, Org.
Am. Chem. Soc., 2003, 125, 13548. Lett., 2011, 13, 1182.
This journal is © The Royal Society of Chemistry 2017
RSC Adv., 2017, 7, 47547–47551 | 47551