A selenolactone-based fluorescent chemodosimeter to monitor mecury/methylmercury species in vitro and in vivo

Article abstract of DOI:10.1016/j.tet.2010.04.042

A fluorescent probe based on selenolactone displays unique fluorescence enhancement and UV-vis spectral change for mercury/methylmercury species, which were attributed to deselenation reaction. The value of this system was successfully demonstrated by its use in detecting inorganic mercury/methylmercury species in cells and zebrafish.

Full text of DOI:10.1016/j.tet.2010.04.042

Tetrahedron 66 (2010) 4016e4021
Contents lists available at ScienceDirect
Tetrahedron
journal homepage: www.elsevier.com/locate/tet
A selenolactone-based fluorescent chemodosimeter to monitor
mecury/methylmercury species in vitro and in vivo
a
,
d
,
y
b
,
y
a
a
Xiaoqiang Chen
, Kyung-Hwa Baek , Youngmee Kim , Sung-Jin Kim ,
b,
a,c,
*
Injae Shin *, Juyoung Yoon
Department of Chemistry and Nano Science, Ewha Womans University, Seoul 120-750, Republic of Korea
Center for Biofunctional Molecules, Department of Chemistry, Yonsei University, Seoul 120-749, Republic of Korea
Department of Bioinspired Science, Ewha Womans University, Seoul 120-750, Republic of Korea
State Key Laboratory of Materials-Oriented Chemical Engineering, College of Chemistry and Chemical Engineering, Nanjing University of Technology, Nanjing 210009, China
a
b
c
d
a r t i c l e i n f o
a b s r t r a c t
Article history:
Received 16 March 2010
Received in revised form
A fluorescent probe based on selenolactone displays unique fluorescence enhancement and UVevis
spectral change for mercury/methylmercury species, which were attributed to deselenation reaction. The
value of this system was successfully demonstrated by its use in detecting inorganic mercury/methyl-
mercury species in cells and zebrafish.
9
April 2010
Accepted 10 April 2010
Ó 2010 Elsevier Ltd. All rights reserved.
Keywords:
Fluorescent chemodosimeter
Selenolactone
Rhodamine
Mecury
Methylmercury
1. Introduction
Typical analytical methods, such as atomic absorption spec-
troscopy, cold vapor atomic fluorescence spectrometry, gas
Mercury exists in the environment as inorganic and organic
mercury species. Inorganic mercury is one of the most prevalent
chromatography, and high performance liquid chromatography,
have been employed to monitor mercury species. However,
1
1
toxic metals in the environment, and gains access to the body orally
or dermally. When absorbed in the human body, these species
result in damage to the brain, kidneys, and endocrine system. On
the other hand, inorganic mercury, released into the environment
through a variety of anthropogenic and natural sources, can be
converted to organomercury mainly through methylation by
many of these methods require complicated, multistep sample
preparation, and sophisticated instrumentation. As a conse-
quence, convenient and simple methods based on optical
detection, such as fluorescence or colorimetric changes are
4
preferable. As part of this effort, a variety of fluorescent probes
for the detection of mercury species with ease and high sensi-
2
1,5
aquatic microorganisms. Organic forms of mercury are much more
tivity have recently been exploited. Surprisingly, most of these
toxic than inorganic mercury species since they can readily pass
through biological membranes. Exposure of methylmercury,
probes only sense inorganic mercury ions and chemosensors to
detect methylmercury species are rare.
3
6
a typical organic mercury, to the human body causes cardiovascular
diseases, autoimmune effects, hearing impairment, blindness, and
death. Therefore, the detection of inorganic and organic mercury
species is of great interest in the aspect of both environment and
human health.
Rhodamine derivatives have received increasing attention
in designing chemosensors for metal ions. If rhodamine
7
3
a
derivatives contain a spiro ring system, they are non-fluorescent
and colorless. However, when the spiro rings in rhodamine
derivatives are opened by stimulus, they exhibit strong fluores-
cence emission and a pink color. Owing to the extremely high
affinity between mercury and selenium, we design here a fluo-
rescent chemodosimeter based on rhodamine B selenolactone
for inorganic mercury and methylmercury species. During the
preparation our manuscript, the titled molecular has been
*
Corresponding authors. Tel.: þ82 2 3277 2400; fax: þ82 2 3277 3419 (J.Y.); tel.:
þ82 2 2123 2631; fax: 82 2 364 7050 (I.S.); e-mail addresses: injae@yonsei.ac.kr
(
I.Shin), jyoon@ewha.ac.kr (J.Yoon).
y
8
Equally contributed to this work.
reported as inorganic mercury and silver sensor by Ma et al.
0
040-4020/$ e see front matter Ó 2010 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2010.04.042

X. Chen et al. / Tetrahedron 66 (2010) 4016e4021
4017
However, in our work, we demonstrated the probe can also
detect methylmercury species, and describe its application for
in vitro and in vivo monitoring of inorganic and organic
mercury species.
2
2
. Results and discussion
.1. Synthesis and X-ray crystal structure
The designed fluorescent probe 1 was prepared by reacting
rhodamine
chloroethane under reflux, followed by reaction with selenourea
Fig. 1a). The crude product was purified by silica-gel column
chromatography with CH Cl as eluent to afford 1 in 37% yield.
B
with phosphorous oxychloride in 1,2-di-
(
2
2
The detailed experimental procedures and spectral data are
provided in Experimental section and Supplementary data. The
structure of a probe 1 was also confirmed by X-ray analysis of its
single crystal that was grown in acetonitrile. A unique seleno-
lactone structure was observed as shown in Figure 1b.
Figure. 2. Fluorescence spectra of 1 (10
m
M) with metal ions (100
m
M) in 20 mM
HEPES buffer (pH 7.4, 1% CH CN) (lex¼550 nm).
3
Figure 1. a) Synthesis of a fluorescent probe 1 and (b) its X-ray crystal structure.
D
.2. Optical change of 1with Hg2 and its proposed
mechanism
2þ
2þ
2
of a probe 1 upon the addition of Hg . The Hg concentration-
dependent absorption spectra of 1 at 560 nm indicated that satu-
2
þ
ration reaches after addition of 1 equiv of Hg . Colorless to pink
color change was also observed after treatment of 1 with Hg
(Supplementary data, Fig. S2). The stoichiometry of a binding event
between Hg and 1 was also determined. The results obtained
2
þ
Initially, selective response of 1 to metal ions was examined. For
this study, a probe 1 (10 M) was treated with various metal ions
m
2
þ
3þ
2þ
2þ
2þ
2þ
þ
þ
2þ
2þ
2þ
2þ
(
100
m
M), such as Cu , Ni , Zn , Cd , Co , Cs , Li , Ca , Mn
K , Na , Sr , Fe , Al , Mg , Pb , Fe , Ag , and Hg ions in
,
þ
þ
2þ
2þ
2þ
2þ
3þ
þ
2þ
from Job’s plot show the 1:1 stoichiometry between 1 and Hg
2
0 mM HEPES buffer (pH 7.4, 1% CH
3
CN). UVevis and fluorescence
(Supplementary data, Fig. S3).
2
þ
spectra reveal that a probe 1 is non-fluorescent in aqueous solution
and selectively responds to Hg among the various metal ions
examined (Fig. 2 and Supplementary data, Fig. S1). As large as
On the detection mechanism, the Hg -induced spiro ring
opening of rhodamine followed by deselenation is likely to be
responsible for the fluorescence enhancement and UVevis spectral
change (Scheme 1). To examine this plausible mechanism, a prod-
uct obtained from the reaction of 1 with Hg(ClO
According to MS analysis, a peak at 433.23 corresponding to
2
þ
3
0-fold ‘off-on’ type fluorescence enhancement was observed upon
2
þ
the addition of 10 equiv of Hg (Fig. 2). As shown in Figure 3, there
was also a large enhancement in the UV absorption (
max¼560 nm)
4 2
) was analyzed.
l

4018
X. Chen et al. / Tetrahedron 66 (2010) 4016e4021
þ
Figure. 3. (a) Absorption spectra of 1 (10
m
M) in the presence of various concentrations of Hg2 (0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 20, 30
m
M) in 20 mM HEPES buffer (pH 7.4, 1% CH
3
CN). (b)
2þ
2þ
Hg concentration-dependent absorbance of 1. Absorbance of 1 (10
m
M) was measured at 560 nm in the presence of various amounts of Hg . Each spectrum is recorded at 5 min
2þ
after addition of Hg to 1.
Fig. S7). Furthermore, we investigated potential interference of
fluorescence response of 1 to mercury ions from various metal
N
O
N
ions. The results obtained from fluorescence experiments show
N
O
N
Hg2+
2þ
that 1 retains high selectivity for Hg in the presence of milli-
þ
þ
þ
2þ
molar concentrations of various metal ions including Li , Na , K ,
2
H O
CO -
Se
O
2
2þ
2þ
2þ
2þ
2þ
2þ
2þ
2þ
2þ
Ca , Mg , Cd , Co , Cu , Fe , Mn , Ni , Pb , and Zn
Supplementary data, Fig. S8).
(
1
Rhodamine B
Hg2+
-
HgSe
2.3. Optical change of 1with methylmercury and its proposed
mechanism
N
O
N
+
N
O
N
It should be more significant to monitor methylmercury species
using 1 because organic forms of mercury are more toxic than in-
Se Hg2+
O
Se Hg+
O
organic mercury species. For this study, 1 (10
various concentrations (0e100 M) of CH HgCl in 20 mM HEPES
buffer (pH 7.4, 1% CH CN). Similar UVevis and fluorescence spectra
mM) was treated with
m
3
3
Scheme 1. A plausible mechanism of deselenation of 1 by mercury ions.
to those on inorganic mercury were obtained (Fig. 4). A absorption
band centered at 560 nm appeared with increasing intensity, which
induced a clear color change from colorless to pink color. In addi-
tion, an emissive peak at 580 nm was observed in the presence of
þ
[
rhodamine BþH] was clearly observed, suggesting the formation
of rhodamine B (Supplementary data, Fig. S4). NMR spectroscopic
2
þ
analysis also provided the evidence for deselenation of 1 by Hg
Supplementary data, Fig. S5).
To investigate detection limit of 1 for Hg , 1 (1
the CH HgCl. After addition of 10 equiv methyl mercury to the so-
3
(
lution with sensor for various reaction times, the results show the
2
þ
mM) was treated
enhancement of fluorescence intensity can be completed in 10 min
(Supplementary data, Fig. S9). Both UVevis and fluorescence data
lead to a significant ‘off-on’ signal. Two peaks can be observed from
2
þ
with various concentrations of Hg (0e30 nM). The fluorescence
2
þ
intensity at 580 nm was plotted as a function of the Hg con-
centration (Supplementary data, Fig. S6). The fluorescence in-
the mass spectra of 1 upon the addition of CH HgCl (10 equiv),
3
2þ
þ
þ
tensity of 1 is linearly proportional to the Hg concentration of
corresponding to [rhodamine BþH] and [1-HgCH ] , indicating
3
2
þ
0
e30 nM, and as low as 20 nM concentration of Hg was detected
that the mechanism of reaction between 1 and CH HgCl is similar
3
2
þ
by using 1 with a signal-to-noise ratio of 3. The time-dependent
with the case of Hg . In the procedure of reaction between 1 and
CH HgCl, 1 initially bind with CH HgCl and the following de-
selenation of 1-HgCH happen, so both the peaks of [1-HgCH ]
3 3
and [rhodamine BþH] can be observed from mass spectra
2
þ
fluorescence response of 1 to Hg was monitored at 580 nm un-
der pseudo-first-order kinetic conditions (10 M 1 and 500
Hg ). Under these conditions, the observed rate constant (kobs) at
3
3
þ
m
mM
2
þ
þ
ꢀ1
2þ
pH 7.4 was found to be 0.14 min for Hg (Supplementary data,
(Supplementary data, Fig. S10).
Figure. 4. (a) Absorption spectra of 1 (10
m
M) in the presence of various concentrations of CH
3
HgCl (0, 10, 20, 40, 60, 80, 100
mM) in 20 mM HEPES buffer (pH 7.4, 1% CH
3
CN). (b)
Fluorescence spectra of 1 (10 M) in the presence of various concentrations of CH
m
3
HgCl (0, 10, 20, 40, 60, 80, 100
mM) in 20 mM HEPES buffer (pH 7.4, 1% CH
3
CN) (
l
ex¼550 nm).

X. Chen et al. / Tetrahedron 66 (2010) 4016e4021
4019
2
.4. Sensing inorganic mercury and methylmercury in the
methylmercury species with high selectivity and sensitivity. The
fluorescence enhancement and UVevis spectral change induced
by mercury ions are attributed to deselenation reaction. The
value of this system was successfully demonstrated by its use in
detecting inorganic mercury/methylmercury species in cells
and zebrafish.
cell as well as in the zebra fish
Owing to its chemical and spectroscopic properties, 1 should
be suited to monitoring inorganic mercury and methylmercury in
living cells. To test this proposal, HeLa cells (human epithelial
adenocarcinoma) were incubated with 1 (20 mM) in the culture
media (0.2% DMSO). In the absence of mercury ions or methyl-
mercury, no fluorescence was exhibited inside the cells (Fig. 5a).
4
4
. Experimental
However, when the cells were treated with 1 (20
mM) and mer-
.1. General methods
cury ions or methylmercury (each 40 M), a remarkable increase
m
in fluorescence intensity was observed, indicating the detection
of inorganic mercury ions and methylmercury by 1 in cells
Unless otherwise noted, materials were obtained from com-
mercial suppliers and were used without further purification.
Chromatography was carried out on silica gel 60 (230e400 mesh
ASTM; Merck). Thin layer chromatography (TLC) was carried out
using Merck 60 F254 plates with a thickness of 0.25 mm. Preparative
TLC was performed using Merck 60 F254 plates with a thickness of
(
Fig. 5b and c).
1
13
1
2
mm. H NMR and C NMR spectra were recorded using Bruker
50. Mass spectra were obtained using a Jeol JMS 700 high reso-
lution mass spectrometer. UV absorption spectra were obtained on
UVIKON 933 Double Beam UV/VIS Spectrometer. Fluorescence
emission spectra were obtained using RF-5301/PC Spectro-
fluorophotometer (Shimadzu).
4.2. Preparation of stock solutions for fluorescent/UVevis
study
Stock solutions (10 mM) of the perchlorate salts of metal ions
and methylmercury in distilled water were prepared. Stock solu-
tions of 1 (1 mM) were also prepared in acetonitrile. In a typical
experiment, test solutions were prepared by placing 30 mL of the
probe stock solution into a test tube, diluting the solution to 3 mL
with 0.02 M HEPES (pH 7.4), and adding an appropriate buffer of
each analytes stock. Normally, excitation was at 550 nm. Both the
excitation and emission slit widths were 1.5 nm/1.5 nm. Fluores-
cence spectra were measured after addition of analytes for 10 min.
2
þ
For low concentration titration of Hg , fluorescence spectra
2
þ
were measured after addition of Hg for 10 min, and both the
excitation and emission slit widths were 3 nm, respectively. Simi-
Figure. 5. Images of cells incubated with 20
m
M 1 (0.2% DMSO) and 40
HgCl. (a) Images of HeLa cells treated with 1 in the absence, (b) presence of
M HgCl and (c) presence of 40 M CH HgCl (left, light microscopic images; right,
m
M HgCl
2
or
larly, for concentration titration of CH
absorption spectra were measured after addition of CH
0 min.
3
HgCl, fluorescence/UVevis
4
4
0
0
m
m
M CH
3
HgCl for
3
2
m
3
1
fluorescence images).
4
.3. Synthesis of compound 1
We then made attempt to monitor the mercury species ac-
cumulated in living organisms using 1. Zebrafish is a good animal
model to monitor ions using sensors due to convenient detection
of ions by fluorescence microscopy and permeability of ions and
To a stirred solution of rhodamine B (1 g, 2.2 mmol) in 1,2-di-
chloroethane (10 mL), phosphorus oxychloride (2 mL) was added
dropwise. After refluxed for 4 h, the reaction mixture was cooled
and evaporated in vacuo. The crude acid chloride was dissolved in
THF (6 mL), and the resulting solution was then added dropwise to
a mixed solution of selenourea (500 mg, 4.1 mmol) and triethyl-
amine (6 mL) in THF (25 mL)/water (5 mL) at room temperature.
After stirring over night, the solvent was removed under reduced
pressure. Then, 30 mL of water was added, and the formed pre-
cipitate was filtered. The precipitate was washed several times with
water and dried. The crude product was purified by silica-gel col-
9
sensors in fish. For this study, adult zebrafish (three months old
with identifiable organs) was pre-incubated with 500 nM mer-
cury ions or 500 nM methylmercury in water for 24 h (Fig. 6).
And then the treated zebrafish was further exposed to 20 mM of
1
for 1 h. Zebrafish was dissected to isolate tissues and organs
that were examined using fluorescence microscopy. Inorganic
mercury and methylmercury species were detected in the gall-
bladder, eggs and fin, and weakly monitored in gills and heart by
1
. The results obtained from cell and zebrafish experiments show
that 1 can pass through cells and fish, and then reacts with HgCl
or CH HgCl to form the fluorescent product.
umn chromatography with CH
1
2
Cl
2
as eluent, affording 0.410 mg of
, 250 MHz) d (ppm): 7.79 (d, H,
2
1
1
in 37% yield. H NMR (CDCl
3
3
J¼6.9 Hz), 7.46e7.34 (m, 2H), 7.18 (d, 1H, J¼6.6 Hz), 6.62 (d, 2H,
J¼8.3 Hz), 6.24 (s, 2H), 6.20 (d, 2H, J¼8.5 Hz), 3.26 (q, 8H, J¼7.0 Hz),
13
3
. Conclusions
1.08 (t,12H, J¼7.0 Hz). C NMR (CDCl
3
, 62.5 MHz) d (ppm): 201.688,
158.732, 152.283, 148.191, 140.878, 134.121, 130.090, 128.418,
In summary, we have developed a new selenolactone-based
fluorescent probe for the detection of inorganic mercury and
128.158, 122.522, 110.957, 108.130, 97.449, 62.725, 44.371, 12.634.
þ
FABMS m/z¼507.1548 [MþH] , calcd for C28
H
31
N
2
O
2
Se¼507.1553.

4020
X. Chen et al. / Tetrahedron 66 (2010) 4016e4021
Figure. 6. Images of zebrafish organs treated with 20
2 3
mM 1 (0.2% DMSO) and 500 nM HgCl or 500 nM CH HgCl. (a) Images of zebrafish organs treated with 1 in the absence of
HgCl or CH HgCl, (b) presence of 500 nM HgCl or (c) presence of 500 nM CH
2
3
2
3
HgCl (upper, microscopic images; lower, fluorescence images).
4
.4. Imaging of mammalian cells incubated with probe and
Foundation of Korea (NRF) (20090083065), the National Creative
Research Initiative and WCU (R32-2008-000-10217-0) programs.
Mass spectra data were obtained from the Korea Basic Science In-
HgCl or CH HgCl
2
3
HeLa cells (human epithelial adenocarcinoma) were seeded in
stitute (Daegu) on a Jeol JMS 700 high resolution mass spectrometer.
3
a 24-well plate at a density of 2ꢁ10 cells per well in culture media
(
RPMI-1640 supplemented with 10% fetal bovine serum(FBS)). Af-
Supplementary data
ter 24 h, 20
m
M 1 in the culture media (0.2% DMSO) was added to
ꢂ
the cells and the cells were incubated for 1 h at 37 C. After washing
Experimental details, Synthesis and characterization of sensor
twice with the 400
DPBS, without calcium and magnesium) to remove the remaining
probe, the cells were further treated with 40 M HgCl or 40
CH HgCl in DPBS for 10 min. The treated cells imaged by fluores-
mL of Dulbecco’s phosphate buffered saline
1; UVevis spectra of 1 with various metal ions; The detection limit
(
assays; Competition experiments and the determination of rate
m
2
mM
2þ 1
constant; The job-plot of sensor 1 with Hg ; H NMR and mass
2þ
3
spectra of sensor 1 upon the addition of Hg ; Mass spectra of
cence microscopy (Excitation at 510e560 nm, emission at 590 nm,
Eclipse TE200-S, Nikon, Japan).
3
sensor 1 upon the addition of CH HgCl. Supplementary data asso-
ciated with this article can be found in online version at
doi:10.1016/j.tet.2010.04.042.
4
3
.5. Detection of mercury ion or CH HgCl-containing
zebrafish organs incubated with the probe
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ꢂ
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