Reversible and Sensitive Hg2+ Detection by a Cell-Permeable Ytterbium Complex

Article abstract of DOI:10.1021/acs.inorgchem.7b02243

A cell-permeable ytterbium complex shows reversible binding with Hg²⁺ in aqueous solution and in vitroby off-on visible and NIR emission. The fast response and 150 nM sensitivity of Hg²⁺ detection is based upon FRET and the lanthanid

Full text of DOI:10.1021/acs.inorgchem.7b02243

Article
pubs.acs.org/IC
Cite This: Inorg. Chem. XXXX, XXX, XXX−XXX
Reversible and Sensitive Hg2+ Detection by a Cell-Permeable
Ytterbium Complex
Guochen Bao,†,‡ Shuai Zha,† Zhenyu Liu,§,∥ Yan-Ho Fung,† Chi-Fai Chan,† Hongguang Li,†
Pak-Ho Chu,† Dayong Jin,*,‡ Peter A. Tanner,*,† and Ka-Leung Wong*,†
†Department of Chemistry, Hong Kong Baptist University, Kowloon Tong, Hong Kong SAR, People’s Republic of China
‡Institute for Biomedical Materials and Devices (IBMD), Faculty of Science, University of Technology Sydney, Sydney, New South
Wales 2007, Australia
§Department of Applied Biological and Chemical Technology, The Hong Kong Polytechnic University, Hung Hom, Hong Kong
SAR, People’s Republic of China
∥Department of Applied Biological and Chemical Technology, The Hong Kong Polytechnic University Shenzhen Research Institute,
Shenzhen 518057, People’s Republic ofChina
S
* Supporting Information
ABSTRACT: A cell-permeable ytterbium complex shows
reversible binding with Hg2+ in aqueous solution and in
vitroby off−on visible and NIR emission. The fast response
and 150 nM sensitivity of Hg2+ detection is based upon FRET
and the lanthanide antenna effect. The reversible Hg2+
detection can be performed in vitro, and the binding
mechanism is suggested by NMR employing the motif
structure in a La complex and by DFT calculations.
overcome. Most sensors require a mixed solution of water and
organic solvent due to their poor water solubility.6,9−11 The
narrow Stokes shift of the organic dye also limits its
applications due to the interference of exciting light.6,11
Fluorescence resonance energy transfer (FRET) is a tool to
overcome this problem for the chemical sensing of ions.12
FRET is based upon the strong distance-dependent interaction
between an excited donor and an acceptor, permitting clear
observation of the acceptor emission.13 Lanthanide chelates are
good candidates for the development of luminescence sensors,
possessing wide wavelength shifts between the donor
absorption and metal acceptor emission, long luminescence
lifetimes (microsecond to millisecond), and characteristic,
sharp luminescence.14−18 Our previously reported Yb(III)-
based Hg2+ sensor YbPor-L exhibited some of these character-
istics with reasonable sensitivity and selectivity.9 Notably, the
sensor emission is located in the NIR spectral region and can
penetrate biological tissues. However, the sensor suffers from
poor water solubility, only having response in mainly organic
solvents, and it cannot be incorporated into living cells or
tissues. The detection limit is insensitive for many applications,
lying on the micromolar scale (10 μM) in a mixed solution of
organic solvent and buffer.9 Furthermore, the wavelength of the
INTRODUCTION
■
Heavy metal pollution has exceeded regulatory limits in many
parts of the world due to the rapid and careless development of
industries, and this problem has increasingly gained concern.1
Among the hazardous contaminants, the mercury(II) ion is
notably one of the most dangerous threats to human health due
to its strong affinity toward thiol groups, resulting in the
dysfunction of most proteins and enzymes.2 Moreover, with its
persistent bioaggregation and nonbiodegradability, this pollu-
tant can accumulate in the human body through the food chain;
even at low concentrations it causes harmful diseases such as
brain and nervous system damage, kidney failure, and cognitive
disorder.3−7 Therefore, concerns over the wide-reaching
hazards of mercury have motivated chemists to develop
selective Hg2+ probes for biological and environmental sensing
and monitoring applications.
Fluorescent sensors enable quantitative detection of heavy
metal ion concentrations and are useful tools for monitoring
mercury contamination. Considerable efforts have been made
to develop various fluorescence-based sensors such as with the
use of rosamine,8 semisquaraines,3 and porphyrins.9 The
rhodamine B based sensor is a reversible chemosensor with a
novel design.10 The metal-induced ring-opening process offers
distinct photophysical advantages in terms of sensitivity,
selectivity, and response time.4,11 However, just as for other
organic dye based sensors, significant challenges still need to be
Received: August 31, 2017
© XXXX American Chemical Society
A
DOI: 10.1021/acs.inorgchem.7b02243
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
visible response signal is very close to the excitation wavelength.
These drawbacks make it unsuitable for use in cells and spurred
us to develop a more sensitive and biocompatible probe for
Hg2+ monitoring.
Herein, we report the design and synthesis of a dual channel
sensor, GBYb001, the combination of an Yb3+-based complex
with a rhodamine B sensing unit (Figure 1). By introduction of
Information). All of the target products and intermediates were
fully characterized by various spectroscopic techniques, as
detailed in the Supporting Information.
In HEPES buffer, GBYb001 exhibits the intense absorption
of the py moiety, with a maximum at 325 nm (ε = 26180 M−1
cm−1), together with the characteristic absorption of rhodamine
B indicated by the weak band at 565 nm (Figure S4 in the
Supporting Information). Upon photoexcitation of the py
chromophore, the complex displayed a weak red emission (λmax
591 nm), corresponding to the π → π* transition of the
rhodamine B moiety. The emission of the substituted pyridine
unit was almost quenched due to FRET (Figure S5 in the
Supporting Information). This is demonstrated in the
excitation spectrum of rhodamine B emission (Figure S6 in
the Supporting Information), where not only rhodamine B
absorption but also the substituted pyridine absorption is
present. Hence, the rhodamine B emission can be well-
separated from the excitation wavelength. There is an efficient
spectral overlap between the emission spectrum of the
intermediate 11 (GB002, part of GBYb001) and the excitation
spectrum of the rhodamine B unit (Figure S7 in the Supporting
Information). The room-temperature emission of 11 is deemed
to originate from a singlet excited state, and it is quenched in
the presence of the lanthanide ion in GBYb001.
Under 355 nm excitation of GBYb001 in CH3CN solvent, a
weak characteristic NIR emission (around 980 nm) is also
2
observed, due to the intraconfigurational F5/2
→
2F7/2
Figure 1. Structure of complexes GBYb001 and GBYb002.
transition of Yb3+ (Figure S8 in the Supporting Information).
Since Yb3+ does not have an absorption band at the excitation
wavelength, the emission is due to energy transfer to the Yb3+
acceptor from the py chromophore or rhodamine B donor.
Direct excitation at 570 nm does not excite Yb3+ emission so
that the donor to the Yb3+ acceptor is the py chromophore.
The donor nonradiative transition is electric dipole allowed,
and that of the acceptor is electric quadrupole and forced
electric dipole allowed.
an amide chain substituted cyclen as the coordinating unit of
the Yb3+ cation, the resulting positively charged complex
exhibited excellent water solubility. A carbodithioate moiety
serves as the “catching” unit of Hg2+. Moreover, it then triggers
the ring-opening process of the rhodamine B unit, which gives
the sensor high selectivity and sensitivity. The construction is
completed with the well-designed substituted 4-
(phenylethynyl)pyridine (py) unit, which harvests photons
and transfers energy through FRET to the ring-opened
rhodamine B and Yb3+ ions. This new sensor displays selective
turn-on emission responses in both the visible and NIR regions
in the presence of Hg2+. Both emission channels are far
removed from the excitation wavelength, and the quick
detection response, low detection limit, and reversible property
make it practical for biological applications.
Upon addition of Hg2+ ion (using Hg(ClO4)2 as the source;
note that metal perchlorates are usually explosive and should be
used with caution21) to the buffered solution of GBYb001, the
solution turned from colorless to red within 1 s. Consequently,
a 22-fold enhancement of absorption intensity was observed
(with a 10 nm bathochromic shift) for the 575 nm peak (Figure
2). At the same time, the absorption band at 325 nm decreased
slightly in intensity. This is not due to dilution but indicates a
structural change of the complex. However, no obvious change
was observed for a similar addition of Hg2+ to a solution of the
control compound GBYb002 (Figure S10 in the Supporting
Information). This demonstrates that GBYb001 exists in the
spirocyclic form and that the addition of Hg2+ triggers ring
opening to occur. It takes place rapidly in the buffer solution at
room temperature. The binding stoichiometry of GBYb001
was determined to be 1:1 by a Job plot from the absorption
spectrum, where the absorbance at 575 nm reaches a maximum
when the mole fraction is 50% (Figure 2, inset). The binding
constant for Hg2+ in buffer solution with GBYb001 was
evaluated by nonlinear least-squares analysis22 of the absorption
intensity at 575 nm: Kb = (2.05 0.30) × 105 M−1.
RESULTS AND DISCUSSION
■
GBYb001 was synthesized by connecting a three-chain-
substituted cyclen with the py moiety and carbodithioic and
rhodamine B fragments through a series of synthetic steps and
then coordinating with Yb3+ in aqueous MeOH (Scheme 1).
Compounds 3, 5, and 7 were synthesized according to the
literature9,19,20 (Schemes S1−S3 in the Supporting Informa-
tion). Compound 10 was synthesized by Sonogashira coupling
of compound 7 with tert-butyl (4-iodophenyl)carbamate to
form compound 8, followed by substitution with compound 5
and N-Boc deprotection.19 Compound 11 was synthesized via
amidation of intermediate 10 with compound 3 at room
temperature. Compound 11 was then substituted with
hydrazine hydrate and rhodamine B to form ligand 13
(GB001),9 which was followed by coordination with Yb3+ to
form the complex GBYb001. The control GBYb002 was also
synthesized together with the intermediate 11 (GB002) using
the same strategy (Schemes 1 and Scheme S4 in the Supporting
The changes in fluorescence intensity of GBYb001 were
measured in HEPES buffer solution or in CH3CN. Upon the
addition of Hg2+, GBYb001 exhibited a significant turn-on
emission in both the visible (∼596 nm) and NIR regions
(∼980 nm) upon excitation of the py unit (Figure 3). We
rationalize that the visible emission enhancement at 596 nm
B
DOI: 10.1021/acs.inorgchem.7b02243
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
a
Scheme 1. Synthesis of Hg2+ Probe GBYb001 and its La Structure Motif Complex GBLa001
a
Legend: (a) Pd(PPh3)4, CuI, tert-butyl (4-iodophenyl)carbamate, DIPEA, THF, room temperature, 3 days; (b) MsCl, DIPEA, DCM, room
temperature, 1 h; (c) K2CO3, 5, CH3CN, 50 °C, 19 h; (d) HCl(aq), MeOH, 0 °C to room temperature, 6 h; (e) 3, EDCI, HOBt, DIPEA, CH3CN,
room temperature, 36 h; (f) hydrazine hydrate, acetic acid, THF, EtOH, reflux, 2 h; (g) rhodamine B, POCl3, Et3N, 1,2-dichloroethane, reflux, 5 h;
(h) Et3N, DCM, room temperature, 12 h; (i) LnCl3(aq), MeOH, room temperature, 24 h.
GBYb001 exhibit an enhancement of rhodamine B fluores-
cence when either the py moiety or the rhodamine B unit is
excited (Figure S6 in the Supporting Information). The
normalized excitation spectra, before and after addition of
Hg2+ (Figure S11 in the Supporting Information), show that
the relative increase of intensity of the py moiety excitation
band is greater than that of the rhodamine B excitation band.
Hence, the energy transfer from py is more efficient for the
ring-opened form. Figure 3 shows that the observed enhance-
ment of emission intensity is linearly proportional to the
concentration of Hg2+ up to the saturation limit (∼20 μM), and
the limit of detection (LOD) is estimated to be 150 nM (Figure
S12 in the Supporting Information). This LOD is 67 times
lower than that of our previously reported mercury sensor
YbPor-L.9 The enhancement of NIR emission from Yb(III)
Figure 2. Changes in the absorption spectrum of GBYb001 (5 μM) in
HEPES buffer solution upon titration with Hg2+ (0 → 20 equiv). Inset:
Job plot at 575 nm of this addition, [GBYb001] + [Hg2+] = 5 μM.
2
(2F5/2 → F7/2) is due to the absorption band shift of the
chromophore unit in CH3CN (Figure S13 in the Supporting
Information): the energy is transferred from the py
chromophore to Yb(III) through the antenna effect so that
there is a wide wavelength gap between excitation and
emission. However, no Yb(III) emission is observed under
570 nm excitation, when the rhodamine unit is excited,
indicating the absence of energy transfer from rhodamine B to
occurs because of the increase in absorption of the rhodamine
B moiety (hence the increased spectral overlap) induced by the
ring-opening mechanism, thereby enabling more efficient
FRET from the py chromophore to the rhodamine B fragment.
The excitation spectra following the addition of Hg2+ to
C
DOI: 10.1021/acs.inorgchem.7b02243
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
Figure 3. (a) Visible fluorescence response (λex 346 nm) of GBYb001 (5 μM) upon addition of Hg2+ in HEPES buffer. (b) NIR emission (λex 355
nm) of GBYb001 (10 μM) in CH3CN upon addition of Hg2+. (c, d) Plots of the enhancement at 596 and 980 nm, respectively.
Figure 4. (a) Visible fluorescence ratio of GBYb001 (5 μM, λex 525 nm) in HEPES buffer at 596 nm and (b) NIR emission ratio of GBYb001 (10
μM, λex = 355 nm) in CH3CN (with 1% of water) at 980 nm. Metal ions: 1, blank (normalized as F0); 2, Hg2+; 3, Cu2+; 4, Cu+; 5, Co2+; 6, Cd2+; 7,
Ca2+; 8, K+; 9, Li+; 10, Fe3+; 11, Fe2+; 12, Cs2+; 13, Mg2+; 14, Pb2+; 15, Sn2+; 16, Ni2+; 17, Al3+; 18, Na+.
Yb3+. The decay of NIR emission of GBYb001 in CH3CN after
the addition of Hg2+ is monoexponential with a lifetime of 2.31
μs (Figure S14 in the Supporting Information) and with a
quantum yield of 0.014% (Figure S15 in the Supporting
Information). This long lifetime distinguishes the sensor from
fluorescent organic dyes with nanoscale lifetimes, and the limit
of detection is estimated to be 5.0 μM (Figure S16 in the
Supporting Information), which is 2 times lower than that in
our previous work.9 Moreover, with emission lying in the first
biological window, which has less light scattering, low skin
absorption, and hence enhanced escape from deeper tissues,23
the NIR emission makes our sensor potentially suitable for
biological applications.
To verify the sensor specificity, both the visible and NIR
dual-response emission spectra of GBYb001 were examined in
the presence of various environmentally and biologically
important metal ions, under the same conditions as for Hg2+
ions. The presence of common ions in cells, Na+, K+, Ca2+, and
Mg2+, caused little change in the visible or NIR emission and
did not interfere with the binding of Hg2+, even at 1 mM
concentration (Figure 4 and Figure S17 in the Supporting
Information). The GBYb001 sensor was also selective for Hg2+
in comparison with a wide range of other heavy metal,
transition metal, alkali metal, and alkali earth metal ions (Figure
4). Such discriminatory photophysical properties in both the
D
DOI: 10.1021/acs.inorgchem.7b02243
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
Figure 5. (a) Proposed mechanism of spiro-ring-opening and -closing process triggered by Hg2+ and S2−. (b) 1H NMR spectra of GBLa001 in d6-
DMSO upon addition of Hg2+ and then S2−.
visible and NIR ranges indicate the potential application for
biological samples.
slightly shifted downfield to 10.55 ppm upon addition of Hg2+
ions. The signal at 7.39 ppm disappeared, whereas a new signal
at 8.28 ppm appeared. These features are assigned respectively
to the aromatic hydrogens which are adjacent to the spiro
carbon and the carbonyl group of the spiro ring. These
hydrogens exhibited a large downfield shift due to the electron-
withdrawing effect of Hg2+ connected to the oxygen anion
generated by the ring-opening process. The other hydrogens on
the same aromatic ring also showed slight downfield shifts.
Similar shifts could also be found for hydrogens on the other
two phenyl groups, while the hydrogens on the pyridine ring
(8.38 and 7.20 ppm) and the tricyclic ring of the rhodamine
The reversibility of GBYb001 upon Hg2+ binding was next
investigated. Cellular thiol compounds, such as cysteine,
glutathione (GSH), and various thiol-containing peptides and
proteins, play crucial roles in mercury detoxification.8 Because
of the high binding ability of Hg2+ toward these cellular
compounds, it is predicted that the thiol group will strip the
bound Hg2+ from the GBYb001-Hg complex, resulting in the
recovery of the low-fluorescent Hg2+-free sensor. Taking
advantage of its high dissociation ability in buffer solution, we
chose Na2S as the thiol source to examine the reversibility. As
expected, upon addition of S2− anions to the solution of
GBYb001-Hg, an immediate decrease in fluorescence intensity
to the initial level of the free probe was observed. The
enhancement of emission could be recovered when Hg2+ was
added again to the buffer solution (Figure S18 in the
Supporting Information). The stability of GBYb001 estimated
by HPLC (Figures S19 and S20 in the Supporting Information)
shows that GBYb001 is relatively stable in HEPES buffer and
even in the presence of S2−. This reversible binding property of
GBYb001 and Hg2+ suggests that this probe could be used to
monitor not only the cellular uptake of mercury ions but also
the increase of the cellular thiol groups, which eliminates the
cellular uptaken mercury in vivo.
1
unit (6.32−6.52 ppm) exhibited no change. The H NMR
spectrum also provides evidence for the reversibility of this
probe. Upon addition of S2−, the signals recovered their initial
positions due to the removal of Hg2+ by the S2− anion, while
the oxygen anion was recovered to the amide group and the
ring was closed. This correlated with the change in GBYb001
emission upon binding with Hg2+ and S2−.
The enhancement of the energy transfer mechanism for the
ring-opened form was probed by DFT calculations24−26 upon
molecular fragments of GBYb001 (refer to the Supporting
Information). The relative geometry of the rhodamine and the
py part is displayed in Figure 6a. The HOMO and LUMO of
the py moiety are shown in Figure 6b, and the lowest singlet
transition is mainly polarized along the triple bond axis. Figure
6c,d show the ring-closed and ring-opened fragments,
respectively. The lowest singlet transition is more intense for
the ring-opened form and the respective S0 → S1 transitions are
almost orthogonally polarized, with that of the ring-opened
form more nearly parallel to the py axis. Importantly, the
In order to investigate the mechanism of spiro ring opening
1
and recovery, H NMR using a motif structure of the Yb
complex, GBLa001, was performed to evaluate its interaction
with Hg2+ and S2− in DMSO-d6 (Figure 5 and Figure S21 in the
Supporting Information). The signal at 10.52 ppm, which is
ascribed to the amide between the two aromatic rings, was
E
DOI: 10.1021/acs.inorgchem.7b02243
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
then exposed to 1 mM of S2− for 1 h at 37 °C in the dark. The
observed increase in fluorescence was reversed back to the
original levels (Figure 7e). These results are consistent with the
observation in HEPES buffer that S2− reversibly recovered the
Hg2+-free sensor. Cellular uptake efficiency and cytotoxicity are
vital properties for a real-time biosensor which can sensitively
monitor biosamples. The MTT reduction assay of GBYb001
on MRC-5 cells indicated low cytotoxicity after their treatment
with various concentrations in the dark for 24 h, with an IC50
value of 88.5 μM (Figure S22 in the Supporting Information).
The cellular uptake was investigated via flow cytometry by
treating MRC-5 cells with the probe for different times. As
shown in Figure S23 in the Supporting Information, GBYb001
showed excellent cellular uptake in living MRC-5 cells and
almost reached a maximum within 0.5 h. The cellular
experiment results indicate that GBYb001 is suitable for
visualizing the change in intracellular concentration of Hg2+ and
also could be used to monitor detoxification of biological thiol
species toward Hg2+ at cellular levels.
CONCLUSIONS
■
In summary, the reversible dual-channel FRET and antenna
effect based sensor GBYb001 was designed and synthesized by
combination of an ytterbium complex and a rhodamine B unit.
The sensor exhibited high selectivity and sensitivity and quick
response time to Hg2+ ions with responding visible and NIR
signals. The ring-opening and recovery mechanism was
deciphered by 1H NMR spectra, employing the structure
motif of the analogous La complex. With large excitation−
emission wavelength shifts on both emission channels and
excellent water solubility, GBYb001 was successfully employed
to monitor the changes of Hg2+ in living cells.
Figure 6. (a) Orientation of py and rhodamine parts. (b) py fragment
with LUMO (top) and HOMO (bottom). (c) Ring-closed fragment
with LUMO (left) and HOMO (right). (d) Ring-opened fragment
with LUMO (left) and HOMO (right). The dipole moments are
indicated by red arrows.
electron delocalization across three rings exists in the ring-
opened form but is broken in the ring-closed form.
The practical application of GBYb001 in fluorescence
imaging for Hg2+ was investigated in living cells using confocal
imaging microscopy. MRC-5 cells incubated with GBYb001 (5
μM) exhibited very weak but detectable fluorescence in the
living cells. However, a gradual increase in fluorescence was
observed after the cells were incubated with 2.5, 5, and 10 μM
of Hg2+ for 0.5 h at 37 °C in the dark (Figure 7a−d). In order
to investigate the reversible fluorescence response of GBYb001
in living cells, the same cells treated with 10 μM of Hg2+ were
EXPERIMENTAL SECTION
■
Materials and Characterization. All chemicals were purchased
and used as received without further purification. The solvents
specified were dried by standard procedures. NMR spectra were
recorded on a Bruker400 (400 Hz) nuclear magnetic resonance
spectrometer with chemical shifts expressed as parts per million (ppm)
and coupling constants J as hertz (Hz). High-resolution mass spectra
Figure 7. Confocal microscopic images of MRC-5 cells pretreated with 5 μM of GBYb001 for 1 h and then treated with (a) 0 μM, (b) 2.5 μM, (c) 5
μM, and (d) 10 μM Hg2+ for 0.5 h. (e) Fluorescence images of the same cells of (d) further treated with 1 mM of S2− and incubated for 1 h. The top
row gives fluorescence images, the middle row bright field images, and the bottom row overlays.
F
DOI: 10.1021/acs.inorgchem.7b02243
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
were taken on a Bruker Autoflex matrix assisted laser desorption/
ionization time-of-flight (MALDI-TOF) instrument or an electrospray
ionization (ESI) mass spectrometer.
confocal laser-scanning microscope equipped with a Ti:sapphire laser.
The samples were excited at a wavelength of 552 nm with the signal
for imaging within the range of 570−670 nm.
MTT Cell Viability Assay. MRC-5 cells (1 × 105) were treated
with GBYb001 for 24 h at six concentrations (1, 5, 15, 30, 50, and 100
μM). The cell monolayers were rinsed once with phosphate-buffered
saline (PBS) and incubated with 500 mg mL−1 MTT solution. The
cellular inhibitory potency of the mercury sensor was examined by
treating the cells with MTT for 3 h to allow formazan production
during cell metabolism. After that time, the formazan crystals were
dissolved in DMSO with oscillation. Finally, the absorbance of the
solution was measured with a Biotek PowerWave XS microplate reader
at a wavelength of 570 nm.
Photophysical Measurements. UV/vis spectra were recorded
with an Agilent Cary 8454 UV−vis spectrophotometer. The
measurements of emission and excitation spectra, emission decay,
and quantum yield were performed using a Horiba Fluorolog-3
spectrofluorometer with a xenon lamp or a Nd3+:YAG laser as
excitation source. The visible range measurements were recorded using
HEPES buffer (1 mM, pH 7.4), whereas those in the NIR spectral
range were made with the use of CH3CN. The metal ion sources (note
that metal perchlorates are usually explosive and should be used with
caution21) for the selectivity experiment were taken from Hg(ClO4)2·
6H2O, CuCl2, Co(ClO4)2·6H2O, Cd(ClO4)2·6H2O, CaCl2, KBr, LiBr,
Fe(NO3)3·9H2O, FeCl2·4H2O, Cs2CO3, MgSO4, Pb(NO3)2, SnCl2·
2H2O, Ni(ClO4)2·6H2O, Al(NO3)3·9H2O, NaCl, and Cu-
(CH3CN)4PF6. These metal species are soluble in water (Table S2
in the Supporting Information). The aqueous solutions (Cu-
(CH3CN)4PF6 used a solvent mixture of water and CH3CN) of
these metal salts were used to prepare the final metal cation solutions
of 0.05 mM in HEPES buffer and 0.1 mM in CH3CN (with 1% of
water). The metal ion solutions in both water and CH3CN (with 1%
of water) were clear without any precipitate. To further confirm the
dissolution of these salts in the solvent CH3CN (with 1% of water), we
dissolved each salt in CH3CN/water (v/v = 99/1). The results showed
that all these salts can be well dissolved at a concentration of 0.1 mM
in this solvent. Quantum yields, ΦY, were measured using the standard
Yb(tta)3phen (1.1% NIR emission quantum yield in toluene)
according to the formula27
Flow Cytometry Measurements of Cellular Uptake. MRC-5
cells (105 per sample) were seeded onto 35 mm Petri dishes and
incubated overnight. Then the cells were incubated with 5 μM
GBYb001 for 0, 0.5, 1, or 2 h. Then, they were incubated with Hg2+
for a further 0.5 h. Cells were harvested with trypsin and washed twice
with PBS. The uptake of GBYb001 by MRC-5 cells was analyzed by a
BD Accuri C6 flow cytometer. The cells were excited with a 488 nm
argon laser, and the emission was collected in the FL-2 channel (with a
585 nm long-pass filter). A total of 10000 events were analyzed.
DFT Calculations. Geometry optimizations and TDDFT calcu-
lations were performed using ORCA 4.0.124 with BP86 and B3LYP
functionals and the def2-TZVP or def2-SVP basis sets with the
auxiliary basis set def2/J.25,26 The optimized geometries did not have
any imaginary frequencies.
Synthetic Procedures. Synthesis of tert-Butyl (4-((2-
(Hydroxymethyl)pyridin-4-yl)ethynyl)phenyl)carbamate (8). To a
solution of tert-butyl (4-iodophenyl)carbamate (2.88 g, 9.01 mmol) in
80 mL of THF were added DIPEA (13.08 mL, 75.10 mmol),
Pd(PPh3)4 (173 mg, 0.15 mmol), CuI (57 mg, 0.30 mmol), and (4-
ethynylpyridin-2-yl)methanol (7; 1.00 g, 7.51 mmol) under a nitrogen
atmosphere. The reaction mixture was stirred at room temperature for
3 days. A 100 mL portion of water was added, and the contents were
extracted with DCM (100 mL × 3). The organic phases were
combined, dried over anhydrous Na2SO4, filtered, and purified by
chromatography on silica gel with hexane/ethyl acetate (2/1 to 1/1, v/
v) as eluent, affording the product as a white solid (2.10 g, 86.2%
yield). 1H NMR (400 MHz, CDCl3): δ 8.53 (d, J = 5.1 Hz, 1H), 7.48
(d, J = 8.7 Hz, 2H), 7.39 (d, J = 8.7 Hz, 2H), 7.34 (s, 1H), 7.28 (d, J =
5.1 Hz, 1H), 6.61 (s, 1H), 4.76 (d, J = 4.1 Hz, 2H), 3.62 (t, J = 4.5 Hz,
1H), 1.53 (s, 9H). 13C NMR (101 MHz, CDCl3): δ 159.14, 152.31,
148.48, 139.43, 132.90, 132.40, 124.15, 122.18, 118.08, 116.14, 94.26,
86.08, 81.14, 64.05, 28.31. MALDI-TOF MS: calcd. for [M + H+]
325.1547, found 325.1552.
ΦY = (GY/GS)(nY/nS)2ΦS
(1)
where G is the slope of the plot of integrated emission intensity vs
absorbance, n is the refractive index of the solvent employed, Φ is the
quantum yield, Y represents the sample to be measured, and S is the
standard sample.
Binding Constant. The binding constant Kb was obtained by a
nonlinear least-squares analysis of the absorption or emission spectrum
of the material versus concentration of Hg2+ with the formula:22
⎡
⎛
⎜
⎝
⎞
⎟
⎠
Y
− Y0
2cL
1
Kb
⎢
⎢
⎣
lim
Y = Y0 +
c + c
+
L
Hg
⎤
2
⎛
⎞
1
⎥
⎥
⎦
2
−
c + c
+
− 4cLcHg
⎜
⎝
⎟
L
Hg
Kb
⎠
(2)
Synthesis of tert-Butyl (4-((2-((4,7,10-Tris(2-(tert-butylamino)-2-
oxoethyl)-1,4,7,10-tetraazacyclododecan-1-yl)methyl)pyridin-4-yl)-
ethynyl)phenyl)carbamate (9). To a solution of tert-butyl (4-((2-
(hydroxymethyl)pyridin-4-yl)ethynyl)phenyl)carbamate (8; 973 mg,
3.00 mmol) and DIPEA (5.23 mL, 30.00 mmol) in 150 mL of dry
DCM was added dropwise MsCl (0.70 mL, 9.00 mmol). The reaction
mixture was stirred for 1 h at room temperature and then quenched
with water (100 mL). Then it was extracted with DCM (100 mL × 3),
washed with saturated aqueous NaHCO3 (50 mL), and dried over
anhydrous Na2SO4. The solvent was removed under reduced pressure,
and the residue was quickly purified by chromatography on silica gel
with DCM/ethyl acetate (1/1, v/v) as eluent, affording an
intermediate as a white solid (1.11 g, 92.3% yield) which was
immediately used for the next step. To a solution of the intermediate
(1.05 g, 2.61 mmol) and K2CO3 (2.77 g, 20.07 mmol) in ACN (250
mL) was added 2,2′,2′′-(1,4,7,10-tetraazacyclododecane-1,4,7-triyl)-
tris(N-(tert-butyl)acetamide) (5; 1.03 g, 2.01 mmol). The reaction
mixture was stirred at 50 °C for 19 h. The solid was filtered off, and
the solvent was removed. The residue was purified by chromatography
on neutral Al2O3 with DCM/methanol (50/1, v/v) as eluent, affording
where Y is the measured intensity (absorption or emission), Y0 is the
initial value (without addition of Hg2+), Ylim is the limiting value, and
cL and cHg are the concentrations of ligand and Hg2+, respectively.
HPLC Analysis. The measurements of complexes using reverse-
phase HPLC were conducted at room temperature using an Agilent
1200 HPLC system with DAD (column: Vision HT C18 HL 5 u,
length 250 mm, Serial No. 5151920, i.d. 4.6 mm). The mobile phase
was Milli-Q water (with 0.05% trifluoroacetic acid) and CH3CN with a
flow rate of 1 mL/min. The solvent gradient ratio is given in Table S1
in the Supporting Information.
Cell Culture. Human normal lung fibroblast (MRC-5) cells were
maintained in minimum essential medium (MEM) supplemented with
10% fetal bovine serum (FBS) and antibiotics (penicillin, 50 mg mL−1;
streptomycin, 50 mg mL−1). The cells were incubated at 37 °C in a
humidified environment with 5% CO2.
In Vitro Confocal Microscopy. To investigate the suitability of
the mercury sensor for bioapplications, MRC-5 cells (1 × 105) were
imaged. After incubation with 5 μM GBYb001 for 1 h, x equiv (x =
0.5, 1, 2) of Hg2+ ions was loaded for further 0.5 h incubation. Then
the cells were washed with PBS three times before imaging. After
imaging, the cells (with 2 equiv of Hg2+) were further incubated with 1
mM Na2S for 1 h, and images were taken again to test the reversibility
in living cells. All of the images were acquired on a Leica TCS SP8
1
the product as a yellow solid (1.60 g, 90.0% yield in two steps). H
NMR (400 MHz, DMSO): δ 9.68 (s, 1H), 8.36 (d, J = 5.1 Hz, 1H),
7.83 (s, 2H), 7.65 (s, 1H), 7.56 (s, 1H), 7.53 (d, J = 8.8 Hz, 2H), 7.46
(d, J = 8.8 Hz, 2H), 7.36 (d, J = 5.1 Hz, 1H), 3.97−3.44 (br, 2H),
G
DOI: 10.1021/acs.inorgchem.7b02243
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
3.19−2.56 (br, 12H), 2.46−1.82 (br, 10H), 1.48 (s, 9H), 1.29 (s, 9H),
1.21 (s, 18H). 13C NMR (101 MHz, DMSO): δ 170.54, 169.90,
158.61, 152.55, 148.94, 140.89, 132.47, 131.21, 125.02, 123.39, 117.91,
114.21, 94.17, 85.88, 79.64, 58.04, 57.96, 57.26, 54.93, 50.42, 50.38,
28.28, 28.13, 28.08. MALDI-TOF MS: calcd for [M + Na+] 840.5470,
found 840.5500.
7.65 (s, 1H), 7.61 (s, 1H), 7.56 (d, J = 8.7 Hz, 2H), 7.40 (dd, J = 5.1,
1.1 Hz, 1H), 7.32 (s, 2H), 4.61 (s, 2H), 3.71 (m, 6H), 2.66 (br, 12H),
2.40−1.80 (m, 14H), 1.30 (s, 9H), 1.22 (s, 18H). 13C NMR (101
MHz, DMSO) δ 189.99, 170.54, 169.88, 165.43, 158.65, 148.96,
141.07, 140.54, 135.79, 132.66, 132.33, 131.10, 127.92, 125.10, 124.25,
123.45, 120.05, 115.76, 93.94, 86.27, 58.07, 57.87, 57.21, 55.56,50.59,
50.40, 50.34, 29.34, 28.26, 28.11, 25.57, 23.73. MALDI-TOF MS:
calcd for [M + H+] 1023.5783, found 1023.5765.
Synthesis of 2,2′,2′′-(10-((4-((4-Aminophenyl)ethynyl)pyridin-2-
yl)methyl)-1,4,7,10-tetraazacyclododecane-1,4,7-triyl)tris(N-(tert-
butyl)acetamide) (10). To a solution of tert-butyl (4-((2-((4,7,10-
tris(2-(tert-butylamino)-2-oxoethyl)-1,4,7,10-tetraazacyclododecan-1-
yl)methyl)pyridin-4-yl)ethynyl)phenyl)carbamate (9; 1.00 g, 1.22
mmol) in MeOH (30 mL) was added 6 M aqueous HCl (30 mL)
under an ice bath. The reaction mixture was warmed to room
temperature and stirred for 6 h. The pH of the solution was adjusted
to 9 with 1.0 M aqueous NaOH, the solution was extracted with DCM
(100 mL × 3), and the extracted material was dried over anhydrous
Na2SO4. The solvent was removed, and the residue was purified by
chromatography on neutral Al2O3 with elution by DCM/methanol
(50/1, v/v), giving the product as a yellow solid (750 mg, 85.5%
yield). 1H NMR (400 MHz, DMSO): δ 8.31 (d, J = 5.1 Hz, 1H), 7.82
(s, 2H), 7.65 (s, 1H), 7.43 (s, 1H), 7.28 (dd, J = 5.1, 1.4 Hz, 1H), 7.21
(d, J = 8.6 Hz, 2H), 6.56 (d, J = 8.6 Hz, 2H), 5.75 (s, 2H), 3.65 (br,
2H), 2.72 (br, 12H), 2.19 (br, 10H), 1.30 (s, 9H), 1.21 (s, 18H). 13C
NMR (101 MHz, DMSO): δ 170.52, 169.93, 158.42, 150.40, 148.86,
133.15, 132.01, 124.53, 123.04, 113.58, 106.68, 96.54, 84.62, 58.03,
57.36, 54.93, 50.43, 50.39, 28.28, 28.13. MALDI-TOF MS: calcd for
[M + H+] 718.5127, found 718.5089.
Synthesis of 2-Oxo-2-(4-((4-((2-((4,7,10-tris(2-(tert-butylamino)-
2-oxoethyl)-1,4,7,10-tetraazacyclododecan-1-yl)methyl)pyridin-4-
yl)ethynyl)phenyl)carbamoyl)phenyl)ethyl Pyrrolidine-1-carbodi-
thioate (11). To a solution of 4-(2-((pyrrolidine-1-carbonothioyl)-
thio)acetyl)benzoic acid (3; 172 mg, 0.56 mmol) in 25 mL of dry
MeCN were added DIPEA (0.24 mL, 1.39 mmol), EDCI (160 mg,
0.84 mmol), and HOBt (112 mg, 0.84 mmol). The reaction mixture
was stirred for 0.5 h at room temperature, and 2,2′,2′′-(10-((4-((4-
aminophenyl)ethynyl)pyridin-2-yl)methyl)-1,4,7,10-tetraazacyclodo-
decane-1,4,7-triyl)tris(N-(tert-butyl)acetamide) (10; 200 mg, 0.28
mmol) was added. The reaction mixture was stirred for another 36
h at room temperature. Most of the solvent was removed under
reduced pressure, 30 mL of water was added, extraction with DCM
(30 mL × 3) was performed, and the extractant was dried over
anhydrous Na2SO4. The solvent was removed, and the residue was
purified by chromatography on neutral Al2O3 with DCM/methanol
(50/1, v/v) as eluent, giving the product as a yellow solid (164 mg,
58.6% yield). 1H NMR (400 MHz, DMSO): δ 10.70 (s, 1H), 8.39 (d, J
= 5.0 Hz, 1H), 8.19 (d, J = 8.5 Hz, 2H), 8.09 (d, J = 8.5 Hz, 2H), 7.91
(d, J = 8.8 Hz, 2H), 7.82 (s, 2H), 7.63 (d, J = 8.3 Hz, 2H), 7.59 (d, J =
8.6 Hz, 2H), 7.41 (d, J = 6.2 Hz, 1H), 4.98 (s, 2H), 3.73 (m, 6H), 2.66
(m, 12H), 2.39−1.87 (m, 14H), 1.30 (s, 9H), 1.22 (s, 18H). 13C NMR
(101 MHz, DMSO): δ 192.84, 189.99, 170.55, 169.89, 165.12, 158.67,
148.97, 140.23, 138.59, 133.14, 132.39, 131.06, 128.24, 125.14, 123.47,
120.22, 116.17, 113.56, 93.83, 86.40, 58.10, 57.90, 57.22, 55.40, 54.93,
50.81, 50.41, 50.35, 49.39, 43.35, 28.27, 28.12, 25.74, 23.88. MALDI-
TOF MS: calcd for [M + Na+] 1031.5334, found 1031.5319.
Synthesis of 2-((3′,6′-Bis(diethylamino)-3-oxospiro[isoindoline-
1,9′-xanthen]-2-yl)imino)-2-(4-((4-((2-((4,7,10-tris(2-(tert-butylami-
no)-2-oxoethyl)-1,4,7,10-tetraazacyclododecan-1-yl)methyl)-
pyridin-4-yl)ethynyl)phenyl)carbamoyl)phenyl)ethyl Pyrrolidine-1-
carbodithioate (13; GB001). Rhodamine B (43 mg, 0.10 mmol)
and POCl3 (0.20 mL) were refluxed in 1,2-dichloroethane (4 mL) for
5 h, and then the solvent was removed. The obtained crude rhodamine
B acid chloride was dissolved in 10 mL of dry DCM together with
trimethylamine (0.30 mL) and 2-hydrazono-2-(4-((4-((2-((4,7,10-
tris(2-(tert-butylamino)-2-oxoethyl)-1,4,7,10-tetraazacyclododecan-1-
yl)methyl)pyridin-4-yl)ethynyl)phenyl)carbamoyl)phenyl)ethyl pyrro-
lidine-1-carbodithioate (12; 50 mg, 0.05 mmol) and stirred for 12 h at
room temperature. After addition of 10 mL of water, extraction with
DCM (10 mL × 4), and drying over anhydrous Na2SO4, the crude
product was purified by chromatography on silica gel with DCM/
MeOH (100/1 to 50/1, v/v) to give the desired product as a red solid
(50 mg, 71.0% yield). 1H NMR (400 MHz, DMSO): δ 10.51 (s, 1H),
8.38 (d, J = 5.1 Hz, 1H), 7.88 (m, 7H), 7.62 (m, 8H), 7.39 (d, J = 5.8
Hz, 1H), 7.20 (d, J = 6.8 Hz, 1H), 6.49 (d, J = 8.8 Hz, 2H), 6.43−6.27
(m, 4H), 4.73 (s, 2H), 3.74 (m, 4H), 3.31 (q, 8H), 2.71 (br, 14H),
2.33 (br, 8H), 2.00−1.77 (br, 6H), 1.30 (s, 9H), 1.21 (s, 18H), 1.08 (t,
J = 6.9 Hz, 12H). 13C NMR (101 MHz, DMSO): δ 189.43, 170.56,
169.90, 165.51, 165.01, 160.36, 158.68, 153.15, 150.81, 148.97, 148.35,
140.26, 138.02, 136.26, 133.37, 132.38, 131.07, 129.77, 128.93, 128.27,
127.86, 127.17, 125.14, 124.06, 123.47, 123.19, 120.08, 116.04, 107.93,
105.97, 97.24, 93.84, 86.36, 66.97, 58.10, 57.88, 57.24, 55.78, 54.92,
50.41, 50.36, 30.71, 28.26, 28.12, 25.50, 23.65, 12.41. MALDI-TOF
MS: calcd for [M + Na+] 1469.7753, found 1469.7783
Synthesis of GBYb001 (14a). To a solution of 13 (GB001; 14 mg.
0.01 mmol) in 1.0 mL of MeOH was added 0.01 M aqueous YbCl3
(1.05 mL, 0.0105 mmol), and the mixture was stirred for 24 h at room
temperature. The solvent was removed, and the residue was dissolved
in 2 mL of water and washed with DCM (2 mL × 3). The water was
removed, and the residue was dried under vacuum, giving a purple
solid as product (15 mg, 83.3% yield). ESI-MS: calcd for [M − H2O −
3Cl− − 2H+] 1618.7, found 1618.9; calcd for [M − H2O − 3Cl−
−
H+]/2 809.9. HPLC retention time: 16.07 min.
Synthesis of GBLa001 (14b). To a solution of 13 (GB001; 5 mg,
0.0035 mmol) in 0.7 mL of MeOH was added 0.005 M aqueous LaCl3
(0.71 mL, 0.00354 mmol), and the mixture was stirred for 24 h at
room temperature. The solvent was removed, and the residue was
dissolved in 2 mL of water and washed with DCM (3 × 1 mL). The
water was removed, and the residue was dried under vacuum, giving a
1
purple solid as the product (5.8 mg, 93.3% yield). H NMR (400
Synthesis of 2-Hydrazono-2-(4-((4-((2-((4,7,10-tris(2-(tert-butyla-
mino)-2-oxoethyl)-1,4,7,10-tetraazacyclododecan-1-yl)methyl)-
pyridin-4-yl)ethynyl)phenyl)carbamoyl)phenyl)ethyl Pyrrolidine-1-
carbodithioate (12). To a solution of 2-oxo-2-(4-((4-((2-((4,7,10-
tris(2-(tert-butylamino)-2-oxoethyl)-1,4,7,10-tetraazacyclododecan-1-
yl)methyl)pyridin-4-yl)ethynyl)phenyl)carbamoyl)phenyl)ethyl pyrro-
lidine-1-carbodithioate (11; 230 mg, 0.23 mmol) in THF (12 mL) and
ethanol (12 mL) were added hydrazine hydrate (0.23 mL) and acetic
acid (0.23 mL). Then the reaction mixture was heated to reflux and
stirred for 2 h. The contents were cooled, and most of the solvent was
removed. A 40 mL portion of water and 3 mL of saturated aqueous
NaHCO3 were added, followed by extraction with DCM (30 mL × 3)
and drying over anhydrous Na2SO4. The solvent was removed, and the
residue was chromatographed on neutral Al2O3 with DCM/methanol
(50/1, v/v) as eluent, giving the product as a yellow solid (128 mg,
54.9% yield). 1H NMR (400 MHz, DMSO): δ 10.46 (s, 1H), 8.38 (d, J
= 5.1 Hz, 1H), 7.92 (m, 4H), 7.83 (s, 2H), 7.75 (d, J = 8.6 Hz, 2H),
MHz, DMSO): δ 10.51 (s, 1H), 8.38 (d, J = 5.2 Hz, 1H), 7.95−7.76
(m, 7H), 7.74−7.52 (m, 8H), 7.39 (d, J = 5.2 Hz, 1H), 7.20 (d, J = 7.2
Hz, 1H), 6.49 (d, J = 8.9 Hz, 2H), 6.42−6.27 (m, 4H), 4.72 (s, 4H),
3.74 (s, 8H), 3.31−3.29 (m, 14H), 2.65 (d, J = 14.3 Hz, 8H), 2.28 (d, J
= 35.9 Hz, 6H), 1.89 (dd, J = 21.8, 6.3 Hz, 9H), 1.30 (s, 1H), 1.18 (d, J
= 26.4 Hz, 18H), 1.08 (7, J = 6.9 Hz, 12H). HPLC retention time:
16.06 min.
Synthesis of GBYb002 (15). To a solution of 11 (GB002; 6.5 mg.
0.0065 mmol) in 1 mL of MeOH was added 0.005 M aqueous YbCl3
(1.00 mL, 0.0065 mmol), and the mixture was stirred for 24 h at room
temperature. The solvent was removed, and the residue was dissolved
in 2 mL of water and washed with DCM (3 × 1 mL). The water was
removed, and the residue was dried under vacuum, giving a yellow
solid as the product (8.0 mg, 92.0% yield). HPLC retention time:
15.02 min.
H
DOI: 10.1021/acs.inorgchem.7b02243
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
(11) Yang, Y.-K.; Yook, K.-J.; Tae, J. A rhodamine-based fluorescent
and colorimetric chemodosimeter for the rapid detection of Hg2+ ions
in aqueous media. J. Am. Chem. Soc. 2005, 127, 16760−16761.
(12) Ahamed, B. N.; Ghosh, P. An integrated system of pyrene and
rhodamine-6G for selective colorimetric and fluorometric sensing of
mercury(II). Inorg. Chim. Acta 2011, 372, 100−107.
(13) Broussard, J. A.; Rappaz, B.; Webb, D. J.; Brown, C. M.
Fluorescence resonance energy transfer microscopy as demonstrated
by measuring the activation of the serine/threonine kinase Akt. Nat.
Protoc. 2013, 8, 265−281.
ASSOCIATED CONTENT
■
S
* Supporting Information
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.inorg-
chem.7b02243.
Details of the experimental procedure, synthesis,
characterization data, photophysical properties, mecha-
nism, cytotoxicity, and cellular uptake (PDF)
(14) Ning, Y.; Ke, X. S.; Hu, J. Y.; Liu, Y. W.; Ma, F.; Sun, H. L.;
Zhang, J. L. Bioinspired orientation of beta-substituents on porphyrin
antenna ligands switches ytterbium(III) NIR emission with
Thermosensitivity. Inorg. Chem. 2017, 56, 1897−1905.
(15) Ke, X. S.; Yang, B. Y.; Cheng, X.; Chan, S. L.; Zhang, J. L.
Ytterbium(III) porpholactones: beta-lactonization of porphyrin ligands
enhances sensitization efficiency of lanthanide near-infrared lumines-
cence. Chem. - Eur. J. 2014, 20, 4324−4333.
AUTHOR INFORMATION
■
Corresponding Authors
*E-mail for D.J.: dayong.jin@uts.edu.au.
*E-mail for P.A.T.: peter.a.tanner@gmail.com.
*E-mail for K.-L.W.: klwong@hkbu.edu.hk.
(16) Heffern, M. C.; Matosziuk, L. M.; Meade, T. J. Lanthanide
probes for bioresponsive imaging. Chem. Rev. 2014, 114, 4496−539.
(17) Hildebrandt, N.; Spillmann, C. M.; Algar, W. R.; Pons, T.;
Stewart, M. H.; Oh, E.; Susumu, K.; Diaz, S. A.; Delehanty, J. B.;
Medintz, I. L. Energy transfer with semiconductor quantum dot
bioconjugates: a versatile platform for biosensing, energy harvesting,
and other developing applications. Chem. Rev. 2017, 117, 536−711.
(18) Hu, J.-Y.; Ning, Y.; Meng, Y.-S.; Zhang, J.; Wu, Z.-Y.; Gao, S.;
Zhang, J.-L. Highly near-IR emissive ytterbium(III) complexes with
unprecedented quantum yields. Chem. Sci. 2017, 8, 2702−2709.
(19) Li, H.; Lan, R.; Chan, C.-F.; Bao, G.; Xie, C.; Chu, P.-H.; Tai,
W. C. S.; Zha, S.; Zhang, J.-X.; Wong, K.-L. A luminescent lanthanide
approach towards direct visualization of primary cilia in living cells.
Chem. Commun. 2017, 53, 7084−7087.
(20) Li, H.; Lan, R.; Chan, C.-F.; Jiang, L.; Dai, L.; Kwong, D. W. J.;
Lam, M. H.-W.; Wong, K.-L. Real-time in situ monitoring via
europium emission of the photo-release of antitumor cisplatin from a
Eu-Pt complex. Chem. Commun. 2015, 51, 14022−14025.
(21) Sitong, C.; Weiming, G.; Bo, Z.; Tonglai, Z.; Li, Y. Methyl
carbazate energetic complexes: Transition metal perchlorates −
Syntheses, crystal structures and properties. Polyhedron 2016, 117,
110−116.
(22) Bourson, J.; Pouget, J.; Valeur, B. Ion-responsive fluorescent
compounds. 4. effect of cation binding on the photophysical properties
of a coumarin linked to monoaza- and diaza-crown ethers. J. Phys.
Chem. 1993, 97, 4552−4557.
(23) Smith, A. M.; Mancini, M. C.; Nie, S. Bioimaging: second
window for in vivo imaging. Nat. Nanotechnol. 2009, 4, 710−711.
(24) Neese, F. The ORCA program system. WIREs Comput. Mol. Sci.
2012, 2, 73−78.
(25) Weigend, F. Accurate Coulomb-fitting basis sets for H to Rn.
Phys. Chem. Chem. Phys. 2006, 8, 1057−1065.
ORCID
Hongguang Li: 0000-0002-6579-7300
Dayong Jin: 0000-0003-1046-2666
Peter A. Tanner: 0000-0002-4681-6203
Ka-Leung Wong: 0000-0002-3750-5980
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
This work was funded by grants from The Hong Kong
Research Grants Council (HKBU 22301615) and Hong Kong
Baptist University (FRG 1/16-17/016 and SDF 15-0324-P03).
REFERENCES
■
(1) Sun, Q.; Aguila, B.; Perman, J.; Earl, L. D.; Abney, C. W.; Cheng,
Y.; Wei, H.; Nguyen, N.; Wojtas, L.; Ma, S. Postsynthetically modified
covalent organic frameworks for efficient and effective mercury
removal. J. Am. Chem. Soc. 2017, 139, 2786−2793.
(2) Yan, Z.; Xue, H.; Berning, K.; Lam, Y. W.; Lee, C. S.
Identification of multifunctional graphene-gold nanocomposite for
environment-friendly enriching, separating, and detecting Hg2+
simultaneously. ACS Appl. Mater. Interfaces 2014, 6, 22761−22768.
(3) Li, Y.; He, S.; Lu, Y.; Zeng, X. Novel hemicyanine dye as
colorimetric and fluorometric dual-modal chemosensor for mercury in
water. Org. Biomol. Chem. 2011, 9, 2606−2609.
(4) Ko, S.-K.; Yang, Y.-K.; Tae, J.; Shin, I. In vivo monitoring of
mercury ions using a rhodamine-based molecular probe. J. Am. Chem.
Soc. 2006, 128, 14150−14155.
(5) Huang, N.; Zhai, L.; Xu, H.; Jiang, D. Stable covalent organic
frameworks for exceptional mercury removal from aqueous solutions.
J. Am. Chem. Soc. 2017, 139, 2428−2434.
(6) Duan, W.; Han, Y.; Liu, Q.; Cui, J.; Gong, S.; Ma, Y.; Zhang, C.;
Sun, Z. Design and synthesis of novel rhodamine-based chemo-
dosimeters derived from [2.2]paracyclophane and their application in
detection of Hg2+ ion. Tetrahedron Lett. 2017, 58, 271−278.
(7) Liu, B. Highly sensitive oligonucleotide-based fluorometric
detection of mercury(II) in aqueous media. Biosens. Bioelectron.
2008, 24, 756−760.
(8) Taki, M.; Akaoka, K.; Iyoshi, S.; Yamamoto, Y. Rosamine-based
fluorescent sensor with femtomolar affinity for the reversible detection
of a mercury ion. Inorg. Chem. 2012, 51, 13075−71307.
(26) Weigend, F.; Ahlrichs, R. Balanced basis sets of split valence,
triple zeta valence and quadruple zeta valence quality for H to Rn:
Design and assessment of accuracy. Phys. Chem. Chem. Phys. 2005, 7,
3297−3305.
(27) Zhang, T.; Zhu, X.; Cheng, C. C. W.; Kwok, W.-M.; Tam, H.-L.;
Hao, J.; Kwong, D. W. J.; Wong, W.-K.; Wong, K.-L. Water-soluble
mitochondria-specific ytterbium complex with impressive NIR
emission. J. Am. Chem. Soc. 2011, 133, 20120−20122.
(9) Zhang, T.; Chan, C. F.; Lan, R.; Wong, W. K.; Wong, K. L.
Highly selective and responsive visible to NIR ytterbium emissive
probe for monitoring mercury(II). Chem. - Eur. J. 2014, 20, 970−973.
(10) Kim, S. K.; Swamy, K. M. K.; Chung, S.-Y.; Kim, H. N.; Kim, M.
J.; Jeong, Y.; Yoon, J. New fluorescent and colorimetric chemosensors
based on the rhodamine and boronic acid groups for the detection of
Hg2+. Tetrahedron Lett. 2010, 51, 3286−3289.
I
DOI: 10.1021/acs.inorgchem.7b02243
Inorg. Chem. XXXX, XXX, XXX−XXX