A gadolinium(III) complex based dual-modal probe for MRI and fluorescence sensing of fluoride ions in aqueous medium and: In vivo

Article abstract of DOI:10.1039/c6dt02229d

A novel Gd(iii) complex, Gd(TTA)₃-DPPZ, was designed and assembled as a dual-modal probe for the simultaneous fluorescence and magnetic resonance imaging (MRI) detection of fluoride ions in aqueous media and in vivo. In this system, the Gd(iii) center is not only serving as a MRI signal output unit, but also as a binding site for fluoride ions. When appropriate equivalents of fluoride ions were added into the solution of Gd(TTA)₃-DPPZ, the replacement of the coordination water led to a decrease of the longitudinal relaxivity (r₁) as well as distinct spectroscopic changes, by which MRI/fluorescence dual-modal fluoride ion sensing was achieved. In the presence of fluoride ions, a 2-fold fluorescence emission enhancement of Gd(TTA)₃-DPPZ, and a notable decrease of the UV-vis absorption spectrum were observed. The fluorescence detection limit for fluoride ions was established at 70 nM. Gd(TTA)₃-DPPZ also exhibits about 75% decrease of the longitudinal relaxivity (r₁) upon addition of fluoride ions in aqueous medium. The appropriate blood circulation time of Gd(TTA)₃-DPPZ allows its potential application in MRI in vivo. The results demonstrated that Gd(TTA)₃-DPPZ could serve as a potential MRI/fluorescence bimodal imaging agent for the specific and high-sensitive sensing of fluoride ions in vivo.

Full text of DOI:10.1039/c6dt02229d

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Gadolinium(III) Complex based Dual-Modal Probe for MRI
and Fluorescence Sensing of Fluoride ion in Aqueous
Medium and in vivo
Received 00th January 20xx,
a
b
b
a
a,c
a
Yue Wang, Renfeng Song, Ke Guo, Qingtao Meng, * Run Zhang, Xiangfeng Kong and Zhiqiang
Zhang *
a
Accepted 00th January 20xx
DOI: 10.1039/x0xx00000x
www.rsc.org/
3
A novel Gd(III) complex, Gd(TTA) -DPPZ was designed and assembled as a dual-modal probe for the simultaneous
fluorescence and magnetic resonance imaging (MRI) detection of fluoride ion in aqueous media and in vivo. In this system,
Gd(III) center is not only serving as a MRI signal output unit, but also proving a binding site for fluoride ion. When apropos
equivalents of fluoride ions were added into the solution of Gd(TTA)
led to decrease of the longitudinal relaxivity (r ) as well as the distinct spectroscopic changes, by which MRI/fluorescence
dual-modal fluoride ion sensing was achieved. In the present of fluoride ions, 2-fold fluorescence emission enhancement
of Gd(TTA) -DPPZ , and a notable decrease of the UV–vis absorption spectrum were observed. The fluorescent detection
limit for fluoride ion was established at 70 nM. Gd(TTA) -DPPZ also exhibits about 75% decrease of the longitudinal
relaxivity (r ) upon addition of fluoride ions in aqueous medium. The appropriate blood circulation time of Gd(TTA) -DPPZ
allows potential application in MRI in vivo. The results demonstrated that Gd(TTA) -DPPZ could serve as a potential
MRI/fluorescence bimodal imaging agent for the specific and high-sensitive sensing of fluoride ions in vivo.
3
-DPPZ, the replacement of the coordination water
1
3
3
1
3
3
6
-8
three dimensions without photobleaching or light scattering.
Introduction
Unfortunately, as each detection method has its own
considerations, MRI technique has just been able to resolve
objects larger than a few micrometers in size, thus exhibiting
To elucidate the important roles of bioactive ions and
molecules to health and disease, biologists and biochemists
are initiating a broad-based program to develop new chemical
approaches to study aspects of their uptake, trafficking, export,
9
much lower resolution than optical analysis. Therefore,
integration of fluorescence and MRI technique in one setting is
appealing due to the complementary nature of high
penetration depth of MRI and high resolution of fluorescence
1
and functions in living systems. At present, fluorescence
imaging, due to its high sensitivity, operational simplicity,
specificity, and biocompatibility, is recognised as one of the
most powerful tools to visualize these ions and molecules in
1
0
analysis.
Currently,
Gd(III)
complexes
based
MRI/fluorescence dual-modal probes have been widely used
for sensing and imaging of metal ions and biological molecules
2
,3
complicated biological processes.
Although fluorescence
1
1-14
in both aqueous medium and biological systems.
However,
imaging probes have been widely exploited in biotechnology
and biomedical research fields, non-invasive in vivo molecular
imaging applications were limited due to the shallow
to the best of our knowledge, few of Gd(III) complexes based
MRI/fluorescence probes have been developed specific for the
detection of anions.
4
,5
penetration depth of incidence light. In contrast to optical
microscopy imaging technology, magnetic resonance imaging
Anions play fundamental roles in biological, security and
1
5-17
environmental science.
Among various important anions,
(MRI) has recently been explored as a non-invasive imaging
fluoride ion in biological system, as the smallest and most
electronegative anion, has been received increasing attention
in recently years. It has been well documented that intake of
technique that allows images of intact, opaque organisms in
acute amount of fluoride anions is beneficial to the treatment
18-20
a.
School of Chemical Engineering, University of Science and Technology Liaoning,
1
of osteoporosis and dental health.
However, excessive
85 QianshanZhong Road, Anshan, 114051, P. R. China. Email:
qtmeng@ustl.edu.cn; zhangzhiqiang@ustl.edu.cn. Tel: Tel: +86-421-5928009
Ansteel Mining Engineering Corporation, 27 Lvhua Street, Anshan,114002,P. R.
China
Australian Institute for Bioengineering and Nanotechnology, The University of and so on.
Queensland, Brisbane, 4072, Australia
intake of fluoride ion may induce various diseases, such as
gastrointestinal dysfunction, dental fluorosis, bone fluorosis,
b.
c.
2
1,22
Therefore, rapid, sensitive, specific, and
accurate detection of fluoride ion in vivo in-situ is of great
† Footnotes relaꢀng to the ꢀtle and/or authors should appear here.
Electronic Supplementary Information (ESI) available: [details of any
importance for investigating its functions in environmental and
supplementary information available should be included here]. See biological samples. In particular, to meet the requirements in
DOI: 10.1039/x0xx00000x
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the practical applications in biological samples, receptors that coordinate structure in which Gd(III) is surrounded by two
could be used for specific detection of fluoride ions in aqueous nitrogen atoms from phenanthroline derivative, six oxygen
solution are highly desirable. But detection of fluoride in water atoms of tris(2-thenoyltrifluoroacetonate) and one
3
8
remains a challenge due to the high free energies of hydration coordinated water molecule. In the presence of fluoride ions,
2
3
of this anion. Among numerous anion receptors, organic the replacement of water molecules led to the decreasing the
lanthanide complexes have been recognised to be the longitudinal relaxivity (r ) as well as the distinct spectroscopic
1
3
9
excellent candidates to develop of molecule imaging probes changes, realizing MRI/fluorescent dual modal sensing of
for the detection of anions because of their unique fluoride ion in aqueous and biological samples.
2
4-26
photophysical and photochemical properties.
By virtue of
high affinity of the targeted anions and hard Lewis acid nature
of lanthanide ions, the specific interaction of anions with
lanthanide(III) center led to the liberation of the coordinated
water molecule. Consequently, specific response in signals,
Results and Discussion
3
Synthesis and characterization of Gd(TTA) -DPPZ
2
7
The designed neutral and unsaturated complex, Gd(TTA)
DPPZ, was synthesized by a one-step complexation of TTA and
,5,9,14-tetraaza-benzotriphenylene (DPPZ) with Gd(III) ions in
ethanol (Scheme 1). The structure and purity of Gd(TTA) DPPZ
3
-
such as colour, MRI and fluorescence could be achieved as
8,29
the basic mechanism for anions sensing.
2
4
3
-
CF
O-
3
H
2
O
C
S
F
3
C
was well characterized by ESI-MS, HPLC, and elemental
analysis. As shown in Fig. 1, ESI-MS spectrum of Gd(TTA)3-
DPPZ in solution exhibited two intense peaks at m/z =
1125.9744 and 1142.0786, which can be assigned to the
O
O
O
F
3
N
N
N
O-
O
N
N
N
N
GdCl
3
+
Gd
O-
N
C
2
H
5
OH/Et N
3
S
O
S
S
+
+
3
F C
species of [Gd(TTA)
respecꢀvely (Fig. 1 and Fig. S2, ESI†). HPLC analysis exhibited
that the retention time of Gd(TTA) DPPZ was at 2.16 min by
3 3
-DPPZ + Na] and [Gd(TTA) -DPPZ + K] ,
Gd(TTA)
3
-DPPZ
3
-
Scheme 1 Proposed structures of Gd(TTA) -DPPZ
3
using methanol as the eluent. The purity of Gd(TTA)
3
-DPPZ was
determined to be 99.3%.
Gd(TTA)
0.0 (Fig. S3, ESI†), indicaꢀng that the complex Gd(TTA)
is suitable for application under physiological conditions.
Gd(TTA) DPPZ shows desired stability in aqueous medium
THF: H O = 5:5) at pH = 7.4. As shown in Fig. S4, there were no
obvious changes of fluorescent intensity within 30 h, indicating
that Gd(TTA) DPPZ is stable under the test condition.
3
-DPPZ showed pH independent in the range of 4.0–
1
3
-DPPZ
3
-
(
2
3
-
Spectroscopic studies of Gd(TTA)
3
-DPPZ in the presence of anions
0.75
Fig. 1 ESI-MS spectrum of Gd(TTA)
3
-DPPZ.
3
−
PO4
2
Due to the high magnetic moment (μ = 63 μB ), and a
2
0.60
8
symmetric electronic ground state, S
7 2
/ of Gd(III) ions, Gd(III)
0.45
0.30
0.15
0.00
−
H PO
complexes have long been clinically used as the MRI contrast
0
2
4
3
agent.
As the Solomon-Bloembergen-Morgan theory
described, the relaxivity of Gd(III) complexes are governed by a
variety of factors including the number of bound water
−
F
molecules (q), the rotational tumbling times (τ
R
) and the mean
3
1
residence lifetime of Gd(III)-bound water molecules (τ
M
).
Typically, the MRI signal of Gd(III) complexes are expected to
300
350
400
450
be finely tuned by changing in q upon treatment of targeted
Wavelength (nm)
32,33
ions or molecules in aqueous solution.
Inspired by this
in this work, a Gd(III) complex, Gd(TTA) DPPZ
was developed for the detection of fluoride ions in both
aqueous medium and mice. Gd(TTA) DPPZ was designed by
employing -diketonate derivative,
thenoyltrifluoroacetonate (TTA) as the ligand due to its ideal
3
4-36
3 2 2
Fig. 2 UV-vis absorption spectra of Gd(TTA) -DPPZ (10 μM) in H O (THF: H O = 5:5, pH =
strategy,
3
-
,
–
–
–
–
–
–
–
7
3 4 2 4
.4) upon addition of various anions: 0.7 mM of Br , NO , OH , I , HSO , AcO , H PO ,
–
–
3–
4
F ; and 100 mM Cl ; 1 mM PO .
3
-
a
β
3
7
complexation with lanthanide ions. The Gd(III) centre also
provides high electrostatic interaction to bind negatively
3
charged fluoride ion. Gd(TTA) -DPPZ has a mononuclear nine-
2
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1
.0
.8
.6
.4
.2
0.0
Gd(TTA) -DPPZ + various anions
3
−
F
Gd(TTA) -DPPZ + various anions + fluoride ion
3
0.60
0.45
0.30
0.15
0.00
0
0
0
0
300
350
400
450
Wavelength (nm)
1
2
3
4
5
6
7
8
9 10 11
Fig.
3
UV-vis absorption spectra of Gd(TTA)
3
-DPPZ (10 μM) in the presence of
Fig. 5 Changes in fluorescence intensity of Gd(TTA) -DPPZ (10 μM) toward fluoride ion
3
–
increasing amount of fluoride ions (0-0.7 mM) in H
2 2
O (THF: H O = 5:5, pH = 7.4).
in the presence of various competing anions in H O (THF: H O = 5:5, pH = 7.4): (1) Br
2
2
–
–
–
–
(
3
0.7 mM), (2) Cl (100 mM), (3) NO (0.7 mM), (4) OH (0.7 mM), (5) I (0.7 mM), (6)
–
–
3–
–
–
By virtue of the high affinity of the fluoride with HSO
4
(0.7 mM), (7) AcO (0.7 mM), (8) PO
4
2 4
(1 mM), (9) H PO (0.7 mM), (10) F (0.7
mM), (11) Anions mixed. The intensities were recorded at 420 nm, excitation at 340 nm.
3
lanthanide(III) ions, Gd(TTA) -DPPZ was expected to act as a
potential indirect probe for fluoride ion sensing via
Fluorescent titration analysis was then conducted to
displacement of coordinated water molecule. Thus, the
demonstrate the capability of Gd(TTA)3-DPPZ ensemble as the
response of fluoride ion by Gd(TTA)
investigated by spectrophotometric titration in aqueous
medium (THF: H O = 5:5, pH = 7.4). As showed in Fig. 2,
Gd(TTA) DPPZ displayed a major absorption band with a
3
-DPPZ complex was firstly
probe for fluoride ion sensing in aqueous medium (THF: H O =
2
5
:5, pH = 7.4). As shown in Fig. 4, the fluorescence emission of
2
Gd(TTA)3-DPPZ was gradually switched “ON”. A ca. 2-fold
enhancement of fluorescence intensity was observed when
the addition of 0.7 mM fluoride ions. The fluorescence
enhancement could be attributed to the displacement of
coordination water molecules by fluoride ions in close
3
-
maximum absorption peak at about 340 nm in aqueous
medium, which can be attributed to over-lap of the
thenoyltrifluoroacetone (TTA) ligand and phenanthroline
4
0
derivative (DPPZ) (Fig. S5, ESI†). As shown in Fig. 2, upon the
–
4
1
–
–
proximity to the Gd(III). In addition, the increase in
fluorescence intensity was found partly contributed by the
interacꢀon of fluoride ion and TTA ligand (Fig. S6, ESI†). No
changes in absorption and fluorescence spectra of DPPZ ligand
was noticed in the presence of fluoride ions. The enhancement
of fluorescence intensities showed a good linearity with the
concentrations of fluoride ions in the range of 0–50 μM and
the detection limit was estimated to be 70 nM based on a
3
addition of diverse anions, including 0.7 mM of AcO , Br , NO ,
–
–
–
-
3-
I , HSO
changes in absorption spectra of Gd(TTA)
observed. The absorption spectrum was slightly changed upon
4
, OH , even 100 mM Cl and 1 mM PO
4
, no obvious
3
-DPPZ were
–
2 4
the titration of 0.7 mM H PO . In contrast, a remarkable
decrease in the absorbance peak at 340 nm with a 20 nm
bathochromic shift of absorbance band were observed when
fluoride ions (0-0.7 mM) was added (Fig. 3). The results
4
2,43
3
σ/slope by reported method (Fig. S7, ESI†).
In addition,
demonstrated that Gd(TTA)
3
-DPPZ can be employed as a
the selectivity of Gd(TTA)3-DPPZ towards fluoride ion was also
evaluated by fluorescence analysis. As shown in Fig. 5, no
significant fluorescence enhancements were observed when
specific probe for fluoride ion sensing in aqueous solution.
–
–
–
–
–
–
Gd(TTA)3-DPPZ was treated with AcO , Br , NO , I , HSO , OH ,
3
4
–
and tremendously excessive amounts of Cl (100 mM) and
3
PO4 (1 mM). The addition of H PO into Gd(TTA)3-DPPZ
–
–
2
4
solution led to slight increase in fluorescent intensity
compared to that of fluoride ions (4.5 times smaller). The
excellent selectivity could be attributed to the higher affinity
of Gd(TTA)3-DPPZ system to fluoride ion over other typically
anions. In addition, to evaluate the utility of Gd(TTA)3-DPPZ for
the selective detection of fluoride ion in a complicated
environment, Gd(TTA)3-DPPZ solution was treated with
fluoride ion in the presence of different competitive anion
species. All potentially competitive anions exerted no or little
influence on the fluorescence detection of fluoride ion,
Fig. 4 Fluorescence spectra of Gd(TTA)
amounts of fluoride ions (0–0.7 mM) in H
Normalized fluorescence intensities of Gd(TTA)
3
-DPPZ (10 μM) in the presence of different suggesting that Gd(TTA)
O (THF: H O = 5:5, pH = 7.4). Insert:
-DPPZ (10 μM) at 420 nm as a function
3
-
DPPZ is
a
fluoride-specific
2
2
fluorescence probe even in complicated samples.
3
of fluoride ion concentration. Excitation was performed at 340 nm.
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0
0
0
0
0
.20
.15
.10
.05
Y = 2.07976X + 0.01147
0.60
None
1
2
4
6
8
10
11
2
R
= 0.9993
3
5
7
9
0.45
0.30
0.15
0.00
.00
0
.00
0.02
0.04
0.06
0.08
−
6
1
2
3
4
5
6
7
8
9 10 11
1
/[F ](10 )
Fig. 6 Benesi-Hildebrand plot of Gd(TTA)
3
-DPPZ (2 μM) in H
2
O (THF: H
2
O = 5:5, pH = 7.4)
Fig. 8 Longitudinal relaxivity (r
anions of interest in H O (THF: H
measurements at a proton frequency of 20 MHz) of Gd(TTA)
1
) responses of Gd(TTA)
3
-DPPZ (0.2 mM ) to various
-weighted MR images (T
-DPPZ (0.2 m) in the
based on 1:1 binding stoichiometry with fluoride ions. The intensities were recorded at
20 nm, excitation at 340 nm.
2
2
O = 5:5, pH = 7.4). Insert: T
1
1
4
3
–
–
–
–
presence of (1) Br (0.7 mM), (2) Cl (100 mM), (3) NO
3
(0.7 mM), (4) OH (0.7 mM), (5)
–
–
–
3–
–
I (0.7 mM), (6) HSO
4
(0.7 mM), (7) AcO (0.7 mM), (8) PO
4
2 4
(1 mM), (9) H PO (0.7
CF
O-
N
N
3
–
H
2
O
C
S
mM), (10) F (0.7 mM), (11) Anions mixed, respectively.
CF
O-
3
F
S
O
O
F
3
N
N
O-
F3C
Gd
O
-
N
N
N
Next, we demonstrated the displacement approach by the
F-
Gd
O
O-
O
O
N
studies on MRI response of Gd(TTA)3-DPPZ towards fluoride
S
O-
S
S
O
F
3
C
S
F
3
C
ion. The MRI responses ability of Gd(TTA)
toward fluoride ions were then determined using
measurements at a proton frequency of 20 MHz (298 K, pH =
.4). As shown in Fig. 7, Gd(TTA)3-DPPZ(0.2 mM) exhibits
3
-DPPZ (0.2 mM)
3
Gd(TTA) -DPPZ
T
1
3
Scheme 2 The proposed mechanism for fluoride ion sensing by Gd(TTA) -DPPZ
7
To verify the replacement of waters with fluoride ions,
-1 -1
relative stable longitudinal relaxivity (r = 2.36 mM ·s ) in H O
2
1
the binding mode of Gd(TTA)3-DPPZ toward fluoride ion was
4
determined by using the Benesi–Hildebrand equation. As
(
THF: H O = 5:5, pH = 7.4) arising from one inner-sphere water
2
4
45
molecule (q = 1). The relaxivity of Gd(TTA) -DPPZ was
3
shown in Fig. 6, the plotting of 1/(F − F ) versus 1/[fluoride]
0
2
showed a good linear relationship (R = 0.9993), which
-1 -1
gradually decreased to 0.581 mM ·s with the increase of the
concentrations of fluoride ion (0−0.7 mM), which
demonstrated that the replacement of coordination water
indicates a stable 1:1 stoichiometry complexation species, and
3 −1
the association constant K was calculated to be 7.35 × 10 M .
a
with fluoride ion. Additionally, the corresponding T -weighted
1
The results further indicated that the coordination waters
replacement mechanism is responsible for the spectroscopic
responses towards fluoride ions.
images of Gd(TTA)3-DPPZ(0.2 mM) demonstrated a continuous
decrease in spot brightness as increasing of fluoride ion
concentrations (Fig. 7 insert). This together with the high
longitudinal relaxivity (r ) manifests the applicability of
1
MRI Responses toward fluoride
Gd(TTA)3-DPPZ as an efficient T MRI probe.
1
Interestingly, the relaxivity changes of Gd(TTA)3-DPPZ were
fluoride ion specifically over other physiologically important
anions. As shown in Fig. 8, upon addition of the competitive
–
–
–
–
–
–
anions (0.3 mM) including AcO , Br , Cl , NO , I , HSO , and
3
4
–
OH to the solution containing Gd(TTA) -DPPZ (0.2 mM) does
3
not interfere with the responses of the longitudinal relaxivity
–
r ). The addition of H PO into Gd(TTA)3-DPPZ solution only
(
1
2
4
led to slight decreasing of the longitudinal relaxivity. We
reasoned that the selective MRI response of Gd(TTA)3-DPPZ
towards fluoride ion is due to the strong coordination ability of
fluoride ions towards Gd(III) ions. In addition, a distinctly
decreased imaging intensity in the presence of 0.3 mM
fluoride ions is indeed exhibited, whereas discernible
differences are not observed upon addition of equimolar
–
–
–
–
–
–
–
–
amounts of AcO , Br , Cl , NO , I , HSO , OH , and H PO (Fig.
3
4
2
4
8, insert).
Fig. 7 Changes in the longitudinal relaxivity (r
function of fluoride ions concentration (0-0.7 mM) in H
Insert: -weighted MR images of Gd(TTA) -DPPZ recorded versus different
concentrations of fluoride ions.
1
) of Gd(TTA)
3
-DPPZ (0.2 mM) as a
2
O (THF: H
2
O = 5:5, pH = 7.4).
T
1
3
4
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Conclusions
In this study, we presented a novel Gd(III) complex based dual
modal probe, Gd(TTA) DPPZ for fluoride ion sensing. Upon
the addition of fluoride ions into the aqueous solution of
Gd(TTA) DPPZ, the replacement of the coordination water
molecules led to the decreasing the longitudinal relaxivity (r
3
-
3
-
1
)
as well as the distinct spectroscopic changes, realizing
MRI/fluorescence dual modal fluoride ion sensing. The new
developed dual modal probe presents sensitively response
towards fluoride ion in aqueous solution. To demonstrate its
3
biological applications, Gd(TTA) -DPPZ was then successfully
applied to visualise fluoride ions in abdomen of live mice by
MRI images. Given these promising results, the dual modal
Fig.
1
9 In vivo MR pseudocolor images of living white mice. T -weighted MRI
sagittalsection (top) and transaction (bottom) images after intraperitoneal injection of probe reported herein may not only ensure high sensitive and
(
a) None, (b) Gd(TTA)
3
-DPPZ (0.2 mL, 1 mM), and (c) fluoride ions (0.2 mL, 5 mM), selective detection of fluoride ions in aqueous solution and in
sequentially.
biological samples, but also provide a new flexible strategy for
the rational design of dual modal probes for anions sensing.
Experiment
Reagents and Instruments
All reagents and solvents were of analytical reagent grade and
used without further purification unless otherwise noted. 10-
phenanthroline (99%), triethylamine (99%) and o-
phenylenediamine (99%) were purchased from Sinopharm
Chemical
Thenoyltrifluoroacetonate (TTA) (99%) and Gadolinium
chloride (GdCl ) (99.9%) were purchased from Aladdin.
Reagent
Co.,
Ltd.
(China);
2-
1
Fig. 10 In vivo T -weighted MR pseudocolor images of micepre- and post-injection of
3
Gd(TTA) -DPPZ (0.4 mL, 1 mM).
3
Encouraged by the remarkable longitudinal relaxivity (r
1
)
Tetrabutyl ammonium fluoride trihydrate (97%), tetrabutyl
ammonium chloride (97%), tetrabutyl ammonium bromide
response abilities of Gd(TTA) -DPPZ (0.2 mM) toward fluoride
3
ion, we proceeded to evaluate the potential application of the
(
98%), tetrabutyl ammonium iodide (98%), tetrabutyl
contrast agent for MRI imaging in vivo. Prior to the MRI, the
ammonium hydrogensulfate (97%), tetrabutyl ammonium
dihydrogen phosphate (98%), and tetrabutyl ammonium
acetate (97%) were purchased from Shanghai Chemical
Reagent Co., Ltd. (China). Fresh stock solutions of anion (TBA
3
cytotoxicity of Gd(TTA) -DPPZ was evaluated by the reduction
activity of the methyl thiazolyltetrazolium (MTT [3-(4,5-
dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide]) assay
in human breast carcinoma (MDA-MB-231) cell lines. The
cellular viability was estimated to be more than 50% after
salts, 20 mM) in H
13
2
O were prepared for further experiments.
1
H-NMR and
C-NMR spectra were recorded with an
4
6
incubation with Gd(TTA)
The MRI imaging experiments were performed through
intraperitoneal injection of Gd(TTA) DPPZ (0.2 mL, 1 mM) into
a white mice (10 g) and imaged in a 0.5 T MRI instrument. It
should be noted that the injected dose of Gd(TTA) DPPZ is
As shown in Fig.
DPPZ, a 38.5% contrast
3
-DPPZ (1 mM) for 6 h (Fig. S8, ESI†).
AVANCE600MHZ spectrometer (BRUKER) with chemical shifts
reported as ppm (in DMSO, TMS as internal standard). ESI-MS
analyses were carried out on a HPLC-Q-Tof MS spectrometer
using methanol as the eluent (Agilent). The elemental analyses
of C, H, N were performed on a Vario EL III elemental analyzer.
Fluorescence spectra were determined with LS 55
luminescence spectrometer (Perkin Elmer, USA). The
absorption spectra were measured with a Lambda 900
UV/VIS/NIR spectrophotometer (Perkin Elmer, USA). MR
imaging was performed on an MesoMR23-060H-I Analyst
Analyzing & Imaging system (Shanghai Niumag Corp., China)
using a 0.5 T magnet, point resolution = 256 × 128 mm, section
thickness = 1 mm, TE = 18.2 ms, TR= 400 ms, and number of
acquisitions = 4.
3
-
3
-
4
7-49
much low than the reported MRI in mice.
(b), after the injection of Gd(TTA)
9
3
-
enhancement at the site of injection was observed compared
with the baseline of the pre-injection image (Fig. 9 a). However,
the sequentially injection of fluoride ions (0.2 mL, 5 mM) on
the abdomen of the mice caused the T
the interest portions to exhibit significant contrast dark effect
Fig. 9, c). In addition, the successive bright MRI action of the
Gd(TTA) DPPZ on mice model was achieved at different time
1
-weight MR images of
(
3
-
points, even after 20 h (Fig. 10), suggesting that the contrast
agents could continuously improve contrast in tissues and
have a relatively longer blood circulation time. These 4,5,9,14-tetraaza-benzotriphenylene (DPPZ) was synthesized
3
Synthesis of Gd(TTA) -DPPZ
4
0
3
preliminary images demonstrate that Gd(TTA) -
DPPZ functions exactly according to the literature procedure. To 1,10-
successful for the MRI imaging of fluoride ion in vivo.
phenanthroline-5,6-dione (0.420 g, 2 mmol) in 20 mL of
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ARTICLE
ethanol was added o-phenylenediamine (0.238 g, 2.2 mmol) specific relaxivity values of r
Journal Name
1
were calculated through the
–1
and 0.05mmolof 4-methylbenzenesulfonicacid. The mixture curve fitting of 1/T
1
(s ) vs. the fluoride concentration (mM).
was heated at 80 C for 10 h, the crude product was filtered In vivo MR imaging experiments were performed using a 0.5T
and then recrystallized from ethanol to give the pure desired systems. A 0.2 mL of Gd(TTA) DPPZ (1 mM, DMSO: H O = 5:5,
o
3
-
2
1
product (DPPZ) in 78 % yield. H NMR (DMSO-d, 600 MHz) pH = 7.4)) was first injected into white mouse (10 g) through
δ(ppm): 9.45 (d, 2H), 9.19 (d, 2H), 8.34 (d, 2H), 8.04 (d, intraperitoneal and MR imaging was immediately followed
1
3
H),7.91(d, 2H). C NMR (DMSO-d, 150 MHz) δ(ppm): 152.3, under the Niumag 0.5 T scanner. After the MR imaging, 0.2 mL
2
147.8, 141.6, 140.7, 133.0, 129.2, 124.5, 117.6, 114.8. ESI-MS of fluoride ion (5 mM) aqueous solution was then injected into
(
positive mode, m/z) Calcd for C18
H
10
N
4
: 305.0803 [DPPZ
+
the same mice in the same place and imaged again.
+
Na] ; Found: 305.0798.
Gd(TTA) DPPZ was obtained by one-pot synthesis method
according to the conventional method with minor
3
-
Acknowledgements
5
0
modifications as follows. TTA (0.666 g, 1 mmol) and
triethylamine (3 mmol) were added to 20 mL ethanol, and
stirred for 10 minutes. Then, DPPZ (0.282 g, 1 mmol) and
gadolinium chloride (0.263 g, 1 mmol) were added. The
reaction mixture was refluxed for 3 h whilst stirring to yield a
yellow precipitate. After cooling to room temperature, the
precipitate was washed with ethanol and dried under vacuum
This work is supported by the National Natural Science
Foundation of China (No. 21301011), the Key Laboratory
Program of Educational Department of Liaoning Province
(
LZ2015047), the State Key Laboratory of Fine Chemicals
KF1305), and the National Natural Science Foundation of
(
China (No. 21542017).
to obtain the targeted Gd(III) Complex, Gd(TTA)
3
-DPPZ in 85%
yield with a HPLC purity of 99.3%. Mp. 198.0-198.7. ESI-mass Notes and references
spectra (positive mode, m/z): Calcd for C42
H
22
F
9
GdN
+
4 6 3
O S :
1
2
E. L. Que and C. J. Chang, J. Am. Chem. Soc., 2006, 128
5942–15943.
(a) Y. Fujikawa, Y. Urano, T. Komatsu, K. Hanaoka, H. Kojima,
,
+
Na] ,
1
102.9797; Found: 1125.9744 [Gd(TTA)
+
3
-
DPPZ
1
1141.0812 [Gd(TTA)
3
-
DPPZ + K] , respectively. Elemental
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Analysis: Calculated: C, 43.86; H, 2.11; N, 5.75. Found: C, 43.63;
H, 2.18; N, 5.87.
1
3
General procedures of spectra detection
Stock solutions of Gd(TTA)
mixed solution of H O and THF (v/v 5:5, pH = 7.4). Excitation
wavelength for Gd(TTA) DPPZ was 340 nm. Before
3
-DPPZ were prepared in
4
5
2
3
-
spectroscopic measurements, the solution was freshly
prepared by diluting the high concentration stock solution to
corresponding solution (10 μM). Each time a 3 mL solution of
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8
9
4
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Association constant calculation
Generally, for the formation of 1:1 complexation species
2
formed by Gd(TTA)
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-
DPPZ and fluoride ion, the Benesi-
5
1
Hildebrand equation was used as shown below.
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-
F −
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K
a
( F
m
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) [ F
]
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nm of Gd(TTA) DPPZ in the presence and absence of fluoride
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K is the binding constant.
,
Longitudinal relaxivity (r
All MR relaxivity measurements were performed on an
MesoMR23-060H-I Analyst Analyzing Imaging system
Shanghai Niumag Corp.). T
acquired using a multi-slice gradient echo sequence. The
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Graphical abstract
A novel Gd(III) complex based dual-modal probe, Gd(TTA)
fluorescence and longitudinal relaxivity (r ) responses to fluoride ion (F ) in aqueous media and
in vivo. In the presence of fluoride ions, the replacement of the coordinated water molecules
results in decreasing the longitudinal relaxivity (r ) as well as the remarkable spectroscopic
responses, thereby fluoride ion was detected by MRI/fluorescence dual bimodal modalities.
3
-DPPZ exhibits simultaneous
－
1
1