Paper
RSC Advances
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43.36, 142.87, 129.33, 127.09, 126.84, 124.27, 123.18, 122.13,
19.35, 118.76, 117.98, 116.35, 101.58, 99.45, 92.19, 71.66,
1.35, 71.03, 63.14, 47.77, 38.56, 6.98. HRMS (ESI) calcd for
+
C H N O S [M + H] : 632.2435, found: 632.2421.
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34 6 4
Preparation of the test solution
Rhodamine B based probes 3a–c stock solutions (200 mM) were
prepared in methanol. Stock solutions of metal ions were
+
+
2+
2+
2+
prepared with hydrochloride salts of Na , K , Ca , Cd , Mg ,
2
+
2+
2+
3+
2+
2+
2+
2+
3+
3+
Co , Mn , Cu , Al , Zn , Ni , Fe , Hg , Cr , Fe , and the
nitrate salt of Ag in distilled water. Before spectroscopic
+
measurements, the solutions of 3a–c were freshly prepared by
diluting the high concentration stock solution to corresponding
solution. All the measurements were made according to the
following procedure. Test solutions were prepared by placing 1
mL of the probe solution into a glass tube, adding an appro-
priate aliquot of each metal stock, and diluting the solution to
Scheme 1 Synthesis of 3a–c.
10 mL with methanol–water (4/6, v/v) solution. To make the
metal ions chelate with the probe sufficiently, solutions were
shaken for 10 s and waited for 20 min before determination.
The absorbance was recorded at 562 nm and the uorescence
intensity was recorded at 583 nm. The excitation and emission
wavelength bandpasses were both set as 2.5 nm and the exci-
tation wavelength was set at 555 nm.
oxychloride (5 mL). Aer being heated to reux for 4 h, the
solvent and excess amount of phosphorus oxychloride was
removed by evaporation to give the corresponding acid chlo-
ride, which was dissolved in acetonitrile without further puri-
cation. Then a solution of 1a (0.59 g, 3 mmol), triethylamine
(2 mL) in acetonitrile (20 mL) was added. Aer reuxing for 12
h, the solvent was removed under reduced pressure to give a
violent-oil. Water was then added to the mixture and the
aqueous was extracted with dichloromethane (15 mL ꢀ 3). The
Cell culture and uorescence imaging
The human cancer cell line HepG2 (liver cells) were cultured in
RPMI 1640 supplemented with 10% FBS. Immediately before
the experiments, cells were pretreated with probes 3a–c (20 mM)
organic layer was dried over anhydrous MgSO and ltered. The
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crude product was puried by silica gel column chromatog-
ꢁ
1
for 1 h at 37 C in humidied air and 5% CO , washed three
2
raphy to give 3a (white solid) in 71.2% yield. H NMR (400 MHz,
times with PBS and imaged. Aer incubation with FeCl (20 mM)
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CDCl
3
) d (ppm) 8.78 (s, 1H), 8.20 (dd, J
.09 (d, J ¼ 8.0 Hz, 1H), 7.70–7.50 (m, 4H), 7.27 (d, J ¼ 8.0 Hz,
H), 6.50 (s, 2H), 6.39 (d, J ¼ 8.0 Hz, 2H), 6.18 (d, J ¼ 8.0 Hz, 2H),
1
¼ 8.0, J
2
¼ 8.0 Hz, 2H),
ꢁ
for another 1.5 h at 37 C, cells were washed 3 times with PBS to
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3
3
remove remaining FeCl and imaged.
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.30 (q, J ¼ 4.0 Hz, 8H), 1.14 (t, J ¼ 6.0 Hz, 12H). C NMR (100
MHz, CDCl
3
) d 165.83, 153.58, 153.40, 148.50, 134.24, 128.37, Results and discussion
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28.21, 127.71, 127.27, 126.86, 124.46, 123.05, 106.78, 104.97,
7.49, 76.85, 76.53, 76.21, 68.03, 43.74, 12.18. HRMS (ESI) calcd
Synthesis and crystal structure
+
The general synthetic procedure is given in Scheme 1. The target
compound 3a was easily synthesized by the reaction of rhoda-
mine B acid chloride (2) and 1a. Title compounds 3b and 3c
were also prepared by similar procedures. The structures of
compounds 3a–c were characterized by H NMR, C NMR, and
HRMS analyses. Crystals of compounds 3a–c were obtained
from a mixture of methanol–dichloromethane. In Fig. 1, a
unique spirolactam structure ring formation of 3a was observed
for C H N O S [M + H] : 602.2584, found: 602.2620.
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35 5 2
Compounds 3b and 3c were prepared with the similar
synthetic method to 3a.
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Compound 3b (white solid): yield: 69.5%. H NMR (400 MHz,
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CDCl
3
) d (ppm) 8.06 (d, J ¼ 7.5, 1H), 7.82 (d, J ¼ 8.6, 2H), 7.62–
.53 (m, 2H), 7.29–7.17 (m, 1H), 6.89 (d, J ¼ 8.7, 2H), 6.47 (d, J ¼
.4, 2H), 6.39 (d, J ¼ 8.8, 2H), 6.16 (dd, J ¼ 8.9, J ¼ 2.4, 2H),
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2
3
1
2
1
3
.81 (s, 3H), 3.29 (q, J ¼ 7.0, 8H), 1.13 (t, J ¼ 7.0, 12H). C NMR
(the crystal data of 3a–c are shown in ESI†).
(
100 MHz, CDCl ) d 165.75, 162.12, 160.66, 153.56, 153.40,
3
1
1
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48.46, 134.19, 128.32, 128.19, 127.76, 127.29, 124.43, 123.02,
13.77, 106.73, 105.00, 97.45, 76.88, 76.56, 76.24, 67.92, 54.85,
Spectroscopic properties
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3+
3.74, 12.20. HRMS (ESI) calcd for C37
32.2690, found: 632.2714.
H
37
N
5
O
3
S [M + H] : Upon binding with Fe , the probes 3a–c exhibited similar
spectroscopic properties. The R moiety had an effect on the
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Compound 3c (yellow solid): yield: 69.5%. H NMR (400 uorescence intensities of the probes. However, no obvious
MHz, CDCl ) d (ppm) 8.07 (d, J ¼ 8.0 Hz, 1H), 7.88 (d, J ¼ 3.5 Hz, effects were found to be caused by the R moiety on the other
3
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H), 7.63–7.54 (m, 2H), 7.25 (d, J ¼ 7.9 Hz, 1H), 7.37 (s, 3H), 6.48 spectral properties of the probes. Thus, 3a is chosen for further
(
2
d, J ¼ 1.5 Hz, 2H), 6.39 (d, J ¼ 8.8 Hz, 2H), 6.17 (d, J ¼ 7.0 Hz, discussion, optical spectra of 3b and 3c are shown in the ESI.†
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H), 3.30 (q, J ¼ 8.0 Hz, 8H), 1.13 (t, J ¼ 6.0 Hz, 12H). C NMR
The UV-vis titration of the probe 3a was carried out in
(100 MHz, CDCl
3
) d 160.69, 154.53, 149.71, 148.47, 148.06, methanol–water (4/6, v/v) solution (Fig. 2a). Initially, free probe
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RSC Adv., 2014, 4, 14248–14253 | 14249