2
Tetrahedron
hydrosulfide used for SH2 generation) and other chemicals for
A naphthalimide-indoline hybrid (1) was synthesized as depicted
in Scheme 2. Compounds 217, 318, and 419 were synthesized
according to the literature procedures. Condensation of 2 with
1,2,3,3-tetramethyl-3H-indolium iodide in presence of trifluoroacetic
acid (TFA) as a catalyst in DMF gave probe 1. The structures of 1-4
were confirmed by 1H NMR, 13C NMR, and ESI-MS analyses (Figs.
S4-S6). Interestingly, unlike other fluorophore-indolium hybrid
materials,20 probe 1 showed a doublet peak at 3.62 ppm assigned to
the proton (Ha) of indoline moiety in 1H NMR spectrum (Fig. S4). In
addition, the tertiary carbon (Ca) of probe 1 was clearly observed at
80.8 ppm in 13C NMR spectrum (Fig. S5).
synthesis and analysis were purchased from Aldrich, TCI, Alfa and
used as received. All solvents were HPLC reagent grade, and
distilled water was used in the analytical experiments. NMR was
recorded at Bruker 400 MHz instrument and all chemical shifts are
reported in ppm value using TMS as an internal reference. ESI-MS
data were obtained using liquid chromatography mass spectrometer
(LC/MS) at the Korea Basic Science Institute.
UV/Vis absorption and Fluorescence Spectroscopy
Stock solutions of probes, perchlorate salts of metal ions, and
TBA salts of anions were prepared in CH3CN. The pH buffer
solutions were prepared by using 50 mM of potassium chloride (for
pH 1-2 buffer), potassium hydrogen phthalate (for pH 3-5 buffer),
potassium dihydrogen phosphate (for pH 6-8 buffer), sodium
tetraborate (for pH 9-10 buffer), and sodium bicarbonate (for pH 11
buffer). The pH was adjusted by adding 0.1 M of NaOH or 0.1 M of
HCl solution. Stock solutions of reactive oxygen species were
prepared by using literature procedures.15 Briefly, H2O2, tert-
butylhydroperoxide (HOOtBu), and hypochlorite (NaOCl) were
delivered from 35%, 70%, and 11-14% aqueous solutions
respectively. Hydroxyl radical (HO•) and tert-butoxy radical (tBuO•)
were generated by the reaction of 10 mM (NH4)2Fe(SO4)2, with 10
O
O
O
O
N
O
O
N
O
CuCN
Butylamine
EtOH, 92%
DMF, 59%
Br
Br
CN
3
4
O
N
O
-
mM H2O2 or HOOtBu, respectively. Superoxide (O2 ) was delivered
O
N
O
N
I
Ni-Al
from 10 mM of potassium oxide (KO2) in 10 mM pH 7.4 PBS
solution. The Cu+ was delivered from [Cu(MeCN)4][PF6] in CH3CN
solution.16 UV/Vis absorption and fluorescence spectra were
recorded using UV-2600 (Shimadzu), and RF-6000 (Shimadzu)
spectrophotometers, respectively. Excitation was provided at 390 nm
with excitation and emission slit widths at 5 nm, respectively.
Formic acid, H2O
40%
DMF, TFA
32%
Ha
N
a
O
2
1
Scheme 2. Synthetic routes to a naphthalimide-indoline hybrid (1).
Synthetic procedures
Synthesis of 2-4: Compounds 217, 318, and 419 were prepared
according to the literature procedures.
Optical properties of probe 1
Synthesis of 1: A mixture of 2 (120 mg, 0.43 mmol), 1,2,3,3-
tetramethyl-3H-indolium iodide (260 mg, 0.86 mmol) and
trifluoroacetic acid (TFA) (3.0 mL, 26.4 mmol) in
resulting solution was heated at reflux for 3h at 120 °C. After cooling
to room temperature, the reaction mixture was diluted with ethyl
acetate (EA), and washed with water. The organic layer was then
collected, and dried with anhydrous Na2SO4. After removal of the
solvents, the crude product was purified by silica gel column
chromatography using EA/hexanes (v/v, 1:7) as the eluent to yield 1
First of all, UV/Vis absorption and fluorescence spectral changes
of 1 were monitored in various pH solutions. In Fig. 1a, as the pH
changed from 11 to 1.0, fluorescence intensity (FI) at 430 nm was
increased. The FI at 430 nm was very weak in pH span of 11 to 3.0,
while 29-fold increase was seen as the pH changed from 3.0 to 1.0
(see inset of Fig. 1a). In addition, a blue fluorescence was clearly
observed in the pH 1.0 buffer solution. However, negligible changes
were seen in the absorption spectra of 1 in Fig. S1. These findings
support the notion that the pH-dependent fluorescent turn-on signal
is due to a PET process as suggested in scheme 1. Moreover, probe 1
exhibited a gradual fluorescence increase at 430 nm when the pH
acidifies from 3.0 to 1.0 in Fig. 1b, and it was plotted in Fig. 1c. A
plot of pH vs log[(Imax-I)/(I-Imin)] was also produced based on the
Henderson-Hasselbach type equation (log[(Imax - I)/(I - Imin)] = pKa –
pH) (Fig. 1d).21 The pKa of probe 1 turned out to be 1.60 ± 0.018,
which implied that probe 1 could be used for measuring the pH range
of 2.5 ~ 1.0. We thus demonstrated that probe 1 can give a
fluorescence turn-on at the below pH 2.5, and could be useful for
monitoring of the highly toxic acid solutions such as HCl and HF.
1
as a yellow solid (60 mg, 32%). H NMR (CDCl3, 400 MHz): δ 0.99
(t, J = 7.0 Hz, 3H); 1.17 (s, 3H); 1.44-1.50 (m, 5H); 1.71-1.76 (m,
2H); 2.79 (s, 3H); 3.62 (d, J = 8.5 Hz, 1H); 4.19 (t, J = 7.2 Hz, 2H);
6.54-6.58 (dd, J1 = 15.8 Hz, J2 = 8.3 Hz, 1H); 6.61(d, J = 8.0 Hz,
1H); 6.81 (t, J = 7.2 Hz, 1H); 7.08 (d, J = 7.0 Hz, 1H); 7.17 (t, J =
7.5 Hz, 1H); 7.48 (d, J = 15.5 Hz, 1H); 7.79 (t, J = 7.5 Hz, 1H); 7.92
(d, J = 7.5 Hz, 1H); 8.51 (d, J = 8.5 Hz, 1H); 8.58 (d, J = 7.5 Hz,
1H); 8.64 (d, J = 7.5 Hz, 1H). 13C NMR (CDCl3, 100 MHz): 14.0,
20.5, 24.7, 26.1, 30.3, 35.0, 40.4, 45.0, 80.8, 108.3, 119.0, 121.9,
122.0, 123.3, 124.7, 127.0, 127.9, 128.7, 129.5, 129.6, 130.1, 131.2,
131.3, 135.4, 138.8, 141.0, 151.4, 164.1, 164.4 ppm. ESI-MS m/z
(M+) calcd for C29H30N2O2 438.2307, found 439.23 06 (M+H+).