J. Wang, C.-S. Ha / Tetrahedron 65 (2009) 6959–6964
6963
Gemimi-2000 (300 MHz) spectrometer. Electrospray Ionization
(ESI) Mass-Spectrometry was performed using agilent 1100 LC/
MSD SL instrument. The UV–vis spectra were measured using
a Hitachi U-2010 spectrometer. The fluorescence emission spectra
were measured using a Hitachi F-4500 spectrometer. Stock buffer
solutions (20 mM) of various pH values were prepared in a MeOH/
H2O cosolvent (v/v, 6/4). PHP (potassium hydrogen phthalate, pH
2.5–5.0), MES (2-morpholineoethanesulfonic acid, pH 5.5–6.5),
HEPES (4-(2-hydroxyethyl)piperazine-1-ethanesulfonic acid, pH
7.0–8.0), EPPS (4-(2-hydroxyethyl)piperazine-1-propanesulfonic
acid, pH 8.2–8.5), and CHES (2-(cyclohexylamino)-1-ethanesulfonic
acid, 9.0–10.0) were used to cover different pH ranges. pH above 10
was obtained by adding small amount of NaOH. 0.06 mM of 1 and
10.0 mM of buffer were used for both absorption and fluorescence
measurements.
was purified by column chromatography and eluted with a solvent
gradient ranging from 10 to 20% ethyl acetate in petroleum ether to
yield 1 as an orange solid (425 mg, 75% yield). 1H NMR (300 MHz,
CDCl3, 25 ꢂC, TMS):
d
¼7.01–7.94 (m, 8H), 5.81 (m, 1H), 4.95(t, 2H),
2.69 (m, 2H), 2.05 (m, 2H), 1.79 (m, 2H), 1.29–1.33 (m, 10H). MS-ESI
(m/z): [Mþ1]þ 381.3.
Acknowledgements
This work was supported by the Korea Science and Engineering
Foundation (KOSEF) Grant funded by the Ministry of Education,
Science and Technology, Korea (MEST) (Acceleration Research
Program (No. 2009-0078791)), a grant from the Fundamental R&D
program for Core Technology of Materials funded by the Ministry of
Knowledge Economy, Korea, the Korea-China Joint Research Center
Program of the Korea Foundation of International Cooperation for
Science and Technology, the Brain Korea 21 Project, and the MEST
for the scholarship for foreign students (J.W.).
4.2. pKa determination
The pKa values were determined spectrophotometrically.46 The
spectra were observed from 200 nm to 600 nm initially and after
each subsequent pH adjustment. The pH adjustments and spec-
troscopic measurements were made until an end-point was
reached, and the pKa values were obtained using the following
equation:
Supplementary data
Supplementary data associated with this article can be found in
References and notes
ꢀ
ꢁ
ꢀ
A ꢀ AIn
pKa ¼ pH þ log10
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AHIn ꢀ A
where A is the absorbance, Inꢀ and HIn are the deprotonated form
(at 477 nm) and the protonated form (at 325 nm) of the compound,
respectively. The reliability of an individual pKa value was de-
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4.3. Quantum yield measurements
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Quantum yields for fluorescence were measured by comparing
the integrated area of the corrected emission spectrum of the
samples with that of a solution of fluorescein in 0.1 N NaOH, which
has a quantum efficiency of 0.95.14,47 The quantum efficiency of the
metal-free 1 was measured by using a dilute sample of
1
(1ꢁ10ꢀ6 M) in 10 mM HEPES, pH¼7.0. The quantum efficiency of
metal-bound compound was measured by using a dilute sample of
1 (8ꢁ10ꢀ7 M) and 5 equiv ZnCl2 in 10 mM HEPES, pH¼7.0. The
concentration of the reference was adjusted to match the absor-
bance of the test sample at the wavelength of excitation. Emission
for 1 and 1–Zn2þ was integrated from 550 to 650 nm with excita-
tion at 507 nm. The quantum yields were calculated with the fol-
lowing equation:
ꢀ
ꢁꢀ ꢁꢀ
ꢁ
2
As
Ax
Fx
Fs
hx
hs
FFðxÞ ¼
FFðsÞ
where s is the standard, x is the unknown, A is the absorbance at the
excitation wavelength, F is the integrated area under the emission
curve,
yield.
h is the refractive index of the solvent and FF is the quantum
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4.4. Synthesis of compound 1
10-Undecenoyl chloride (2.3 mmol, 466 mg) was added to
a mixture of 2,20-dihydroxyazobenzene35,48 (1.5 mmol, 321 mg),
K2CO3 (4.5 mmol, 621 mg) and 18-crown-6 (50 mg) in dry acetone
(50 ml) and the mixture was refluxed for 15 h. After cooling to room
temperature, the mixture was filtered and evaporated. The residue
was dissolved in ethyl acetate, washed with water and dried over
MgSO4. The resulting residue was then dried. The crude product