Chemiluminescence change of polyphenol dendrimers with different core molecules

Article abstract of DOI:10.1021/ol802129a

(Chemical Equation Presented) Second generation polyphenol dendrimers (PDs) with different core molecules were synthesized, and their chemiluminescence (CL) was measured by reacting the PDs with H₂O₂ under alkaline conditions. All of the PDs showed a strong CL, more than 120-fold greater than that of gallic acid. Various CL intensities of the PDs were obtained using different core molecules in the PDs. The distance between each dendron in the PD structure is crucial in the PD CL intensity.

Full text of DOI:10.1021/ol802129a

ORGANIC
LETTERS
2008
Vol. 10, No. 22
5171-5174
Chemiluminescence Change of
Polyphenol Dendrimers with Different
Core Molecules
Hiroki Agawa,† Manabu Nakazono,† Shinkoh Nanbu,‡ and Kiyoshi Zaitsu*,†
Graduate School of Pharmaceutical Sciences, Kyushu UniVersity, 3-1-1 Maidashi,
Higashi-ku, Fukuoka 812-8582, Japan, and Research Institute for Information
Technology, Kyushu UniVersity, 6-10-1 Hakozaki, Higashi-ku, Fukuoka 812-8581,
Japan
zaitsu@phar.kyushu-u.ac.jp
Received September 11, 2008
ABSTRACT
Second generation polyphenol dendrimers (PDs) with different core molecules were synthesized, and their chemiluminescence (CL) was
measured by reacting the PDs with H2O2 under alkaline conditions. All of the PDs showed a strong CL, more than 120-fold greater than that
of gallic acid. Various CL intensities of the PDs were obtained using different core molecules in the PDs. The distance between each dendron
in the PD structure is crucial in the PD CL intensity.
Polyphenols, such as pyrogallol and gallic acid (3,4,5-
trihydroxybenzoic acid, GA), produce singlet oxygen (1O2)
in the presence of alkali and H2O2 and emit light (Figure
1).1,2 The CL emission wavelength (634 nm) of 1O2 is long
compared to that of other CL compounds.1 This indicates
that polyphenols, a selective 1O2 source, are useful as
selective probes for CL assays. However, the CL intensities
of the polyphenols are weak compared to that of well-known
luminescent compounds, such as luminol,3 acridinium ester,4
and 1,2-dioxetane derivatives.5 When a polyphenol with a
strong and long-lasting CL is synthesized by a facile
synthesis method, the polyphenol can be practically used as
an analytical probe. We propose that polyphenols having
many emitting units (GA units) can produce a strong CL
1
and should be useful for the specific sources of O2.
Dendrimers are constructed from the core, branch, and
periphery moieties and can be designed into various mol-
ecules.6 For example, biodegradable, self-assembled den-
drimers and dendrimers as a host or catalyst have been
† Graduate School of Pharmaceutical Sciences.
‡ Research Institute for Information Technology.
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10.1021/ol802129a CCC: $40.75
Published on Web 10/28/2008
2008 American Chemical Society

Scheme 1. Synthesis of 1-11
Figure 1. Generation process of singlet oxygen during polyphenol
chemiluminescence.
reported.7-10 We found that second generation poly(3,4,5-
trihydroxybenzoate ester) dendrimers (PDs) with pyrocat-
echol and 1,3,5-trihydroxybenzene as core molecules (com-
pounds 1 and 2, Scheme 1), which have many GA units,
showed a very strong CL compared to that of GA in the
presence of alkali and H2O2.11 There have been few studies
of the PDs and their CL. Thus, we synthesized second
generation PDs with different core molecules. The change
in the CL intensities of the PDs with the change in the core
molecules was evaluated. The CL spectrum of the PD was
measured to identify the CL species. We tried to investigate
the relationship between the structures of the PDs and the
CL. The photophysical properties of the PDs were evaluated.
These experimental results should provide a significant
information for developing luminescent PDs.
Compounds 1-11 were synthesized by a divergent method
(Scheme 1). In the divergent method, gradual esterification/
deprotection is required. We used benzyl groups to protect
the hydroxyl groups. The protecting groups can be easily
cleaved by catalytic hydrogenation. The esterification suc-
cessfully proceeded for all the tested core molecules and gave
a protected first generation dendrimer (5-50% yields). The
second step, debenzylation of the protected dendrimers,
proceeded with good yields (80-100%). The two steps
described above were repeated. Yields of the third and final
steps were 15-50% and 60-100%, respectively.
We measured the CL of the second generation PDs.12 The
reaction conditions (NaOH and H2O2 conc) that gave the
maximun CL intensity for each PD are shown in Table 1.
The CL intensities were recorded under very different
conditions for 1-11. All of the synthesized PDs showed a
strong and long-lasting CL (Figure 2).
These CLs lasted for more than 5 min, and their CL
intensities were at least 120-fold stronger than that of GA
(Table 1). The times to reach the maximum photon counts
were 30-70 s after the addition of H2O2. It was also found
that while the CL intensities of the PDs with pyrocatechol
(1), 1,3,5-trihydroxybenzene (2), naphthalenediol (3-6), 1,4-
butanediol (7), and 1,6-hexanediol (8) as core molecules were
120- to 360-fold stronger than that of GA, those of the PDs
with 1,10-decanediol (9), 1,12-dodecanediol (10), and 1,16-
hexadecanediol (11) as core molecules were 360-, 350-, and
300-fold stronger than that of GA (Table 1). Among the PDs
with linear diols as the core molecule, the CL intensities
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(12) The CL measurements of 1-11 are as follows: To 200 µL of 10
µM 1-11 in CH3OH was added 100 µL of 50-150 mM NaOH. After the
solution stood for 25 s, the CL reaction was initiated by the addition of
100 µL of 50-1250 mM H2O2. The CL emission was measured for 5 min,
and the integral photon counts were used for estimation of the CL intensities.
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Org. Lett., Vol. 10, No. 22, 2008

Table 1. Relative CL Intensities of 1-11
integral
photon
count
(× 104)
relative
CL intensity
per GA in
periphery
no. of
methylene
groups in
NaOH
(mM)
relative
CL intensityb
compda
H2O2 (mM)
core molecule
GA
1
2
3
4
5
6
7
8
200
100
100
75
75
67
75
75
125
100
100
67
750
750
250
1000
1000
100
750
500
500
250
250
250
0.5
115
180
90
60
65
65
70
75
1
230
360
180
120
130
130
140
150
360
350
300
1
38
40
30
20
22
22
23
25
60
58
50
4
6
10
12
16
9
10
11
180
175
150
a 10 µM in CH3OH. b CL intensity of GA in CH3OH was taken as 1.
greatly changed with the change in the length of the core
molecule, and the PD with 1,10-decanediol (9) as the core
molecule showed the strongest CL (Table 1). The increase
in the CL intensities was obtained by increasing the number
of methylene groups (4-10) in the linear alkyl chain of the
core molecule. The GA units in the periphery of 9 are three
units smaller than that of 2; however, the CL intensity is
still similar in each case. On the basis of these results, the
core molecule has a significant effect on the CL of the PDs.
emission wavelength was 630 nm. This maximum emission
wavelength matched that of O2. We measured the CL of 9
1
in the presence of 1,4-diazabicyclo[2,2,2]octane (DABCO)
and D2O (Figure 3).14 DABCO is a selective quencher of
Figure 3. Time course of CL of 9 in CL development in the
presence of DABCO and D2O. The final concentaration of 9 was
4.7 µM. [NaOH] ) 23 mM. [H2O2] ) 58 mM. I: D2O. II: [DABCO]
) 0 (H2O). III: [DABCO] ) 3.5 mM. IV: [DABCO] ) 7 mM. V:
[DABCO] ) 35 mM. VI: [DABCO] ) 70 mM.
Figure 2. Time course of CL of GA, 1, 6, 7, 9, and 11 in the CL
development. The final concentrations of GA, 1, 6, 7, 9 and 11
were 5 µM. 1: [NaOH] ) 25 mM, [H2O2] ) 188 mM. 6: [NaOH]
) 19 mM, [H2O2] ) 188 mM. 7: [NaOH] ) 19 mM, [H2O2] )
125 mM. 9: [NaOH] ) 25 mM, [H2O2] ) 63 mM. 11: [NaOH] )
17 mM, [H2O2] ) 63 mM. GA: [NaOH] ) 50 mM, [H2O2] ) 188
mM.
1O2.15 D2O is a solvent which increases the lifetime of 1O2.16
DABCO apparently quenched the CL intensities of 9. The
CL intensities decreased with an increase in the concentration
of DABCO. The addition of D2O apparently increased the
CL intensities of 9. Thus, we concluded that the final CL
1
species of the PDs was O2.
The CL spectrum of 2 was measured.13 Compound 2
strongly emitted in the 560-660 nm range. The maximum
(14) To 200 µL of 10 µM 9 in CH3OH were added 30 µL of D2O or
0.05-1 M DABCO and 100 µL of 100 mM NaOH. After allowing the
solution to stand for 25 s, the CL reaction was initiated by the addition of
100 µL of 250 mM H2O2. The CL emission was measured for 5 min.
(15) Ouannes, C.; Wilson, T. J. Am. Chem. Soc. 1968, 90, 6527–6528.
(16) Ogilby, P. R.; Foote, C. S. J. Am. Chem. Soc. 1983, 105, 3423–
3430.
(13) To 200 µL of 100 µM 2 in CH3OH was added 100 µL of 75 mM
NaOH. After the solution stood for 25 s, the CL reaction was initiated by
the addition of 100 µL of 500 mM H2O2. Differential spectra were obtained
from each photon count using 20 spectrofilters (350-720 nm).
Org. Lett., Vol. 10, No. 22, 2008
5173

Table 2. Absorption and Fluorescence properties of 1, 3, 5, 8,
and 11: Maximun Absorption Wavelength (λabs), Molar
Absorption Coefficients (ε), Maximum Emission Wavelength
(λem), and FL Quantum Yield (Φf)
Stokes
shift
(nm)
λabs
ε (× 104)
Φf
(× 10-3
b
c
compda (nm) (M-1 cm-1
)
λem (nm)
)
1
3
5
8
11
283
283
287
285
285
8.4
6.1
6.8
6.8
7.7
369
345
369
379
368
86
62
82
94
83
2
1
1
4
1
a 1 µM in CH3OH. b FL spectra were corrected. c Quantum yield (quinine
sulfate in 0.05 M H2SO4, Φ ) 0.51).
Figure 4. Optimized structures of 4 (a), 6 (b), 7 (c), and 9 (d)
using density function theory (B3LYP, cc-pVDZ).
confirmed that the CL intensities of 5 and 9 did not change
in the presence of naphthalene or 1,5-naphthalenediol. Thus,
naphthalene did not decrease the CL intensities of the PDs.
1
A single crystal of the PDs was not obtained for an X-ray
crystallography study. The optimized structures of the PDs
were calculated by the ab initio molecular orbital (MO)
method. Our calculations started with the lower level method
based on molecular mechanics (MM), and the sequential
optimization was carried out by the Hartree-Fock (HF)
method with the minimal basis set (STO-3G).17,18 The
obtained molecular conformation was employed to perform
the final geometry optimization by the B3LYP level density
functional theory19,20 with Dunning’s correlation-consistent,
polarized-valence, double-ꢀ (cc-pVDZ) basis set.21 Thus, all
of the fully optimized structures for the second generation
PDs were obtained. The general process for the generation
The produced O2 molecules were not quenched by naph-
thalene. From these results, it was confirmed that the CL
intensities of PDs showed the amount of produced 1O2, which
should depend on the amount of purpurogallin produced
(Figure 1). Compounds 9-11 gave approximately the
maximum CL intensity (Table 1). There is an optimal
distance between each dendron of PD to produce the
maximum CL intensity. Focusing on compound 9, which
produced the maximum CL intensity, the distance between
each dendron in optimized compound 9 was about 14 Å
(Figure 4d). Thus, the optimal distance between each dendron
of a second generation of PD is about 14 Å to give the
maximum CL intensity. This distance should provide suf-
ficient space for the production of purpurogallin by inter-
molecular reaction at the peripheral moiety in PD. We found
that the distance between each dendron in the PD structure
is a crucial factor in PD CL intensity.
1,2
1
of O2 in polyphenol CL has been evaluated (Figure 1).
In this CL process, the purpurogallin derivative is produced.
This CL process may occur both in intra- and inter-GA units
in the periphery of the PD. When peripheral GA units have
a π-π stacking structure, the GA units are close to each
other, and it is difficult to form the purpurogallin derivative.
On the contrary, on the basis of the present results of the
molecular modeling studies, the peripheral GA units of PDs
do not stack their structures by a π-π interaction of the
benzene rings, and the GA units are not close to each other
(Figure 4). This indicated that the formation of the purpuro-
gallin derivative easily proceeded and 1O2 should have been
easily produced.
The absorption and fluorescence properties are shown in
Table 2. Compounds 1 and 3-11 were fluorescent, but the
quantum yield was very low. The absorption wavelengths
of the PDs were 220-350 nm, and the emission wavelength
of 2 was in the range of 550-660 nm. This indicated that
the PDs did not absorb the CL of produced 1O2. We
In summary, we developed various PDs that have strong
CL intensities. The CL intensity of the PD with 1,10-
decanediol as the core molecule was the strongest among
all the PDs. There is no report on the notable change in the
CL intensities of the PDs by changing their core molecules.
We showed that the core molecule was crucial for the CL
of the PDs. Our study provided significant information for
developing polyphenols which have strong CL intensities.
Furthermore, these PDs are very interesting as compounds
1
which selectively produce large amounts of O2.
Acknowledgment. The authors thank the Japan Society
for the Promotion of Science for their financial support (Grant
15590044). The computations were mainly performed at the
computer facilities of the Research Center for Computational
Science of The Okazaki National Institutes.
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Supporting Information Available: Experimental details
and supplementary figures. This material is available free
of charge via the Internet at http://pubs.acs.org.
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(21) Woon, D. E.; Dunning, T. H, Jr J. Chem. Phys. 1993, 98, 1358–
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