Construction of a novel INHIBIT logic gate through a fine-tuned assembly of anthryl fluorophores via selective anion recognition and host-guest interactions

Article abstract of DOI:10.1039/c5ra20120a

A novel ligand (AAP) based on an anthryl fluorophore was rationally designed and synthesized. The presence of H₂PO₄^- (Pi) could induce the effective assembly of the ligand which leads to a strong excimer emission, while β-cyclodextrin (β-CD) disassembled the Pi-ligand complex through a host-guest interaction with terminal adamantane groups. This disassembly causes a considerable decrement in emissive intensity as well as a clear blue-shift in emissive wavelength. By manipulating the assembly and disassembly of anthryl fluorophores with Pi and β-CD, a novel INHIBIT logic gate was constructed using Pi and β-CD as the chemical inputs and fluorescence emission as the output.

Full text of DOI:10.1039/c5ra20120a

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Construction of a novel INHIBIT logic gate through
a fine-tuned assembly of anthryl fluorophores via
selective anion recognition and host–guest
interactions†
Cite this: RSC Adv., 2016, 6, 805
Received 5th October 2015
Accepted 14th December 2015
a
a
b
a
a
c
Lei Zhang,* Yilong He, Na Zhang, Daosheng Liu, Jiao Han and Weitao Gong
DOI: 10.1039/c5ra20120a
www.rsc.org/advances
A novel ligand (AAP) based on an anthryl fluorophore was rationally especially by changing the optical properties. Despite the
4ꢀ
designed and synthesized. The presence of H
2
PO (Pi) could induce striking number of INHIBIT gates developed in recent years,
the effective assembly of the ligand which leads to a strong excimer their design mechanisms are controlled by intramolecular
2
0,21
emission, while b-cyclodextrin (b-CD) disassembled the Pi–ligand charge transfer (ICT),
photo-induced electron transfer
22
23
complex through a host–guest interaction with terminal adamantane (PET) and uorescent resonance energy transfer (FRET). In
groups. This disassembly causes a considerable decrement in emissive this sense, development of INHIBIT logic gate with new design
intensity as well as a clear blue-shift in emissive wavelength. By mechanisms is an attractive challenge.
manipulating the assembly and disassembly of anthryl fluorophores
Anthryl uorophore was used to obtain novel multi-
with Pi and b-CD, a novel INHIBIT logic gate was constructed using Pi responsive
and b-CD as the chemical inputs and fluorescence emission as the phenomena.
uorescent
assembly
and
dis-assembly
24–26
If one can tune the assembly properties of
output.
anthryl moiety by introducing different inputs, novel logic gates
could be constructed. Until now, however, few relative reports
were found with respect to logic gates built on the assembly of
anthryl uorophore to the best of our knowledge.
1
. Introduction
Anion-induced self-assembly has attracted much attention
recently, since it provides a new and efficient strategy to build
functional supramolecular structures. Beer and co-workers re-
A molecular logic gate, mimicking the real functions of a semi-
conductor logic gate in modern computing, extends informa-
tion processing to the molecular level and thus has attracted
much attention in the eld of supramolecular chemistry.
Since the discovery of the rst AND gate in solution by A. P. de
Silva, molecular logic gates have experienced rapid growth and
various types of logic gates, such as NAND, OR, XNOR, XOR,
NOR, NOT and INHIBIT, have been established.
them, the INHIBIT gate involves a combination of AND and
NOT logic functions and deserves increasing attention due to its
non-commutative, in which the output signal is inhibited by
only one powerful input.
usually derived from some switchable molecular systems,
ported a novel anion-templating strategy for the construction of
27–29
rotaxanes and catenanes as efficient anions sensors.
Wu and
1
–7
co-workers presented the anion-induced assembly process to
build novel double and triple helical supramolecular struc-
8
30,31
tures.
In our previous work, a series of selective chemo-
ꢀ
sensors containing anthryl uorophore towards H
in polar solvents, even in aqueous solution were achieved.
2
PO
4
anions
9–15
Among
32–34
In
that case, the high selectivity is derived from the subtle control
of the assembly of anthryl moiety by ligand structure, anions
and solvent polarity.
16–19
The operation of INHIBIT gate is
In this work, a new ligand AAP was designed and synthesized
as a potential INHIBIT logic gate. It is composed of two amide-
pyridinium moieties as binding sites and an anthryl uo-
rophore as the signaling part. Adamantane group was intro-
duced at the two terminals for controlling the assembly
behavior via potential host–guest interaction with b-CD. The
detailed design rationale is exhibited in Fig. 1 and it is based on
the following hypotheses: (1) under the role of Pi, the ligand AAP
could assemble to form Pi–AAP complex according to our
a
College of Chemistry, Chemical Engineering and Environmental Engineering,
Liaoning Shihua University, No. 1 Dandong Road, Fushun 113001, Liaoning, China.
E-mail: lnpuzhanglei@163.com; Tel: +86-024-56861711
b
Department of Chemical Engineering, Fushun Vocational Technology Institute,
Fushun 113122, Liaoning, China
c
State Key Laboratory of Fine Chemicals, School of Chemical Engineering, School of
Chemistry, Dalian University of Technology, Dalian 116024, P. R. China
†
Electronic supplementary information (ESI) available: Details of experimental previous reports. In this case, two anthracene groups are
1 13
procedures, characterization of ligand AAP, including H NMR, C NMR and
located closer, which would lead to a different emissive
HR-MS. See DOI: 10.1039/c5ra20120a
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Scheme 1 Synthetic route of AAP.
Fig.
1 Schematic representation of the proposed Pi-induced
assembly and b-CD induced dis-assembly processes.
adamantanecarbonyl chloride (1.192 g, 6 mmol) in dry benzene
(
50 mL) was added dropwise under vigorous stirring. The
ꢁ
wavelength compared with the pure ligand, (2) terminal ada- mixture was stirred at 0 C for another two hours and then
mantane moieties are known to be easily incorporated into the allowed to obtain room temperature overnight. The solution
cavity of b-CD by host–guest interactions. If the formation of Pi– was washed with water and the organic phase was dried over
AAP complex could be disturbed by this host–guest interaction anhydrous MgSO . Aer ltration, the solvent was removed on
4
between adamantane and b-CD, the assembly behavior of a rotary evaporator and puried by column chromatography
anthryl uorophore might change accordingly giving rise to with ethyl acetate as the eluent which gave N-(1-adamantoyl)-3-
1
differences in uorescence property. In a word, taking advan- aminopyridine (0.97 g, 76%) as a yellowish powder. H NMR
tage of Pi anion and b-CD as two different chemical inputs and (400 MHz, DMSO-d ) d (ppm): 9.35 (s, 1H), 8.83 (d, J ¼ 1.9 Hz,
6

uorescence emission as the output, a potential INHIBIT logic 1H), 8.29–8.20 (m, 1H), 8.08 (d, J ¼ 8.3 Hz, 1H), 7.32 (dd, J ¼ 8.2,
1
gate will be achieved.
4.7 Hz, 1H), 2.02 (s, 3H), 1.92 (s, 6H), 1.71 (s, 6H). The H-NMR
data are in agreement with those found in the literature.
Synthesis of AAP. To a 100 mL round bottom ask, N-(1-
adamantoyl)-3-aminopyridine (0.769 g, 3 mmol) and 9,10-
bis(chloromethyl)anthracene (0.413 g, 1.5 mmol) were added.
2
. Experimental
2.1. Material and characterization
All the chemicals were purchased from commercial sources and Then dry CH
used without further purication unless mentioned. Acetoni- heated to 82 C and kept reuxing for 40 h until a yellow
trile was pre-dried by shaking with type 4A molecular sieves, precipitate was formed. The precipitate was ltered and washed
3
CN (30 mL) was added and the suspension was
ꢁ
and then distilled over calcium hydride before use. Other several times with CH
3
CN. The crude product was puried by
solvents were used as received. H and C NMR spectra were silica gel column chromatography (CH Cl : CH
OH ¼ 5 : 3) to
recorded on a Bruker Av400 NMR spectrometer at 400 MHz and give a yellow solid. Then the yellow solid was dissolved in DMF.
26 MHz, respectively. Chemical shis are given in parts per Aer dropwise addition of excess saturated aqueous KPF
million (ppm) relative to tetramethylsilane (TMS). High reso- solution, 50 mL H O was added in one portion and a light
1
13
2
2
3
1
6
2
lution mass spectra (HRMS) were recorded on a Waters GC-TOF yellow precipitate was formed. The precipitate was ltered and
and LC/Q-TOF mass spectrometer. Fluorescence spectra were washed with water repeatedly. Aer drying in vacuum, AAP (0.77
obtained from a Jasco FP-8300 spectrouorometer. UV-Vis g, 58%) was obtained as a yellow powder which was used
1
absorption spectra were all taken on a Hitachi UV-4100 spec- without further purication. H NMR (400 MHz, DMSO-d
6
)
trophotometer. Quartz cells with 1 cm path length were used.
d (ppm): 10.15 (s, 2H), 9.68 (s, 2H), 8.61 (d, J ¼ 8.6 Hz, 2H), 8.56
(
dd, J ¼ 6.9, 3.2 Hz, 4H), 8.37 (d, J ¼ 6.1 Hz, 2H), 7.96 (dd, J ¼ 8.6,
6
6
.1 Hz, 2H), 7.77 (dd, J ¼ 6.9, 3.1 Hz, 4H), 7.06 (s, 4H), 2.03 (s,
2.2. Synthetic procedures
13
H), 1.89 (s, 12H), 1.70 (d, J ¼ 6.5 Hz, 12H). C NMR (126 MHz,
The synthetic route of AAP was shown in Scheme 1.
DMSO-d
6
) d 177.18, 139.63, 137.86, 135.01, 134.80, 131.42,
Synthesis of N-(1-adamantoyl)-3-aminopyridine. N-(1-
Adamantoyl)-3-aminopyridine was synthesized according to
1
3
7
30.56, 128.23, 128.15, 127.13, 126.01, 124.63, 56.21, 41.27,
2+
52 4 2
7.85, 36.35, 35.75, 27.35, 26.82. ESI-MS calcd for C48H N O :
35
a
reported method with some modications.
1-Ada-
2+
16.4090 [M] ; found: 358.2043 (m/2z).
mantanecarboxylic acid was converted into the acid chloride by
ꢁ
treating with thionyl chloride at 80 C in benzene for 3 hours,
thus obtaining 1-adamantanecarbonyl chloride. Aer that, 3-
aminopyridine (0.47 g, 5 mmol) and triethylamine (1.3 mL, 10
3
. Results and discussion
mmol) were suspended in 50 mL of dry benzene and cooled in To verify our conjecture, the sensing ability of ligand AAP
an ice bath. To this suspension,
a
solution of 1- towards different anions was rst studied to gure out the
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selectivity of anion-induced assembly properties of AAP. Pure
AAP in CH CN exhibited almost no uorescence owing to the
3
quenching effect of photo-induced electron transfer (PET) from
33
anthryl moiety to pyridinium. Among various anions tested,
only Pi induced clear uorescence change, while others such as
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
I , F , OH , CN , Cl , Br , NO
3
and AcO , showed neglect-
able changes (Fig. 2a), indicating that AAP can be used as the
selective Pi sensing agent. This result is in accordance with our
previous results. Compared with that of pure ligand, the Pi–AAP
complex exhibited strong green uorescence centered at 500
nm, which is the well-known excimer emission of anthryl uo-
32
rophore, conrming the anion-induced assembly of AAP.
UV-Vis absorption experiment provides further evidence
about Pi-induced self-assembly of ligand AAP, by showing the
apparent red-shi in absorption of anthryl uorophore upon
titration of Pi into ligand AAP. As reported, the longer wave-
length absorption band compared with the pure AAP indicated
the formation of association of anthryl uorophore in ground
state (Fig. 2b). The clear red-shi of the absorption bands of
1
Fig. 3 H NMR spectra of (1) AAP; (2) after addition of Pi (0.5 equiv.); (3)
then after addition of b-CD (0.5 equiv.).
showed clear shiing towards higher magnetic eld aer the
addition of 0.5 equiv. Pi. This result further demonstrates the
binding of Pi with AAP. Fig. S5† shows the uorescent titration
data for AAP with Pi. The Job plot for the binding between AAP
and Pi showed a 1 : 1 stoichiometry (Fig. S6†). From the uo-
rescence titration, the binding constant and detection limit of
36–38
1
anthracene indicates the formation of J-aggregate.
The H
NMR spectra before and aer the addition of Pi into AAP were
also recorded and shown in Fig. 3. Protons of the anthryl moiety
5
ꢀ1
AAP toward Pi was calculated to be (5.3 ꢂ 0.1) ꢃ 10 M and
ꢀ7
1
.842 ꢃ 10 M respectively.
Once conrming the formation of Pi–AAP complex, which
showed elegant assembled excimer emission of anthryl uo-
rophore, our attention transferred to how to dis-assemble or
disturb this Pi–AAP complex aiming to change the uorescence.
Considering the selective binding between adamantane moiety
and b-CD as previously reported, the uorescence change due to
the addition of b-CD into Pi–AAP complex was therefore inves-
tigated. Upon titration with b-CD, as shown in Fig. 4a, the
excimer emission coming from Pi–AAP complex decreased. In
contrast, a new uorescence emission centered at about 440 nm
increased, which is the classical monomer emission of anthryl

uorophore. Accordingly, a clear uorescence color change
from green to blue was observed (Fig. 4a inset). This result
indicated the dis-assembly behavior of Pi–AAP complex aer the
addition of b-CD. In UV-Vis absorption titration between Pi–AAP
complex and b-CD, the apparent blue-shi of anthryl uo-
rophore further evidences the b-CD induced dis-association of
Pi–AAP complex in ground state (Fig. 4b). The occurrence of dis-
assembly Pi–AAP complex was due to the host–guest interaction
1
between adamantane and b-CD. The H NMR investigation of
Pi–AAP complex solution before and aer addition of b-CD
evidences the formation host–guest complex. Signals of meth-
ylene protons on adamantyl group showed downeld shi aer
39
addition of b-CD (Fig. 3 inset).
Changes in uorescence due to reverse addition of b-CD and
Pi to AAP were also studied. Some interesting results obtained
were shown in Fig. 5. When b-CD was rst introduced into pure
AAP solution instead of Pi, still rather weak uorescence of
anthryl uorophore was obtained together with a subtle wave-
length change. This result means the presence of host–guest
Fig. 2 (a) Fluorescence spectra of AAP (5.0 mM) upon addition of interaction between adamantane and b-CD. More interestingly,
various anions (5 equiv.) in CH
spectra of AAP (5.0 mM) upon addition of various amounts of Pi in
CH CN.
3
CN (lex ¼ 360 nm). (b) Absorption
when Pi was added into the AAP–b-CD complex solution, Pi-
induced excimer emission was not found, enhancement of
3
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Fig. 5 (a) Fluorescence spectra of AAP (5.0 mM) upon addition of b-CD
(
1 equiv.) and Pi (1 equiv.) in CH
spectra of AAP–b-CD complex (5.0 mM) upon addition of different
amounts of Pi in CH
CN (lex ¼ 360 nm).
3
CN (lex ¼ 360 nm). (b) Fluorescence
Fig. 4 (a) Fluorescence spectra of AAP–Pi complex (5.0 mM) upon
3
addition of various amounts of b-CD in CH
Absorption spectra of AAP–Pi complex (5.0 mM) upon addition of
various amounts of b-CD in CH CN.
3
CN (lex ¼ 360 nm). (b)
3
monomer emission was alone observed (Fig. 5b). This result
indicated that the Pi-induced assembly of ligand AAP was
inhibited by the formation of AAP–b-CD complex. As for the
enhancement of monomer emission, it might be due to the
block of photo-induced electron transfer (PET) from anthryl
moiety to pyridinium by the interaction with Pi anions.
These results obtained above demonstrated clearly that the
assembly phenomena of anthryl uorophore in ligand AAP
could be tuned by introducing Pi and b-CD as two chemical
inputs. Pi could induce the assembly of AAP to give excimer
emission, and b-CD could inhibit this Pi-induced assembly
through the host–guest interaction. Accordingly, this system
correlates very well with an INHIBIT logic gate as shown in
Fig. 6. In considering the INHIBIT logic gate properties of AAP,
in our system, Pi and b-CD act as two chemical inputs, while the
excimer emission at 500 nm acts as the output. The output is “0”
and the gate is “OFF” when (1) both the Pi and b-CD are absent,
Fig. 6 Output and the corresponding truth tables for the INHIBIT
gates (lex ¼ 360 nm) of AAP using Pi (input 1) and b-CD (input 2) as
inputs.
(2) b-CD alone is present, (3) both the Pi and b-CD are present.
Correspondingly if the output is “1” and the gate is “ON” only
when Pi alone is present. Thus, a new INHIBIT gate is
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constructed by controlling the assembly phenomena of anthryl 14 A. R. Chowdhury, P. Ghosh, B. G. Roy, S. K. Mukhopadhyay,

uorophore by inputting different chemical stimuli.
P. Mitra and P. Banerjee, RSC Adv., 2015, 5, 62017–62023.
5 P. Ghosh, B. G. Roy, S. Jana, S. K. Mukhopadhyay and
P. Banerjee, Phys. Chem. Chem. Phys., 2015, 17, 20288–20295.
6 K. C. Chang, I. H. Su, Y. Y. Wang and W. S. Chung, Eur. J. Org.
Chem., 2010, 4700–4704.
1
1
4
. Conclusions
In summary, a potential INHIBIT logic gate based on an anthryl

uorophore was rationally designed and synthesized. Under the 17 D. Sarkar, A. Pramanik, S. Jana, P. Karmakar and
ꢀ
role of H
2
PO
4
, anthryl uorophore could assemble to give
T. K. Mondal, Sens. Actuators, B, 2015, 209, 138–146.
apparent excimer uorescent emission, while b-CD could 18 S. Mardanya, S. Karmakar, S. Das and S. Baitalik, Sens.
inhibit this Pi-induced assembly process via host–guest inter-
Actuators, B, 2015, 209, 701–713.
action with adamantane moieties. Based on this phenomena, 19 A. R. Chowdhury, P. Ghosh, B. G. Roy, S. K. Mukhopadhyay,
a novel INHIBIT gate was constructed. This is the rst example
of INHIBIT gate that combines anion-induced assembly and
N. C. Murmu and P. Banerjee, Sens. Actuators, B, 2015, 220,
347–355.
host–guest triggered inhibition. Further work will be focused on 20 V. Luxami and S. Kumar, Dalton Trans., 2012, 41, 4588–4593.
the exploration of the detailed structure–property relationship 21 A. Coskun, E. Deniz and E. U. Akkaya, Org. Lett., 2005, 7,
for the construction of novel logic gates.
5187–5189.
22 S. H. Lee, J. Y. Kim, S. K. Kim, J. H. Lee and J. S. Kim,
Tetrahedron, 2004, 60, 5171–5176.
Acknowledgements
2
3 M. Yuan, W. Zhou, X. Liu, M. Zhu, J. Li, X. Yin, H. Zheng,
Z. Zuo, C. Ouyang, H. Liu, Y. Li and D. Zhu, J. Org. Chem.,
2008, 73, 5008–5014.
The authors are grateful for nancial support from the National
Natural Science Foundation of China (No. 21206016) and the
Fundamental Research Funds for the Central Universities 24 S. Malkondu, D. Turhan and A. Kocak, Tetrahedron Lett.,
(DUT14LK08) and the Science Research General Foundation of
2015, 56, 162–167.
Liaoning Education Department (L2014157).
25 D. Zhai, W. Xu, L. Zhang and Y. T. Chang, Chem. Soc. Rev.,
2014, 43, 2402–2411.
2
6 Y. J. Huang, W. J. Ouyang, X. Wu, Z. Li, J. S. Fossey,
T. D. James and Y. B. Jiang, J. Am. Chem. Soc., 2013, 135,
1700–1703.
Notes and references
1
2
3
4
5
J. Andr ´e asson and U. Pischel, Chem. Soc. Rev., 2010, 39, 174–
88.
J. Andr ´e asson and U. Pischel, Chem. Soc. Rev., 2015, 44,
053–1069.
1
27 M. J. Langton, O. A. Blackburn, T. Lang, S. Faulkner and
P. D. Beer, Angew. Chem., Int. Ed., 2014, 53, 11463–11466.
28 M. S. Vickers and P. D. Beer, Chem. Soc. Rev., 2007, 36, 211–
225.
29 B. R. Mullaney, A. L. Thompson and P. D. Beer, Angew.
Chem., Int. Ed., 2014, 53, 11642–11646.
1
K. He, Y. Li, B. Xiang, P. Zhao, Y. Hu, Y. Huang, W. Li, Z. Nie
and S. Yao, Chem. Sci., 2015, 6, 3556–3564.
A. J. M. Huxley, M. Schroeder, H. Q. N. Gunaratne and
A. P. de Silva, Angew. Chem., Int. Ed., 2014, 53, 3622–3625.
S. Kou, H. N. Lee, D. van Noort, K. M. K. Swamy, S. H. Kim,
30 C. Jia, B. Wu, S. Li, Z. Yang, Q. Zhao, J. Liang, Q. S. Li and
X. J. Yang, Chem. Commun., 2010, 46, 5376–5378.
J. H. Soh, K. M. Lee, S. W. Nam, J. Yoon and S. Park, Angew. 31 J. Zhao, D. Yang, Y. Zhao, X. J. Yang, Y. Y. Wang and B. Wu,
Chem., Int. Ed., 2008, 47, 872–876. Angew. Chem., Int. Ed., 2014, 53, 6632–6636.
J. Ling, B. Daly, V. A. D. Silverson and A. P. de Silva, Chem. 32 W. T. Gong, D. Na, L. Fang, H. Mehdi and G. L. Ning, Org.
Commun., 2015, 51, 8403–8409. Biomol. Chem., 2015, 13, 1979–1982.
A. Sreejith and A. Ajayaghosh, Indian J. Chem., Sect. A: Inorg., 33 W. T. Gong, Q. L. Zhang, F. R. Wang, B. Gao, Y. Lin and
Bio-inorg., Phys., Theor. Anal. Chem., 2012, 51, 47–56.
G. L. Ning, Org. Biomol. Chem., 2012, 10, 7578–7583.
A. P. de Silva, H. Q. N. Gunaratne, T. Gunnlaugsson, 34 W. T. Gong, S. Bao, F. R. Wang, J. W. Ye, G. L. Ning and
6
7
8
A. J. M. Huxley, C. P. McCoy, J. T. Rademacher and
T. E. Rice, Chem. Rev., 1997, 97, 1515–1566.
D. C. Magri, M. C. Fava and C. J. Mallia, Chem. Commun.,
K. Hiratani, Tetrahedron Lett., 2011, 52, 630–634.
35 V. A. Ermokhin, N. A. Klenova and P. P. Purygin, Pharm.
Chem. J., 2008, 42, 175–176.
9
2
014, 50, 1009–1011.
36 Y. Molard, D. M. Bassani, J. P. Desvergne, P. N. Horton,
M. B. Hursthouse and J. H. R. Tucker, Angew. Chem., Int.
Ed., 2005, 44, 1072–1075.
1
1
1
0 E. T. Ecik, A. Atilgan, R. Guliyev, T. B. Uyar, A. Gumus and
E. U. Akkaya, Dalton Trans., 2014, 43, 67–70.
1 D. C. Magri, G. J. Brown, G. D. McClean and A. P. de Silva, J. 37 H. K. Cho, D. H. Lee and J. I. Hong, Chem. Commun., 2005,
Am. Chem. Soc., 2006, 128, 4950–4951.
1690–1692.
2 C. P. Collier, E. W. Wong, M. Belohradsk ´y , F. M. Raymo, 38 F. Fages, J. P. Desvergne, H. B. Laurent, J. M. Lehn,
J. F. Stoddart, P. J. Kuekes, R. S. Williams and J. R. Heath,
Science, 1999, 285, 391–394.
Y. Barrans, P. Marsau, M. Meyer and A. M. A. Gary, J. Org.
Chem., 1994, 59, 5264–5271.
13 A. P. de Silva, I. M. Dixon, H. Q. N. Gunaratne, 39 K. Ohga, Y. Takashima, H. Takahashi, Y. Kawaguchi,
T. Gunnlaugsson, P. R. S. Maxwell and T. E. Rice, J. Am.
Chem. Soc., 1999, 121, 1393–1394.
H. Yamaguchi and A. Harada, Macromolecules, 2005, 38,
5897–5904.
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