A pentaquinone-based 4-2 bit photonic encoder

Article abstract of DOI:10.1039/c0dt01436b

A new pentaquinone-based chemosensor armed with phenolic moieties has been synthesized. The fluorescence behaviour of the chemosensor in the presence of different chemical inputs mimics the functions of a digital encoder.

Full text of DOI:10.1039/c0dt01436b

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PAPER
A pentaquinone-based 4-2 bit photonic encoder†
Vandana Bhalla,* Roopa, Ankush Gupta, Abhimanew Dhir and Manoj Kumar*
Received 21st October 2010, Accepted 24th January 2011
DOI: 10.1039/c0dt01436b
A new pentaquinone-based chemosensor armed with phenolic moieties has been synthesized. The
fluorescence behaviour of the chemosensor in the presence of different chemical inputs mimics the
functions of a digital encoder.
Introduction
Experimental
Recently, there has been lot of interest in the synthesis of
conjugated polycyclic molecules for mimicking the operations of
electronic devices in two related but conceptually different fields
i.e. (a) molecular electronics with current driven functions and (b)
molecular switching based on chemical, photonic or electrochemi-
cal inputs and outputs.1 Among the different conjugated polycyclic
compounds, pentacene is of particular interest because of its
high hole mobility in comparison to other organic compounds,
and much effort has been devoted to synthesizing pentacene-
based derivatives with substituents at different positions.2,3 In
this regard, a 6, 13 pentaquinone derivative has been used as an
important precursor for the design and synthesis of stable and
solution-processable pentacene derivatives. However, the role of
pentaquinone derivatives in molecular switching with chemical
and photonic inputs and outputs, respectively, is still unexplored.
Our research work involves the development of chemosensors for
the construction of molecular switches and logic-based molecular
devices.4 In continuation of our research work, we have now
designed and synthesized a pentaquinone-based chemosensor that
mimics the functions of a 4-2 bit photonic encoder. An encoder
is an electronic device, circuit, transducer, software program or
algorithm that converts information from one format or code into
another for the purpose of standardization, speed, secrecy, security
or saving space by size shrinking. There are different types of
encoders. A 4-2 bit encoder converts 4 bits of data into 2 bits.
Earlier, Andreasson et al.5 reported a molecular encoder based
on photochromic systems with different wavelengths as inputs
and outputs. Later, Balzani et al. reported a molecular encoder
based on bipyridyl system.6 However, a molecular encoder with
cations and anions as chemical inputs and fluorescence emission as
an output is still unprecedented. The present manuscript focuses
on an encoder with ionic chemical inputs. To the best of our
knowledge, this is the first report in which a pentaquinone-based
derivative has been used for the construction of 4-2 bit photonic
encoder.
General information
All reagents were purchased from Aldrich and were used without
further purification. THF was dried over sodium and ben-
zophenone, and kept over molecular sieves overnight before
use. UV-vis spectra were recorded on a SHIMADZU UV-2450
spectrophotometer, with a quartz cuvette (path length, 1 cm).
The cell holder was thermostatted at 25 ◦C. Fluorescence spectra
were recorded using a SHIMADZU 5301 PC spectrofluorimeter.
1H and 13C NMR spectra were recorded on a JEOL-FT NMR-
AL 300 MHz spectrophotometer using CDCl3 as the solvent and
tetramethylsilane (SiMe4) as the internal standard. UV-vis studies
were performed in dry THF. Data are reported as follows: chemical
shifts in ppm (d), multiplicity (s = singlet, d = doublet, br = broad
singlet m = multiplet), coupling constants J (Hz), integration and
interpretation. Silica gel 60 (60–120 mesh) was used for column
chromatography. Solutions of compound 5 and perchlorate salts
were prepared in dry THF.
Synthesis of compounds 1, 2 and 4
Compounds 1, 2 and 4 were synthesized according to procedures
reported in the literature.7–9
Synthesis of compound 3
To a solution of 1 (0.8 g, 1.72 mmol) and 2 (0.91 g, 4.14 mmol)
in dioxane were added K2CO3 (0.95 g, 6.8 mmol), distilled H2O
(8 mL) and [Pd(Cl)2(PPh3)2] (0.302 g, 0.43 mmol) under N2, and
the reaction mixture was refluxed overnight. The dioxane was then
removed under vacuum and the residue so obtained treated with
water, extracted with dichloromethane and dried over anhydrous
Na2SO4. The organic layer was evaporated and the compound
purified by column chromatography using (95 : 5 CHCl3 : MeOH)
as an eluent to give 0.26 g (31%) of compound 3 as a red solid; mp:
>260 ◦C; 1H NMR (300 MHz, CDCl3): d = 6.63 [d, 4H, J = 8.1 Hz,
ArH], 7.08 [d, 4H, J = 8.4 Hz, ArH], 7.69–7.71 [m, 2H, ArH], 8.07
[s, 2H, ArH], 8.11–8.13 [m, 2H, ArH], 8.93 [s, 2H, ArH], 8.95 [s,
2H, ArH]; MALDI TOF: m/z 491 (M + 1)+. Elemental analysis
calc. for C34H22N2O2: C, 83.25; H, 4.52; N, 5.71; found: C, 83.10;
H, 4.32; N, 5.55%.
Department of Chemistry, UGC-Centre for Advance Studies-1, Guru Nanak
Dev University, Amritsar, Punjab, India. E-mail: mksharmaa@yahoo.co.in;
Fax: +91 (0)183 2258820; Tel: +91 (0)183 2258802 9 ext. 3205
† Electronic supplementary information (ESI) available. Binding studies
of 5 and spectral data. See DOI: 10.1039/c0dt01436b
5176 | Dalton Trans., 2011, 40, 5176–5179
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Synthesis of compound 5
13.71 ppm, respectively (see ESI Fig. S16†). The mass spectrum
of compound 5 showed a parent ion peak at m/z 1066 (M+) (see
ESI Fig. S18†). These spectroscopic data corroborate structure 5
for this compound.
Compound 5 was synthesized by the portion-wise addition of 4
(0.047 g, 0.153 mmol) to a stirred solution of diamine 3 (0.03 g,
0.061 mmol) in (2 : 1 THF–EtOH). A yellow solid precipitated
after refluxing the reaction mixture for 3 d. The solid compound
was filtered and washed with ethanol to give 0.03 g of 5 (46%);
The binding behaviour of compound 5 was studied toward
different cations and anions by UV-vis and fluorescence spec-
troscopy. All the titration experiments were carried out in dry
THF by adding aliquots of different metal ions. The absorption
spectrum of 5 (1 ¥ 10-5 M) is characterized by the presence of
a typical absorption band at 362 nm (see ESI Fig. S3†). Of the
various metal ions tested (Cu2+, Hg2+, Pb2+, Zn2+, Ni2+, Cd2+,
Fe3+, Fe2+, Ba2+, Co2+, Ag+ K+, Na+ and Li+), a new band was
formed at 391 nm upon the addition of 100 equiv. of Hg2+ and
Fe3+ ions (see ESI Fig. S3 and S4, respectively†). It was observed
that two isosbestic points at 345 and 377 nm were formed upon
the addition of Fe3+ ions to the solution of 5 (see ESI Fig. S4†).
However, only one isosbestic point at 345 nm was observed upon
the addition of Hg2+ ions (see ESI Fig. S3†), indicating that
both ions interact with 5 in contrasting modes. The formation
of a new band at 391 nm is attributed to an intramolecular
charge transfer (ICT) mechanism occurring in the presence of Fe3+
and Hg2+ ions. In addition to cation binding properties, we also
investigated the sensing properties of 5 towards different anions
mp: 160–170 ◦C; IR nmax (KBr pellet, cm-1) 1620 cm-1 (C
N
1
stretching); H NMR (300 MHz, CDCl3): d = 0.88 [t, 6H, J =
6.45 Hz, CH3)], 1.27 [br, 36H, CH2], 1.75–1.82 [m, 4H, CH2], 3.99
[t, 4H, J = 6.6 Hz, OCH2], 6.48 [d, 4H, J = 9 Hz, ArH], 7.21–7.31
[m, 10H, ArH], 7.70–7.73 [m, 2H, ArH], 8.12–8.15 [m, 2H, ArH],
8.17 [s, 2H, ArH], 8.56 [s, 2H, N CH], 8.95 [s, 2H, ArH], 8.98
[s, 2H, ArH], 13.71 [br, 2H, OH]; 13C NMR (75 MHz, CDCl3):
d = 14.108 [CH3], 22.679 [CH2], 25.976 [CH2], 29.067 [CH2],
29.339 [CH2], 29.586 [CH2], 29.627 [CH2], 31.91 [CH2], 68.264
[OCH2], 101.535 [ArC], 107.708 [ArC], 112.917 [ArC], 120.936
[ArC], 129.483 [ArC], 129.73 [ArC], 130.101 [ArC], 130.859 [ArC],
131.428 [ArC], 133.554 [ArC], 134.428 [ArC], 135.211 [ArC],
138.260 [ArC], 141.969 [ArC], 147.458 [ArC], 161.411 [ArC],
163.751 [ArC], 164.032 [ArC]; MALDI TOF: m/z 1066 (M)+.
Elemental analysis calc. for C72H78N2O6: C, 81.02; H, 7.37; N,
2.62%; found: C, 81.22; H, 7.29; N, 2.54%.
(CN-, F-, Cl-, Br-, I-, HSO4 , CH3COO-, H2PO4- and NO3 ) using
tetrabutylammonium as the counter-cation. Upon the addition of
increasing amounts of F-/CN- (0–500 equiv.) ions to solutions
of 5, the absorption peak at 362 nm gradually moved to a longer
wavelength, finally reaching a maximum value at 420 nm with an
isosbestic point at 406 nm (see ESI Fig. S5†). We also carried out
the UV-vis titration of 5 with a relatively strong base, Bu4NOH,
which is known to deprotonate phenolic moieties. It was observed
that upon the addition of Bu4NOH to a solution of 5, a new
band corresponding to the deprotonated form of 5 was formed at
465 nm with an isosbestic point at 435 nm (see ESI Fig. S6†). On
basis of these results, we propose that the UV-vis spectral changes
in Fig. S3 and S4 are due to the formation of a hydrogen bond
between the phenolic proton and F-/CN-.
The fluorescence emission spectrum of 5 (1 ¥ 10-5M) in THF
showed a characteristic emission band at 550 nm when excited at
340 nm (Fig. 1), which is attributed to a very fast enol-imine (5a)
to keto-amine (5b) tautomerism, involving the phenomenon of
excited state intramolecular proton transfer (ESIPT) (Scheme 2).
Upon the addition of Hg2+ ions to a solution of 5, significant
changes were observed in the emission spectra. Upon the addition
of 2 equiv. of Hg2+ ions, a slight decrease in the emission band of 5
-
-
Results and discussion
The Suzuki–Miyaura cross coupling of compound 17 with boronic
ester 28 catalyzed by Pd(Cl)2(PPh3)2 furnished diamine 3 in 31%
yield (Scheme 1). The 1H NMR spectrum of 3 showed two doublets
(4H each) at 6.63 and 7.08 ppm, two multiplets (2H each) from
7.69–7.71 and 8.11–8.15 ppm, and three singlets (2H each) at
8.07, 8.93 and 8.95 ppm, corresponding to aromatic protons (see
ESI Fig. S14†). The mass spectrum of compound 3 showed a
parent ion peak at m/z 491 (M + 1)+ (see ESI Fig. S15†). These
spectroscopic data corroborate structure 3 for this compound.
Further condensation of diamine 3 with 2.5 mol equiv. of 4-
dodecyloxy-2-hydroxy benzaldehyde 49 furnished compound 5 in
1
46% yield (Scheme 1). The H NMR spectrum of 5 showed one
triplet (6H) at 0.88 ppm for CH3 protons, a broad signal (36H) at
1.27 ppm for CH2 protons, a multiplet (4H) from 1.75–1.82 ppm
for CH2 protons, a triplet (4H) for OCH2 protons, one doublet
(4H) at 6.48 ppm, three multiplets (10H, 2H, 2H) from 7.21–7.31,
7.70–7.73 and 8.12–8.15 ppm, three singlets (4H each) at 8.17, 8.95
and 8.98 ppm for aromatic protons, one singlet (2H) at 8.56 for
amino protons and one broad signal (2H) for phenolic protons at
Scheme 1
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Scheme 2
Zn2+, Ni2+, Cd2+, Fe3+, Fe2+, Ba2+, Co2+, Ag+, Na+, K+ and Li+.
The addition of 1000 equiv. of these metal ions quenched the
fluorescence emission of 5 to different extents (see ESI Fig. S12†),
except for Fe3+, which showed the complete quenching of the
emission of 5 (see ESI Fig. S11†). Thus, it is obvious that the Fe3+
ion coordinates in a different manner to the Hg2+ ion, as revealed
by UV and fluorescence studies. We propose that the Fe3+ ion
probably coordinates only with the phenolic oxygen atom, which
causes the inhibition of ESIPT, quenching the emission band at
550 nm. The binding constant (log b1) of 5 with Fe3+ ions was
found to be 5.13 using the non-linear regression analysis program
SPECFIT,11 which gave a good fit for a 1 : 1 species. Job’s plot12
also proved a 1 : 1 stoichiometry (host/guest) (see ESI Fig. S9†).
We also carried out a reversibility experiment that proved that
Fe3+ binding to compound 5 is reversible. The addition of 3000
equiv. of tetrabutyl ammonium fluoride (TBAF-) to the 5·Fe3+
complex restored the fluorescence signal of 5, which is ascribed
to the affinity of fluoride ions for Fe3+ ions (see ESI Fig. S21†).
We also investigated the binding behaviour of 5 towards various
Fig. 1 Fluorescence spectra of 5 (1 ¥ 10-5 M) in response to the presence
of Hg2+ ions (0–340 equiv.) in THF; lex = 340 nm.
at 550 nm was observed (Fig. 1). On addition of 2.5 equiv. of Hg2+
ions, the fluorescence emission increased again and reached its
original value with the appearance of a new blue-shifted band at
461 nm (Fig. 1). Both the bands at 550 and 461 nm increased
simultaneously upon the addition of 340 equiv. of Hg2+ ions
(Fig. 1). Upon further addition of Hg2+ ions (560 equiv.), the
band at 461 nm increased continuously, while the band at 550 nm
slowly disappeared (see ESI Fig. S7†). These results proclaim
that the subsequent addition of Hg2+ ions to the solution of 5
results in inhibition of ESIPT with the simultaneous formation
of a supramolecular complex with inhibition of the photoinduced
electron transfer (PET)10 from the imino nitrogen atoms to the
phenolic moiety. The binding constant (log b1) of 5 with Hg2+
ions was found to be 5.23 using the non-linear regression analysis
program SPECFIT,11 which gave a good fit for a 1 : 1 species.
Job’s plot12 also proved 1 : 1 stoichiometry (host/guest) (see ESI
Fig. S9†). The fluorescence quantum yield (ff)13 of compound 5
in its free and Hg2+-bound state was found to be 0.06 and 0.28,
respectively, which proved its reliability as a good Hg2+ sensor.
This assumption was confirmed with the help of the IR spectrum
of 5, in which the peak at 1620 cm-1 and a broad band at 3441 cm-1,
ascribed to C N and OH stretching, respectively, were found to
shift to lower wavenumbers of 1614 and 3432 cm-1, respectively,
upon Hg2+ binding (see ESI Fig. 19 and 20†). Thus, we believe
that the coordination of Hg2+ ions to 5 occurs through imino
nitrogen and phenolic oxygen atoms. The signals in the 1H NMR
spectrum of 5 broadened upon the addition of 1.0 equiv. of Hg2+
ions CDCl3 : CD3CN (8 : 2), which indicates the formation of a
complex between 5 and Hg2+ ions. Under the same conditions
as used above for the Hg2+ ions, we also tested the fluorescence
behaviour of receptor 5 toward metal ions such as Cu2+, Pb2+,
anions (CN-, F-, Cl-, Br-, I-, HSO4 , CH3COO-, H2PO4 and
-
-
-
NO3 ) by fluorescence spectroscopy under the same conditions as
used for the cations. It was observed that upon the addition of only
F- and CN-, the emission at 550 nm was quenched, and on further
addition, a new band was formed at 461 nm, which was continually
enhanced up to the addition of 3000 equiv. of F- (see ESI Fig. S8†)
and CN- ions (Fig. 2). This fluorescence behaviour of 5 towards F-
and CN- is ascribed to the formation of hydrogen-bonded species
(vide supra). The binding constant (log b1) of 5 with CN- and F-
ions was found to be 4.89 and 4.57, respectively, using the non-
linear regression analysis program SPECFIT,11 which gave a good
fit for a 1 : 1 species. Job’s12 plot also proved a 1 : 1 stoichiometry
Fig. 2 Fluorescence spectra of 5 (1 ¥ 10-5 M) in response to the presence
of CN- ions (0–3000 equiv.) in THF; lex = 340 nm.
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Table 1 Truth table
Sr no. Input ‘D0’ Input ‘D1’ Input ‘D2’ Input ‘D3’ Output ‘X’Output ‘Y’
1
2
3
4
1
0
0
0
0
1
0
0
0
0
1
0
0
0
0
1
0
0
1
1
0
1
0
1
for CN-/F- ions (host/guest) (see ESI Fig. S10†). The addition of
other anions, except for F- and CN-, quenched the fluorescence
emission of 5 to different extents (see ESI Fig. S13†).
Fig. 3 Logic circuit of the 4-2 bit encoder.
In the above experiments, high equivalents of cations and
anions were added to solutions of compound 5 to generate an
appropriate fluorescence response. The use of high equivalents of
cations/anions is due to an efficient ESIPT phenomenon that is
prevalent in compound 5. In the case of anions, another reason
could be the weak acidity of the phenolic protons.
encoder. Such molecules could replace traditional electronic
elements for use in computing and data communication.
Acknowledgements
There has been a lot of interest in the development of materials
that could protect information at the molecular level. Molecular
keypad locks have been developed for this purpose.14,4c,4d However,
the amount of data that can be protected or the quantity of
information stored has not been taken into consideration while
developing these keypad locks. An encoder is a device that can
also compress data for storage and transmission. It converts coded
inputs into other coded outputs. Hence, the compressed data is also
hidden and protected. Therefore, an encoder can perform both
the function of protector and compressor of information. Thus, in
continuation of our research program to mimic electronic devices,
we examined our system as a molecular encoder. To acquire a 4-2
bit photonic encoder, we envisaged D0 = Fe3+ (1000 equiv.), D1
= CN- and F- (3000 equiv.), D2 = [{Cu2+, Pb2+, Zn2+, Ni2+, Cd2+,
Fe2+, Ba2+, Co2+, Ag+, Na+, K+ and Li+} (1000 equiv.) {Cl-, Br-, I-,
We are thankful to CSIR (ref. no. 01(2167)07/EMR-II), DST (ref.
no. SR/FT/CS/10-2006) and Guru Nanak Dev University for
laboratory facilities.
References
1 (a) A. P. De Silva, N. D. McClenaghan, C. P. McCoy, Molecular Level
Electronics, Imaging and Information, Energy and Environment, in
Electron Transfer in Chemistry, vol. 5, ed. V. Balzani, Wiley-VCH,
Weinheim, 2001; (b) Molecular Devices and Machines. A Journey Into
the Nano World, ed. V. Balzini, M. Venturi and A. Credi, Wiley-VCH,
Weinheim, 2003; (c) M. A. Ratner, J. Jortner, in Molecular Electronics,
ed. M. Ratner and J. Jortner, Blackwell, Oxford, 1997; (d) V. Balzani,
M. G. Lopez and J. F. Stoddart, Acc. Chem. Res., 1998, 31, 405;
(e) K. E. Drexler, Nanosystems: Molecular Machinery, Manufacturing
and Computation, Wiley New York, 1992.
2 (a) H. Meng, M. Bendikov, G. Mitchell, R. Helgeson, F. Wudl, Z. Bao,
T. Siegrist, C. Kloc and C. H. Chen, Adv. Mater., 2003, 15, 1090; (b) H.
Klauk, M. Halik, U. Zschieschang, G. Schmid, W. Radlik and W. J.
Weber, J. Appl. Phys., 2002, 92, 5259; (c) Y. Sakamoto, T. Suzuki, M.
Kobayashi, Y. Gao, Y. Fukai, Y. Inoue, F. Sato and S. Tokito, J. Am.
Chem. Soc., 2004, 126, 8138.
3 (a) J. E. Anthony, Chem. Rev., 2006, 106, 5028; (b) J. E. Anthony, J. S.
Brooks, D. L. Eaton and S. R. Parkin, J. Am. Chem. Soc., 2001, 123,
9482; (c) M. M. Payne, S. R. Parkin, J. E. Anthony, C. C. Kuo and T. N.
Jackson, J. Am. Chem. Soc., 2005, 127, 4986.
4 (a) M. Kumar, A. Dhir and V. Bhalla, Chem. Commun., 2010, 46, 6744;
(b) M. Kumar, R. Kumar and V. Bhalla, Tetrahedron Lett., 2010, 51,
5559; (c) M. Kumar, R. Kumar and V. Bhalla, Chem. Commun., 2009,
7384; (d) M. Kumar, A. Dhir and V. Bhalla, Org. Lett., 2009, 11, 2567;
(e) A. Dhir, V. Bhalla and M. Kumar, Org. Lett., 2008, 10, 4891; (f) A.
Dhir, V. Bhalla and M. Kumar, Tetrahedron Lett., 2008, 49, 4227.
5 J. Andreasson, S. D. Straight, T. A. Moore, A. L. Moore and D. Gust,
J. Am. Chem. Soc., 2008, 130, 11122.
6 P. Ceroni, G. Bergamini and V. Balzani, Angew. Chem., Int. Ed., 2009,
48, 8516.
7 C. R. Swartz, S. R. Parkin, J. E. Bullock and J. E. Anthony, Org. Lett.,
2005, 7, 3163.
8 V. Bhalla, R. Tejpal, M. Kumar, R. K. Puri and R. K. Mahajan,
Tetrahedron Lett., 2009, 50, 2649.
9 C. K. Lai, C. H. Chang and C. H. Tsai, J. Mater. Chem., 1998, 8,
599.
10 (a) I. Aoki, T. Sakaki and S. Shinkai, J. Chem. Soc., Chem. Commun.,
1992, 730; (b) J. H. Bu, Q. Y. Zheng, C. F. Chen and Z. T. Huang, Org.
Lett., 2004, 6, 3301.
11 H. Gampp, M. Maeder, C. J. Meyer and A. D. Zuberbuhler, Talanta,
1985, 32, 95.
12 P. Job, Ann. Chim., 1928, 9, 113.
HSO4 , CH3COO-, H2PO4- and NO3 } (3000 equiv.) and D3 = Hg2+
(340 equiv.) as four chemical inputs and emission wavelengths of
550 and 461 nm as two photonic outputs, ‘X’ and ‘Y’, respectively.
By the operation of input D0 to system 5, the emission at 550 nm
gets quenched and there is no output emission at 461 nm (see
ESI Fig. S11†), i.e. both outputs ‘X’ and ‘Y’ are in the off state ‘0’
(Truth table 1). Reset of the system is achievable upon the addition
of F- ions (vide supra). The operation of input D1 to the system
quenches the emission at 550 nm and forms a band at 461 nm,
i.e. output X is in the off state ‘0’ and output ‘Y’ is in the on state
‘1’ (Truth table 1) (see ESI Fig. S8† and Fig. 2). The operation of
input D2 to system 5 quenches the emission at 550 nm to a certain
extent (see ESI Fig. S12 and 13†). Thus, output X is in the on state
‘1’ and output ‘Y’ is in the off state ‘0’.
-
-
When system 5 is operated by input D3, the emission intensity
is observed at both wavelengths (Fig. 1). Therefore, both outputs
‘X’ and ‘Y’ are in the on state, i.e. ‘1’ (Truth table 1).
From truth table 1, the outputs are expressed as:
X = D2 + D3; Y = D1 + D3.
Therefore, a logic diagram for the 4-2 encoder is obtained, as
shown in Fig. 3.
Conclusions
13 J. N. Demas and G. A. Grosby, J. Phys. Chem., 1971, 75, 991.
14 (a) D. Margulies;, C. E. Felder, G. Melman and A. Shanzer, J. Am.
Chem. Soc., 2007, 129, 347; (b) M. Suresh, A. Ghosh and A. Das,
Chem. Commun., 2008, 3906.
In conclusion we have designed and synthesized a new chemosen-
sor based on a pentaquinone derivative that mimics a 4-2 bit
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The Royal Society of Chemistry 2011
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©