Sol-gel selection of hybrid G-quadruplex architectures from dynamic supramolecular guanosine libraries

Article abstract of DOI:10.1039/c0jm01248c

We report an original strategy to transcribe and to fix the self-assembly of G-quadruplex architectures in self-organized nanohybrids. In the first resolution step the G-quartet is pre-amplified in solution in the presence of metal cations from a dynamic pool of ribbon-type or cyclic supramolecular architectures. Then in a second selection sol-gel step the G-quadruplex is irreversibly fixed in a siloxane inorganic network. The interface between the guanosine moiety and the heterosiloxane 3 is based on a double reversible covalent iminoboronate connection. This contributes to the high levels of adaptability and correlation in the self-organization of the supramolecular G-quadruplex and the inorganic siloxane systems. Biomimetic-type hybrids can be generated by using this strategy.

Full text of DOI:10.1039/c0jm01248c

View Article Online / Journal Homepage / Table of Contents for this issue
PAPER
www.rsc.org/materials | Journal of Materials Chemistry
Sol–gel selection of hybrid G-quadruplex architectures from dynamic
supramolecular guanosine libraries†‡
*
Simona Mihai, Yann Le Duc, Didier Cot and Mihail Barboiu
Received 28th April 2010, Accepted 2nd July 2010
DOI: 10.1039/c0jm01248c
We report an original strategy to transcribe and to fix the self-assembly of G-quadruplex architectures
in self-organized nanohybrids. In the first resolution step the G-quartet is pre-amplified in solution in
the presence of metal cations from a dynamic pool of ribbon-type or cyclic supramolecular
architectures. Then in a second selection sol–gel step the G-quadruplex is irreversibly fixed in a siloxane
inorganic network. The interface between the guanosine moiety and the heterosiloxane 3 is based on
a double reversible covalent iminoboronate connection. This contributes to the high levels of
adaptability and correlation in the self-organization of the supramolecular G-quadruplex and the
inorganic siloxane systems. Biomimetic-type hybrids can be generated by using this strategy.
templating the eight carbonyl oxygens of two sandwiched
1. Introduction
G-quartets in the G-quadruplex, the columnar device formed by
the vertical stacking of four G-quartets.9 It plays a very
Constitutional dynamic chemistry (CDC)1 that expresses the
adaptive behaviour of molecular and supramolecular systems
brings into play the self-evolution of such dynamic systems
toward the selection of discrete architectures from mixtures of
exchanging components. These concepts may be connected with
the simple definition of dynamic multicomponent self-assembly
in chemical and biological systems.2 The spontaneous formation
of higher order superstructures from simple molecular blocks
concerns inter-exchanging supramolecular architectures, and
often yields discrete devices and materials. By virtue of the
reversible interchanges, the components can adapt to internal
and external constraints. Kinetic resolution,3,4 self-assembly
processes followed by covalent modification5 or the use of crys-
tallization6,7 are useful strategies to control and to drive supra-
molecular self-organization toward producing functional
complex systems. Previous investigations have highlighted the
wide potential of resolution strategies controlled in the second
step by an irreversible enzymatic3 or crystallization6,7 tandem
process. The control of supra-molecular self-organization by
a phase-change can also be driven by using the sol–gel process,6–8
providing a simple method for synthesis of well-defined hybrid
constitutional materials.5h In this context, the supramolecular
H-bonded macrocycle of four guanine building blocks, the
G-quartet, has been proposed as a powerful scaffold for the
construction of synthetic supramolecular devices and materials.8
The G-quartet architecture represents a dynamic supramo-
lecular system in which the G-quartet is reversibly exchanging
with linear ribbons (Fig.1).5a,b It is stabilized by cations,
Adaptive Supramolecular Nanosystems Group, Institut European des
Membranes ENSCM/UMII/UMR CNRS 5635, Place Eugene Bataillon
CC047, France. E-mail: mihai.barboiu@iemm.univ-montp2.fr; Fax:
(+33)467149119
† Electronic supplementary information (ESI) available: NMR XPRD
and ATG data. See DOI: 10.1039/c0jm01248c
‡ This paper is part of a Journal of Materials Chemistry themed issue on
Advanced Hybrid Materials, inspired by the symposium on Advanced
Hybrid Materials: Stakes and Concepts, E-MRS 2010 meeting in
Strasbourg. Guest editors: Pierre Rabu and Andreas Taubert.
Fig. 1 CD spectra at room temperature in CH3OH of 5 (10ꢀ4 M) (black
line), 5 + 0.25 eq. KTf or 5 + 0.25 eq. BaTf2 (red line) and 5 + 1 eq. KTf or
5 + 1 eq. BaTf2 (blue line).
This journal is ª The Royal Society of Chemistry 2010
J. Mater. Chem., 2010, 20, 9443–9448 | 9443

View Article Online
important role in biology in particular in nucleic acid tellomers of
potential interest to cancer therapy.8 New strategies using
reversible polymerization or phase-change-driven selection were
successfully used to generate G-quadruplex functional nano-
structures.10,11 In our group, the guanine building block and the
sol–gel chemistry were used to conceive hybrid chiral materials at
nanometric and micrometric scales. Our efforts involved the
synthesis and the self-assembly of a guanine-siloxane monomer
GSi (Fig.1), resulting in the formation of G-ribbons, G-quartet
and G-quadruplex supramolecular architectures, dynamically
exchanging in solution. The generation of G-quadruplex hybrid
materials can be achieved by mixing the GSi derivative with
potassium triflate, where G-quartet superstructures have been
amplified. Then the sol-gel selection process has been followed by
a second inorganic transcription into inorganic silica replica
materials, by calcination.5a Dynamic nanomaterials, character-
ized by their aptitude to continuously organize at the macro-
scopic level the generation of their own components with
different blocks forming in coupled equilibria, have been used as
of metal cations from a dynamic pool of oligomeric ribbon-type
or cyclic supramolecular architectures (Scheme 1). Then in
a second sol–gel step the polycondensation reactions of the
inorganic alkoxysilane network take place around the tubular
twisted superstructure of the G-quadruplex. It should be noted
that the dynamic G-quadruplex architectures are irreversibly
fixed in a covalently bonded siloxane network and the structural
constitution of the G-quadruplex is transcribed in the hybrid
material. These results provides new insights into the basic
features that control the convergence of supramolecular self-
organization toward functional hybrid materials.
2. Experimental
2.1. Materials and methods
All reagents were obtained from Aldrich and used without
further purification. All organic solutions were routinely dried by
1
using sodium sulfate (Na2SO4). H, 13C and 29Si NMR spectra
a
straightforward approach for the design of functional
were recorded on an ARX 300 MHz Bruker spectrometer in d4-
MeOD using the residual solvent peak as a reference. 29Si MAS
NMR was performed on a Bruker ASX 400 spectrometer. ESI-
MS studies were performed in the positive and negative ion mode
using a quadrupole mass spectrometer (Micromass, Platform II).
Samples were continuously introduced into the mass spectro-
meter through a Waters 616 HPLC pump (60 ꢁC; extraction cone
voltage: Vc ¼ 30 V). X-ray powder diffraction measurements
G-quartet membranes5b and surfaces.11d Despite such progress,
considerable challenges still lie ahead and a more significant one
is the dynamic convergence between supramolecular self-
assembly of G-quartet architectures and the resolution process
(polymerization, phase change). The reversibility of interactions
between the G-quartet and polymeric components might be
a crucial factor and accordingly, a reversible covalent connection
might render the emergence of self-adaptive system mesophases,
which may mutually adapt their 3D spatial distribution based on
their own structural constitution during the simultaneous
formation of mixed self-organized domains.
ꢁ
were performed with Cu-Ka radiation at 20 C using a Philips
X’Pert Diffractometer equipped with an Xcelerator detector.
Thermogravimetric analysis (Hi-Res TGA 2950, TA Instru-
ments, Nitrogen, 50–600 ꢁC at 10 ꢁC minꢀ1) and differential
scanning calorimetry (DSC 2920 Modulated, TA Instruments)
were used to evaluate the thermal stability of the hybrid materials
A-E. CD spectra (220–400 nm) were collected on a MOS-450/
AF-Biologic CD spectrometer with a rate of 0.5 nm/step, using
Herein we report an original strategy to transcribe and to fix
the supramolecular self-assembly of the dynamic constitutional
G-quartet architectures, in self-organized nanohybrids.12 In the
first resolution step the G-quartet is pre-amplified in the presence
Scheme 1 Cation-template resolution of a dynamic supramolecular guanine system in which the G-quartet is reversibly exchanging with linear ribbons
followed by a secondary irreversible sol–gel selection of G-quadruplex hybrid materials.5a
9444 | J. Mater. Chem., 2010, 20, 9443–9448
This journal is ª The Royal Society of Chemistry 2010

View Article Online
10 mm quartz cells, at room temperature. The measurements
were carried out on MeOH solutions (10ꢀ4 M of 3) and on
mixtures of 3/4 (1/1, mol/mol) briefly ultrasonicated with various
amounts of K+ and Ba2+ ions. The SEM micrographs were
obtained with high resolution transmission electron microscopy
(HRTEM) JEOL 2010 FEG apparatus, working with an accel-
The 1H, 13C NMR and ESI-MS spectra are in agreement with the
proposed formula.
3.1.2. Generation of G-quartet architectures in solution.
Compounds 1 and guanosine, 4 generate G-quartet architectures
by K+ or Ba2+ cation templating, based on three-encoded features:
a) the hybrid materials might be considered to contain super-
structures resulting from the combination of cross-linked arrays
of G-quartets cross-linked by appending iminoboronate groups
connected to the silica matrix, reminiscent of the guanine hybrids
recently reported by our group;5a
ꢀ
erating voltage of 200 kV and a point resolution of 2.0 A.
2.2. Synthesis of 2-((3-(triethoxysilyl)propylimino)methyl)
phenylboronic acid, 3
3-(triethoxysilyl)propan-1-amine 2 (0.8 mL; 3.3 mmol) was
added to a chloroformic solution (20 mL) of 2-formyl-phenyl-
boronic acid, 1 (0.50 g; 3.3 mmol). The mixture was refluxed for
6 h. The solvent was removed under vacuum to give 3 as a yellow
oil. (74%) 1H-NMR (MeOD, 300 MHz): d 0.55 (t, 2H); 1.04–1.17
(m, 9H); 1.99 (m, 4H); 3.33 (t, 2H); 3.85 (dd, 6H); 4.55 (s, 2H);
7.37 (m, 1H); 7.57 (t, 2H); 7.64 (d, 1H); 8.71 (s, 1H). 13C-NMR
(MeOD, 300 MHz): d 156.7, 153.7, 150.7, 136.2, 136.1, 129.7;
126.8; 116.7; 106.5; 103.0; 88.3; 87.7; 86.5; 84.5; 84.3; 83.1; 82.3;
80.8; 61.6.
b) the linkage between the guanosine moiety and the imino-
boronic monomer, 3 is based on a double reversible covalent
connection. The imino moiety contributes to the stabilisation of
the reversible boronate-guanosine ester bond by the formation of
a dative N–B bond.13 This then contributes towards dynamic
adaptative behaviour on the molecular level in a double
‘‘dynamer’’-type system:5b it combines reversible supramolecular
H-bonding (G-quartets) with the reversible polycondensation
(iminoboronate bonds) of components. This might contribute to
the high levels of adaptability and correlation in the self-orga-
nization of the dynamic supramolecular G-quartets and the rigid
inorganic siloxane components;
2.3. General procedure for synthesis of AK+-DK+, ABa2+-DBa
2+
c) biomimetic guanosine-type hybrids can be generated using
this strategy.
and the reference E hybrid materials
In a typical run, 3 mL of methanolic solution of 3 (2.5 ꢂ 10ꢀ3 M)
was mixed with 1 eq. of guanosine 4, 0.25 or 1 eq. of templating
metal salt (KTf or BaTf2) and 3 eq. of benzylamine as catalyst.
Whereas hybrids AK+, CK+, ABa2+, CBa2+ were prepared by a sol–
gel process in the presence of 6 eq. of deionized water the hybrids
The generation of G-quartet architectures can be achieved by
using the mixtures of 1 and guanosine 4 (1/1, mol/mol), resulting
in the formation of 5 and potassium or barium triflates. Unfor-
tunately such mixtures of 5/KTf or BaTf2 are soluble only in
methanol and the 1H NMR experiments are inadequate to
indicate the self-association of the G-quartet due the exchange of
NH1 amide and for NH2 amine protons with the solvent.
Next, we used CD spectroscopy to gain evidence that 5 forms
supramolecular chiral superstructures in the presence of ions in
methanol (Fig. 1). In accordance with the NMR results, a weak
Cotton effect was observed in the CD spectrum of a methanolic
solution of 5 which can be ascribed to the intrinsic supramole-
cular chirality, resulting from twisted supra-molecular geometry
in which the molecular guanosine components associate and
indicating that the G-quadruplex is either unstructured or
exchanging very fast in solution (Fig. 1a,b black lines). After
addition of 0.25 equiv. of KTf or 0.25 equiv. of BaTf2 the
corresponding CD spectra (Fig. 1a,b red lines) shows a negative
Cotton effect with a zero crossing at l ¼ 320 nm or l ¼ 310 nm,
respectively in the region of the iminoboronic chromophores.
This effect might be induced by the formation of the G-quartets
induced by steric interactions between the chiral sugars groups
on the G unit and further inducing asymmetric interactions
between iminoboronic pendant chromophores. The observed
CD signals in the presence of the cations indicates that chiral
aggregates are forming in the presence of metal ions. It is inter-
esting to note that related oligo(p-phenylene-vinylene)-G11a and
oligo-thiophene-G11b D4-symmetric octamers, with the append-
ing group attached to the 50-position of the G ribose, showed
a similar negative Cotton effect. Interestingly, increasing the
amount of metals ions to 1 equiv. the corresponding CD spectra
(Fig. 1a,b blue lines) shows a positive Cotton effect (zero crossing
at l ¼ 314 nm) for the K+ cations and a negative Cotton effect
(zero crossing at l ¼ 330 nm) for the Ba2+ cations corresponding
2+
BK+, DK+, BBa2+, DBa were prepared by using only the air
humidity (Table 1). The solutions were briefly stirred and
allowed to react at room temperature under static conditions for
1 week. Then samples were slowly evaporated at room temper-
ature to give yellow powders. A reference sol–gel sample E was
prepared in the absence of ionic salts, under the same conditions.
3. Results and discussions
3.1. Concept, design and synthesis of G-quartet hybrid
materials
3.1.1. Design of hybrid molecular component. 2-((3-triethoxy-
silyl)propylimino)methyl)phenylboronic acid 3 was obtained by
refluxing stoichiometric amounts of 2-formyl-phenylboronic acid
1 and 3-(triethoxysilyl)propan-1-amine 2 in CHCl3 (Scheme 2).
Table 1 The sol–gel synthetic protocol and temperature of 50% mass
2+
decomposition, T50% of the hybrid materials, AK+-DK+, ABa2+-DBa
3
4
KTf
BaTf2
H2O
(equiv.) (equiv.) (equiv.) (equiv.) (equiv.)g T50%/ꢁC
+
AK
BK
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
—
—
—
—
1
—
6
—
6
—
6
—
6
487
509
467
450
483
480
464
473
425
+
+
CK
DK
0.25
0.25
—
—
—
—
—
+
2+
ABa
B Ba
2+
2+
1
C Ba
D Ba
E
0.25
0.25
—
2+
—
This journal is ª The Royal Society of Chemistry 2010
J. Mater. Chem., 2010, 20, 9443–9448 | 9445

View Article Online
Scheme 2 The synthesis of iminoboronateguanosine precursor 5 followed by ion-template resolution of G-quartet architectures and sol–gel selection of
hybrid materials AK+-DK+, ABa2+-DBa
2+
.
to a helical self assembly of iminoboronic pendant chromo-
phores.14 Moreover this indirect CD signature of chiral super-
structures closely resembles the previously calculated CD spectra
by Gray et al.15 of G-quadruplexes whose adjacent G-quartets
have opposite polarities.
and the presence of the nB–N ¼ 814 cmꢀ1 band, mostly
2+
predominant in the FTIR spectra of AK+-DK+, ABa2+-DBa
.
29Si MAS NMR spectroscopic experiments are in agreement
2+
for both AK+-DK+, ABa2+-DBa and the reference E hybrid
materials, with total condensated hybrid materials (the conden-
sation number and the condensation degree are 2.80–2.90 and
93–97% respectively), with major cross linked T3 C–Si(OSi)3
(70 ppm ꢃ95%) units and minor T1 C–Si(OSi)(OH)2 (24%), T2
C–Si(OSi)2(OH) (59 ppm ꢃ5%) units, showing a predominant
3D arrangement. Moreover, that the self assembly processes
occur differently in the presence or in the absence of K+ temp-
lating ions, seems not to influence the hydrolysis-condensation
reactions of the alkoxysilane groups during the sol–gel process.
3.1.3. Generation of G-quartet architectures in solid state.
Having shown that compound 5 equilibrated with K+ and Ba2+
ions forms G-quadruplex superstructures in solution we next
evaluated their ability to form higher order superstructures in the
solid state, by using a sol–gel resolution process.4a The generation
of G-quadruplex hybrid materials AK+-DK+ or ABa2+-DBa2+ can be
achieved by mixing guanosine
4
and 2-((3-(triethoxy-
silyl)propylimino)methyl)phenyl boronic acid, 3 in methanolic
solutions with potassium or barium triflates, followed by a sol–
gel process performed at room temperature and using benzyl-
amine as a catalyst (Scheme 2, Table 1). We also carried out the
sol–gel process, in the absence of K+ or Ba2+ cations, resulting in
the formation of a G-hybrid material, E. Finally, the organic
constituents of these materials have been calcinated to obtain
inorganic silica replica architectures induced by the self-organi-
zation of G-quadruplex superstructures.
3.4. X-Ray powder diffraction characterization of G-quadruplex
hybrid materials
Further valuable insights on the self-organization of AK+-DK+ or
ABa2+-DBa2+ and reference E hybrid materials are obtained from
the X-ray powder diffraction (XPRD) (Fig. 3 and S2†).
3.2. FTIR and solid state NMR spectroscopic analyses
FTIR and NMR spectroscopic analyses demonstrate the
formation of a self-organized organic-inorganic network. The
FTIR spectra of the hybrid materials AK+-DK+, ABa2+-DBa2+ or E
allowed us to observe the nSi–O–Si broad vibration at 900–
1200 cmꢀ1 instead of nSi-OEt vibrations (950, 1070 and 1100 cmꢀ1
)
which were noticed for the molecular precursor 3. Clear evidence
for H-bonding and metal ions complexation was obtained from
2+
FTIR analysis of solids AK+-DK+, ABa2+-DBa and E. Free
nC]O ¼ 727 cmꢀ1 (hybrid E) was downshifted to 1680 cmꢀ1
+
(hybrids AK+-DK
,
ABa2+-DBa2+), indicating the G-quartets
formation (Fig. 2). The formation of iminoboronate esters
stabilized by a donor N/B dative bond is supported the
vibration shifts of the –N]C bonds: nC]N ¼ 1640 to 1605 cmꢀ1
Fig. 2 FTIR spectra of G-hybrid material, E and of G-quadruplex
hybrid materials AK+and ABa
2+
.
9446 | J. Mater. Chem., 2010, 20, 9443–9448
This journal is ª The Royal Society of Chemistry 2010

View Article Online
2+
Fig. 4 Scanning electron microscopy images of BBa hybrid material
after the sol–gel step (bottom) and after the calcination step (lower).
+
2+
decomposition of AK+-DK or ABa2+-DBa and reference E
hybrid materials. Table 1 shows the T50% temperature for which
50% weight decomposes. The formation G-quadruplex struc-
+
2+
tures induce a higher T50% for AK+-DK and ABa2+-DBa mate-
rials than reference material E. Scanning electron microscopy
+
(SEM) micrographs reveal that the hybrid materials AK+-DK
and ABa2+-DBa2+ (Fig. 4) have micrometric plate-like or nanorod
morphologies. Moreover, while the classical hybrids are compact
dense solids with a granular morphology, the constitutional
hybrids Ai and Bi consist of crystalline rods of micrometric
dimension. It is interesting to note that similar superior long-
range organisation at micrometric length have been previously
observed.16 This phenomenon is certainly dependent on the
superior emergence of collective domains adapting along the
G-quadruplex reversible interfaces. This may increase the size of
self-organized domains, increasing the dimension of resulted
microdomains of such constitutional hybrids.16
Fig. 3 High angles XPRD patterns of the compounds 5, 5 + 0.25 equiv.
of M+, 5 + 1 equiv. of M+ (M+ ¼ K+, Ba+2) and of the hybrid materials a)
2+
AK+-DK+ and b) ABa2+-DBa
.
4. Conclusions
In conclusion, the results presented here reveal an original
strategy to transcribe and to fix supramolecular G-quadruplex
architectures in self-organized constitutional hybrids. In parti-
cular, the use of a dynamic iminoboronate interface between the
organic (supramolecular) and inorganic siloxane networks
represents a useful strategy for improving their compatibility.
Dynamic self-assembly of supramolecular systems prepared
under thermodynamic control, may in principle be connected to
a kinetically controlled sol–gel process in order to extract and
select the interpenetrated self-organized networks under
a specific set of experimental conditions. Such ‘‘dynamic
convergence’’ between supramolecular self-assembly and an
inorganic sol–gel process which can synergistically communicate,
leads to higher self-organized hybrid materials with increased
micrometric scales. Sol–gel selection of constitutional architec-
tures from dynamic combinatorial libraries toward systems
materials, as highly interconnected networks of reactional and
constitutional materials, should expand the fundamental
understanding of nanoscale structures and properties as it relates
to creating products and manufacturing processes. More gener-
ally, applying such consideration to hybrid materials, leads to the
definition of constitutional hybrid materials, in which organic
(supramolecular)/inorganic domains are reversibly connected.17
Considering the simplicity of this strategy, possible applications
The XRPD patterns of the G-quadruplex hybrids AK+-DK+ and
ABa2+-DBa2+ present well-resolved peaks (Fig. 3). It is noted that
the crystallinity of the Ba2+-templated materials ABa2+-DBa is
high compared with the K+-templated analogs, as previously
observed16 in view of the signal peaks, indicative of long-range
structured material.15,16 This feature was not observed for the
2 +
XRPD patterns of the non-templated G-hybrid material, E
+
(Fig. 3, blue, patterns). The metal ion templated materials AK
+
-
DK and ABa2+-DBa present a peak at 2q ¼ 26.8 (d ¼ 3.3 A),
2+
ꢀ
representative for the p–p stacking distꢁance between two planar
G-quartets.5b,11e This peak at 2q ¼ 26.7 (d ¼ 3.3 A), is strongly
ꢀ
amplified by simple addition of metal ion templates before the
sol–gel process (Fig. 3, the black and red patterns are compared
to the blue one) by simply mixing 5 with metal ions. Further if we
proceed with the sol–gel results in the formation ꢁof polymerized
ꢀ
hybrids. We observed that the peak at 2q ¼ 26.7 (d ¼ 3.3 A) is
+
more intense for CK and DK or CBa and DBa materials
+
2+
2+
prepared in the presence of stoichiometric amounts of metal ions.
3.5. Thermal and morphological studies
To study the stability of the hybrid materials under the influence
of the G-quadruplex superstructure, we explored the thermal
This journal is ª The Royal Society of Chemistry 2010
J. Mater. Chem., 2010, 20, 9443–9448 | 9447

View Article Online
Commun., 2010, 46, 2441–2443; (g) E. Mahon, T. Aastrup and
M. Barboiu, Chem. Commun., 2010, 46, 5491, DOI: 10.1039/
c002652b.
of the synthesis to more complex architectures might be very
effective, producing novel expressions of complex matter.
8 (a) J. T. Davis and G. P. Spada, Chem. Soc. Rev., 2007, 36, 296–313;
(b) J. T. Davis, Angew. Chem., Int. Ed., 2004, 43, 668–698.
9 (a) T. Giorgi, S. Lena, P. Mariani, M. A. Cremonini, S. Masiero,
S. Pieracini, J. P. Rabe, P. Samori, G. P. Spada and G. Gotarelli,
J. Am. Chem. Soc., 2003, 125, 14741–17479; (b) S. Pieraccini,
S. Masiero, O. Pandoli, P. Samori, G. P. Spada and G. Gotarelli,
Org. Lett., 2006, 8, 3125–3128.
10 (a) A. Ghoussoub and J.-M. Lehn, Chem. Commun., 2005, 5763–5765;
(b) V. Setnicka, M. Urbanova, K. Volka, S. Nampally and
J.-M. Lehn, Chem.–Eur. J., 2006, 12, 8735–8743; (c)
N. Sreenivasachary and J.-M. Lehn, Chem.–Asian J., 2008, 3, 134–
139; (d) W. C. Drewe and S. Neidle, Chem. Commun., 2008, 5295–
5297; (e) C. Graziano, S. Masiero, S. Pieracini, M. Lucarini and
G. P. Spada, Org. Lett., 2008, 10, 1739–1742; (f) E. Buhler,
S. Nampally, S.-J. Candau and J.-M. Lehn, J. Am. Chem. Soc.,
2007, 129, 10058–10059; (g) M. Nikan and J. C. Sherman, Angew.
Chem., Int. Ed., 2008, 47, 4900–4902.
11 (a) D. Gonzalez-Rodriguez, P. G. A. Janssen, R. Martin-Rapun, I. De
Cat, S. De Feyter, A. P. H. J. Schenning and E. W. Meijer, J. Am.
Chem. Soc., 2010, 132, 4710–4719; (b) S. Pieraccini, S. Bonacchi,
S. Lena, S. Masiero, M. Montalti, N. Zaccheroni and G. P. Spada,
Org. Biomol. Chem., 2010, 8, 774–781; (c) S. Lena, S. Masiero,
S. Pieraccini and G. P. Spada, Chem.–Eur. J., 2009, 15, 7792–7806;
(d) A. Ciesielski, S. Lena, S. Masiero, G. P. Spada and P. Samori,
Angew. Chem. Int. Ed., 2010, 49, 1963–1966; (e) M. Li,
R. J. Oakley, H. Bevan, B. M. Smarsly, S. Mann and C. F. J. Faul,
Chem. Mater., 2009, 21, 3270–3274.
Acknowledgements
This work, conducted under the European Heads of Research
Councils and European Science Foundation EURYI (European
Young Investigator) Awards scheme in 2004, was supported by
funds from the participating organizations of EURYI and the
EC Sixth Framework Program. See www.esf.org/euryi.
Notes and references
1 (a) J.-M. Lehn, Chem. Soc. Rev., 2007, 36, 151–160; (b) J. A. Thomas,
Chem. Soc. Rev., 2007, 36, 856–868; (c) M. Barboiu and J.-M. Lehn,
Proc. Natl. Acad. Sci. U. S. A., 2002, 99, 5201–5206.
2 (a) M. Kindermann, I. Stahl, M. Reimond, W. M. Pankau and G. von
Kiedrovski, Angew. Chem., Int. Ed., 2005, 44, 6750–6755; (b)
J. Stankiewicz and L. H. Eckardt, Angew. Chem., Int. Ed., 2006, 45,
342–344; (c) R. F. Ludlow and S. Otto, Chem. Soc. Rev., 2008, 37,
101–108.
€
3 (a) P. Vongvilai, M. Angelin, R. Larsson and O. Ramstrom, Angew.
Chem., Int. Ed., 2007, 46, 948–950; (b) R. Larsson and
€
O. Ramstrom, Eur. J. Org. Chem., 2006, 285–291; (c) R. Larsson,
Z. Pei and O. Ramstrom, Angew. Chem., Int. Ed., 2004, 43, 3716–
€
€
3718; (d) M. Angelin, P. Vongvilai, A. Fischer and O. Ramstrom,
Chem. Commun., 2008, 768–770; (e) M. Angelin, P. Vongvilai,
A. Fischer and O. Ramstrom, J. Org. Chem., 2008, 73, 3593–3595.
€
12 (a) C. Sanchez, H. Arribart and M. M. Girau-Guille, Nat. Mater.,
2005, 4, 277–288; (b) J. J. E. Moreau, L. Vellutini, M. Wong Chi
4 (a) S. Xu and N. Giuseppone, J. Am. Chem. Soc., 2008, 130, 1826–
1827; (b) R. Nguyen, L. Allouche, E. Buhler and N. Giuseppone,
Angew. Chem., Int. Ed., 2009, 48, 1093–1096 and references therein;
(c) R. Nguyen, E. Buhler and N. Giuseppone, Macromolecules,
€
2009, 42, 5913–5915; (d) L. Tauk, A. P. Schroder, G. Decher and
N. Giuseppone, Nat. Chem., 2009, 1, 649–654.
ꢁ
Man, C. Bied, J. L. Bantignies, P. Dieudonne and J. L. Sauvajol,
J. Am. Chem. Soc., 2001, 123, 7957–7958; (c) R. J. P. Corriu, Eur.
J. Inorg. Chem., 2001, (5), 1109–1121; (d) K. J. C. van Bommel,
A. Frigerri and S. Shinkai, Angew. Chem., Int. Ed., 2003, 42, 980–
999; (e) M. Barboiu, C. Guizard, C. Luca, B. Albu, N. Hovnanian
and J. Palmeri, J. Membr. Sci., 1999, 161, 193–206; (f) M. Barboiu,
C. Guizard, C. Luca, N. Hovnanian, J. Palmeri and L. Cot,
J. Membr. Sci., 2000, 174, 277–286; (g) M. Barboiu, C. Guizard,
N. Hovnanian, J. Palmeri, C. Reibel, C. Luca and L. Cot,
J. Membr. Sci., 2000, 172, 91–103; (h) O. Villamo, C. Barboiu,
M. Barboiu, W. Yau-Chun-Wan and N. Hovnanian, J. Membr.
Sci., 2002, 204, 97–110; (i) C. Guizard, A. Bac, M. Barboiu and
N. Hovnanian, Sep. Purif. Technol., 2001, 25, 167–180; (j)
M. Barboiu, N. Hovnanian, C. Luca and L. Cot, Tetrahedron,
1999, 55, 9221–9232; (k) M. Barboiu, C. Luca, C. Guizard,
N. Hovnanian, L. Cot and G. Popescu, J. Membr. Sci., 1997, 129,
197–207; (l) M. Barboiu, C. Guizard, N. Hovnanian and L. Cot,
Sep. Purif. Technol., 2001, 25, 211–218; (m) M. Michau,
ꢁ
5 (a) C. Arnal-Herault, M. Michau, A. Pasc-Banu and M. Barboiu,
Angew. Chem., Int. Ed., 2007, 46, 4268–4272; (b) C. Arnal-Herault,
ꢁ
A. Pasc-Banu, M. Michau, D. Cot, E. Petit and M. Barboiu,
Angew. Chem., Int. Ed., 2007, 46, 8409–8413; (c) M. Michau,
ꢁ
M. Barboiu, R. Caraballo, C. Arnal-Herault, P. Periat, A. van der
Lee and A. Pasc, Chem.–Eur. J., 2008, 14, 1776–1783; (d)
A. Cazacu, C. Tong, A. van der Lee, T. M. Fyles and M. Barboiu,
J. Am. Chem. Soc., 2006, 128, 9541–9548; (e) M. Barboiu,
G. Vaughan and A. van der Lee, Org. Lett., 2003, 5, 3073–3076; (f)
M. Barboiu, J. Inclusion Phenom. Macrocyclic Chem., 2004, 49,
133–137; (g) M. Barboiu, S. Cerneaux, A. van der Lee and
G. Vaughan, J. Am. Chem. Soc., 2004, 126, 3545–3550; (h)
ꢁ
C. Arnal-Herault, M. Barboiu, A. Pasc, M. Michau, P. Perriat and
A. van der Lee, Chem.–Eur. J., 2007, 13, 6792–6800.
ꢁ
R. Caraballo, C. Arnal-Herault and M. Barboiu, J. Membr. Sci.,
6 (a) P. N. W. Baxter, J.-M. Lehn and K. Rissanen, Chem. Commun.,
1997, 1323–1324; (b) M. Hutin, C. J. Cramer, L. Gagliardi,
L. A. R. Shahi, G. Bernardinelli, R. Cerny and J. R. Nitschke,
J. Am. Chem. Soc., 2007, 129, 8774–8780; (c) P. N. W. Baxter,
J.-M. Lehn, G. Baum and D. Fenske, Chem.–Eur. J., 2000, 6, 4510–
4517; (d) C. D. Pentecost, K. S. Chichak, A. J. Peters,
G. W. V. Cave, S. J. Cantrill and J. F. Stoddart, Angew. Chem., Int.
Ed., 2007, 46, 218–222; (e) C.-F. Chow, S. Fujii and J.-M. Lehn,
2008, 321, 22–30; (n) M. Michau and M. Barboiu, J. Mater. Chem.,
2009, 19, 6124–6131.
13 (a) T. D. James, H. Shinmori and S. Shinkai, Chem. Commun., 1997,
71–72; (b) L. Zhu, S. H. Shabbir, M. Gray, V. M. Lynch, S. Sorey and
E. V. Anslyn, J. Am. Chem. Soc., 2006, 128, 1222–1232; (c)
ꢁ
A. M. Kelly, Y. Perez-Fuertes, S. Arimori, S. D. Bull and
T. D. James, Org. Lett., 2006, 8, 1971–1974.
€
14 (a) K. Hanabusa, M. Yamada, M. Kimura and H. Shirai, Angew.
Chem., Int. Ed. Engl., 1996, 35, 1949–1951; (b) K. Hanabusa,
K. Shimura, K. Hirose, M. Kimura and H. Shirai, Chem. Lett.,
1996, 25, 885–886.
15 D. M. Gray, J.-D. Wen, C. W. Gray, R. Repges, C. Repges, G. Raabe
and J. Fleinschhauer, Chirality, 2008, 20, 431–440.
16 S. Mihai, A. Cazacu, C. Arnal-Herault, G. Nasr, A. Meffre, A. van
der Lee and M. Barboiu, New J. Chem., 2009, 33, 2335–2343.
17 A. Cazacu, Y. M. Legrand, A. Pasc, G. Nasr, A. van der Lee,
E. Mahon and M. Barboiu, Proc. Natl. Acad. Sci. U. S. A., 2009,
106, 8117–8122.
Chem. Commun., 2007, 4363–4365; (f) A. Muller, L. Toma,
H. Bogge, C. Scaffer and A. Stammler, Angew. Chem., Int. Ed.,
2005, 44, 7757–7761.
7 (a) F. Dumitru, E. Petit, A. van der Lee and M. Barboiu, Eur. J. Inorg.
Chem., 2005, 4255–4262; (b) Y. M. Legrand, A. van der Lee and
M. Barboiu, Inorg. Chem., 2007, 46, 9540–9547; (c) M. Barboiu,
E. Petit, A. van der Lee and G. Vaughan, Inorg. Chem., 2006, 45,
484–486; (d) M. Barboiu, F. Dumitru, Y.-M. Legrand, E. Petit and
A. van der Lee, Chem. Commun., 2009, 2192–2194; (e) F. Dumitru,
Y. M. Legrand, A. van der Lee and M. Barboiu, Chem. Commun.,
2009, 2667–2669; (f) E. Mahon, T. Aastrup and M. Barboiu, Chem.
9448 | J. Mater. Chem., 2010, 20, 9443–9448
This journal is ª The Royal Society of Chemistry 2010