Kinetic selection of polymeric guanosine architectures from dynamic supramolecular libraries

Article abstract of DOI:10.1016/j.crci.2015.03.019

We report an original strategy to transcribe and to fix supramolecular guanosine architectures in self-organized polymers. In the first resolution step, the G-quartet and G-quadruplex architectures are pre-amplified in solution in the presence of K^+<

Full text of DOI:10.1016/j.crci.2015.03.019

C. R. Chimie 18 (2015) 960–965
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Full paper/M e´ moire
Kinetic selection of polymeric guanosine architectures from
dynamic supramolecular libraries
S e´ lection cin e´ tique des architectures polym e` res de guanosine a` partir des
librairies supramol e´ culaires dynamiques
1
Anca Meffre , Eddy Petit, Didier Cot, Mihail Barboiu *
Adaptive Supramolecular Nanosystems Group, Institut europ e´ en des membranes, ENSCM–UMII, UMR CNRS 5635, place Eug e` ne-Bataillon,
CC047, 34095 Montpellier cedex, France
A R T I C L E I N F O
A B S T R A C T
Article history:
We report an original strategy to transcribe and to fix supramolecular guanosine
architectures in self-organized polymers. In the first resolution step, the G-quartet and G-
Received 13 January 2015
Accepted after revision 9 March 2015
Available online 20 August 2015
+
quadruplex architectures are pre-amplified in solution in the presence of K cations from a
dynamic pool of ribbon-type or cyclic supramolecular architectures. Then in a second
selection polymerization step, the G-quadruplex is kinetically fixed in a covalent
polymethacrylate network via an irreversible amplification step. Both supramolecular
and polymeric components mutually (synergistically) adapt their spatial constitution
during simultaneous (collective) formation of micrometric self-organized hybrid domains.
This contributes to the high level of adaptability and correlativity of the self-organization of
the supramolecular G-quadruplexes and of the polymeric systems. Biomimetic-type
hybrid systems can be generated by using this strategy.
Keywords:
G-quadruplex
Self-assembly
H-bonding
Hybrid polymers
Constitutional materials
ß 2015 Acad e´ mie des sciences. Published by Elsevier Masson SAS. All rights reserved.
1
. Introduction
Constitutional self-assembly provides evolutional
behaviours [3]. These new concepts may be connected
today with the simple definition of Dynamic Multicompo-
nent Self-assembly in chemical and biological systems
[4]. They concern collections of molecular/supramolecular
objects reversibly exchanging and continuously organizing
at the nano- or macroscopic levels.
A representative example is related to the architecture,
the H-bonded supramolecular macrocycle formed by the
self-assembly of four guanosines and stabilized by alkali
cations. It may embody an important constitutional
approaches for the generation of functional systems
through the implementation of reversible exchanges
between different complex architectures of variable
functionality [1,2]. Much efforts continue to be undertaken
on complex systems, which have been identified as an
especially promising means to explore the chemical space
with natural selection of their structural and functional
(
spatial and interactional) reorganization with different
G-networks, dynamically exchanging between G-ribbons
and G-quartets or their stacked tubular G-quadruplexes
*
Corresponding author.
E-mail address: mihail-dumitru.barboiu@univ-montp2.fr
(
Fig. 1) [5a].
(
M. Barboiu).
1
Although discovered in the 1960s [5b], the functionality
Present address: Universit e´ de Toulouse, INSA, UPS, laboratoire de
of the artificial G-quadruplexes as ion-channels and their
direct quantification in human cells have been only
physique et chimie des nano-objets, LPCNO, 135, avenue de Rangueil,
1077 Toulouse, France.
3
http://dx.doi.org/10.1016/j.crci.2015.03.019
631-0748/ß 2015 Acad e´ mie des sciences. Published by Elsevier Masson SAS. All rights reserved.
1

A. Meffre et al. / C. R. Chimie 18 (2015) 960–965
961
Fig. 1. Dynamic exchanges between supramolecular architectures G-ribbons, G-quartets or G-quadruplexes in the presence of ionic chemical effectors (red
sphere).
recently emphasized [6]. Liposomes [7], surfaces [8],
dynamers [9], hybrid materials [10,11], mesoporous silica
superstructures can be also achieved by using the
reversible metathesis polymerization reaction, as previ-
ously demonstrated by Davis et al. [15].
[
12] or silicon [13] have been used as scaffolding matrices
to stabilize and to orient the anisotropic directional G-
mesophases.
We hypothesized that the stabilization of guanosine
supramolecular architectures may be obtained via a
We have recently showed that sol–gel selection can be
used as an irreversible kinetic process in order to stabilize
the G-quadruplex and to provide long-range amplification
of its supramolecular chirality into hybrid organic-
inorganic twisted nanorods. This may be followed by a
second inorganic transcription via calcination into inorganic
replica materials, when silica microsprings can be obtained
classical polymerization process. Herein we describe this
0
strategy by using 5 -methacrylate guanosine, G
m
, self-
assembling in solution in G-quadruplexes, followed by
their irreversible transcription in an organic polymeric
network via intermolecular cross-linking of methacrylate
end groups. These results provide new insights into the
basic features that control the convergence of supramo-
lecular self-organization and polymerization process
toward functional materials at the nano(micro)level.
[
10]. A second used strategy is related to the implementa-
tion of dynamic hydrophobic non-covalent [11a] or
reversible-covalent iminoboronate [11a] interactions be-
tween the supramolecular G-quadruplexes and the silox-
ane/polymeric constituents. The reversibility of the
interactions between components represents a crucial
factor and, accordingly, a dynamic reversible hydrophobic
interface might render the emergence of organic/inorganic
mesophases self-adaptive. They mutually may adapt their
2. Experimental
2.1. Materials and methods
All reagents were obtained from Aldrich and used
without further purification. All organic solutions were
3
D spatial distribution based on their own structural
2 4
routinely dried by using sodium sulfate (Na SO ). Poly-
constitution, during the simultaneous formation of hybrid
self-organized domains. [14] It is known that the
multicomponent self-assembly of the G-quadruplexes
merizations were performed under an inert atmosphere of
nitrogen, using standard Schlenk techniques. Tetrahydro-
furan was dried and distilled prior to use over Na. The

9
62
A. Meffre et al. / C. R. Chimie 18 (2015) 960–965
ꢀ
2
initiator, AIBN, was recristallized from ether and stored at
[G ] = 10 M) and the initiator, AIBN (1.86 mg,
m
1
13
ꢀ
15 8C. H and C NMR spectra were recorded on an ARX
0.0114 mmol) was added. Three freeze-pump-thaw cycles
were performed. The reaction mixture was stirred at 60 8C
for four days. The solvent was removed in vacuo. The
polymer was precipitated with excess hexane, and dried
3
00 MHz Bruker spectrometer in d -DMSO or CDCl using
6
3
the residual solvent peaks as references. ESI–MS studies
were performed in the positive and negative ion mode
1
using
a
quadrupole mass spectrometer (Micromass,
under vacuum. Conversion: > 95%; yield: 75%. H NMR
Platform II). The samples were continuously introduced
into the mass spectrometer through a Waters 616 HPLC
(DMSO-d6, 300 MHz)
5H, aromatics); 6.61 (bs, 2H, NH2); 5.90–6.30 (bs, 2H, H1 ,
H6); 5.10–5.60 (m, 2H, H2 , H3 ); 4.53 (m, 3H, H4 , H5 ).
d
(ppm) 7.90 (bs, 1H8); 7.10–7.70 (m,
0
0
0
0
0
pump (60 8C; extraction cone voltage: V
powder diffraction measurements were performed with
Cu K radiation at 20 8C using a Philips X’Pert Diffractom-
eter equipped with an Xcelerator detector. The SEM
micrographs were obtained with High-Resolution
Transmission Electron Microscopy (HRTEM) JEOL
c
= 30 V). X-ray
a
2.1.3.2. Synthesis in the presence of alkali cations. Gm
(50 mg, 0.114 mmol) was dissolved in THF freshly distilled
ꢀ2
a
(11 ml, [Gm] = 10 M); KCF SO 8:1 mol:mmol and then
3 3
the initiator, AIBN (1.86 mg, 0.0114 mmol), were added.
Three freeze–pump–thaw cycles were performed. The
reaction mixture was stirred at 60 8C for two days. The
solvent was removed in vacuo. The polymer was precipi-
tated with excess hexane, and dried under vacuum.
Conversion: > 95%; yield: 75%.
2
010 FEG apparatus, working with an accelerating voltage
˚
of 200 kV and a point resolution of 2.0 A.
0 0
.1.1. 2 ,3 -O-Benzylidene guanosine
2
0
0
1
The precursor, 2 ,3 -O-benzylidene guanosine was
6
H NMR (DMSO-d ,
prepared according to the reported procedures [16]. Gua-
nosine (5 g, 17.65 mmol) was suspended in benzalde-
3
00 MHz):
d
(ppm) 7.90 (bs, 1H8); 7.10–7.70 (m, 5H,
0
aromatics); 6.61 (bs, 2H, NH2); 5.90–6.30 (bs, 2H, H1 , H6);
5
hyde (50 ml). An excess of ZnCl
2
(13.25 g; 97.18 mmol)
0
0
0
0
.10–5.60 (m, 2H, H2 , H3 ); 4.53 (m, 3H, H4 , H5 ).
was added. After stirring at room temperature for one
night, the reaction mixture was washed with ether and
cold water. The crude solid was recrystallized from an
3. Results and discussion
ethanol/water (3:1) mixture to give a yellow product.
3
.1. Design of hybrid molecular components
1
Yield: 84%. H NMR (d
6
-DMSO, 300 MHz)
); 7.48-7.31 (m, 5H,
); 6.11 et 5.85 (2s, 1H, H );
); 5.25 (m, 1H, H ); 5.05 (m, 2H, H , OH);
); 3.55 (m, 2H, H ).
d (ppm) 10.65
0
0
0
(
s, 1H, NH); 7, 90 et 7.85 (2s, 1H, H
7
5 -Methacrylate-2 ,3 -O-benzylidene-guanosine, Gm,
has been prepared in two steps:
aromatics); 6.45 (s, 2H, NH
2
6
6
.02 (2d, 1H, H
1
0
2
0
0
3
4
.20 (m, 1H, H
4
0
5
0
ꢁ
ꢁ
furanose protection with benzaldehyde leading to acetal
G* as an equimolar diastereisomeric mixture [16],
followed by;
a reaction with methacryloyl chloride to afford the
compound Gm as a white powder.
0
0
0
2
.1.2. 5 -Methacrylate-2 ,3 -O-benzylid e` ne-guanosine, G
2
m
0
0
,3 -O-Benzylid e` ne-guanosine (2.3 g, 6.73 mmol) was
dissolved in anhydrous DMF (60 ml). Three equivalents
of triethylamine (2.04 g, 20.20 mmol), DMAP (0.41 g,
3
.37 mmol) and methacryloyl chloride (0.98 g, 9.42 mmol)
were successively added. The mixture was stirred at room
temperature for one night. The solvent was removed in
vacuo, and the residue treated with chloroform (30 ml) and
water (60 ml). The organic layers were separated, dried
1
13
The H, C NMR, ESI-MS spectra are in agreement with
the proposed formula. The generation of G-quartet
architectures can be achieved by using mixtures of Gm,
potassium triflate, and KTf in different molar ratios (Fig. 1).
4
(MgSO ) and evaporated in vacuo. The resulting mixture
was purified by silica gel column chromatography (10%
3.2. Generation of G-quartet architectures in solution
methanol in chloroform) to give the product as a yellow
1
solid. Yield: 56%. H NMR (d
6
-DMSO, 300 MHz):
); 7.57–7.42 (m,
); 6.20 (2s, 1H, H ); 6.08
); 6.14 et 5.68 (2s, 2H, CH =); 5.42 (m, 1H, H );
.32 (m, 1H, H ); 4.53 (m, 1H, H ); 4.48 (m, 2H, H ); 1.86
, 300 MHz) (ppm) 166.30
16); 156.75 (C11); 153.78 (C10); 150.54 et 150.45 (C
45.97 et 145.39 (C17); 136.01 (C
15); 128.40 (C13); 126.97 (C14); 126.31 (C18); 117.04 (C
06.73 et 103.09 (C ); 88.19 (C ); 84.78 et 84.27 (C
); 81.87 et 81.59 (C ); 64.75 et 64.50 (C ); 17.95 (C19).
ESI–MS (30 V, ESI–MS, CH CN) m/z = 440.53 [M + H] .
d
(ppm)
The formation of H-bonded self-assembled architectu-
1
1
5
0.80 (bs, 1H, NH); 7.89 et 7.87 (2s, 1H, H
H, aromatics); 6.61 (bs, 2H, NH
7
res of Gm has been studied in solution by H NMR
1
2
6
spectroscopy and ESI-MS spectrometry. The H NMR
(2d, 1H, H
1
0
2
2
0
spectrum of Gm in DMSO-d6 shows well-defined sharp
signals, mostly indicative of the presence of monomeric
5
3
3
0
4
0
5
0
1
(2s, 3H, CH
3
). C NMR (DMSO-d
6
d
3
species in solution. In CDCl , the peaks broaden, indicating
(C
9
);
);
a dynamic equilibrium. These fast exchanges at the NMR
time scale are considerably slowed down by lowering the
temperature (up to –50 8C), when three sets of signals at d
12.25, 12.38, 12.48 ppm, showing N–H and NH2 cross-
peaks (Fig. 2a), reminiscent of a slow exchange between H-
bonded interdigitated ribbons A and B and G-quartets
1
7
); 135.50 (C12); 129.80
(C
8
1
6
1
2
); 83.11
(C
3
4
5
+
3
(
Fig. 1), as previously observed [17].
The addition of the KTf (K : Gm 1:8, mol: mol) to a
+
2.1.3. Polymerization procedures
1
CDCl
3
solution of Gm causes significant changes in the H
2
.1.3.1. Synthesis in the absence of alkali cations. G
.114 mmol) was dissolved in THF freshly distilled (11 ml,
m
(50 mg,
NMR spectrum (Fig. 2b–d). At 25 8C, the latter shows two
peaks for the N–H proton: one sharp peak at 12.7 ppm and
0

A. Meffre et al. / C. R. Chimie 18 (2015) 960–965
963
1
Fig. 2. H NMR titration (300 MHz, CDCl
3
) of Gm with KTf: a: Gm at 25 8C followed by the addition of; b: 1/8 equiv KTf at 25 8C; c: 1/8 equiv KTf at –50 8C; d:
1
/4 equiv KTf at 25 8C.
one broad peak at 9.7 ppm, reminiscent of the dominating
presence of a symmetrical D4 octamer in a fast dynamic
exchange with the corresponding G-quadruplex (Fig. 2b).
Lowering the temperature, these signals are sharpening
and slowly shifting (Fig. 2c). They correspond to two
different inner and outer quartets of the G-quadruplex,
exchanging slowly with G-octamers in solution at the NMR
distribution, indicating the presence of a triple-charged ion
3
+
and a formula of [Gm]16[3K]
.
3.3. Polymerization processes of Gm
+
Having shown that mixtures of Gm equilibrated with K
cations form G-octamer and G-quadruplex superstructures
in equilibrium in solution, we next evaluated their ability
to form higher-order superstructures in the polymeric
state, by using a kinetically irreversible polymerization
step. The generation polymethacrylate G-quadruplex ma-
+
time scale. [18] The (Gm)8K octamer is stable over a
1
temperature range of approximately 60 8C. The H NMR
3
spectra in CDCl , recorded at different temperatures, show
small chemical shifts for the protons NH(1) and NH(2),
indicating strong hydrogen bonding (Fig. 2e). Upon further
n
terial, {GmK} , can be achieved by using a pre-equilibrated
+
addition of the potassium triflate (K : Gm 1:4, mol: mol), a
guanosine derivative, Gm, and KTf in THF, followed by a
polymerization process performed in the presence of AIBN
at 60 8C. We also carried out for reference the polymeriza-
new set of broad signals appears, consistent with the
formation of unsymmetrical exchanging species in solu-
tion (Fig. 2d). Further valuable insights are obtained from
the ESI mass spectra of compound Gm and of the related
+
tion process in the absence of K cations, resulting in
the formation of a polymethacrylate G-ribbon material,
+
K :Gm 1:8 mol:mol mixture. The positive ESI–MS spec-
n
{Gm} . Then, these polymers were precipitated with
trum of Gm clearly shows the presence of protonated
hexane, and dried under vacuum.
monomers, dimers, trimers, and tetramers as follows:
FTIR and NMR spectroscopic analyses of these materials
demonstrate the formation of polymerized methacrylate
networks. The polymerization reactions have been moni-
+
+
+
m/z = 440 [Gm + H ], 495 [Gm + 3H
2
O + H ], 879 [2Gm + H ],
+
+
9
3
2
35 [2Gm + 3H O + H ], 1318 [3Gm + H ], 1372 [3*Gm +
+
+
1
H
2
O + H ], 1757 [4Gm + H ]. When eight or more equiva-
tored by H NMR after the disappearance of the signals at
lents of KTf are added to the solution of Gm, the ion pattern
changes significantly; a new peak at m/z = 2382 is mainly
present in the spectrum. This peak correspond to a species
with a molar ratio Gm:K of 16:3 mol:mol. High-resolution
measurements gave a 0.33 amu spacing in the isotopic
5.7 ppm corresponding to the methacrylate groups spec-
tra. These reactions may be considered to be complete after
four days for the G-ribbon material, {Gm}
polymeric G-quadruplex material, {GmK} , can be achieved
in two days. This indicates that the polymerization
n
, while the
+
n

9
64
A. Meffre et al. / C. R. Chimie 18 (2015) 960–965
+
processes are favoured in the presence or in the absence of
K templating ions, which may self-assemble the methac-
molecular precursor Gm. Evidence for H-bonding and K
+
complexation was obtained from the vibration shifts of the
rylate groups on the periphery of the tubular G-quadruplex
superstructures in a more favourable spatial distribution
for the polymerization process. The FTIR spectrum of
polymeric materials shows the disappearance of the broad
–C=O bonds, detected before and after the polymerization
+
reaction, only in the presence of
K
cations, at
ꢀ
1
n
C=O = 1686 to 1654 cm
Further insights into the self-organization and mor-
.
ꢀ1
nMeth vibrations at 1631 cm , initially observed for the
phology of the polymeric materials were obtained by X-ray
powder diffraction (XRPD). The XRPD patterns of the G-
ribbon, {Gm}
present well-resolved peaks. It is noted that the crystal-
linity of the resulting G-quadruplex, {GmK} , polymer is
higher when compared with the Gm precursor and the
non-templated G-ribbon, {Gm} , analog, in view of the
n n
, and G-quadruplex, {GmK} , materials
n
n
more sharper signal peaks, indicative of long-range
structured material. For the Gm precursor, the Bragg
diffraction peak at 2
u
= 3.48 corresponds to a characteristic
distance d = 25.6 A, compatible with the length of (Gm)
whereas the peak at 2 = 6.88 corresponds to a distance
d = 13.1 A, which is the monomeric length. After polymeri-
zation, the large Bragg diffraction peak at = 4.58
corresponds to a characteristic distance d = 22.4 A, com-
patible with the more compact G-ribbon, {Gm} , polymeric
´
˚
2
,
u
´
˚
2
˚
u
n
analogue. This contraction of the unpolymerized system,
resulting in the formation of a more compact polymeric
structure, has been as previously observed for similar
systems. [19] The XRPD pattern of the G-quadruplex,
{
2
GmK}, polymer presents a Bragg diffraction peak at
´
˚
u = 3.28, corresponding to a distance d = 27.5 A, compati-
ble with the diameter of the G-quartet superstructure. In
the wide-angle region, an additional peak appears at 2
´
˚
u
p
= 26.58, corresponding to d = 3.6 A and indicative of the
stacking distance between two planar G-quartets.
Scanning electron microscopy (SEM) micrographs
reveal that the Gm precursor, the G-ribbon, {Gm} , and
p-
n
the G-quadruplex, {GmK}, materials present superior long-
range organisation at micrometric level, as previously
observed for similar materils [10,11]. Moreover, while the
initial precursor Gm is a compact dense solid with a
microfiber morphology, the G-ribbon, {Gm} , and the
n
G-quadruplex, {GmK}, polymeric analogues consist of
crystalline microrods and microsprings, respectively
(
Fig. 3). This morphology is certainly dependent on the
superior emergence of collective domains adapting along
the G-quadruplex supramolecular polymer interfaces.
Interestingly, the latter has a slightly twisted rod-like
morphology, related to the transfer of the supramolecular
chirality of G-quadruplex at the micrometric scale in the
resulted polymeric system (see a similar example in ref.
[10]).
4. Conclusions
In conclusion, the results presented here reveal a new
strategy for transcribing and fixing the supramolecular
guanosine architectures in self-organized constitutional
polymeric networks. In particular, the use of a classical
polymerization process represents a useful strategy for
improving the compatibility of supramolecular G-guano-
sine and polymethacrylate networks. A dynamic self-
assembly of supramolecular systems prepared under
thermodynamic control may in principle be connected
Fig. 3. SEM images of a: Gm microfibers and polymeric, b: {Gm}
microfibers, or c: {GmK} microsprings.
n
n

A. Meffre et al. / C. R. Chimie 18 (2015) 960–965
965
[
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Acknowledgement
(
(
This work was financially supported by DYNANO,
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