Nanostructuring organo-silicas: Combination of intermolecular interactions and molecular recognition properties to generate self-assembled hybrids with phenylene or adenine...thymine bridging units

Article abstract of DOI:10.1039/b419376h

Owing to Hydrophobic interactions, silyl linkers containing long alkylene chains allowed the synthesis of self-organised hybrids. Lamellar organo-silicas with phenylene or a hydrogen-bonded adenine...thymine complex as the bridging units are reported. The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2005.

Full text of DOI:10.1039/b419376h

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L E T T E R
Nanostructuring organo-silicas: combination of intermolecular
interactions and molecular recognition properties to generate
self-assembled hybrids with phenylene or adenineꢀ ꢀ ꢀthymine
bridging unitsw
¨
ˆ
Joel J. E. Moreau,* Benoıt P. Pichon, Guilhem Arrachart, Michel Wong Chi Man and
Catherine Bied
´ ´
Laboratoire de Heterochimie Moleculaire et Macromoleculaire (CNRS UMR 5076), Ecole
Nationale Superieure de Chimie de Montpellier, 8 rue de l’Ecole Normale, 34296 Montpellier
´
´
´
cedex 05, France. E-mail: jmoreau@cit.enscm.fr; Fax: +33 (0)4 67 14 72 12;
Tel: +33 (0)4 67 14 72 11
Received (in Montpellier, France) 27th December 2004, Accepted 28th February 2005
First published as an Advance Article on the web 31st March 2005
Owing to hydrophobic interactions, silyl linkers containing long
alkylene chains allowed the synthesis of self-organised hybrids.
Lamellar organo-silicas with phenylene or a hydrogen-bonded
adenineꢀ ꢀ ꢀthymine complex as the bridging units are reported.
material’s synthesis: (i) as a linker, to ensure the covalent
attachment between the organic and the inorganic compo-
nents, and (ii) as a structure-directing motif, owing to its
hydrophobic properties for the nanostructuring of the hybrid
(Scheme 1).
We report here the use of C10 and C11 alkylenes to self-direct
the organisation of organic substructures in a hybrid network
(Scheme 1). First we chose a simple phenylene bridging unit
since it was shown to give amorphous or short-range ordered
hybrids in the absence of a structure-directing agent except for
reactions in the solid state.1,2,11,12,16 Additionally, the use of
C10 or C11 alkylene chains should allow to generate nano-
structured materials by combining self-organisation properties,
resulting from the presence of a long hydrocarbon chains, with
molecular recognition properties based on H-bonding inter-
actions.17
The phenylene unit was linked to a functional Si(OEt)3
group through a long alkylene spacer using three different
procedures, according to Scheme 2. The intermolecular inter-
actions in 1 and 2 combine hydrogen bonding and hydro-
phobic self-association. Interactions between two molecules of
2, forming two intermolecular H-bonds, are expected to be
weaker than between two molecules of 1, which can give four
intermolecular H-bonds. Bis(silylated) linker 3, which has no
H-bonding group,16 was synthesised for comparison. The IR
Since the first report of bridged organo-polysilsesqui-
oxanes,1,2 the hydrolysis-condensation of bis(trialkoxysilyl)
organic molecules has led to a variety of silica hybrids with
covalent linkages between the organic and the silicate net-
work.3,4 Materials with unique functionalities have resulted
from mixing organic and inorganic substructures at the mole-
cular level.5,6 A step beyond the synthesis of new hybrids
consists in structuring the solid on the nanoscopic scale in
order to ensure appropriate tuning of the properties.7 The
creation of hybrids with well-ordered mesopore structures was
obtained by using external organic surfactant templates,8 first
applied in the synthesis of a silica mesophase.9
Hybrid silsesquioxanes offer unique synthetic routes since
the organic component can itself exhibit self-assembling prop-
erties and may direct the formation of the three-dimensional
hybrid network by a self-organisation process. In connection
to this, the use of hydrophobic trialkoxysilyl alkanes was first
shown to allow the synthesis of layered or hexagonal silica-
based materials.10 Interestingly, weak interactions between
aromatic units led to birefringent anisotropic or nanostruc-
tured hybrids.11,12 We recently reported the use of H-bonding
interactions for nanostructuring hybrids.13,14 For the first time,
a self-organised hybrid silica with a long-range ordered struc-
ture was obtained. The synthesis of lamellar hybrid solids with
a crystalline arrangement of the organic substructures was
achieved by combining H-bonding with p-stacking or hydro-
phobic interactions in the solid state.14,15
spectrum of 1 showed vibrations at 1633 (nCO) and 1582 (dNH
)
To obtain hybrid silsesquioxanes with targeted properties,
the attachment of a trialkoxysilyl group (Scheme 1) to an
organic molecule with appropriate properties is required. It is
usually achieved by direct linkage through an hydrolytically
stable Si–C bond or by use of readily available two- or three-
carbon linkers.1–5 We were interested in exploring the use of
long hydrocarbon chains, which may play a double role in the
w Electronic supplementary information (ESI) available: 13C solid state
NMR spectrum of L2; 29Si solid state NMR spectra of L1 and L2;
IR spectra of L1 and L4. See http://www.rsc.org/suppdata/nj/
b4/b419376h/
Scheme 1 Synthesis of organised versus amorphous hybrids.
T h i s j o u r n a l i s & T h e R o y a l S o c i e t y o f C h e m i s t r y a n d t h e
C e n t r e N a t i o n a l d e l a R e c h e r c h e S c i e n t i f i q u e 2 0 0 5
N e w J . C h e m . , 2 0 0 5 , 2 9 , 6 5 3 – 6 5 8
653

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Fig. 1 Powder X-ray diffraction diagrams of hybrids L1–L3.
Scheme 2 Synthesis of hydrophobic precursors 1–3: (i) 10-isocyanato-
decyltriethoxysilane, CH2Cl2; (ii) 11-aminoundecyltriethoxysilane,
CH2Cl2; (iii) 11-bromoundecene, K2CO3, CH3CN then HSi(OEt)3,
Pt, THF.
showed the expected resonances in agreement with the compo-
sitions described in Scheme 3 (see electronic supplementary
information, ESI). 29Si NMR spectra exhibited T2 [C–Si
(OSi)2(OH)] and T3 [C–Si(OSi)3] units with a majority of T2.
The degree of condensation of the silicate networks varied
from 72% to 79–80% for materials L1–L3, respectively. Con-
firming strong interactions between the organic substructures,
the IR spectra showed H-bonded urea in L1: nCO ¼ 1634;
dNH ¼ 1581 cmꢁ1 (Dn ¼ 53 cmꢁ1, see ESI) and amide in L2:
cmꢁ1. The observed low Dn value (nCO ꢁ dNH) of 51 cmꢁ1 is
evidence for strong intermolecular H-bonding.18 Interestingly,
this value is much lower than the one observed for a similar
molecule having a C3 instead of a C10 carbon chain (Dn ¼ 60
cmꢁ1).15 The hydrophobic interactions between the long alkyl
chains of 1 provide a synergetic effect and a significant
reinforcement of the H-bonds. The IR spectrum of 2 is
nCO ¼ 1644; dNH ¼ 1552 cmꢁ1
.
also consistent with H-bonding association (nCO ¼ 1637 cmꢁ1
,
Evidence of the lamellar structure of the materials was
obtained upon examination of the X-ray powder diffraction
diagram of L1–L3 (Fig. 1). L1 showed several sharp Bragg
diffraction peaks. The one at the low q value of 0.177 Aꢁ1
corresponds to a characteristic distance d ¼ 35.4 A, compatible
with the length of the organic spacer. Other peaks at higher
q values corresponding to d values of 17.7, 11.8, 8.9 and 7.1 A
can be associated to the second, third, fourth and fifth orders
of the first peak. These peaks correspond to the X-ray reflec-
tions of a unique family of reticular planes, indicating that the
structure of L1 appears to be mainly characterised by a
periodicity in one direction. A similar long-range ordered
lamellar structure can be proposed for L2 and L3 (Fig. 1).
The observed main characteristic distances of 38.4 and 34.8 A
are also compatible with the length of the organic spacer. As
already observed for related lamellar hybrids, the intensities of
the XRD peaks due to the spacing 002 are larger than those of
the 001 and other diffraction peaks. The diffraction peaks
at 4.5–4.6 A are associated to characteristic distances of
H-bonded functional groups.15 The peaks in the diffraction
spectrum of L2 appeared broader than those observed for L1.
This is indicative of a decrease of the correlation length:20
x(L1) ¼ 369 A, x(L2) ¼ 103 A, and of the ordering. This is in
agreement with a decrease of the interactions between the
organic spacers in L2 containing H-bonded amido groups
compared to L1 with stronger H-bonded urea groups.
dNH ¼ 1548 cmꢁ1).
The hydrolysis-condensation of 1–3 to form silsesquioxane
hybrids L1–L3 was achieved in water to favour self-organisa-
tion by hydrophobic interactions (Scheme 3).19 After 3 days at
60–80 1C, the white solids, which formed quantitatively, were
collected after drying at 110 1C. Solid state 13C and 29Si NMR
The most interesting feature came from the examination of
the Bragg peaks in the diffraction diagram of L3. A related
material with C5 alkylene spacer generated in a thin Teflon-
coated cell exhibited birefringent properties.16 Here, peaks for
d values of 34.8 and 17.4 A can be assigned to 001 and 002
reflection planes of an ordered lamellar structure. The interac-
tions between spacer, only arising from the hydrophobic
eleven-carbon chains, are directing the formation of the layered
hybrid material L3. The calculated correlation length for L3
(x ¼ 216 A) is higher than that for L2. This shows that the long
chain organic linker without an H-bonding motif, as in 3, can
direct the organisation of the hybrid network
Scheme 3 Acid-catalysed hydrolysis-condensation19 of 1–3 giving
lamellar hybrids L1–L3, respectively.
654
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Scheme 4 Synthesis of the adenine (A) and thymine (T) precursors.
This led us to explore whether we would be able to combine
these structuring properties by use of interactions between long
hydrocarbon chain with molecular recognition properties in-
volving H-bonding interactions in order to assemble and to
organise two different organosilicon precursors. We first
synthesised the silylated derivatives of adenine and thymine
(Scheme 4).
The monosilylation of these compounds was achieved by
alkenylation21 with bromoundecene, followed by the hydro-
silylation of the terminal double bond with HSi(OEt)3 in the
presence of a Pt catalyst to give functional derivatives A and T.
In chloroform solution, the two precursors A and T, with
complementary nucleic bases, formed the 1 : 1 complex Aꢀ ꢀ ꢀT.
Evidence for the formation of a 1 : 1 complex of the silylated
derivatives containing adenine and thymine nucleic bases was
obtained from liquid 1H NMR examination of CDCl3 solu-
tions (6 ꢂ 10ꢁ2 M) of pure A, pure T and a 1 : 1 mixture of A
and T. In comparison with the solutions of the pure A and T
compounds, the 1 : 1 mixture showed significant upfield shifts
of the NH2 protons of the adenine fragment (from 5.8 to 6.2
ppm) and of the N3–H proton of the thymine mooiety (from
8.8 to 11.2 ppm). These upfield shifts are characteristic of a 1 : 1
adenineꢀ ꢀ ꢀthymine complex22 and reveal the existence of strong
hydrogen bonding between A and T in solution. The hydrolysis
of this 1 : 1 Aꢀ ꢀ ꢀT complex was achieved at 65 1C for 3.5 days in
water with NaOH as catalyst (Scheme 5).
Fig. 2 29Si (a) and 13C (b) solid state NMR of the adenineꢀ ꢀ ꢀthymine
bridged silsesquioxane L4.
which are characteristic of the sp2 carbons of the adenine
(labelled a in the spectrum) and of the thymine (labelled t in
the spectrum) units and are consistent with the existence of the
Aꢀ ꢀ ꢀT complex in the solid material.
The X-ray powder diffraction of L4 showed Bragg peaks
(Fig. 3). The first two peaks at 0.195 and 0.386 Aꢁ1 could be
assigned as the first and second order peaks, respectively, of
reticular planes of a lamellar form. The first peak corresponds
to a characteristic distance of 32.2 A, which is consistent with
the length of the organic spacer in the (Aꢀ ꢀ ꢀT) complex. It is
shorter than the similar distances in L1–L3, probably due to a
The resulting hybrid L4 was analysed by solid state NMR
spectroscopy. 29Si solid state NMR [Fig. 2(a)] exhibited a
single signal at ꢁ67.9 ppm, indicative of a high degree of
condensation of the hybrid siloxane network. 13C solid state
NMR [Fig. 2(b)] showed signals in the region 110–161 ppm,
Scheme 5 Schematic representation of the formation of a thy-
mineꢀ ꢀ ꢀadenine bridged silsesquioxane.
Fig. 3 Powder X-ray diffraction of the adenineꢀ ꢀ ꢀthymine-bridged
silsesquioxane L4.
N e w J . C h e m . , 2 0 0 5 , 2 9 , 6 5 3 – 6 5 8
655

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different arrangement of the organic units with a bent or a
tilted angle in the layered structure.
4 mmol). After 5 min, terephthaloyle chloride (231 mg, 1
mmol) dissolved in CH2Cl2 (5 ml) was added dropwise. After
standing overnight at room temperature, the solvent was
evaporated and the precipitate was washed with pentane. The
powder was then dissolved in cyclohexane and the hot solution
was filtered. The solvent was evaporated to give 2 as a white
powder. Yield: 82%; m.p.: 134–137 1C; IR (KBr, cmꢁ1): 1548
(dNH), 1637 (nCO), 3301 (nNH); 1H NMR (DMSO d6, d): 0.62 (t,
4H, CH2Si), 1.15–1.45 (m, 50H, CH3 and CH2), 1.6 (m, 4H,
CH2), 3.19 (qd, 4H, CH2), 3.54 (s, 4H, CH2), 3.8 (qd, 12H,
OCH2), 5.37 (m, 2H, NH), 7.24 (s, 4H, Har); 13C NMR
(DMSO d6, d): 9.8 (CH2Si), 18.1 (CH3), 22.2, 26.3, 28.5,
28.6, 28.7, 28.8, 28.9, 29.0, 33.2, 42.0 (CH2), 57.5 (CH2O),
128.6 (CHar) and 134.4 (Car), 169.8 (CO); 29Si NMR (50 MHz,
DMSO d6, d): ꢁ45.2; FAB-MS: 779 [M ꢁ EtO]1 (44%); anal.
calcd for C44H84N2O8Si2 (%): C 64.03, H 10.26, N 3.39, found:
C 62.28, H 10.32, N 3.53.
These preliminary results indicate that H-bonding interac-
tions between adenine and thymine moieties allow association
into a 1 : 1 complex and its organisation into a lamellar solid,
owing to the structure-directing effects of the long hydrocar-
bon linkers. It is interesting to note that a variety of nano-
structured materials may result from the combination of
molecular recognition and self-assembling properties.
In conclusion, the use of silylated linkers containing C10 or
C11 alkylene chains has been shown here to generate nano-
structured bridged silsesquioxanes by a self-organisation pro-
cess. It should allow the attachment of bridging organic
substructures with various functionalities. Organic units not
able to self-assemble could be used, provided the linker con-
tains a hydrophobic segment as structure-directing motif. It
appears that similarly organised solids can be created by using
H-bonding interactions between urea groups or hydrophobic
interactions between long hydrocarbon chains. Compared to
H-bonding linkers,13–15 long hydrocarbon linkers have the
advantage to give soluble and easy-to-handle precursors. The
hydrolysis-condensation can be easily achieved upon disper-
sion of the precursor in water to give nanostructured hybrids.
Moreover, the introduction of nucleic acid base pairs in
bridged silsesquioxanes shows that, in association with struc-
ture-directing motives, molecular recognition properties can
lead to nanostructured materials incorporating two different
organic subunits. Molecular recognition properties based on
hydrogen-bonding interactions having a high potential to
associate organic substructures, this approach offers interesting
possibility to generate bio-inspired materials. We are currently
investigating the generation of self-organised solids with aniso-
tropic properties. For example, these may find uses as materials
for electronics, optics or biosensors.6,7
1,4-Bis(11-undeceneoxy)benzene. Hydroquinone (550 mg,
5 mmol) was dissolved under nitrogen in CH3CN (50 ml).
Then, potassium carbonate (1.52 g, 11 mmol) was added,
followed, after 5 min, by 11-bromoundecene (2.4 ml, 11 mmol).
The mixture was left under reflux for 24 h and was then added
to a solution of NaOH (0.1 N). The precipitate was filtered,
then crystallised in methanol. Yield: 82%; m.p.: 59 1C; IR
1
(CHCl3, cmꢁ1): 1514 (nC¼C), 2851 (ns CH ), 2921 (nas CH ); H
2
2
NMR (CDCl3, d): 1.3–1.4 (m, 24H, CH2), 1.78 (qt, 4H, CH2),
2.07 (qd, 4H, CH ), 3.92 (t, 4H, OCH ), 4.98 (m, 4H, CH ),
Q
Q
2
2
2
5.85 (m, 2H, CH ), 6.84 (s, 4H, CH ); 13C NMR (CDCl3, d):
26.0 (CH2), 28.9, 29.1, 29.3 at 29.6 (4 CH2), 33.8 (CH2), 68.6
ar
(CH O), 114.1 (C ), 115.4 (CH ), 139.2 (C ), 153.2 (C ).
ar
Q
Q
2
ar
FAB-MS: 414 [M þ 1]1 (63%); anal. calcd for C28H46O2 (%):
C 81.10, H 11.18; found: C 79.62, H 11.18
Experimental
1,4-Bis[(triethoxysilyl)undecyloxy]benzene (3). This com-
pound was obtained following synthetic procedures for related
precursors with C5 alkylene chains.16 1,4-Bis(11-undecene-
oxy)benzene (500 mg, 1.2 mmol) was dissolved in dry THF
(20 ml). Triethoxysilylane (1.33 ml, 7.2 mmol) and Karstedt
catalysis (53 ml, 1%) were added. After one night at room
temperature, the solvent was evaporated, giving 3 as a colour-
less oil. Yield: 89%; IR (KBr, cmꢁ1): 1075–1101 (nSiO), 1508
Powder X-ray diffraction (PXRD) measurements were per-
formed at 20 1C at the ‘‘Groupe de Dynamique des Phases
Condensees’’ in Montpellier (France) in glass capillaries with a
´
copper rotating anode X-ray source (4 kW). LKa ¼ 1.542 A.
Collection range of 2y: 0–171 for the wide angle and 0.35–41 for
the small angle.
(nC¼C), 2856–2976 (nCH ,CH ); 1H NMR (CDCl3, d): 0.60
Precursor synthesis
3
(t, 4H, CH2Si), 1.21 (t, 24H, CH3), 1.1–1.5 (m, 36H, CH2),
1.71 (qt, 4H, CH2), 3.78 (qd, 12H, OCH2), 6.77 (s, 4H, Har);
13C NMR (CDCl3, d): 10.3 (CH2Si), 18.3 (CH3), 22.7, 26.0,
29.2 and 29.4 (CH2), 29.5 at 29.6 (5 CH2) and 33.1 (CH2), 58.2
(CH2O), 115.3 (CHar) and 153.3 (Car); 29Si NMR (50 MHz,
CDCl3, d): ꢁ45.2; FAB-MS: 742 [M þ 1]1 (14%).
1,4-Bis[(triethoxysilyl)decylureido]benzene (1). In a Schlenk
tube, 1,4-diaminobenzene (550 mg, 5.09 mmol) was dissolved
in CH2Cl2 (40 ml) under nitrogen atmosphere. 3-(Triethoxy-
silyl)propylisocyanate (4.09 g, 11.86 mmol) was added and the
mixture was stirred overnight at room temperature. The sol-
vent was evaporated and the precipitate was washed with
pentane. The solution was filtered to remove the solvent and
excess 3-(triethoxysilyl)propylisocyanate. The resulting brown
solid was dried in vacuo to give 1. Yield: 91%; m.p.: 244 1C; IR
(KBr, cmꢁ1): 1582 (dNH), 1633 (nCO), 3325 (nNH); 1H NMR
(DMSO d6, d): 0.53 (t, 4H, CH2Si), 1.13 (t, 18H, CH3), 1.2 at
1.4 (m, 36H, CH2), 3.72 (qd, 12H, OCH2), 5.97 (t, 2H, NH),
7.20 (s, 4H, Har), 8.13 (s, 2H, NH); 13C NMR (50 MHz,
DMSO d6, d): 9.8 (CH2Si), 18.1 (CH3), 22.3, 26.3, 28.6, 28.7,
28.8, 28.9, 29.8 and 32.3 (CH2), 39.7 (CH2N), 57.5 (CH2O),
118.2 (CHar) and 134.2 (Car), 155.3 (CO); 29Si NMR (50 MHz,
DMSO d6, d): ꢁ45.1; FAB-MS: 799 [M þ 1]1 (51%); anal.
calcd for C40H78N4O8Si2 (%): C 60.11, H 9.84, N 7.01; found:
C 59.56, H 9.83, N 7.44.
N-9-Undecenyladenine. A suspension of sodium adenine in
dry DMF (150 ml), prepared from adenine (2 g, 14.8 mmol)
and sodium hydride (0.355 g, 14.8 mmol), was stirred for 2 h.
11-Bromo-1-undecene (5.1 g, 22 mmol) was added dropwise
and the mixture was heated to 70 1C for 8 h, giving a clear
solution. The clear reaction mixture was concentrated to
dryness under reduced pressure; the remaining solid was
washed with dichloromethane and filtered. The solvent was
eliminated in vacuo leading to an oil. N-9-Undecenyladenine
was separated from N-7-undecenyl adenine by silica gel column
chromatography (eluent: CHCl3–EtOH, 6 : 1 v/v). A white
solid was obtained. Yield: 65%; m.p.: 105 1C; 1H NMR
(CDCl3, d): 1.18 (m, 12H, 6 CH2), 1.8–1.9 (m, 4H, 2CH2),
1,4-Bis[(triethoxysilyl)undecylamido]benzene (2). In
a
4.12 (t, 2H, NCH ), 4.86 (m, 2H, CH ), 5.5–5.8 (m, 1H,
Q
2 2
Schlenk tube, 11-(amino)undecyltriethoxysilane (734 mg, 2.20
mmol) was dissolved in dry CH2Cl2 (15 ml), under nitrogen
atmosphere, followed by addition of triethylamine (404 mg,
CH ), 6.78 (s, 2H, NH ), 7.7 (s, 1H, C H), 8.3 (s, 1H, C H);
Q
2 2 8
13C NMR (CDCl3, d): 26.5–33.5, 43.78, 114, 119.5, 138.9,
140.1, 149.9, 155.8.
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The characteristics of L1 are the following: IR (KBr, cmꢁ1):
1581 (dNH), 1634 (nCO) and 3330 (nNH); 13C CPMAS NMR d:
11.4, 31.8 (7C), 40.1, 58.2, 125.0, 133.0, 158.7; 29Si CPMAS
NMR d: ꢁ47.7, ꢁ57.7, ꢁ67.6 (T1, T2 and T3); anal. found (%):
C 55.29, H 8.45, N 9.22, Si 10.60.
N-9-(Triethoxysilylundecyl)adenine (A). To a stirred solution
of N-9-undecenyladenine (0.84 g, 2.9 mmol) in anhydrous THF
(10 ml) heated to reflux was added triethoxysilane (1.34 ml,
7.25 mmol) under nitrogen atmosphere, followed by the Kar-
stedt catalyst (50 ml, 10.4% Pt). The reflux was pursued over-
night, then the solvent was evaporated and the white
precipitate obtained was washed several times with pentane.
The white powder, which was filtered off, was dried in vacuo.
Yield: 85%; m.p: 64 1C. 1H NMR (CDCl3, d): 0.55 (t, 2H,
CH2Si), 1.16 (m, 25H, 3 CH3 and 8 CH2), 1.8 (m, 2H, CH2), 3.7
(q, 6H, OCH2), 4.09 (t, 2H, NCH2), 6.78 (s, 2H, NH2), 7.7 (s,
1H, C2H), 8.2 (s, 1H, C8H). 13C NMR (CDCl3, d): 10.3, 18.2,
22–33, 43.9, 119.6, 140.2, 149.9, 155.8. 29Si NMR (CDCl3, d):
ꢁ44.48 (CH2–Si). FAB-MS: 452 [M þ 1]1 (100%). IR (KBr,
cmꢁ1): 3500–3000, 2976, 2926, 2854, 1640, 1614, 1416, 1309,
1105, 1079, 956, 795; anal. calcd for C14H25N5O3Si (%): C
58.50, H 9.15, N 15.51; found: C 58.11, H 9.02, N 15.8.
L2. Following the procedure for L1 above with 1,4-bis
[(triethoxysilyl)undecylamidomethyl]benzene (2; 140 mg, 0.17
mmol), L2 was obtained as a yellow powder. The characteristics
of L2 are the following: IR (KBr, cmꢁ1): 1552 (dNH), 1644 (nCO
)
and 3299 (nNH); 13C CPMAS NMR d: 14.5, 31.3 (9C), 40.4,
53.6, 129.9, 132.9, 172.6; 29Si CPMAS NMR d: ꢁ57.7, ꢁ66.7,
(T2 and T3); anal. found (%): C 55.68, H 8.23, N 4.11, Si 11.82.
L3. Following the procedure for L1 above (but omitting the
DMSO) with 1,4-bis[(triethoxysilyl)undecyloxy]benzene (3;
125 mg, 0.17 mmol), L3 was obtained as a yellow powder.
The characteristics of L3 are the following: IR (KBr, cmꢁ1):
N-1-Undecenylthymine. In a Schlenk tube, a mixture of
thymine (2.24 g, 17.8 mmol), 1,1,1,3,3,3-hexamethyldisilazane
(HMDS, 11.4 ml, 54 mmol), and trimethylchlorosilane
(TMSCl, 1.1 ml, 8.9 mmol) was refluxed under nitrogen atmos-
phere until a clear solution was obtained. The excess of HMDS
was evaporated. To the resulting 2,4-bis(trimethylsilyl)thymine
were added dry DMF (15 ml) and 11-bromo-1-undecene (5 g,
21.4 mmol). The mixture was stirred for 11 days at 80 1C under
an inert atmosphere. After removal of the solvent, the remain-
ing oil was chromatographed (CH2Cl2–EtOH 10 : 1 v/v) giving
a solid recrystallised from toluene (yield: 70%). M.p: 97.5 1C;
1H NMR (CDCl3, d): 1.24 (m, 12H, 6 CH2), 1.62 (m, 2H, CH2),
1.9–2 (m, 5H, CH2 and CH3), 3.65 (t, 2H, NCH2), 4.9 (m, 2H,
CH ), 5.7–5.9 (m, 1H, CH ), 6.97 (s, 1H, C H), 9.9 (br s,
1039–1111 (nSiO), 1511 (dCQC), 2853–2925 (nCH ) and 3431
2
(nSiOH); 13C CPMAS NMR d: 11.4, 31.8 (8C), 40.1, 58.2, 125.0,
133.0; 29Si CPMAS NMR d: ꢁ47.9, ꢁ57.5, ꢁ66.9 (T1, T2 and
T3); anal. found (%): C 44.36, H 6.42, N 10.81, Si 15.40.
L4. N-9-(Triethoxysilylundecyl)adenine (113 mg, 0.25 mmol)
and N-1-(triethoxysilylundecyl)thymine (111 mg, 0.25 mmol)
were completely dissolved in dry THF (0.25 ml) to facilitate
the formation of the Aꢀ ꢀ ꢀT complex. After concentrating the
mixture, the residue was dissolved in an aqueous sodium
hydroxide solution (40 mg NaOH in 2.5 ml H2O). The solution
was left to stand for 3.5 days at 65 1C. The resulting gel was
filtered, washed successively with water, ethanol and acetone.
The solid L4 was collected, after drying, as a colourless powder.
The characteristics of L4 are the following: IR (KBr, cmꢁ1, see
ESI): 3400–3200, 2923, 2852, 1660, 1603, 1510, 1466, 1142, 1020;
13C CPMAS NMR d: 14.3, 30.6, 44.3, 110.6, 119.3, 139.4, 150.3,
153, 157.2 160.9; 29Si CPMAS NMR d: ꢁ67.9 (T3).
Q
2
Q
6
1H, NH);13C NMR (CDCl3, d): 12.3, 26–33, 48.5, 110.5, 114.1,
139, 140.4, 151.16, 164.7.
N-1-(Triethoxysilylundecyl)thymine (T). In a Schlenk tube, a
mixture of N-1-undecenylthymine (0.835 g, 3 mmol) and
TMSCl (0.77 ml, 6 mmol) in dry toluene (40 ml) was stirred
under nitrogen atmosphere. A solution of triethylamine (0.84
ml, 6 mmol) in dry toluene (10 ml) was added dropwise. The
mixture was stirred at room temperature for 12 h, then the
precipitate obtained was filtered; the filtrate was concentrated
under reduce pressure. To the protected undecenylthymine was
added anhydrous THF (5 ml), triethoxysilane (1.7 ml, 9 mmol),
and platinum Karstedt catalyst (2.4% Pt, 70 ml). The stirring
was continued overnight, then the solvent was evaporated and
the white precipitate obtained was washed several times with
pentane. The white powder, which was filtered off, was dried in
Acknowledgements
The authors gratefully acknowledge funding from the ‘‘Minis-
tere de la Recherche de France’’ (ACI Nanosciences-Nano-
technologies) and the CNRS.
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