As stated above, silylated precursors involving A and T
giving a solid recrystallized from toluene. Yield: 70%; mp:
1
moieties and long alkylene chains can lead to nanostructured
97.5 uC; H NMR (CDCl , d/ppm): 1.24 (m, 12H, 6 CH ), 1.62
3
2
2
1
silicas. Two non-silylated compounds, namely N9-undece-
2 2 3
(m, 2H, CH ), 1.90–2.00 (m, 5H, CH and CH ), 3.65 (t, 2H,
nyladenine (A-C ) and N1-undecenylthymine (T-C ) (Fig. 2)
1
NCH ), 4.90 (m, 2H, LCH ), 5.7–5.9 (m, 1H, CHL), 6.97 (s,
1
11
2
2
1
13
1H, CH), 9.90 (br, s, 1H, NH); C NMR (CDCl , d/ppm):
were first studied in order to validate the H DQ NMR
approach. The main goal here was to characterize precisely
A/A, T/T and A/T pairings by non-ambiguous spectroscopic
3
12.3, 26.0–33.0, 48.5, 110.5, 114.1, 139.0, 140.4, 151.2, 164.7;
1
C CP MAS NMR (d/ppm): 12.8, 25.8, 26.2, 30.1–31.4,
3
features. In a second step, new materials involving C -silylated
3
34.5, 35.0, 50.1, 108.1, 108.8, 114.7, 115.4, 138.2, 138.8, 145.4,
151.5, 167.8.
A and T molecules were shown to correspond to nanostruc-
1
tured hybrid silicas. The H DQ NMR approach was applied
in order to describe A and T pairings within several deriva-
Synthesis of A/T-C11
tives. Homo- and hetero-assemblies were fully characterized.
The 1 : 1 hetero-assembly A/T-C11 was synthesized as follows.
In a test tube, 0.25 mmol of A-C11 (72.0 mg) and 0.25 mmol of
T-C11 (70.0 mg) were mixed in 0.25 ml of THF. The solvent
was slowly evaporated at room temperature. The resulting
residue was then dried under vacuum. A white powder was
Experimental
The overall experimental schemes are presented in Fig. 2. A
and T molecules were first modified by alkenylation with
1
3
2
bromo-allene and bromo-undecene. As stated above, the
0
obtained (mp: 78.2 uC); C CP MAS NMR (d/ppm): 15.6,
2
7.8, 30.1, 32.3–35.5, 36.3, 46.6, 112.0, 114.1, 114.9, 118.4,
selective alkenylation was performed on the N9 atom from A
1
38.1, 139.1, 141.7, 150.4, 154.2, 156.2, 165.6.
and the N1 atom from T (A-Cn and T-C ). The silylated
n
precursors were obtained by hydrosilylation of the terminal
Synthesis of silylated-A-C
3
double bond with HSi(OEt)
leading to silylated-A-C , -T-C
Hydrolysis and condensation of the ethoxy groups led finally
3
in the presence of a Pt catalyst
(
n
n
and -A/T-C , here n = 3).
n
N9-Allyladenine (2.9 mmol) was dissolved in freshly distilled
THF (10.0 ml) in a Schlenk tube. HSi(OEt) (7.25 mmol) and
3
to hybrid samples (named hybrid-A-C
thereafter, here n = 3).
n n n
, -T-C and -A/T-C
the platinum catalyst (50 ml of a 10.4% solution) were added
and the solution was stirred under reflux overnight. The
catalysts used were a 10.4% Pt solution in isopropanol kindly
provided by Rhodia or a 2.4% Pt soultion in xylene from
ABCR, for adenine and thymine derivatives, respectively.
THF was removed in vacuo and the white residue was
washed and centrifuged 3 times with dried pentane. A white
solid corresponding to N9-(triethoxysilylpropyl)adenine was
Synthesis of A-C11 (N9-undecenyladenine)
2
1
The synthesis of A-C11 has been presented previously and is
summarized here. Sodium adenine in dry THF (2 g, 14.8 mmol
of adenine (A) and 0.355 g, 14.8 mmol of sodium hydride) was
stirred for 2 hours. 11-Bromo-1-undecene (5.1 g, 22.0 mmol)
was added dropwise. The obtained mixture was heated for
obtained after drying under vacuum. Yield: 80%; mp: 109 uC;
1
3 2
H NMR (CDCl , d/ppm): 0.55 (t, 2H, CH Si), 1.14 (t, 9H,
8
hours (70 uC) leading to a clear solution. This solution was
OCH CH ), 3.75 (q, 6H, OCH ), 4.15 (t, 2H, NCH ), 6.30 (s,
2
then concentrated to dryness under reduced pressure; the
obtained solid was washed with dichloromethane and filtered.
The solvent was then eliminated in vacuo leading to an oil.
N9-Undecenyladenine was separated from N7-undecenyl-
3
2
2
1
3
2
H, NH ), 7.78 (s, 1H, CH), 8.29 (s, 1H, CH); C NMR
2
(
3
CDCl , d/ppm): 7.5, 18.2, 23.7, 46.0, 58.4, 119.0, 149.9, 152.8,
2
9
0
155.8; Si NMR (CDCl
(FAB+, m/z): 340 (100%); elemental analyses: calcd for
Si (%): C 49.53, H 7.42, N 20.63; found: C
3
, d/ppm): 245.0 (T units); MS
adenine by silica gel column chromatography (eluent: CHCl
3
–
EtOH, 6 : 1 v/v). A white solid was obtained. Yield: 65%; mp:
C H N O
14 25 5 3
1
1
1
5
8
1
05 uC; H NMR (CDCl , d/ppm): 1.18 (m, 12H, 6 CH ), 1.80–
49.20, H 7.44, N 21.52.
3
2
.90 (m, 4H, 2 CH ), 4.12 (t, 2H, NCH ), 4.86 (m, 2H, LCH ),
2
2
2
.50–5.80 (m, 1H, CHL), 6.78 (s, 2H, NH
2
), 7.70 (s, 1H, CH),
Synthesis of silylated-T-C
3
1
.30 (s, 1H, CH); C NMR (CDCl
3
3
, d/ppm): 26.5–33.5, 43.8,
N1-Allylthymine (3 mmol) and chlorotrimethylsilane TMSCl
6 mmol) were mixed with dry toluene (40 ml) in a Schlenk
tube under nitrogen atmosphere. A solution of Et N (6 mmol)
1
3
14.0, 119.5, 138.9, 140.1, 149.9, 155.8; C CP MAS NMR
(
(d/ppm): 27.7, 29.8, 32.0–33.5, 36.0, 43.2, 45.9, 117.5, 118.5,
3
1
19.7, 135.8, 137.1, 139.9, 149.8, 151.8, 153.3, 156.4.
in toluene (10 ml) was added dropwise and the mixture was
stirred for 20 h at room temperature. Triethylammonium
chloride was filtered off and the volatiles were pumped off
leading to a slurry yellowish paste. This paste was then
Synthesis of T-C11 (N1-undecenylthymine)
In a Schlenk tube, thymine (T) (2.24 g, 17.8 mmol), 1,1,1,3,3,3-
hexamethyldisilazane (HMDS, 11.4 ml, 54.0 mmol) and
trimethylchlorosilane (TMSCl, 1.1 ml, 9.9 mmol) were refluxed
dissolved in THF. HSi(OEt)
catalyst (2.4% Pt, 70 ml) were then added and the mixture was
left under reaction overnight. THF and residual HSi(OEt)
3
3
(1.7 ml, 9 mmol) and Karstedt
under N
2
until a clear solution was obtained. The excess of
HMDS was eliminated. To the resulting 2,4-bis(trimethyl-
silyl)thymine were added dry DMF (15.0 ml) and 11-bromo-1-
undecene (5 g, 21.4 mmol). The solution was stirred for 11 days
at 80 uC under an inert gas. After removal of the solvent, the
were removed in vacuo. The residue was washed and cen-
trifuged 3 times with dried pentane. A white solid correspond-
ing to N1-(triethoxysilylpropyl)thymine was obtained after
removal of pentane under vacuum. Yield: 85%; mp: 129 uC;
1
remaining oil was chromatographed (CH
Cl
2 2
–EtOH 10 : 1 v/v)
H NMR (CDCl
3 2
, d/ppm): 0.58 (t, 2H, CH Si), 1.19 (t, 9H,
3
94 | J. Mater. Chem., 2008, 18, 392–399
This journal is ß The Royal Society of Chemistry 2008