Hydrogen bonding-directed quantitative self-assembly of cyclotriveratrylene capsules and their encapsulation of C60 and C70

Article abstract of DOI:10.1021/jo102577a

Under the direction of intramolecular three-center hydrogen bonding, two cyclotriveratrylene (CTV)-based capsules are assembled quantitatively from C₃-symmetric CTV precursors by forming three imine bonds from arylamide-derived foldamer segments. ¹H and ¹³C NMR and UV/vis experiments reveal that the capsules strongly encapsulate C₆₀ and C₇₀ in discrete solvents.

Full text of DOI:10.1021/jo102577a

NOTE
pubs.acs.org/joc
Hydrogen Bonding-Directed Quantitative Self-Assembly of
Cyclotriveratrylene Capsules and Their Encapsulation of C60 and C70
Lu Wang, Gui-Tao Wang, Xin Zhao,* Xi-Kui Jiang, and Zhan-Ting Li*
State Key Laboratory of Bioorganic and Natural Products Chemistry, Shanghai Institute of Organic Chemistry, Chinese Academy of
Sciences, 345 Lingling Lu, Shanghai 200032, China
S Supporting Information
b
ABSTRACT: Under the direction of intramolecular three-center
hydrogen bonding, two cyclotriveratrylene (CTV)-based capsules
are assembled quantitatively from C3-symmetric CTV precursors by
forming three imine bonds from arylamide-derived foldamer seg-
1
ments. H and 13C NMR and UV/vis experiments reveal that the
capsules strongly encapsulate C60 and C70 in discrete solvents.
ydrogen bonding-induced aromatic amide oligomers may
adopt folded or extended conformations,1 depending on
interested in developing novel CTV-based capsules through
DCC-based macrocyclization of hydrogen bonded arylamide
segments. We herein report the quantitative construction of
two such CTV-derived capsules, i.e., 1a and 1b, by making use of
this approach and their encapsulation of C60 and C70 in discrete
solvents.
H
the position of the substituents on the aromatic rings.2 In recent
years, this family of preorganized frameworks has found increas-
ing applications in the construction of shape-persistent macro-
cyclic systems.3 In this context, a variety of macrocycles of
discrete sizes have been prepared through the formation of
amide bonds.4ꢀ9 Examples of the transition metal ionꢀligand
coordination and 1,2,3-triazole-derived macrocycles have also
been reported.10,11 We recently found that, by using the dynamic
combinatorial chemistry (DCC) to build reversible imine or
hydrazone bonds,12 complicated macrocyclic structures can be
constructed in very high or quantitative yields from readily
accessible precursors,13 which opens the possibility of quick
assembly of new functional macrocyclic systems.
Cyclotriveratrylenes (CTVs) are a family of rigid concave
cyclophanes that have been widely utilized in supramolecular
chemistry.14,15 Particularly, their concave skeletons form com-
plexes with convex surfaces of fullerenes via complementary
stacking in the solid state.16ꢀ18 Since fullerenes are significantly
larger than the CTV backbone, considerable efforts have been
devoted to designing CTV-based receptors to achieve increased
binding affinity for fullerenes. In the past decade, a number of
aromatic units bearing CTVs have been developed,19ꢀ23 which
display enhanced binding capacity due to additional stacking
between the appended aromatic units and fullerenes. It is also
revealed that CTV dimers connected with rigid phenylacetylenic
spacers exhibit stronger binding capacity because two CTV units
can generate a tweezer or are incorporated into a macrocyclic
structure to cooperatively interact with fullerenes.24 Given the
spherical feature of fullerenes, three-dimensional capsular recep-
tors should be ideal for encapsulating them. Nevertheless, to the
best of our knowledge, CTV-based receptors of this kind are not
available, although hydrogen bonding-driven dimeric CTV cap-
sules were reported.25 We previously found that hydrogen
bonded arylamide foldamers or macrocycles stacked with full-
erenes in both the solution and solid state.26,27 We thus became
The synthetic routes for 1a and 1b are provided in Scheme 1.
Tribromides 2a and 2b28 werefirst prepared according to reported
methods and then treated with an excess of sodium azide in
DMF to afford 3a and 3b in 91% and 90% yields. Then, 6 was
prepared in 82% yield from 4 and 5 in DMF and further
hydrolyzed to give 7 quantitatively. The acid was then coupled
with 813c in chloroform to afford 9 in 89% yield. Treatment of
9 with 3a or 3b in the presence of cuprous iodide in chloro-
form and acetonitrile afforded 10a and 10b in 74% and 76%
yields. Finally, the two compounds were converted into 1a and
1b in chloroform in the presence of an excess of trifluoroacetic
Received: December 28, 2010
Published: March 21, 2011
r
2011 American Chemical Society
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|

The Journal of Organic Chemistry
NOTE
Scheme 1. Synthesis of Capsular Molecules 1a and 1b
Figure 1. Partial 1H NMR spectra (400 MHz) of (a) 1b þ C60 (1:1), (b)
1b, and (c) 1b þ C70 (1:1) in CDCl3 and CS2 (1:1, v/v) ([1b] = 5.0 mM).
1
The downfield signals of 1b in the H NMR spectrum were
fully assigned based on the COSY and NOESY experiments,
which also revealed NOEs between H-1,2 and H-4, H-3 and H-6,
and H-5 and H-7 (see the structure for numbering). These
observations suggested a close contact between the two cyclic
units. Adding 1 equiv of C60 or C70 caused these NOEs to
disappear, indicating that they were encapsulated in the cavity of
1b to increase the distance of the two cyclic units of 1b. Addition
of the fullerenes also induced the signals of H-2, H-3, and H-7 of
1b to shift slightly (Figure 1). The largest shifting was observed
for the H-7 signal induced by C70 (Δδ = 0.053 ppm). These shifts
were small, but distinct and repeatable.27b,29 The mixing also
caused the signal of C60 in 13C NMR to shift upfield by 0.1 ppm,
again supporting its encapsulation by 1b.
Diffusion-ordered spectroscopic (DOSY) experiments for 1b
provided additional evidence for encapsulation.27b,30 The diffu-
sion coefficients (D) obtained based on H-5ꢀ7 in the absence
and presence of C60 or C70 are presented in Table 1. It can be
found that addition of C60 or C70 led to significant decrease of
the D values of 1b probed with all three signals. The values of the
same mixtures obtained with different probes exhibited a similar
changing tendency, which was in accordance with the above 1H
NMR observations, indicating that C60 and C70 were encapsu-
lated in 1b and thus led to an increase of the apparent size of 1b.
The values of the C70 mixture were generally lower than those of
the C60 mixture, reflecting the increased apparent size. Vapor
pressure osmometry (VPO) experiments in toluene also sup-
ported the formation of the complexes. The number-average
molecular weights of 1b, 1b@C60, and 1b@C70 were determined
to be 2500, 3200, and 3500 u, respectively, which are comparable
to the corresponding calculated values (2340, 3060, and 3180 u).
Adding C60 or C70 to the solution of 1b also caused a
significant decrease of its absorption bands. Quantitative titration
experiments were then performed (Figure 2). By applying the
results to the BenesiꢀHildebrand (BH) plot,31 we determined
the association constants (Kassoc) of complexes 1b@C60 and
1b@C70 to be 1.9 ꢁ 105 and 2.4 ꢁ 104 Mꢀ1 in chloroform and
1.5 ꢁ 105 and 1.2 ꢁ 105 Mꢀ1 in chlorobenzene. Under the same
conditions, adding C60 or C70 to the solution of 10b in the two
solvents did not induce perceptible changes of the absorption of
10b. The absorption of a simple triimine-based macrocycle13c
was weakened by C60 or C70, but no fixed stoichiometry could be
derived from the BenesiꢀHildebrand equations. These results
clearly showed that the strong 1:1 encapsulation of 1b for C60
and C70 was driven by cooperative stacking of its two aromatic
segments with the fullerenes.
acid (TFA). The reactions were also performed in chloroform-
d and tracked by using H NMR. It was revealed that at the
early stage, the solution gave rise to complicated signals,
implying the formation of multiple products. The spectra
gradually became simplified and evolved into one set of signals
after ca. 48 h, as revealed for reactions for the formation of
other related macrocycles.13c
In principle, the target molecules may have two isomers,
depending on the relative orientation of the CTV and triimine
macrocyclic units. Their 1H NMR spectra in CDCl3 or DMSO-d6
exhibited one set of signals of high resolution, suggesting that
only one of the isomers was formed. Molecular dynamics
simulations for the two isomers of 1a and 1b showed that the
isomers with the methoxyl and imine groups being located to the
opposite sides of the related linkers (see the structure, vide ante)
were energetically favorable as compared to that with the two
groups being located to the same side of the linker. The
simulations also showed that, when the linkers adopted the
extended conformation, both 1a and 1b could produce a cavity
to host C60 or C70. Therefore, their encapsulation for the two
fullerenes was investigated.
1
The encapsulation of 1a for C60 and C70 was also investigated.
On the basis of the UV/vis titrations, the Kassoc values for their 1:1
complexes were estimated to be 7.7 ꢁ 104 and 6.4 ꢁ 103 Mꢀ1 in
chloroform and 1.1 ꢁ 104 and 1.2 ꢁ 103 Mꢀ1 in chlorobenzene,
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NOTE
Table 1. Diffusion coefficients of 1b in the Absence and Presence of C60 and C70 at 25 °C (1:1, 5 mM) in CDCl3 and CS2 (1:1, v/v)
by DOSY
1b
1b þ C60
D (10ꢀ9 m2/s)
1b þ C70
D (10ꢀ9 m2/s)
proton
δ (ppm)
D (10ꢀ9 m2/s)
δ (ppm)
δ (ppm)
H-5
H-6
H-7
9.623
9.046
7.794
3.169
3.182
3.119
9.628
9.046
7.779
0.508
0.506
0.503
9.620
9.044
7.821
0.488
0.481
0.481
1
a white solid (5.29 g, 82%). H NMR (400 MHz, CDCl3): δ 9.92
(s, 1H), 8.32 (d, J = 2.2 Hz, 1H), 8.01 (dd, J1 = 8.7 Hz, J2 = 2.2 Hz, 1H),
7.09 (d, J = 8.7 Hz, 1H), 4.26 (t, J = 7.1 Hz, 2H), 3.92 (s, 3H), 2.78 (td,
J1 = 7.1 Hz, J2 = 2.7 Hz, 2H), 2.09ꢀ2.04 (m, 1H). 13C NMR (100 MHz,
CDCl3): δ 189.7, 165.2, 162.1, 134.1, 134.0, 129.2, 120.9, 113.2, 79.3,
70.3, 67.0, 52.0, 19.1. MS (EI): m/z 232 [M]þ. Anal. Calcd for
C13H12O4: C, 67.23; H, 5.21. Found: C, 67.20; H, 5.19.
Compound 7. A solution of 6 (2.00 g, 8.60 mmol) and lithium
hydroxide monohydrate (1.45, 34.4 mmol) in a mixture of THF (20 mL),
methanol (10 mL), and water (5 mL) was stirred for 4 h and then
neutralized with hydrochloric acid (1 N) to pH 3. The mixture was then
concentrated to ca. 10 mL and the resulting slurry was extracted with
AcOEt (200 mL). The organic phase was washed with water (2 ꢁ 80 mL)
and brine (80 mL), then dried over sodium sulfate. After removal of the
solvent under reducedpressure, compound7 was obtainedasa white solid
(1.85 g, 100%). 1H NMR (400 MHz, DMSO-d6): δ 12.98 (s, 1H), 9.91
(s, 1H), 8.16 (d, J = 2.2 Hz, 1H), 8.03 (dd, J1 = 8.6 Hz, J2 = 2.2 Hz, 1H),
7.35 (d, J = 8.6 Hz, 1H), 4.26 (t, J = 6.7 Hz, 2H), 3.34 (s, 1H), 2.67
(t, J = 6.6 Hz, 2H). 13C NMR (100 MHz, DMSO-d6): δ 191.2, 166.4,
161.4, 134.1, 132.5, 129.0, 122.3, 1134.0, 80.8, 72.7, 67.0, 18.7. MS (ESI):
m/z 218.0 [M]þ. Anal. Calcd for C12H10O4: C, 66.05; H, 4.62. Found: C,
66.01; H, 4.59.
Figure 2. Absorption spectral changes of 1b (1.0 ꢁ 10ꢀ5 M) with the
addition of C70 (0ꢀ30 ꢁ 10ꢀ5 M) in chloroform (inset: the Benesiꢀ
Hildebrand plot with a 1:1 stoichiometry).
respectively. These relatively large values indicate that this molecule
is also a good receptor for the two fullerenes, although its cavity is
smaller than that of 1b.
In summary, we have developed a strategy to quickly build
CTV-based capsular structures by combining hydrogen bonding-
induced preorganization of aromatic amide segments with the
DCC principle. The new capsules are good receptors for full-
erenes. Future works will point to the development of new
porous or multiply layered architectures. Particularly, the possi-
bility of building systems with closed space for molecular
recognition or tunable function will be exploited.
Compound 9. To a stirred solution of 7 (0.14 g, 0.66 mmol) and
NEt3 (0.1 L) in chloroform (4 mL), cooled in an ice-bath, was added
isobutylchloroformate (0.086 mL, 0.66 mmol). Stirring was continued for
40 min and then a solution of 8 (0.26 g, 0.55 mmol) in CHCl3 (2 mL) was
added slowly. After the mixture was stirred for 48 h, 100 mL of CHCl3 was
added. The solution was washed with water (2 ꢁ 50 mL) and brine
(50 mL), then dried over Na2SO4. The solvent was then removed under
reduced pressure and the resulting residue was purified by column chroma-
tography (petroleum ether/EtOAc 6:1) to give 9 as a white solid (0.38 g,
’ EXPERIMENTAL SECTION
1
89%). H NMR (400 MHz, CDCl3): δ 9.99 (s, 1H), 9.69 (s, 1H), 8.99
(s, 1H), 8.82 (s, 1H), 8.11ꢀ7.98 (m, 1H), 7.15 (d, J = 8.7 Hz, 1H), 6.78 (s,
1H), 6.51 (s, 1H), 4.43 (t, J= 7.2 Hz, 2H), 4.05ꢀ3.96 (m, 4H), 2.83 (dd, J1 =
7.2 Hz, J2 = 4.5 Hz, 2H), 2.07ꢀ2.05 (m, 1H), 1.88ꢀ1.72 (m, 4H), 1.53 (s,
9H), 1.48ꢀ1.15 (m, 20H), 0.87ꢀ0.83 (m, 6H). 13C NMR (100 MHz,
CDCl3):δ190.4, 161.1, 160.1, 152.6, 144.5, 144.3, 136.7, 132.0, 130.4, 123.3,
121.3, 120.7, 113.7, 113.1, 98.1, 78.6, 77.3, 77.0, 76.7, 71.2, 69.6, 69.2, 67.4,
31.6 (d), 29.2 (d), 29.1, 28.2, 25.9, 25.8, 22.5 (d), 19.2, 14.0, 13.9. MS
(MALDI-TOF): m/z 687.7 [M þ Na]þ, 703.7 [M þ K]þ. HRMS (FT):
calcd for C39H56N2O7Na [M þ H]þ 687.3980, found 687.3984.
Compound 3b. A solution of 2b (1.39 g, 1.70 mmol) and NaN3
(1.10 g, 17.0 mmol) in DMF (30 mL) was stirred at rt for 12 h and then
concentrated. The resulting residue was extracted with CH2Cl2 (30 mL).
The organic phase was washed with water (3 ꢁ 10 mL) and brine
(10 mL), then dried over MgSO4. Upon removal of the solvent, the crude
productwasrecrystallizedfrom AcOEt toyield3basa yellow solid(1.07g,
90%). 1H NMR (400 MHz, CDCl3): δ 6.83 (s, 3H), 6.82 (s, 3H), 4.75
(d, J = 13.7 Hz, 3H), 4.08ꢀ3.92 (m, 6H), 3.81 (s, 9H), 3.53 (d, J =
13.8 Hz, 3H), 3.34 (t, J = 6.7 Hz, 6H), 1.92ꢀ1.72 (m, 12H). 13C NMR
(100 MHz, CDCl3): δ 148.3, 147.0, 132.3, 131.8, 115.5, 113.8, 68.6, 56.2,
51.1, 36.4, 26.4, 25.7. MS (ESI): m/z 722.4 [M þ Na]þ. HRMS (ESI):
calcd for C36H45N9Na1O6 [M þ H]þ 722.3385, found 722.3392.
Compound 6. A suspension of 4 (5.00 g, 27.8 mmol), 5 (7.50 g,
33.3 mmol), K2CO3 (11.5 g, 83.2 mmol), and KI (0.20 g, 1.20 mmol) in
DMF (120 mL) was stirred at 80 °C for 12 h and then cooled to rt. The
solid was filtered off and the filtrate concentrated with a rotavapor. The
resulting slurry was extracted with AcOEt (500 mL). The organic phase
was washed with water (4 ꢁ 200 mL) and brine (200 mL) and dried over
MgSO4. After removal of the solvent, the resulting residue was purified
by column chromatography (petroleum ether/AcOEt 15:1) to give 6 as
Compound 10b. A suspension of 3b (1.06 g, 1.50 mmol) and 9
(2.57 g, 4.50 mmol), CuI (0.17 g, 0.90 mmol), and DIPEA (1.56 mL,
9.00 mmol) in a mixture of CHCl3 (15 mL) and MeCN (15 mL) was
stirred for 24 h. The solid was filtrated and the filtrate concentrated under
reduced pressure. The resulting residue was triturated with CHCl3
(40 mL) and the solution was washed with water (2 ꢁ 20 mL) and brine
(20 mL), then dried over Na2SO4. Upon removal of the solvent, the crude
product was purified by column chromatography (CH2Cl2/MeOH 50:1)
to give 10b as a white solid (3.00 g, 76%). 1H NMR (400 MHz, CDCl3):
δ 9.87 (s, 3H), 9.59 (s, 3H), 9.07 (s, 3H), 8.65 (d, J = 2.1 Hz, 3H), 7.92
(dd, J1 = 8.6 Hz, J2 = 2.1 Hz, 3H), 7.46 (s, 3H), 7.12 (d, J = 8.6 Hz, 3H),
3533
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NOTE
6.82ꢀ6.72 (m, 9H), 6.48 (s, 3H), 4.68 (d, J = 13.6 Hz, 3H), 4.59
(t, J = 6.0 Hz, 6H), 4.22 (t, J = 6.9 Hz, 6H), 4.04ꢀ3.78 (m, 18H), 3.72
(s, 9H), 3.48 (d, J = 13.6 Hz, 3H), 3.32 (t, J = 6.0 Hz, 6H), 1.90ꢀ1.85
(m, 6H), 1.82ꢀ1.69 (m, 12H), 1.68ꢀ1.55 (m, 6H), 1.48 (s, 27H),
1.43ꢀ1.11 (m, 60H), 0.86 (t, J = 6.8 Hz, 9H), 0.79 (t, J = 6.8 Hz, 9H). 13
C NMR (100 MHz, CDCl3): δ 190.3, 161.3, 160.3, 152.6, 147.9, 146.7,
144.2, 143.8, 142.8, 136.1, 132.2, 132.1, 131.7, 130.1, 123.3, 122.4, 121.4,
120.9, 114.9, 113.5, 113.1, 112.9, 98.2, 79.9, 69.7, 69.2, 68.7, 68.3, 56.0,
49.5, 36.2, 31.6, 31.5, 29.5, 29.2, 29.1 (d), 29.0 (d), 28.2, 27.1, 25.9, 25.7,
25.6, 22.5, 22.4, 13.9 (d). MS (MALDI-TOF): m/z 2416.5 [M ꢀ 3Boc
þ Na]þ, 2516.6 [M ꢀ Boc þ Na]þ.
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Compound 1b. A solution of 10b (0.13 g, 0.05 mmol) and TFA
(0.20 mL, 2 0.00 mmol) in CHCl3 (10 mL) was stirred at 60 °C for 48 h
and then diluted with CHCl3 (100 mL). The solution was washed with
saturated NaHCO3 solution (2 ꢁ 50 mL), water (2 ꢁ 50 mL), and brine
(50 mL), then dried over Na2SO4. Removal of the solvent afforded 1b as
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1
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a yellow solid (0.12 g, 100%). H NMR (400 MHz, CDCl3): δ 9.62
(s, 3H), 9.03 (s, 3H), 8.72 (d, J = 2.2 Hz, 3H), 8.51 (dd, J1 = 8.6 Hz,
J2 = 2.2 Hz, 3H), 8.33 (s, 3H), 7.74 (s, 3H), 7.22 (d, J = 8.6 Hz, 3H), 6.47
(s, 3H), 6.37 (s, 3H), 5.86 (s, 3H), 5.43 (d, J = 13.3 Hz, 3H), 4.70ꢀ4.47
(m, 9H), 4.13ꢀ4.00 (m, 9H), 3.97ꢀ3.83 (m, 6H), 3.59 (d, J = 13.3 Hz,
3H), 3.56ꢀ3.47 (m, 6H), 3.45ꢀ3.35 (m, 6H), 3.09 (s, 9H), 2.02ꢀ1.86
(m, 6H), 1.73 (m, 12H), 1.64ꢀ1.50 (m, 6H), 1.48ꢀ1.18 (m, 60H),
0.95ꢀ0.81 (m, 18H). 13C NMR (100 MHz, CDCl3): δ 160.6, 157.9,
156.6, 149.9, 148.1, 146.4, 145.9, 143.7, 137.2, 132.4, 132.3, 132.0, 130.6,
130.2, 123.5, 121.6, 121.3, 113.6, 113.1, 112.9, 112.1, 99.1, 70.6, 68.9,
68.5, 68.1, 54.8, 48.8, 38.5, 31.8, 31.7, 29.4 (d), 29.3 (d), 29.2, 28.7, 28.4,
26.1, 25.9, 25.8, 23.6, 22.7, 22.6, 14.1, 14.0. MS (MALDI-TOF):
m/z 2339.5 [M þ H]þ, 2361.8 [M þ Na]þ. HRMS (FT): calcd for
C138H184N15O18 [M þ H]þ 2339.3895, found 2339.3938.
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’ ASSOCIATED CONTENT
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1H and 13C NMR and UV/vis spectra, and dynamic simulation
details. This material is available free of charge via the Internet at
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’ AUTHOR INFORMATION
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Corresponding Author
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’ ACKNOWLEDGMENT
We are grateful for MOST of China (2007CB808001), NSFC
(20732007, 20921091, 20872167, 20974118), and STCSM (09
XD1405300) for financial support.
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