Nanorods versus nanovesicles from amphiphilic dendrofullerenes

Article abstract of DOI:10.1021/ja206769a

Three new amphiphilic dendrofullerenes endowed with 4, 8, and 16 carboxylic groups have been efficiently prepared by using a click chemistry methodology. These amphiphilic fullerene derivatives aggregate forming micelles, nanorods, or hollow vesicles depe

Full text of DOI:10.1021/ja206769a

COMMUNICATION
pubs.acs.org/JACS
Nanorods versus Nanovesicles from Amphiphilic Dendrofullerenes
Antonio Mu~noz,† Beatriz M. Illescas,† Macarena Sꢀanchez-Navarro,†,‡ Javier Rojo,*,‡ and Nazario Martín*,†,§
†Departamento de Química Orgꢀanica, Facultad de Química, Universidad Complutense, 28040 Madrid, Spain
‡Glycosystems Laboratory, Instituto de Investigaciones Químicas, CSIC - Universidad de Sevilla, Amꢀerico Vespucio,
49. Isla de la Cartuja 41092 Sevilla, Spain
§Instituto Madrile~no de Estudios Avanzados en Nanociencia (IMDEA-Nanociencia), Campus UAM, Cantoblanco, E-28049,
Madrid, Spain
S Supporting Information
b
ABSTRACT: Three new amphiphilic dendrofullerenes
endowed with 4, 8, and 16 carboxylic groups have been
efficiently prepared by using a click chemistry methodology.
These amphiphilic fullerene derivatives aggregate forming
micelles, nanorods, or hollow vesicles depending on the
concentration and on the solid substrate.
he unique physical and chemical properties of fullerenes
have been successfully used in the development of two main
T
scientific areas, biological applications1 and functional materials.2
The first research topic requires working with water-soluble
biocompatible materials, which has generated the evolution of
strategies to overcome the natural hydrophobic character of
fullerenes.3 One of these strategies implies the use of dendritic
fullerene derivatives.4 On the other hand, the most promising
applications of fullerene-based materials are related to the
development of organic electronic devices, such as field effect
transistors (OFETs) or solar cells (SCs).5 In both fields, the
study of self-organization of fullerene derivatives to obtain
functional supramolecular architectures is nowadays an impor-
tant scientific challenge.6 Thus, for instance, the investigation of
the aggregation of fullerene containing amphiphiles has led to the
formation of micelles, vesicles, and other structures.7 In some
cases, this aggregation can be controlled by an external stimulus,
such as pH, which could be useful for the design of targeted drug
delivery systems.8 Nakamura and co-workers have reported the
formation of bilayer vesicles with small water permeability
coefficient from nonpolar/polar/nonpolar amphiphiles consti-
tuted by the potassium complexes of penta-substituted fullerene
anions.9
Figure 1. Structure of new amphiphilic dendrofullerenes (DF) (number
refers to the content of carboxylic groups).
of the CS state (τ ∼ 1.4 ms) 6 orders of magnitude longer than that
obtained for the monomeric ZnPcÀC60 dyad (τ ∼ 3.0 ns).11
Recently, the utility of copper-catalized azideÀalkyne cycload-
dition (CuAAC) reaction to obtain highly functionalized fulle-
rene derivatives has been demonstrated.12 In this paper, we
report on the synthesis of new amphiphilic dendrofullerenes
(Figure 1) by using the above-mentioned click-chemistry meth-
odology. The study of the aggregation behavior of such fullerene-
based amphiphiles has shown the formation of nanorods, mi-
celles, or vesicles depending on the nature of the solid substrate
employed for the deposition of the dendrimeric fullerene solu-
tions or on the concentration of this solution.
From the point of view of the construction of functional
materials, it has been proved that a change in the morphology of
the material can give rise to the modification of its physicochem-
ical properties. Thus, the chiroselective assembly of a chiral
porphyrinÀfullerene dyad has demonstrated a better ambipolar
charge-carrier mobility for nanofibers obtained from the enan-
tiopure compound than for the spherical aggregates resulting
from the racemic dyad.10 Guldi, Torres, Prato, and co-workers
have reported the increased lifetime of the photogenerated charge-
separated (CS) state resulting when a phthalocyanineÀC60 am-
phiphilic derivative (ZnPcÀC60) is ordered into one-dimensional
nanotubules. The ordered nanotubular structure showed a lifetime
The synthesis of fullerene dendrimers was carried out by
Huisgen Cu-catalyzed coupling reaction of alkyne functionalized
fullerene derivatives (1 and 2, see Supporting Information (SI))
with azide substituted dendrons endowed with a variable number
Received: July 20, 2011
Published: September 14, 2011
r
2011 American Chemical Society
16758
dx.doi.org/10.1021/ja206769a J. Am. Chem. Soc. 2011, 133, 16758–16761
|

Journal of the American Chemical Society
COMMUNICATION
Figure 3. (a) SEM image (1.0 Â 10À4 M in THF, glass substrate) of
hollow vesicles formed from DF-8; (b) X-ray diffraction patterns at room
temperature (top) andSAXSresult forDF-8 (THF, 1 Â 10À4 M) (down).
distribution of spherical aggregates was observed, with heights
around 13À16 nm (Figure 2a). Taking into account that the
estimated size of one molecule is ∼3.2 nm, it seems that a small
number of molecules are aggregated to form micelles. Interest-
ingly, when we deposited the above-mentioned solution on
HOPG, the formation of some nanorods with average diameters
around 3.3 and 6.6 nm and several micrometers in length
(Figure 2b,c and Figure S3) was observed. These aggregates
clearly present a rope-like structure and the found diameters are
in agreement with the dimensions calculated for one or two of
these dendrofullerenes. In fact, it can be observed that nanowires
formed by only one molecule merge to form the two-molecule
height rods. The formation of these rods is probably made
feasible by the better interaction of the hydrophobic part of
the molecule, that is, the fullerene moiety, with HOPG.14 We
speculate that the more favorable interaction of the fullerenes
with the surface, in first instance, and, second, H-bonding and
van der Waals interactions between the dendrimeric moieties will
favor the formation of the wires. AFM images obtained for DF-4
and DF-16 on HOPG exhibit only the formation of spherical
aggregates of sizes from 6À8 nm to 30À35 nm, thus, corre-
sponding to the aggregation of few molecules (Figure S1).
Scanning electron microscopy (SEM) analysis of a solution of
dendrofullerenes (10À4 M) in THF on glass substrate showed
the formation of vesicles in the case of DF-4 and DF-8 (Figure 3a
and Figure S4). It is interesting to note that the formation of
these vesicles is more extensive for DF-8 than for DF-4, while for
DF-16, vesicles are not observed at all at this concentration
(Figure S5). It could be explained by the bigger size of the
hydrophilic part compared to the hydrophobic fullerene moiety
in DF-16, which probably prevents the formation of the spherical
aggregates observed in the less concentrated solutions to find a
more favorable interaction between the molecules.
Figure 2. (a) Tapping mode AFM height image of aggregates formed
in THF/H2O 2/1 (1.2 Â 10À5 M) after deposition of DF-8 on mica;
(b) phase images acquired by tapping-mode AFM of compound DF-8
(1.2 Â 10À5 M in THF/H2O 2/1) deposited on HOPG; c) cross-
sectional height profiles corresponding to (i) and (ii) marked in panel b.
of carboxylic groups (3 and 4, SI).13 Under the CuAAC condi-
tions, dendrimeric fullerene adducts 5À7 (SI) were obtained in
good yields (72À84%).
Deprotection of acid groups was carried out by treating the
TMS-protected derivatives 5À7 with trifluoroacetic acid under
mild conditions, leading to the corresponding dendrofulle-
renes with 4, 8, or 16 acid groups (DF-4, DF-8 and DF-16,
respectively) in 94À95% yields.
These new derivatives were fully characterized by standard
spectroscopic and analytical techniques (see the SI for full
experimental details and characterization). Thus, the click reac-
tion was easily confirmed by the presence of the signals char-
acteristic of the 1,2,3-triazole units as a broad singlet around
7.6À8.2 ppm in the 1H NMR spectra and the typical signals at
δ ∼ 124 and 140À144 in the 13C NMR spectra. Also, the
disappearance of the alkyne signal in the IR spectra around
2100 cmÀ1 is evidence of the complete functionalization of the
fullerene derivatives. Finally, MALDI-TOF spectra of all new
compounds were in agreement with the proposed structures.
Aggregation behavior of new amphiphilic derivatives DF-4,
DF-8, and DF-16 was investigated by AFM, SEM, TEM, SAXS,
and XRD. To study the aggregation structures by AFM, water
was added to a solution of DF in THF (1.2 Â 10À5 M) up to a
proportion of THF/H2O (v/v) 2/1. AFM for compound DF-8
was carried out on mica and on highly oriented pyrolytic graphite
(HOPG). When DF-8 was deposited on mica, an extensive
16759
dx.doi.org/10.1021/ja206769a |J. Am. Chem. Soc. 2011, 133, 16758–16761

Journal of the American Chemical Society
COMMUNICATION
The observed vesicles are on average ∼400 nm in diameter.
DLS experiments in solution (THF and THF/H2O) have also
demonstrated the formation of aggregates (Table S1). However,
the analysis of these data has not allowed defining the particular
morphology of the aggregates forming in solution. It should be
reasonable to think that vesicles are also formed.
’ ACKNOWLEDGMENT
Financial support by the MICINN of Spain (CTQ2008-
00795/BQU, CTQ2008-01694), the CAM (MADRISOLAR-2
S2009/PPQ-1533), and Consolider-Ingenio CSD2007-00010,
Nanociencia Molecular), and the EU (FUNMOL FP7-212942-1)
is greatly appreciated. A.M. thanks the MICINN for an FPI
Studentship. This Communication is dedicated to the memory of
Prof. Rafael Suau.
Analysis of DF-4 and DF-8 on carbon-coated grids by
transmission electron microscopy (TEM) showed the formation
of hollow vesicles with diameters varying from 200À300 nm to
a few micrometers (Figure S8). Vesicles resulting from DF-4 are
bigger than those obtained from DF-8, probably as a conse-
quence of a more expanded conical shape for the former.
To get a deeper understanding of the structure of these
spherical particles, we characterized them by X-ray diffraction
(XRD) and small-angle X-ray scattering (SAXS). A sample
prepared using the same method as in AFM and TEM analyses
was employed for XRD characterization. The XRD pattern of
DF-8 showed a broad peak at 2θ = 8°, corresponding to a d
spacing of ∼1 nm (Figure 3b and Figure S6). This distance
fits well with the size of a molecule of fullerene, and therefore, it
could be accounting for the disposition of fullerene molecules
packed in contact with each other. This tight contact of
the fullerene moieties in the vesicle membranes has been justified
by the high cohesive forces between C60 molecules.9c,15 In the
corresponding intensity profile as a function of the scattering
vector (q) obtained from SAXS (Figure 3b and Figure S7), we
can see two scattering peaks at q1 = 0.47 nmÀ1 and q2 = 0.95 nmÀ1
which suggest a structure with a period of d = 2π/qmax = 13.4 nm.
This value is consistent with the size estimated for four molecules of
DF-8. The q2 value observed corresponds to a distance of 6.6 nm,
which indicates the presence of two molecules of dendroful-
lerene. These data suggest that the shell of the vesicles is
probably formed by a multilamellar packing of the molecules
where the bilayers interact through H-bonding between polar
carboxylic acid groups (Figure 3b).
In conclusion, we have described a very efficient procedure to
obtain amphiphilic fullerene based molecules by using a click
chemistry methodology. We have studied the aggregation beha-
vior of these amphiphiles and found that the morphology of the
supramolecular architectures formed varies depending on the
surface and on the concentration of the samples analyzed.16 This
kind of aggregation could find applications on the design of new
functional materials and in biological sciences. Work is currently
in progress to determine the interest of these systems in the
preparation of photovoltaic devices, where organization and
morphology of the active materials at the nanometer scale is a
key issue.5d
’ REFERENCES
(1) (a) Nakamura, E.; Isobe, H. Chem. Rec. 2010, 10, 260–270.
(b) Medicinal Chemistry and Pharmacological Potential of Fullerenes
and Carbon Nanotubes; Cataldo, F., Da Ros, T., Eds.; Springer: Berlin,
2008. (c) Nakamura, E.; Isobe, H. Acc. Chem. Res. 2003, 36, 807–815.
(d) Da Ros, T.; Prato, M. Chem. Commun. 1999, 663–669.
(2) (a) Montellano Lꢀopez, A.; Mateo-Alonso, A.; Prato, M. J. Mater.
Chem. 2011, 21, 1305–1318. (b) Giacalone, F.; Martín, N. Adv. Mater.
2010, 22, 4220–4248. (c) Guldi, D. M.; Illescas, B. M.; Atienza, C. M.;
Wielopolski, M.; Martín, N. Chem. Soc. Rev. 2009, 38, 1587–1597.
(3) (a) Beuerle, F.; Hirsch, A. Chem.—Eur. J. 2009, 15, 7434–7446.
(b) Itoh, T.; Mishiro, M.; Matsumoto, K.; Hayase, S.; Kawatsura, M.;
Morimoto, M. Tetrahedron 2008, 64, 1823–1828. (c) Yang, J.; Alemany,
L. B.; Driver, J.; Hartgerink, J. D.; Barron, A. R. Chem.—Eur. J. 2007,
13, 2530–2545. (d) Kunsagi-Mate, S.; Szabo, K.; Bitter, I.; Nagy, G.;
Kollar, L. Tetrahedron Lett. 2004, 45, 1387–1390. (e) Rio, Y.;
Nierengarten, J.-F. Tetrahedron Lett. 2002, 43, 4321–4324. (f) Bergamin,
M.; Da Ros, T.; Spalluto, G.; Boutorine, A.; Prato, M. Chem. Commun.
2001, 17–18. (g) Murthy, C. N.; Geckeler, K. E. Chem. Commun.
2001, 1194–1195. (h) Djojo, F.; Hirsch, A. Chem.—Eur. J. 1998,
4, 344–356.
(4) (a) Kahnt, A.; Guldi, D. M.; Brettreich, M.; Hartnagel, U.;
Hirsch, A. J. Mater. Chem. 2010, 20, 83–89. (b) Witte, P.; Beuerle, F.;
Hartnagel, U.; Lebovitz, R.; Savouchkina, A.; Sali, S.; Guldi, D. M.;
Chronakisd, N.; Hirsch, A. Org. Biomol. Chem. 2007, 5, 3599–3613.
(c) Partha, R.; Lackey, M.; Hirsch, A.; Casscells, S. W.; Conyers, J. L.
J. Nanobiotechnol. 2007, 5, 6. (d) Gallani, J.-L.; Felder, D.; Guillon, D.;
Heinrich, B.; Nierengarten, J.-F. Langmuir 2002, 18, 2908–2913. For
recent reviews, see:(e) Cid Martín, J. J.; Nierengarten, J.-F. In Chemistry
of Nanocarbons; Akasaka, T., Wudl, F., Nagase, S., Eds.; Wiley-VCH:
Weinheim, 2010; pp 73À92. (f) Rosen, B. M.; Wilson, C. J.; Wilson,
D. A.; Peterca, M.; Imam, M. R.; Percec, V. Chem. Rev. 2009, 109,
6275–6540.
(5) (a) Segura, J. L.; Martín, N.; Guldi, D. M. Chem. Soc. Rev. 2005,
34, 31–47. (b) Mallik, A. B.; Locklin, J.; Mannsfeld, S. C. B.; Reese, C.;
Roberts, M. S.; Senatore, M. L.; Zi, H.; Bao, Z. In Organic Field-Effect
Transistors; Bao, Z., Locklin, J., Eds.; CRC Press: Boca Raton, FL, 2007.
(c) Mas-Torrent, M.; Rovira, C. Chem. Soc. Rev. 2008, 37, 827–838.
(d) Delgado, J. L.; Bouit, P.-A.; Filippone, S.; Herranz, M. A.; Martín, N.
Chem. Commun. 2010, 46, 4853–4865. (e) Hasobe, T. Phys. Chem.
Chem. Phys. 2010, 12, 44–57.
(6) Babu, S. S.; M€ohwald, H.; Nakanishi, T. Chem. Soc. Rev. 2010,
39, 4021–4035.
(7) (a) Charvet, R.; Acharya, S.; Hill, J. P.; Akada, M.; Liao, M.; Seki,
S.; Honsho, Y.; Saeki, a.; Ariga, K. J. Am. Chem. Soc. 2009,
131, 18030–18031. (b) Li, W.; Yamamoto, Y.; Fukushima, T.; Saeki,
A.; Seki, S.; Tagawa, S.; Masunaga, H.; Sasaki, S.; Takata, M.; Aida, T.
J. Am. Chem. Soc. 2008, 130, 8886–8887. (c) Tsunashima, R.; Noro, S.-I.;
Akutagawa, T.; Nakamura, T.; Kawakami, H.; Toma, K. Chem.—Eur.
J. 2008, 14, 8169–8176. (d) Kato, H.; B€ottcher, C.; Hirsch, A. Eur. J. Org.
Chem. 2007, 2659–2666. (e) Nakanishi, T.; Ariga, K.; Michinobu, T.;
Yoshida, K.; Takahash, H.; Teranishi, T.; M€ohwald, H.; Kurth, D. G.
Small 2007, 3, 2019–2023. (f) Schade, B.; Ludwig, K.; B€ottcher, C.;
Hartnagel, U.; Hirsch, A. Angew. Chem., Int. Ed. 2007, 46, 4393–4396.
(g) Nakanishi, T.; Schmitt, W.; Michinobu, T.; Kurth, D. G.; Ariga, K.
Chem. Commun. 2005, 5982–5984. (h) Charvet, R.; Jiang, D.-L.; Aida, T.
Chem. Commun. 2004, 2664–2665.
’ ASSOCIATED CONTENT
S
Supporting Information. Experimental procedures and
b
complete spectroscopic and structural characterization, including
Figures S1ÀS8. This material is available free of charge via the
Internet at http://pubs.acs.org.
’ AUTHOR INFORMATION
Corresponding Author
nazmar@quim.ucm.es; javier.rojo@iiq.csic.es
16760
dx.doi.org/10.1021/ja206769a |J. Am. Chem. Soc. 2011, 133, 16758–16761

Journal of the American Chemical Society
COMMUNICATION
(8) Burghardt, S.; Hirsch, A.; Schade, B.; Ludwig, K.; B€ottcher, C.
Angew. Chem., Int. Ed. 2005, 44, 2976–2979.
(9) (a) Zhou, S.; Burger, C.; Chu, B.; Sawamura, M.; Nagahama, N.;
Toganoh, M.; Hackler, U. E.; Isobe, H.; Nakamura, E. Science 2001,
291, 1944–1947. (b) Homma, T.; Harano, K.; Isobe, H.; Nakamura, E.
Angew. Chem., Int. Ed. 2010, 49, 1665–1668. (c) Homma, T.; Harano, K.;
Isobe, H.; Nakamura, E. J. Am. Chem. Soc. 2011, 133, 6364–6370.
(10) Hizume, Y.; Tashiro, K.; Charvet, R.; Yamamoto, Y.; Saeki, A.;
Seki, S.; Aida, T. J. Am. Chem. Soc. 2010, 132, 6628–6629.
(11) Guldi, D. M.;Gouloumis, A.;Vꢀazquez, P.; Torres, T.; Georgakilas,
V.; Prato, M. J. Am. Chem. Soc. 2005, 127, 5811–5813.
(12) (a) Iehl, J.;PereiradeFreits, R.;Delavaux-Nicot, B.;Nierengarten,
J.-F. Chem. Commun. 2008, 2450–2452. (b) Iehl, J.; Nierengarten, J.-F.
Chem.—Eur. J. 2009, 15, 7306–7309. (c) Nierengarten, J.-F.; Iehl, J.;
Oerthel, V.; Holler, M.; Illescas, B. M.; Mu~noz, A.; Martín, N.; Rojo, J.;
Sꢀanchez-Navarro, M.; Cecioni, S.; Vidal, S.; Buffet, K.; Durka, M.; Vincent,
S. P. Chem. Commun. 2010, 46, 3860–3862. (d) Sꢀanchez-Navarro, M.;
Mu~noz, A.; Illescas, B. M.; Rojo, J.; Martín, N. Chem.—Eur. J. 2011,
17, 766–769.
(13) Luczkowiak, J.; Sattin, S.; Sutkeviciutꢀe, I.; Reina, J. J.; Sꢀanchez-
Navarro, M.; Thꢀepaut, M.; Martínez-Prats, L.; Daghetti, A.; Fieschi, F.;
Delgado, R.; Bernardi, A.; Rojo, J. Bioconjugate Chem. 2011, 22, 1354–1365.
(14) The formation of the nanorods can be reasonably accounted for
by the favorable πÀπ interactions between the fullerene molecules and
the HOPG surface. In this regard, solvophobic and πÀπ interactions are
the dominating forces in supramolecular organization of fullerenes.
(15) Li, C.-Z.; Matsuo, Y.; Nakamura, E. J. Am. Chem. Soc. 2010,
132, 15514–15515.
(16) When more concentrated solutions were used (∼10À3 M),
only a homogeneous layer of the materials for the three compounds
studied (DF-4, DF-8, and DF-16) was observed.
16761
dx.doi.org/10.1021/ja206769a |J. Am. Chem. Soc. 2011, 133, 16758–16761