Modulated morphology in the self-organization of a rectangular amphiphile

Article abstract of DOI:10.1002/chem.200900303

The rectangular oligo(phenylene ethynylene) amphiphile 1 has been synthesized to investigate its self-assembling features in solution and onto surfaces. Concentrationdependent and variable-temperature NMR experiments firstly demonstrate the influence of t

Full text of DOI:10.1002/chem.200900303

DOI: 10.1002/chem.200900303
Modulated Morphology in the Self-Organization of a Rectangular
mphiphile
AHCTUNGTRENNUNG
Fꢀtima Garcꢁa, Gustavo Fernꢀndez, and Luis Sꢀnchez*[a]
Abstract:
The
rectangular
valent interactions also conditions the
thermodynamics of the self-assembly
process and concentration-dependent
UV/Vis investigations show a linear
correlation between the polarity of the
solvent and the Ka values (Ka ꢀ5.2ꢂ
105 mÀ1 for CH3CN/H2O mixtures and
4.4ꢂ104 mÀ1 for benzene). Moreover,
these UV/Vis studies prove the organi-
zation of this compound following the
indefinite self-association model. Mi-
croscopy techniques reveal that the
morphology and dimensionality of the
assemblies formed from 1 can be finely
modulated. Although polar solvents
yield hollow vesicles or toroidal 3D ob-
jects, depending upon concentration,
the utilization of non-polar benzene re-
sults in the formation of unimolecular
wires that can grow to form networks
upon increasing concentration. These
findings support the direct relationship
existing between the self-assembling
features of this amphiphile in solution
and onto surfaces.
oligo(phenylACHTUNGTRENNUNGene ethynylene) amphi-
phile 1 has been synthesized to investi-
gate its self-assembling features in solu-
tion and onto surfaces. Concentration-
dependent and variable-temperature
NMR experiments firstly demonstrate
the influence of the solvent in the sta-
bilization of the non-covalent forces in-
volved in the association of 1, namely,
p–p stacking interactions between the
aromatic fragments and van der Waals,
hydrogen-bonding and/or solvophobic
forces between the triethyleneglycol
chains. This subtle balance of non-co-
Keywords: amphiphiles · micelles ·
supramolecular chemistry · toroids ·
vesicles
Introduction
Small block molecules in which the relative proportion be-
tween a rigid aromatic and hydrophobic core and its sur-
rounding flexible coils, which can behave as hydrophobic or
hydrophilic units, are outstanding examples of artificial am-
phiphilic systems capable to self-organize into a variety of
well-ordered non-covalent architectures.[5] Modifications in
the number, the length or the shape of the aromatic units
and/or in the length or nature (linear or branched) of the
oligoether hydrophilic chains change the subtle balance of
the different non-covalent interactions between the hydro-
phobic and hydrophilic groups and induce the self-aggrega-
tion of small amphiphilic molecules into organized non-co-
valent architectures like micelles,[6] fibres,[7] or vesicles.[8]
Very recently, we have reported on the solvent-controlled
self-assembly of a C3-symmetric radial oligo(phenylene ethy-
nylene) (OPE) amphiphile. This amphiphile self-assembles
into vesicles, networks or rods depending on the nature of
the solvent used. Whereas the use of polar solvents induces
the rearrangement of the amphiphile into hollow vesicles, in
moderate-to-low polarity solvents the dimensionality of the
objects formed in solution and on solid substrates decreases
gradually upon decreasing solvent polarity.[9]
Amphiphilic systems, that is, those systems that bear hydro-
philic and hydrophobic fragments in a determined propor-
tion, are ubiquitous in living organisms and have found ap-
plication in industrial and domestic utilities.[1] The spontane-
ous self-assembly that these compounds achieve, a conse-
quence of the synergy of a number of weak forces in a deli-
cate balance, can be finely tuned by subtle modifications in
the chemical structure or in the external conditions like con-
centration, temperature, time, etc. These modifications can
generate supramolecular arrays of different morphology
and/or dimensionality.[2] A direct effect of this “soft-matter
polymorphism”[3] is the change in the dimensionality and
the morphology of the supramolecular ensembles, and also
in their physico-chemical properties and applications.[4]
[a] F. Garcꢀa, Dr. G. Fernꢁndez, Dr. L. Sꢁnchez
Departamento de Quꢀmica Orgꢁnica
Facultad de Ciencias Quꢀmicas
Ciudad Universitaria s/n. 28040 Madrid (Spain)
Fax : (+34)913944103
E-mail: lusamar@quim.ucm.es
The creation of the above mentioned superstructures is
dominated by p–p interactions of the aromatic backbone
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/chem.200900303.
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FULL PAPER
surrounded by a variable number or hydrophilic chains.
Nevertheless, p–p interactions—considered as the sum of
several non-covalent forces like electrostatic, attractive and
(m/z 3378) are clearly noticeable (Figure 1). This observa-
tion provided a first insight into the strong tendency of 1 to
self-assemble by means of p–p interactions and especially,
by the influence of the solvophobic component.[16]
repulsive orbital interactions and solvophobic effects[10]
—
are not the only supramolecular forces participating in the
self-assembly and some other non-covalent forces cooperate
and play a crucial role in the formation of the supramolec-
ular ensembles.[11] The self-assembly of small amphiphilic
molecules is, therefore, a useful benchmark to understand
and quantify all these non-covalent forces that finally con-
trol the creation of structures with variable morphologies.
Herein, we report on the synthesis and self-assembling
features of a simple rectangular OPE amphiphile 1 in which
a central aromatic core is surrounded by four hydrophilic
triethyleneglycol (TEG) chains. Based on our previous re-
sults on radial amphiphilic OPEs, we now set up to investi-
gate how subtle changes in the chemical structure and, in
consequence, in the hydrophylic/hydrophobic ratio of this
class of amphiphiles strongly influence their self-assembly
process and, hence, the final morphology of the aggregates.
Figure 1. MALDI-TOF (ditranol) mass spectrum of amphiphile 1. The
inset shows the formation of aggregates in the gas phase.
Results and Discussion
Self-assembly in solution: The self-assembly of 1 in solution
Synthesis: Rectangular-shaped amphiphile 1 was straightfor-
wardly obtained in only four synthetic steps and its synthesis
is depicted in Scheme 1. The peripheral hydrophilic aromat-
has been investigated by using concentration-dependent and
variable-temperature (VT) H NMR experiments as well as
1
concentration-dependent UV/Vis investigations in different
solvents. The 1H NMR spectra
of
1 in CD3CN (300 MHz,
298 K) at concentrations be-
tween 1.5 and 100 mm is shown
in Figure S2 in the Supporting
Information. As the concentra-
tion increases, a slight shielding
of most resonances is observed,
which indicates the formation
of aggregates of 1. This shift
pattern, in which all the reso-
nances are affected upon in-
Scheme 1. Synthesis of the rectangular amphiphilic OPE 1.
creasing concentration, clearly
indicates that the radial OPE
ic units (2) were prepared by following a Mitsunobuꢄs proto-
col[12] as previously reported.[9] The synthesis of the central
aromatic moiety (3a)[13] was achieved by using a Sonoga-
shira cross-coupling reaction[14] between 1,2,4,5-tetrabromo-
benzene and (trimethylsilyl)-acetylene (TMS) and subse-
quent deprotection with K2CO3. A final Sonogashira cross-
coupling reaction between 2 and 3b[13] affords compound 1
in 69% yield. Compound 1 has been fully characterized by
using NMR, FTIR and UV/Vis spectroscopy and MALDI-
TOF spectrometry (see the Supporting Information).
MALDI-TOF spectrometry not only provides structural
information, but is also a powerful tool to investigate the ca-
pability of organic substances to interact supramolecular-
ly.[15] For the case of compound 1, besides the molecular
peak at m/z 1126 (Figure S1 in the Supporting Information),
signals corresponding to the dimer (m/z 2252) and trimer
systems are arranged in an eclipsed fashion. The self-assem-
bly process is induced by a face-to-face p-stacking of the ar-
omatic units reinforced by the van der Waals contacts be-
tween the peripheral TEG chains.[9] To further investigate
the role that the stacking aromatic interactions and other
non-covalent forces play in the self-assembly of amphiphile
1
1, we also performed VT H NMR experiments in deuterat-
ed acetonitrile (Figure 2). A clear broadening and slight
shielding of most resonances, especially the TEG chains, is
observed upon decreasing temperature. A detailed analysis
of the concentration and temperature dependence of the
chemical shifts shows a linear behaviour, although with dif-
*
^
ferent slope values for the aromatic ( ) or aliphatic ( ) res-
onances (Figure 2b,c). The dissimilar effect of the concentra-
tion and temperature on the d value for these signals could
be attributable to the different nature and participation
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L. Sꢁnchez et al.
ments carried out in deuterated benzene (Figure S3) show
little changes in all resonances. As the concentration in-
creases, the proton corresponding to the central aromatic
ring experiences a slight upfield shift whereas only one of
the peripheral para-substituted aromatic protons shifts
downfield. VT 1H NMR studies confirm this tendency,
which suggests the mentioned rotated aggregation of mole-
cules of 1 to form a columnar stack. Similarly to the analysis
carried out in CD3CN, the concentration and temperature
dependence of the chemical shifts in C6D6 corroborates a
linear behaviour with a steeper slope for the aromatic pro-
tons than that for the aliphatic ones (Figure S3).
The slight shifts observed in the NMR studies and the
linear behaviour observed for the concentration and temper-
ature variation of the chemical shifts could be indicative of
a high value for the binding constant (Ka). Thus, an accurate
calculation of this thermodynamical parameter by using this
technique would need highly diluted concentrations not de-
tectable in the NMR time-scale. To determine a precise
value for Ka, we carried out concentration-dependent UV/
Vis studies utilizing CH3CN as solvent. The UV/Vis spectra
of 1 in CH3CN (298 K) at different concentrations is shown
in Figure S4. As the concentration increases the depletion of
the absorption band at lꢀ280 nm is accompanied by the
emergence of two new broad transitions that spread into the
visible region up to lꢀ400 nm (Figure S4b). The first band
is assigned to small or free species of 1, whereas the two less
energetic waves correspond to larger supramolecular aggre-
gates resulting from the p–p interactions between the aro-
matic units of 1. The spectroscopic changes observed in the
concentration-dependent UV/Vis experiments were fitted to
the isodesmic model[20] applied to the molar extinction coef-
ficient[9,21] at a wavelength of 328 nm affording large Ka
values (ꢀ3.8ꢂ105 mÀ1), which demonstrates the great ability
of 1 to self-assemble in polar solvents. The effect exerted by
water molecules on the self-association of 1 has been also
investigated by concentration-dependent UV/Vis experi-
ments in CH3CN/H2O (1:1) mixtures (Figure 3a). These
studies show similar spectra than those registered in pure
CH3CN with an identical pattern of absorption bands. How-
ever, in this case, a Ka value of 5.2ꢂ105 mÀ1, practically twice
the value observed in CH3CN, was calculated.
1
Figure 2. a) Partial H NMR spectra (CD3CN, 300 MHz, 4 mm) of 1 at dif-
The larger Ka value determined for the more polar
CH3CN/H2O mixture reveals the importance of water in the
stabilization of some of the non-covalent forces involved in
the self-assembly of 1, namely, the interactions between
polar TEG chains,[5] and the solvophobic interactions be-
tween the aromatic fragments. In these conditions, water
molecules can choose between a weak interaction with the
aromatic and nonpolar OPE backbone of 1 and a much
more energetically favourable interaction with another sol-
vent molecule. Highly polar solvents are predisposed to
form a cage around nonpolar solutes, like hydrocarbons, to
minimize solvent-solute interactions.[10] This positive solute–
solute solvophobic interaction among OPE fragments of ad-
jacent molecules of 1 strengthens the global p-stacking of
the aromatic rings and increases the Ka values. Furthermore,
ferent temperatures. Linear relationship of chemical shifts corresponding
*
to the proton at dꢀ7.7 and ꢀ4.1 ppm against b) temperature ( , slope=
^
*
7.5, R=À0.94; , slope=3.8, R=0.96) and c) concentration ( , slope=
^
7.5, R=À0.96; , slope=4.0, R=À0.94).
degree of the non-covalent forces involved in the interaction
of the aromatic fragments or the TEG chains. Although p–p
interactions between the aromatic central core of 1 domi-
nate its self-assembly, other supramolecular forces (solvo-
phobic, H-bonding) coming from the TEG chains contribute
in a lesser extent.[11a,17–19]
Decreasing the polarity of the solvent should induce the
coiling of the TEG chains and the association of 1 in a rotat-
ed fashion.[9] Concentration-dependent 1H NMR experi-
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Self-Organization of an Amphiphile
FULL PAPER
ure 3b).[20–22] The an value, together with the Ka, is indicative
of the propensity of the system to form supramolecular
stacks. As expected, the increase of an, and therefore the
self-aggregation process, starts at lower concentrations for
the more polar H2O/MeCN mixtures than in MeCN or ben-
zene. A similar trend is observed for the average amphiphile
number per stack (N) (Figure S6).[20–22]
The association studies of 1 in solution have been comple-
mented by dynamic light scattering (DLS) measurements
(Figure 4). This technique allows an accurate determination
Figure 3. a) Normalized UV/Vis absorption spectra of 1 (CH3CN/H2O,
1:1, 298 K, 2.5ꢂ10À4 to 4.5ꢂ10À8 m). Arrows indicate the direction of
change with increasing concentration. The inset in (a) shows the fit of De
(328 nm) to the isodesmic model;[9,21] b) molar fraction of aggregates (an)
*
of 1 as a function of concentration in different solvents; H2O/MeCN ( ),
[22]
^
*
MeCN ( ), C6H6 ( ).
Figure 4. a) Distribution of hydrodynamic radii of aggregates of 1 in dif-
À4
ferent solvents; MeCN, 10À4 m ( ); H2O/MeCN, 10 m ( ); H2O/MeCN,
~
^
polar solvent molecules act as cement inducing the attrac-
tive interaction between the hydrophilic TEG chains. The
significance of the solvent in the thermodynamics of the
self-assembly of 1 has been further corroborated by using
non-polar benzene. The corresponding concentration-depen-
dent UV/Vis studies show a similar pattern for the absorp-
tion bands than the observed in the studies developed in
MeCN or H2O/MeCN mixtures but a Ka value of 4.4ꢂ
104 mÀ1, an order of magnitude lower that the value calculat-
ed for polar solvents, was obtained (Figure S5). The decreas-
ing trend observed for Ka with decreasing the polarity of the
solvent demonstrates the relevance of solvophobic interac-
tions in the association of amphiphile 1.[10]
10À6 m ( ). b) Autocorrelation functions for a ꢀ10À4 m solution of 1 in
*
acetonitrile/H2O (1:1). The inset shows the angular dependence of appar-
ent diffusion coefficient versus the angle q.
of the particle size and shape. Narrow distributions of aggre-
gates with calculated hydrodynamic radii (RH) of around
100 and 200 nm were observed for ꢀ10À4 m solutions of 1 in
CH3CN and 1/1 CH3CN/H2O mixtures, respectively. For the
latter case, CONTIN analysis of the DLS autocorrelation
functions (Figure 3b) demonstrates the lack of angular de-
pendence for the apparent diffusion coefficient (Dapp) (inset
in Figure 4b), which could be indicative of the formation of
spherical objects.[6a,23]
The validity of the isodesmic model for the self- assembly
of 1 has been further corroborated by the determination of
the molar fraction of n-mer aggregates (an) in the experi-
mental conditions of concentration and solvents (Fig-
The DLS analysis for a ꢀ10À6 m solution of 1 in CH3CN/
H2O (1:1) mixtures showed, unexpectedly, a broad distribu-
tion for the aggregates centred at a RH value of around
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L. Sꢁnchez et al.
150 nm, a size larger than that calculated for more concen-
trated conditions (Figure 4a). This broad distribution could
imply the presence of species of different morphology.[24] On
the other hand, using non-polar benzene to determine the
RH value in benzene only resulted in the apparition of broad
and variable contributions that indicates the presence of
fluctuating species whose size and/or shape changes rapidly.
ters and heights of 220Æ13 and 25Æ1 nm, respectively, for
the CH3CN/H2O mixtures (Figure 4a).[25]
Fluorescence microscopy images of 1 in these conditions
provide first evidence on the hollow nature of the vesicles
(Figure S9). In this case, hollow circular objects with an
average diameter of ꢀ200 nm were observed, in a very good
agreement with the previous AFM images. In addition,
TEM images registered from ꢀ10À4 m CH3CN/H2O mixtures
of 1 onto carbon-coated grids and negatively stained with
uranyl acetate, confirm the formation of hollow vesicles
with diameters in the range of 200 nm (Figure 5b). The for-
mation of unimolecular p-stacked curved segments of 1 be-
tween the aromatic moieties and the van der Waals contacts
between the TEG chains could account for the mechanism
of vesicle formation (Scheme 2 and Figure S1). At this rela-
tively high content of amphiphilic molecules, hollow spheri-
cal objects guarantee the maximal area of exposure for the
hydrophilic TEG chains to interact with polar solvents.
To clarify the unexpected increasing in size of the aggre-
gates upon decreasing concentration observed in DLS ex-
periments, we also performed AFM experiments from a so-
lution of 1 (ꢀ10À6 m) in H2O/MeCN (1:1). AFM images of a
fresh solution prepared under these conditions, drop-cast
onto mica, displayed the formation of toroidal objects[26]
with average external and internal diameters of around 250
and 150 nm, respectively, and ꢀ7 nm profile height
(Figure 6, Figure S10a,b). The cross-sectional diameter,
Self-assembly onto surfaces: All the above studies, carried
out in solution, demonstrate the presence of aggregated spe-
cies that could be effectively transferred onto a substrate.
The morphology and dimensionality of these aggregates has
been examined by atomic force microscopy (AFM) utilizing
different experimental conditions (Scheme 2). Thus, AFM
images of ꢀ10À4 m solutions of 1 in polar solvents (CH3CN
or CH3CN/H2O mixtures) drop-cast onto mica displayed
flattened spherical vesicles (Figure S8 and Figure 5). In good
agreement with DLS measurements, the vesicles show mean
diameters of 80Æ10 nm and heights of 12Æ2 nm for the
ꢀ10À4 m solution of 1 in CH3CN, being the average diame-
Scheme 2. Schematic representation of the self-assembly of compound 1
at different conditions to form 3D hollow vesicles or toroids.
Figure 6. Height tapping-mode AFM images (air, 298 K) of a drop-cast of
1
on mica from freshly prepared ꢀ10À6
m MeCN/H2O mixtures [(z
scale=20 nm, for a), and z scale=12 nm, for b)]. The inset in b) shows
the height profile along the line. c) TEM image of 1 from freshly pre-
pared ꢀ10À6 m MeCN/H2O mixtures, stained with uranyl acetate.
clearly superior to the gyration radius of 1, suggests the for-
mation of longitudinal arrays of two molecules of amphi-
phile 1 that curve to form the toroidal objects. In addition,
many of these toroids are interconnected by wires of around
2 nm height (inset in Figure 6b) that could be formed by the
p-stacking of 1 into wire-like micelles. The presence of clus-
ters of different morphology could justify the previously
mentioned broad distribution of RH observed in the DLS
analysis.
Figure 5. a) Height tapping-mode AFM image (mica, air, 298 K) of 1 in
MeCN/H2O (ꢀ10À4 m, z scale=90 nm). The inset in a) corresponds to
the mean diameter Lorentzian distribution of the vesicles. b) TEM
image, stained with uranyl acetate, of vesicles of 1 from ꢀ10À4 m, MeCN/
H2O mixtures.
Upon aging this sample for a week, the growing in size
and overlapping of the toroids is noticeable (Figure S10c,d).
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The toroidal nature of the supramolecular assembly of 1 has
been confirmed by TEM imaging (Figure 6c). The inner and
outer diameters for the toroids visualized by TEM images
are of around 170 and 220 nm, in good correlation with
AFM images. These data, together with those extracted
from the experiments performed in solution, demonstrate
that the presence of water in the self-assembly of 1 is a cru-
cial factor to control the size, as occurs at concentrations of
10À4 m, and the morphology of the supramolecular objects.
AFM images of a ꢀ10À6 m solution of 1 in CH3CN showed
micellar hockey puck-like objects with a mean height profile
of ꢀ3 nm (Figure S11). This height profile suggests a single
molecule coil-rod-coil[27] aggregation mechanism to form 0D
supramolecular ensembles (Scheme S1).
coiled TEG chains induces compound 1 to rotate through
the hydrophobic central core to form wires as a consequence
of the joint effect of p–p stacking of molecules of 1 and the
positive solvent-solute interactions (Scheme S1).[9,10]
In sharp contrast, un-uniform micellar clusters with aver-
age height of ꢀ7 nm, many of them showing in-plane holes,
appear in the AFM images when a more concentrated and
freshly prepared (ꢀ10À4 m) solution of 1 in benzene is uti-
lized (Scheme 1, Figure 7b, and Figure S12b). At this con-
centration, small columnar stacks of molecules of 1, inter-
twined by their TEG chains, could be adsorbed onto the
mica surface forming the micellar cluster. After aging the
same sample, the rearrangement of these stacks gives rise to
the formation of the micellar clusters into a 2D grid-like
network with in-plane ellipsoid pores and with a broad
height distribution (Figure 7c–e, and Figure S12c).
Finally, considering the rotated stacked aggregation sug-
1
gested by the H NMR experiments carried out in benzene,
we have also investigated the morphology of the arrays
formed from solutions of 1 in this solvent onto mica. As
occurs in DLS measurements, AFM images demonstrate the
strong dependence of the morphology on concentration and
time. Similarly to our previous triangular radial amphi-
phile,[9] freshly prepared or aged ꢀ10À6 m solutions of 1 in
this solvent yield 1D wire-like micelles with average height
of ꢀ3.5 nm (Scheme S1, Figure 7a, and Figure S12a). The
hydrophilic character of the TEG chains provokes their coil-
ing in this nonpolar solvent and, therefore, a negligible inter-
action between them, as it is observed in the corresponding
concentration-dependent 1H NMR studies in C6D6. The
Conclusions
In summary, we have demonstrated that a simple rectangu-
lar amphiphile is readily capable to self-organize to form
distinct supramolecular assemblies. The delicate balance of
attractive non-covalent forces, mainly solvophobic and p–p
stacking interactions between the hydrophobic aromatic
part and van der Waals contacts, solvophobic interactions
and/or hydrogen bonding between the hydrophilic TEG
chains, changes due to the concentration and/or solvent po-
larity. At ꢀ10À4 m solutions of 1 in polar solvents, unimolec-
ular curved segments interact to form hollow vesicles whose
size increases with increasing polarity. The situation changes
drastically at lower concentrations (ꢀ10À6 m) and only the
presence of water in the solvent mixture allows the forma-
tion of rather unusual toroids. These results imply that 3D
supramolecular architectures of variable morphology could
be produced from simple modifications in the external con-
ditions utilized to self-assemble rectangular amphiphiles
unlike our previous results from the analogous triangular
OPE in which only vesicles are observed in polar solvents.[9]
In addition, the utilization of non polar benzene, favours the
apparition of one-dimensional structures that can grow until
forming networks, due to the rotated stacking of 1. The mor-
phology of the arrays formed from this amphiphile onto sur-
faces is, therefore, directly related with the self-association
features observed in solution.
Experimental Section
Amphiphile 1: 1-(2-(2-(2-methoxyethoxy)ethoxy)ethoxy)-4-iodobenzene
(2) (1.98 g, 5.41 mmol), bis-(triphenylphosphine)-palladium(II)-chloride
(0.04 g, 0.06 mmol) and copper (I) iodide (0.01 g, 0.07 mmol) were dis-
solved in triethylamine (40 mL). The mixture was subjected to several
vacuum/argon cycles and 1,2,4,5-tetraethynylbenzene (3b) (0.21 g,
1.23 mmol) was added. The mixture was heated at 708C for 2 h and then
was allowed to reach room temperature and stirred overnight. After
evaporation of the solvent under reduced pressure, the residue was puri-
fied by column chromatography (silica gel, CHCl3/EtOH 99:1) affording
Figure 7. Height tapping-mode AFM images (air, 298 K) of a drop-cast of
1 on mica in benzene: a) ꢀ10À6 m, (z scale=13 nm); b) ꢀ10À4 m, freshly
prepared (z scale=10 nm); c) ꢀ10À4 m, aged (z scale=70 nm); d) and
e) show the height and phase AFM images of the rectangular area in c)
(z scale=60 nm).
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L. Sꢁnchez et al.
1 as a brown oil (0.82 g, 59%); 1H NMR (CDCl3, 300 MHz) d=7.68 (s,
2H, Ha), 7.48 (d, 8H, Hb, J=8.85 Hz), 6.90 (d, 8H, Hc, J=8.85 Hz),
4.15 (t, 8H, Hd, J=6 Hz), 3.87 (t, 8H, He, J=6 Hz), 3.76–3.54 (m, 32H,
Hf+g+ h+i); 3.39 ppm (s, 12H, Hj); 13C NMR (CDCl3, 75Mz): d=159.5,
134.7, 132.5, 125.4, 115.7, 111.9, 95.7, 85.2, 73.2, 71.9, 71.1, 71.0, 70.0, 67.8,
57.5 ppm; FTIR (neat) n˜ =649, 722, 832, 926, 1059, 1108, 1133, 1175,
1199, 1249, 1284, 1352, 1454, 1514, 1568, 1604, 2203, 2873, 2924 cmÀ1; MS
(MALDI-TOF) m/z: 1126.5; (HRMS): calcd for C66H78O16 [M],
1126.53210; found: 1126.52844.
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Acknowledgements
We are thankful to Centro de Microscopꢀa y Citometrꢀa (UCM) for mi-
croscopy imaging; Unidad de Espectrocopꢀa de Infrarrojo-Ramꢁn-Corre-
laciꢅn (UCM) for DLS experiments, and Dr. M. Alonso (UAM) for
MALDI-TOF spectra. This work has been supported by UCM (UCM-
SCH-PR34/07-15826). F.G. and G.F. are indebted to IMDEA-Nanocien-
cia and MEC for a starting research and FPU grants. The authors grate-
fully acknowledge Prof. N. Martꢀn and his research group.
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6746
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Chem. Eur. J. 2009, 15, 6740 – 6747

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Received: February 4, 2009
Published online: June 4, 2009
Chem. Eur. J. 2009, 15, 6740 – 6747
ꢃ 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
6747