Self-assembled dendrimers with uniform structure

Article abstract of DOI:10.1039/b803519a

Calix[4]arenes substituted at their wide rim by four aryl urea residues (1) form hydrogen-bonded dimers in apolar solvents. Replacement of one urea residue by an acetamido moiety leads to calix[4]arene derivatives (5) which form hydrogen-bonded tetramers under the same conditions. Both self-assembly processes occur independently. Therefore, molecules have been prepared in which a tetra-urea calix[4]arene and a tri-urea mono acetamide derivative are covalently connected between their narrow rims by a long, mainly aliphatic chain [-O-(CH₂)_n-C(O)-NH-(CH₂)_m-O-] (7). In the presence of an equimolar amount of tetra-tosyl urea calix[4]arene (2) they form dendritic assemblies since the well known heterodimerization of tetra-tosyl and tetra-aryl urea calix[4]arenes prevents the formation of a cross-linked structure. Covalent connection of adjacent urea residues leads to tetra-loop derivatives (3) that cannot form homodimers, but instead form heterodimers with tetra-aryl or tetra-tosylureas. Therefore, similar dendrimers should be available using the selective dimerization observed for 3. The formation of a single, structurally uniform dendrimer from eight building blocks is confirmed by ¹H NMR spectra, showing only peaks that are also found for respective model assemblies. Translational diffusion coefficients of the assemblies have been determined using ¹H DOSY NMR.

Full text of DOI:10.1039/b803519a

View Article Online / Journal Homepage / Table of Contents for this issue
PAPER
www.rsc.org/obc | Organic & Biomolecular Chemistry
Self-assembled dendrimers with uniform structure†
Yuliya Rudzevich,*a Valentyn Rudzevich,‡a Chulsoon Moon,b Gunther Brunklausb and Volker Bo¨hmer*a
Received 29th February 2008, Accepted 26th March 2008
First published as an Advance Article on the web 28th April 2008
DOI: 10.1039/b803519a
Calix[4]arenes substituted at their wide rim by four aryl urea residues (1) form hydrogen-bonded dimers
in apolar solvents. Replacement of one urea residue by an acetamido moiety leads to calix[4]arene
derivatives (5) which form hydrogen-bonded tetramers under the same conditions. Both self-assembly
processes occur independently. Therefore, molecules have been prepared in which a tetra-urea
calix[4]arene and a tri-urea mono acetamide derivative are covalently connected between their narrow
rims by a long, mainly aliphatic chain [-O-(CH2)n-C(O)-NH-(CH2)m-O-] (7). In the presence of an
equimolar amount of tetra-tosyl urea calix[4]arene (2) they form dendritic assemblies since the well
known heterodimerization of tetra-tosyl and tetra-aryl urea calix[4]arenes prevents the formation of a
cross-linked structure. Covalent connection of adjacent urea residues leads to tetra-loop derivatives (3)
that cannot form homodimers, but instead form heterodimers with tetra-aryl or tetra-tosylureas.
Therefore, similar dendrimers should be available using the selective dimerization observed for 3. The
formation of a single, structurally uniform dendrimer from eight building blocks is confirmed by 1H
NMR spectra, showing only peaks that are also found for respective model assemblies. Translational
diffusion coefficients of the assemblies have been determined using 1H DOSY NMR.
Introduction
Self-organisation on the molecular level is the driving force
responsible for selective formation of essential assemblies in living
systems. This principle is not only frequently used to construct
rather intricate artificial arrangements but also to synthesize novel
compounds or materials. Indeed, dimeric capsules,1–3 tetramers,4
hexamers,5 rosettes,6 supramolecular polymers7 and dendrimers8
have been obtained via self-assembly.
Fig. 1 Dimeric capsule formed by tetra-arylurea derivatives 1; (a) side
Among others, calix[4]arenes substituted by urea functions at
their wide rim are often used as building blocks for such structures.
In apolar, aprotic solvents they form dimeric capsules that are
view, (b) top view; alkyl substituents are omitted for clarity.
=
stabilized by a seam of hydrogen bonds between NH and C O
This heterodimerization of 1 and 2 has been employed to
construct various linear polymers from building blocks consisting
of tetra-urea derivatives covalently connected via their narrow
rims13 and to characterise multiple tetra-urea calix[4]arenes13,14
that could be used as cores for dendritic structures. In addition, it
constitutes the basis for the controlled synthesis of calix[4]arene-
based bis-, tris- and tetra-loop (3a) compounds via defined
metathesis using 2a as a template.15
Likewise, an exclusive heterodimerisation may be afforded by
steric factors. The tetra-loop tetra-ureas 3 cannot homodimerise
since this would require a sterically unfavourable overlapping of
the loops.15b,16 However, in the presence of stoichiometric amounts
of “open-chain” tetra-ureas 1 or 2 it readily forms heterodimers 1·3
or 2·3, thus facilitating the synthesis of topologically interesting
catenanes17 and rotaxanes.18,19 We will show subsequently how
these observations can be used to design and to realize well defined
hydrogen-bonded dendrimers, uniform in size and in structure.
In most cases self-assembled dendrimers consist of (several)
dendrons that are kept together by hydrogen bonding only
in the core.8d To the best of our knowledge until now only
two dendrimers were completely built up via self-organisation.
The first reported example20 was based on a system of two
groups of the urea functions9 (Fig. 1). A suitable guest (often
a solvent molecule) is commonly included, filling the internal
volume of the capsule.
The nature of residues connected to urea fragments strongly
influences the dimerization. When two different aryl or alkyl ureas
are mixed together, two possible homodimers and a heterodimer
are usually obtained in a more or less statistical ratio.10 However, a
stoichiometric mixture of tetra-aryl and tetra-sulfonyl ureas 1 and
2 (Fig. 2) exclusively yields the heterodimeric assembly 1·2.11,12
aAbteilung Lehramt Chemie, Fachbereich Chemie, Pharmazie und Geo-
wissenschaften, Johannes Gutenberg-Universita¨t Mainz, Duesbergweg
10-14, D-55099, Mainz, Germany. E-mail: rudzevic@mail.uni-mainz.de,
vboehmer@mail.uni-mainz.de; Fax: +49 6131 3925419; Tel: +49 6131
3922319
bMax Planck Institut fu¨r Polymerforschung, Postfach 3148, D-55021, Mainz,
Germany
† Electronic supplementary information (ESI) available: Synthetic scheme,
experimental procedures and spectroscopic data for compounds 3c and 5f,
1H NMR spectra for building blocks 6–8. See DOI: 10.1039/b803519a
‡ Permanent address: Institute of Organic Chemistry, NAS of Ukraine,
Murmanska str. 5, 02094 Kyiv-94, Ukraine.
2270 | Org. Biomol. Chem., 2008, 6, 2270–2275
This journal is
The Royal Society of Chemistry 2008
©

View Article Online
Fig. 2 General formulae and schematic representations of compounds 1–8.
complementary hydrogen-bonding motifs. However, the molecu-
lar assemblies still may be different in size and structure, since
the ratio of the building blocks determines only the average
size.21
In this paper we describe a second example of such a dendrimer
which is also uniform in size and structure.
In contrast, the first structurally uniform hydrogen-bonded
dendrimer was realized using three (self)-complementary units of
types 1, 2 and 4.8f The formation of such an assembly was based on
the homodimerisation of tri-urea triphenylmethanes 4 (as the core)
and the exclusive heterodimerization of tetra-tolyl and tetra-tosyl
ureas 1 and 2, which obey the self-sorting principle.16,22 Hence,
a well defined dendrimer8f was formed upon mixing of building
block 4–13 and capping unit 2 in a 1 : 3 ratio.
Results and discussion
General idea
Self-organisation leading to structurally uniform dendrimers (as
described above) is based on the following rules:
– the core must be formed by self-assembly of a single, self-
complementary unit;
This journal is
The Royal Society of Chemistry 2008
Org. Biomol. Chem., 2008, 6, 2270–2275 | 2271
©

View Article Online
– the exclusive heterodimerization of pairs of different units is
needed to build up each subsequent shell;
– all units must obey the self-sorting principle.
The tri-urea triphenylmethane 4, which was used as a core
in the earlier example, forms homodimers independently from
the dimerization of tetra-urea calix[4]arenes and thus fulfils the
requirements for the central unit. This is due to the different
number of urea functions and the different shape of compounds 4
and 1–3.
Furthermore, mismatch of the corresponding hydrogen-
bonding patterns of two assemblies allows for such selectivities. In
apolar solvents, tri-urea monoacetamide 5a yields tetramers whose
stabilizing hydrogen-bonding network is entirely different from
that observed for tetra-urea dimers (Fig. 3).4 The four acetamide
groups are placed in the middle of the assembly, while each amide
oxygen is hydrogen-bonded to both an amide-NH and an urea-
NH of two neighbouring calixarenes (Fig. 3a). Two of three urea
carbonyl oxygens are connected with the urea protons of the
neighbouring calixarenes by three-centred hydrogen bonds, while
Fig. 4 Sections of the 1H NMR spectra (CDCl3, 400 MHz) of (a) the
heterodimer 1a·3a, (b) the tetrameric tritolyl urea monoacetamide 5a4,
(c) a 1 : 1 : 3 mixture of 1a, 3a and 5a (an arbitrary amount), which shows
only signals present in (a) and (b).
=
the remaining C O and one NH are not involved in hydrogen
bonding.
Fig. 5 Envisaged formation of dendritic structures via selective di- and
tetramerization of urea derivatives of calix[4]arenes.
Fig. 3 Schematic drawing of (a) the hydrogen-bonding pattern of tetramer
5a4, (b) a space-filling representation of tetramer 5a4 based on its single
crystal X-ray structure,4 (c) a schematic representation of the tetrameric
assembly 5a4.
Synthesis and self-assembly studies
Coupling of tritolyl urea monoacetamides 5b and 5d24 (bearing
one acid function) and respective tetra-urea derivatives 1b14 or
3c25 (possessing one amino group) using PyBOP in DMF leads to
the bis-calixarene building blocks 6 and 7 in 70–85% yield.
When tri-urea acetamide 5 and the tetra-urea 1 are mixed in an
apolar solvent, both tetramerisation of 5 and homodimerization of
1 occur independently and simultaneously. This self-sorting prin-
ciple holds also when a second (different) tetra-urea calix[4]arene
is present in the mixture.23 Therefore, when 5 is added to a 1 : 1
mixture of 1 and 2 (or 3) only the tetramer 54 and the heterodimer
1·2 (or 1·3) exist, as clearly proved by the 1H NMR spectra shown
in Fig. 4.
Using the approach outlined above, we have designed dendritic
assemblies (Fig. 5) that are both uniform in size and structure
and adopt a more spherical shape in comparison to the earlier
example. Covalent connection of tri-urea monoacetamide 5b with
tetra-loop derivative 3c or tetra-tolyl urea 1b, respectively, forms
the central building blocks 6 and 7, while the tetra-ureas 2 are
used as capping units. When these building blocks are mixed in
a 1 : 1 ratio, dendritic assemblies as shown in Fig. 5 should be
formed. The four functional groups (protected amino functions)
at the narrow rim of 2b could be either used to attach specific
moieties (e.g. dyes to model light-harvesting systems) at the surface
of the assembly or for further growth of the dendrimer to the next
generation.
1
A representative H NMR spectrum (DMSO-d6) of building
block 6 confirming its structure is partly presented in Fig. 6.
One singlet of acetamide NH and the set of resonances for all
remaining NH protons are found in the expected region. At 75 ◦C
the characteristic NH signal of the amide bond connecting two
calixarenes via their aliphatic arms (-CH2NHC(O)CH2-) can be
observed separately at 7.78 ppm. In the aromatic part two doublets
for the ArH protons of the tolyl residues in 5b appear in a 1 : 2
ratio, while the other two are overlapping with one of the four
singlets of the calixarene skeleton of 5b. The remaining signals
correspond to aromatic protons of the tetra-loop derivative 3c.
Upon mixing of building block 6 with either tetra-tolyl urea
1a or tetra-tosyl urea 2a in a 1 : 1 ratio, formation of a dendritic
assembly with 16 Y residues on the surface is anticipated (Fig. 5).
However, no evidence for the correct assembly could be observed
1
in the H NMR spectrum of the mixture of 6 + 1a in CDCl3
or C2D2Cl4 (Fig. 7a). All signals corresponding to a tetrameric
structure were absent, while among the rest of the resonances,
those corresponding to the homodimer 1a·1a were detected. When
tetra-tosyl urea 2a was used instead of 1a as a capping unit
2272 | Org. Biomol. Chem., 2008, 6, 2270–2275
This journal is
The Royal Society of Chemistry 2008
©

View Article Online
Fig. 6 Part of the 1H NMR spectrum of 6 in DMSO-d6.
reasons. Either the spacer between the two calixarenes is too short
and the dendrimer cannot be formed due to steric congestion, or
the amide bonds connecting the two calixarenes in 6 and 7a are
placed too close to the hydrogen-bonding system of the envisaged
tetramer and thus intervene with this assembly and prevent its
formation.
The 1H NMR spectrum of the model compound 5f26 in CDCl3,
showing only broad signals instead of the expected peaks of
the tetramer, confirmed the latter assumption. To overcome this
problem the building block 7b was prepared, in which the amide
bond is separated from the calixarene skeleton of tri-urea mono-
acetamide derivative by 10 carbon atoms.
The building block 7b was mixed in a 1 : 1 ratio either with tetra-
loop compound 3a or tetra-tosyl urea 2b to afford the respective
assemblies. In the first case, formation of the desired dendrimer
occurred, however, small additional signals were also present in the
spectrum.27 In contrast, in the mixture of 7b with tetra-tosyl urea
2b only the signals of the target assemblies (7b·2b)4 were observed
(Fig. 8). No identification for other assembly can be found by
NMR. Taking into account that one CHCl3 molecule may be
included in each dimeric capsule, the calculated molecular mass
of the structurally uniform dendritic assembly of 12 molecules
(7b·2b)4 is 20 206 g mol−1.
Fig. 7 Parts of the 1H NMR spectra (CDCl3, 400 MHz) of the
stoichiometric mixtures of (a) 6 + 1a, (b) 6 + 2a, (c) 6, (d) 3b + 5c.
1
the corresponding H spectrum became even more complicated
(Fig. 7b), but again no evidence for the tetramer was found.
Searching for an explanation we recorded the spectrum of
building block 6 without addition of the capping units 1a (or 2a).
Instead of the expected peaks of a tetramer we observed a different
set of slightly broadened signals that were also present in the
mixtures of 6 + 1a and 6 + 2a (Fig. 7a–c). This observation strongly
suggests that the tri-urea monoacetamides 5, which usually do
not heterodimerize with “open-chain” tetra-ureas 1, are able to
form dimers with tetra-loop derivatives 3. Indeed, when 3b and 5c
were mixed together formation of the respective heterodimer was
observed (Fig. 7d). This means that linear polymers are formed if
only building block 6 is present in solution; however, it does not
yet explain the absence of the desired assembly in the presence of
1a or 2a. Similar experiments with the building block 7a lead to
the same results.
Since in the model three-component mixtures of open-chain
ureas 1a or 2a, tetra-loop urea 3a and monoacetamide 5a only the
expected tetramer 5a4 and the heterodimers 1a·3a or 2a·3a were
observed (Fig. 4), the results obtained can be explained by two
Fig. 8 Parts of the 1H NMR spectra (CDCl3, 400 MHz) of (a) the
heterodimer 1a·2a, (b) the tetramer formed by 5e, (c) the stoichiometric
mixture of 7b and 2b – the dendritic structure (7b·2b)4.
This journal is
The Royal Society of Chemistry 2008
Org. Biomol. Chem., 2008, 6, 2270–2275 | 2273
©

View Article Online
1H DOSY experiments28 were performed for the tetramer
formed by 5c, for a bis-calixarene 8 (a model of the building block
7b) and for the dendrimer (7b·2b)4. The diffusion coefficients of
2.8 × 10−10, 2.0 × 10−10, 1.5 × 10−10 m2 s−1 corresponding to
hydrodynamic radii of 1.4, 2.0 and 2.6 nm respectively were found
(Fig. 9). Thus the Rh of the new assembly is 0.5 nm larger than
that of the previously published example8f (2.1 nm). Obviously
the tetrahedral core in dendrimer (7b·2b)4 leads to a less dense
packing.
Waters/Micromass QTof Ultima 3 mass spectrometer. All solvents
were HPLC grade and used without further purification.
As previously verified,29 data for elemental analyses of organic
calixarenes are often misleading, due to inclusion of solvent
molecules, and cannot be considered appropriate criteria of purity.
Nevertheless, the identities of the reported compounds were
unambiguously established by their spectroscopic data.
General procedure for the synthesis of building blocks 6–8
Et3N (0.3 mL) was added to a solution of the respective
acid24 (0.15 mmol), amine14,25 (0.13 mmol) and (benzotriazole-
1-yloxy)trispyrrolidinophosphonium hexafluorophosphate (Py-
BOP) (0.15 mmol) in DMF (peptide synthesis grade, 4 mL).
The reaction mixture was stirred for 24 h at room temperature
and then diluted with water (15 mL). The formed precipitate was
filtered off, washed with MeOH (4 × 5 mL) and dried in air. In
the case of the compound 7b it was extracted with CHCl3–THF
(2 : 1, 3 × 30 mL). The organic layer was washed with brine, dried
(MgSO4), concentrated to a volume of 5–10 mL and the product
was precipitated with MeOH.
Bis-calix[4]arene 6. Compound 6 was obtained as a◦ white
powder in 85% yield; m.p.: slow decomposition above 280 C; 1H
NMR (400 MHz, DMSO-d6), d: 0.88–1.02 (18H, m, CH3), 1.20–
1.42 (64H, m, CH2), 1.63 (16H, m, CH2), 1.78–2.02 (15H, m, CH2
and C(O)CH3), 2.21 (9H, s, TolCH3), 3.13 (8H, m, ArCH2Ar),
3.27 (2H, br s, NHCH2), 3.70–3.93 (30H, m, OCH2), 4.36 (10H,
m, OCH2 and ArCH2Ar), 6.04 (4H, s, ArH), 6.51 (4H, s, ArH),
6.52 (4H, s, ArH), 6.71 (2H, s, ArH), 6.75 (2H, s, ArH), 6.86
(8H, s, ArH), 6.92 (2H, s, ArH), 7.01–7.04 (8H, m, ArHTol and
ArH), 7.21 (4H, d, 3J = 7.8 Hz, ArHTol ), 7.26 (2H, d, 3J = 7.8 Hz,
ArHTol ), 8.06–8.44 (15H, m, NHurea and CH2C(O)NH), 9.54 (1H, s,
Fig. 9 Schematic representations and hydrodynamic radii of (a) the
tetramer formed by 5c, (b) the model tetramer 84, (c) the dendrimer
(7b·2b)4, (d) the dendrimer8f having the dimeric triurea triphenylmethane
42 as a core.
NHC(O)CH3); m/z (ESI) 3038.6 (5) [M+ + Na], 1530.8 (63) [M2+
+
Na].
Bis-calix[4]arene 7a. Compound 7a was obtained as a white
powder in 80% yield; m.p.: slow decomposition above 280 ◦C; 1H
NMR (400 MHz, DMSO-d6), d: 0.86–1.04 (18H, m, CH3), 1.34
(12H, m, CH2), 1.56 (2H, m, CH2), 1.75–1.98 (17H, m, CH2 and
C(O)CH3), 2.21 (21H, s, TolCH3), 3.11 (8H, m, ArCH2Ar), 3.26
(2H, br s, NHCH2), 3.69–3.88 (14H, m, OCH2), 4.27–4.45 (10H,
m, OCH2 and ArCH2Ar), 6.68–6.89 (16H, m, ArH), 7.02 (16H,
br s, ArHTol ), 7.22 (12H, br s, ArHTol ), 8.04–8.33 (15H, m, NHurea
and CH2C(O)NH), 9.55 (1H, s, NHC(O)CH3); m/z (ESI) 2414.1
(3) [M+ + Na], 1218.1 (79) [M2+ + Na].
Conclusions
The well established preparative chemistry of calix[4]arenes allows
the synthesis of specific derivatives which are not only able to self-
assemble, but also to take part in self-sorting processes. Using
these properties we constructed a dendrimer, which is uniform in
size and structure and has molecular weight of more than 20 000 g
mol−1. The formation of the desired assembly was proved by H
1
and 1H DOSY NMR spectroscopy. Moreover, it was shown that
the formation of the correct aggregate may be supported and the
undesired assemblies can be suppressed by only slight changes in
the chemical structure of the dendrons.
Bis-calix[4]arene 7b. Compound 7b was obtained as a white
powder in 75% yield; m.p.: slow decomposition above 225 ◦C; 1H
NMR (400 MHz, DMSO-d6), d: 0.91–1.02 (18H, m, CH3), 1.18–
1.43 (26H, m, CH2), 1.48 (2H, m, CH2), 1.89 (19H, m, CH2 and
In addition it was found that the triurea monoacetamides of
type 5 (which usually tetramerize even in the presence of tetra-
ureas of type 1) form heterodimers with the tetra-loop tetra-ureas
3 if the latter has no other better partner.
3
C(O)CH3), 2.02 (2H, t, J = 7.1 Hz, C(O)CH2), 2.21 (21H, s,
TolCH3), 2.97–3.14 (10H, m, ArCH2Ar and NHCH2), 3.69–3.85
2
(16H, m, OCH2), 4.33 (8H, d, J = 12.2 Hz, ArCH2Ar), 6.69–
6.86 (14H, m, ArH), 6.95–7.07 (16H, m, ArH), 7.16–7.29 (14H,
3
Experimental
m, ArH), 7.69 (1H, t, J = 5.4 Hz, C(O)NH), 8.07–8.31 (14H,
m, NH), 9.47 (1H, s, NHC(O)CH3); m/z (ESI) 2539.3 (26) [M+ +
1
Melting points are uncorrected. H NMR spectra were recorded
Na], 1281.2 (100) [M2+ + Na].
on a Bruker Avance DRX 400 spectrometer at 400 MHz.
Chemical shifts are reported in d units (ppm) with reference
to the residual solvent peaks. Mass spectra were recorded on a
Bis-calix[4]arene 8. Compound 8 was obtained as a white
powder in 86% yield; m.p.: slow decomposition above 185 ◦C;
2274 | Org. Biomol. Chem., 2008, 6, 2270–2275
This journal is
The Royal Society of Chemistry 2008
©

View Article Online
(400 MHz, DMSO-d6), d: 0.90–1.03 (18H, m, CH3), 1.18–1.42
(26H, m, CH2), 1.47 (2H, m, CH2), 1.73 (2H, m, CH2), 1.77–1.95
(17H, m, CH2 and C(O)CH3), 2.02 (2H, t, 3J = 7.1 Hz, C(O)CH2),
2.21 (9H, s, TolCH3), 2.61 (2H, m, NHCH2), 2.97–3.12 (8H, m,
ArCH2Ar), 3.60–3.68 (4H, m, OCH2), 3.70–3.82 (6H, m, OCH2),
3.88–3.99 (6H, m, OCH2), 4.28–4.39 (8H, m, ArCH2Ar), 6.73
(2H, s, ArH), 6.76 (2H, s, ArH), 6.81 (2H, s, ArH), 6.96–7.06
(8H, m, ArH), 7.21 (4H, d, 3J = 8.3 Hz, ArH), 7.26 (2H, d, 3J =
8.3 Hz, ArH), 7.59 (4H, s, ArH), 7.65 (2H, s, ArH), 7.66 (2H, s,
ArH), 7.68 (1H, t, 3J = 5.6 Hz, C(O)NH), 8.13 (2H, s, NH), 8.15
(1H, s, NH), 8.23 (2H, s, NH), 8.30 (1H, s, NH), 9.47 (1H, s,
NHC(O)CH3); m/z (ESI) 2206.4 (100) [M+ + Et3N].
8 (a) S.-H. Hwang, C. D. Shreiner, C. N. Moorefield and G. R. Newkome,
New J. Chem., 2007, 31, 1192–1197; (b) E. C. Constable, Chem. Soc.
Rev., 2007, 36, 246–253; (c) S.-Y. Kim, Y. H. Ko, J. W. Lee, S. Sakamoto,
K. Yamaguchi and K. Kim, Chem.–Asian J., 2007, 2, 747–754; (d) F.
Huang, D. S. Nagvekar, C. Slebodnick and H. W. Gibson, J. Am.
Chem. Soc., 2005, 127, 484–485; (e) Y. Ma, S. V. Kolotuchin and
S. C. Zimmerman, J. Am. Chem. Soc., 2002, 124, 13757–13769; (f) Y.
Rudzevich, V. Rudzevich, C. Moon, I. Schnell, K. Fischer and V.
Bo¨hmer, J. Am. Chem. Soc., 2005, 127, 14168–14169; (g) K. C.-F.
Leung, P. M. Mendes, S. N. Magonov, B. H. Northrop, S. Kim, K.
Patel, A. H. Flood, H.-R. Tseng and J. F. Stoddart, J. Am. Chem. Soc.,
2006, 128, 10707–10715.
9 For X-ray structures, see: (a) O. Mogck, E. F. Paulus, V. Bo¨hmer,
I. Thondorf and W. Vogt, Chem. Commun., 1996, 2533–2534; (b) I.
Thondorf, F. Broda, K. Rissanen, M. Vysotsky and V. Bo¨hmer,
J. Chem. Soc., Perkin Trans. 2, 2002, 1796–1800; (c) M. O. Vysotsky,
M. Bolte, I. Thondorf and V. Bo¨hmer, Chem.–Eur. J., 2003, 9, 3375–
3382.
Acknowledgements
10 O. Mogck, V. Bo¨hmer and W. Vogt, Tetrahedron, 1996, 52, 8489–
8496.
We thank the Deutsche Forschungsgemeinschaft for financial
support (grants Bo 523/14 and SFB 625).
11 R. K. Castellano, B. H. Kim and J. Rebek, Jr., J. Am. Chem. Soc., 1997,
119, 12671–12672.
12 (a) G.-K. Li, Y. Yang, C.-F. Chen and Z.-T. Huang, Tetrahedron Lett.,
2007, 48, 6096–6099; (b) I. Thondorf, Y. Rudzevich, V. Rudzevich and
V. B o¨hmer, Org. Biomol. Chem., 2007, 5, 2775–2782; (c) M. Bolte, I.
Thondorf, V. Bo¨hmer, V. Rudzevich and Y. Rudzevich, CrystEngComm,
2008, 10, 270–272.
References
1 For a reviews see: (a) J. Rebek, Jr., Chem. Commun., 2000, 637–643;
(b) V. Bo¨hmer and M. O. Vysotsky, Aust. J. Chem., 2001, 54, 671–
677; (c) Y. Rudzevich, A. Bogdan, M. O. Vysotsky and V. Bo¨hmer in
Calixarenes in the Nanoworld, ed. J. Vicens and J. Harrowfield, Springer,
Dordrecht, 2007, pp. 21–46; (d) J. Rebek, Jr., Chem. Commun., 2007,
2777–2789.
13 R. K. Castellano and J. Rebek, Jr., J. Am. Chem. Soc., 1998, 120, 3657–
3663.
14 Y. Rudzevich, K. Fischer, M. Schmidt and V. Bo¨hmer, Org. Biomol.
Chem., 2005, 3, 3916–3925.
15 (a) M. O. Vysotsky, A. Bogdan, L. Wang and V. Bo¨hmer, Chem.
Commun., 2004, 1268–1269; (b) Y. Rudzevich, Y. Cao, V. Rudzevich
and V. Bo¨hmer, Chem.–Eur. J., 2008, 14, 3346–3354.
16 D. Braekers, C. Peters, A. Bogdan, Y. Rudzevich, V. Bo¨hmer and J. F.
Desreux, J. Org. Chem., 2008, 73, 701–706.
17 (a) M. O. Vysotsky, A. Bogdan, T. Ikai, Y. Okamoto and V. Bo¨hmer,
Chem.–Eur. J., 2004, 10, 3324–3330; (b) O. Molokanova, A. Bogdan,
M. O. Vysotsky, M. Bolte, T. Ikai, Y. Okamoto and V. Bo¨hmer, Chem.–
Eur. J., 2007, 13, 6157–6170.
18 (a) C. Gaeta, M. O. Vysotsky, A. Bogdan and V. Bo¨hmer,, J. Am. Chem.
Soc., 2005, 127, 13136–13137; (b) O. Molokanova, M. O. Vysotsky, Y.
2 For calixarene-based capsules see also: (a) J. J. Gonza´lez, R. Ferdani,
E. Albertini, J. M. Blasco, A. Arduini, A. Pochini, P. Prados and J. de
Mendoza, Chem.–Eur. J., 2000, 6, 73–80; (b) R. Zadmard, T. Schrader,
T. Grawe and A. Kraft, Org. Lett., 2002, 4, 1687–1690; (c) J. M. C. A.
Kerckhoffs, F. W. B. van Leeuwen, A. L. Spek, H. Kooijman, M. Crego-
Calama and D. N. Reinhoudt, Angew. Chem., Int. Ed., 2003, 42, 5717–
5722.
3 For tripodal capsules, see: (a) Y. Rudzevich, V. Rudzevich, D.
Schollmeyer, I. Thondorf and V. Bo¨hmer, Org. Lett., 2005, 7, 613–
616; (b) Y. Rudzevich, V. Rudzevich, D. Schollmeyer, I. Thondorf and
V. B o¨hmer, Org. Biomol. Chem., 2006, 4, 3938–3944; (c) M. Alajar´ın,
´
¨
Cao, I. Thondorf and V. Bohmer, Angew. Chem., Int. Ed., 2006, 45,
A. Pastor, R.-A. Orenes, E. Mart´ınez-Viviente, H. Ru¨gger and P. S.
8051–8055.
Pregosin, Chem.–Eur. J., 2007, 13, 1559–1569 and references cited
therein.
4 A. Shivanyuk, M. Saadioui, F. Broda, I. Thondorf, M. O. Vysotsky,
K. Rissanen, E. Kolehmainen and V. Bo¨hmer, Chem.–Eur. J., 2004, 10,
2138–2148.
19 For a review, see: A. Bogdan, Y. Rudzevich, M. O. Vysotsky and V.
Bo¨hmer, Chem. Commun., 2006, 2941–2952.
20 A. Franz, W. Bauer and A. Hirsch, Angew. Chem., Int. Ed., 2005, 44,
1564–1567.
21 For a similar example using metal complexation see ref. 8b.
22 (a) A. Wu and L. Isaacs, J. Am. Chem. Soc., 2003, 125, 4831–4835;
(b) P. Mukhopadhyay, A. Wu and L. Isaacs, J. Org. Chem., 2004, 69,
6157–6164.
5 (a) T. Gerkensmeier, W. Iwanek, C. Agena, R. Fro¨hlich, S. Kotila, C.
Na¨ther and J. Mattay, Eur. J. Org. Chem., 1999, 2257–2262; (b) A.
Shivanyuk and J. Rebek, Jr., Chem. Commun., 2001, 2374–2375; (c) L.
Avram and Y. Cohen, J. Am. Chem. Soc., 2002, 124, 15148–15149;
(d) M. Yamanaka, A. Shivanyuk and J. Rebek, Jr., J. Am. Chem. Soc.,
2004, 126, 2939–2943; (e) S. J. Dalgarno, D. B. Bassil, S. A. Tucker and
J. L. Atwood, Angew. Chem., Int. Ed., 2006, 45, 7019–7022.
6 (a) D. N. Reinhoudt and M. Crego-Calama, Science, 2002, 295, 2403–
2407; (b) V. Paraschiv, M. Crego-Calama, T. Ishi-i, C. J. Padberg, P.
Timmerman and D. N. Reinhoudt, J. Am. Chem. Soc., 2002, 124, 7638–
7639.
7 For a review, see: (a) L. Brunsveld, B. J. B. Folmer, E. W. Meijer and R. P.
Sijbesma, Chem. Rev., 2001, 101, 4071–4097. For selected examples, see:
(b) R. K. Castellano, C. Nuckolls, S. H. Eichhorn, M. R. Wood, A. J.
Lovinger and J. Rebek, Jr., Angew. Chem., Int. Ed., 1999, 38, 2603–
2606; (c) L. Pirondini, A. G. Stendardo, S. Geremia, M. Campagnolo,
P. Samor`ı, J. P. Rabe, R. Fokkens and E. Dalcanale, Angew. Chem.,
Int. Ed., 2003, 42, 1384–1387; (d) H. Xu, E. M. Hampe and D. M.
Rudkevich, Chem. Commun., 2003, 2828–2829; (e) H. Hofmeier, A. El-
ghayoury, A. P. H. J. Schenning and U. S. Schubert, Chem. Commun.,
2004, 318–319; (f) A. Taubert, A. Napoli and W. Meier, Curr. Opin.
Chem. Biol., 2004, 8, 598–603; (g) J. Wm. Wackerly and J. S. Moore,
Macromolecules, 2006, 39, 7269–7276; (h) F. Huang, D. S. Nagvekar,
X. Zhou and H. W. Gibson, Macromolecules, 2007, 40, 3561–3567;
(i) E. M. Todd and S. C. Zimmerman, J. Am. Chem. Soc., 2007, 129,
14534–14535.
23 Each mixture of 1, 2, and 5 (except 5f) contains only the tetramer 54,
the heterodimer 1·2 and either the homodimer 1·1 (c(1) > c(2)) or the
homodimer 2·2 (c(1) < c(2)).
24 Y. Rudzevich, V. Rudzevich, M. Bolte and V. Bo¨hmer, Synthesis, 2008,
754–762.
25 For the synthesis of 3c see the ESI†.
26 The long chain with carboxylic function at the end was introduced also
for the further elongation of the spacer; for the synthesis of 5f see the
ESI†.
27 Due to such problems caused by using the tetra-loop compound we
abandoned the synthesis of the dendrimer shown in Fig. 5, left.
28 The experimental setup of the Stejskal-Tanner BPPLED Sequence
(E. O. Stejskal and J. E. Tanner, J. Chem. Phys., 1965, 42, 288–292; D.
Wu, A. Chen and C. S. Johnson, Jr., J. Magn. Reson., Ser. A, 1995, 115,
260–264) was performed following standard procedures (C. S. Johnson,
Jr., Prog. Nucl. Magn. Reson. Spectrosc., 1999, 34, 202–256; B. Antalek,
Conc. Magn. Reson., 2002, 14, 225–258) using water as reference for
the self-diffusion coefficient.
29 (a) V. Bo¨hmer, K. Jung, M. Scho¨n and A. Wolff, J. Org. Chem., 1992,
57, 790–792; (b) F. Sansone, S. Barboso, A. Casnati, M. Fabbi, A.
Pochini, F. Ugozzoli and R. Ungaro, Eur. J. Org. Chem., 1998, 897–
905.
This journal is
The Royal Society of Chemistry 2008
Org. Biomol. Chem., 2008, 6, 2270–2275 | 2275
©