Tetraurea calix[4]arenes with sulfur functions: Synthesis, dimerization to capsules, and self-assembly on gold

Article abstract of DOI:10.1039/b616358k

Various calix[4]arene derivatives, fixed in the cone conformation by decylether groups and functionalized at their wide rim by urea residues, were synthesized. In two compounds (4f,g) sulfur functions were attached to the urea groups via different spacers in order to allow binding to metal surfaces. While they exist as single molecules in polar solvents, tetraurea calix[4]arenes of this type (4) combine to form dimeric capsules in aprotic, apolar solvents. A solvent molecule is usually included in such a capsule, if no guest with a higher affinity is present. In the presence of an equimolar amount of the tetratosylurea 5, the exclusive formation of heterodimers, consisting of one molecule of 4 and 5, is observed. The homo- and heterodimerization of the newly prepared derivatives 4f,g were studied by ¹H NMR to establish the conditions under which they exhibit the desired dimerization behaviour. Self-assembled monolayers (SAMs) were formed using the single calix[4]arenes 4f,g and the heterodimeric capsules 4g·5. Chloroform, dichloromethane and ferrocenium cations were used as guests in these immobilized heterodimeric capsules. The particular supramolecular architecture of the heterodimers should ensure that, after the immobilization on the metal surface, decomposition of the capsules and release or exchange of the guest is impossible or at least hindered. The self-assembly process and the stability of SAMs formed by capsules filled with ferrocenium cations in electrolyte solutions were tested with surface plasmon spectroscopy. The inclusion of guests, such as dichloromethane or ferrocenium, in the immobilized capsules were confirmed by classical surface plasmon spectroscopy, by gold nanoparticle absorption spectroscopy and by time-of flight secondary ion mass spectrometry (ToF-SIMS). The film stability and quality was tested by cyclic voltammetry. The Royal Society of Chemistry 2007.

Full text of DOI:10.1039/b616358k

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PAPER
www.rsc.org/obc | Organic & Biomolecular Chemistry
Tetraurea calix[4]arenes with sulfur functions: synthesis, dimerization to
capsules, and self-assembly on gold
Songbo Xu,a Ganna Podoprygorina,b Volker Bo¨hmer,*b Zhifeng Ding,c Patrick Rooney,d Chitra Rangand and
Silvia Mittler*a
Received 9th November 2006, Accepted 23rd November 2006
First published as an Advance Article on the web 14th December 2006
DOI: 10.1039/b616358k
Various calix[4]arene derivatives, fixed in the cone conformation by decylether groups and
functionalized at their wide rim by urea residues, were synthesized. In two compounds (4f,g) sulfur
functions were attached to the urea groups via different spacers in order to allow binding to metal
surfaces. While they exist as single molecules in polar solvents, tetraurea calix[4]arenes of this type (4)
combine to form dimeric capsules in aprotic, apolar solvents. A solvent molecule is usually included in
such a capsule, if no guest with a higher affinity is present. In the presence of an equimolar amount of
the tetratosylurea 5, the exclusive formation of heterodimers, consisting of one molecule of 4 and 5, is
observed. The homo- and heterodimerization of the newly prepared derivatives 4f,g were studied by 1H
NMR to establish the conditions under which they exhibit the desired dimerization behaviour.
Self-assembled monolayers (SAMs) were formed using the single calix[4]arenes 4f,g and the
heterodimeric capsules 4g·5. Chloroform, dichloromethane and ferrocenium cations were used as guests
in these immobilized heterodimeric capsules. The particular supramolecular architecture of the
heterodimers should ensure that, after the immobilization on the metal surface, decomposition of the
capsules and release or exchange of the guest is impossible or at least hindered. The self-assembly
process and the stability of SAMs formed by capsules filled with ferrocenium cations in electrolyte
solutions were tested with surface plasmon spectroscopy. The inclusion of guests, such as
dichloromethane or ferrocenium, in the immobilized capsules were confirmed by classical surface
plasmon spectroscopy, by gold nanoparticle absorption spectroscopy and by time-of flight secondary
ion mass spectrometry (ToF-SIMS). The film stability and quality was tested by cyclic voltammetry.
carcerand type,11,12 or reversibly encapsulated in hollow assemblies
held together by electrostatic forces,13 by metal coordination14
Introduction
or by hydrogen bonding.15 In so far as hydrogen bonding is
concerned, dimeric capsules from calix[4]arenes (substituted at
their wide rim by four (aryl) urea groups) have been extensively
studied16 in solution17 and characterized by several single crystal
X-ray structures.18 If such a tetraurea is decorated by suitable
sulfur functions, the formation of SAMs on gold should be
possible. In addition, the attachment to the gold surface may
lead to the permanent inclusion of a guest molecule; similar to
carcerands.
Self-assembled monolayers (SAMs) are ordered molecular
assemblies spontaneously formed by the adsorption of an active
surfactant on a solid surface. In particular, the self-assembly
of organosulfur adsorbates on gold has attracted considerable
attention in recent decade(s).19 The high specificity of the sulfur–
gold interaction (which is strong but reversible) allows for the
introduction of various functional groups into such monolayers
without interfering with the adsorption process. The number of
surface active organosulfur compounds that form monolayers has
increased in recent years. These include dialkyl sulfides20 and di-
sulfides,21 mercaptans,22 thiophenols,23 and various mercapto-sub-
stituted aromatic compounds,23,24 to mention just a few examples.
Dialkyl sulfide groups were attached to calix[4]arenes,25 to
resorcarenes26 and to resorcarene-derived cavitands26 in order to
obtain the respective SAMs on gold. Similar monolayers were
Molecular guest–host systems have attracted enormous interest
in recent years.1–6 Inclusion of a guest without covalent binding
into a host material can serve many purposes, such as solubility
enhancement, protection against degradation by light or oxygen,
separation by chromatography2 or simply removing undesired
substances from a mixture, and is widely used in industrial
products. Typically, most guest–host systems consist of an open
cavity (the host) which allows molecules (the guest) to adsorb
and bind and to desorb again according to chemical equilibrium.
This equilibrium depends on the accessibility of the cavity, the
concentration of the guest and the host and their affinity for each
other.7–10
However, a “guest” molecule may also be more or less perma-
nently included in cage-type molecules of the carcerand or hemi-
aDepartment of Physics and Astronomy, The University of Western Ontario,
Ontario, N6A 3K7, London, Canada. E-mail: smittler@uwo.ca; Fax: +1
(519) 661 2033; Tel: +1 (519) 661 2111 × 88592
bFachbereich Chemie, Pharmazie und Geowissenschaften, Johannes
Gutenberg-Universita¨t Mainz, Duesbergweg 10-14, D-55099, Mainz, Ger-
many. E-mail: vboehmer@mail.uni-mainz.de; Fax: +49 (0)6131 3925419;
Tel: +49 (0)6131 3922319
cDepartment of Chemistry, The University of Western Ontario, Ontario,
N6A 5B7, London, Canada
dDepartment of Physics, University of Windsor, Ontario, N9B 3P4, Windsor,
Canada
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obtained from carceplexes27 and hemicarceplexes,28 The attach-
ment of a thioether residue to one of the melamine residues of a
bis-melamine-substituted calix[4]arene made the construction of
hydrogen-bonded “double rosettes” in self-assembled monolayers
on the gold surface possible.29
As illustrated in Fig. 1, the attachment of sulfur functions to
the ether residues should allow for a more or less unhindered
decomposition of the capsules from the monolayer, leading to a
loss or exchange of guests. Attachment of the sulfur functions
to the urea residues, however, suggests the possibility that such
immobilized capsules cannot fall apart, even if the hydrogen bonds
are broken. The interdigitating urea residues in the dimer should
prevent its disentanglement and keep the guest molecules bound
to the surface, even when equilibrium conditions and osmotic
pressure dictate a release.
of calixarenes,25 resorcarenes26 and cavitands26 or carcerands27,28
derived from them.
The synthesis of such tetraurea calix[4]arenes with sulfur
functions is summarized in Scheme 1. To attach the four urea
groups, the tetraamino calix[4]arene 1 was converted to an active
urethane 2 by acylation with p-nitrophenyl chloroformate (81%),
which was subsequently treated with the anilines 3a–c (75–90%).
The precursors 4a–c were thus available in yields between 60–70%.
While 3a is commercially available, 3b was prepared in four steps by
O-alkylation of p-nitrophenol with N-(d-bromobutyl)phthalimide,
followed by hydrazinolysis, acylation with Boc-anhydride, and
hydrogenation of the nitro group (overall ∼50%). [This exchange
of the protective group (phthalimido against Boc) was necessary,
since a tetraurea obtained analogously with phthalimido groups
could not be deprotected by hydrazine, leaving the urea func-
tions intact.] To obtain 3c, p-hydroxyacetanilide was O-alkylated
with 11-bromoundecene followed by alkaline hydrolysis (overall
∼80%), since the selective hydrogenation of a nitro group is not
possible in this case.
Scheme 1 also indicates the further modification of 4a–c. After
the usual deprotection (cleavage of the Boc group) acylation
with a-lipoic acid anhydride gave 4d and 4f, while 4e was
prepared for comparison with acetic acid anhydride. Addition
of decylmercaptan in the presence of 9-borabicyclo[3.3.1]nonane
converted 4c into 4g in 60% yield.
All tetraurea derivatives 4 were chromatographically pure
(TLC). They were characterized mainly by their 1H NMR spectra,
which confirmed their C4v-symmetrical structure in hydrogen-
bond-breaking solvents, while their dimerization in apolar solvents
led to more complicated spectra reflecting an S8-symmetry for
homodimers and a C4-symmetry for heterodimers. In all relevant
cases the molecular mass was confirmed by ESI-MS or FD-MS.
Fig. 1 Schematic representation of SAMs formed by hydrogen-bonded
heterodimers. a) Attachment of sulfur functions to the ether residues of
the narrow rim; b) attachment of sulfur functions to the urea residues at
the wide rim.
B. Dimerization studies
The dimerization of tetratolylurea (4, R = CH3) with the inclusion
of cobaltocenium as guest was shown using dichloroethane as a
solvent.31 However, this is not suitable for the intended electro-
chemical studies. Thus, conditions under which dimeric capsules
with cobaltocenium as a guest are quantitatively formed within
reasonable times had to first be established. For tetratolylurea,
this has been shown in CD2Cl2, where the signals for homo- or
heterodimers (5 and 6, respectively)32 are seen in the NMR spectra
recorded immediately after the dissolution of a stoichiometric
mixture.33 On the other hand, CDCl3, a better guest itself, shows
slower kinetics, and after 20 h an equilibrium mixture exists where
approximately 15% of the capsules contain CDCl3.
Among the compounds with sulfur functions foreseen for the
formation of SAMs, 4d was practically insoluble in all relevant
solvents (CD2Cl2, CDCl3, C6D6) at room temperature. In 1,1,2,2-
tetrachloroethane (TCE) at 75 ◦C, the monomer can be seen
in addition to irregular aggregates, while with the tetraloop
compound 6 heterodimers are predominantly formed.
Thus, we envisaged tetraaryl urea derivatives substituted by
sulfur functions in the urea residues as target. If their heterodimers
with a suitable partner, e.g. with a tetratosylurea calix[4]arene,
would form SAMs on gold, it should be possible that an included
guest can be permanently trapped. In the following report we
describe the synthesis of these target compounds and the study
of the self-assembly of their monomers or heterodimers on gold
surfaces. We finally try to give a first answer to the question of
whether or not the attachment to the surface makes dissociation
of the capsules, and hence the release of the included guest,
impossible.
Results and discussion
A. Syntheses
There are various methods for introducing sulfur-containing
residues into a molecule and, as a result, enabling its self-assembly
on gold surfaces. Lipoic acid, for instance, is frequently used, since
it is commercially available and can be easily bound/attached
to amino groups via amide linkages.30 Thioether groups offer
another possibility and have been applied to the functionalization
Compounds 4f and 4e (as a simpler model) have only slightly
improved solubility, and conditions for the (exclusive) formation
of the desired dimers were not found. Heterodimers of 4f with
5 or 6 in different solvents and homodimers with cobaltocenium
as a guest in CD2Cl2 were accompanied by irregular aggregates.
Interestingly, in TCE, homodimers of 4f are in equilibrium with the
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Scheme 1 Syntheses of tetraurea calix[4]arenes bearing sulfur functions.
◦
monomeric species at higher temperatures (75–100 C) and with
less defined species/aggregates at room temperature. It seems that
the additional amide functions in 4f are detrimental to controlled
dimerization (although amide functions as such did not prevent
the dimerization), as shown, for instance, by the formation of
“polycaps”.34,35 The difference may be due to the fact that the
amide-containing residues are bound to the urea functions (at the
wide rim) in 4f, which are essential for the dimerization, and not
to the phenolic oxygens at the narrow rim.
in stoichiometric mixtures. Thus, given these observations, 4g
seems to be the most appropriate derivative to form SAMs of
heterodimeric capsules on a gold surface.
In general, these results demonstrate that, except under limited
conditions, the selective formation of dimeric capsules from
tetraurea calix[4]arenes containing additional functional groups
and the desired guest may be a demanding problem. However, as
also shown, this problem can be solved using a wide variety of
structural modifications.
Tetraurea 4g not only forms homodimers, but also heterodimers
with 5 or 6 (Scheme 2) in CDCl3 or C6D6. In CD2Cl2, the inclusion
of cobaltocenium occurs rapidly, and heterodimers with 5 or
6 and cobaltocenium cations as guests are exclusively formed
C. SAMs: formation and properties
The SAMs were usually formed from 10 lM solutions of the
calixarenes 4g or 4f or of their stoichiometric mixture with 5. THF
was used as a solvent for SAMs of a single calixarene (4g or 4f),
and chloroform (or dichloromethane) for heterodimeric capsules
containing the solvent as guest. SAMs of capsules including
ferrocenium as a guest were formed from dichloromethane. Here
the concentration of both calixarenes (e.g. 4g and 5) was increased
to 0.1 mM, and a 20% excess of the ferrocenium salt was added
(c = 0.12 M) in order to shift the equilibrium from solvent-filled to
ferrocenium-filled capsules. Since the gold substrate was immersed
in the pre-fabricated solution, we assume that the capsules are
formed in solution and that the SAMs are formed from completely
filled capsules.
The SAM formation was investigated by surface plasmon
resonance (SPR) spectroscopy, by monitoring the shift of the
surface plasmon resonance while forming the SAM. Details are
reported elsewhere.7–9,36 From these plasmon resonance angle
shifts, the thickness and the refractive index of the various SAMs
on the gold surface were simulated.7–9,36,37 The SPR results for
Scheme 2 Chemical structure of compounds 5 and 6.
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Table 1 Data analysis of SPR experiments for SAMs of 4g, 4f, capsule 4g·5 and capsule 4f·5, filled with solvent or ferrocenium from the resonance angle
shift Dh; n is the refractive index and e is the dielectric constant at 632.8 nm wavelength
˚
SAM
Thickness of SAM/A
e (SAM)
n (SAM)
n (solvent)
4g (in THF)
46.5
48
48
54
50
50
50
2.03
2.14
2.14
2.27
2.19
2.15
2.162
1.425
1.463
1.463
1.507
1.480
1.466
1.47
1.407
1.407
1.446
1.446
1.424
1.424
1.424
4f (in THF)
Capsule 4g·5 (in CHCl3)
Capsule 4f·5 (in CHCl3)
Capsule 4g·5 (in CH2Cl2)
Capsule 4g·5 + ferrocenium (in CH2Cl2) assembled in a 0.1 mM solution
Capsule 4g·5 + ferrocenium (in CH2Cl2) assembled in a 1 mM solution
SAMs of 4g, 4f, and the capsules 4g·5 and 4f·5 filled with
chloroform, dichloromethane and ferrocenium are summarized
in Table 1.
refractive index slightly to 1.466. It is known that tetraurea
calix[4]arene dimers formed in a ferrocenium solution contain
one ferrocenium cation as a guest, while ferrocene itself is not
included.31 The ferrocenium ion exhibits cation–p interactions
with the aromatic groups of the cavity, which compensates for the
weakened hydrogen bonding caused by the large guest molecule.
This cation–p stabilization is missing in the case of the neutral
molecule ferrocene.
The theoretical sizes of the molecules bound to the gold and
the maximum thickness of the SAMs were calculated using an
idealized model. The estimated size/thickness of both 4g and the
˚
capsule 4g·5 is 52 A, since the urea groups of 4g and 5 interdigitate
when the capsule is formed and the back-folded alkyl chains of
the dialkyl sulfide groups in 5 do not contribute to the size of
the capsule. However, they increase the overall density of the film
and, hence, the refractive index. Thus, we expect a slightly higher
refractive index for the capsules in comparison to SAMs of pure
4g or 4f.
In the case of the ferrocenium-filled capsule 4g·5, if SAMs
were formed at an elevated concentration of 1 mM, the film
˚
thickness remained unchanged at 50 A; however, a minor increase
in refractive index could be observed. This is attributed to a slightly
more densely packed film due to an enhanced amount of available
material.
Both capsules (4g·5, 4f·5) are filled with solvent when they are
in solution. Therefore, the refractive index of the SAMs made
up of capsules must depend on the refractive index of the guest
solvent. Single molecules 4g and 4f are not necessarily filled with
a solvent molecule, since they probably assume a “pinched cone”
conformation.
In order to confirm the difference in the SAMs made of capsules
containing dichloromethane or ferrocenium, which should have a
higher refractive index than dichloromethane41,42 as a guest, we
did UV-Vis absorption spectroscopy on gold nanoparticles, both
uncapped and capped with the SAMs under consideration. The
position of the plasmon band of a SAM-capped nanoparticle
yields information about the dielectric constant of the capping
material. Fig. 2 shows a discrete dipole approximation (DDA)43
calculation for hemispherical gold nanoparticles with a radius of
7 nm and a cap of 7 nm of e.g. an organic material, in an aqueous
environment. The refractive index of the cap is systematically
varied from n = 1.33, the blank particle in water, to n = 3.33.
It can clearly be seen that the plasmon band absorption maximum
shifts to higher wavelengths with the increasing refractive index of
the capping material. The double peak structure appearing first at
a refractive index of n = 2 is due to the dipolar and quadrupolar
contributions of the plasmon band, which start to be separated
spectrally under these conditions.44
We prepared simple gold nanoparticle samples by sputtering
gold onto a microscope glass slide with a mean gold film thickness
of 15 nm. These samples were used to prepare SAMs of a
dichloromethane- and a ferrocenium-filled capsule 4g·5. Their
absorption spectra in air are shown in Fig. 3 along with a blank
gold nanoparticle sample. A plasmon band around 545 nm can
clearly been seen for the blank gold nanoparticles. The SAM of
the ferrocenium-filled capsule 4g·5 shows a plasmon resonance at
around 560 nm, whereas that of the dichloromethane-filled capsule
4g·5 has a plasmon band maximum at the longer wavelength
of 570 nm. Again we find that the SAM of ferrocenium-filled
capsules shows a smaller dielectric constant than that of the
dichloromethane-filled one. Assuming the capsule itself does not
change when assembled in dichloromethane, and that one ferroce-
nium is located in the capsule 4g·5, two dichloromethane molecules
SAMs of 4g or 4f obtained in THF, the solvent with the lowest
refractive index used (n = 1.407), show a refractive index of 1.425
˚
˚
with a thickness of 46.5 A, or 1.463 with a thickness of 48 A,
respectively. The higher refractive index for the 4f SAM is due
to a higher density because of the back-folding alkyl chains.38
SAMs of the capsules 4g·5 and 4f·5, which cannot be formed in
the hydrogen-bond-breaking THF, but can be in CHCl3,39 show a
˚
˚
thickness of 48 A and 54 A, respectively. The increase in refractive
index to 1.463 and 1.507 can be attributed to the inclusion of a
CHCl3 guest molecule (n = 1.446) and to the above mentioned
interdigitation.
Surprisingly, the refractive index of SAMs of capsules 4g·5 filled
with dichloromethane increased in comparison to chloroform-
filled SAMs of 4g·5, although dichloromethane has a smaller
refractive index (n = 1.424). They also have a slightly larger film
40
˚
thickness of 50 A. It has been shown recently that heterodimers
of tetraaryl/tetratosylurea calix[4]arenes may contain two guest
dichloromethane molecules. Aside from the better packing in the
SAMs assembled from dichloromethane, it might also be possible
that two dichloromethane molecules are encapsulated in 4g·5.
Both effects should yield a higher film density, and therefore an
increased refractive index relative to the chloroform-filled film.
Although the proper formation of SAMs of 4f and 4f·5 seems
to be possible (despite the fact that 4f·5 is in equilibrium with
its monomers), we decided to concentrate our further studies on
capsule 4g·5.
Filling the capsule 4g·5 with ferrocenium in dichloromethane
does not change the thickness of its SAM but decreases its
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Fig. 2 DDA calculation of hemispherical gold nanoparticles (radius = 7 nm, cap = 7 nm) for capping materials with different refractive indices.
Fig. 4 ToF-SIMS spectra of SAMs of ferrocenium-filled capsules of 4g·5
on gold, formed from (a) a 0.1 mM solution; (b) a 1 mM solution.
absence of ferrocenium (data not shown). The Fe mass peak of
the SAMs assembled from 1 mM 4g·5 with ferrocenium is about
twice as high as that of the 0.1 mM encapsulated ferrocenium.
ToF-SIMS is a quantitative and linear method; we therefore
conclude that in the samples obtained from the more concentrated
solution, about twice the amount of ferrocenium is present in the
SAM due to a shift in the equilibrium between ferrocenium- and
dichloromethane-filled capsules towards the ferrocenium-filled
capsules.
Fig. 3 UV-Vis spectra of SAMs of (a) pure gold; (b) 4g·5 filled with fer-
rocenium on gold nanoparticles, and (c) 4g·5 filled with dichloromethane
on gold nanoparticles.
should be encapsulated in the case of the pure dichloromethane
assembly.
E. Stability of 4g·5 SAMs in electrolytes
D. ToF-SIMS investigations: is ferrocenium present in the
SAMs?
Given the previous results, we can conclude that we are able
to fabricate SAMs of capsule 4g·5 filled with ferrocenium, viz.
encapsulated, immobilized ferrocenium. The next question which
has to be addressed is the stability of these SAMs in a liquid
environment, e.g. in water, in an aqueous electrolyte or in
dichloromethane with tetrabutylammonium hexafluorophosphate
(TBAPF6). The stability was tested with SPR spectroscopy by
taking spectra (always in dichloromethane) of SAMs formed by
capsule 4g·5 filled with dichloromethane or with ferrocenium
before and after immersion in pure Milli-Q-water, in 0.1 M KCl
aqueous solution, in pure CH2Cl2 and in 0.15 M or 0.06 M
TBAPF6 in CH2Cl2 for 2 days.
Both sets of surface plasmon data only indirectly confirm the
presence of the ferrocenium in the capsules. Therefore, in a second,
direct approach with ToF-SIMS, the presence of the ferrocenium
was studied by examining the iron signal of the ferrocenium. Fig. 4
depicts two ToF-SIMS spectra of SAMs of capsule 4g·5 assembled
with ferrocenium at two capsule concentrations: 0.1 mM and
1 mM. Both spectra clearly show the most dominant Fe isotope
(91.720%) with a peak at m/z = 55.935 u for SAMs of capsule 4g·5
assembled with ferrocenium. No mass peak of iron is obtained in
ToF-SIMS spectra for SAMs formed with CH2Cl2 as guests, in the
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Fig. 5 displays as an example the plasmon spectra of an SAM
of capsule 4g·5 filled with ferrocenium (a) before and (b) after
immersion in 0.1 M aqueous KCl solution. Clearly, in this case the
plasmon resonance had shifted slightly towards smaller coupling
angles with the immersion, indicating a loss of material from the
film. Under these conditions the SAM is obviously not stable.
Fig. 6 Cyclic voltammetric current response vs. applied potential for
(a) a pure gold surface and (b) for 4g SAM/Au. Scan rate: 20 mV s−1
.
oxidation peak of the ferrocene–methanol and the reduction peak
of the ferrocenium–methanol. The curve (b) depicts the response
of the gold electrode with the SAM. Clearly, the electrochemical
reactions are hindered and a basically flat, nearly featureless
current–voltage behavior is found. This indicates that the SAMs
blocked the electron transfer between redox couple and the
electrode very well in aqueous solution. The low currents (around
1.5% of that for the bare gold case) from those voltammograms
indicate that the SAMs are well-packed at the electrode. Sweeping
the voltage several times did not change the electrochemical
response, indicating the SAMs are stable over the duration of
these electrochemical tests.
Fig. 5 Plasmon spectra (taken in dichloromethane) of a capsule 4g·5
SAM with ferrocenium immersed for 2 days in 0.1 M aqueous KCl
solution: (a) before and (b) after immersion.
For all aqueous solutions this instability was found for the
SAMs of ferrocenium-filled capsules. A very minor shift in
the surface plasmon resonance curve was found for the SAM
of the ferrocenium -filled capsule 4g·5 with 0.15 M TBAPF6,
but no shift is observed with 0.06 M TBAPF6. The SAMs of
dichloromethane-filled capsules did not yield any shifts in the
tested solvents and were always stable for at least 2 days. Given that
the SAMs of the ferrocenium-filled capsule 4g·5 are not stable in
an aqueous environment, but are stable in dichloromethane with
0.06 M TBAPF6, it should be possible to perform electrochemical
experiments, such as cyclic voltammetry, in dichloromethane with
0.06 M TBAPF6 and, possibly, with 0.15 M TBAPF6.
Conclusions
We were able to fabricate stable SAMs of the “monomeric”
calix[4]arenes 4g and 4f by adsorption from a hydrogen-bond-
breaking solvent (ethanol–chloroform 6 : 4, THF), and of
the heterodimeric capsules 4g·5 and 4f·5 by adsorption from
chloroform, which is also included as a guest. Since independent
1H NMR studies showed that capsule 4f·5 is in equilibrium
with its monomers and does not exclusively form heterodimers,
we concentrated on capsule 4g·5 for our in-depth studies. The
ferrocenium cation is encapsulated in 4g·5 and captured (see
Fig. 1b) when the guest–host system is immobilized by self-
assembly from dichloromethane. The SAMs of capsule 4g·5 filled
with ferrocenium are unstable in water, probably because hydrogen
bonds are broken, but are stable in dichloromethane with salt
concentrations up to 0.15 M TBAPF6. Electrochemistry has
shown densely packed films, which are stable to electrochemical
experiments in an aqueous environment for a few minutes.
The entanglement of the urea residues in heterodimers of
capsule 4g·5 obviously is not sufficient for continued stabilization
of the capsules and of their SAMs when the hydrogen bonds of
the dimers are broken. Therefore, our future studies will focus on
heterodimers formed by tetraureas of type 4g with the tetraloop
tetraureas of type 6, in which the capsules after binding to the
surface have a four-fold rotaxane (with Au as “stopper”) or
catenane structure (with Au as a connection between urea arms).
F. Coverage of gold by SAMs of 4g·5: electrochemistry
Oxidation/reduction reactions of a redox couple in solution are
often used for probing the coverage and quality of monolayers on
a metal surface.7,44 In our case, ferrocene/ferrocenium–methanol
was used. After monolayer formation on the electrode surface, the
current flow through the SAM was probed by cyclovoltammetry.
A closely packed monolayer can block this current between
the electrode with the monolayer and the electrolyte solution
dramatically. This technique is highly sensitive to monolayer
defects.7,44
In Fig. 6 the cyclic voltammogram of an electrode covered by
a SAM fabricated from 4g is shown. The electrochemical data for
SAMs of dichloromethane-filled capsules 4g·5 and ferrocenium-
filled capsules 4g·5 look identical (not shown). The very distinct
cyclic voltammograms (a) depict the pure gold surface with the
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The capsules may then still be opened if the hydrogen bonds are
broken, but they cannot fall apart. Under appropriate geometrical
conditions (e.g. length of the spacer, size of the loops) this may lead
to a permanent encapsulation of an included guest.
amount of Raney-Ni was added and the mixture was vigorously
stirred in a hydrogen atmosphere at rt for 6–8 hours (the
conversion may be monitored by TLC). The catalyst was filtered
off and the solvent was removed in vacuum◦to give the pure aniline
(1.38 g, 85%) as yellowish solid. Mp 46–47 C; 1H NMR (CDCl3),
d: 6.72 (2 H, d, JHH 8.7 Hz, Ar-H), 6.62 (2 H, d, JHH 8.5 Hz,
Ar-H), 4.62 (1 H, br s, N-H), 3.88 (2 H, t, 3JHH 6.1 Hz, -OCH2-),
3.40 (2 H, br s, -NH2), 3.25–3.07 (2 H, m, -CH2-), 1.86–1.54 (4 H,
m, -CH2-), 1.43 (9 H, s, -CH3). m/z (FD) 280.1 (M+).
3
3
Experimental
Syntheses and dimerization
Solvents and all other chemicals were purchased from Acros,
Aldrich and Lancaster, and used without further purification.
1H NMR spectra were recorded on a Bruker DRX400 Avance
instrument (at 400 MHz). FD and ESI mass spectra were measured
on a Finnigan MAT 8230 spectrometer and a Micromass Q-
ToF Ultima3 instrument, respectively. Melting points are un-
corrected. p-Tetraaminocalix[4]arene tetradecylether 1 and p-
tosyltetraurea tetrapentyl ether 5 were prepared according to
published procedures.45 Tetraloop-tetraurea calix[4]arenes 6 were
prepared as described.46
4-(10ꢀ-Undecenyloxy)acetamide. A suspension of 4-acetami-
dophenol (3.00 g, 19.8 mmol) and potassium carbonate (5.49 g,
39.7 mmol) in acetonitrile (150 ml) was refluxed for 1 hour.
11-Bromo-1-undecene (6.02 g, 25.8 mmol) was then added and
the mixture was refluxed for 48 hours. After evaporation the
product was extracted with CHCl3. The organic solution was
washed with aqueous sodium carbonate and water, and dried
(MgSO4). The residue obtained by evaporation was recrystallized
from acet◦onitrile–methanol, yielding the product (5.35 g, 89%).
1
3
Mp 89.5 C; H NMR (CDCl3), d: 7.35 (2 H, d, JHH 8.1 Hz,
Ar-H), 7.02 (1 H, s, N-H), 6.83 (2 H, d, 3JHH 8.1 Hz, Ar-H), 5.88–
p-(N-Phthalimidobutyloxy)nitrobenzene. A suspension of p-
nitrophenol (2.02 g, 14.5 mmol), potassium carbonate (2.21 g,
16 mmol) and bromobutylphthalimide (4.51 g, 16 mmol) in
acetonitrile (80 ml) was refluxed for 24 hours. The hot mixture was
filtered to remove potassium salts, and the filtrate was evaporated.
The oily residue was recrystallized from acetonitrile (50 ml) to
give◦the product (4.15 g, 84%) as white needles. Mp 120 ◦C (lit.,47
119 C); 1H NMR (CDCl3), d: 8.16 (2 H, d, 3JHH 8.8 Hz, Ar-H),
7.89–7.78 (2 H, m, Ar-H), 7.77–7.65 (2 H, m, Ar-H), 6.91 (2 H,
=
=
5.73 (1 H, m, -CH CH2), 5.04–4.86 (2 H, m, -CH CH2), 3.91
(2 H, t, 3JHH 6.2 Hz, -OCH2-), 2.14 (3 H, s, -CH3), 2.08–1.96 (2 H,
m, -OCH2CH2-), 1.82–1.67 (2 H, m, -CH2-), 1.49–1.17 (12 H, m,
-(CH2)6-). m/z (FD) 303.2 (M+).
4-(10ꢀ-Undecenyloxy)aniline 3c. A mixture of the O-alkylated
acetamide (5.35 g, 17.6 mmol) and sodium hydroxide (24.7 g,
617 mmol) was refluxed in EtOH (100 ml) and H2O (10 ml) for
12 h. The solvent was evaporated and the residue was partitioned
between ether and H2O. The organic layer was washed twice with
aqueous sodium carbonate and water and dried (MgSO4). The
residue obtained by evaporation, a brown solid (4.30 g, 93%), was
analytically pure and used in further reactions without additional
3
d, JHH 8.8 Hz, Ar-H), 4.08 (2 H, br t, -OCH2-), 3.77 (2 H, br t,
-OCH2-), 1.97–1.78 (4 H, m, -CH2-). m/z (FD): 340.3 (M+).
p-(Aminobutyloxy)nitrobenzene. A slurry of p-(phthalimido-
butyloxy)nitrobenzene (1.00 g, 2.92 mmol) and hydrazine hydrate
(7.2 ml, 147 mmol) in ethanol (50 ml) was refluxed for 4 hours.
After evaporation the product was extracted from the residue with
dichloromethane. The extract was washed with aqueous sodium
hydroxide and water and dried (MgSO4). Evaporation finally gave
the amine (0.50 g, 80%) as a yellow solid, which◦was used for
◦
1
purification. Mp 37–38 C; H NMR (CDCl3), d: 6.74 (2 H, d,
3
3JHH 8.8 Hz, Ar-H), 6.62 (2 H, d, JHH 8.8 Hz, Ar-H), 5.96–5.68
=
=
(1 H, m, -CH CH2), 5.12–4.85 (2 H, m, -CH CH2), 3.86 (2 H,
t, JHH 6.6 Hz, -OCH2-), 3.39 (2 H, br s, -NH2), 2.18–1.92 (2 H,
3
m, -OCH2CH2-), 1.87–1.56 (2 H, m, -CH2-), 1.54–1.15 (12 H, m,
1
-(CH2)6-). m/z (FD) 261.2 (M+).
the next step without further purification. Mp 40 C; H NMR
3
(CDCl3), d: 8.18 (2 H, d, JHH 9.2 Hz, Ar-H), 6.93 (2 H, d,
Calix[4]arene 2. The solution of tetraamine 1 (2.00 g,
1.91 mmol) in THF (15 ml) was added to the stirred solution of
4-nitrophenylchloroformate (2.55 g, 12.6 mmol) in CHCl3 (22 ml).
The reaction mixture was refluxed for 12 hours. After evaporation,
the residue was triturated with ethyl acetate and stored in a
refrigerator for 4–8 hours. The solid was filtered off, washed with
ethyl acetate and dried to give◦the pure product (2.65 g, 81%) as
3
3JHH 9.2 Hz, Ar-H), 4.06 (2 H, t, JHH 6.2 Hz, -OCH2-), 2.80
(2 H, t, 3JHH 6.8 Hz, -CH2NH2), 1.93–1.57 (6 H, m, -CH2-, -NH2).
m/z (FD) 210.1 (M+).
p-(tert-Butyloxycarbonylamidobutyloxy)nitrobenzene. A solu-
tion of p-(aminobutyloxy)nitrobenzene (1.50 g, 7.13 mmol) and
Boc-anhydride (1.56 g, 7.13 mmol) in THF (80 ml) was stirred at
rt for 24 h. The solvent was evaporated to give an oily residue,
which solidified after drying under vacuum (oil pump). The solid
was triturated with hexane, filtered and dried to give the N-Boc-
protected product (1.87 g, 84%) as yellowish powder. Mp 58–
60 ◦C; 1H NMR (CDCl3), d: 8.18 (2 H, d, 3JHH 9.2 Hz, Ar-H), 6.93
(2 H, d, 3JHH 9.2 Hz, Ar-H), 4.57 (1 H, br s, -NH-), 4.06 (2 H, t,
3JHH 6.2 Hz, -OCH2-), 3.25–3.13 (2 H, m, -CH2NH-), 1.90–1.80
(2 H, m, -CH2-), 1.72–1.62 (2 H, m, -CH2-), 1.43 (9 H, s, -CH3).
m/z (FD) 310.1 (M+).
1
light-yellow powder. Mp 181 C; H NMR (DMSO-d6), d: 9.93
3
(4 H, s, N-H), 8.18 (8 H, d, JHH 7.0 Hz, Ar-H), 7.35 (8 H, d,
3JHH 6.6 Hz, Ar-H), 6.90 (8 H, s, Ar-H), 4.33 (4 H, d, 2JHH 10.6 Hz,
ArCH2Ar), 3.78 (8 H, br s, -OCH2-), 3.08 (4 H, d, 2JHH 10.3 Hz,
ArCH2Ar), 1.87 (8 H, br s, -OCH2CH2-), 1.54–1.03 (56 H, m,
3
-CH2-), 0.84 (12 H, t, JHH 6.8 Hz, -CH3). m/z (FD) 1706.0
(M+).
Calix[4]arene 4a. N-Boc-1,4-phenylene diamine (0.081 g,
0.387 mmol), and diisopropylethylamine (0.050 g, 0.387 mmol)
in DMF (5 ml) were added to a stirred solution of 2 (0.132 g,
0.0774 mmol) in DMF (5 ml). The mixture was stirred at rt for
24 hours. The product was precipitated with water, filtered off
p-(tert-Butyloxycarbonylamidobutyloxy)aniline
Butyloxycarbonylamidobutyloxy)nitrobenzene
3b. p-(tert-
(1.80 g,
5.80 mmol) was dissolved in toluene (50 ml), a catalytic
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and washed several times with water. The crude product was
triturated with acetonitrile and the white powder was purified
by reprecipitation from THF–methanol, yielding the product
(0.137 g, 89%). Mp >195 ◦C (decomposition); 1H NMR (DMSO-
d6), d: 9.11 (4 H, s, N-H), 8.17 (4 H, s, N-H), 8.12 (4 H, s, N-H),
7.29 (8 H, d, 3JHH 8.4 Hz, Ar-H), 7.21 (8 H, d, 3JHH 9.2 Hz, Ar-H),
Calix[4]arene 4d. A solution of calixarene 4a (0.137 g,
0.0691 mmol) in dichloromethane (10 ml) and trifluoroacetic acid
(4 ml) was stirred at rt for 2 h. The solvent was evaporated and the
residue was triturated with Et2O. A solid was filtered off, washed
with Et2O and dried. The salt obtained was dissolved in THF
(10 ml), treated with an excess of Et3N (0.5 ml) and with a-lipoic
acid anhydride (prepared from a-lipoic acid (0.071 g, 0.345 mmol)
and DCC (0.036 g, 0.173 mmol) in benzene (5 ml) as described
in the literature48). The reaction mixture was stirred at rt for 2 h.
The solvent was evaporated and the residue was triturated with
methanol to give the pure product (0.120 g, 74%) as a yellowish
powder. Mp >190 ◦C (decomposition); 1H NMR (DMSO-d6), d:
9.07 (s, N-H, 4 H), 8.23 (4 H, s, N-H), 8.14 (4 H, s, N-H), 7.43
(8 H, d, 3JHH 8.8 Hz, Ar-H), 7.25 (8 H, d, 3JHH 8.4 Hz, Ar-H), 6.79
(8 H, s, Ar-H), 4.31 (4 H, d, 2JHH 11.0 Hz, ArCH2Ar), 3.90 (8 H,
m, -OCH2-), 3.90 (4 H, m, -SCH-), 3.23–2.97 (12 H, m, -SCH2-,
ArCH2Ar), 2.50–2.35 (8 H, m, -CH2-), 2.26 (8 H, br t, -CH2C(O)-),
2.02–1.80 (8 H, m, -CH2-), 1.78–1.48 (16 H, m, -CH2-), 1.49–1.14
(64 H, m, -CH2-), 0.85 (12 H, br t, -CH3). m/z (ESI) 2358.3 (M +
Na+), 1190.7 (M + 2Na+).
2
6.78 (8 H, s, Ar-H), 4.31 (4 H, d, JHH 12.1 Hz, ArCH2Ar), 3.80
(8 H, br t, -OCH2-), 3.08 (4 H, d, 2JHH 12.5 Hz, ArCH2Ar), 1.90
(8 H, m, -OCH2CH2-), 1.45 (36 H, s, -CH3), 1.42–1.15 (56 H, m,
-CH2-), 0.85 (12 H, br t, -CH3). m/z (ESI) 2005.3 (M + Na+),
1014.2 (M + 2Na+).
Calix[4]arene 4b. Prepared as described above for 4a from
2 (0.195 g, 0.114 mmol), aniline 3b (0.130 g, 0.464 mmol) and
diisopropylethylamine (0.070 g, 0.510 mmol) in DMF (10 ml);
reprec◦ipitation from THF–acetonitrile. Yield: 0.195 g (75%). Mp
>165 C (decomposition); 1H NMR (DMSO-d6), d: 8.11 (4 H, s,
N-H), 8.09 (4 H, s, N-H), 7.21 (8 H, d, 3JHH 8.9 Hz, Ar-H), 6.88–
6.69 (20 H, m, Ar-H, N-H), 4.31 (4 H, d, 2JHH 11.9 Hz, ArCH2Ar),
3.87 (8 H, t, 3JHH 6.3 Hz, -OCH2-), 3.79 (8 H, br t, -OCH2-), 3.07
(4 H, d, 2JHH 12.3 Hz, ArCH2Ar), 3.02–2.87 (8 H, m, -NHCH2-),
1.90 (8 H, m, -OCH2CH2-), 1.70–1.58 (8 H, m, -CH2-), 1.56–1.16
(100 H, m and s (1.36) overlapped, -CH2-, -CH3), 0.85 (12 H, br
t, 3JHH 6.3 Hz, -CH3). m/z (ESI) 2293.6 (M + Na+), 1158.3 (M +
2Na+).
Calix[4]arene 4e. A solution of calixarene 4b (0.100 g,
0.0440 mmol) in dichloromethane (10 ml) and trifluoroacetic acid
(1 ml) was stirred at rt for 2 h. The solvent was evaporated, the
residue dissolved in THF (15 ml), and then treated with an excess of
diisopropylethylamine (0.114 g, 0.880 mmol) and acetic anhydride
(0.045 g, 0.440 mmol). The reaction mixture was stirred for 12 h at
rt and evaporated. The oily residue was triturated with acetonitrile;
the solid was filtered off and dried to give the pure product (0.083 g,
93%) as a white powder. Mp >150 ◦C (decomposition); 1H NMR
(DMSO-d6), d: 8.13 (4 H, s, N-H), 8.11 (4 H, s, N-H), 7.82 (4 H, br
t, 3JHH 5.1 Hz, N-H), 7.22 (8 H, d, 3JHH 8.8 Hz, Ar-H), 6.86–6.71
Dimer (4b)2. 1H NMR (CDCl3), d: 9.20 (8 H, s, N-H), 7.70
3
(8 H, d, JHH 8.9 Hz, Ar-H), 7.60 (8 H, s, Ar-H), 7.03 (8 H, s,
N-H), 6.87 (16 H, d, 3JHH 8.9 Hz, Ar-H), 5.96 (8 H, s, Ar-H), 4.59
(8 H, br s, N-H), 4.22 (8 H, d, 2JHH 11.6 Hz, ArCH2Ar), 3.97–3.85
3
(16 H, m, -OCH2-), 3.65 (16 H, t, JHH 7.8 Hz, -OCH2-), 3.24–
3.06 (16 H, m, -NHCH2-), 2.82 (8 H, d, 2JHH 11.9 Hz, ArCH2Ar),
2.02–1.87 (16 H, m, -CH2-), 1.84–1.71 (16 H, m, -CH2-), 1.69–
1.53 (16 H, m, -CH2-), 1.43 (72 H, s, -CH3), 1.38–1.19 (112 H, m,
-CH2-), 0.88 (24 H, t, 3JHH 6.8 Hz, -CH3).
3
(16 H, m, Ar-H), 4.31 (4 H, d, JHH 12.2 Hz, ArCH2Ar), 3.88
(8 H, t, 3JHH 6.4 Hz, -OCH2-), 3.79 (8 H, br t, -OCH2-), 3.14–3.00
(12 H, m, -NHCH2-, ArCH2Ar), 1.98–1.84 (8 H, m, -CH2-), 1.78
(12 H, s, -CH3), 1.72–1.60 (8 H, m, -CH2-), 1.57–1.46 (8 H, m,
-CH2-), 1.46–1.17 (52 H, m, -CH2-), 0.86 (12 H, br t, 3JHH 6.6 Hz,
-CH3). m/z (ESI) 2061.4 (M + Na+), 1042.2 (M + 2Na+).
Calix[4]arene 4c. Prepared as described above for 4a from 2
(0.72 g, 0.42 mmol), aniline 3c (0.50 g, 1.9 mmol) and diisopropyl-
ethylamine (0.27 g, 2.1 mmol) in DMF (35 ml). Trituration with
acetonitrile gave the analytically pure product (0.63 g, 68%) as a
Calix[4]arene 4f. Prepared as described above for 4d from
calixarene 4b (0.195 g, 0.0859 mmol), a-lipoic acid (0.100 g,
0.504 mmol) and DCC (0.050 g, 0.252 mmol) in benzene (5 ml)
and THF (8 ml). When the oily product was triturated with
acetonitrile a solid formed, which was filtered off and dried to give
the pure product (0.156 g, 59%) as a white powder. Mp >145 ◦C
(decomposition); 1H NMR (DMSO-d6), d: 8.12 (s, N-H, 4 H), 8.09
(4 H, s, N-H), 7.78 (4 H, br t, N-H), 7.22 (8 H, d, 3JHH 8.2 Hz, Ar-
H), 6.94–6.63 (16 H, m, Ar-H), 4.43–4.17 (4 H, br d, ArCH2Ar),
3.97–3.66 (16 H, m, -OCH2-), 3.58 (4 H, m, -SCH-), 3.20–2.89
(12 H, m, -SCH2-, ArCH2Ar), 2.50–2.28 (8 H, m, -CH2-), 2.04
(8 H, br t, -CH2C(O)-), 1.96–1.74 (8 H, m, -CH2-), 1.73–1.05
(80 H, m, -CH2-), 0.85 (12 H, br t, -CH3). m/z (MALDI-ToF)
2623.4 (M+).
◦
1
white powder. Mp 155 C (decomposition); H NMR (DMSO-
d6, 80 ◦C), d: 7.89 (4 H, s, N-H), 7.84 (4 H, s, N-H), 7.21
(8 H, d, JHH 8.7 Hz, Ar-H), 6.80 (8 H, s, Ar-H), 6.77 (8 H, d,
JHH 8.7 Hz, Ar-H), 5.87–5.73 (4 H, m, CH CH2), 5.04–4.87
(8 H, m, CH CH2), 4.38 (4 H, d, JHH 12.6 Hz, ArCH2Ar), 3.97–
3
3
=
2
=
2
3.81 (16 H, m, -OCH2-), 3.09 (4 H, d, JHH 12.9 Hz, ArCH2Ar),
2.07–1.97 (8 H, m, -OCH2CH2-), 1.96–1.83 (8 H, m, -OCH2CH2-),
1.74–1.62 (8 H, m, -CH2-), 1.49–1.19 (104 H, m, -CH2-), 0.88
(12 H, br t, -CH3). m/z (ESI) 2217.7 (M + Na+).
Dimer (4c)2. 1H NMR (CDCl3), d: 9.22 (8 H, s, N-H), 7.71
3
2
(8 H, d, JHH 8.8 Hz, Ar-H), 7.60 (8 H, d, JHH 2.4 Hz, Ar-H),
7.02 (8 H, s, N-H), 6.87 (16 H, d, 3JHH 8.8 Hz, Ar-H), 5.94 (8 H,
d, JHH 2.4 Hz, Ar-H), 5.86–5.74 (8 H, m, CH CH2), 5.02–4.88
2
Heterodimer 4f·5. 1H NMR (TCE), d: 10.62 (4 H, s, N-H),
=
2
(16 H, m, CH CH2), 4.20 (8 H, d, JHH 11.2 Hz, ArCH2Ar), 3.94–
8.12 (8 H, d, 3JHH 8.0 Hz, Ar-H), 8.02 (4 H, s, N-H), 7.91 (8 H, s,
=
3.82 (16 H, m, -OCH2-), 3.64 (16 H, br t, 3JHH 8.1 Hz, -OCH2-),
2.81 (8 H, d, 2JHH 11.7 Hz, ArCH2Ar), 2.07–1.99 (16 H, m, -CH2-),
1.98–1.87 (16 H, m, -CH2-), 1.78–1.67 (16 H, m, -CH2-), 1.48–1.19
(208 H, m, -CH2-), 0.88 (24 H, t, 3JHH 6.8 Hz, -CH3).
N-H, Ar-H), 7.59 (8 H, d, JHH 8.3 Hz, Ar-H), 6.50 (8 H, d,
3
3JHH 8.4 Hz, Ar-H), 7.41 (4 H, s, N-H), 6.98 (8 H, s, Ar-H), 6.66
3
3
(8 H, d, JHH 9.1 Hz, Ar-H), 7.48 (4 H, t, JHH 5.6 Hz, N-H),
2
5.26 (4 H, s, Ar-H), 4.54 (4 H, d, JHH 11.5 Hz, ArCH2Ar), 4.09
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2
(4 H, d, 2JHH 11.1 Hz, ArCH2Ar), 4.01–3.65 (16 H, m, -OCH2-),
3.65–3.48 (10 H, m, -OCH2-, -SC*H-), 3.38 (4 H, d, 2JHH 11.1 Hz,
ArCH2Ar), 3.32–3.08 (18 H, m, -NHCH2-, -SCH2-, -SC*H-), 2.71
(4 H, d, 2JHH 12.5 Hz, ArCH2Ar), 2.59–2.32 (20 H, m and s (2.52)
overlapped, -CH3, -CH2-), 2.22–2.02 (16 H, m, -CH2-), 2.00–1.10
(120 H, m, -CH2-), 1.00–0.78 (24 H, m, -CH3).
2.93 (8 H, d, JHH 11.7 Hz, ArCH2Ar), 2.82 (10 H, s, included
3
cobaltocenium), 2.48 (32 H, t, JHH 7.1 Hz, -SCH2-), 2.00–1.86
(16 H, m, -CH2-), 1.78–1.66 (16 H, m, -CH2-), 1.62–1.48 (16 H, m
under water peak, -CH2-), 1.48–1.14 (352 H, m, -CH2-), 0.98–0.82
(48 H, m, -CH3).
Complex of dimer (4g)2 with tetraethylammonium. 1H NMR
(CD2Cl2), d: 8.95 (8 H, s, N-H), 7.79 (24 H, d and s overlapped,
Calix[4]arene 4g. The solution of calixarene 4c (0.31 g,
3JHH 9.3 Hz, Ar-H), 7.00 (16 H, d, JHH 8.8 Hz, Ar-H), 6.36
3
0.14 mmol), 1-decanethiol (0.30 g, 1.7 mmol) in THF (10 ml)
(8 H, s, N-H), 5.61 (8 H, br s, Ar-H), 4.33 (8 H, d, 2JHH 11.7 Hz,
◦
was degassed with nitrogen and cooled to 0–5 C. Then a 0.5 M
3
ArCH2Ar), 3.90 (16 H, m, JHH 6.1 Hz, -OCH2-), 3.76 (16 H, t,
solution of 9-BBN in THF (0.2 ml, 0.1 mmol) was added and
the reaction mixture was stirred for 24 h while being allowed to
warm to rt. The residue obtained after evaporation was triturated
with acetonitrile. The solid formed was filtered off and dried to
give the pure sulfide (0.25 g, 60%) as a white powder. Mp 104 ◦C
3JHH 8.1 Hz, -OCH2-), 2.97 (8 H, d, JHH 12.2 Hz, ArCH2Ar),
2
2.47 (32 H, t, 3JHH 7.3 Hz, -SCH2-), 2.03–1.86 (16 H, m, -CH2-),
1.78–1.64 (16 H, m, -CH2-), 1.62–1.48 (16 H, m under water peak,
-CH2-), 1.48–1.17 (352 H, m, -CH2-), 1.14 (4 H, br s, included
Et4N+, N-CH2-), 0.98–0.82 (48 H, m, -CH3), 0.50 (4 H, br s,
included Et4N+, N-CH2-), –0.15 (6 H, br s, included Et4N+,
N-CH3), –3.29 (6 H, br s, included Et4N+, N-CH3).
1
(decomposition); H NMR (DMSO-d6/CDCl3), d: 8.02 (8 H, s,
N-H), 7.18 (8 H, d, 3JHH 8.8 Hz, Ar-H), 6.76 (8 H, s, Ar-H), 6.71
(8 H, d, 3JHH 8.8 Hz, Ar-H), 4.33 (4 H, d, 2JHH 12.7 Hz, ArCH2Ar),
4.00–3.59 (16 H, m, -OCH2-), 3.04 (4 H, d, 2JHH 11.7 Hz, Ar-CH2-
Ar), 2.41 (16 H, t, -SCH2-), 1.90 (8 H, m, -OCH2CH2-), 1.77–0.99
(192 H, m, -CH2-), 0.96–0.70 (24 H, m, -CH3). m/z (ESI) 2915.4
(M + Na+), 1469.2 (M + 2Na+).
Complex of heterodimer 4g·5 with cobaltocenium. 1H NMR
(CD2Cl2), d: 11.16 (4 H, s, N-H), 8.40 (4 H, s, N-H), 8.14 (8 H,
3
d, JHH 8.3 Hz, Ar-H), 7.93 (4 H, s, N-H), 7.84 (4 H, br s, Ar-
H), 7.59 (8 H, d, JHH 9.3 Hz, Ar-H), 7.53 (8 H, d, JHH 8.3 Hz,
Ar-H), 7.50 (4 H, s, N-H), 7.11 (4 H, br s, Ar-H), 7.00 (4 H,
3
3
Homodimer (4g)2. 1H NMR (CDCl3), d: 9.22 (8 H, s, N-H),
7.71 (8 H, d, 3JHH 8.2 Hz, Ar-H), 7.60 (8 H, s, Ar-H), 7.02 (8 H, s,
N-H), 6.87 (16 H, d, 3JHH 8.2 Hz, Ar-H), 5.94 (8 H, s, Ar-H), 4.21
(8 H, d, 2JHH 11.0 Hz, ArCH2Ar), 3.99–3.79 (16 H, m, -OCH2-),
3.64 (16 H, br t, -OCH2-), 2.81 (8 H, d, 2JHH 11.0 Hz, ArCH2Ar),
2.48 (32 H, t, 3JHH 7.0 Hz, -SCH2-), 2.03–1.84 (16 H, m, -CH2-),
1.81–1.65 (16 H, m, -CH2-), 1.65–1.02 (368 H, m, -CH2-), 1.00–
0.75 (48 H, m, -CH3).
3
br s, Ar-H), 6.69 (8 H, d, JHH 8.8 Hz, Ar-H), 4.86 (4 H, br s,
2
Ar-H), 4.64 (4 H, d, JHH 11.7 Hz, ArCH2Ar), 4.09 (4 H, d,
2JHH 11.7 Hz, ArCH2Ar), 4.04–3.87 (8 H, m, -OCH2-), 3.80–3.65
(8 H, m, -OCH2-), 3.56 (8 H, t, 3JHH 7.8 Hz, -OCH2-), 3.37 (4 H, d,
2JHH 12.2 Hz, ArCH2Ar), 3.05 (10 H, s, included cobaltocenium),
2
2.69 (4 H, d, JHH 11.7 Hz, ArCH2Ar), 2.53 (12 H, s, -CH3),
3
2.52–2.44 (16 H, t (2.49) and t (2.48) overlapped, JHH 7.3 Hz
and JHH 7.3 Hz, -SCH2-), 2.14–2.00 (8 H, m, -CH2-), 2.85–1.72
(8 H, m, -CH2-), 1.66–1.49 (8 H, m, -CH2-), 1.48–1.16 (200 H, m,
-CH2-), 1.00–0.78 (36 H, m, -CH3).
3
Heterodimer 4g·5. 1H NMR (C6D6), d: 11.10 (4 H, s, N-H),
8.66 (4 H, s, N-H), 8.56 (4 H, s, Ar-H), 8.53 (4 H, s, N-H), 8.19
3
3
(8 H, d, JHH 7.8 Hz, Ar-H), 7.96 (8 H, d, JHH 8.8 Hz, Ar-H),
7.85 (4 H, s, N-H), 7.77 (4 H, s, Ar-H), 7.51 (4 H, s, Ar-H),
Complex of heterodimer 4g·6 with cobaltocenium. 1H NMR
(CD2Cl2), d: 9.14 (4 H, s, N-H), 9.01 (4 H, s, N-H), 7.81 (4 H, s,
Ar-H), 7.79 (8 H, d, 3JHH 8.8 Hz, Ar-H), 7.67 (4 H, s, Ar-H), 7.44
3
3
6.78 (8 H, d, JHH 8.3 Hz, Ar-H), 6.68 (8 H, d, JHH 8.8 Hz, Ar-
2
H), 5.55 (4 H, s, Ar-H), 4.92 (4 H, d, JHH 11.2 Hz, ArCH2Ar),
3
(4 H, s, Ar-H), 7.06 (4 H, s, N-H), 7.03 (8 H, d, JHH 8.8 Hz,
4.28 (4 H, d, 2JHH 11.2 Hz, ArCH2Ar), 4.07 (8 H, t, 3JHH 7.6 Hz,
Ar-H), 6.71 (4 H, s, Ar-H), 6.52 (4 H, s, N-H), 6.19 (4 H, s,
Ar-H), 5.68 (4 H, s, Ar-H), 5.43 (4 H, s, Ar-H), 4.25 (4 H, d,
2JHH 11.7 Hz, ArCH2Ar), 4.27 (4 H, d, 2JHH 11.7 Hz, ArCH2Ar),
4.09–3.61 (44 H, m, -OCH2-, -OCH3), 2.98 (4 H, d, 2JHH 12.1 Hz,
ArCH2Ar), 2.86–2.73 (14 H, d and s of included cobaltocenium
overlapped, ArCH2Ar), 2.48 (16 H, m, 3JHH 6.6 Hz, -SCH2-), 1.99–
1.65 (32 H, m, -CH2-), 1.62–0.98 (232 H, m, -CH2-), 0.97–0.80
(24 H, m, -CH3).
2
-OCH2-), 3.96 (4 H, d, JHH 11.7 Hz, ArCH2Ar), 3.57 (8 H, t,
3JHH 7.8 Hz, -OCH2-), 3.53–3.43 (4 H, m, -OCH2-), 3.43–3.32 (4 H,
2
m, -OCH2-), 3.01 (4 H, d, JHH 11.7 Hz, ArCH2Ar), 2.50–2.39
(16 H, m, -SCH2-), 2.38–2.25 (8 H, m, -CH2-), 2.02–1.90 (8 H,
m, -CH2-), 1.85 (12 H, s, -CH3), 1.69–1.09 (208 H, m, -CH2-),
1.03–0.95 (24 H, m, -CH3), 0.92 (12 H, t, 3JHH 7.1 Hz, -CH3).
Heterodimer 4g·6. 1H NMR (C6D6), d: 10.08 (4 H, s, N-H),
9.75 (4 H, s, N-H), 8.22 (4 H, s, Ar-H), 8.17 (4 H, s, Ar-H), 8.08
(8 H, d, 3JHH 8.8 Hz, Ar-H), 7.97 (4 H, s, Ar-H), 7.49 (4 H, s, N-H),
7.27 (4 H, s, Ar-H), 7.01 (4 H, s, N-H), 6.84 (8 H, d, 3JHH 8.3 Hz,
Ar-H), 6.54 (4 H, s, Ar-H), 6.36 (4 H, s, Ar-H), 6.31 (4 H, s, Ar-H),
4.45 (4 H, d, 2JHH 11.7 Hz, ArCH2Ar), 4.32 (4 H, d, 2JHH 11.7 Hz,
ArCH2Ar), 4.15–3.40 (44 H, m, -OCH2-, -OCH3), 3.33–3.08 (8 H,
m, ArCH2Ar), 2.43 (16 H, m, -SCH2-), 2.15–1.94 (8 H, m, -CH2-),
1.80–1.04 (256 H, m, -CH2-), 1.03–0.82 (24 H, m, -CH3).
Preparation and physical characterization of SAMs
The necessary gold substrates (99.99%, the Royal Canadian
Mint) for surface plasmon spectroscopy and electrochemistry
were prepared using an e-beam sputtering system (HOSER) at
a pressure around 5 × 10−6 torr.
For the formation of SAMs, the gold films were immersed for
15–25 h into the following solutions: a) 10 lM of 4g or 4f in
THF for SAMs of a single calix[4]arene; b) 10 lM of 4g or
4f, and 5, in chloroform or dichloromethane for SAMs of the
heterodimeric capsules 4g·5 and 4f·5 with the solvent as guest;
c) for heterodimeric capsules 4g·5 with ferrocenium cation as
guest, a 0.1 mM solution in dichloromethane was used, which
Complex of dimer (4g)2 with cobaltocenium. 1H NMR
(CD2Cl2), d: 9.03 (8 H, s, N-H), 7.75 (24 H, d and s overlapped, 3JHH
8.4 Hz, Ar-H), 6.99 (16 H, d, 3JHH 8.8 Hz, Ar-H), 6.74 (8 H, s, N-
H), 5.64 (8 H, br s, Ar-H), 4.34 (8 H, d, 2JHH 11.7 Hz, ArCH2Ar),
3.98–3.82 (16 H, m, -OCH2-), 3.74 (16 H, t, 3JHH 7.1 Hz, -OCH2-),
566 | Org. Biomol. Chem., 2007, 5, 558–568
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was prepared with 15% excess of 5 and 20% excess of ferrocenium
hexafluorophosphate.
15 V. Bo¨hmer and M. O. Vysotsky, Aust. J. Chem., 2001, 54, 671–677; L. C.
Palmer and J. Rebek, Jr., Org. Biomol. Chem., 2004, 2, 3051–3059; J.
Rebek, Jr., Angew. Chem., Int. Ed., 2005, 44, 2068–2078.
16 For reviews, see: J. Rebek, Jr., Chem. Commun., 2000, 637–643;
A. Bogdan, Y. Rudzevich, M. O. Vysotsky and V. Bo¨hmer, Chem.
Commun., 2006, 2941–2952.
17 For recent publications, see: Y. Rudzevich, M. O. Vysotsky, V. Bo¨hmer,
M. S. Brody, J. Rebek, Jr., F. Broda and I. Thondorf, Org. Biomol.
Chem., 2004, 2, 3080–3084; F. Broda, M. O. Vysotsky, V. Bo¨hmer and
I. Thondorf, Org. Biomol. Chem., 2006, 4, 2424–2432; Y. Rudzevich, V.
Rudzevich, C. Moon, I. Schnell, K. Fischer and V. Bo¨hmer, J. Am.
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13137.
18 O. Mogck, E. F. Paulus, V. Bo¨hmer, I. Thondorf and W. Vogt, Chem.
Commun., 1996, 2533–2534; I. Thondorf, F. Broda, K. Rissanen, M. O.
Vysotsky and V. Bo¨hmer, J. Chem. Soc., Perkin Trans. 2, 2002, 1796–
1800.
19 For reviews, see: A. Ulman, Chem. Rev., 1996, 96, 1533–1554.
20 E. B. Troughton, C. D. Bain, G. M. Whitesides, D. L. Allara and M. D.
Porter, Langmuir, 1988, 4, 365–385; E. Katz, N. Itzhak and I. Willner,
J. Electroanal. Chem., 1992, 336, 357–362.
Surface plasmon spectroscopy experiments were performed
using a home-built surface plasmon spectrophotometer, which
is described elsewhere.7–9,40,41 Absorption spectra were measured
with a Perkin Elmer Lambda 850 spectrometer with clean glass as
reference. A ToF-SIMS (model VI of ION-ToF GmbH, Germany)
with a primary ion beam of Cs at 9 keV was used to obtain the
mass data.
For the electrochemical coverage measurements, a solution
was made of 0.9 mM ferrocene in methanol and 0.1 M KCl as
supporting electrolyte in Milli-Q-water. The electrochemical cell
consisted of a Teflon cylinder with a working electrode at the
bottom. The measurements were performed on an electrochemical
analyzer (CH610A, CH Instruments, Austin, Texas) in a three-
electrode system: gold working electrode (0.845 cm2), a platinum
counter-electrode, and a Ag/AgCl reference electrode. The scan
rate was 20 mV s−1, and the potential range (vs. Ag/AgCl) was
0.45 V.
21 R. G. Nuzzo and D. L. Allara, J. Am. Chem. Soc., 1983, 105, 4481–
4483.
22 J. K. Schoer and R. M. Crooks, Langmuir, 1997, 13, 2323–2332; F.
Cavadas and M. R. Anderson, J. Colloid Interface Sci., 2004, 274, 365–
370; X.-M. Li, T. Auletta, F. C. J. M. van Veggel, J. Huskens and D. N.
Reinhoudt, Org. Biomol. Chem., 2004, 2, 296–300.
Acknowledgements
23 M. A. Bryant, S. L. Joa and J. E. Pemberton, Langmuir, 1992, 9, 753–
756; E. Sabatani, J. Cohen-Boulakia, M. Bruening and I. Rubinstein,
Langmuir, 1993, 9, 2974–2981.
24 W. Hill and B. Wehling, J. Phys. Chem., 1993, 97, 9451–9455; S.
Bharathi, V. Yegnaraman and G. P. Rao, Langmuir, 1993, 9, 1614–
1617.
25 B. H. Huisman, E. U. T. van Velzen, F. C. J. M. van Veggel, J. F. J.
Engbersen and D. N. Reinhoudt, Tetrahedron Lett., 1995, 36, 3273–
3276.
26 E. U. T. van Velzen, J. F. J. Engbersen and D. N. Reinhoudt, J. Am.
Chem. Soc., 1994, 116, 3597–3598; E. U. T. van Velzen, J. F. J.
Engbersen, P. J. de Lange, J. W. G. Mahy and D. N. Reinhoudt, J. Am.
Chem. Soc., 1995, 117, 6853–6862.
The authors like to thank Nancy Bell and Rick Glew from the
Nanofabrication Facility at The University of Western Ontario
(UWO) for the fabrication of some of the gold substrates, as
well as Heng-Yong Nie from Surface Science Western (UWO)
for the ToF-SIMS measurements. The authors like to thank
NSERC, the Ontario Photonics Consortium (through Ontario
Research and Development Challenge Fund (ORDCF)), CFI
and OIF, the Canadian CRC program, as well as the Deutsche
Forschungsgemeinschaft (SFB 625) for financial support.
27 B. H. Huisman, D. M. Rudkevich, F. C. J. M. van Veggel and D. N.
Reinhoudt, J. Am. Chem. Soc., 1996, 118, 3523–3524.
28 B. H. Huisman, D. M. Rudkevich, A. Farrn, W. Verboom, F. C. J. M.
van Veggel and D. N. Reinhoudt, Eur. J. Org. Chem., 2000, 269–
274.
29 J. J. Garcia-Lopez, S. Zapotoczny, P. Timmerman, F. C. J. M van Veggel,
G. J. Vansco, M. Crego-Calama and D. N. Reinhoudt, Chem. Commun.,
2003, 352–353.
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