Calix[6]arene mono-diazonium salt synthesis and covalent immobilization onto glassy carbon electrodes

Article abstract of DOI:10.1016/j.tetlet.2014.06.043

This Letter describes the fast synthesis of a mono-aminated calix[6]arene. The immobilization of this macrocycle onto glassy carbon electrodes via diazonium salt chemistry and the electrochemical characterization of the grafted organic layer are also reported.

Full text of DOI:10.1016/j.tetlet.2014.06.043

Accepted Manuscript
Calix[6]arene mono-diazonium salt synthesis and covalent immobilization onto
glassy carbon electrodes
Caroline Cannizzo, Mathieu Wagner, Jean-Philippe Jasmin, Christine Vautrin-
Ul, Denis Doizi, Christine Lamouroux, Annie Chaussé
PII:
S0040-4039(14)01034-X
DOI:
http://dx.doi.org/10.1016/j.tetlet.2014.06.043
TETL 44767
Reference:
Tetrahedron Letters
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Received Date:
Revised Date:
Accepted Date:
24 March 2014
5 June 2014
6 June 2014
Please cite this article as: Cannizzo, C., Wagner, M., Jasmin, J-P., Vautrin-Ul, C., Doizi, D., Lamouroux, C.,
Chaussé, A., Calix[6]arene mono-diazonium salt synthesis and covalent immobilization onto glassy carbon
electrodes, Tetrahedron Letters (2014), doi: http://dx.doi.org/10.1016/j.tetlet.2014.06.043
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Calix[6]arene mono-diazonium salt synthesis
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and covalent immobilization onto glassy carbon electrodes
Caroline Cannizzo, Mathieu Wagner, Jean-Philippe Jasmin, Christine Vautrin-Ul, Denis Doizi, Christine
Lamouroux, Annie Chaussé

1
Tetrahedron Letters
journal homepage: www.elsevier.com
Calix[6]arene mono-diazonium salt synthesis and covalent immobilization onto
glassy carbon electrodes
Caroline Cannizzoa*, Mathieu Wagnerb, Jean-Philippe Jasmina, Christine Vautrin-Ula, Denis Doizib,
Christine Lamourouxb, Annie Chausséa
a
Laboratoire Analyse et Modélisation pour la Biologie et l’Environnement, UMR 8587, CNRS-Université Evry val d’Essonne-CEA, 1 rue du père Jarlan, 91025
Evry Cedex, France
b
DEN/DPC/SECR/LRMO, CEA Saclay, Gif sur Yvette 91191, France
* Corresponding author. Tel.:+33(0)1 69 47 02 22. E-Mail address: caroline.cannizzo@univ-evry.fr
ARTICLE INFO
ABSTRACT
This paper describes the fast synthesis of a mono-aminated calix[6]arene. The immobilization of
this macrocycle onto glassy carbon electrodes via diazonium salt chemistry and the
electrochemical characterization of the grafted organic layer are also reported.
Article history:
Received
Received in revised form
Accepted
Available online
2009 Elsevier Ltd. All rights reserved.
Keywords:
Calix[6]arene
Diazonium salt
Electrochemical grafting
Covalent modification of carbon electrodes
1. Introduction
The calixarene can be either incorporated into the electrode
material, or placed at the electrode surface by various methods.
Functional electrodes are of great importance in several
research areas, and especially for sensing purposes. The binding
of complexing groups at the surface of the electrode allows the
pre-concentration of the analyte, and thus ensures a better
electrochemical response. In this context, the use of diazonium
salts offers a very versatile method for the covalent grafting of
several organic functions at the surface of conductive
For example, calix[6]arene and an intermolecular complex
between calix[6]arene and methyl viologen were incorporated to
carbon paste modified electrodes, respectively for the detection
of folic acid or the electroanalytical reduction of dioxygen.9,10
Calix[6]arene was incorporated as dopant in polypyrrole for
uranyl complexation11 or, together with TOPO ligand, was
incorporated into a PVC membrane for the preparation of ion
selective electrodes.12 Langmuir-Blodgett films of calix[4]arene
were developed for mercury detection.13 Becker et al. described
2
electrodes.1, Our group recently reported the grafting of 4-
carboxyphenyl diazonium salt for the detection of pollutants such
as copper, lead or uranyl.3-5 In order to ensure a better selectivity
of our sensors, we are now looking for molecules which are more
selective towards a selected analyte. The complexing properties
of macrocycles have been extensively studied, as the size of their
cavity can be carefully choosen to host the desired analyte.
Calixarenes are known as good chelatants for metallic ions, and
especially calix[6]arene has a well-known affinity for the uranyl
ion.6, 7,8 (Scheme 1) Calixarene-grafted electrodes would thus be
of interest for the detection of uranyl in water.
the use of
a negatively charged p-sulfonatocalix[6]arene
interacting with a positively charged monolayer at the surface of
an electrode, for uranyl detection.14 For analytical applications,
the use of more robust bonds than simple electrostatic
interactions are required. Gold electrodes can be easily modified
by SAMs, and several examples of thiolated calixarene
derivatives can be found in the literature:
a thiolated
calix[4]arene derivative was very recently assembled at an
electrode surface for impedimetric biological assay15 , or for the
development of lead9 or uranyl16 sensors. However, for
electroanalytical purposes, thiols present an inconvenient due to
their possible oxidation. Calix[4]arenes bearing polypyrrole
moieties were also polymerized at an electrode.17, 18 The phenolic
moieties of the calixarene itself were also used for its
electropolymerisation at an electrode surface.19 Cailler and
Simonao also patented calix[4]arene derivative bearing pendant
Scheme 1: Structure of calix[6]arene

2
Tetrahedron Letters
arms functionalized by diazonium salts for cesium
complexation.20
2.2. Synthesis of the diazonium salt of calix[6]arene
With uranyl complexation in mind, covalent grafting of the
22
calix[6]arene via the lower rim21,
is impossible as it fully
Diazonium salts are relatively unstable and are mostly used as
obtained in further reactions. Their formation are usually
performed using diazotization agents in acidic water or
acetonitrile.1 In our case, both of the above conditions were
tested on mono-amino calix[6]arene 5, despite its low solubility
in these solvents, even, in a case acetonitrile/sulfolane mixture
(Table 1). There are indeed, to the best of our knowledge, very
few studies reporting the synthesis of diazonium salts in other
solvents. Thus, the formation of diazonium derivative 6 was
performed using NaNO2 in aqueous HBF4 or NOBF4 in
acetonitrile as diazotization agents. As diazonium salt 6 may be
unstable, the reactions were performed at low temperature and
isolated with tetrafluoroborate as counterion.29
participates to the complexation of the metal ions. The upper ring
must thus be functionalized, and the lower ring has to remain
free. Lagrost et al. have recently reported the covalent grafting of
a calix[4]arene, as a template for the nanostructuration of
surfaces.23 The grafting was realized via the formation of a tetra-
diazonium salt at the upper ring of the calixarene, and the
subsequent electrografting on a glassy carbon surface. The
number of anchoring points is not determined in that case, but is
probably more than one per molecule. If one considers detection
applications, the number of grafting points on the calix[6]arene
should not be too elevated; in the case of calix[6]arene the
complexation of ions is not due to the presence of pendant
complexing arms, but to the size of the calixarene cavity itself. In
order to allow the free conformational movements of the
calix[6]arene, the anchoring of the macromolecule by only one
point was preferred, in order to avoid any excess of rigidity in the
film structure. We thus envisaged the synthesis of a calix[6]arene
bearing only one diazonium group. The synthesis was envisaged
as follow: first, the mono-nitration of the calix[6]arene, then the
reduction of the nitro group and finally the formation of the
diazonium salt in order to allow the electrografting of the
macrocycle at the surface of a glassy carbon electrode. Our
results are reported herein.
Table 1. Synthesis of the diazonium salta
N2BF4
diazotization
agent
1.1 equiv
grafting
5
*
0°C
*
5
OH
OH
6
diazotization
agent
Solvent
conditions
reaction
time
Entry
1
CH3CN/(CH2)4SO2
1/1
NOBF4
0.5 h
2. Discussion
aqueous HBF4
10 wt%
2
NaNO2
4 h
2.1. Synthesis of the mono-amino calix[6]arene
aThe crude diazonium salt 6 was engaged as obtained in the grafting step
We chose to use a protection-deprotection procedure: five of
the six phenol groups of the calix[6]arene were protected by
benzoyl groups. This reaction leads to penta-O-benzoylated
calix[6]arene 2 in 55% yield.24 In a second step, mono-nitration
Upon addition of NOBF4 in a suspension of calix-6-arene in an
acetonitrile/sulfolane30 1/1 mixture, the reactants become soluble
and the medium quickly turns to a reddish solution. The desired
product 6 was then obtained by precipitation in diethyl ether
(table 1, entry 1). The experiment was also conducted in a
fluoroboric acid aqueous solution (table 1, entry 2). In this case
the calix[6]arene stays insoluble even after the addition of
sodium nitroxide, and we thus allowed the reaction to be
performed in heterogeneous medium during 4 hours.
Both experiments lead to the formation of diazonium salt 6.
The infrared spectra (see Supplementary Information) showed
in each case the expected characteristic νN=N band at 2222 cm-1. It
is interesting to note that the reaction could be performed in
water despite the lack of solubility of the starting material and of
the desired product.
was then realized with 1.1 equivalent of nitric acid in an acetic
26
acid/dichloromethane mixture to 325,
As expected, mono-
nitration occurred selectively on the para position of the more
reactive free phenol group.27 Compound 3 was the only
compound obtained and the crude was used without further
purification. Hydrolysis of the benzoyl groups was conducted in
a mixture of sodium hydroxide and ethanol, under reflux. At first
insoluble, the penta-protected calix[6]arene became soluble upon
deprotection, leading to the fully deprotected derivative 4 in a
57% yield (two steps). Reduction of the nitro moiety of
compound 4 was performed by zinc dust with hydrazinium
monoformate as hydrogen donor in methanol, at 60°C28 to give
the mono-aminated calix[6]arene 5 in a 70% yield. (Scheme 2)
2.3. Grafting of calix[6]arene on glassy carbon electrode
As it was mentioned before, the solubility of the diazonium salt
of calix[6]arene is very low in acidic water. As a consequence,
the electrografting experiments were performed in acetonitrile.
The grafting step was performed by cyclic voltammetry (10
cycles), from the open circuit potential to – O.9V, using a 1 mM
solution of diazonium salt in
a acetonitrile solution of
tetrabutylammonium tetrafluoroborate (NBu4BF4, 0.1M) as a
supporting electrolyte.
The cyclic voltammogram (Figure 1) shows
a broad
irreversible wave (around – 0.4V) on the first scan that
disappears after a few cyclic voltammetry scans. This behavior is
characteristic of the grafting of diazonium salts: the
disappearance of the wave corresponds to the formation of an
organic layer on the surface that blocks the access of the
diazonium cations to the electrode. Electrode rinsing under
sonication in acetonitrile was performed in order to remove
organic compounds adsorbed but not grafted on the surface.
Scheme 2: Synthetic method. Reagents and conditions: (i) BzCl (5.1
equiv), pyridine, rt, overnight, 55%; (ii) nitric acid (1.1 equiv),
dichloromethane/acetic acid: (3/1), 0 °C, 2 hours then rt, overnight;
(iii) NaOH 15 wt%, EtOH, reflux, 7 hours, 57%; (iv) hydrazinium
monoformate (7 mL), zinc dust (0.9 g), MeOH, 60°C, overnight. Bz
= benzoyl.

3
due to the size of the macrocycle; steric hindrance may account
for the quite low capacitance value and the possible observation
of electrochemical processes at the grafted electrode. This was
already observed by Sustrova et al. who showed by cyclic
voltammetry and EIS that tetra-thiolated calix[4]arene form less
compact monolayers at polycrystalline gold surface than linear
undecanethiol.31
Figure 1: Cyclic voltammograms (first cycles, 0.1 V.s-1.) in ACN +
0.1 M NBu4BF4 at glassy carbon electrode with (black) or without
(grey, dotted line) 1 mM Calix[6]arene diazonium salt.
In order to study the electrochemical behavior of the grafted
electrode, cyclic voltammetry (CV) and electrochemical
impedance spectroscopy (EIS) were performed with grafted
electrodes into electrolyte solutions containing a redox probe, i.e.
potassium ferricyanide.
As can be seen in Figure 2 and Figure 3, significant differences in
the CV and EIS spectra were observed between calixarene-
grafted electrodes and control experiments, whereby similar
electrochemical procedure was performed but in a calixarene-free
solution.
Figure 3: Nyquist plots of electrochemical impedance spectra
obtained at glassy carbon electrode after cycling in a 0.1M
acetonitrile solution of NBu4BF4 with (black) or without (grey)
calix[6]arene in the presence of 1 mM K3Fe(CN)6 electrochemical
probe + 0.1 M KCl aqueous solution. Fixed potential of 180 mV ± 10
mV within the frequency range of 102-106 Hz, 5 points per decades
of frequencies.
For the control non-grafted electrode, cyclic voltammetry in the
presence of ferricyanide probe shows well-defined reduction and
oxidation peaks, with a low peak-to peak potential separation (i.e.
ΔE equals to 75 mV), suggesting a fast and reversible electron
transfer process. In the case of the calixarene-grafted electrode,
the increase in the electron transfer resistance can be detected by
a significant drop in the anodic and cathodic peak currents,
accompanied by an important shift in peak potentials. These
observations are characteristic of a decrease in the electron
transfer kinetics of the ferricyanide probe, due to the blocking
effect of the grafted organic layer.
3. Conclusion
In summary, mono-aminated calix[6]arene was synthesized
and its corresponding diazonium salt was successfully
electrografted at the surface of glassy carbon electrodes.
Characterization of the resulting electrodes shows an expected
blocking effect of the grafted organic layer and the value of the
observed charge transfer resistance suggest that it is probably of
moderated compactness. The well-known affinity of
calix[6]arene towards uranyl make these functional electrodes
good candidates for its selective detection in water samples.
Evaluation of the analytical performances of this electrode
material is currently in progress.
Acknowledgments
This work was partly supported by the CNRS program
GUTEC. We thank N. Aychet (CEA Saclay) and Pr. C.
Jankowski (University of Moncton, Canada) for helpful
discussions concerning calix[6]arene synthesis. Thanks to O.
Maciejak (LAMBE, Evry) for technical help concerning the
NMR experiments.
References and notes
Figure 2: Cyclic Voltammograms obtained at glassy carbon
electrode after cycling in a 0.1M acetonitrile solution of NBu4BF4
with (black) or without (grey) calix[6]arene in the presence of 1 mM
K3Fe(CN)6 electrochemical probe + 0.1 M KCl aqueous solution.
Scan rate is 200 mV.s-1.
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Supplementary Material
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Supplementary data associated with this article can be found
in the online version.