Repositorio institucional de IMDEA Nanociencia

Muñoz-Rodríguez C.

Feng L.

Palmero E.M.

Mix T.

Rial J.

Olsson F.

Skårman B.

Vidarsson H.

Larsson P.-O.

Woodcock T.G.

Bollero, Alberto

Fabrication of bulk τ MnAl–C magnets by hot-pressing from ε-phase gas-atomized and milled powder

Cea T.

Guinea, Francisco

Band structure and insulating states driven by Coulomb interaction in twisted bilayer graphene

Tesis doctoral inédita leída en la Universidad Complutense de Madrid. Fecha de lectura: 27-11-2020

Javier Urieta Mora

Nazario Martín

Universidad Complutense de Madrid

Design and synthesis of organic p-type semiconductors: Toward efficient Perovskite Solar Cells”

Tesis doctoral inédita leída en la Universidad Autónoma de Madrid. Fecha de lectura: 17-7-2020

Julia Villalva

Emilio M. Pérez

Universidad Autónoma de Madrid

"Chemistry of nanomaterials inside out"," mechanically interlocked, endohedral and covalent derivatives of SWNTs and 2D materials"

de la Torre B.

Matěj A.

Sánchez-Grande A.

Cirera B.

Mallada B.

Rodríguez-Sánchez E.

Santos J.

Mendieta-Moreno J.I.

Edalatmanesh S.

Lauwaet K.

Otyepka M.

Medveď M.

Buendía Á.

Miranda, Rodolfo

Martín, Nazario

Jelínek P.

Écija, David

Tailoring π-conjugation and vibrational modes to steer on-surface synthesis of pentalene-bridged ladder polymers

Nishikubo R.

Kanda H.

García-Benito I.

Molina-Ontoria A.

Pozzi G.

Asiri A.M.

Nazeeruddin M.K.

Saeki A.

Optoelectronic and Energy Level Exploration of Bismuth and Antimony-Based Materials for Lead-Free Solar Cells

Rentschler M.

Iglesias S.

Schmid M.-A.

Liu C.

Tschierlei S.

Frey W.

Zhang X.

Karnahl M.

Moonshiram D.

The Coordination Behaviour of CuI Photosensitizers Bearing Multidentate Ligands Investigated by X-ray Absorption Spectroscopy

Gallardo J.

Escalona-Noguero C.

Sot, Begoña

Role of α-Synuclein Regions in Nucleation and Elongation of Amyloid Fiber Assembly

Otero, Roberto

A shift in molecular devices

Naranjo T.

Villalva J.

Pérez, Emilio M.

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Measuring the Stability of Supramolecular Complexes in
the Proximity of Single-Walled Carbon Nanotubes
Teresa Naranjo, Julia Villalva, and Emilio M. Pérez*[a]
Cet article est dédié à Jean-Marie Lehn, père de la chimie supramoléculaire, à l’occasion de son 80ème anniversaire.
The decoration of SWNTs with supramolecular motifs is a
common strategy for their subsequent noncovalent functional-
ization. However, due to the lack of a standard methodology,
there are no quantitative measurements showing the extent to
which the supramolecular equilibria are affected by one of the
host-guest couple being anchored to the SWNT. Here, we use a
method we initially developed to quantify association of small
organic molecules to the walls of SWNTs to compare association
constants of two host-guest systems, a Hamilton receptor-
cyanuric acid derivative and a crown ether-ammonium couple,
in solution and when the host is covalently attached to the
SWNTs. Our data show that association does occur, but the
stability of the complexes is significantly affected, as reflected in
a sizable reduction in their association constant, when
compared to solution.
Measuring is the heart of the scientific method. Hypothesis are
supported or disproven by experimental data. However, when
the scientist cannot measure the system of interest, we resort
to extrapolation of data from the closest measurable system.
This is, for instance, commonplace in the biomedical field,
where the complexity of living systems, and the moral
implications of experimenting with them,[1] often prevents
quantitative measurements, that are instead extrapolated from
in vitro models.[2–4] On a much less complex level, the
supramolecular chemistry of single-walled carbon nanotubes
(SWNTs) has also been dominated by qualitative or extrapolated
quantitative data,[5–9] due to the lack of a standardized method
to measure association constants in supramolecular equilibria
involving SWNTs.[10–11] In particular, host-guest systems with
large binding constants (Ka) in solution have been routinely
used to functionalize SWNTs via noncovalent forces, assuming
that the stability of the supramolecular complexes will remain
intact. The following are some representative examples: Martín
and cols. have recently described the covalent decoration of
SWNTs to later use guanidinium-carboxylate couples to asso-
ciate porphyrin chromophores.[12] Teams led by D’Souza and Ito
used ammonium-crown ether recognition to a very similar end,
in this case using pyrene as a noncovalent anchor to the SWNT
for the ammonium group.[13] Earlier, Stoddart and Heath had
used ammonium-crown ether, and dioxynaphthalene-“blue
box” interactions to build pseudorotaxane architectures on
SWNTs.[14]
We have developed a method to directly measure Ka of
small organic molecules towards SWNTs.[15–16] Our method
benefits from the insolubility of SWNTs: we allow a mixture of a
soluble guest molecule and the SWNTs to reach thermodynamic
equilibrium, and then filter to separate the insoluble SWNT-
guest complex from the soluble free guest. We then quantify
the amount of bound guest molecule through thermogravimet-
ric analysis (TGA). By repeating this experiment at different
initial concentrations of guest molecule, we can plot binding
isotherms and extract association constants by using a standard
binding isotherm.[17] Using this method, we have been able to
determine binding constants of a variety of pyrene-based guest
molecules towards SWNTs, observing clear differences between
size, solvent and electronic effects. We complemented the
experimental results with comprehensive theoretical modelling
by the groups of Ortí and Comer.[16]
In this work, we directly measure Ka of host-guest pairs in
which one of the molecular components is covalently con-
nected to SWNTs, and compare it to the Ka in absence of the
SWNT, to quantify the influence of the nanotube on the
supramolecular equilibria (Figure 1a).
To this end, we decided to study systems featuring both
large and more moderate association constants. As tight
binding host-guest couple (log Ka >5), we chose a Hamilton
receptor-cyanuric acid derivative pair (HR-cy in Figure 1b),[18]
which has been thoroughly studied before,[19] and has been
used by Hirsch and co-workers in a supramolecular approach to
solubilise SWNTs.[20] As weakly binding host-guest pair (log Ka
�3), we chose a 18-crown-6-ammonium system (Crown-Am in
Figure 1b), similar to those used by D’Souza and Ito in
connection with SWNTs.[13] In order to compare the Ka with and
without SWNTs, we tagged the guest molecules with a tris
(bipyridine)ruthenium(II) dye, while the hosts were both
decorated with an aniline group for their covalent attachment
to the SWNTs by means of in situ diazonium chemistry.[21] To
[a] Dr. T. Naranjo, J. Villalva, Prof. E. M. Pérez
IMDEA Nanociencia
Faraday 9, Campus de Cantoblanco
28049 Madrid (Spain)
E-mail: emilio.perez@imdea.org
Supporting information for this article is available on the WWW under
https://doi.org/10.1002/open.202000018
An invited contribution to a Special Collection dedicated to Functional Su-
pramolecular Systems
© 2020 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA. This
is an open access article under the terms of the Creative Commons Attri-
bution Non-Commercial NoDerivs License, which permits use and distribu-
tion in any medium, provided the original work is properly cited, the use is
non-commercial and no modifications or adaptations are made.
ChemistryOpen
Communications
doi.org/10.1002/open.202000018
731ChemistryOpen 2020, 9, 731–734 © 2020 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA
Wiley VCH Dienstag, 30.06.2020
2007 / 161268 [S. 731/734] 1
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that end, a mixture of SWNTs (1 mg ·mL  1) in NMP was
ultrasonicated for 20 min. After this time, the corresponding
host molecule (the aniline derivatized Hamilton receptor or the
4’-Aminobenzo-18-crown-6) and boron trifluoride diethyl ether-
ate were added. Isoamyl nitrite was used as oxidant. The
mixture was stirred for 5 h, filtered through a 0.2 μm-pore PTFE
membrane and washed several times with THF to ensure the
total removal of adsorbed host molecules. The SWNTs products
showed a relatively large degree of functionalization through
TGA (20% for SWNT-HR and 14% for SWNT-Crown, see SI, S4)
while Raman was supportive of the covalent attachment,
showing a significant increase in the ID/IG ratio, from 0.06 in the
pristine SWNTs to 0.12 in both SWNT-HR and SWNT-Crown.
With all the molecular host-guest systems in our hands, we
first determined the Ka of the host-guest couples in solution,
without attachment to the SWNTs, by means of UV-vis titrations
(see SI, S5 for details). For the HR-cy system we measured log
Ka=5.8�0.4 in CH3CN at room temperature, a value that is in
the range of those determined for similar systems.[22–24] In the
case of Crown-Am, we measured log Ka=3.6�0.5, also in
CH3CN at room temperature, again in very good agreement
with precedents in the literature.[25–26]
To measure the binding constants of SWNT-HR-Cy and
SWNT-Crown-Am, we followed the procedure we have de-
scribed above,[15–16] which we originally designed to study direct
adsorption of organic molecules to the SWNT walls, but should
also be applicable to the present problem, as it is based purely
on mass balance. The experimental procedure can be summar-
ized as follows: covalently functionalized SWNTs (1 mg ·mL  1)
were suspended in a solution of known concentration of the
host molecule in CH3CN. This mixture was stirred for 2 h to
allow it to reach equilibrium. After this time, the suspension
was filtered through a 0.2 μm-pore PTFE membrane, retaining
the guest-SWNTs complex. The solid obtained was analysed by
TGA (air, 10 °C ·min-1) to quantify the amount of guest attached.
We measure the weight loss between 250 and 475 °C, where all
the host-guest complex has been burned off, and take the
initial SWNT-HR and SWNT-Crown as references. From the
degree of functionalization and the mass of the sample
analysed, we calculate the total mass of guest attached to the
host, from which its free concentration in equilibrium is
immediate. The same procedure is repeated for several initial
concentrations of the guest molecule, ranging from 0 to near
saturation in the solvent under study. A blank experiment, in
which no guest is added, is run in all cases in order to
determine the adsorbed/encapsulated solvent and this data is
subtracted to the total weight loss. All the experiments were
performed at room temperature.
The binding isotherms are obtained by plotting the degree
of functionalization against the concentration of free host. Both
the case of the SWNT-HR-Cy and the SWNT-Crown-Am showed
the characteristic Langmuir-type shape and fitted very satisfac-
torily (R2 >0.99) to the standard 1 :1 isotherm (Figure 2).[15–16]
From three independent titration experiments for each equili-
brium, we obtained Ka= (9.0�0.7) · 10
3 M  1, that is, log Ka=
3.95�0.03, for SWNT-HR-Cy, and Ka= (5.0�0.6) · 10
2 M  1, or log
Ka=2.7�0.6, for SWNT-Crown-Am.
In order to evaluate the relevance of non-specific physisorp-
tion between the Ru-derivative guest and the SWNTs, the
binding isotherms between guest and non-functionalized
SWNTs were measured. Figure 3 shows the plots obtained for
both guest molecules. Interestingly, the curves are very far from
saturation, in the linear region of the isotherm. Consequently,
the calculated association constants are small. In particular, we
obtained: Ka=37 M
  1, that is, log Ka=1.6, for SWNT-HR-Cy, and
Ka=0.013 M
  1, or log Ka=   1.9, for SWNT-Crown-Am. The small
association constants indicate that the physisorption of the
guest is negligible when compared to the specifically bonded
guest. These data validate the strategy of attaching specific
supramolecular motifs to SWNTs to further functionalize them
in a later stage using host-guest chemistry.
In conclusion, we show that the procedure previously
described by our group for the determination of association
constants towards SWNTs can be used as a reliable method for
the determination of association constants between host-guest
pairs attached to SWNTs. We confirm that binding does occur,
and that it is significantly larger than non-specific physisorption.
The obtained host-guest association constants involving SWNTs
are smaller from that obtained in solution (from log Ka=5.8�
0.4 to log Ka=3.95�0.03 for SWNT-HR-Cy and from log Ka=
3.6�0.5 to log Ka=2.7�0.6, for SWNT-Crown-Am). This
decrease in Ka is an important fact to consider when functional-
izing SWNTs via noncovalent forces. The covalent bond SWNT-
host destabilizes the further attachment of the guest in the
binding sites, compromising the stability of the final complex.
Figure 1. a) Schematic representation of a host-guest binding process (top)
and a host-guest binding process where the host is covalently attached to a
SWNT (bottom). b) Chemical structure of the Hamilton receptor-cyanuric
acid derivative pair (HR-Cy) and the 18-crown-6-ammonium system (Crown-
Am).
ChemistryOpen
Communications
doi.org/10.1002/open.202000018
732ChemistryOpen 2020, 9, 731–734 www.chemistryopen.org © 2020 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA
Wiley VCH Dienstag, 30.06.2020
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Overall, our quantitative analysis confirms that it is a valid
strategy to covalently attach host molecules to the walls of
SWNTs to later functionalize them via host-guest chemistry.
However, when choosing this strategy, the chemist should
consider that, once attached to the SWNTs, the host-guest
association constants are probably smaller than those measured
in solution.
Acknowledgements
We acknowledge funding from the European Union (ERC-StG-
307609, ERC PoC 842606), MINECO (CTQ2014-60541-P and
CTQ2017-86060-P), and the Comunidad de Madrid and the
European Structural Funds for their financial support through
FotoArt-CM project (S2018/NMT-4367) and MAD2D-CM S2013/
MIT-3007. IMDEA Nanociencia acknowledges support from the
“Severo Ochoa” Programme for Centres of Excellence in R&D
(MINECO, grant SEV-2016-0686).
Conflict of Interest
The authors declare no conflict of interest.
Keywords: SWNTs · host-guest chemistry · supramolecular
chemistry · nanoscience
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ChemistryOpen
Communications
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733ChemistryOpen 2020, 9, 731–734 www.chemistryopen.org © 2020 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA
Wiley VCH Dienstag, 30.06.2020
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Revised manuscript received: February 24, 2020
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2007 / 161268 [S. 734/734] 1


Measuring the Stability of Supramolecular Complexes in the Proximity of Single-Walled Carbon Nanotubes

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