An electrochemically controlled supramolecular zip tie based on host-guest chemistry of CB[8]

Article abstract of DOI:10.1039/d0ob01085e

Three molecular threads incorporating two viologen units attached by an oligo-ethylene glycol chain of variable length and an electron rich naphthalene moiety were prepared. The internal viologen unit is connected to the naphthalene by a rigid linker that

Full text of DOI:10.1039/d0ob01085e

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DOI: 10.1039/D0OB01085E.
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DOI: 10.1039/D0OB01085E
ARTICLE
An electrochemically controlled supramolecular zip tie based on
host-guest chemistry of CB[8]
Iago Neira,a Olaya Domarco,a Jose L. Barriada,a Paola Franchi,b Marco Lucarini,b Marcos D. García*a
Received 00th January 20xx,
Accepted 00th January 20xx
and Carlos Peinador*a
DOI: 10.1039/x0xx00000x
Three molecular threads incorporating two viologen units attached by an oligo-ethylene glycol chain of variable length and
an electron rich naphthalene moiety were prepared. The internal viologen unit is connected to the naphthalene by a rigid
linker that prevents the simultaneous complexation of these systems. The axle with the shortest chain (14+) in presence of
CB[8] placed the chain inside the macrocycle in aqueous media. On the contrary, the longer chains in (24+,34+) allow locating
the terminal viologen and the electron rich unit inside the cavity. Upon reduction of the bipyridinium salts, the system
behaves like a zip tie relaxing the chain as a consequence of the insertion of both radical cation moieties within the CB[8]
and making these switches as potential components for molecular machinery.
Continuing our interest on the use of pyridinium salts as
building blocks in supramolecular chemistry,11 and the
development of new CB[n]-based host:guest chemistry,12 we
Introduction
Supramolecular switches are defined as host-guest assemblies,
composed of two or more interacting units, whose association
can be transiently controlled by an external stimulation, such as
light, electrical potential, or chemical effectors.1 The interest in
such systems is manifold,2 as they can be used in man-
controlled practical applications such as the development of
stimuli–responsive catalysis,3 materials4 or molecular
machines.5 In this scenario, the host-guest chemistry of
cucurbit[n]uril (CB[n]s),6,7 represents a versatile platform for the
development of the above-mentioned stimuli-responsive
architectures, especially relevant on the case of CB[8], due to its
ability to form stimuli-responsive 1:2 homo and heteroternary
complexes with appropriate guests.8 In this context, viologens
(N,N’-dialkyl-4,4’-bipyridinium derivatives),9,10 have been
extensively used in conjunction with CB[8], as these π-acceptors
are able to form different redox-responsive complexes (i.e. 1:1
or 1:2 homoternary aggregates depending on the reduction
state of the salt, and 1:2 heteroternary complexes with
appropriate aromatic π-donors as second guests). In both cases,
the appropriate reversibility of the redox processes, allows for
an easy swapping between the 1:1 homoternary complex,
formed by radical pairing of two reduced viologens, and the
non-stimulated form of the responsive aggregate.
present herein the design and study of the supramolecular
translocation switches 1-3CB[8]⇄1’-3’CB[8], envisioned to
produce the controlled gliding of the macrocyclic subunit of the
pseudorotaxane by appropriate redox stimulation. The threads
1-3 are composed by two 4,4’-bipyridinium units (terminal
bipyt2+ and internal bipyi2+), connected by an oligo-ethylene
chain of variable length, and a 2-hydroxynaphthalene unit
attached to bipyi2+ by a rigid p-xylene linker (Scheme 1). This
connection was designed to prevent the simultaneous
complexation of bipyi2+ and naphthalene units inside CB[8], and
to ensure the maintenance of the loop during the operation of
the zip tie.13 In its non-stimulated state, the bipyt2+ and
naphthalene (NAP) units are located inside CB[8] in an end-to-
end pseudorotaxane with no loop formation. Upon reduction,
the supramolecular switch changes to an end-to-interior state,
with a viologen cation radical dimer formed inside the cavity
and the concomitant appearance of the loop. Although similar
end-to-end/end-to-interior systems have been reported by Kim
and Stoddart (Scheme 1),14 our switch potentially allows a strict
control over loop formation extension and contraction, paving
the way for their prospective use on the controlled catch and
release of cations by the oligo-ethylene-containing loop
.
a. Departamento de Química and Centro de Investigaciones, Científicas Avanzadas
(CICA), Universidade da Coruña, Facultad de Ciencias, E-15071 A Coruña, Spain. E-
mail: carlos.peinador@udc.es, marcos.garcia1@udc.es.
b. Department of Chemistry “G. Ciamician” – Alma Mater Studiorum-University of
Bologna, Via San Giacomo 11, Bologna, Italy.
† Electronic Supplementary Information (ESI) available: Synthetic procedures,
characterization data for all new compounds and host-guest complexes See
DOI: 10.1039/x0xx00000x
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losses of one and two PF6 anions at, respectivelyV,iemw /Azrtic=le1O1nl7in6e
1
DOI: 10.1039/D0OB01085E
and 736. The H NMR of this species shows as well symptomatic
resonances in good agreement with the complexation taking
place. For instance, while the signals corresponding to the
naphthol or phenylene moieties remain unchanged, some of
the resonances for the methylene groups in the oligo ethylene
chain are significantly shifted upfield, as well as those protons
of the viologen moieties shifted to higher frequencies (Figure 1).
On the other hand, the observed splitting for the signals of the
CB[8] protons, points out to a different chemical environment
in both portals. Further evidence of the nature of the aggregate
1
was derived from the H NMR spectrum of a 1:0.5 mixture of
14+:CB[8] at r.t., which displays signals resulting from the slow
kinetic exchange on the 1H NMR timescale between complexed
and uncomplexed states. Finally, the kinetic entanglement of
the CB[8] and 1·4PF6 components of the pseudorotaxane is
apparent from DOSY experiments, which show that the proton
resonances arise for the new species correlate with larger
hydrodynamic radii than that of the individual components
(Figure 1d). Taking into account all these observations, it can be
assumed the formation of a [2]pseudorotaxane where the oligo
methylene chain is located inside the CB[8] cavity, with the
Scheme 1: A) Structures of axles reported by Kim (top) and Stoddart (bottom). B) positive charges of the bipyridinium ring interacting with the
Structures of axles 14+-34+ described in this work, CB[8] and schematic
representation of the expected complexation modes for the supramolecular zip
tie studied in this work.
carbonyl groups of CB[8]. The observed preference of this
binding mode over the formation of the intramolecular
heteroternary charge transfer complex involving the bipyt2+ and
NAP moieties is not surprising, accounting for the inadequate
extension of the oligo-ethylene linker on 1·4PF6.
Results and discussion
Synthesis and characterization of molecular components
Regarding the thread components of the zip ties, molecules 14+-
34+ were synthesized from commercially-available 2-naphthol,
4,4’-bipyridine, 1,4-dibromomethyl benzene and the
corresponding oligo(ethylene glycol) dibromides, by using a
series of nucleophilic substitutions (Scheme 2). Compounds 14+-
34+ were adequately characterized by standard spectroscopic
1
techniques, including H NMR and 13C NMR spectroscopy, as
well as high-resolution mass spectrometry.
Figure 1. Partial 1H NMR (D2O/CD3CN 3:2, 500 MHz) spectrum of: a) 1·4PF6 (2 mM);
b) equimolar solution of 1·4PF6 (2 mM) and CB[8]; c) a solution of 1·4PF6 (2 mM)
and CB[8] (1 mM); d) DOSY NMR experiment of solution c). Proton numbering is
given in Scheme 1.
UV-visible spectroscopy was employed to monitor the
interaction between 1·4PF6 and CB[8] in H2O/CH3CN (3:2, v/v).
The decrease in the peak at 261 nm concomitant to the increase
in the concentration of CB[8], fits to a 1:1 binding model with a
Ka = (1.97 ± 0.2) × 105 L mol-1. The fitting curve shows a inflection
Scheme 2: Synthesis of axles 1-3·4PF6.
point at ca. 훘CB[8] = 0.5, and a second isotherm indicating a 1:2
stoichiometry when an excess of cucurbituril is added (see
Supporting Information). This behaviour has been observed
before by Kaifer et al. in similar systems.15 It should be noted
that the 1:2 complex cannot be observed in NMR experiments,
due to the low solubility of CB[8] in most solvents, which does
Interaction between axles 14+-34+ and CB[8]
Addition of an excess of CB[8] to a 2 mM solution of thread
1·4PF6 in D2O/CD3CN (3:2, v/v), leads to the formation of a 1:1
adduct (14+⊂CB[8]), as corroborated by ESI-MS showing the
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not allow to detect a significant excess of free CB[8] by this the viologen residues, which behave as essentiallyViinewdeArpticelenOdnelinnet
technique.
units, revealing no apparent electronic cDoOmI:m10u.1n0i3c9a/tDio0nOBa0m10o8n5gE
In clear contrast with the data compiled for 1·4PF6, the them.
1
binding between CB[8] and 2·4PF6 or 3·4PF6 resulted in a H
On the other hand, the cyclic voltammogram of 14+⊂CB[8]
NMR spectra showing broad signals as a result of a situation shows significant differences with that of the free thread, with
near to coalescence for the equilibrium on the technique the first reduction peak remarkably shifted (∆E = -99 mV),
1
timescale. Conversely, the H NMR spectra recorded at 343 K supporting the initial proximity of the viologen moieties to the
allowed the detection of defined signals, but did not show the CB[8] portals, and indicating a fast shuttling of the host between
remarkable upfield shifts of the oligo-ethylene chain protons bipyt2+and bipyi2+(Figure 3). On the contrary, 24+⊂CB[8] and
observed in 14+⊂CB[8], ruling out the insertion of the linker 34+⊂CB[8] presented an unaltered first reduction potential
inside the macrocyclic host. Moreover, the NAP protons were when compared with free threads. These first reduction peaks
the resonances more affected by coalescence in this occasion, for 24+⊂CB[8] and 34+⊂CB[8] consist of two closely overlapping
suggesting the establishment of intramolecular charge transfer peaks, corresponding to two electrochemically different
complexes. However, no clear charge-transfer band has been viologen units: one resulting from a charge-transfer complex
detected in the UV-Vis spectrum. The formation of the between NAP and bipyt2+ inside CB[8], while the other is in good
[2]pseudorotaxanes 24+⊂CB[8] and 34+⊂CB[8] was also agreement with the non-interacting bipyi2+ unit. A third
supported by ESI-MS, which showed peaks resulting from the reduction peak around -1.35 V corresponds to the species with
loss of two and three hexafluorophosphate ions, and with the reduced units bipyt+・and bipyi+・paired inside CB[8] upon
isotopic distributions in very good agreement to those the first reduction is produced. Interestingly, the third reduction
theoretically calculated (Figure 2).
peak (also in 14+⊂CB[8]) is more visible at slower rather than
faster scan rates reflecting the fact that the formation of [(bipyt+
・)(bipyi+・)]⊂CB[8] is slow in the CV time scale (see Supporting
Information). At fast scan rates (0.5 Vs-1) the intermediate
reduction peak at -0.9 V associated to no interacting bipyi+・and
bipyt+・is clearly more intense than the third peak indicating the
residual formation of [(bipyt+・)(bipyi+・)]⊂CB[8].
Figure 2. Low resolution ESI-MS spectrum, for 24+⊂CB[8] showing the loss PF6 fragments.
Insets: ESI-HRMS isotopic distributions for some of the most relevant peaks
(experimental peaks in black, calculated peaks in red).
Finally, the interaction between threads 14+-34+ and CB[8]
was investigated in pure organic media. The 1H NMR spectra of
1-3·4PF6⊂CB[8] in CD3CN showed a similar behaviour for the
three systems, with the upfield shift experienced by the protons
of the oligo-ethylene chains, supporting the relative location of
the 2-3·4PF6 threads relative to CB[8] as analysed for
1·4PF6⊂CB[8] in aqueous media.
Figure 3. Superposed cyclic voltammetric response on a glassy carbon electrode of: a)
1.0 mM 1·4PF6 (black line), 1.0 mM 14+⊂CB[8] (red line) and b) 1.0 mM 3·4PF6 (black line),
1.0 mM 34+⊂CB[8] (red line). Supporting electrolyte: 0.1 M KCl. Scan rate: 50 mV/s.
The structures of these complexes formed upon the
reduction was also studied by UV-Vis spectroscopy. Addition of
an excess of Na2S2O4 to solutions of 14+-34+⊂CB[8] caused an
immediate change of colour to intense purple. The UV-Vis
spectra of these solutions show an intense and no structured
band (e.g. max = 523 nm for 24+⊂CB[8]), characteristic of the
cation radical species.14b
Electrochemical and UV-Vis studies of the zip tie mechanism
In order to achieve a deeper insight into the structure of the
inclusion complexes obtained, both in their reduced and
oxidized forms, we carried out cyclic voltammetry and UV-Vis
spectroscopy studies for those systems. Therefore, the redox
properties of linear components 1-3·4PF6 in absence and
presence of CB[8] were measured in H2O/CH3CN (3:2, v/v). As
expected, in absence of CB[8], the threads show two
voltammetric peaks at ca. -0.48 and -0.93 V vs Ag/AgCl, with a
sharp second peak that indicates a strong adsorption of the fully
reduced species on the surface of the electrode. Each of these
peaks represents the uptake of two electrons, one by each of
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are in agreement with EPR parameters reported inVtiheweAlirttieclreaOtnulirnee
for the viologen radical cations.16 Reasonably, the loss of
DOI: 10.1039/D0OB01085E
spectra resolution can be attributed to partial overlap of the
spectral lines deriving from the two viologen units which differ
for a diverse substitution pattern in one of the pyridine ring (a
methylene unit is replaced by a methyl group in the terminal
ring of 14+-34+). According to the electrochemical measurements
discussed above, we can conclude that, in the absence of CB[8],
each of viologen residues behaves as essentially independent
units and no apparent electronic communication is observed
among them. In some experiments, a second weak single line
signal was also detected (see Supporting information). This
impurity signal, centered at g-factor=2.0061 corresponds to the
●
SO2 ¯ radical anion and is the result of the known equilibrium of
●
dithionite with its two dissociated SO2 ¯ radical anions.17
When 14+-34+ precursors reacted with Na2S2O4 in the
presence of CB[8] under the same experimental conditions, the
EPR spectrum is mainly characterized by the presence of the
Figure 4. Room temperature EPR spectra of H2O/CH3CN (3/2, v/v) solutions containing
Na2S2O4 (purple line), Na2S2O4 and CB[8] (blue line), compound 24+ and Na2S2O4 in the
absence (red line) and in the presence of CB[8] (black line).
●
signal due to SO2 ¯ and a very weak signal due to viologen
radical cation. In most cases the signal due to viologen cation is
so weak that is hardly detectable (see figure 4). It is well known
EPR measurements
Further evidence supporting the looped structures for the that viologen radical cations dimers are diamagnetic and thus,
inclusion complexes in aqueous media when 14+-34+ are reduced EPR silent.18 Consequently, the absence of the viologen radical
in the presence of CB[8], were obtained by EPR spectroscopy. cation EPR signal observed in the presence of the macrocycle is
Bipyridinium radical cations were generated inside the EPR coherent with the formation of a diamagnetic EPR-silent dimer
cavity by in situ reduction in carefully deoxygenated H2O/CH3CN (bipyt+●)(bipyi+●) inside the cavity of CB[8] itself.
(3/2, v/v) solutions of the diamagnetic precursors 14+-34+ with
In principle, the absence of an EPR signal for viologen radical
excess Na2S2O4 (5–10 equiv.), both in the absence and presence cation could also be attributed to the inhibition by CB[8] of the
of CB[8]. Reduction of 14+-34+ in the absence of CB[8] resulted in reductive reaction. This hypothesis, however, can be discarded
●
strong EPR spectra which show a partially resolved complex because of the detection of the EPR signal due to SO2 ¯ whose
multiline pattern centered at g = 2.0031 (see Figure 4). Although formation can be related to the occurrence of the reaction
the poor resolution of hyperfine structure on the EPR did not between 14+-34+ and dithionite. Actually, no EPR signals were
allow us to determine the values of the corresponding hyperfine visible when Na2S2O4 was simply dissolved in the solution or
splitting constants, both g-factor and overall splitting (ca. 30 G), mixed with CB[8] alone (see Figure 4).
Scheme 3. Cartoon representation of the different interaction modes of 14+-34+ with CB[8] in aqueous and organic media.
In summary, three molecular axles composed by an aromatic
electron-rich system and two viologen units connected by an
Conclusions
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Credi, Making and operating molecular VmiewacAhrtiicnleeOs:nlinae
multidisciplinary challenge, ChemistrDyOOIp: e10n.1,023091/D8,0O7,B1061098.5E
Cucurbiturils and related macrocycles, K. Kim ed., Royal
Society of Chemistry, Cambridge, 2020.
oligo-ethylene chain were synthesized. In aqueous media and in
presence of CB[8] the longer axles 24+ and 34+ locate one of the
bipyridinum units and the naphthol ring inside the CB[8] cavity.
In contrast, the shorter chain of 14+ prevents this insertion mode
forcing the CB[8] to move towards the oligo-ethylene chain
(Scheme 3). Therefore, the eleven atom chain in 14+ is not long
enough to allow the simultaneous insertion in the cavity of
CB[8] of naphthol and bipyt2+ moieties. Monoelectronic
reduction of each bipyridinium unit in 14+-34+⊂CB[8] resulted in
the cation-radical species which are moved into the CB[8]
inducing the axle movement and the loop formation in the
oligo-ethylene chain. In organic media the three axles showed
the same behaviour with the oligo-ethylene chain inside the
CB[8]. Undoubtedly, the absence of hydrophobic interactions
and entropic factors favours the formation of these complexes.
Further investigation into cation catch and release of these
systems is currently ongoing.
6
7
(a) J. W. Lee, S. Samal, N. Selvapalam, H.-J. Kim, and K. Kim,
Cucurbituril homologues and derivatives: new opportunities
in supramolecular chemistry, Acc. Chem. Res., 2003, 36, 621.
(b) K. Kim, N. Selvapalam, Y. H. Ko, K. M. Park, D. Kim, and J.
Kim, Functionalized cucurbiturils and their applications,
Chem. Soc. Rev. 2007, 36, 267. (c) S. J. Barrow, S. Kasera, M.
J. Rowland, J. del Barrio, and O. A. Scherman, Cucurbituril-
based molecular recognition, Chem. Rev., 2015, 115, 12320.
(d) K. I. Assaf, and W. M. Nau, Cucurbiturils: from synthesis
to high-affinity binding and catalysis, Chem. Soc. Rev., 2015,
44, 394. (e) V. Ramalingam and A. Urbach, Org. Lett., 2011,
13, 4898.
(a) L. Zhu, M. Zhu, Y. Zhao, Controlled movement of
cucurbiturils in host-guest systems, ChemPlusChem, 2017,
82, 30. (b) E. Pazos, P. Novo, C. Peinador, A. E. Kaifer, and M.
D. García, Cucurbit[8]uril (CB[8])-based supramolecular
switches, Angew. Chem. Int. Ed., 2019, 58, 403.
8
9
(a) P. M. S. Monk, The Viologens: Physicochemical
Properties, Synthesis, and Applications of the Salts of 4,4′-
bipyridine, John Wiley & Sons, Chichester, 1998; (b) P. M. S.
Monk, R. D. Fairweather, J. A. Duffy and M. D. Ingram,
Conflicts of interest
There are no conflicts to declare.
Evidence
for
the
product
of
the
viologen
comproportionation reaction being a spin-paired radical
Acknowledgements
cation dimer, J. Chem. Soc., Perkin Trans. 2, 1992, 2039.
This research was supported by the Ministerio de Economía y
Competitividad (MINECO FEDER, CTQ2016-75629-P) and Xunta
de Galicia (ED431C2018/39). I. N. thanks the MECD (FPU
program) for financial support. M. L. thanks Italian Ministry of
10 For selected recent reviews on viologens: (a) M. Deska, J.
Kozlowska, and W. Sliwa, Rotaxanes and pseudorotaxanes
with threads containing viologen units, ARKIVOC, 2013, 1,
66. (b) L. Striepe, T. Baumgartner, Viologens and their
application as functional materials, Chem. Eur. J., 2017, 23,
16924. (c) K. Madasamy, D. Velayutham, V. Suryanarayanan,
M. Kathiresan, and K.-C. Ho, Viologen-based electrochromic
materials and devices, J. Mat. Chem. C, 2019, 7, 4622.
Education,
University
and
Research
(PRIN,
prot.
2017E44A9P_003).
11 (a) A. Blanco-Gómez, I. Neira, J. L. Barriada, M. Melle-
Franco, C. Peinador, and M. D. García, Thinking outside the
“Blue Box”: from molecular to supramolecular pH-
responsiveness, Chem. Sci., 2019, 10, 10680. (b) A. Blanco-
Gómez, Á. Fernández-Blanco, V. Blanco, J. Rodríguez, C.
Peinador, and Marcos D. Garcia, Thinking outside the “Blue
Notes and references
1
R. Klajn, J. F. Stoddart, and B. A. Grzybowski, Nanoparticles
functionalised with reversible molecular and
supramolecular switches, Chem. Soc. Rev., 2010, 39, 2203.
M. Xue, Y. Yang, X. Chi, X. Yan, and F. Huang, Development
of pseudorotaxanes and rotaxanes: from synthesis to
stimuli-responsive motions to applications, Chem. Rev.,
2015, 115, 7398.
(a) V. Blanco, D. A. Leigh, and V. Marco, Artificial switchable
catalysts, Chem. Soc. Rev. 2015, 44, 5341. (b) J. Choudhury,
Recent developments on artificial switchable catalysis,
Tetrahedron Lett., 2018, 59, 487. (c) N. Kumagai, and M.
Shibasaki, Catalytic chemical transformations with
conformationally dynamic catalytic systems, Catal. Sci.
Technol., 2013, 3, 41.
G. Yu, K. Jie, F. Huang, Supramolecular amphiphiles based
on host-guest molecular recognition motifs, Chem. Rev.,
2015, 115, 7240. (b) P. Wei, X. Yan, F. Huang,
Supramolecular polymers constructed by orthogonal self-
assembly based on host-guest and metal-ligand
interactions, Chem. Soc. Rev., 2015, 44, 815. (c) S. Dong, B.
Zheng, F. Wang, F. Huang, Supramolecular polymers
constructed from macrocycle-based host-guest molecular
recognition motifs, Acc. Chem. Res., 2014, 47, 1982.
(a) S. Erbas-Cakmak, D. A. Leigh, C. T. McTernan, and A. L.
Nussbaumer, Artificial molecular machines, Chem. Rev.,
2015, 115, 10081. (b) S. Kassem, T. van Leeuwen, A. S.
Lubbe, M. R. Wilson, B. L. Feringa, and D. A. Leigh, Artificial
molecular motors, Chem. Soc. Rev., 2017, 46, 2592.(c) M.
Baroncini, L. Casimiro, C. de Vet, J. Groppi, S. Silvi, and A.
2
Box”: induced fit within
a unique self-assembled
polycationic cyclophane, J. Am. Chem. Soc., 2019, 141, 3959.
(c) I. Neira, C. Alvariño, O. Domarco, V. Blanco, C. Peinador,
M. D. García, and J. M. Quintela, Tuning of the self-threading
of ring-in-ring structures in aqueous media, Chem. Eur. J.,
2019, 25, 14834. (d) T. Rama, A. Blanco-Gómez, I. Neira, O.
Domarco, M. D. García, J. M. Quintela, and C. Peinador,
3
4
Integrative
self-sorting
of
into
bipyridinium/diazapyrenium-based
ligands
pseudo[1]rotaxanes, Chem. Eur. J., 2017, 23, 16743. (e) A.
Blanco-Gómez, T. Rama, O. Domarco, I. Neira, V. Blanco, J.
M.; Quintela, M. D. García, and C. Peinador, Amplification of
a metallacyclic receptor out of a dynamic combinatorial
library, Dalton Trans., 2017, 46, 15671. (f) O. Domarco, I.
Neira, T. Rama, A. Blanco-Gómez, M. D. García, C. Peinador,
J. M. Quintela, Synthesis of non-symmetric viologen-
containing ditopic ligands and their Pd(II)/Pt(II)-directed
self-assembly, Org. Biomol. Chem., 2017, 15,3594. (g) T.
Rama, E. M. López-Vidal, M. D. García, C. Peinador, J. M.
Quintela, Complexation and catenation in aqueous media
using a self-assembled PdIImetallacyclic receptor, Chem.
Eur. J., 2015, 21, 9482.
5
12 (a) I. Neira, A. Blanco-Gómez, J. M. Quintela, C. Peinador,
and Marcos D. Garcia, Adjusting the dynamism of covalent
imine chemistry in the aqueous synthesis of cucurbit[7]uril-
based [2]rotaxanes, Org. Lett., 2019, 21, 8976. (b) I. Neira,
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ARTICLE
M. D. García, C. Peinador, and A. E. Kaifer, Terminal
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carboxylate effects on the thermodynamics and kinetics of
cucurbit[7]uril binding to guests containing a central
bis(pyridinium)-xylylene site, J. Org. Chem., 2019, 84, 2325.
13 K. Kim, D. Kim, J. W. Lee, Y. H. Ko and K. Kim, Growth of
poly(pseudorotaxane) on gold using host-stabilized charge-
transfer interaction, Chem. Commun., 2004, 848.
DOI: 10.1039/D0OB01085E
14 (a) J. W. Lee, I. Hwang, W. S. Jeon, Y. H. Ko, S. Sakamoto, K.
Yamaguchi, and K. Kim, Synthetic molecular machine based
on reversible end-to-interior and end-to-end loop formation
triggered by electrochemical stimuli, Chem. Asian J., 2008,
3, 1277. (b) A. Trabolsi, M. Hmadeh, N. M. Khashab, D. C.
Friedman, M. E. Belowich, N. Humbert, M. Elhabiri, H. A.
Khatib, A.-M. Albrecht-Gary, and J. F. Stoddart, Redox-
driven switching in pseudorotaxanes, New J. Chem. 2009,
33, 254.
15 A. E. Kaifer, W. Li, S. Silvi and V. Sindelar, Pronounced pH
effects on the kinetics of cucurbit[7]uril-based
pseudorotaxane formation and dissociation, Chem.
Commun., 2012, 48, 6693.
16 (a) T. M. Bockman, and J. K. Kochi, Isolation and oxidation-
reduction of methylviologen cation radicals. Novel
disproportionation in charge-transfer salts by x-ray
crystallography, J. Org. Chem. 1990, 55, 4127. (b) G.
Ragazzon, C. Schäfer, P. Franchi, S. Silvi, B. Colasson, M.
Lucarini, and A. Credi, Remote electrochemical modulation
of pKa in a rotaxane by co-conformational allostery, PNAS
2018, 115, 9385.
17 M. Marchini, M. Baroncini, G. Bergamini, P. Ceroni, M.
D’Angelantonio, P. Franchi, M. Lucarini, F. Negri, T. Szreder,
and M. Venturi, Hierarchical growth of supramolecular
structures driven by pimerization of tetrahedrally arranged
bipyridinium units, Chem. Eur. J. 2017, 23, 6380.
18 (a) M. R. Geraskina, A. T. Buck, and A. H. Winter, An Organic
Spin Crossover Material in Water from a covalently linked
radical dyad, J. Org. Chem. 2014, 79, 7723. (b) A. G. Evans, J.
C. Evans, and M. W. Baker, Electron spin resonance study of
the dimerization equilibrium of the radical cation of 1,1'-
diethyl-4,4'-bipyridylium diiodide in metanol, J. Am. Chem.
Soc. 1977, 99, 5882. (c) A. G. Evans, J. C. Evans, and M. W.
Baker, Bipyridyl radical cations. Part I. Electron spin
resonance study of the dimerisation equilibrium of
morphamquat radical cation in metanol, J. Chem. Soc.
Perkin Trans. 2 1975, 1310. (d) A. G. Evans, J. C. Evans, and
M. W. Baker, Study of bipyridyl radical cations. Part 5. Effect
of structure on the dimerisation equilibrium, J. Chem. Soc.
Perkin Trans. 2 1977, 1787. (e) K. Tsukahara, J. Kaneko, T.
Miyaji, K. Abe, M. Matsuoka, T. Hara, T. Tanase, and S. Yano,
Syntheses, characterizations, and redox behavior of
optically active viologens and bisviologens, Bull. Chem. Soc.
Jpn. 1999, 72, 139. (f) A. T. Buck, J. T. Paletta, S. A.
Khindurangala, C. L. Beck, and A. H. Winter, A noncovalently
reversible paramagnetic switch in water, J. Am. Chem. Soc.
2013, 135, 10594.
6 | J. Name., 2012, 00, 1-3
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