Transmembrane anion transport mediated by adamantyl-functionalised imidazolium salts

Article abstract of DOI:10.1080/10610278.2014.969265

We present the design, synthesis and transmembrane anion transport properties of a new class of mobile organic transporters, possessing a central imidazolium cation and two external adamantyl units. We demonstrate herein that the imidazolium cation can be incorporated in the structure of active mobile anion transporters. Depending on the nature of the counter-anion of the salt, as well as the extravesicular anions, different anion selectivities were obtained. We show the importance of the H2 proton of the imidazolium cation in order to obtain a higher binding constant of the chloride anion. Furthermore, we demonstrate the importance of the flexibility of the spacers between the adamantyl groups and the imidazolium cation in the transport process.

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Supramolecular Chemistry
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Transmembrane anion transport mediated by
adamantyl-functionalised imidazolium salts
Julien Gravela & Andreea R. Schmitzera
a Département de Chimie, Université de Montréal, 2900 Edouard Montpetit, CP 6128, succ.
Centre ville, Montréal, Québec, Canada
Published online: 16 Oct 2014.
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Supramolecular Chemistry, 2014
http://dx.doi.org/10.1080/10610278.2014.969265
Transmembrane anion transport mediated by adamantyl-functionalised imidazolium salts
Julien Gravel and Andreea R. Schmitzer*
´ ´ ´ ´ ´
Departement de Chimie, Universite de Montreal, 2900 Edouard Montpetit, CP 6128, succ. Centre ville, Montreal, Quebec, Canada
(Received 21 August 2014; accepted 22 September 2014)
We present the design, synthesis and transmembrane anion transport properties of a new class of mobile organic
transporters, possessing a central imidazolium cation and two external adamantyl units. We demonstrate herein that the
imidazolium cation can be incorporated in the structure of active mobile anion transporters. Depending on the nature of
the counter-anion of the salt, as well as the extravesicular anions, different anion selectivities were obtained. We show the
importance of the H2 proton of the imidazolium cation in order to obtain a higher binding constant of the chloride anion.
Furthermore, we demonstrate the importance of the flexibility of the spacers between the adamantyl groups and the
imidazolium cation in the transport process.
Keywords: anion transmembrane transport; mobile transporter; imidazolium salts
1. Introduction
group recently reported the preparation of imidazolium,
benzimidazole and benzimidazolium-based anion trans-
porters that can self-assemble into ion channels via p-
stacking intermolecular interactions to allow anion
diffusion (9–13). Mechanistic studies revealed that the
transport of chloride across the membrane was possible
through anion–p interactions with the aromatic units of
the transporter (9). In order to get a better understanding of
the role of the imidazolium cation in the transport process,
as well as the influence of the structure of the transporter in
terms of self-aggregation capacity in the bilayer, we
designed a new family of imidazolium salts bearing
adamantyl moieties (Figure 1).
Anion transport across cell membrane is an important
biological process which is regulated by transmembrane
ion channels (1). The malfunction of chloride channels
generally results in a multitude of diseases, such as
osteoporosis or formation of kidney stones (2). Cystic
fibrosis represents the most common disease involving
anion transport in the human body (3). This disease is the
result of an altered chloride ion diffusion caused by a
mutation of the cystic fibrosis transmembrane regulator
(CFTR) protein (2, 3).
Interest regarding the design and development of
artificial anion transporters as possible solutions to cure
such malfunctions has increased significantly over the past
decades (4). Therefore, supramolecular chemists focused
their attention on the use of small molecules which possess
the capacity to act as anion transporters, both to regulate
these ion gradient disorders and to better understand the
importance of such processes in biological systems.
In terms of mechanisms, synthetic transporters can operate
via two distinct mechanisms. The first one involves the
formation of a transmembrane channel, which can be
formed by a single molecule, or by a supramolecular
assembly of several molecules, depending on the size of
the monomer. On the other hand, the second mechanism of
anion transport involves small molecules acting as mobile
carriers. They can cross the cell membrane as an anion–
transporter complex, allowing ionic exchange between the
extra- and intravesicular media (5). The activity of ion
transporters is generally based on the exploitation of weak
interactions between ions and the transporter, such as
hydrogen bonds (6), anion–p (7) or cation–p (8). Our
We first hypothesised that the presence of adamantyl
groups on the imidazolium central cation still confers the
transporter the required lipophilicity to penetrate and
diffuse through a phospholipid membrane (14), but the
presence of the two adamantyl groups avoids their self-
aggregation and formation of transmembrane channels.
Herein, we present the transmembrane transport properties
of adamantyl-functionalised imidazolium carriers, demon-
strating the importance of the nature of their counter-anion
and its impact on the anion transport process. Finally,
kinetic studies allow us to demonstrate the mobile anion
transport mechanism.
2. Results and discussion
2.1 Synthesis
Synthesis of imidazolium salt 1a was adapted from an
existing procedure (15, 16). The symmetric imidazolium
*Corresponding author. Email: ar.schmitzer@umontreal.ca
q 2014 Taylor & Francis

2
J. Gravel and A.R. Schmitzer
Figure 1. Adamantyl-imidazolium salts (n ¼ 0–2).
Figure 4. Synthesis of imidazolium salts 8b, 9b, 9c and 9d.
Reagents and conditions: (a) NaBF4, MeOH; (b) KPF6, MeOH;
(c) LiNTf2, MeOH.
Figure 2. Synthesis of imidazolium salts 1a and 1b. Reagents
and conditions: (a) formaldehyde, glyoxal, HBr, MeOH; (b)
LiNTf2, MeOH.
salt was obtained through the condensation of formal-
dehyde, adamantylamine and glyoxal, in the presence of
HBr (Figure 2).
Figure 5. Synthesis of imidazolium salts 10b and 11b. Reagents
and conditions: LiNTf2, MeOH.
All other imidazolium bromide salts were prepared
following a general procedure. First, the corresponding
adamantane alcohol was brominated (17, 18). Then, two
successive nucleophilic substitutions were performed
using the corresponding imidazole in order to generate
the bromide salts 8a, 9a, 10a and 11a (Figure 3). Finally,
the anion metathesis yielded compounds 1b, 8b, 9b–9d,
10b and 11b as air-stable salts (Figures 2, 4 and 5).
probe that possesses the particularity to have its
fluorescence quenched in the presence of chloride anions.
Thus, a raise in fluorescence while the transporter is
injected indicates a transport of Cl– outside of the lipo-
somes (19). At the end of each fluorescence experiments,
Triton-X was added in order to lyse the liposomes and
observe full lucigenin fluorescence.
As shown in Figure 6, bringing more flexibility
between the adamantyl groups and the imidazolium cation
tends to raise the transport efficiency, the most efficient
transporter being 9a. In addition, transporter 11a was
designed to investigate the contribution of the most acidic
proton of the imidazolium ring H2. This proton is known to
be involved in hydrogen-bond formation with anions (20).
Replacing this H2 proton by a methyl group prevents the
2.2 Transmembrane anion transport activity
and mechanism
We first studied the influence of the nature of the cationic
unit regarding the chloride transport properties. Our assays
were conducted using standard Egg Yolk Phosphatidyl
Choline (EYPC) liposomes containing a 100 mM NaCl
and 2 mM lucigenin solution. Lucigenin is a fluorescent
Figure 3. Synthesis of imidazolium salts 8a, 9a, 10a and 11a. Reagents and conditions: (a) HBr; (b) imidazole, NaH, DMF;
(c) 2-methylimidazole, NaH, DMF; (d) (n ¼ 1), 2, DMF, microwave; (e) (n ¼ 2), 3, DMF.

Supramolecular Chemistry
3
activity of these salts follows the Hofmeister sequence, as
we previously reported (9), following the order: Br– ,
BF4– , PF6– , NTf2–. This result is directly correlated to
the capacity of these molecules to partition and insert into
the phospholipid bilayer.
In order to confirm our initial hypothesis on the capacity
of these molecules to act as mobile ionic transporters, we
performed chloride transport studies in hybrid EYPC:
cholesterol liposomes (7:3) (Figure 8). Cholesterol has the
property to rigidify the liposomes membrane by increasing
the energy barrier of normal phospholipids movements
inside the membrane (phospholipids rotations, lateral
diffusion or phospholipid flip–flop) (21). In the case of a
transmembrane ion channel, the chloride transport is
independent on the nature of the phospholipid used, but the
transport rate in the case of mobile carriers is slowed down
by a lower diffusion in a rigidified membrane, which is
translated by a large difference between the normal and the
rigidified liposomes.
Figure 6. Relative chloride transport activity of different
bromide imidazolium salts at 15 mol% relative to EYPC.
Intravesicular: 2 mM lucigenin, 100 mM NaCl, 10 mM phosphate
buffer (pH ¼ 6.2). Extravesicular: 100 mM NaNO3, 10 mM
phosphate buffer (pH ¼ 6.2).
As shown in Figure 8, the chloride efflux is slower in
cholesterol-doped EYPC liposomes, which is a character-
istic for a mobile ion carrier. Similar results were obtained
for transporters 9a and 11b (Figures S1 and S2 in the ESI).
Kinetic parameters of the transport process were
determined by varying the concentrations of the carrier in
both types of liposomes (Figure 9).
hydrogen-bond formation, resulting in a less efficient
transporter. One main advantage of using imidazolium
salts as synthetic anion transporters is that it is easily
possible to replace their counter-anion. As compound 9
showed the best transport efficiency, we decided to use it as
scaffold and study the influence of the nature of different
counter-anions with compounds 9a–9d (Figure 7).
The transport assays were performed with transporters
possessing the same cation, but different counter-anions
and showed that the most efficient transporter bears the
more lipophilic anion (Figure 7). The chloride transport
For each transport experiment, an initial rate (Vo) was
measured after the injection of the transporter at less than
10% of the maximum transport process and the results
were transposed on a graph for a Hill analysis (Figure 10).
Figures 9 and 10 clearly show that transporter 9d
becomes slower and less efficient in rigidified liposomes,
at high concentrations. Table 1 shows that Hill
coefficients and EC50 values are different depending on
the composition of the liposomes. Originally, the Hill
coefficient described the number of monomers needed to
aggregate into an active assembly in the chloride transport
process. However, obtaining Hill coefficient values
superior to 1 is quite characteristic for synthetic
transporters forming unstable supramolecular structures
(22). The trend observed in these experiments is that the
Hill coefficient is higher in a more rigidified membrane.
Our hypothesis is that there is an equilibrium between the
complexed monomer with a chloride and the free
monomer inside the bilayer, and the transport process
occurs via a cooperative interaction between the
monomers, but not by a channel-forming mechanism.
In the case of the rigidified liposomes, where the diffusion
of the transporter inside the membrane is decreased, the
transport essentially requires a larger number of mobile
monomers in order to perform the transport. The property
of these adamantyl-functionalised salts to act as mobile
transporters is also supported by the transport assays
performed in dipalmitoylphosphatidylcholine (DPPC)
liposomes (Figure S3 in the ESI). Because the transport
Figure 7. Relative chloride transport activity of imidazolium
salt 9 bearing different counter-anion (9a–9d) at 15 mol%
relative to EYPC. Intravesicular: 2 mM lucigenin, 100 mM NaCl,
10 mM phosphate buffer (pH ¼ 6.2). Extravesicular: 100 mM
NaNO3, 10 mM phosphate buffer (pH ¼ 6.2).

4
J. Gravel and A.R. Schmitzer
Figure 8. Relative chloride transport activity of imidazolium salt 9d at 20 mol% relative to EYPC or EYPC:cholesterol (7:3).
Intravesicular: 2 mM lucigenin, 100 mM NaCl, 10 mM phosphate buffer (pH ¼ 6.2). Extravesicular: 100 mM NaNO3, 10 mM phosphate
buffer (pH ¼ 6.2).
Figure 9. Relative chloride transport activity of transporter 9d at different concentrations in (A) EYPC liposomes and (B) EYPC:
cholesterol 7:3 liposomes. Intravesicular: 2 mM lucigenin, 100 mM NaCl, 10 mM phosphate buffer (pH ¼ 6.2). Extravesicular: 100 mM
NaNO3, 10 mM phosphate buffer (pH ¼ 6.2).
in rigidified membrane may be influenced by a different
partition of the transporter (6), classical U-tube
experiments were performed with compound 9d and
confirmed the proposed carrier mechanism (Figure S18 in
the ESI).
binding of the chloride. As previously shown, a better
chloride association increases the transport efficiency, but
this is not the only parameter that governs the transport
process. Indeed, the flexibility of the cation also plays an
important role in the transport process. Even though
molecule 9a seems to strongly bind chloride anions, data
could not be fitted into a 1:1 model and its association
constant could not be calculated (Figure S12 in the ESI).
However, as we previously showed, transporter 9a bearing
a bromide counterion is less efficient than its analogue 9d
bearing an NTf2 counterion.
For a mobile ion carrier, the binding efficiency of the
chloride anion is crucial for the transport process. This
mechanism implies that the carrier binds the anion in the
intravesicular solution, penetrates and diffuses through
the phospholipid bilayer as a complex and releases it in the
extravesicular solution. We determined the chloride-
binding association constant of different transporters,
possessing different cationic structures (Table 2) (23).
The results shown in Table 2 suggest that the H2
proton on the imidazolium cation is very important for the
As the difference in their transport activity cannot be
explained by the binding of the chloride during the
transport process, we decided to perform an anion
selectivity assay. The principle is the same as in the

Supramolecular Chemistry
5
Figure 10. Hill plot analysis obtained from data shown in Figure 9 in EYPC liposomes (squares) and EYPC:cholesterol 7:3 liposomes
(circles). The concentration of the transporter is reported relative to the lipid concentration.
Table 1. Kinetic parameters of molecule 9d.
Liposome composition
Hill coefficient
EC50 (%)a
EYPC
EYPC:cholesterol 7:3
4.5 ^ 0.6
7 ^ 1
17.7 ^ 0.9
12.5 ^ 0.5
a Relative to the lipid concentration.
Table 2. Binding constants of chloridea with transporters 1b,
8b, 9a, 9d, 10b and 11b in chloroform.
Compound
Ka (M–1
)
1b
8b
9a
9d
10b
11b
1224
1578
–
1356
172
191
b
Figure 11. Relative chloride transport activity of imidazolium
salt 9a at 15 mol% relative to EYPC. Intravesicular: 2 mM
lucigenin, 100 mM NaCl, 10 mM phosphate buffer (pH ¼ 6.2).
Extravesicular: 100 mM NaX or Na2X, 10 mM phosphate buffer
(pH ¼ 6.2 or 7.4 for NaHCO3).
a Added as TBAC salt, fitting a 1:1 model.
b Data could not be fitted into a 1:1 model (ESI).
lucigenin-based fluorescence assays, but the extravesicular
free anions are varied (Figures 11 and 12).
(24). The anion selectivity in these experiments still
follows the Hofmeister sequence. Bromide being more
labile than the NTf2–, a quick anion exchange can take
place with the excess of anions of the extravesicular
solution, before undergoing the anion transport process.
In other words, these results suggest that the actual salt
involved in the chloride transport is the one bearing the
The results shown in Figures 11 and 12 demonstrate
completely different behaviours of transporters 9a and 9d
in the presence of different extravesicular anions.
Transporter 9a shows an anion selectivity following the
order of the hydration energy of each extravesicular free
anion: SO24– (–1080 kJ/mol) , HCO3– (–360 kJ/mol)
, NO3– (–320 kJ/mol) , ClO4– (–260 kJ/mol) (Figure 11)

6
J. Gravel and A.R. Schmitzer
1,3,6-pyrenetrisulfonate (HPTS) were performed
(Figure 14). HPTS is a pH-sensitive probe that possesses
a protonated and a deprotonated (pKa < 7.4) (25) form
with different excitation wavelengths, respectively, 403
and 460 nm, and the same emission wavelength at 510 nm.
The ratio of emission between the protonated (I0) and the
deprotonated (I1) form is directly related to the pH of the
solution containing the probe, hence to the transport of
protons across the phospholipid bilayer (26).
The anion selectivity observed in the HPTS assays
follows almost the same order as the one observed in the
lucigenin-based transport assays (Figure 14), although in
this case a greater alkalinisation of the liposomes for the
bicarbonate anion (pKa ¼ 6.4) (27) can be observed. This
is probably simply due to the bicarbonate, acting as a base,
and alkanisation is not only indicative of proton efflux, but
also related to an acid–base reaction between the
bicarbonate anion and the intravesicular solution, i.e. the
bicarbonate influx. In the case of the sulfate (pKa ¼ 1.9)
(27), nitrate (pKa ¼ –1.64) (28) and perchlorate (pKa < –8)
(28) anions, they follow exactly the same order as in the
lucigenin-based transport assays (Figure 12). The pKa of
their acid–base couples are too low to deprotonate the
HPTS probe. In these experiments, the pH changes can
only be related to OH– or Hþ flux. After addition of the
transporter 9d to the external solution containing the
sulfate anions, an alkalinisation of the liposomes occurs.
The sulfate is poorly membrane permeable, hence the
alkalinisation process is likely caused by Hþ diffusion
(26). This means that the SO24–/Cl– antiport and Cl–/Hþ
symport processes are greatly favoured, compared with the
other anions used. In the case of the perchlorate anion, the
pH variation is not the same, only a light acidification of
the interior of the liposomes being observed. This result is
Figure 12. Relative chloride transport activity of imidazolium
salt 9d at 15 mol% relative to EYPC. Intravesicular: 2 mM
lucigenin, 100 mM NaCl, 10 mM phosphate buffer (pH ¼ 6.2).
Extravesicular: 100 mM NaX or Na2X, 10 mM phosphate buffer
(pH ¼ 6.2 or 7.4 for NaHCO3).
extravesicular anion (Figure 13). In the case of the sulfate
anion, the most hydrated anion, the newly formed sulfate
salt is completely solvated and cannot penetrate into the
bilayer anymore, explaining the lack of chloride transport.
Transporter 9d (Figure 12) shows a completely
different anion selectivity: NO3– , ClO4– , HCO3–
, SO24–, where sulfates as extravesicular anions increase
the chloride transport efficiency. This result not only
confirms the anion transport selectivity of transporter 9d,
but also shows an odd anion selectivity, not related to the
hydration energy of extravesicular anions. In order to get a
better understanding of the selectivity observed for
transporter 9d, transport studies using the 8-hydroxy-
Figure 13. Anion metathesis between transporter molecule 9a and extravesicular anion before undergoing chloride transport process.

Supramolecular Chemistry
7
as the transport process is a complex one, where multiple
equilibria are involved and where media with different
polarities have to be crossed from one side of the
membrane to the other one. The mobile transporter needs a
good complexation of the anion during the transport
process, but has to be able to release it on the other side of
the membrane. A greater flexibility in the transporter’s
structure may benefit to a conformational change
depending on the polarity of the media, resulting in
different binding affinities to the transported anion.
4. Supporting Information
Procedures for the syntheses of the imidazolium salts, their
characterisation,liposomespreparation,fluorescenceassays,
NMR titrations and U-tube experiments can be found here:
http://dx.doi.org/10.1080/10610278.2014.969265
Figure 14. HPTS-based transport assay of imidazolium salt 9d
at 15 mol% relative to EYPC. Intravesicular: 0.1 mM HPTS,
100 mM NaCl, 10 mM phosphate buffer (pH ¼ 6.2).
Extravesicular: 100 mM NaX or Na2X, 10 mM phosphate
buffer (pH ¼ 6.2 or pH ¼ 7.4 for NaHCO3).
Acknowledgements
The authors gratefully acknowledge the Natural Sciences and
Engineering Research Council of Canada (NSERC), the Fonds
´ ´
Quebecois de la Recherche sur la Nature et les Technologies
´
(FRQ-NT) and Universite de Montreal for the financial support.
The authors also thank Le Centre Regional de RMN and Le
more consistent with a Cl–/ClO4– antiport process. Finally,
in the case of the nitrate anion, a faster NO3–/Hþ symport
process than the Cl–/NO3– antiport process can be
observed.
´
´
´
Centre Regional de Spectrometrie de Masse for their assistance in
this research.
´
The correlation of these results with those obtained
from the lucigenin-based transport assays (Figure 12)
shows that it is possible to tune the chloride transport
process of molecule 9d by favouring its Cl–/Hþ symport
and X–/Cl– antiport process while preventing the X–/Hþ
symport. This hypothesis is also supported by the results
obtained when perchlorate was used as an internal anion
(Figure S16 in the ESI).
References
(1) Saier, M.H., Jr, J. Membr. Biol. 2000, 175, 165–180.
(2) Jentsch, T.J.; Maritzen, T.; Zdebik, A.A. J. Clin. Invest.
2005, 115, 2039–2046.
(3) Higgins, C. Nature 1992, 358, 356–536.
(4) Busschaert, N.; Gale, P.A. Angew. Chem. Int. Ed. 2013, 52,
1374–1382.
(5) Busschaert, N.; Kirby, I.L.; Young, S.; Coles, S.J.; Horton,
P.N.; Light, M.E.; Gale, P.A. Angew. Chem. Int. Ed. 2012,
51, 4426–4430.
(6) Cranwell, P.B.; Hiscock, J.R.; Haynes, C.J.; Light, M.E.;
Wells, N.J.; Gale, P.A. Chem. Commun. 2013, 49, 874–
876.
(7) Jentzsch, A.V.; Emery, D.; Mareda, J.; Metrangolo, P.;
Resnati, G.; Matile, S. Angew. Chem. Int. Ed. 2011, 50,
11675–11678.
´
(8) Michau, M.; Caraballo, R.; Arnal-Herault, C.; Barboiu, M.
J. Membr. Sci. 2008, 321, 22–30.
(9) Elie, C.R.; Noujeim, N.; Pardin, C.; Schmitzer, A.R. Chem.
Commun. 2011, 47, 1788–1790.
(10) Elie, C.R.; Charbonneau, M.; Schmitzer, A.R. MedChem-
Commun. 2012, 3, 1231–1234.
(11) Elie, C.R.; Hebert, A.; Charbonneau, M.; Haiun, A.;
Schmitzer, A.R. Org. Biomol. Chem. 2013, 11, 923–928.
(12) Vidal, M.; Elie, C.R.; Campbell, S.; Claing, A.; Schmitzer,
A.R. MedChemCommun. 2014, 5, 436–440.
(13) Kempf, J.; Noujeim, N.; Schmitzer, A.R. RSC Adv. 2014, 4,
42293–42298.
(14) Sekutor, M.; Stimac, A.; Mlinaric-Majerski, K.; Frkanec, R.
Org. Biomol. Chem. 2014, 12, 6005–6013.
(15) Arduengo, III, A.J. US Patent, 5,007,414. 1991.
3. Conclusion
In conclusion, we successfully designed a new class of
mobile anion transporters, possessing a central imidazo-
lium cation and two external adamantyl units. These salts
possess the capacity to transport chloride outside
liposomes, acting as mobile transmembrane carriers.
We demonstrated herein that the imidazolium cation can
also be incorporated in the structure of mobile
transporters. Depending on the nature of the counter-
anion of the salt, as well as the extravesicular anions,
different anion selectivities were obtained. We confirmed
the importance of the H2 proton of the imidazolium cation
in order to obtain a higher binding constant between the
chloride anion and the imidazolium salt. We also
demonstrated the importance of the flexibility of the
spacers between the adamantyl groups and the imidazo-
lium cation in the transport process. This is not surprising

8
J. Gravel and A.R. Schmitzer
(16) Archer, R.H.; Zones, S.I.; Davis, M.E. Microporous
Mesoporous Mater. 2010, 130, 255–265.
(17) Shahane, S.; Toupet, L.; Fischmeister, C.; Bruneau, C. Eur.
J. Inorg. Chem. 2013, 2013, 54–60.
(23) Cabrer, P.R.; A.-Parilla, E.; Meijide, F.; Seijas, J.A.; Nunez,
E.R.; Tato, J.V. Langmuir 1999, 15, 5489–5495.
(24) Smith, D.W. J. Chem. Ed. 1977, 54, 540–542.
(25) Wolfbeis, O.S.; Fuerlinger, E.; Kroneis, H.; Marsoner, H.
Fresenius Z. Anal. Chem. 1983, 314, 119–124.
(26) Berezin, S.K.; Davis, J.T. J. Am. Chem. Soc. 2009, 131,
2458–2459.
¨
(18) Belser, T.; Stohr, M.; Pfaltz, A. J. Am. Chem. Soc. 2005,
127, 8720–8731.
(19) McNally, B.A.; Koulov, A.V.; Smith, B.D.; Joos, J.B.;
Davis, A.P. Chem. Commun. 2005, 1087–1089.
(20) Tsuzuki, S.; Tokuda, H.; Mikami, M. Phys. Chem. Chem.
Phys. 2007, 9, 4780–4784.
(21) Bennett, W.F.; MacCallum, J.L.; Tieleman, D.P. J. Am.
Chem. Soc. 2009, 131, 1972–1978.
(27) CRC Handbook of Chemistry and Physics, CRC Handbook
of Chemistry and Physics, 95th ed.; Taylor & Francis: Boca
Raton, FL, 2014.
(28) Housecroft, C.E.; Sharpe, A.G. Inorganic Chemistry, 2nd
ed.; Pearson Prentice Hall: Harlow, UK, 2005.
(22) Jentzsch, A.V.; Hennig, A.; Mareda, J.; Matile, S. Acc.
Chem. Res. 2013, 46, 2791–2800.

Supramolecular Chemistry
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Julien Gravel and Andreea R. Schmitzer
Transmembrane anion transport mediated by adamantyl-functionalised imidazolium salts
1–9