Binding study on 1-adamantylalkyl(benz)imidazolium salts to cyclodextrins and cucurbit[n]urils

Article abstract of DOI:10.1039/d0nj00738b

Multitopic guests are used as key components of molecular triggers, switchers, sensors, or reactors in recent supramolecular chemistry studies. The increasing complexity of these compounds correlates with the need for versatile, synthetically available binding motifs (building blocks) with tuneable supramolecular properties. The utilisation of a favoured 1-adamantylmethyl moiety in ammonium, imidazolium and pyridinium salts is sometimes restricted by synthetic difficulties most likely related to the adamantane cage bulkiness. Therefore, we prepared a series of new adamantylated (benz)imidazolium salts with longer flexible linkers between the adamantane cage and cationic moiety. We tested the supramolecular properties of these binding motifs towards the natural cyclodextrins α-CD, β-CD and γ-CD and cucurbit[n]urils (n= 7, 8) using NMR, mass spectrometry and titration calorimetry. All tested guests formed 1:1 complexes with the abovementioned hosts, retaining binding strengths, selectivity, and complex geometries in comparison to the parent methylene-linked homologues. We did not confirm our original concern that longer linkers would negatively affect the binding strength towards CBns due to the reduction in the ion-dipole interaction contribution. Therefore, we believe that adamantylalkyl imidazolium binding motifs can be used for multitopic supramolecular guest construction.

Full text of DOI:10.1039/d0nj00738b

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Binding study on 1-adamantylalkyl(benz)imidazolium salts towards
cyclodextrins and cucurbit[n]urils
Kristýna Jelínková, Jelica Kovačević, Eva Wrzecionková, Zdeňka Prucková, Michal Rouchal,
*
Lenka Dastychová, and Robert Vícha
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Department of Chemistry, Faculty of Technology, Tomas Bata University in Zlín,
Vavrečkova 275, 760 01 Zlín, Czech Republic
∗
Corresponding author. Tel.: +420-576031103; e-mail: rvicha@utb.cz
Abstract
Multitopic guests are used as key components of molecular triggers, switchers, sensors, or
reactors in recent supramolecular chemistry studies. The increasing complexity of these
compounds correlates with the need for versatile, synthetically available binding motifs
(
building blocks) with tuneable supramolecular properties. The utilisation of a favoured 1-
adamantylmethyl moiety within ammonium, imidazolium and pyridinium salts is sometimes
restricted by synthetic difficulties most likely related to adamantane cage bulkiness. Therefore,
we prepared a series of new adamantylated (benz)imidazolium salts with longer flexible linkers
between the adamantane cage and cationic moiety. We tested supramolecular properties of
these binding motifs towards natural cyclodextrins α-CD, β-CD and γ-CD and cucurbit[n]urils
(
n=7,8) using NMR, mass spectrometry and titration calorimetry. All tested guests formed 1:1
complexes with abovementioned hosts retaining binding strengths, selectivity, and complex
geometries in comparison to the parent methylene-linked homologues. We did not confirm our
original concern that longer linkers would negatively affect the binding strength towards CBns
due to reducing the ion-dipole interaction contribution. Therefore, we believe that
adamantylalkyl imidazolium binding motifs can be used for multitopic supramolecular guest
construction.
Keywords: adamantane, cucurbit[n]uril, cyclodextrins, host-guest systems, supramolecular
chemistry.
1
. Introduction
Host-guest chemistry plays a significant role in the world of supramolecular chemistry. Well-
defined and structurally organised supramolecular systems are formed employing non-covalent
interactions in the sense of molecular recognition and self-assembly concept. In specific
situations, when axle-like guests consist of more than one binding site (generally, n sites) with
suitable affinities towards particular macrocycles, stable supramolecular arrangements can be
1
prepared in a [n]pseudorotaxane manner. Indeed, the binding strengths of particular sites must
be well-tuned. Therefore, characterisation of binding properties of model guests is fundamental
for designing more complex multitopic guests which can have advanced functions. A properly
organised tritopic guest serves as an axis of an enantioselective reactor made of [4]rotaxane
with a chiral cavity of γ-CD, which contributes (Z,E)-1,3-cyclooctadiene up to 15.3% ee via
photoisomerisation of (Z,Z)-1,3-cyclooctadiene with the highest value for enantioselectivity of
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the supramolecular isomerisation. Another advanced supramolecular system is a doubly
photoresponsive multitopic guest composed of azobenzene and stilbene moieties that can be
3
isomerised separately with UV light of different wavelength. The molecular shuttle of α-CD
is driven by photochemical reversible isomerisation of photosensitive units.
Natural and inexpensive cyclodextrins (CDs) and highly symmetric and selective
cucurbit[n]urils (CBns) are the most extensively studied families of macrocyclic hosts.
Cyclodextrins are cyclic oligosaccharides which can be prepared by enzymatic decomposition
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of starch. Molecules of the most common natural cyclodextrins, α-, β- and γ-CD, consist of 6,
7 and 8
D-glucopyranoside units linked by α(1→4) glycosidic bonds, respectively. These
macrocycles adopt a hollow truncated cone with non-symmetric portals shape. Cyclodextrins
have attracted the attention for their biocompatibility, nontoxicity and capability of forming
inclusion complexes with positively charged or neutral guests. Since cyclodextrins are
inherently chiral, they have been employed in catalysis or separation techniques.
Cucurbit[n]urils are synthetic macrocycles oligomers prepared by condensation of n glycoluril
units and formaldehyde. Although the structure of CB6 was determined in 1980s, the family
of known CBns was enriched with CB5, CB7 and CB8, which were discovered by Kim in
000. CBn molecules are highly rigid, barrel-like shaped convex cylinders with two symmetric
carbonyl-rimmed portals and hydrophobic cavity. The geometry and electronic properties of
CBns are best suited for positively charged guests derived from a hydrocarbon parent skeleton.
Geometric compatibility of the host interior cavity and nonpolar guest parent hydrocarbon
combined with positively charged moieties properly located in the centres of host portals can
lead to highly stable host-guest complexes.
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Particularly, CB7 forms ultrahigh-affinity host-
1
2
guest pairs with dicationic derivatives of ferrocene and cage hydrocarbons, such as
1
3,14
15,16
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adamantane,
diamantane,
bicyclo[2.2.2]octane or cubane.
Our research group focused on the synthesis and study of binding properties of various
multitopic guests. We have reported several guests with terminal adamantane-based binding
sites which were prepared via quaternisation using 1-adamantylmethyl iodide.18,19,20 However,
we faced serious synthetic difficulties, most likely related to the bulkiness of the adamantane
cage, which disabled the preparation of some promising guests. Therefore, we decided to
synthesise a series of model guests with an extended linker between the adamantane cage and
cationic moiety. We prepared three methylimidazolium and three methylbenzimidazolium salts
with 2-(1-adamantyl)ethyl, 3-(1-adamantyl)propyl and 3-(3,5-dimethyladamantan-1-yl)propyl
substituents, respectively (see Figure 1 for structures). Subsequently, we concentrated on
binding properties of the model guests towards CDs and CBns to examine whether ethylene
and propylene linkers influence affinity towards macrocycles. The binding behaviour was
investigated by means of NMR and mass spectrometry. Association constants were determined
by isothermal titration calorimetry.
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a
Figure 1 Structures of the hosts (n=6,7,8) and the guests under consideration ( published
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previously; this study).
2
. Results and Discussion
2.1 Chemistry
The adamantyl based imidazolium and benzimidazolium salts 9a and 10a with methylene linker
between the adamantane cage and (benz)imidazolium cation (see Figure 1 for structures) were
prepared in our previous work.21 The (benz)imidazolium salts 9b–9d and 10b–10d were
prepared according to synthetic pathways shown in Scheme 1. We synthesised the compound
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b using two different pathways. The first pathway involved the radical addition of 1-
bromoadamantane to the acrylonitrile, nitrile hydrolysis and reduction to produce alcohol 6b in
a moderate overall yield of 54%.22,23 The alternative pathway started from adamantane-1-
carboxylic acid (1a), which was transformed to the aldehyde 2 via subsequent reduction with
LiAlH
4
and Swern oxidation. Aldehyde
2
was reacted with oxolan-2-
ylmethyl(triphenyl)phosphonium bromide under Wittig conditions to produce acetal 3.
Subsequent hydrolyses and hydrogenation afforded the critical intermediate 3-(1-
adamantyl)propan-1-ol in the acceptable yield of 28% regarding the carboxylic acid 1a. While
the former approach was more efficient, the latter avoids handling of unpleasant organotin
compounds. Alcohols 6a and 6c were obtained via a reduction from carboxylic acid 1b and via
the abovementioned three-step approach from 1-bromo-3,5-dimethyladamantane (5b),
respectively. The alcohols 6 were converted to the corresponding bromoderivatives 7 via
convenient Appel’s bromination to avoid undesired elimination reactions. The ethylene
(benz)imidazolium salts 9 and 10 are available from bromoderivatives 7 either by a sequence
of N-substitution on the (benz)imidazole precursor and final methylation (as demonstrated for
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0b) or directly by quaternisation using 1-methyl(benz)imidazole. Although both these
DOI: 10.1039/D0NJ00738B
methods provided comparable overall yields, the latter is of higher importance since it mimics
the final introduction of terminal binding sites into molecules of multitopic ligands. Therefore,
we demonstrated that bromides 7 could be used as quaternisation agents to provide final guests
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and 10 in satisfactory yields.
Scheme 1 The synthetic pathways leading to the guests under consideration.
2.2 Host-guest Studies
2
.2.1 NMR experiments
We started our investigation of supramolecular properties through NMR experiments. Initially,
we studied the behaviour of our (benz)imidazolium salts with host molecules α-CD, β-CD, γ-
1
CD, CB6, CB7 and CB8 using H NMR titration. It is a well-known phenomenon that CDs
markedly deshield protons located inside their cavities. Since the most downfield shifted signals
in all cases were that of adamantyl groups, we infer that guests 9b–9d and 10b–10d interact
with cyclodextrins with their adamantane cages in inclusion manner.
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Table 1 Maximal complexation-induced shifts (CIS) for the most affected H-atoms of the
guests.
guest
host
CISmax H( ) [ppm] CISmax [ppm]
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α-CD
β-CD
γ-CD
α-CD
β-CD
γ-CD
α-CD
β-CD
γ-CD
α-CD
β-CD
γ-CD
α-CD
β-CD
γ-CD
α-CD
β-CD
γ-CD
0.107
0.218
9b
R=H
0.052
0.108
0.217
0.027
0.125
0.226
0.089
0.127
0.228
0.055
0.120
0.232
0.011
0.108a
0.081 H(
0.105 H(
)
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9
c
R=H
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d
R=Me
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R=H
0.118 H(
0.067 H(
)
)
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0.065 H( )
0.102 H( )
0.127 H( )
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0.288a
0.097a
R=Me
a
values were roughly estimated due to overlapping of the signals
Table 1 summarises the observed complexation induced shifts (CISs) for important guest H-
atoms. As usual for inclusion complexes of adamantane-derived guests and CDs, the most
affected H-atoms were those at bridgehead positions or the methyl substituents in positions 3
and 5 (numbering of the adamantyl substituent). However, it is worthy of attention that the H-
atoms at the linker between the adamantane cage and (benz)imidazolium core were most
influenced by complexation in the case of guests 9b, 9c, 10b and 10c. This fact indicates the
different orientation of the binding partners. Surprisingly, maximum CIS observed for the
interactions of all examined guests with α-CD were comparable with that for complexes with
γ-CD. This trend positively correlates with the stability of the corresponding complexes, as can
be seen in Table 1. Additionally, two-dimensional ROESY experiments show the interactions
between adamantane hydrogens and hydrogens of the inner cavity of CDs for all examined
cyclodextrins as depicted for the guest 10c in Figure 2. The 1:1 stoichiometry of host-guest
complexes with CDs was determined by Job plot in all cases as can be seen in Figures S79–
S94.
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Figure 2 Portions of ROESY spectra recorded for 1:1 mixtures of the guest 10c and α-CD, β-
CD, γ-CD, respectively from left to right. Figure 1 illustrates the assignment of the CD’s signals.
NMR titrations of guests 9b, 9c, 10b, 10c with CB7 revealed that these guests interact with
CB7 in slow exchange mode according to the NMR timescale. New sets of signals assigned to
the 1-adamantyl cage, which appeared in the course of addition of CB7 solution, were
significantly shifted to a higher field (for spectra, see Figure 3 (left) and Figures S23, S29, S35
and S41). This observation implies the inclusion of the adamantyl binding site into the CB7
cavity.24 Guests 9d and 10d, which consist of 3,5-dimethyladamantyl cages, also form a
supramolecular complex with CB7. However, in this case, only one set of guest signals was
observed within the titration experiment to indicate a fast exchange binding mode. In contrast
to the guest based on singly substituted adamantane cages, the Me—N and all
(benz)imidazolium hydrogen signals of the guests 9d and 10d were shifted upfield while the
signals of the H-atoms at the 1,3-dimethyladamantane cage were shifted downfield (Figure 3,
right and Figures S47 and S53). Therefore, we infer that CB7, which is more rigid than β-CD,
encapsulates predominantly (benz)imidazoyl parts of guests while 1,3-dimethyladamantyl is
located close to the CB7 portals. These results are interesting from a mechanistic point of view.
Masson demonstrated that ammonium cations are passed through the CBn cavity in a
2
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deprotonated form. Indeed, permanent cations, e.g. quaternary ammonium or imidazolium
salts, cannot be discharged and must travel through the cavity in a charged form. Our results
indicate that there is even an energy minimum arrangement with a cationic moiety of the guest
situated inside the CB7 cavity. As can be expected considering the larger cavity of CB8, this
macrocycle can encapsulate even bulkier 1,3-dimethyladamantane 9d and 10d cages. However,
experiments with CB8 were accompanied with difficulties related to the poor solubility of CB8
in water. The titrations were performed using fine dispersion of CB8 in 50 mM NaCl solution
to support dissolving of CB8 by cation-portal interactions. Nevertheless, the portion of
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dissolved CB8 was very small and no changes in spectra were observed after the first addition,
as can be seen in Figure 4 (line 2). In order to be able to observe the interactions between CB8
and guests 9b–9d and 10b–10d clearly, the mixtures were heated at 55 °C for 24 hours in NMR
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cuvettes prior to the H NMR spectra being recorded. Figure 4 shows the upfield shift of
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adamantane signals to imply their inclusion inside the CB8 cavity. Note that signal of C(2)—H
appeared (Figure 4, left, line 3) as a result of well-known D/H exchange between the guest and
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H
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O molecules inside the CB8 cavity. Finally, it should be mentioned that we detected no
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interaction of our guests with CB6 according to H NMR spectra (see Figures S22, S28, S34,
S40, S46 and S52).
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Figure 3 Stacking plot of portions of the H NMR spectra recorded within titration of the guest
9c (left) and 9d (right) with CB7 in D
CB7 were as follows: for 9c 1.24 and 0.74 (line 1), 0.93 and 1.10 (line 2) and 0.74 and 1.33
line 3); for 9d 1.28 and 0.72 (line 1), 0.96 and 1.08 (line 2) and 0.77 and 1.29 (line 3),
respectively.
2
O at 303 K. Total concentrations (in mM) of guest and
(
1
Figure 4 Stacking plot of portions of the H NMR spectra recorded within titration of the guest
9c (left) and 9d (right) with CB8 in 50 mM NaCl solution in D O at 303 K. Total concentrations
in mM) of guest and CB8 were as follows: for 9c 1.29 and 0.75 (line 1), 0.97 and 1.12 (line
2
(
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) and 0.77 and 1.35 (line 3); for 9d 1.23 and 0.75 (line 1), 0.93 and 1.12 (line 2) and 0.74 and
DOI: 10.1039/D0NJ00738B
1.35 (line 3), respectively.
2
.2.2 Titration calorimetry
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The initial intention of our work was to find new binding motifs, which can be used instead of
adamantylmethyl. Therefore, we determined the association constants of new model guests
(
9b–9d, 10b–10d) using ITC and compared the values with previously reported results for the
guests 9a and 10a.21 ITC results (Table 2) confirmed 1:1 stoichiometry of all examined
complexes (see Table S1 and Figure S95–S112 for complete titration data). The pK values of
all tested adamantane-based guests with β-CD were observed within a range of 4.7–5.7.
However, the values clearly increased with prolongation of the linker between the adamantane
cage and (benz)imidazolium moiety (all discussed trends can be seen in Figure 5). It is worth
noting that this increase was higher in the benzimidazolia series, i.e. 10× from 10a to 10c and
only 7.1× from 9a to 9c. This phenomenon could be attributed to the bulkier benzimidazolium
core, which more negatively affects the binding strength sitting closer to the CD portal. The
size of the guest also positively correlates with the K values of binding to γ-CD, which varied
2
−1
4
−1
from 8.9×10 M for 9b to 8.4×10 M for 10c. It should be noted that bindings of all examined
guests with γ-CD are entropy-driven with minimal enthalpy contribution. Finally, we tested the
smallest member of the cyclodextrin family, i.e. α-CD, to observe K values in the range of 270–
00 M−1.
5
Figure 5 Plot of log K against the number of C-atoms (m) in the linker between the adamantane
cage and the cationic moiety of the guest (see Figure 1 for guest structures).
8

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Considering the affinity of positively charged adamantane-based guests towards CB7, we
should reflect on the contribution of host/guest desolvation and ion-dipole interactions. It is
well-known that the adamantane cage perfectly fits the interior cavity of CB7. Within a
complex, the centre of gravity of the adamantane cage is located close to the centre of gravity
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
of the CB7 macrocycle and any movement of the adamantane cage along the virtual C
7
axis of
CB7 increases the complex energy significantly. The contribution of this hydrophobic effect
8
−1 27
has been quantified as approximately 10 M . The ion-dipole interaction can contribute
3
−1
approximately 10 M for single cation optimally positioned in the CB7 portal. Prolongation
of the linker between the adamantane cage and cationic moiety should lead to lowering of the
1
1
−1
ion-dipole contribution. Therefore, we were surprised that K value increased from 7.6×10 M
1
2
−1
for 9a to 8.6×10 M for 9c. This phenomenon can be attributed to the flexible linker, which
can be bent to allow the cation reaching a position closer to the portal. An exception to this
trend was observed in the benzimidazolium series where the bulky benzimidazolium cation
most likely hindered the better orientation of the cation of the guest 10c within the CB7 portal.
The titration experiments with CB8 are in concert with a well-known fact that the 3,5-
1
4
dimethyladamantane cage shows high selectivity towards CB7/CB8. Thus, the guest 9d and
0d display the log(KCB8/KCB7) value of 8.3 and 8.1, respectively. It should be noted that the
1
inclusion complexes were reported for 3,5-dimethyladamantaneamine (log(KCB8/KCB7)=7.2) in
a previous publication from Isaacs.14 In contrast, our guests 9d and 10d bind the CB7
macrocycle at the (benz)imidazoliumalkyl site as NMR data suggested. However, the binding
1
4
4
−1
strength of our guests 9d and 10d towards CB7 match that of memantine, i.e. log K~10 M ,
and it is approximately 10× higher towards CB8.
Table 2 ITC results.
3
−∆H [kJ∙mol−1]
−1
−1
guest
host
K [dm ∙mol]
∆S [kJ∙mol ∙K ]
a
(6.8±0.3)×104
(7.6±0.5)×1011 c
(1.1±0.1)×1011 d
2.9×102
(1.9±0.5)×105
8.9×102
(5.6±0.8)×1012 c
(1.3±0.3)×1011 d
3.0×102
(4.9±0.1)×105
1.2×104
β-CD
CB7
CB8
31.4±1.8
91.3±1.2
53.1±1.1
21
−11.1
−54.7
36.4
22
9
a
a
b
α-CD
β-CD
γ-CD
CB7
31.3±0.2
1.2
−2.4
52.8
−50.9
40.2
−39
9b
89.4±1.3
52.3±0.9
26
b
CB8
α-CD
β-CD
γ-CD
CB7
33.21±0.15
−0.9
−0.6
81.2
−35.3
40.2
−59
9
c
(8.6±0.4)×1012 c
(4.3±0.9)×1010 d
7.7×102
85.7±1.4
49.5±1.2
35
b
CB8
α-CD
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β-CD
γ-CD
CB7
8.4×104
(8.3±1.5)×103
(1.7±0.4)×1012 e
(5.0±0.4)×104
(1.0±0.6)×109 f
(3.0±0.4)×109 d
5.0×102
(1.7±0.3)×105
3.4×103
(3.4±0.3)×1010 f
(7.5±1.4)×1010 d
2.7×102
52.8
9
d
18.2±0.2
67.3±1.2
27.3±1.3
89±3
14.9
12.0
0.1
b
CB8
a
β-CD
CB7
CB8
1
0a
a
−120.7
40.4
5
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
b
48.6±1.9
14
α-CD
β-CD
γ-CD
CB7
30.2±0.2
5.3
0.5
1
0b
50.2
−68.5
41.1
−46
89±3
b
CB8
50.9±1.1
28
α-CD
β-CD
γ-CD
CB7
(5.0±0.1)×105
2.1×104
32.3±0.4
−1.19
−33.1
86.7
−92.4
37.5
−65
1
0c
(4.1±1.1)×109
(5.9±0.8)×1010 d
6.1×102
f
84±4
b
CB8
50.7±1.0
36
α-CD
β-CD
γ-CD
CB7
(3.2±0.1)×105
8.0×104
(1.7±0.1)×104
39.8±1.5
12.2
−25.9
53.6
−7.6
12.0
1
0d
26.9±0.6
67.7±1.3
b
(2.0±0.3)×1012 e
CB8
a
21
According to the previously published paper. Experiments were conducted in water at 303.15 K unless
b
c
otherwise stated. Performed in 50 mM NaCl solution. Competitors were used as follows: 1,6-
d
e
f
hexamethylenediamine∙2HCl, methyl viologen dichloride, amantadine∙HCl,
L-phenylalanine.
2.2.3 Mass-spectrometry
To support our hypotheses regarding complex formation and stoichiometry by an additional
independent method, we analysed binary mixtures of ligands and macrocycles using ESI-MS.
In all cases, we clearly observed signals related to the 1:1 complexes as can be seen in Figures
+
S55–S78. Table S2 lists the calculated and experimental m/z values for [G@H] . The
complexes with α-CD were the only exception since we were not able to optimise experimental
conditions to observe such weak supramolecular aggregates. Interestingly, we observed only
one fragmentation pathway of the guest bound within the complex with CB7 instead of two
pathways, which were observed for free guests. As displayed for the guest 9c in Scheme S1,
the guest molecular cation (m/z 259) can release either neutral 3-(1-adamantyl)prop-1-ene to
produce methylimidazolium cation (m/z 83) or neutral methylimidazole to produce 1-
adamantylpropyl cation (m/z 177). Figure 6a shows the corresponding MS and tandem MS2.
This fragmentation pattern is the same for all the guests 9b–9d and 10b–10d. In contrast, ion
related to the 9c@CB7 (m/z 1421) release exclusively neutral 3-(1-adamantyl)prop-1-ene to
produce methylimidazolium@CB7 (m/z 1245) as can be seen in Figure 6b. We previously
demonstrated that imidazolium salts with a molecular structure allowing slippage of the CB7
1
0

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unit along the molecular axle but away from the adamantane cage strongly prefer releasing of
the neutral adamantane fragment and keeping the positive charge on the imidazolium moiety.19
These results concert with the hypothesis that ion-dipole interactions play a much more critical
role than the hydrophobic effect in the gas phase; though, the contribution of the hydrophobic
effect is much higher than that of ion-dipole interactions in water environments.
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
Figure 6 Mass spectra recorded for the guest 9c (a) and its 1:1 mixture with CB7 (b) in water.
The first-order mass spectra (1), MS/MS tandem mass spectra (2).
3
. Conclusion
This study aimed to examine whether adamantylalkyl(methyl)imidazolium binding motifs with
ethylene and propylene linkers between the adamantane cage and (benz)imidazolium cation
have appropriate supramolecular properties to be used instead of homologues with shorter
methylene linkers for the construction of more complex multitopic guests since longer linkers
are more convenient from a synthetic point of view. Therefore, we prepared a series of new
adamantylated (benz)imidazolium salts and described their supramolecular properties using
NMR, ITC, and mass spectrometry. Combining data from these experiments, we can conclude
that all synthesised guests, i.e. 9b–9d and 10b–10d, form 1:1 complexes with α-CD, β-CD, γ-
CD, CB7 and CB8. The binding strength of cyclodextrins decreases in the order β-CD>γ-
5
−1
CD>α-CD and the values of the association constants are in orders of magnitude of 10 M ,
3
4
−1
2
−1
1
0 –10 M and 10 M , respectively.
Initially, we assumed that prolongation of the linker between the adamantane cage and cationic
moiety could decrease the contribution of the ion-dipole interaction and, consequently, the
stability of the complex with CBn. However, our results do not display such a trend. Even, some
ligands with longer linkers bind the CBn stronger than a corresponding ligand with methylene
linker (see, for instance, 9b@CB7/8, 9c@CB7, 10b@CB7/8, 10c@CB7/8). We infer that this
1
1

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1
1
1
1
1
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2
2
2
2
2
2
2
2
3
3
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3
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phenomenon can be related to the better accommodation of the more flexible guest to optimise
ion-dipole contributions.
Finally, we conclude that new binding motifs, i.e. 1-adamantylalkyl(benz)imidazolia and 3,5-
dimethyladamantan-1-ylalkyl(benz)imidazolia, are suitable candidates which can be used for
the construction of more complex supramolecular components as an alternative to
adamantylmethyl homologues.
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
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4
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0
1
2
3
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5
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7
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9
0
4
4
. Experimental Section
.1 General
All solvents, reagents and starting compounds (if not mentioned otherwise) were of analytical
grade, purchased from commercial sources and used without further purification. 1-(1-
Adamantylalkyl)imidazole and 1-(1-adamantylalkyl)benzimidazole were prepared as described
previously. Melting points were measured on a Kofler block and are uncorrected. Elemental
analyses (C, H and N) were determined with a Thermo Fisher Scientific Flash EA 1112. NMR
spectra were recorded at 303 K on a Bruker Avance III 500 spectrometer operating at
frequencies of 500.11 MHz ( H) and 125.77 MHz ( C) and on a Bruker Avance III 300
spectrometer operating at frequencies of 300.13 MHz ( H) and 75.77 MHz ( C). H and
C NMR chemical shifts were referenced to the signal of the solvent [ H: δ(residual HDO) =
1
13
1
13
1
13
1
13
4
.70 ppm, δ(residual DMSO-d
5
) = 2.50 ppm; C: δ(DMSO-d ) = 39.52 ppm]. The spin-lock
6
for ROESY was adjusted to 400 ms. The signal multiplicity is indicated by “s” for singlet, “d”
for doublet, “t” for triplet, and “um” for unresolved multiplet. IR spectra were recorded using
a Smart OMNI-Transmission Nicolet iS10 spectrophotometer. Samples were measured in KBr
pellets. Electrospray mass spectra (ESI-MS) were recorded using an amaZon X ion-trap mass
spectrometer (Bruker Daltonics, Bremen, Germany) equipped with an electrospray ionisation
source. All the experiments were conducted in the positive-ion polarity mode. The instrumental
conditions used to measure the single (benz)imidazolium salts and their mixtures with the host
molecules were different; therefore, they are described separately. Single (benz)imidazolium
salts: Individual samples (with concentrations of 0.5 μg·cm ) were infused into the ESI source
in methanol:water (1:1, v:v) solutions using a syringe pump with a constant flow rate of 3
μl·min . The other instrumental conditions were as follows: an electrospray voltage of −4.2
kV, a capillary exit voltage of 140 V, a drying gas temperature of 220 °C, a drying gas flow
rate of 6.0 dm ·min and a nebulizer pressure of 55.16 kPa. Host-guest complexes: An aqueous
solution of the guest molecule (6.25 μ ) and the corresponding host molecule (1.0 eq of CBn
and 3.0 eq of CD, respectively) was infused into the ESI source at a constant flow rate of 3
μl·min . The other instrumental conditions were as follows: an electrospray voltage of −4.0
kV, a capillary exit voltage of 140 V up to −50 V, a drying gas temperature of 300 °C, a drying
gas flow rate of 6.0 dm ·min , and a nebuliser pressure of 206.84 kPa. Nitrogen was used as
both the nebulising and drying gas for all of the experiments. Tandem mass spectra were
collected using CID with He as the collision gas after the isolation of the required ions.
−
3
−1
3
−1
M
−1
3
−1
Isothermal titration calorimetry measurements were carried out in H
MicroCal instrument at 303 K. The concentrations of the host in the cell and the guest in the
microsyringe were approximately 0.13–0.15 and 0.46–0.50 m , respectively. The raw
2
O using a VP-ITC
M
experimental data were analysed with the MicroCal ORIGIN software. The heats of dilution
were taken into account for each guest compound. The data were fitted to a theoretical titration
curve using the ‘One Set of Binding Sites’ model. A 1,6-hexamethylenediamine·2HCl
(
HMDCl), L-phenylalanine, methyl viologen dichloride (MV·2 HCl), and amantadine·HCl
1
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with respective association constants KCB7=2.05×10 M , KCB7=5.16×10 M , KCB8=7.05×10
−1
9
−1
M , KCB8=2.89×10 M were used as competitors. The complexation enthalpies for the
multistep titration experiments were calculated as the sum of the enthalpies of each
complexation step. The values of K obtained from the competitive titrations were verified using
different concentrations of competitors. All titrations with CB7, CB8 and β-CD were performed
in triplicate. Titrations with α-CD and γ-CD were performed only once.
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
3
-(3,5-dimethyladamantan-1-yl)-1-propanol (6c)
-(3,5-Dimethyladamantan-1-yl)propionic acid (1.504 g, 6.36 mmol) was prepared from 1-
3
2
2,23
bromoadamantane according to the literature.
Subsequently, alcohol 6c was prepared
20
according to a protocol reported by Babjaková et al. to get a colourless oil (1.267 g, 90 %).
H NMR (400 MHz, CDCl ): δ 0.81 (m, 6H), 1.05–1.15 (um, 8H), 1.31 (m, 6H), 1.53 (m, 2H),
.0 (m, 1H), 3.61 (t, 2H, J=13.6 Hz) ppm. C{ H} NMR (CDCl ): δ 26.1, 29.8, 30.7, 31.2,
3.7, 39.7, 41.0, 43.4, 48.9, 51.3, 64.0 ppm. IR: 457 (w), 507 (w), 533 (w), 668 (w), 698(m),
53 (w), 889 (w), 920 (w), 938 (w), 962 (m), 1011 (m), 1059 (s), 1154 (w), 1170 (w), 1256 (w),
341 (m), 1357 (m), 1373 (m), 1454 (s), 1635 (w), 2839–2942 (bs), 3364 (bs) cm .
MS (EI: 200°C, 70eV): 41(9), 55(9), 91(11), 93(12), 95(5), 105(10), 107(53), 108(5), 121(7),
163(100), 164(13) m/z (%).
1
3
13
1
2
3
7
1
3
−
1
3
-(3,5-dimethyladamantan-1-yl)-1-bromopropane (7c)
Alcohol 6c (0.2000 g, 0.90 mmol) was dissolved in dry CH
and cooled down to 0 °C in an ice bath. CBr (1.0090 g, 3.04 mmol) was added followed by the
addition of triphenylphosphine (1.260 g, 4.81 mmol) in small portions. The mixture was stirred
for 3 h at 0 °C and then poured into cold pentane and stirred for 20 min. The liquid phase was
evaporated to dryness and the solid was washed with cold pentane. Pentane fractions were
evaporated and purified by column chromatography on silica gel using petroleum ether as a
mobile phase to get colourless oil 7c (0.2010 g, 78%). H NMR (400 MHz, CDCl
H), 1.01–1.14 (um, 6H), 1.12 (m, 2H), 1.30 (m, 6H), 1.83 (m, 2H), 2.05 (m, 1H), 3.37 (t, 2H,
3
2
Cl (30 cm ) under inert atmosphere
2
4
1
3
): δ 0.81 (m,
6
1
3
1
J=14.0 Hz) ppm. C{ H} NMR (CDCl
8.8, 51.3 ppm. IR: 409 (w), 465 (w), 561 (m), 645 (w), 657 (m), 721(w), 736 (w), 754 (w),
778 (w), 810 (m), 836 (w), 913 (m), 938 (w), 970 (w), 990 (w), 1037 (w), 1098 (m), 1179 (w),
3
): δ 26.7, 29.8, 30.6, 31.2, 33.8, 34.9, 41.0, 42.4, 43.4,
4
1
1
(
207 (m), 1241 (m), 1256 (m), 1272 (m), 1287 (w), 1298 (w), 1316 (w), 1346 (w), 1361 (w),
346 (w), 1361 (w), 14451 (bm), 2635 (w), 2656 (w), 2672 (w), 2751 (w), 2900 (bs) cm . MS
EI: 200°C, 70eV) 41(13), 55(9), 79(7), 81(5), 91(11), 93(10), 105(8), 107(45), 163(100),
−1
1
64(13), 269(1), 271(1) m/z (%).
1-(2-(1-adamantyl)ethyl)benzimidazole (9)
The benzimidazole (146 mg, 1.24 mmol) was dissolved in dry DMF (7.5 cm ) and sodium
hydride (60 % dispersion in mineral oil, 79 mg, 1.98 mmol) was added. When gas evolution
3
stopped, 2-(1-adamantyl)-1-bromoethane (7a) (200 mg, 8.22 mmol) was added. The mixture
was heated at 80 °C for 24 h. The reaction mixture was poured on ice and extracted 3× 5 cm3
with dichloromethane. The combined extract was washed with water, dried over Na
evaporated. The title compound was obtained as a colourless solid (180 mg, 78%). M.p.: 128–
133 °C. Calcd. for C19 (280.41) C 81.38, H 8.63, N 9.99 (%). Found C 81.15, H 8.72, N
9.85 (%). H NMR (500 MHz, CDCl ): δ 1.62 (m, 6H), 1.66 (m, 5H), 1.77 (m, 3H), 2.03 (m,
H), 4.18 (m, 2H), 7.31 (m, 2H), 7.39 (d, 1H, J=7.5 Hz), 7.81 (d, 1H, J=8.0 Hz), 7.94 (s, 1H)
): δ 28.4, 29.6, 32.0, 36.9, 40.1, 42.2, 43.9, 109.6, 120.3, 122.0,
22.7, 133.6, 142.6, 143.6 ppm. IR: 430 (w), 480 (w), 469 (w), 631 (w), 640 (w), 669 (w), 740
s), 768 (w), 779 (w), 813 (w), 878 (w), 889 (w), 926 (w), 973 (w), 1005 (w), 1057 (w), 1097
w), 1161 (m), 1200(m), 1240 (m), 1273 (w), 1288 (m), 1331 (w), 1346 (w), 1365 (w), 1365
2
SO and
4
H
24
N
2
1
3
3
13
1
ppm. C{ H} NMR (CDCl
3
1
(
(
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4
4
5
5
5
5
5
5
5
5
5
5
6
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DOI: 10.1039/D0NJ00738B
(
2
m), 1385 (s), 1452 (s), 1496 (s), 1585 (w), 1616 (w), 1747 (w), 1770 (w), 1884 (w), 1921 (w),
−1
345 (w), 2846 (s), 2902 (s), 2918 (s), 2979 (w), 3033 (w), 3050 (w), 3095 (w) cm . ESI-MS:
+
m/z 281.3 [M]
.
1
-(2-(1-adamantyl)ethyl)-3-methylbenzimidazolium iodide (10b)
1-(2-(1-adamantyl)ethyl)benzimidazole (9) (200 mg, 71 mmol) was dissolved in methyl iodide
4.56 g, 32.13 mmol). The mixture was heated at 80 °C and after 24 h it was cooled to room
temperature. The product was precipitated by the addition of diethyl ether, washed by THF and
dried using reduced pressure. Compound 10b was obtained as a colourless solid 200 mg (66%).
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
(
M.p.: 153–158 °C. Calcd. for C20
H
27
N
2
I∙1.5 H
C 53.48, H 6.38, N 6.22 (%). H NMR (400 MHz, DMSO-d
1.98 (m, 3H), 4.07 (s, 3H), 4.49 (m, 2H), 7.71 (m, 2H), 8.03 (m, 2H), 9.76 (s, 1H) ppm. C{ H}
NMR (DMSO-d ): δ 27.8, 31.7, 33.2, 36.4, 41.4, 42.1, 42.4, 113.4, 113.5, 126.4, 130.8, 131.8,
42.5 ppm. IR: 424 (w), 559 (w), 602 (w), 669 (w), 762 (s), 849 (w), 1012 (w), 1063 (w), 1097
2
O (449.37) C 53.46, H 6.73, N 6.23 (%). Found
1
6
): δ 1.62 (m, 6H), 1.72 (um, 8H),
1
3
1
6
1
(
(
(
w), 1130 (w), 1163 (w), 1203 (w), 1221 (w), 1255 (m), 1281 (w), 1346 (m), 1385 (w), 1448
m), 1461 (m), 1489 (w), 1567 (s), 1618 (w), 1655 (w), 1805 (w), 1846 (w), 2345 (w), 2362
w), 2645 (w), 2674 (w), 2846 (s), 2898 (s), 3014 (m), 3043 (m), 3137 (w), 3442 (bs), 3502 (bs)
−
1
+
cm . ESI-MS: m/z 295.3 [M]
.
1-(2-(1-adamantyl)ethyl)-3-methylimidazolium bromide (9b)
Compound 7a (200 mg, 0.82 mmol) and 1-methylimidazole (81 mg, 0.99 mmol) were heated
under inert atmosphere in dry acetonitrile (5 cm ) at 82 °C for 168 h. The reaction mixture was
cooled down and freshly distilled diethyl ether was added at room temperature. The precipitate
was centrifuged, washed with diethyl ether (3×10 cm ) and dried in vacuo to get 148 mg (55%)
3
3
of 9b as a colourless solid. M.p.: 188–189 °C. Calcd. for C16
H
25BrN
2
∙2.1 H
2
O (363.12) C 52.92,
): δ
.52 (m, 6H), 1.66 (um, 8H), 1.94 (m, 3H), 3.85 (s, 3H), 4.19 (m, 2H), 7.71 (s, 1H), 7.82 (s,
1
H 8.11, N 7.71 (%). Found C 52.85, H 7.87, N 7.74 (%). H NMR (400 MHz, DMSO-d
6
1
1
4
(
(
13
1
H), 9.25 (s, 1H) ppm. C{ H} NMR (DMSO-d
6
): δ 27.8, 31.6, 35.7, 36.3, 39.3, 41.4, 43.5,
4.4, 122.3, 123.4, 136.5 ppm. IR: 619 (m), 666 (w), 767 (w), 813 (w), 965 (w), 972 (w), 1020
w), 1104 (w), 1169 (m), 1307 (w), 1318 (w), 1344 (w), 1364 (w), 1371 (w), 1428 (w), 1449
m), 1573 (m), 1620 (w), 1630 (w), 2349 (w), 2657 (w), 2674 (w), 2846 (s), 2899 (s), 3069 (m),
−
1
+
+
79 − +
3143 (m), 3450 (bs) cm . ESI-MS: m/z 245.0 [M] m/z 569.3 [2∙M + Br ] .
,
1
-(3-(1-adamantyl)propyl)-3-methylimidazolium bromide(9c)
Compound 9c was prepared according the same procedure as described above for 9b using 7b
0.344 g, 1.34 mmol) to get 0.138 g (30 %) of 9c as a colourless solid. M.p.: 143–146 °C. Calcd.
∙0.9 H O (355.52) C 57.43, H 8.17, N 7.87 (%). Found C 57.51, H 8.02, N 7.88
%). H NMR (400 MHz, DMSO-d ): δ 1.00 (m, 2H), 1.43 (m, 6H), 1.62 (m, 6H), 1.75 (m,
2H), 1.91 (m, 1H), 3.85 (s, 3H), 4.11 (t, 2H, J=7.2 Hz), 7.69 (d, 1H, , J=1.6 Hz), 7.77 (d, 1H,
): δ 23.0, 27.9, 31.5, 35.7, 36.52, 39.7,
1.7, 49.5, 122.2, 123.6, 136.5 ppm. IR: 595 (m), 605 (m), 620 (w), 649 (w), 754 (m), 810 (w),
16 (w), 840 (w), 971 (w), 1001 (w), 1008 (w), 1071 (w), 1100 (w), 1168 (s), 1227 (w), 1256
(
for C17
(
H27BrN
2
2
1
6
1
3
1
J=1.6 Hz), 9.12 (s, 1H), ppm. C{ H} NMR (DMSO-d
4
8
6
(
(
(
w), 1290 (w), 1318 (w), 1343 (w), 1364 (w), 1383 (w), 1436 (m), 1565 (m), 1616 (m), 1622
w), 2656 (w), 2670 (w), 2845 (s), 2898 (s), 2924 (s), 3074 (m), 3142 (m), 3426 (bm), 3487
−
1
+
+
79 − +
bm) cm . ESI-MS: m/z 259.1 [M] m/z 597.3 [2∙M + Br ] .
,
1
-(3-(1-adamantyl)propyl)-3-methylbenzimidazolium bromide (10c)
Compound 10c was prepared according the same procedure as described above for 9b using 7b
0.2600 g, 1.01 mmol) to get 0.3580 g (91 %) of 10c as an off-white solid. M.p.: 122–123 °C.
Calcd. for C21 ∙1.3 H O (412.79) C 61.10, H 7.72, N 6.79 (%). Found C 61.02, H 7.59,
(
H29BrN
2
2
1
4

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2
3
4
5
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7
8
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DOI: 10.1039/D0NJ00738B
N 6.72 (%). H NMR (400 MHz, DMSO-d ): δ 1.12 (m, 2H), 1.43 (m, 6H), 1.61 (m, 6H), 1.89
6
(
(
um, 5H), 4.08 (s, 3H), 4.44 (t, 2H, J=7.2 Hz), 7.70 (um, 2H), 8.02 (m, 1H), 8.07 (m, 1H), 9.72
1
3
1
s, 1H) ppm. C{ H} NMR (DMSO-d
24.4, 126.5, 130.9, 131.8, 142.6 ppm. IR: 420 (w), 460 (w), 467 (m), 605 (w), 759 (s), 812
w), 879 (w), 977(w), 1013 (w), 1026 (w), 1059 (w), 1069 (w), 1097 (w),1102 (w), 1134 (w),
1212 (w), 1224 (w), 1268 (w), 1281 (w), 1313 (w), 1347 (m), 1355 (m), 1381 (w), 1421 (m),
6
): δ 22.1, 27.9, 31.6, 36.5, 39.9, 41.7, 47.2, 113.5, 113.5,
1
(
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
432 (s), 1450 (m), 1485 (s), 1568 (w), 1619 (m), 1991 (w), 2048 (w), 2345 (w), 2426 (w),
446 (w), 2636 (w), 2657 (w), 2673 (w), 2843 (s), 2900 (bs), 2989 (m), 3024 (m), 3069 (w),
137 (w), 3398 (bs), 3466 (bs) cm . ESI-MS: m/z 309.2 [M]
−1
+
+
79 − +
,
m/z 697.4 [2∙M + Br ] .
1
-(3-(3,5-dimethyladamantan-1-yl)propyl)-3-methylimidazolium bromide(9d)
Compound 9d was prepared according the same procedure as described above for 9b using 7c
(0.497 g, 1.74 mmol) to get 0.372 g (58 %) of 9d as a colourless solid. M.p.: 179–181 °C. Calcd.
for C19
(
(
H
31BrN
2
∙0.6 H
%). H NMR (400 MHz, DMSO-d
m, 2H), 2.0 (m, 1H), 3.85 (s, 3H), 4.11 (t, 2H, J=7.2 Hz), 7.70 (d, 1H, J=1.6 Hz), 7.78 (d, 1H,
2
O (378.18) C 60.34, H 8.58, N 7.40 (%). Found C 60.31, H 8.46, N 7.53
1
6
): δ 0.78 (s, 6H), 1.01–1.07 (um, 8H), 1.26 (um, 6H), 1.74
13
1
J=1.6 Hz), 9.12 (s, 1H), ppm. C{ H} NMR (DMSO-d
7.0, 40.0, 42.6, 47.9, 49.2, 50.8, 121.6, 123.7, 136.4 ppm. IR: 620 (m), 632 (m), 655 (w), 740
(w), 770 (m), 844 (bw), 1040 (w), 1163 (s), 1174 (s), 1242 (w), 1269 (w), 1303 (w), 1337 (w),
1359 (w), 1374 (w), 1381 (m), 1455 (s), 1475 (m), 1565 (s), 1636 (bw), 1747 (w), 2842 (s),
859 (m), 2902 (s), 2938 (m), 3060 (m), 3114 (w), 3123 (w), 3151 (w), 3448 (bm) cm . ESI-
MS: m/z 287.2 [M] m/z 653.4 [2∙M + Br ] .
6
): δ 22.7, 28.9, 30.1, 30.9, 33.0, 36.1,
3
−1
2
+
+
79 − +
,
1
-(3-(3,5-dimethyladamantan-1-yl)propyl)-3-methylbenzimidazolium bromide (10d)
Compound 10d was prepared according the same procedure as described above for 9b using 7c
(0.425 g, 1.49 mmol) to get 0.356 g (57 %) of 10d as an off-white solid. M.p.: 108–110 °C.
Calcd. for C23
H33BrN
2
∙1.5 H
2
O (444.45) C 62.12, H 8.16, N 6.30 (%). Found C 62.13, H 7.87,
): δ 0.77 (s, 6H), 1.04–1.09 (um, 8H), 1.26 (m, 6H),
.87 (m, 2H), 1.99 (m, 3H), 4.08 (s, 3H), 4.43 (t, 2H, J=7.2 Hz), 7.70 (um, 2H), 8.02 (m, 1H),
1
N 6.31 (%). H NMR (400 MHz, DMSO-d
6
1
8
3
13
1
.07 (m, 1H), 9.72 (s, 1H) ppm. C{ H} NMR (DMSO-d
9.4, 40.3, 42.8, 47.2, 48.1, 50.7, 113.4, 113.5, 126.4, 130.9, 131.8, 142.6 ppm. IR: 423 (w),
467 (w), 568 (w), 610 (w), 755 (s), 760 (m), 774 (w), 789 (w), 887 (w), 939 (w), 965 (w), 1013
(w), 1030 (w),1101 (w), 1133 (w), 1140 (w), 1165 (w), 1215 (w), 1280 (w), 1357 (m), 1371
m), 1421 (m), 1432 (s), 1450 (m), 1487 (w), 1570 (s), 1617 (m), 1799 (w), 2837 (s), 2861 (s),
6
): δ 22.4, 29.0, 30.4, 30.8, 32.9, 33.4,
(
2
−1
896 (s), 2943 (s), 3013 (m), 3072 (w), 3140 (w), 3385 (bs), 3442 (bs), 3481 (bs) cm . ESI-
MS: m/z 337.2 [M] m/z 753.4 [2∙M + Br ] .
+
+
79 − +
,
Acknowledgements
This work was supported by the Internal Funding Agency of the Tomas Bata University in
Zlín under Grant IGA/FT/2019/007.
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For Table of Contents
Adamantane-based imidazolium salts with flexible
linkers between the adamantane cage and imidazolium
moiety were synthesised. Supramolecular behaviour
towards natural cyclodextrins -CD, -CD and -CD and
cucurbit[n]urils (n=7,8) was studied.
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