"This	is	the	peer	reviewed	version	of	the	following	article:	Chem. Eur. J. 2016, 22 (38),
13496 ,	which	has	been	published	in	final	form	at	[10.1002/chem.201601690].	This	
article	may	be	used	for	non-commercial	purposes	in	accordance	with	Wiley	Terms	
and	Conditions	for	Self-Archiving."	

Molecular basis for the recognition of higher fullerenes into
ureidopyrimidinone-cyclotriveratrylene self-assembled capsules
Elisa Huerta,[a] Stefano Artin Serapian,[a] Eva Santos,[a] Enrique Cequier,[a] Carles Bo,*[a] and Javier de
Mendoza*[a]

[a]

Prof. C. Bo, Prof. J. de Mendoza, Dr. E. Huerta, Dr. E. Santos, Dr.
S. A. Serapian, Dr. E. Cequier
Catalan Institute of Chemical Research (ICIQ)
The Barcelona Institute of Science and Technology
Av. Països Catalans, 16
43007 Tarragona, Spain
E-mail: cbo@iciq.es
Supporting information for this article is available on the WWW in
PDF format at the following link:
Results of the DFT studies are available online on the ioChem-BD
platform. See http://dx.doi.org/10.19061/iochem-bd-1-7.

Abstract: Fullerenes C60, C70, and C84 may be readily encaged within a hydrogen-bonded dimeric capsule, based on two concave
cyclotriveratrylene (CTV) scaffolds each bearing three self-complementary 2-ureido-4-[1H]-pyrimidinone (UPy) subunits. We herein report
NMR and CD studies—complemented by dispersion-corrected density functional theory calculations—aiming to characterize such capsulefullerene complexes both structurally and energetically. Six fullerenes are considered: in agreement with experiment, calculations find that
encapsulation is most favorable for C84 (on a par with C90), and follows the trend C60<C70<C76<C78<C84≈C90. As also found by NMR, the most
stable capsules are formed by monomers of identical stereochemistry; with UPy and the CTV’s OMe groups in mutual anti orientation; and
UPy-CTV ethylene linkers within the capsular surface plane. Up to C78, encapsulation is favored by increasing host-guest contacts, but the
trend is thereafter increasingly inhibited by growing capsule strain.

Introduction
Despite the widespread interest in fullerenes[1] and endohedral fullerenes,[2] the chemistry and properties of higher members of this
family of carbon allotropes (known as ‘higher fullerenes’; >C70) remains mostly unexplored, mainly due to their low abundance, poor
solubility and difficult separation. To date, the most efficient method to purify higher fullerenes is by multiple runs of recycling HPLC.[3]
Most of the alternative methods for fullerene separation and purification (i.e by sublimation,[4] reversible chemical reactions,[5]
selective complexation with Lewis acids,[6] or host-guest chemistry)[7] are only selective towards the major component C60; examples
in literature where C70 or higher fullerenes are preferred are scarce.[8] Although preferential precipitation of C70 over C60 has indeed
been reported with p-halohomooxacalix[3]arenes, subsequent release of the fullerene and retrieval of the valuable host proved
difficult due to the complex’s high stability.[9]
In the case of higher fullerenes, some successful and elegant examples have been described over the past decade.[10] For
example, Fukazawa et al.[11] have employed a double calix[5]arene container to extract C94 and C96 from fullerene mixtures in an
elegant way. At temperatures above 100 °C, the container undergoes a syn-anti isomerization (from the C-shaped conformer to its
S-shaped counterpart), causing the trapped fullerenes to be released. In another approach by Aida et al.,[12] macrocyclic zinc

porphyrin dimers were employed for direct extraction of ≥C76 species from fullerene mixtures: after repeated extractions, this allowed
enrichment with the rare fullerenes C102 – C110. Recently, the same group reported the enantioselective extraction of the chiral
fullerene C76 (7% e.e.) from a racemic mixture, using an asymmetrically distorted porphyrin dimer.[13] Despite the inherent elegance
of these processes, all of them require chromatography at some stage.

Scheme 1. Structural formula of the capsule monomer 1 (top); and the hydrogen-bonded homochiral capsule 12 with a C70 guest (red; bottom). In the latter
structure, one of the three UPy dimers is omitted for clarity.

We have previously conceived and synthesized a hydrogen-bonded, self-assembled dimeric capsule 12 that readily
encapsulates fullerenes such as C60, C70,[14] and C84[15] (Scheme 1). Each monomer 1 is constituted by a modified concave
cyclotriveratrylene (CTV) platform, known for its complementarity to the convex surface of C60.[16] This CTV is endowed with three
short chains bearing 2-ureido-4-[1H]-pyrimidinone (UPy) moieties:[17] each of these can achieve dimerization with a UPy moiety
belonging to another monomer 1 through a robust quadruple array of hydrogen bonds (Scheme 1 and Fig. 1), providing a total of 12
favorable hydrogen bonds in the resulting dimer 12. Single solid-liquid extractions of crude fullerene mixtures (fullerite) with solutions
of the capsule in tetrahydrofuran (THF) promote selective encapsulation of fullerenes, which can then be easily separated from the
remaining fullerenes by filtration. Subsequent addition of some trifluoroacetic acid to the solution breaks the hydrogen bonds,
rupturing the capsules and allowing encapsulated guests to precipitate. Recycling of the host is simply achieved by evaporation.
Remarkably, no chromatography or tedious separation procedures are thus necessary with this method.
We herein present a detailed computational study, featuring dispersion-corrected[18] density functional theory (DFT), with the
aim of uncovering those energetic and structural factors that, at a molecular level, govern the formation of the most stable host-guest
complexes. Our in silico results are crucially supported by experimental data.
Indeed, on top of accurately reproducing experimentally observed capsule selectivity towards fullerenes (preference for C84
over C70, and even more over C60),[14-15] our calculations are also able to correctly predict the preferred structural conformation of the

12 capsules as detected by NMR. Selectivity trends found by our calculations and previous experiments are here furthermore
reconfirmed by racemization studies featuring CD spectroscopy.
We structure our discussion as follows: we begin by outlining the NMR characterization of the various capsule conformers and
tautomers, also discussing some key structural features of the capsules. We subsequently present the outcome of our DFT
calculations, whereby energetic and structural implications of capsule-fullerene complex formation are analysed in detail, and in
relation to six fullerene sizes (C60, C70, C76, C78, C84, and C90) and several 12 conformers. In the closing part of the discussion, we
report our racemization study based on CD spectroscopy. We finally provide our conclusions.

Results and Discussion
NMR Characterization
Before proceeding with the theoretical study, a number of structural aspects of the fullerene@12 complexes had to be verified by 1H
NMR, to help pinpoint their experimentally preferred conformations. These structural aspects and their assessment by NMR are
discussed in the following subsections; related methodological details are reported as Supporting Information.

	

Figure 1. Tautomers and dimers formed by 2-ureidopyrimidinone moieties.

Tautomerism: In solution, ureidopyrimidinones exist in a tautomeric equilibrium (Fig. 1), but only the 4[1H]-pyrimidinone and the
pyrimidyl-4-ol tautomers are able to self-assemble as dimers in apolar solvents; the former is usually the more stable of the two, since
it contains a particularly favorable quadruple sequence DDAA of hydrogen bond donors (D) and acceptors (A).[17] Experimentally,
structure 12 displayed the classical NMR pattern of the 4[1H]-pyrimidinone tautomer (NH signals at 12.77, 12.03, and 10.66 ppm, see
Fig. S3 in Supporting Information), whereas no signals for pyrimidin-4-ol dimers were observed;[19] we therefore only considered the
4[1H]-pyrimidinone DDAA tautomer in our calculations.

	

Figure 2. The two enantiomeric forms of chiral cyclotriveratrylene (CTV).

Chirality: CTV scaffolds containing three OMe and three OR groups are chiral[20] due to their bowl shaped architecture and their
slow inversion (Fig. 2) ): if the CTV dome is oriented upwards and the UPy groups point downwards, M chirality arises when the
UPyO-(aromatic ring)-OMe sequence is encountered in the counterclockwise direction; P chirality when it is encountered clockwise.
Consequently, self-assembled capsules 12 may either be homochiral (i.e. formed by a racemic pair of M-M monomers or P-P
monomers), or meso (achiral, where one of the monomers is M, and the other is P).
The prevalence of homochiral over achiral (meso) capsules was demonstrated experimentally by 1H NMR. Initially, compound 1
was resolved into its two enantiomers by semi-preparative chiral HPLC in dichloromethane/methanol 9:1 (+0.1% TFA). Once isolated,
the CD spectra of the two major peaks in the HPLC chromatogram (named arbitrarily fraction I and fraction II, see Fig. S1 in
Supporting Information) showed mirror images, clearly indicating that they correspond to the two enantiomeric species (Supporting
Information, Fig. S2). Then, after adding 0.5 equivalents of C70 to ensure capsule formation, 1H-NMR spectra were recorded: of the
racemic mixture; of each of the pure enantiomers; and of a 1:1 mixture of the two.

1:1 Mixture
13.5

13.0

12.5

12.0

11.5

11.0

10.5

10.0

9.5

ppm

Fraction II

Fraction I

é

é

• •
13.5

13.0

13.5

13.0

•

12.5

12.5

12.0

12.0

•
11.5

11.5

é

•
11.0

•
10.5

11.0

10.5

Racemic
10.0

10.0

9.5

9.5

ppm

ppm

1

Figure 3. H NMR spectra (NH region) of racemic capsules 12; enantiopure homochiral Fractions (I and II); and the 1:1 mixture of the two; all after the addition of
C70. (!) denotes NH signals corresponding to homochiral capsules; (•) denotes NH signals corresponding to meso self-assembled capsules.

The NH region of each homochiral fraction in the presence of C70 showed only three downfield shifted signals, as expected from
the high symmetry of the complex and from the strong hydrogen bonds present (Fig. 3). On the contrary, adding C70 to the racemic
mixture of 1 led to the appearance of additional minor NMR signals, corresponding to non-equivalent NH protons of meso 12. Upon
mixing both homochiral fractions of 1, the spectrum obtained in the presence of C70 was identical to that of the capsule resulting from
the racemic mixture. It was therefore concluded that homochiral capsules prevail in solution over meso capsules, in a ratio of ca. 7:3.
We finally note that preliminary 1H NMR spectra of a 1:2 mixture of racemic C76[1d] and racemic monomers 1 display a unique
set of downfield-shifted signals.[21] This suggests that monomers of 1 are driven to self-assemble into homochiral capsules only
(Supporting Information, Fig. S6), with a particular homochiral capsule possibly being favored by a particular enantiomer of C76.

	

Figure 4. Possible conformations of the chain linking the CTV and UPy moieties (α or β); combined with the different possible orientations of CTV and UPy with
respect to each other (A or S). See text for details.

Orientation and conformation of CTV-UPy linkers: Upon fullerene encapsulation, the three O-CH2CH2-N chains linking the CTV
and UPy moieties on each 1 (six in total) may adopt one of two possible conformations (Fig. 4). Inspection of a simple CPK capsulefullerene model reveals that the dihedral angle C(OMe)-C-O-CH2 in the six linkers could either be at ca. 90º (pointing away from the
capsule surface, in an orientation that we will henceforth denote as ‘α’), or at 180º (in the plane of the capsule surface, henceforth ‘β’).
A hypothetical conformation at 0º would on the other hand be sterically inaccessible. Similarly, the dihedral angle about the six CH2CH2 bonds (O-CH2-CH2-N) must be gauche in order to provide 12 with the necessary curvature to envelop the almost spherical guest:
an anti conformation would instead project the hydrogen-bonded platform away from the fullerene surface. In addition, as also
illustrated in Fig. 4, urea NH protons on each UPy could either point away from the OCH3 group of the CTV scaffold (we will refer to
this as an A or anti orientation), or in the same direction (S or syn orientation).
All these elements considered, the four most likely conformations of homochiral 12 should be SαSα, SβSβ, AαAα, and AβAβ. It
also follows that, to maintain hydrogen bonding between their UPy moieties, meso capsules must adopt one of the three
conformations AαSα, AαSβ, and AβSα (AβSβ being inaccessible).

C
E1

B

D

E2
D

G

F1
F2

NH(1)

A1
A2
B

C

D

NH(2)

NH(3)

G
E1

A2

F2

E2 A1

F1

CB

G

6.5

6.5

6.0

6.0

A2

5.5

5.5

5.0

5.0

E1 E2

4.5

4.5

4.0

4.0

F1 A1
F2

3.5

3.5

ppm

ppm

1

Figure 5. H-NMR spectra (CDCl3, 400 MHz, 3.2-7.0 ppm region shown) accounting for the AβAβ chain conformation (as shown in model). Bottom spectrum: free
monomeric host (1 + TFA). Top spectrum: homochiral dimer with C70 (C70@12).

Through the use of different NMR techniques, as discussed below, it was possible to establish that conformation AβAβ prevails
in solution. All signals were unequivocally assigned by a complement of 2D and 3D (COSY and HSQC) NMR methods (see
Supporting Information, Figs. S3 to S5). Aside from the typical deshielding of the three NH signals of each monomer, accounting for
a strong hydrogen bonded network (see Fig. 3), the central part of the NMR spectrum is indicative of linker conformation α or β.
Upon encapsulation of C70, several proton signals corresponding to the O-CH2-CH2-N linker (Fig. 5) did indeed undergo clear upfield
or downfield shifts
One of the CH2 protons adjacent to the nitrogen (namely F2), shows an intense vicinal coupling with the proton of the urea,
compatible with their mutual anti orientation where the coupling constant reaches a maximum value,[22] and is at the same time
strongly deshielded due to its proximity to the carbonyl group. On the contrary, protons C, D, E2, F1, and G, close to the fullerene
surface, are shielded. Proton E1, pointing away, clearly remains unaffected. These anisotropic effects are fully compatible with all six
UPy-CTV linkers in 12 adopting the β conformation.
On the other hand, the anti (A) rather than syn (S) orientation of NH protons and methoxy groups was established by means of
NOESY experiments (Fig. 6). As per the AβAβ model shown in Fig. 6a, one would expect methoxy protons in CTV (labeled D) to
show spatial coupling both with pyrimidinone protons in UPy (labeled G), and with those in the first CH2 of the C11H23 chain (labelled
H). On the contrary, in SβSβ (model in Fig. 6b) spatial coupling would only be expected between D and G protons alone, with H
protons in the aliphatic chain being too far to show any spatial coupling. Indeed, the NOESY spectrum of the homochiral C70@12
complex reveals coupling between the spins of all three classes of protons, indicating anti orientation and, hence, AβAβ.

Figure 6. Detail of a) AβAβ and b) Sβ Sβ models showing the spatial proximity of D, G and H protons (top), and partial NOESY (400 MHz, CDCl3, in blue) spectrum
of the homochiral C70@12 complex (bottom). H-H COSY (in red) is overlaid for clarity.

Theoretical Studies
Encapsulation energy components: Encapsulation of C60, C70, C76, C78, C84 and C90 inside 12 was investigated energetically (vide
infra) by carrying out a series of theoretical calculations with the program ADF (v. 2013.01),[23] using density functional theory (DFT)
together with dispersion corrections (details in Supporting Information).[18] Coordinates of all optimized fullerene@12 structures are
also available as Supporting Information; finally, all calculations reported here are also entirely available on-line.[24]
For the higher fullerenes C76, C78, and C84, we choose the isomers that are reported to have the highest experimental
abundance:[25] D2 (one enantiomer only);[24] C2v; and D2 respectively. In the case of C90, we choose its D5h isomer in virtue of its
higher symmetry; we also note that this is the most abundant C90 isomer occurring in soot generated from Sm2O3-doped graphite
rods.[26]
To begin with (Table 1), C60 and C70 are independently considered inside all of the seven accessible capsule conformers (four
homochiral, three meso, as explained earlier). However, for C76, C78, C84, and C90 complexes, investigation is subsequently limited to
the five 12 conformers that are shown in Table 1 to yield the most favorable encapsulation energies with C70. Data for four of these
(AβAβ, AαAα, SβSβ, AαSβ) are plotted in Fig. 7 jointly with some of the data from Table 1, and are fully discussed below; data for the
fifth conformer (AβSα) are only plotted in Fig. S7 (Supporting Information) for completeness. We note that in the same Fig. S7, for
better visualization, we have also plotted all of the data in Table 1. In practice, omitting conformers AαSα and SαSα from the possible
complexes of C76@12 to C90@12 conveniently enabled us to reduce the overall number of species considered from 42 to 34.

Table 1. Total encapsulation energies ΔEtot, and components thereof (all
-1
in kcal·mol ; see text for definitions), for fullerenes C60 and C70, inside
each of the seven accessible conformations of capsule 12 considered in
this work. All are calculated at the BP86-D3(BJ)/TZP level, with the effects
of THF implicitly modeled using the conductor-like screening model
[27]
(COSMO).
Graphical plots of these data are provided as Supporting
Information (Fig. S7), and are also included in part in Fig. 7.
Host
Conformation

Guest

ΔEHBonds

ΔErearr

ΔEH-G

ΔEtot

21.6

-119.5

-214.1

C60

-110.5

24.4

-100.4

-186.5

-107.5

20.7

-122.2

-209.1

C60

-112.2

31.8

-97.2

-177.6

-110.0

24.3

-117.3

-203.0

C60

-107.2

33.0

-88.7

-162.8

-106.6

29.7

-109.2

-186.2

C60

-100.9

22.5

-103.2

-181.6

-99.4

18.7

-127.3

-208.1

C60

-108.9

27.4

-93.8

-175.2

-108.3

23.2

-113.2

-198.2

C60

-97.2

27.8

-105.6

-175.1

C70

Aα Sβ

-116.2

C70

Aα Sα

-190.4

C70

Sβ Sβ

-98.2

C70

Sα Sα

27.7

C70

Aβ Sα

-119.9

C70

Aα Aα

C60
C70

Aβ Aβ

-105.0

19.8

-122.8

-208.1

To facilitate its quantification, the total energy released upon host-guest encapsulation (ΔEtot) is broken up into three smaller
components (Eq. 1),
ΔEtot = ΔEH-G + ΔEHBonds + ΔErearr

(1)

each of which is determined separately as defined and discussed below.
We begin by determining the host-guest interaction energy (ΔEH-G) for each complex. This is the energy released when a free
fullerene is encapsulated in a pre-formed, empty 12 capsule to form a full fullerene@12 complex. The procedure first requires
structural optimization of the full fullerene@12 complex; and single-point energy calculations of both the free fullerene and the empty
12 capsule.[28] Hence, ΔEH-G is computed by subtracting the binding energies of the free fullerene and empty capsule from that of
optimized fullerene@12.
We should here point out that use of D3(BJ) dispersion corrections in our calculations,[18] as well as implicit inclusion of THF
effects using the conductor-like screening model (COSMO; details in Supporting Information),[27] were both considered essential to
achieve a correct treatment of the π-π interactions that dominate ΔEH-G. In fact, all of the calculated values for ΔEH-G are expectedly
large and negative (attractive). Our goal in this study is merely that of qualitatively comparing relative host-fullerene stabilities, rather
than quantifying association constants. Nonetheless, we should still note that Grimme, Antony, and Sure additionally recommend to
include entropic contributions when treating supramolecular complexes of this kind.[29]
We next compute ΔEHBonds. This is the energy released by the formation of 12 hydrogen bonds, which occurs when any two
individual CTV-UPy monomers 1, already rearranged (deformed) into their respective capsule conformations (i.e. S or A; α or β),
combine to form an empty capsule 12. Quantification of ΔEHBonds, which is also always found to be negative, only requires additional
single-point energy calculations to be separately carried out on the two instances of 1 composing 12, still in their deformed states;
binding energies thus obtained are simply subtracted from the binding energy of 12, which is already known from the calculation of
ΔEH-G.
The final step is the calculation of ΔErearr, which represents the energetic cost of rearranging (deforming) the two instances of 1
from their optimal state in solution to the conformation they will adopt to form 12. Quantification of ΔErearr thus requires both halfcapsules to be fully and separately optimized. The value is obtained by subtracting the binding energy of each optimized 1 from that
of its rearranged (unoptimized) counterpart, and is the only component of ΔEtot to have a positive value. It also follows from this that
the sum of ΔEHBonds and ΔErearr actually determines the total energy released upon formation of an empty capsule.
Energy studies on complexes of C60 and C70: We begin by commenting values and trends in detail for C60 and C70 (Table 1;
leftmost points in Fig. 7); then proceed to examine them for remaining fullerenes (Fig. 7) from a more general point of view.

Turning first to ΔErearr values in Table 1, we find that, for encapsulation of both C60 and C70, monomers composing the SβSβ
capsule have the lowest cost of deformation. In the case of C60@12, these are followed by AαAα capsule monomers, and, in third
place, by monomers composing AαSα, AβAβ, and AαSβ (all bearing similar deformation costs). For C70@12, on the other hand, AαAα
capsule monomers are beaten into third place by AαSβ capsule monomers, whose ΔErearr drops more markedly. The highest cost of
rearrangement is instead borne by monomers of the SαSα capsule, both in the case of C60 and in the case of C70.
In terms of ΔEHBonds (cf. Table 1 again), the most favorable values for C60@12 and C70@12 complexes are found when 12 is in
AβAβ conformation, followed by values for 12 in the AβSα conformation (ca. 6-8 kcal mol-1 higher). The third most favorable ΔEHBonds
values are for 12 in the AαAα conformation in the case of C60@12, and in the AαSα conformation in the case of C70@12. On the other
hand, the most unfavorable ΔEHBonds values are found for 12 in the AαSβ and SβSβ conformations.
The most favorable ΔEH-G values in the case of C60 and C70 (Table 1) were obtained for their interactions with the AαSβ and SβSβ
capsules, with the former prevailing over the latter in the case of C60, and vice versa in the case of C70. At third place for both
fullerenes are the ΔEH-G values calculated for the homochiral capsule AαAα; the least favorable host-guest contacts are made in the
SαSα capsule.
Thus, upon summing the three components as per Eq. 1, the most favorable (negative) ΔEtot overall for both C60@12 and
C70@12 is obtained with the capsule AβAβ, aided by its moderate-to-strong favorability in ΔEH-G and ΔErearr. The second-best capsule
for both fullerenes is the syn counterpart SβSβ, followed by AαAα in the case of C60 and AαSβ in the case of C70 (the sole occurrence of
a meso capsule).
a)

b)

c)

d)

..
Figure 7. Evolution of a) ΔErearr; b) ΔEHBonds; c) ΔEH-G; and d) ΔEtot (cf. Eq. 1) for fullerenes C60, C70, C76, C78, C84, and C90 encapsulated within the four most
energetically favored conformations of C70@12 (cf. Table 1): AβAβ, AαAα, SβSβ, and AαSβ. Numerical values for each of these plots are also provided as Supporting
Information (Table S1), and those for C60 and C70 also appear in Table 1. The color code is explained in b); lines are guides for the eye. All values are calculated
at the BP86-D3(BJ)/TZP level.

Upon analyzing the trends when moving from C60 to C70, we should first of all note a generalized decrease in all ΔErearr values
(cf. two leftmost points in Fig. 7a and, more exhaustively, Fig. S7a), meaning that deformation of host monomers is always
energetically cheaper when accepting the latter guest. The decrease in cost ranges from -3.4 kcal mol-1 (12 in SαSα conformation) to
as much as -8.0 kcal mol-1 (12 in AαSβ).

For six of the seven hosts, ΔEHBonds (Figs. 7b and S7b) is roughly similar with C60 and C70 alike, with only a slight decrease in
favorability observed when hosting the latter fullerene (+0.5 to +3.7 kcal·mol-1). On the other hand, AαSβ is in this case an evident
outlier: its hydrogen bond formation when hosting C70 is actually decisively more favorable (negative) by as much as
-7.9 kcal mol-1.
This unusual favorable trend in ΔEHBonds, combined with the aforementioned highest decrease in ΔErearr, means that, when
switching the guest from C60 to C70, the total energy of forming the AαSβ capsule from free monomers of 1 (i.e. ΔEHBonds + ΔErearr)
undergoes an exceptionally high increase in favorability (-15.8 kcal mol-1). Such an increase is far more modest in the six remaining
capsules,
ranging
from
-0.8
to
-5.3 kcal mol-1.
It is nonetheless equally evident that the remaining component ΔEH-G (cf. leftmost points in Figs. 7c and S7c) has by far the
largest influence on ΔEtot (Figs. 7d and S7d). Indeed, as more π-π interactions are formed once C60 is replaced by C70, capsulefullerene interaction energies become more favorable (negative) by as much as -17.2 to -24.1 kcal mol-1: all six these increases in
favorability far outrank those observed for ΔEHBonds and ΔErearr combined, even in the case of the outlier conformer AαSβ.
All these factors considered, it comes as no surprise that ΔEtot is always significantly more favorable for C70@12 than it is for
C60@12, regardless of what conformation 12 is in. Gains in favorability range from -22.6 kcal mol-1 for the formation of C70@AαAα over
C60@AαAα to the -33.0 kcal mol-1 of C70@AαSβ over C60@AαSβ, which of course benefits from the unexpected trend in ΔEHBonds.
Energy studies on remaining complexes: We now turn to complexes of fullerenes C76, C78, C84, and C90, which we here only
discuss with 12 in AβAβ, AαAα, SβSβ, AαSβ conformation (and with 12 in AβSα conformation as Supporting Information). In this part of
the discussion, we shall hence refer to the four plots in Fig. 7 in their entirety, and from a qualitative point of view; the reader is
nonetheless reminded that values for these plots are fully tabulated in Table S1.
The four plots of ΔEtot and its components all reveal an interesting evolution beyond C70: examining these in the same order as
before, we begin with ΔErearr (Fig. 7a). The first thing to note is that the cost of rearranging SβSβ monomers consistently remains the
lowest right up to C90. The highest cost is borne by AβAβ up to C84; in the case of the largest guest C90, however, rearrangement
costs of both the AαSβ and AαAα capsules undergo a late ‘surge’ whereby they overtake AβAβ. More in general, a late surge in ΔErearr
is observed in all four capsule conformers considered, even though it is evidently more modest for SβSβ and AβAβ. In the case of
AβAβ, this (very modest) surge already begins between C70@AβAβ and C76@AβAβ; on the other hand, when moving from C70 to C84,
ΔErearr of remaining conformers is seen to decrease slightly.
In the case of ΔEHBonds (Fig. 7b), the general order of favorability detected for C70 is preserved up to C90, with AβAβ the most
favorable 12 conformer, SβSβ the most unfavorable, and AαSβ and AαAα tending to be close together, and in between. Between C70
and C84, the favorability of forming hydrogen bonds shows almost no variation, but once more, there is a surge in unfavorability
(ΔEHBonds less negative) between C84 and C90.
Trends in ΔEH-G (Fig. 7c) are far more uniform, even though the order of favorability changes frequently between capsule
conformers. For example, AαSβ is the conformer that exhibits the most favorable host-guest interaction with C60, but the least
favorable with C90; also, for guests between C76 and C90, the most favorable ΔEH-G values are alternatively found for AαAα and SβSβ.
Despite this, all plots clearly show that, except for a hump at C84, all host-guest interactions undergo a consistently large increase in
favorability, with C90 more favored than C60 by, on average, 47 kcal mol-1.
Exactly as observed for C60 and C70, such predominance of ΔEH-G over ΔErearr and ΔEHBonds is fully reflected in ΔEtot plots for
encapsulation of guests up to C84 (Fig. 7d). However, the late surges in ΔErearr and ΔEHBonds observed between C84 and C90 begin to
counteract the beneficial effects of ΔEH-G and as a consequence, between C78 and C90, ΔEtot plots are seen to approach plateaus. In
fact, in the case of AαAα, the trend is even reversed: encapsulation of C90 by AαAα actually returns to be less favorable than C76.
Most crucially, it can also be concluded that the affinity of all capsule conformers towards C84 is higher than that towards C70,
which in turn is significantly higher than that towards C60: this is fully consistent with the experimental results.[14-15] Moreover, it can
be seen that AβAβ is consistently found to have the most favorable ΔEtot values with respect to all other conformers: such energetic
preference is also in full agreement with our NMR results. Based on these results, we can establish a scale of affinity as follows
between the 12 capsule and the set of fullerenes studied: C60<C70<C76<C78<C84≈C90.
Structural studies: Table 2 lists a series of key geometric parameters, measured in each of the six optimized fullerene@12
complexes evaluated in this study, only considering 12 capsules in the AβAβ conformation due to its detected energetic preference,
both theoretically and experimentally. Where possible, these are compared with equivalent parameters obtained for an optimized
empty 12 in the same conformation, and at the same level of theory. Atoms are numbered according to the scheme illustrated in
Table 2, whose footnotes explain the parameters in more detail.
(N)H···O hydrogen bond lengths (2-8’ / 2’-8) are very similar in all cases, and generally close to their value of 1.658 Å in the
empty AβAβ capsule; furthermore values do not show any particular trend in relation to increasing guest size. On the other hand,
deviation from the empty capsule is more evident in the case of central (N)H···N bond lengths (4-6’ / 4’-6), which are all longer than
the 1.815 Å template. As guest size progressively increases from C60 / C70 to C84, so do bond lengths (1.823 / 1.820 to 1.848 Å); for
the even larger but decidedly prolate C90, equatorial strain on 12 is released, and (N)H···N distances return to 1.829 Å.

Angles associated with these hydrogen bonds (1-2-8’ / 1’-2’-8 and 3-4-6’ / 3’-4’-6, respectively) show degrees of correlation with
guest size that are similar to those of their parent bonds. In the case of 1-2-8’ / 1’-2’-8, we again see little correlation with fullerene
size, although angles in all complexes (except for 172.5º in C90@12) are consistently found to be smaller than the 169.9º of empty 12
(166.7º to 167.7º). On the other hand, 3-4-6’ / 3’-4’-6 angles exhibit an extremely interesting evolution with fullerene size. First of all,
mirroring the trend in 2-8’ / 2’-8 bonds (all longer than in the free dimer), all angles are found to be less planar than the 178.0º found
in the empty capsule. Even more importantly, if their degree of deviation from 178.0º is plotted against fullerene size, one can see
(Fig. 8) that it is almost superimposable on the ΔEHBonds plot for the AβAβ capsule; this suggests that 3-4-6’ / 3’-4’-6 angles and their
associated ‘equatorial’ hydrogen bonds have a particularly important effect on the overall energy released upon hydrogen bond
formation.

Table 2. Average geometric parameters measured in optimized fullerene@12 complexes, and in the empty 12 capsule, with 12 always in AβAβ conformation.
Distances are reported in Å; angles in º. All parameters are averages, except the distance between CTV domes, of which there is only one instance in every 12.
Parameters are numbered according to the scheme in the above inset.
Average Parameter

No guest

C60

C70

C76

C78

C84

C90

Dist 2-8’ / 2’-8

1.658

1.652

1.660

1.659

1.654

1.651

1.662

Dist 4-6’ / 4’-6

1.815

1.823

1.820

1.828

1.831

1.848

1.829

Angle 1-2-8’ / 1’-2’-8

169.9

166.7

167.2

167.2

167.7

167.3

172.5

Angle 3-4-6’ / 3’-4’-6

178.0

174.7

172.4

171.8

172.4

173.2

171.6

16.4

16.4

16.4

16.4

15.7

17.4

Dist CTV domes
Angle CTV
Dist UPy

[a]

17.7

[b]

109.5

[e]

102.3

107.6

110.5

112.1

113.0

113.7

-

[d]

Average H-G distance

[c]

10.8

10.9

11.2

11.1

11.9

11.0

-

3.275

3.288

3.230

3.212

3.207

3.162

[a] Distance between the two centroids at the middle of each CTV macro-ring. [b] Angle formed by the centroids of two adjacent CTV aromatic rings and their
methylene bridging carbon. [c] Free monomer 1 in Aβ conformation. [d] Average distance from centroids of two 3-5 bonds in adjacent UPy dimers. [e] Average
of the distance between each guest atom and its closest host atom.

Figure 8. Size of the angle 3-4-6’ / 3’-4’-6 in º (cf. Table 2), superimposed on the ΔEHbonds plot for AβAβ capsule-fullerene complexes (cf. Fig. 7b). Note the inverted
scale for the angle plot.

Figure 9. Deviation from 109.5º of the average angle between CTV ring centroids and CH2 units; superimposed on the ΔErearr plot for AβAβ capsule-fullerene
complexes (cf. Fig. 7a).

Turning to the two CTV ‘domes’, the distance between their centroids remains constant at 16.4 Å for the quasi-spherical guests
C60 to C78, and drops to 15.7 Å for C84. On the contrary, for the prolate guest C90 we observe an elongation to 17.4 Å, much closer to
the 17.7 Å observed in the free AβAβ capsule.
At any rate, the most striking parameter related to CTV is the average angle formed by the centroids of the aromatic rings and
methylenic carbons in the dome: this has a clear correlation with guest size, and consistently increases from 102.3º in C60@12 to
113.7º in C90@12. We furthermore note that the corresponding angle in optimized monomer 1 (Aβ conformation) is 109.5º: if the
magnitude of the deviation from 109.5º is plotted for each of the six fullerene@12 complexes against fullerene size, we find that there
is rough agreement with the plot for ΔErearr (Fig. 9). In other words, this suggests that squeezing (C60, C70) or stretching (C76 to C90)
CTV angles constitutes a significant part of the overall cost of deforming capsule monomers 1 from their optimized state.
The lack of trends in the distance between UPy2 centroids (10.8 – 11.9 Å), which is similar to the absence of patterns in (N)H···O
lengths and angles, is another indication that the increasing geometric distortion caused by increasing fullerene size is mainly
distributed at the ‘CTV poles’ of the capsules rather than at their ‘UPy equator’. Nonetheless, (N)H···N bonds are obviously still
distorted to some extent too.
Finally, we set out to measure, in each host-guest complex, the average of the shortest contacts between guest atoms and host
atoms: mean values for such contacts are tabulated in the last line of Table 2. It is clear from these values that the contacts made by

C60 (3.275 Å) and C70 (3.288 Å) are the loosest, and that there is a progressive increase in tightness before reaching C84 (3.207 Å)
and C90 (3.162 Å). Increasingly tight contacts help to explain the increasing energetic favorability (negativity) of ΔEH-G, which in turn
so strongly contributes to the overall ΔEtot.

Thermal Stability vs. Racemization of Homochiral Capsules
In the opening part of this section, we presented experimental evidence on some structural aspects of the 12 capsules and their
complexes with fullerenes, namely: tautomerism of the UPy dimeric subunits; conformation of the linker chain between the CTV
platform and the UPy subunits; and orientation of methoxy groups in CTV with respect to urea protons in UPy (in turn linked to the
homochiral or meso nature of the 12 capsules). These observations helped to reduce the amount of DFT calculations, by restricting
conformational space to explore and the number of isomers to consider. The outcome of the calculations is also in agreement with
experiment, with the trend in energetic stabilities C84>C70>C60 perfectly matching selectivities observed in fullerenes extraction from
fullerite. To complement these observations on energetic stabilities, we performed a study on how different fullerenes affect the
racemization rate of homochiral capsules.
Racemization requires a complete inversion of the CTV domes in capsule monomers: this means that in order for it to occur,
dimeric capsules must break at least in part. Consequently, one should expect racemization to be more favored for the less stable
host-guest complexes, and our study should enable us to establish a link between stability and racemization rate. The rate of the
“crown-to-crown” interconversion leading to racemization is also sensitive to temperature,[20, 30] and we make use of this in our study.
Thus, racemization of free host monomers 1 was monitored by CD in tetrachloroethane at three different temperatures, and
compared to racemization in C60@12, C70@12, and C84@12 under the same conditions. Spectra were collected every ten minutes
until total racemization took place (Supporting Information, Figs. S8 to S12). In all cases, racemization was seen to follow first order
kinetics. Thermodynamic parameters derived from kinetic data (Supporting Information, Table S2) were fitted to Eyring plots (Fig.
S13).

	

Figure 10. Deuterated CTV derivative 2, studied by Collet and Gabard.

[30]

-1

Table 3. Thermodynamic transition state parameters (all in kcal mol ) of
[30]
CTV derivatives 1 and 2; and the complexes of 12 with fullerenes C60, C70,
and C84.
[a]

Compound

Ea

1

23.9

C60@12
C70@12
C84@12
2

[30]

33.0
38.5

ΔH

≠

23.3
32.4
37.9

ΔS

ΔG

≠

-5.6 × 10

-3

≠

[b]

25.0

20.8 × 10

-3

26.2

35.4 × 10

-3

27.4

66.0

65.6

121.8 × 10

26.5

25.9

-1.9 × 10

-3

29.3

-3

26.5

[a] Values derived from the Arrhenius equation. [b] At 298 K.

For 1, thermodynamic parameters associated with racemization (Table 3) were very similar to those obtained by Collet and
Gabard[30] for the racemization of monomers of their compound 2 (Fig. 10), despite the fact that these are deuterated, and therefore
unable to dimerize.
For filled homochiral capsules, on the other hand, racemization rates definitely showed dependence on the volume of the
included guest: indeed, the enthalpic barrier ΔH clearly increases with fullerene size, in full agreement with the higher stabilities
found by calculations, and the previously determined binding constants.[15] We nonetheless note that, possibly due to the greater
rotational frustration suffered by larger fullerenes after encapsulation, the entropic barrier ΔS is also seen to increase with guest size:
as a result, at 298 K, enthalpy-entropy compensation restores free energies of activation (ΔG ) to more or less similar values.
≠

≠

≠

Conclusions
We have herein reported a series of experimental (1H NMR, CD) and theoretical studies (dispersion-corrected DFT) on a series of
dimeric capsules, in different conformations, hosting six different fullerene guests: C60, C70, and C84 were considered both
experimentally and theoretically; whereas the previously unstudied C76, C78, and C90 were only considered theoretically. The
specially designed monomers 1 composing such host capsules were based on a cyclotriveratrylene (CTV) core, equipped with three
2-ureido-4-[1H]-pyrimidinone (UPy) moieties each bearing an array of two hydrogen bond donors and two acceptors; this enabled
facile dimerization into 12 via hydrogen bonding.
The aim of our work, wherein we have observed full agreement between theory and experiment, was to provide an explanation
as to why, in previous studies,[14-15] such capsules were experimentally seen to prefer C84 as a guest over C70 and C60.
Our 1H NMR findings (1D, NOESY, COSY, HSQC) crucially confirmed that, in THF, the 2-ureido-4-[1H]-pyrimidinone tautomer
of UPy was indeed the most prevalent one. In addition, homochiral 12 capsules—where both monomers 1 are of the same chirality P
or M—were found to prevail over meso capsules—where they have contrasting chirality.
In full accordance with NMR, our calculations further predicted that, regardless of the fullerene guest, and out of seven
conformations tested, the capsules’ energetically preferred conformation is always AβAβ. This entails all UPy urea protons in capsule
monomers being oriented anti to CTV methoxy groups (rather than syn), and all CTV-UPy ethylene linkers staying within the plane of
the capsule’s surface (rather than projecting out).
Again in agreement with previous experimental results for C60, C70, and C84, we also established that the total encapsulation
energy for the six fullerene guests studied follows the trend C60>C70>C76>C78>C84≈C90 (where more negative values correspond to
more favorable encapsulation). At first (guests C60 to C78), this trend is predominantly driven by increasingly favorable host-guest
interactions, arising from an increasing number of tighter host-guest contacts: these are able to overcome the increasing energetic
penalties associated with guest-induced distortion and guest-induced disruption of capsules’ hydrogen bonds. Eventually, however,
these two energetic penalties begin to contrast the beneficial effects of host-guest interactions, and this is at the origin of C84@12 and
C90@12 having similar formation energies.
Racemization studies, based on CD spectra recorded at different temperatures, were also able to show that with C84 as a guest,
disruption of homochiral capsules is less favored than with C70 or C60. This represents another encouraging piece of evidence in
favor of our computational findings.

Experimental Section
Fullerenes and other chemicals were purchased from commercial sources, and used without further purification. Solvents were dried and distilled using
conventional methods,[31] or with a Solvent Purification System (SPS). Compound 1 was synthesized as reported elsewhere.[14] NMR spectra were
performed on Bruker Advance 400 Ultrashield (1H: 400 MHz, 13C: 100 MHz) or 500 Ultrashield (1H: 500 MHz, 13C: 125 MHz) spectrometers. Deuterated
solvents used are indicated in each case. Chemical shifts (δ) are expressed in ppm, and are referred to the residual peak of the solvent. High
performance liquid chromatography (HPLC) analyses were carried out on an Agilent Technologies Series 1100 apparatus, with UV-diode array
detector. HPLC grade solvents were purchased from Scharlab and Carlo Erba and were used with no further purification. Separation of enantiomers
was accomplished in a Chiralpak-IC 250 x 7.8mm, 5 µm column from Daicel. The mobile phase was a mixture of DCM/MeOH (90:10 v/v) + 0.1% TFA,
flow rate = 0.95 mL/min and detection wavelength 254 nm at 25 °C. CD measurements were carried out in a Chirascan circular dichroism spectrometer
from Applied Photophysics, with simultaneous measurement of UV-vis and CD spectra in the 165 – 900 nm range. The device was equipped with a
Peltier thermal control unit (-40/+100 ºC) with the possibility of temperature ramp control. Experiments were performed using 10-4 M solutions of each
enantiomer, with HPLC grade chloroform as the solvent. The blank and each of the samples were measured three times using a 0.5 mm path length
light polarized cuvette.

Acknowledgements
Financial support was provided by Spanish Ministerio de Economia y Competitividad (MINECO, projects CTQ2008-00183, CTQ201129054-C02-02, CTQ2011-28677, and CTQ2014-52824-R), the Generalitat de Catalunya (2009SGR-00259, 2014SGR-00409), the
ICIQ foundation, Consolider Igenio 2010 (grant CDS2006-0003), and European FEDER funds, all of which are deeply acknowledged.
E. H. also thanks MINECO for a FPI studentship. S. A. S. thanks the Marie Curie/COFUND scheme ref. 291787-ICIQ-IPMP for
funding. The Severo Ochoa Excellence Accreditation (SEV-2013-0319) is also gratefully acknowledged.

Keywords: selective purification of fullerenes • supramolecular chemistry • density functional theory • NMR • circular dichroism

[1]

a) T. J. S. Dennis, T. Kai, T. Tomiyama and H. Shinohara, Chem. Commun. 1998, 619-620; b) F. Diederich, R. Ettl, Y. Rubin, R. L. Whetten, R. Beck, M.
Álvarez, S. Anz, D. Sensharma, F. Wudl, K. C. Khemani and A. Koch, Science 1991, 252, 548-551; c) F. Diederich, R. L. Whetten, C. Thilgen, R. Ettl, I.
Chao and M. M. Álvarez, Science 1991, 254, 1768-1770; d) R. Ettl, I. Chao, F. Diederich and R. L. Whetten, Nature 1991, 353, 149-153; e) A. S. Boutorine,
H. Tokuyama, M. Takasugi, H. Isobe, E. Nakamura and C. Helene, Angew. Chem., Int. Ed. 1994, 33, 2462-2465; f) T. Hasobe, H. Imahori, P. V. Kamat, T.
K. Ahn, S. K. Kim, D. Kim, A. Fujimoto, T. Hirakawa and S. Fukuzumi, J. Am. Chem. Soc. 2005, 127, 1216-1228; g) G. L. Marcorin, T. Da Ros, S.
Castellano, G. Stefancich, I. Bonin, S. Miertus and M. Prato, Org. Lett. 2000, 2, 3955-3958; h) C. M. Sayes, J. D. Fortner, W. Guo, D. Lyon, A. M. Boyd, K.
D. Ausman, Y. J. Tao, B. Sitharaman, L. J. Wilson, J. B. Hughes, J. L. West and V. L. Colvin, Nano Lett. 2004, 4, 1881-1887; i) M. Segura, L. Sanchez, J.
de Mendoza, N. Martin and D. M. Guldi, J. Am. Chem. Soc. 2003, 125, 15093-15100; j) M. M. Wienk, J. M. Kroon, W. J. H. Verhees, J. Knol, J. C.
Hummelen, P. A. van Hal and R. A. J. Janssen, Angew. Chem., Int. Ed. 2003, 42, 3371-3375; k) Y. Yamakoshi, N. Umezawa, A. Ryu, K. Arakane, N.
Miyata, Y. Goda, T. Masumizu and T. Nagano, J. Am. Chem. Soc. 2003, 125, 12803-12809.

[2]

a) H. Kato, Y. Kanazawa, M. Okumura, A. Taninaka, T. Yokawa and H. Shinohara, J. Am. Chem. Soc. 2003, 125, 4391-4397; b) S. Kobayashi, S. Mori, S.
Iida, H. Ando, T. Takenobu, Y. Taguchi, A. Fujiwara, A. Taninaka, H. Shinohara and Y. Iwasa, J. Am. Chem. Soc. 2003, 125, 8116-8117; c) M. Saunders,
R. J. Cross, H. A. Jimenez-Vazquez, R. Shimshi and A. Khong, Science 1996, 271, 1693-1697; d) M. Saunders, H. A. Jimenez-Vazquez, R. J. Cross, S.
Mroczkowski, D. I. Freedberg and F. A. L. Anet, Nature 1994, 367, 256-258.

[3]

a) L. Isaacs, A. Wehrsig and F. Diederich, Helv. Chim. Acta 1993, 76, 1231-1250; b) K. C. Khemani, M. Prato and F. Wudl, J. Org. Chem. 1992, 57, 32543256; c) D. H. Parker, K. Chatterjee, P. Wurz, K. R. Lykke, M. J. Pellin and L. M. Stock, Carbon 1992, 30, 1167-1182; d) W. A. Scrivens, P. V. Bedworth
and J. M. Tour, J. Am. Chem. Soc. 1992, 114, 7917-7919.

[4]

K. Nakamura, T. Sasaki, R. Ogawa and T. Nakai, Jpn. Kokai Tokkyo Koho 1997, JP 09227111 A 19970902.

[5]

R. D. Bolskar and J. M. Alford, Chem. Commun. 2003, 1292-1293.

[6]

I. Bucsi, R. Aniszfeld, T. Shamma, G. K. S. Prakash and G. A. Olah, Proc. Natl. Acad. Sci. U. S. A. 1994, 91, 9019-9021.

[7]

a) T. Andersson, K. Nilsson, M. Sundahl, G. Westman and O. Wennerstrom, J. Chem. Soc., Chem. Commun. 1992, 604-606; b) J. L. Atwood, G. A.
Koutsantonis and C. L. Raston, Nature 1994, 368, 229-231; c) T. Suzuki, K. Nakashima and S. Shinkai, Chem. Lett. 1994, 699-702.

[8]

a) T. Kawauchi, A. Kitaura, M. Kawauchi, T. Takeichi, J. Kumaki, H. Iida and E. Yashima, J. Am. Chem. Soc. 2010, 132, 12191-12193; b) M.-J. Li, C.-H.
Huang, C.-C. Lai and S.-H. Chiu, Org. Lett. 2012, 14, 6146-6149.

[9]

N. Komatsu, Org. Biomol. Chem. 2003, 1, 204-209.

[10]

C. García-Simón, M. Costas and X. Ribas, Chem. Soc. Rev. 2016, 45, 40-62.

[11]

T. Haino, C. Fukunaga and Y. Fukazawa, Org. Lett. 2006, 8, 3545-3548.

[12]

Y. Shoji, K. Tashiro and T. Aida, J. Am. Chem. Soc. 2004, 126, 6570-6571.

[13]

Y. Shoji, K. Tashiro and T. Aida, J. Am. Chem. Soc. 2010, 132, 5928-5929.

[14]

E. Huerta, G. A. Metselaar, A. Fragoso, E. Santos, C. Bo and J. de Mendoza, Angew. Chem., Int. Ed. 2007, 46, 202-205.

[15]

E. Huerta, E. Cequier and J. de Mendoza, Chem. Commun. 2007, 5016-5018.

[16]

J. W. Steed, P. C. Junk, J. L. Atwood, M. J. Barnes, C. L. Raston and R. S. Burkhalter, J. Am. Chem. Soc. 1994, 116, 10346-10347.

[17]

a) B. J. B. Folmer, R. P. Sijbesma, H. Kooijman, A. L. Spek and E. W. Meijer, J. Am. Chem. Soc. 1999, 121, 9001-9007; b) R. P. Sijbesma, F. H. Beijer, L.
Brunsveld, B. J. B. Folmer, J. Hirschberg, R. F. M. Lange, J. K. L. Lowe and E. W. Meijer, Science 1997, 278, 1601-1604; c) S. H. M. Söntjens, R. P.
Sijbesma, M. H. P. van Genderen and E. W. Meijer, J. Am. Chem. Soc. 2000, 122, 7487-7493; d) F. H. Beijer, H. Kooijman, A. L. Spek, R. P. Sijbesma and
E. W. Meijer, Angew. Chem., Int. Ed. 1998, 37, 75-78.

[18]

a) S. Grimme, J. Antony, S. Ehrlich and H. Krieg, J. Chem. Phys. 2010, 132, 154104-154122; b) S. Grimme, S. Ehrlich and L. Goerigk, J. Comput. Chem.
2011, 32, 1456-1465; c) E. R. Johnson and A. D. Becke, J. Chem. Phys. 2006, 124, 174104-174112.

[19]

F. H. Beijer, R. P. Sijbesma, H. Kooijman, A. L. Spek and E. W. Meijer, J. Am. Chem. Soc. 1998, 120, 6761-6769.

[20]

a) J. Canceill, A. Collet, J. Gabard, G. Gottarelli and G. P. Spada, J. Am. Chem. Soc. 1985, 107, 1299-1308; b) J. Canceill, A. Collet and G. Gottarelli, J.
Am. Chem. Soc. 1984, 106, 5997-6003; c) A. Collet and G. Gottarelli, J. Am. Chem. Soc. 1981, 103, 204-205; d) A. Collet and J. Jacques, Tetrahedron Lett.
1978, 1265-1268.

[21]

Y. Shoji, K. Tashiro and T. Aida, J. Am. Chem. Soc. 2006, 128, 10690-10691.

[22]

a) M. Karplus, J. Chem. Phys. 1959, 30, 11-15; b) M. Karplus, J. Am. Chem. Soc. 1963, 85, 2870-2871.

[23]

a) G. te Velde, F. M. Bickelhaupt, E. J. Baerends, C. Fonseca Guerra, S. J. A. van Gisbergen, J. G. Snijders and T. Ziegler, J. Comput. Chem. 2001, 22,
931-967; b) C. Fonseca Guerra, J. G. Snijders, G. te Velde and E. J. Baerends, Theor. Chem. Acc. 1998, 99, 391-403.

[24]

http://dx.doi.org/10.19061/iochem-bd-1-7

[25]

a) F. Diederich and R. L. Whetten, Acc. Chem. Res. 1992, 25, 119-126; b) R. Taylor, G. J. Langley, A. G. Avent, T. J. S. Dennis, H. W. Kroto and D. R. M.
Walton, J. Chem. Soc., Perkin Trans. 2 1993, 1029-1036.

[26]

H. Yang, C. M. Beavers, Z. Wang, A. Jiang, Z. Liu, H. Jin, B. Q. Mercado, M. M. Olmstead and A. L. Balch, Angew. Chem., Int. Ed. 2010, 49, 886-890.

[27]

a) A. Klamt and G. Schüürmann, J. Chem. Soc. Perkin Trans. 2 1993, 799-805; b) A. Klamt, J. Phys. Chem. 1995, 99, 2224-2235; c) A. Klamt and V.

[28]

As verified by means of structural optimizations on free fullerenes, neither did these suffer any deformation with respect to their structure inside the capsule,

Jonas, J. Chem. Phys. 1996, 105, 9972-9981; d) A. Klamt, V. Jonas, T. Bürger and J. C. W. Lohrenz, J. Phys. Chem. A 1998, 102, 5074-5085.
nor was their binding energy lowered any further.
[29]

a) S. Grimme, Chem. - Eur. J. 2012, 18, 9955-9964; b) J. Antony, R. Sure and S. Grimme, Chem. Commun. 2015, 51, 1764-1774.

[30]

A. Collet and J. Gabard, J. Org. Chem. 1980, 45, 5400-5401.

[31]

D. D. Perrin, W. L. F. Amarego and D. R. Perrin, Purification of Laboratory Chemicals, 2

nd

ed., Pergamon Press, Oxford, 1980.

Entry for the Table of Contents
Layout 1:

FULL PAPER
Supramolecular dimeric capsules,
based on cyclotriveratrylene equipped
with self-complementary
ureidopyrimidinone moieties, show
selectivity towards C84 and C70 over
C60. Combining theory and
experiment, we here explore the
molecular basis of such selectivity,
with fascinating conclusions.

Elisa Huerta, Stefano Artin Serapian,
Eva Santos, Enrique Cequier, Carles
Bo,* and Javier de Mendoza*
Page No. – Page No.
Molecular basis for the recognition of
higher fullerenes into
ureidopyrimidinonecyclotriveratrylene self-assembled
capsules