A calix[5]arene-based heterotetratopic host for molecular recognition of long-chain, ion-paired α,ω-alkanediyldiammonium salts

Article abstract of DOI:10.1002/anie.200500985

(Chemical Equation Presented) The anions went in two by two: Separate ion-pair binding of nano-sized α,ω-alkanediyldiammonium dichloride salts is achieved in organic media with high efficiency and selectivity by a heterotetratopic receptor that comprises

Full text of DOI:10.1002/anie.200500985

Communications
Host–Guest Chemistry
Following our specific interest in the development of
neutral multisite receptors for biogenic (poly)ammonium
salts,[14] we report herein the synthesis and unique molecular
recognition abilities of the first heterotetratopic receptor, 1,
which consists of two convergent, conformationally fixed,
cone calix[5]arene units (cation-binding sites) that are
covalently linked at their upper rims by means of a 1,4-
bis(ureido)phenylene spacer (anion-binding sites). Host 1
readily forms overall charge-neutral, unimolecular capsules
(ligand-separated ion-pair complexes) of nanoscale dimen-
sions by tight encapsulation[15] of linear a,w-alkanediyldiam-
monium ions, which range from 1,12-dodecane- to 1,16-
hexadecanediammonium, inside the inner space defined by
the two converging calix[5]arene cavities by simultaneously
binding each of the two counteranions to the peripheral
ureido functions through hydrogen bonds.
The target biscalixarene 1 was synthesized in six steps
from the known 31-benzyloxy-p-tert-butylcalix[5]arene (2)[16]
according to the sequence illustrated in Scheme 1. The
exhaustive O-alkylation of 2 with 4-methylpent-1-yl tosylate
and K2CO3 in CH3CN at reflux produced pentaether 3 in 77%
yield which, upon Pd/C-catalyzed hydrogenolysis in EtOAc,
gave monohydroxy intermediate 4 in 93% yield. The
DOI: 10.1002/anie.200500985
A Calix[5]arene-Based Heterotetratopic Host for
Molecular Recognition of Long-Chain, Ion-Paired
a,w-Alkanediyldiammonium Salts**
Domenico Garozzo, Giuseppe Gattuso, Anna Notti,
Andrea Pappalardo, Sebastiano Pappalardo,*
Melchiorre F. Parisi,* Marta Perez, and Ilenia Pisagatti
Ion-pair recognition, that is, the simultaneous complexation
of cation and anion guest species by neutral hosts, is an
emerging field of topical interest in supramolecular chemistry
with great potential for biological, analytical, and environ-
mental applications.[1] It is well known that the ion-binding
process with neutral receptors is adversely affected by the ion-
pairing of guest salts,[2] so that it is common practice to make
use of salts with weakly coordinating counterions,[3] which
result in enhanced host-guest associations. On the other hand,
the ion-pairing interference can be circumvented either by
using an appropriate combination of anion and cation
receptors (binary host strategy)[4] or by designing specific
heteroditopic receptors that take advantage of favorably
positioned binding sites as well as induce positive cooperative
and allosteric effects.[5] So far a plethora of heteroditopic
receptors have been developed for inorganic ion pairs,[6] but
much less has been reported for organic salts.[5c,7]
The molecular recognition of a,w-alkanediyldiammonium
salts has been actively investigated with different classes of
artificial homo(poly)topic receptors. Among these, cylindrical
macrotricyclic hosts,[8] cucurbiturils,[9] crown ether[10] and
glycoluril derivatives,[11] bimetallic porphyrin dimers,[12] as
well as p-tert-butylcalix[5]arenes[13] have been employed.
However, none of the receptors used so far has been equipped
with complementary counterion-binding sites.
[*] Prof. S. Pappalardo
Dipartimento di Scienze Chimiche
Università di Catania
Viale A. Doria 6, 95125 Catania (Italy)
Fax: (+39)095-580-138
E-mail: spappalardo@dipchi.unict.it
Dr. G. Gattuso, Dr. A. Notti, Dr. A. Pappalardo, Prof. M. F. Parisi,
Dr. I. Pisagatti
Dipartimento di Chimica Organica e Biologica
Università di Messina
Salita Sperone 31, 98166 Messina (Italy)
Fax: (+39)090-393-895
E-mail: mparisi@unime.it
Dr. D. Garozzo, Dr. M. Perez
CNR, ICTP Catania
Viale Regina Margherita 6, 95125 Catania (Italy)
Scheme 1. Synthesis of 1: a) TsO(CH2)3CH(CH3)2, K2CO3, CH3CN,
reflux, 12 h, 77%; b) H2, Pd/C, EtOAc, room temperature, 4 h, 93%;
c) 68% HNO3/AcOH, CH2Cl2, 08C, 25 min, 77%; d) TsO(CH2)3CH-
(CH3)2, NaH, THF, reflux, 48 h, 70%; e) SnCl2·2H2O, EtOAc/EtOH,
reflux, 24 h, 68%; f) 1,4-C6H4-(NCO)2, CHCl3, room temperature, 6 h,
66%. Ts=p-toluenesulfonyl; Bn=benzyl.
[**] We thank the MIUR (PRIN2003 project) for financial support, Prof.
P. Finocchiaro for helpful discussions, and Prof. M. E. Amato for the
acquisition of TROESY NMR spectra.
Supporting information for this article is available on the WWW
under http://www.angewandte.org or from the author.
4892
ꢀ 2005 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Angew. Chem. Int. Ed. 2005, 44, 4892 –4896

Angewandte
Chemie
subsequent selective ipso-nitration of 4 with 68% HNO3 and
acetic acid in CH2Cl2 afforded 5-nitro derivative 5 in 77%
yield. Further O-alkylation of the residual hydroxy group with
4-methylpent-1-yl tosylate and NaH in dry THF furnished the
5-nitro pentaether 6 in 70% yield which was converted into 5-
amino-calixarene
7 in 68% yield by reduction with
SnCl2·2H2O in EtOH/EtOAc at reflux. Final coupling of
two molecules of 7 with 1,4-phenylene diisocyanate in dry
CHCl3 led to biscalix[5]arene 1 in 66% yield.
The binding affinity of receptor 1 for linear, long-chain
a,w-alkanediyldiammonium (C8–C16) dichloride salts, as well
as the host-guest architectures they form,
were investigated by a combination of
1H NMR spectroscopy and electrospray
mass spectrometry (ESI-MS). The
former method takes advantage of the
large upfield shifts experienced by the
methylene resonances of the guest upon
encapsulation of the dication[4a,14] and the
downfield shifts of the NH resonances of
the host (in nonprotic media) which signal the simultaneous
binding of the counteranions. ESI-MS exploits the remark-
able tendency of the p-basic calix[5]arene cavity to include
alkylammonium guests, thus providing ion labels for the
detection of encapsulated complexes in the gas phase.[13,17,18]
The affinity of 1 for a,w-alkanediyldiammonium dichlor-
ide salts was initially investigated by 1H NMR titration
experiments in (CDCl2)2/CD3OD (2:1 V/V). Addition of the
guest salt (up to 4 equivalents) to a solution of 1 (1.0 ” 10À3 m)
caused the formation of very strong inclusion complexes,
whose host–guest stoichiometries (1:1 and/or 2:1) and geo-
metries depend on the length of the diammonium ion and the
[host]/[guest] ratio (see Figure 1). The 1H NMR spectra of the
inclusion complexes of calix[5]arenes with alkylammonium
guest ions normally show distinct signals for the free and
complexed host and guest species in slow exchange on the
1H NMR timescale.[13,14,18] Here, signals corresponding to the
free host and guests could barely be seen in the spectra of
equimolar host–guest mixtures of 1 with the longer alkyl-
diammonium (C12–C16) dichloride salts, which suggests very
high association constants (Ka > 106 mÀ1) for the formation of
the capsular (C-shaped) 1:1 host–guest complexes with Cs
symmetry. Similar results were observed using other solvent
systems (including neat (CDCl2)2, CDCl3, and CD2Cl2, or
mixtures thereof with up to 50% content of CD3OD), or on
changing—in the case of C12—the nature of the counteranion
(diacetate, dibromide, and dipicrate salts). Notably, the
spectra did not change upon further addition of salt or on
tenfold dilution of the solution.
Figure 1. Schematic representation of the influence of the spanning of
the guest a,w-alkanediyldiammonium ions on the complexation path-
ways leading to C-shaped and/or S-shaped inclusion complexes with
host 1.
equivalent of salt caused the almost exclusive formation of
the C-shaped 1:1 complex, as revealed by the presence of a set
of five upfield methylene resonances for the included dication
(Figure 2b).[19] Upon further addition of salt, a second more-
spread set of signals for the included guest became evident in
the highfield region of the spectra (d = À1.9 to 0.7 ppm) as a
result of the incipient formation of the S-shaped 1:2 host–
guest complex (Figure 2c and d). This conclusion is validated
by the triplet detected at d = 2.55 ppm which is assigned to the
a’-CH2 protons of the guest and is judged of diagnostic value
for the S-shaped complexes.[18] The latter architecture was the
only host–guest species present in solution when a total of
four equivalents of C10·2ClÀ had been added to 1 (Figure 2e).
The use of nonprotic solvents revealed the beneficial
effect of the ureido functions of 1 which facilitate the
loosening of the ion-paired salt and the association of the
In contrast, titration experiments of 1 with the shorter
alkyldiammonium (C8 and C10) dichloride guest salts gave rise
to changes in the 1H NMR spectra that are consistent with the
initial formation of the S-shaped (for C8) or C-shaped (for
C10) 1:1 host–guest complexes for equimolar host–guest
solutions and which eventually evolved toward the formation
of the S-shaped 1:2 host–guest complexes (C2h symmetry)
after further addition of salt (Figure 1). This is clearly shown
by the evolution of the 1H NMR spectra in the titration
experiment of 1 with C10·2ClÀ (Figure 2). Addition of one
Angew. Chem. Int. Ed. 2005, 44, 4892 –4896ꢀ 2005 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.angewandte.org 4893

Communications
The slow exchange in the capsular complexes of 1 with
diammonium salts allowed TROESY (transverse rotating-
frame Overhauser effect spectroscopy) NMR spectroscopy to
be carried out at room temperature, and the spectra obtained
were fully consistent with the expected structure and sym-
metry of the complexes. Most importantly, the TROESY
spectra (Figure 3b) showed clear intermolecular NOE cross
Figure 2. Highfield regions of the 1H NMR spectra (300 MHz;
22Æ18C; 2:1 (CDCl2)2/CD3OD) recorded during the titration experi-
ment of 1 (1.0”10À3 m) with C10·2ClÀ: a) 1; b) 1/C10·2ClÀ (1:1); c) 1/
C10·2ClÀ (1:1.5); d) 1/C10·2ClÀ (1:2); e) 1/C10·2ClÀ (1:4). The triplet
labeled with an asterisk refers to the a- and a’-CH2 of uncomplexed
C10·2ClÀ, which is present in excess.
anion by formation of six-membered chelate rings with halide
or picrate anions and eight-membered chelate rings with
carboxylate anions.[20]
The shifts of the N-H resonances of 1 upon ligand-
separated ion-pair complexation of the various C12 salts in
(CDCl2)2 provide a qualitative picture of the strength of the
anion-binding site (Table 1). Entries 3–6 suggest an anti-
Hofmeister[21] trend in the complexation of the counteranion
by heterotetratopic 1, with the largest Dd values being
À
Figure 3. a) Structure of the C-shaped capsular 1·C12·2CH3CO2 com-
observed for the more densely charged ClÀ and CH3CO2
À
plex with labeling of the relevant hydrogen atoms showing NOE inter-
actions between the host and guest. b) Selected region of the TROESY
anions (in (CDCl2)2: CH3CO2À ꢀ ClÀ > BrÀ > PicÀ). A com-
parison between entries 2 and 4 shows also that the encap-
sulation of the dication enhances the acidity of the urea NH
groups through an electron-withdrawing effect to result in a
better uptake of chloride anions (positive allosteric effect).[5]
NMR spectrum (500 MHz) of 1·C12·2 CH3CO2 (5.0”10À3 m in
À
(CDCl2)2). ax=axial.
+
peaks between the host and the guest. In particular, the NH3
protons of the salt showed NOE peaks to the axial bridging
methylene protons as well as to a- and b-oxymethylene
protons of the lower rim substituents of the calix[5]arene
moieties (Figure 3a), which provides evidence that the
ammonium end group is held in position by hydrogen-
bonding interactions with the ethereal oxygens. Moreover,
the encapsulated e-methylene protons of the C12 guest and the
aromatic protons of the host gave rise to a cross peak.
The formation of capsular complexes between 1 and long-
chain a,w-alkanediyldiammmonium dichloride salts is further
corroborated by the positive ESI mass spectra of equimolar
host–guest mixtures which show prominent doubly-charged
ions that correspond to [1·Cn]2+ (base peak) and low-intensity
ion peaks for [1·CnCl]+.[22]
Table 1: Variation of the chemical shift of urea NH resonances of 1
(300 MHz, 1.0”10À3 m in (CDCl2)2) after the addition of one equivalent
of guest salt.
Entry
Guest
d [ppm]
Dd [ppm]
[a]
[a]
NHa[a]
NHb
NHa[a]
NHb
1
2
3
4
5
6
none
6.44
7.21[b]
8.91
8.81
8.28
5.88
nBu4N+ClÀ
C12·2CH3CO2
C12·2ClÀ
6.63[b]
8.60
8.51
8.08
0.77
2.47
2.37
1.84
0.75
2.72
2.63
2.20
À
C12·2BrÀ
C12·2PicÀ
7.40[c]
1.24
[a] NHa and NHb refer to the two groups close to the calixarene unit and
the 1,4-phenylene moiety, respectively. [b] Fast complexation equilibrium
on the NMR timescale; data refer to the addition of two equivalents of
salt. [c] Broad signal, partly buried under the aromatic protons of the
calixarene units. Pic=picrate.
The binding selectivity of 1 for the guest salts studied here
was eventually determined by decreasing in highly coordinat-
ing solvents the cooperativity factors that arise from the
4894 www.angewandte.org
ꢀ 2005 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Angew. Chem. Int. Ed. 2005, 44, 4892 –4896

Angewandte
Chemie
molecular Chemistry of Anions (Eds.: A. Bianchi, K. Bowman-
anion-binding sites. Addition of dimethyl sulfoxide (DMSO)
to a solution of 1 in chloroform led to a strong solvation of the
hydrogen-bond donor sites of the ureido functions.[23,24] This
solvation caused a weakening of the binding ability of 1
toward ion-paired salts[25] and allowed the determination of
James, E. Garcia-Espana), VCH, Weinheim, 1997.
[4] a) G. Cafeo, G. Gattuso, F. H. Kohnke, A. Notti, S. Occhipinti, S.
Pappalardo, M. F. Parisi, Angew. Chem. 2002, 114, 2226 – 2230;
Angew. Chem. Int. Ed. 2002, 41, 2122 – 2126; b) K. Kavallieratos,
B. A. Moyer, Chem. Commun. 2001, 1620 – 1621.
[5] a) L. Kovbasyuk, R. Krꢀmer, Chem. Rev. 2004, 104, 3163 – 3187;
b) A. J. Evans, P. D. Beer, Dalton Trans. 2003, 4451 – 4456; c) A.
Arduini, G. Giorgi, A. Pochini, A. Secchi, F. Ugozzoli, J. Org.
Chem. 2001, 66, 8302 – 8308.
1
the association constants by H NMR spectroscopy. Table 2
shows that among the substrates investigated the longer C12
and C16 guest salts are more tightly bound than C8 and C10 by 1
as the result of capsular complexation.
[6] For representative examples, see: a) J. M. Mahoney, A. M.
Beatty, B. D. Smith, Inorg. Chem. 2004, 43, 7617 – 7621, and
references therein; b) M. Barboiu, G. Vaughan, A. van der Lee,
Org. Lett. 2003, 5, 3073 – 3076; c) M.-L. Lehaire, R. Scopelliti, H.
Piotrowski, K. Severin, Angew. Chem. 2002, 114, 1477 – 1480;
Angew. Chem. Int. Ed. 2002, 41, 1419 – 1422; d) M. J. Deetz, M.
Shang, B. D. Smith, J. Am. Chem. Soc. 2000, 122, 6201 – 6207;
e) D. J. White, N. Laing, H. Miller, S. Parsone, S. Coles, P. A.
Tasker, Chem. Commun. 1999, 2077 – 2078; f) J. Scheerder,
J. P. M. van Duynhoven, J. F. J. Engbersen, D. N. Reinhoudt,
Angew. Chem. 1996, 108, 1172 – 1175; Angew. Chem. Int. Ed.
Engl. 1996, 35, 1090 – 1093.
[7] a) T. Haino, M. Nakamura, N. Kato, M. Hiraoka, Y. Fukazawa,
Tetrahedron Lett. 2004, 45, 2281 – 2284; b) G. Tumcharern, T.
Tuntulani, S. J. Coles, M. B. Hursthouse, J. D. Kilburn, Org. Lett.
2003, 5, 4971 – 4974; c) J. M. Mahoney, J. P. Davis, A. M. Beatty,
B. D. Smith, J. Org. Chem. 2003, 68, 9819 – 9820; d) J. L. Atwood,
A. Szumna, Chem. Commun. 2003, 940 – 941.
Table 2: Association constants (Ka) of a,w-alkanediyldiammonium
dichloride salts with receptor 1 in CDCl3/[D6]DMSO (3:2).[a]
H3N+(CH2)n+NH3·2ClÀ
Ka [mÀ1
]
n=8
212[b]
163[b]
n=10
n=12
n=14
n=16
2.4”103
[c]
–
2.6”103
[a] Determined by 1H NMR spectroscopy at 22Æ18C using equimolar
(1”10À3 m) host–guest mixtures. Values are derived from the average of
at least three independent measurements (standard errorꢁ15%). [b] Ka
values refer to the S-shaped 1:1 complex. [c] Measurements of Ka were
precluded by the limited solubility of the salt.
[8] F. Fages, J.-P. Desvergne, K. Kampke, H. Bouas-Laurent, J.-M.
Lehn, M. Meyer, A.-M. Albrecht-Gary, J. Am. Chem. Soc. 1993,
115, 3658 – 3664.
[9] a) J. W. Lee, S. Samal, N. Selvapalam, H.-J. Kim, K. Kim, Acc.
Chem. Res. 2003, 36, 621 – 630; b) W. L. Mock, N.-Y. Shih, J. Org.
Chem. 1983, 48, 3618 – 3619.
[10] K. Tsubaki, H. Tanaka, T. Futura, K. Tanaka, T. Kinoshita, K.
Fuji, Tetrahedron 2002, 58, 5611 – 5617.
[11] J. W. H. Smeets, R. P. Sijibesma, L. van Dalen, A. L. Spek,
W. J. J. Smeets, R. J. M. Nolte, J. Org. Chem. 1989, 54, 3710 –
3717.
[12] a) M. J. Crossley, P. Thordarson, Angew. Chem. 2002, 114, 1785 –
1788; Angew. Chem. Int. Ed. 2002, 41, 1709 – 1712; b) Y. Kubo, Y.
Murai, J.-i. Yamanaka, S. Tokita, Y. Ishimaru, Tetrahedron Lett.
1999, 40, 6019 – 6023.
[13] D. Garozzo, G. Gattuso, F. H. Kohnke, P. Malvagna, A. Notti, S.
Occhipinti, S. Pappalardo, M. F. Parisi, I. Pisagatti, Tetrahedron
Lett. 2002, 43, 7663– 7667.
[14] a) F. P. Ballistreri, A. Notti, S. Pappalardo, M. F. Parisi, I.
Pisagatti, Org. Lett. 2003, 5, 1071 – 1074; b) F. Arnaud-Neu, S.
Fuangswasdi, A. Notti, S. Pappalardo, M. F. Parisi, Angew.
Chem. 1998, 110, 120 – 122; Angew. Chem. Int. Ed. 1998, 37, 112 –
114.
The binding selectivity order of 1 toward C12, C14, and C16
as chloride salts was estimated from the ESI-MS distribution
percentages[26] of the relevant capsular complexes ([1·Cn]2+
ions). A competitive complexation experiment of 1 with a
mixture of the three salts (1/C12·2ClÀ/C14·2ClÀ/C16·2ClÀ =
1:1:1:1; c = 1.0 ” 10À4 m in CHCl3/CH3OH (1:1)) gave the
order
tively).[27,28]
In conclusion, we have synthesized a novel heterotetra-
C14 > C16 > C12 (60.5, 24.6, and 14.9%, respec-
topic receptor, 1, that efficiently and selectively forms ligand-
separated ion-pair complexes with long-chain a,w-alkane-
diyldiammonium dichloride salts by combining the coopera-
tive action of two converging calix[5]arene cavities in the
encapsulation of the dication with the ability of the two ureido
functions to bind the relevant counteranions. Future work will
be directed toward the design of new heteropolytopic systems
with specific recognition patterns.
Received: March 17, 2005
Published online: July 6, 2005
[15] For a review on molecular encapsulation, see: F. Hof, S. L. Craig,
C. Nuckolls, J. Rebek, Jr., Angew. Chem. 2002, 114, 1556 – 1578;
Angew. Chem. Int. Ed. 2002, 41, 1488 – 1508.
[16] D. R. Stewart, M. Krawiec, R. M. Kashyap, W. H. Watson, C. D.
Gutsche, J. Am. Chem. Soc. 1995, 117, 586 – 601.
Keywords: calixarenes · host–guest systems ·
inclusion compounds · ion pairs · molecular recognition
.
[17] C. A. Schalley, R. K. Castellano, M. S. Brody, D. M. Rudkevich,
G. Siuzdak, J. Rebek, Jr., J. Am. Chem. Soc. 1999, 121, 4568 –
4579.
[1] Reviews: a) P. A. Gale, Coord. Chem. Rev. 2003, 240, 191 – 221;
b) P. D. Beer, P. A. Gale, Angew. Chem. 2001, 113, 502 – 532;
Angew. Chem. Int. Ed. 2001, 40, 486 – 516.
[18] D. Garozzo, G. Gattuso, F. H. Kohnke, A. Notti, S. Pappalardo,
M. F. Parisi, I. Pisagatti, A. J. P. White, D. J. Williams, Org. Lett.
2003, 5, 4025 – 4028.
[19] The guest is rather short to span the two calix[5]arene cavities,
and the shielding experienced by the included chain is less
effective than that observed with the longer, more tightly bound
guest salts.
[2] a) A. Arduini, E. Brindani, G. Giorgi, A. Pochini, A. Secchi, J.
Org. Chem. 2002, 67, 6188 – 6194; b) S. Bartoli, S. Roelens, J. Am.
Chem. Soc. 2002, 124, 8307 – 8315; c) V. Böhmer, A. Dalla Cort,
L. Mandolini, J. Org. Chem. 2001, 66, 1900 – 1902; d) R. Shukla,
T. Kida, B. D. Smith, Org. Lett. 2000, 2, 3099 – 3102.
[3] a) I. Krossing, I. Raabe, Angew. Chem. 2004, 116, 2116 – 2142;
Angew. Chem. Int. Ed. 2004, 43, 2066 – 2090; b) The Supra-
Angew. Chem. Int. Ed. 2005, 44, 4892 –4896ꢀ 2005 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.angewandte.org 4895

Communications
[20] For a very recent report on the possible geometries of urea–
anion complexes, see: B. P. Hay, T. K. Firman, B. A. Moyer, J.
Am. Chem. Soc. 2005, 127, 1810 – 1819.
[21] F. Hofmeister, Arch. Exp. Pathol. Pharmakol. 1888, 24, 247 – 260.
[22] The ESI mass spectra recorded at higher concentrations (ca.
10À4 m) show additional peaks of low intensity that correspond to
m+1
[(1·Cn)mCl(mÀ1)
]
(m ꢂ 2), which may imply a chloride-driven
self-assembly of the capsular complexes through an intercapsu-
lar 2:1 urea–chloride binding mode[20] in the gas phase.
[23] E. Fan, S. A. Van Arman, S. Kincaid, A. D. Hamilton, J. Am.
Chem. Soc. 1993, 115, 369 – 370.
[24] Heteroditopic calix[4]arenes endowed with a ureido function-
ality have been reported to strongly coordinate thorugh hydro-
gen bonding to DMSO molecules; see: A. Arduini, E. Brindani,
G. Giorgi, A. Pochini, A. Secchi, Tetrahedron 2003, 59, 7587 –
7594.
[25] The importance of the ureido functions on the host properties of
1 is demonstrated by the inability of the model p-tert-butyl-
penta-O-isohexyl calix[5]arene, which lacks a ureido group at
the upper rim, to form an inclusion complex with the ion-paired
n-dodecylammonium chloride in 3:2 CDCl3/[D6]DMSO.
[26] G. Ferguson, A. J. Lough, A. Notti, S. Pappalardo, M. F. Parisi,
G. Resnati, Collect. Czech. Chem. Commun. 2004, 69, 1109 –
1125, and references therein.
[27] Again, a possible chloride-driven self-assembly of the various
capsular complexes is clearly indicated by the presence of mixed
assemblies (see Supporting Information).
[28] 1H NMR competitive complexation experiments under similar
experimental conditions showed an analogous trend in the
relative binding selectivities.
4896 www.angewandte.org
ꢀ 2005 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Angew. Chem. Int. Ed. 2005, 44, 4892 –4896