Cation complexation of quinocrown ethers in electrospray ionization mass spectrometry. A comparison with benzocrown ethers

Article abstract of DOI:10.1039/a808752k

The alkali metal complexation of 15-to 18-membered ring quinocrown ethers Q15-18, 18- and 24-membered diquinocrown ethers DQ18,24, and 18-membered quinobenzocrown ether QB18 is compared with that of the corresponding benzocrown ethers B15-18 and dibenzo crown ethers DB18,24 in electrospray ionization mass spectrometry (ESI-MS). The quinocrown ethers exhibit lower cation affinity than the benzocrown ethers, although the two crown series essentially show the same ion selectivity except 18-membered DQ18 which preferentially binds Na⁺. The reduced binding ability of the quinocrowns is interpreted in terms of the deformation of the crown rings by the steric repulsion with the quinone carbonyls as well as the electron withdrawing ability of the fused quinone.

Full text of DOI:10.1039/a808752k

View Article Online / Journal Homepage / Table of Contents for this issue
Cation complexation of quinocrown ethers in electrospray
ionization mass spectrometry. A comparison with benzocrown
ethers
Akihiko Tsuda,a Hiroshi Moriwakib and Takumi Oshima*a
a Department of Materials Chemistry, Graduate School of Engineering, Osaka University,
Machikaneyama 1-16, Toyonaka, Osaka 560, Japan
b Osaka City Institute of Public Health & Environmental Science, 8-34 Tojo-cho, Tennoji
Osaka 543-0026, Japan
Received (in Cambridge) 9th November 1998, Accepted 30th March 1999
The alkali metal complexation of 15- to 18-membered ring quinocrown ethers Q15–18, 18- and 24-membered
diquinocrown ethers DQ18,24, and 18-membered quinobenzocrown ether QB18 is compared with that of the
corresponding benzocrown ethers B15–18 and dibenzo crown ethers DB18,24 in electrospray ionization mass
spectrometry (ESI-MS). The quinocrown ethers exhibit lower cation affinity than the benzocrown ethers, although
the two crown series essentially show the same ion selectivity except 18-membered DQ18 which preferentially binds
Naϩ. The reduced binding ability of the quinocrowns is interpreted in terms of the deformation of the crown rings
by the steric repulsion with the quinone carbonyls as well as the electron withdrawing ability of the fused quinone.
n
Introduction
O
O
O
O
Since the pioneering work of Pedersen,1 the cation binding abil-
ity of crown ethers has attracted much attention and numerous
studies have been performed that are reported in many papers
and summarized in reviews and books.2 During recent years,
much effort has been expended in order to clarify the host–
guest complexation of crown ethers by mass spectrometry
(ESI,3 FAB,4 CI,5 PD6, etc.). Electrospray ionization mass spec-
trometry (ESI-MS) in particular was found to be a powerful
analytical method for the characterization and identification of
these ion complexes and is now being increasingly employed for
an assessment of these complexation behaviors.7–11
In a previous paper, we have reported that diphenyl-
substituted 11- to 20-membered ring crown ether acetals show
selective cation complexation for alkali metal ions and NH4ϩ in
ESI-MS.8 Their reduced binding ability was rationalized by
considering the ring-contracted deformation, the hydrophobic
effects of the diphenyl group and the poor solvation energies of
the complexes.
Here, we will extend the ESI-MS analysis to the quinone-
fused 15- to 24-membered ring crown ethers, Q15–21, DQ18,24
and QB18 (abbreviated hereafter as quino-15-crown-5 Q15,
quino-18-crown-6 Q18, quino-21-crown-7 Q21, diquino-18-
crown-6 DQ18, diquino-24-crown-8 DQ24, and quinobenzo-
18-crown-6 QB18, according to generally accepted convention)
to explore the effects of the fused quinone on their cation bind-
ing ability as compared with the corresponding 15- to 24-
membered benzocrown ethers B15–21 and DB18,24 (benzo-15-
crown-5 B15, benzo-18-crown-6 B18, benzo-21-crown-7 B21,
dibenzo-18-crown-6 DB18, and dibenzo-24-crown-8 DB24).
O
O
O
O
O
O
O
O
O
O
O
n
O
O
n
Q15 n = 1
Q18 n = 2
Q21 n = 3
DQ18 n = 1
DQ24 n = 2
O
O
O
O
O
O
O
O
QB18
n
O
O
O
O
O
O
O
O
O
O
O
n
n
B15 n = 1
B18 n = 2
B21 n = 3
DB18 n = 1
DB24 n = 2
crown complexes were observed along with those of the 1:2
ion–crown complexes for rather small membered crown ethers
(Q15 and B15 for monofused crowns and DQ18, QB18, and
DB18 for difused crowns). In all measurements, the bare alkali
metal ions and solvated metal ions were more or less detected.
A representative ESI-MS spectrum for cation complexation of
DQ18 is shown in Fig. 1. To assess the selective cation binding
ability, the relative intensities (IM) of ESI mass spectra of the
1:1 and 1:2 ion–crown complexes were obtained for each
crown by dividing the respective peak height by that of the most
intense base peak. Isotope corrections were applicable to the
Results and discussion
Cation complexation of quinocrown ethers and benzocrown
ethers
The first set of ESI-MS experiments was carried out in a
methanol solution containing a crown (0.1 mM) and a mixture
of five alkali metal perchlorates (each 0.1 mM). In these
measurements, major mass peaks attributable to the 1:1 ion–
J. Chem. Soc., Perkin Trans. 2, 1999, 1235–1240
1235

View Article Online
Table 1 Peak intensity data for ESI-MS analysis for complexation of
crown ethers with alkali metal ionsa
Relative intensity IM(%)c
Complexb
n
Li
Na
K
Rb
25
(8)
72
45
(29)
40
(37)
100
100
Cs
Quinocrown ethers
[(Q15)nؒM]ϩ
1
2
1
1
2
1
2
1
1
31
(0)
8
100
(0)
92
12
(0)
36
17
(18)
25
(18)
70
70
(42)
100
100
(8)
61
(15)
80
[(Q18)nؒM]ϩ
46
71
(0)
100
(0)
44
[(QB18)nؒM]ϩ
9
(0)
21
(0)
21
12
[(DQ18)nؒM]ϩ
[(Q21)nؒM]ϩ
[(DQ24)nؒM]ϩ
51
95
Benzocrown ethers
Fig. 2 Plot of relative binding constant vs. metal ion radius for 1:1
benzocrown–ion complexes (ref. 2c,e); B15 benzo-15-crown-5, B18
benzo-18-crown-6, DB18 dibenzo-18-crown-6, DB24 dibenzo-24-
crown-8.
[(B15)nؒM]ϩ
1
2
1
1
2
1
1
10
(0)
3
6
(0)
9
100
(0)
24
35
(0)
18
61
(22)
100
100
(0)
73
81
28
(10)
49
11
(4)
7
19
(8)
79
81
[(B18)nؒM]ϩ
[(DB18)nؒM]ϩ
44
(15)
100
100
[(B21)nؒM]ϩ
compare the plots of the relative Krel vs. metal ion radius (Fig.
2) with the corresponding plots of IM (Fig. 3) (vide infra). It was
found that the Krel profile of each benzocrown ether very closely
resembles the corresponding IM profile. Keeping this in mind,
we employed IM to at least qualitatively represent the selective
cation binding ability.
[(DB24)nؒM]ϩ
9
57
a Solvent: methanol; crown ether (0.1 mM) and metal ion (each 0.1
mM). b Counter anion perchlorate was omitted. M = Li, Na, K, Rb or
Cs as indicated. c The values in parentheses are the IM for 1:2 ion–crown
complexes.
The 1:1 ion–crown complexes
The metal ion responsible for the 1:1 base peak (IM = 100) was
Naϩ for quino-15-crown-5 Q15 and diquino-18-crown-6 DQ18,
Kϩ for quino-18-crown-6 Q18 and quinobenzo-18-crown-6
QB18, Rbϩ for quino-21-crown-7 Q21 and diquino-24-crown-8
DQ24. Here it should be noted that the 18-membered diquino-
crown DQ18 binds Naϩ in preference to the expected Kϩ. On
the other hand, for the benzocrown series, the 1:1 base peak
was observed at Naϩ for benzo-15-crown-5 B15, at Kϩ for
benzo-18-crown-6 B18 and dibenzo-18-crown-6 DB18, and at
Rbϩ for benzo-21-crown-8 B21 and dibenzo-24-crown-8 DB24,
respectively. These selective cation binding properties can be
more explicitly visualized in the comparative plots of IM vs.
metal ion radius (Å) for the same membered crowns (Fig. 3a–
d). The cation selectivities of the benzocrowns B15, B18, DB18,
and DB24 based on the ESI-MS data were also essentially com-
patible with the actual complex stabilities determined by the
other measurements commonly employed,2c,e e.g., calorimetry,
conductivity, ion selective electrode, potentiometry, and NMR
(Fig. 2).
The binding profile of quino-15-crown-5 Q15 is similar to
that of the benzo-15-crown-5 B15 except for reduced Naϩ/Kϩ
selectivity for Q15 (Fig. 3a). These crowns are too large to
envelop the smallest alkali metal ion Liϩ (ionic radius 0.60
Å)12 by considering the cavity radius (0.86–1.1 Å)13 for B15.
The maximal peaks at Naϩ (ionic radius 0.95 Å)12 are probably
due to the size-fitted ion-in-the-hole complex.14 A decrease as
the ion radius increases from Naϩ to Csϩ (Kϩ 1.33 Å, Rbϩ 1.48,
Csϩ 1.69)12 is related to the decreasing binding ability with the
increasing ion radius. For these larger cations, Q15 and B15
would exhibit mass spectra attributable to the “nesting” com-
plexes or the less-favorable “perching” ones.15 The poor Naϩ/
Kϩ selectivity of Q15 as compared with B15 may be due to the
decrease in the absolute binding ability of Q15. In practice, Q15
showed lower complexation ability towards Kϩ than B15 (vide
infra).
Fig. 1 ESI mass spectrum of diquino-18-crown-6 DQ18 binding Mϩ
(= Liϩ, Naϩ, Kϩ, Rbϩ, Csϩ). [DQ18] = 0.1 mM, [MClO4] = 0.1 mM,
solvent; methanol.
experimental data for Liϩ, Kϩ and Rbϩ complexes. The data set
is summarized in Table 1.
Here, some attention needs to be drawn to whether the
relative peak height can be used to suggest the metal–host
selectivity. The quantification of the ESI-MS peak intensity of
the complexes remains unclear, since the desolvation process is
highly dependent on the solvation energy of each of the ionic
species as well as on the needle biased voltage. For example, a
possible misinterpretation of the ESI-MS data was reported for
the cyclodextrin inclusion of amino acids and small peptides.9
In contrast, for the complexations of crown ether or cryptand
with alkali metal cation, several workers argued that the peak
intensities of the respective complexes in the gas phase have a
good correlation to their actual complex stability constants in
solution.10 Very recently, however, Liu et al. reported for the
lariat crown ethers that the calibration for the relative cationiz-
ation efficiencies of the metallated crown is essential for com-
parison of the selectivities in the metal–crown interactions.11
For the quinocrown ethers, we have no evidence for the valid-
ity of the ESI-MS for a quantitative estimation of the cation
selectivities from the relative intensities IM. The thermodynamic
data for cation complexation of quinocrown ethers are not
known, though the log K values for the corresponding benzo-
crown ethers are reported.2c,e These situations prompted us to
These effects of quinone fusion can be rationalized by the
strong electron accepting ability as well as the much enhanced
distortion of crown ring. In the PM3 calculations16 for these
two crowns, the most striking difference is the unfavorable steric
effect of the quinone carbonyls which induce the adjacent
1236
J. Chem. Soc., Perkin Trans. 2, 1999, 1235–1240

View Article Online
Fig. 3 Plots of relative intensity (IM) of ESI mass spectra vs. metal ion radius for 1:1 crown–ion complexes; (a) Q15 quino-15-crown-5 and B15
benzo-15-crown-5; (b) Q18 quino-18-crown-6, DQ18 diquino-18-crown-6, QB18 quinobenzo-18-crown-6, B18 benzo-18-crown-6 and DB18
dibenzo-18-crown-6; (c) Q21 quino-21-crown-7 and B21 benzo-21-crown-7; (d) DQ24 diquino-24-crown-8 and DB24 dibenzo-24-crown-8.
ability. Such a steric hindrance seems to be one of the reasons
for our finding that an attempt to synthesize the lower quino-
12-crown-4 instead gave the dimeric diquino-24-crown-8
DQ24 (see Experimental section).
As for the 18-membered crown ethers investigated, the base
peak was attained as expected, at Kϩ with the exception of
diquino-18-crown-6 DQ18, which gave the base peak at Naϩ
(Fig. 3b). The shift of the base peak cation to the smaller Naϩ is
ascribed to the substantial decrease in the effective ring cavity
of DQ18 as compared with the other 18-membered crowns
(cavity radius of 1.3–1.6 Å).14 The abnormal binding behavior
of DQ18 must therefore be caused by the double quinone con-
Fig. 4 View of the molecular structure of (a) Q15 quino-15-crown-5
straint which exerts additive steric effects on the crown ether
and (b) B15 benzo-15-crown-5. Hydrogens have been omitted for
clarity.
ring, even more diminishing the conformational freedom of the
ring cavity. Among the four Kϩ selective crowns, their selectivity
for this cation seems to decrease in the order B18 > DB18 >
oxyethylene units to adopt an extraordinary flipped-out struc-
ture with respect to the quinone moiety (Fig. 4). The torsion
angles (θ) across the conjunct C–O bonds are calculated to be
much larger for Q15 (57 and Ϫ56Њ) than for B15 (23 and Ϫ23Њ).
The calculated distances between the facing oxygen atoms
range from 3.8 to 6.2 Å for Q15 and from 4.6 to 5.1 Å for B15,
respectively. Such a constrained and folded ring deformation
was realized in the X-ray structure analysis of Q15,17 although
the comparable B1518 is known to adopt a quasi-rectangular
crystalline conformation. As a result, Q15 seems to adopt a
bent ellipsoidal structure narrowing the effective ring cavity,
whereas B15 has a rectangular one (close to square).
Q18 > QB18. Benzocrowns B18 and DB18 provided similar
binding profiles regardless of the number of fused benzenes,
although quinocrown Q18 exhibited less selective complex-
ation. The Kϩ selectivity, furthermore, decreases in the case of
quinobenzocrown QB18 compared with that of Q18. These
findings imply that even monoquinone-fusion brings about a
more noticeable reduction in the binding selectivity as well as
in its affinity, and the increasing ring rigidity by fusion of an
additional benzene ring to the quinocrown ring results in
the enhancement of this effect.
Quino-21-crown-7 Q21 gave a base peak at Rbϩ similarly to
benzo-21-crown-7 B21 (Fig. 3c). Ambiguity in predicting which
cation, Rbϩ or Csϩ, is more preferentially bound by the 21-
membered ring crown compounds can be seen (cavity radius
1.7–2.15 Å).14 The vagueness in observing a more selective
These structural features caused by fused quinone rings also
seem to be the case for all quinocrowns and more or less result
in the deformation of the ring to reduce the complexation
J. Chem. Soc., Perkin Trans. 2, 1999, 1235–1240
1237

View Article Online
Table 2 Peak intensity data for ESI-MS analysis for complexation of
cation would be due to more increased ring flexibility owing to
the incorporation of one additional oxyethylene unit as com-
pared with the 18-membered crown compound. The two
crowns Q21 and B21 showed similar binding plots except for
the somewhat higher deviation of Q21 for the smaller Liϩ and
Naϩ. The reduced Naϩ/Rbϩ selectivity for Q21 is probably due
to the intrinsic poor binding affinity as described in the later
section. A straightforward application of the size-fitted ion-in-
the-hole concept is no longer enough to account for the com-
plexation of a highly flexible large ring compound like Q21, in
which the incorporated cation can be bound by the wrapping or
capsulating coordination of ring oxygen atoms.19
Diquino-24-crown-8 DQ24 and dibenzo-24-crown-8 DB24
also gave base peaks at Rbϩ, in which these two crowns showed
very similar binding profiles (Fig. 3d). DB24 is reported to have
a comparable binding affinity for Kϩ–Csϩ probably because of
the highly flexible crown ring. Though small, the steric effect of
double quinone-fusion appears in the binding profile of DQ24
as compared with DB24. One can easily see a slight rise and
drop of IM for the smaller Kϩ and the larger Csϩ, respectively.
Such opposite deviation around Rbϩ may be accounted for by
the decrease in the effective ring cavity of DQ24 as experienced
for the diquino-18-crown-6.
a mixture of crown ethers with Kϩ a
Relative intensity IM(%)
1:1 Complexb
1:2 Complexb
[Q15ؒK]ϩ
[Q18ؒK]ϩ
[QB18ؒK]ϩ
[DQ18ؒK]ϩ
[Q21ؒK]ϩ
[DQ24ؒK]ϩ
9
22
17
4
14
8
[B15ؒK]ϩ
[B18ؒK]ϩ
21
100
[(Q15)2ؒK]ϩ
[Q15ؒB15ؒK]ϩ
[(B15)2ؒK]ϩ
7
3
2
[DB18ؒK]ϩ
[B21ؒK]ϩ
68
61
40
[DB24ؒK]ϩ
a Solvent: methanol; crown (0.1 mM) and metal ion (each 0.1 mM).
b Counter anion was omitted.
The 1:2 ion–crown complexes
The 1:2 ion–crown complexes were observed mainly for the
smaller 15-membered quino- and benzocrowns Q15 and B15,
and 18-membered diquino-, quinobenzo-, and dibenzocrowns
DQ18, QB18 and DB18. The values of IM are given in paren-
theses in Table 1. The formation of such multiple-complexes is
general for a variety of crowns with a relatively smaller ring
size.20 The 1:2 maximum peak tended to appear at the next
largest alkali metal ion than that responsible for the 1:1 base
complexes. This shift was also the case for the 1:2 complexes of
diphenyl-substituted crown ether acetals, previously reported.8
Here, an exception is that diquino-18-crown-6 DQ18, which
gave a 1:1 base peak at Naϩ, gave the maximum 1:2 peak at the
next largest Rbϩ. The irregularity of DQ18 infers that the
actual ring cavity is not reduced to a size comparable to the 15-
membered ring, thereby this diquinocrown can sandwich the
originally expected Rbϩ. It is also noteworthy that the quino-
crowns provide a maximum 1:2 peak (IM) about twice as large
as do the corresponding benzocrowns. Of further interest is that
the ratio of 1:2 ion–crown complexes, in comparison with 18-
membered crown ethers, also increases in the order DB18 <
QB18 < DQ18, though the monosubstituted 18-membered
crowns Q18 and B18 do not give these possible 1:2 complex
peaks. Apparently, as described above, the fusion of quinone
distorts the crown ring more effectively than that of benzene.
Furthermore, the double fusion of quinone or benzene is
responsible for the more effective decrease in the ring cavity,
being suitable for multiple-complexation.
Fig. 5 Plots of relative intensity (IM) of ESI mass spectra vs. crown
ring sizes (N: numbers of ring atoms) for 1:1 crown–Kϩ complexes;
Q15 quino-15-crown-5, Q18 quino-18-crown-6, Q21 quino-21-crown-
7, DQ18 diquino-18-crown-6, DQ24 diquino-24-crown-8, QB18
quinobenzo-18-crown-6, B15 benzo-15-crown-5, B18 benzo-18-crown-
6, B21 benzo-21-crown-7, DB18 dibenzo-18-crown-6, and DB24
dibenzo-24-crown-8.
The Kϩ binding ability can be more definitely shown by the
plots of IM vs. the crown ring size for the 1:1 complexes (Fig. 5).
For mono-fused crowns, familiar profiles were observed for
both series of crowns, with the maximum peak at the Kϩ fitted
18-membered ring. However, the quinocrowns apparently
showed poor binding affinity towards this metal ion. Further-
more, incorporation of two quinones or a couple of quinone
and benzene groups brought about the astonishing drop in the
affinity of DQ18, DQ24 as well as QB18. These characteristic
properties are again due to the steric deformation of quino-
crown rings in addition to the electron-withdrawing ability of
the acceptor quinone.
Besides the homogeneous dimers, where both crowns are the
same, heterogeneous dimers consisting of two different crowns
were also detected between Q15 and B15 (Table 2). The IM
intensity is several times higher for quinocrowns Q15 than
benzocrown B15. The absence of a possible dimer complex for
DQ18 is explained by its greatly lowered binding ability.
Relative binding affinities of crown ethers towards Kϩ
Next we examined the complexation of a mixture of quino-
crowns and benzocrowns towards the selected Kϩ in order to
know the binding abilities. The ESI-MS mass spectra of the 1:1
Kϩ–crown complexes were considerably weaker for quino-
crowns than for the corresponding benzocrowns (Table 2). The
most intensive peak (taken as the base peak IM = 100%) is
observed for B18, the weakest one (IM = 4%) for DQ18. The
IM ratios of benzocrown to quinocrown varied in the range
of about 2–17. It is noted here that the di-fused crowns gave
rather high IM ratios of 5–17 as compared with 2.3–4.6 for the
mono-fused crowns. This means that double quinone fusion
brings about the remarkable drop in the binding ability. Within
a series of crowns, the mono-fused 18-membered ring provided
the strongest peak as expected from the ion-in-the-hole
concept.14
Conclusion
In the present ESI-MS study, we have found that 15- to
21-membered monoquinocrown ethers Q15–21, 18- and 24-
membered diquinocrown ethers DQ18,24 and 18-membered
quinobenzocrown ether QB18 exhibit cation selectivities for
the 1:1 and 1:2 bound complexes with alkali metal ions. The
cation selectivities were essentially the same as those of the
corresponding benzocrown ethers. The only exception was
the 18-membered diquinocrown ether DQ18 which provided
the maximum 1:1 ion–crown mass peak at Naϩ, although the
corresponding dibenzocrown DB18 preferentially bound Kϩ.
All the quinocrown ethers were found to be inferior to the
corresponding benzocrowns in binding affinities for alkali
metal cations. These binding behaviors of quinocrowns were
1238
J. Chem. Soc., Perkin Trans. 2, 1999, 1235–1240

View Article Online
attributable to the steric repulsion and the electron withdrawal
of the fused quinone moiety which will bring about the deform-
ation of the crown ring as well as the mitigation in the ion–
dipole interaction.
(60%), 45 (98%); Found: C, 56.11; H, 7.08. Calc. for C18H26O9:
C, 55.95; H, 6.78%.
10,13,23,26-Tetraoxo-2,5,8,15,18,21-hexaoxatricyclo-
[20.4.0.49,14]hexaicosa-122,914,1112,2425-tetraene
(diquino-18-
crown-6 DQ18). A solution of 3-benzyloxypyrocatechol 4 (2 g,
9.25 mmol), diethylene glycol ditosylate (3.83 g, 9.25 mmol) and
sodium hydroxide (2.96 g, 74 mmol) in dry dioxane (200 ml)
was stirred for 24 h at 80 ЊC. The precipitate was filtered off and
the filtrate was evaporated under reduced pressure to give a
viscous residue. The residue was extracted with benzene to give
3,3Ј-dibenzyloxydibenzo-18-crown-6 5 (2.72 g) as a brown oil.
Subsequently, a mixture of 5 (2.72 g) and Pd carbon (0.5 g) in
dioxane (3 ml) was stirred under an atmosphere of hydrogen for
3 days. The catalyst was filtered off and the solvent was evapor-
ated under reduced pressure to give 3,3Ј-dihydroxydibenzo-18-
crown-6 6 (1.4 g) as an oil. Fremy’s salt (3.8 g, 14 mmol) was
added to a stirred suspension of 6 (0.88 g) in 5% aqueous
sodium acetate (280 ml) containing a small amount of benzene
(30 ml). After the mixture had been stirred at room temperature
for 30 min, it was extracted with benzene (3 × 70 ml). The com-
bined organic layers were dried (MgSO4) and concentrated
under reduced pressure. The residue was recrystallized from
chloroform–hexane to give DQ18 (0.23 g, overall yield 33%) as
Experimental
Melting points were measured with a Yanagimoto melting-
point apparatus and were uncorrected. NMR spectra were
recorded on a JEOL EX-270 spectrometer in a CDCl3 solution
using tetramethylsilane (TMS) as an internal standard. IR
spectra were recorded on a JASCO FT/IR-300E spectrometer.
Mass (EI) spectra were determined with a JEOL JMS-DX303
spectrometer and a SHIMADZU GCMS-QP200A gas chrom-
atograph mass spectrometer. ESI-MS was performed on a
HITACHI M-1200 AP ES mass spectrometer equipped with a
standard electrospray ion source. The drift and needle voltage
was set to 60 and 3000 volts, respectively. A 70 ЊC N2 gas was
used for the desolvation of charged droplets. The nebulizer
temperature was 180 ЊC. Solutions containing crowns (0.1 mM)
and metals (each 0.1 mM) were infused into the ion source in
a continuous flow at about 1 ml minϪ1 with a syringe pump.
Elemental analyses were performed on a Yanaco CHN corder
MT-5. Molecular structures were calculated by PM3, MOPAC
Version 94.10 in CAChe, Version 3.7, CAChe Scientific, 1994.
1
orange needles, mp 197–198 ЊC. H-NMR (270 MHz, CDCl3)
δ 3.82–3.79 (m, 8H), 4.54–4.51 (m, 8H) and 6.59 (s, 4H); IR
(KBr) 2901, 1654, 1591, 1474, 1379, 1331, 1295, 1205, 1177,
1140, 1080, 1034, 843, and 677 cmϪ1; MS (EI) m/z 420 (Mϩ,
48%), 194 (100%), 179 (25%), 166 (70%), 138 (45%); Found: C,
57.35; H, 4.63. Calc. for C20H20O10: C, 57.15; H, 4.80%.
Materials
All alkali metal perchlorates were extra pure and were used
without further purification. Spectrally pure methanol (Dojin
Co. Ltd) was used in sample solutions. The benzocrowns B15,
B18, DB18 and DB24 were of commercial origin and were used
without further purification. The quinocrowns Q15, Q18 and
benzocrown B21 were prepared according to the published
methods.1b,21 The quinocrown Q21, diquinocrowns DQ18 and
DQ24, and quinobenzocrown QB18 were synthesized by the
modification of the literature methods22 as follows.
13,16,29,32-Tetraoxo-2,5,8,11,18,21,24,27-octaoxatricyclo-
[26.4.0.4.12,17]dotriaconta-128,1217,1415,3031-tetraene (diquino-24-
crown-8 DQ24). A solution of 3-benzyloxypyrocatecol 3 (5.1 g,
23.6 mmol), triethylene glycol ditosylate (10.8 g, 23.6 mmol)
and sodium hydroxide (7.6 g, 189 mmol) in dry dioxane (500
ml) was stirred for 24 h at 80 ЊC. The precipitate was filtered off
and the filtrate was evaporated under reduced pressure to give a
viscous residue. The residue was extracted with benzene to give
3,3Ј-dibenzyloxydibenzo-24-crown-8 7 (7.56 g) as a brown oil.
Subsequently, a mixture of 7 (7.56 g) and Pd carbon (1 g) in
dioxane (10 ml) was stirred under an atmosphere of hydrogen
for 3 days. The catalyst was filtered off and the solvent evapor-
ated under the reduced pressure to give 3,3Ј-dihydroxydibenzo-
24-crown-8 8 (4.2 g) as an oil. Fremy’s salt (3.8 g, 14 mmol) was
added to a stirred suspension of 8 (0.77 g) in 5% aqueous
sodium acetate (280 ml) containing a small amount of benzene
(30 ml). After the mixture had been stirred at room temperature
for 30 min, it was extracted with benzene (3 × 70 ml). The com-
bined organic layers were dried (MgSO4) and concentrated
under reduced pressure. The residue was chromatographed on a
silica gel with chloroform as an eluent to give DQ24 (0.32 g,
overall yield 29%). Recrystallization from hexane–benzene gave
22,25-Dioxo-2,5,8,11,14,17,20-heptaoxabicyclo[19.4.0]penta-
icosa-121,2324-diene (quino-21-crown-7 Q21). Sodium hydroxide
(9.6 g, 240 mmol) was added to a stirred solution of 1-
benzyloxy-2,3-bis(2Ј-hydroxyethoxy)benzene 1 (9.1 g, 30 mmol)
and tetraethylene glycol ditosylate (15.1 g, 30 mmol) in dry
dioxane (500 ml), then the solution was heated at 80 ЊC for 24 h.
The precipitate was filtered off and the filtrate was evaporated
under reduced pressure to give a viscous residue. The resi-
due was extracted with benzene to give 3-benzyloxybenzo-21-
crown-7† 2 (13.2 g). Subsequently, a mixture of 2 (13.2 g) and
Pd carbon (1 g) in dioxane (10 ml) was stirred under an atmos-
phere of hydrogen for 3 days. The catalyst was filtered off and
the solvent was evaporated under reduced pressure to give 3-
hydroxybenzo-21-crown-7 3 (11.1 g) as an oil. Fremy’s salt (3.8
g, 14 mmol) was added to a stirred suspension of 3 (0.86 g) in
5% aqueous sodium acetate (280 ml) containing a small amount
of benzene (30 ml). After the mixture had been stirred at room
temperature for 30 min, it was extracted with benzene (3 × 70
ml). The combined organic layers were dried (MgSO4) and
concentrated under reduced pressure. The residue was chrom-
atographed on a silica gel with chloroform–THF (3:1 by
volume) as an eluent to give Q21 (409 mg, 46%) as a red oil.
1H-NMR (270 MHz, CDCl3) δ 3.66 (s, 8H), 3.68 (s, 8H), 3.81–
3.85 (m, 4H), 4.45–4.49 (m, 4H) and 6.58 (s, 2H); IR (KBr)
1
crystalline DQ24 as orange needles; mp 115–116 ЊC. H-NMR
(270 MHz, CDCl3) δ 3.68 (s, 8H), 3.76–3.79 (m, 8H), 4.45–4.48
(m, 8H) and 6.58 (s, 4H); IR (KBr) 2873, 1677, 1654, 1587,
1560, 1286, 1201, 1165, 1075 and 845 cmϪ1; MS (EI) m/z 508
(Mϩ, 6%), 420 (10.2%), 194 (55.96%), 167 (100%), 138 (29.7%)
and 73 (23%); Found: C, 56.77; H, 5.77. Calc. for C24H28O12:
C, 56.69; H, 5.55%.
23,26-Dioxo-2,5,8,15,18,21-hexaoxatricyclo[20.4.0.49,14]-
hexaicosa-122,914,1011,1213,2425-pentaene (quinobenzo-18-crown-6
QB18). Sodium hydroxide (2.7 g, 67.5 mmol) was added to a
stirred solution of 1-benzyloxy-2,3-bis(2Ј-hydroxyethoxy)benz-
ene 1 (2.56 g, 8.42 mmol) and 2,3-bis(2Ј-tosyloxyethoxy)-
benzene (4.26 g, 8.42 mmol) in dry dioxane (300 ml), then
the solution was heated at 80 ЊC for 24 h. The precipitate
was filtered off and the filtrate was evaporated under reduced
pressure to give a viscous residue. The residue was extracted
2917, 1655, 1591, 1351, 1298, 1180, 1108, 951 and 845 cmϪ1
;
MS (EI) m/z 388 (Mϩ, 20%), 298 (18%), 194 (30%), 179 (15%),
166 (100%), 138 (82%), 117 (21%), 89 (36%), 82 (49%), 73
† The numbering of the benzyloxy group refers to its position on the
benzene ring, and not to the overall numbering of the compound. This
also applies similarly for compounds 1, 3, 5, 6, 7, 8 and 10 in the rest of
the Experimental.
J. Chem. Soc., Perkin Trans. 2, 1999, 1235–1240
1239

View Article Online
6 N. Malhotra, P. Roepstorff, T. K. Hansene and J. Becher, J. Am.
Chem. Soc., 1990, 112, 3709.
with benzene to give 3Ј-benzyloxydibenzo-18-crown-6 1 (3.74
g). Subsequently, a mixture of 1 (3.74 g) and Pd carbon (0.5 g)
in dioxane (5 ml) was stirred under an atmosphere of hydrogen
for 3 days. The catalyst was filtered off and the solvent was
evaporated under reduced pressure to give 3Ј-hydroxydibenzo-
18-crown-6 10 (3 g) as an oil. Fremy’s salt (3.8 g, 14 mmol) was
added to a stirred suspension of 10 (0.72 g) in 5% aqueous
sodium acetate (280 ml) containing a small amount of THF
(30 ml). After the mixture had been stirred at room temperature
for 30 min, it was extracted with benzene (3 × 50 ml). The
combined organic layers were dried (MgSO4) and concentrated
under reduced pressure. The residue was chromatographed on a
silica gel with chloroform as an eluent to give QB18 (320 mg,
7 (a) S. F. Wang, C. K. Meng and J. B. Fenn, J. Phys. Chem., 1988, 92,
546; (b) E. Leize, A. V. Dorsselaer, R. Kramer and J.-M. Lehn,
J. Chem. Soc., Chem. Commun., 1993, 990; (c) S. R. Wilson and
Y. Wu, J. Chem. Soc., Chem. Commun., 1993, 784; (d ) S. R. Wilson
and M. L. Tulchinsky, J. Org. Chem., 1993, 58, 6; (e) J. B. Cunniff
and P. Vouros, Rapid Commun. Mass Spectrom., 1994, 8, 715;
( f ) C. D. Buchecker, E. Leize, J.-F. Nierengarten, J.-P. Sauvage and
A. V. Dorsselaer, J. Chem. Soc., Chem. Commun., 1994, 2257; (g)
R. Colton, S. Mitchell and J. C. Traeger, Inorg. Chem. Acta, 1995,
231, 87; (h) K. C. Russell, E. Leize, A. V. Dorsselaer and J.-M. Lehn,
Angew. Chem., Int. Ed. Engl., 1995, 34, 209; (i) M. Sawada,
Y. Takai, T. Kanada, R. Arakawa, M. Okamoto, H. Done,
T. Matsumoto, K. Naemura, K. Hirase and Y. Tobe, Chem.
Commun., 1996, 1735; (j) B. R. Gibny, H. Wang, J. W. Kamph and
V. L. Pecoraro, Inorg. Chem., 1996, 35, 6184; (k) K. Wang and
G. W. Gokel, J. Org. Chem., 1996, 61, 4693; (l) B. Hasenknoph,
J. M. Lehn, N. Boumediene, A. D. Gervais, A. V. Dorsselaer,
B. Kneisel and D. Fenske, J. Am. Chem. Soc., 1997, 119, 10956.
8 T. Oshima, F. Matsuda, K. Fukushima, H. Tamura, G.
Matsubayashi and R. Arakawa, J. Chem. Soc., Perkin Trans. 2, 1998,
145.
1
43%) as orange needles; mp 111–112 ЊC; H-NMR (270 MHz,
CDCl3) δ 3.89–3.96 (m, 8H), 4.15–4.18 (m, 4H), 4.52–4.55 (m,
4H), and 6.54 (s, 2H); IR (KBr) 3064, 2926, 1672, 1655, 1588,
1508, 1454, 1329, 1280, 1260, 1184, 1133, 1079, 932 and 843
cmϪ1; MS (EI) m/z 390 (Mϩ, 100%), 194 (19%), 180 (12%), 168
(14%), 167 (35%), 138 (82%), 136 (85%), 80 (11%); Found: C,
61.72; H, 5.66. Calc. for C20H22O8: C, 61.53; H, 5.68%.
9 (a) J. B. Cunniff and P. Vouros, J. Am. Soc. Mass Spectrom., 1996,
6, 437; (b) M. Goodall, P. M. Kelly, D. Parker, K. Gloe and H.
Stephan, J. Chem. Soc., Perkin Trans. 2, 1997, 59.
10 (a) E. Leize, A. Jaffrezic and A. V. Dorsselaer, J. Mass Spectrom.,
1996, 31, 537; (b) K. A. Hirsch, S. R. Wilson and J. S. Moore, J. Am.
Chem. Soc., 1997, 119, 10401; (c) F. Sobott, W. Kleinkofort and
B. Brutschy, Anal. Chem., 1997, 69, 3587.
References
1 (a) C. J. Pedersen, J. Am. Chem. Soc., 1967, 89, 2495; (b) C. J.
Pedersen, J. Am. Chem. Soc., 1967, 89, 7017.
2 (a) J. J. Christensen, D. J. Eatough and R. M. Izatt, Chem. Rev.,
1974, 74, 351; (b) Michio Hiraoka, Crown compounds their
characteristics and applications, Kodansha, Japan, 1978; (c) R. M.
Izatt, J. S. Bradshaw, S. A. Nielsen, J. D. Lamb and J. J. Christensen,
Chem. Rev., 1985, 85, 271; (d) Y. Inoue and G. W. Gokel, Cation
Binding by Macrocycles, Marcel Dekker, New York, 1990; (e) R. M.
Izatt, J. S. Bradshaw and R. L. Bruening, Chem. Rev., 1991, 91, 1721;
( f ) Supramolecular Chemistry: An Introduction, Fritz Vögtle,
Maruzene and Willy, Tokyo, 1995; (g) J.-M. Lehn, Supramolecular
Chemistry, Verlag, Weinheim, 1995; (h) J. C. Ma and D. A.
Dougherty, Chem. Rev., 1997, 97, 1303; (i) K. A. Connors, Chem.
Rev., 1997, 97, 1325; (j) F. P. Schmidtchen and M. Berger, Chem.
Rev., 1997, 97, 1609; (k) M. M. Conn and J. Rebek, Chem. Rev.,
1997, 97, 1647; (l) F. Zeng and S. C. Zimmermann, Chem. Rev.,
1997, 97, 1681; (m) A. Ikeda and S. Shinkai, Chem. Rev., 1997, 97,
1713.
11 D. S. Young, H. Y. Hung and L. K. Liu, J. Mass Spectrom., 1997, 32,
432.
12 (a) M. Sawada, Y. Takai, T. Kaneda, R. Arakawa, M. Okamoto,
H. Doe, T. Matsuo, K. Naemura, K. Hirose and Y. Tobe, Chem.
Commun., 1996, 1735; (b) M. Sawada, Y. Takai, H. Yamada,
J. Nishida, T. Kaneda, R. Arakawa, M. Okamoto, K. Hirose,
T. Tanaka and K. Naemura, J. Chem. Soc., Perkin Trans. 2, 1998,
701.
13 R. M. Izatt and J. J. Christensen, Synthetic Multidentate Macrocyclic
Compounds, Academic Press, New York, 1978, pp. 207–243.
14 R. D. Shannon, Acta Crystallogr., Sect. A, 1976, 32, 751.
15 C. J. Pedersen and H. K. Frensdorff, Angew. Chem., Int. Ed. Engl.,
1972, 11, 16.
16 (a) M. A. Bush and M. R. Truter, J. Chem. Soc., Chem. Commun.,
1970, 1439; (b) N. S. Poonia, J. Am. Chem. Soc., 1974, 96, 1012;
(c) O. A. Raevsky, V. P. Solov’ev, A. F. Solotnov, H.-J. Schneider and
V. Rudiger, J. Org. Chem., 1996, 61, 8113.
17 H. Imahori, K. Hagiwara, M. Aoki, T. Akiyama, S. Taniguti,
Y. Okada, M. Shirakawa and Y. Sakata, J. Am. Chem. Soc., 1996,
118, 11771.
3 (a) G. J. Van Berkel, S. A. McLuckey and G. L. Glish, Anal. Chem.,
1991, 63, 1098; (b) R. B. Cody, J. Tamura and B. D. Musselmann,
Anal. Chem., 1992, 64, 1561.
4 (a) D. P. Michaud, J. N. Kyranos, T. F. Brennan and P. Vouros, Anal.
Chem., 1990, 62, 1069; (b) M. Takayama, T. Fukai, T. Nomura and
T. Yamauchi, Org. Mass Spectrom., 1991, 26, 655; (c) J. C. Medina,
T. T. Goodnow, M. T. Bojas, J. L. Atwood, B. C. Lynn, A. E. Kaifer
and G. W. Gokel, J. Am. Chem. Soc., 1992, 114, 10583; (d)
T. Takahashi, A. Uchiyama, K. Yamada, B. C. Lynn and G. W.
Gokel, Tetrahedron Lett., 1992, 33, 3825; (e) M. Sawada,
Y. Okuyama, M. Shimizu, Y. Takai, Y. Hidaka, H. Yamada,
T. Tanaka, T. Kanada, K. Hirase, S. Shimizu and S. Takahashi,
J. Am. Chem. Soc., 1993, 115, 7381.
18 A. Tsuda, T. Kawamoto and T. Oshima, Acta Crystallogr., Sect. C,
1998, 54, 1364.
19 I. R. Hanson, Acta Crystallogr., Sect. B, 1978, 34, 1026.
20 D. Live and S. I. Chan, J. Am. Chem. Soc., 1976, 98, 3769.
21 (a) N. S. Poonia, J. Am. Chem. Soc., 1974, 96, 1012; (b) J. C. Peters,
A. L. Odom and C. C. Cummins, Chem. Commun., 1997, 1995.
22 F. Dietl, G. Gierer and A. Merz, Synthesis, 1985, 626.
5 (a) A. K. Bose, O. Prakash, G. Y. Hu and J. Edasery, J. Org. Chem.,
1983, 48, 782; (b) J. Brodbelt, S. Maleknia, C. C. Liou and R. Lagou,
J. Am. Chem. Soc., 1991, 113, 5913.
Paper 8/08752K
1240
J. Chem. Soc., Perkin Trans. 2, 1999, 1235–1240