Synthesis of pyridinocrownophanes exhibiting high Ag+-affinity

Article abstract of DOI:10.3987/com-99-s(i)1

Crownophanes possessing a pyridine moiety were prepared by means of intramolecular [2 + 2] photocycloaddition of the styrene derivatives. The crown compounds having six to ten ethereal oxygens selectively extracted Ag⁺ with high efficiency in the liquid-liquid extraction. The high extractability and efficiency were maintained even at low pH region of the extraction system. From ESI-MS analysis, it was found that the crownophanes formed some kinds of complexes having 1:1 and 2:1 stoichiometry (host/guest) with Ag⁺ and Pb²⁺ in MeCN-H₂O homogeneous system.

Full text of DOI:10.3987/com-99-s(i)1

HETEROCYCLES, Vol. 54, No. 1, 2001, pp. 123 - 130, Received, 18th August, 1999
SYNTHESIS OF PYRIDINOCROWNOPHANES EXHIBITING HIGH Ag+-
AFFINITY
Seiichi Inokuma, Koichi Kimura, Takashi Funaki, and Jun Nishimura*
Department of Chemistry, Gunma University, 1-5-1 Tenjin-cho, Kiryu 376-8515,
Japan
Abstract-Crownophanes possessing a pyridine moiety were prepared by means of
intramolecular [2 + 2] photocycloaddition of the styrene derivatives. The crown
compounds having six to ten ethereal oxygens selectively extracted Ag+ with high
efficiency in the liquid-liquid extraction. The high extractability and efficiency
were maintained even at low pH region of the extraction system. From ESI-MS
analysis, it was found that the crownophanes formed some kinds of complexes
having 1:1 and 2:1 stoichiometry (host/guest) with Ag+ and Pb2+ in MeCN-H O
2
homogeneous system.
Nitrogen atom has been found to show high affinity toward heavy metal cations such as Ag+ and Pb2+ ions
when it is employed as dentate(s) of a crown ether or ligating site(s) of its in side chain(s).1,2 In particular,
pyridine ring(s) arranged in an appropriate position of host molecules have been found to exhibit interesting
complexing behavior.3-7 Recently, we have conveniently and efficiently prepared crownophanes bridged
by cyclobutane ring by means of intramolecular [2 + 2] photocycloaddition of styrene derivatives with
oligo(oxyethylene) linkage.8 We have also prepared lariat crownophanes having pyridine residues in the
side chains by the photocycloaddition, followed by attachment of side arms, and clarified some interesting
complexation behavior with heavy metal cations.9,10 For example, one of the lariat crownophanes showed
high extractability toward Ag+ ion even at high proton concentration (pH<1).9 In this paper, we would
like to describe the synthesis and complexing properties of crownophanes possessing pyridine moiety in the
polyether linkage (pyridinocrownophanes).
EXPERIMENTAL
Apparatus. IR spectra were obtained on a Hitachi 270-50 spectrophotometer. 1H NMR spectra were
taken at 500 MHz using tetramethysilane as an internal standard. Elemental analysis was carried out in
Technical Research Center for Instrumental Analysis, Gunma University. Electrospray ionization mass
spectra (ESI-MS) were obtained on a following conditions: A sample solution was sprayed at a flow rate of
2 μL min-1 at the tip of needle biased by a voltage of 4.5 kV higher than that of a counter electrode.
Reagents. Toluene and THF were purified by distillation over Na after prolonged reflux under a
nitrogen atmosphere.
Guaranteed reagent grade CH2Cl2 was distilled before use.
2,6-
Bis[(tosyloxy)methyl)]pyri-dine was prepared by reported method.11 Reagent grade dibenzopyridino-18-
crown-6 (5) was used without further purification. Paracrownophane (6) was prepared by the method
reported previousy.8 AgNO3, Pb(NO3)2, Cu(NO3)2, Mn(NO3)2, Zn(NO3)2, Ni(NO3)2, Co(NO3)2, and
Fe(NO3) 3 were of commercially available highest grade and used after vacuum drying. All aqueous
solutions were prepared with distilled, deionized water.
Preparation of oligoethyleneglycol mono(p-bromophenyl) ethers. 2-(p-Bromo-
phenoxy)ethanol
(1a) was prepared as follows: A mixture of p-bromophenol (25.0 g, 0.145 mol) and 2-chloroethanol
(116.3 g, 1.45 mol) in 10% aqueous NaOH solution (600 mL) was stirred under a nitrogen atmosphere at
rt. After 24 h, the mixture was extracted with CH2Cl2 (3 x 300 mL). The CH2Cl2 extracts were
combined, washed with 10% aqueous NaOH (2 x 500 mL) and with water (3 x 500 mL), dried over
anhydrous MgSO4. After the solvent was evaporated, the residue was recrystallized from hexane-ethanol
o
to give 1a as white crystals (30.1 g, 96%). mp 52.0-53.0 C. 1H NMR (CDCl3) δ=7.39 (2H, ABq,
J=6.7 Hz), 6.82(2H, ABq, J=6.7 Hz), 4.06 (2H, m), 3.96 (2H, m).
Oligoethylene glycol mono(p-bromophenyl) ether was prepared in a following manner: A mixture of 4-
bromophenol (20.00 g, 0.115 mol), oligoethylene glycol monotosylate (0.058 mol), pulverized K2CO3
(23.91 g, 0.173 mol), and DMF (250 mL) was stirred under a nitrogen atmosphere at 50 oC for 24 h. The

mixture was cooled and poured into a separatory funnel together with 800 mL of water. The aqueous
solution was extracted with CH2Cl2. The CH2Cl2 layer was washed with water (500 mL), 10% aqueous
NaOH (500 mL), and again water (500 mL). The CH2Cl2 layer dried over anhydrous MgSO4 was filtered
and evaporated in vacuo. The residue was flash chromatographed (SiO2, toluene-ethyl acetate(1:1)) to
give 1b-d as transparent viscous liquid. 1b (95%). 1H NMR (CDCl3) δ=7.37 (2H, ABq, J=6.5 Hz),
6.81(2H, ABq, J=6.5 Hz), 4.11 (2H, m), 3.86 (2H, m), 3.77 (2H, m), 3.67 (2H, m). 1c (94%). 1H
NMR (CDCl3) δ=7.37 (2H, ABq, J=6.5 Hz), 6.81(2H, ABq, J=6.5 Hz), 4.11 (2H, m), 3.85 (2H, m),
3.65 (8H, m). 1d (95% yield). 1H NMR (CDCl3) δ=7.37 (2H, ABq, J=6.5 Hz), 6.81(2H, ABq, J=6.5
Hz), 4.11 (2H, m), 3.84 (2H, m), 3.64 (12H, m).
Preparation of oligoethyleneglycol mono(p-vinylphenyl)
ethers (2a-d).
A solution of
oligoethyleneglycol mono(p-bromophenyl) ethers (46.0 mmol), tributylvinylstannane (17.5 g, 55.0 mmol),
Pd(PPh3)4 (1.33 g, 1.15 mmol), and 2,6-di-tert-butyl-4-methylphenol (15 mg) in toluene (120 mL) was
heated to reflux for 20 h. After the mixture was cooled to ambient temperature, a large excess of
2 mol dm-3 aqueous KF solution was added, and the resulting mixture was stirred overnight at the same
temperature. The organic layer was separated from the sludge and aqueous layer and then dried over
MgSO4. The concentrated crude material was purified by column chromatography (SiO2, a gradient mixed
solution of toluene and acetone) to afford the vinyl derivatives. 2a (50%). White solid (mp 59.5-60.2
oC, hexane-ethanol). 1H NMR (CDCl3) δ=7.35 (2H, ABq, J=6.7 Hz), 6.88(2H, ABq, J=6.7 Hz), 6.66
(1H, dd, J=20.0 and 10.0), 5.62 (1H, d, J=20.0), 5.14 (1H, d, J=10.0), 4.09 (2H, m), 3.96 (2H, m).
1
2b (31%). Transparent viscous liquid. H NMR (CDCl3) δ=7.31 (2H, ABq, J=6.7 Hz), 6.86(2H, ABq,
J=6.7 Hz), 6.64 (1H, dd, J=17.5 and 10.0), 5.58 (1H, d, J=17.5), 5.12 (1H, d, J=10), 4.12 (2H, m), 3.85
(2H, m), 3.74 (2H, m), 3.66 (2H, m). 2c (48%). Transparent viscous liquid. 1H NMR (CDCl3)
δ=7.31 (2H, ABq, J=6.7 Hz), 6.86(2H, ABq, J=6.7 Hz), 6.65 (1H, dd, J=17.5 and 10.0), 5.61 (1H, d,
J=17.5), 5.13 (1H, d, J=10.0), 4.13 (2H, m), 3.87 (2H, m), 3.73 (6H, m), 3.63 (2H, m). 2d (67%).
Transparent viscous liquid. 1H NMR (CDCl3) δ=7.31 (2H, ABq, J=8.9 Hz), 6.86(2H, ABq, J=8.9 Hz),
6.65 (1H, dd, J=17.5 and 8.0), 5.60 (1H, d, J=17.5), 5.12 (1H, d, J=8.0), 4.13 (2H, m), 3.85 (2H, m),
3.69 (10 H, m), 3.60 (2H, m).
Preparation of 2,6-bis[ (p-vinylphenyl)oligo(oxyethylenoxy)methyl]pyridine (3a-d).
A
THF solution (50 mL) of alcohol (2) (5.36 mmol) was added to a suspension of NaH (60% in mineral oil,
0.29 g, 7.15 mmol, washed with hexane) with stirring at ambient temperature over a period of 1 h. The
reaction mixture was allowed to reflux and stirred for 1 h. After the mixture was cooled to -70 oC, 2,6-
bis[(tosyloxy)methyl)]pyridine (0.80 g, 1.79 mmol) dissolved in 35 mL of THF was added dropwise in it
o
in 2 h. The mixture was stirred at -70 C for 1 h and then at ambient temperature for 24 h. A small
amount of water was carefully added to destroy excess NaH. The solid material was filtered off. The
filtrate was evaporated in vacuo and the residue was purified by column chromatography (SiO2, a gradient
solution of toluene and ethyl acetate) to give 3. 3a (86% yield). White solid (mp 67.5-68.5 oC, hexane-
1
ethanol). H NMR (CDCl3) δ=7.70 (1H, br.), 7.38 (2H, d, J=9.1), 7.34 (4H, ABq, J=8.5 Hz), 6.88(4H,
ABq, J=8.5 Hz), 6.66 (2H, dd, J=17.5 and 12.5), 5.61 (2H, d, J=17.5), 5.13 (2H, d, J=12.5), 4.97 (4H,
m), 4.21 (4H, m), 3.99 (4H, m). 3b (65% yield). Transparent viscous liquid. 1H NMR (CDCl3)
δ=7.65 (1H, t, J=7.5), 7.35 (2H, d, J=7.5), 7.32 (4H, ABq, J=8.8 Hz), 6.87(4H, ABq, J=8.8 Hz), 6.64
(2H, dd, J=17.5 and 10.8), 5.60 (2H, d, J=17.5), 5.12 (2H, d, J=10.8), 4.67 (4H, s), 4.15 (4H, m), 3.88
1
(4H, m), 3.76 (8H, m). 3c (67% yield). Transparent viscous liquid. H NMR (CDCl3) δ=7.66
(1H, t, J=7.5), 7.36 (2H, d, J=7.5), 7.32 (4H, ABq, J=10.0 Hz), 6.86(4H, ABq, J=10.0 Hz), 6.65 (2H,
dd, J=15.5 and 12.5), 5.60 (2H, d, J=15.0), 5.12 (2H, d, J=12.5), 4.66 (4H, s), 4.13 (4H, m), 3.86 (4H,
m), 3.72 (16H, m). 3d (63% yield). Transparent viscous liquid. 1H NMR (CDCl3) δ=7.66 (1H, t,
J=7.5), 7.35 (2H, d, J=7.5), 7.29 (4H, ABq, J=10.0 Hz), 6.84(4H, ABq, J=10.0 Hz), 6.62 (2H, dd,
J=15.0 and 10.0), 5.58 (2H, d, J=15.0), 5.12 (2H, d, J=10.0), 4.08 (4H, m), 3.81 (4H, m), 3.66 (24 H,
m).
Preparation of pyridinocrownophanes (4). Into a 1000-mL flask with a magnetic stirring and N
2
inlet was placed 2.0 mmol of olefin (3) dissolved in acetonitrile (800 mL), and nitrogen gas was bubbled in
it for 20 min. The solution was irradiated by a 400-W high-pressure mercury lamp through a Pyrex
filter. The progress of the reaction was followed by HPLC. After the disappearance of the olefin (ca.1.5h),the
reaction mixture was evaporated. The crude reaction product was purified by column chromatography
(SiO2, a gradient solution of toluene and ethyl acetate) to afford 4. 4a (23% yield). White solid (mp

o
97.8~98.6 C, hexane-ethanol). IR (KBr) 3054, 3026, 2924, 2894, 2849, 1613, 1598, 1593, 1510,
1480, 1261, 1211, 1103, 903, 827 cm-1. 1H NMR (CDCl3) δ=7.41 (1H, t, J=7.3), 7.31 (2H, d, J=7.3),
6.78 (4H, ABq, J=8.7 Hz), 6.56(4H, ABq, J=8.7 Hz), 4.68 (4H, s), 4.05 (4H, m), 3.86 (2H, m), 3.82
(4H, m), 2.37 (4H, m). ESI-MS m/z 431 (M+). Anal. Calcd for C27H29NO4: C, 75.15; H, 6.77; N,3.25,
Found: C, 75.24; H, 6.68; N, 3.28. 4b (38% yield). Pale yellow viscous liquid. IR (neat) 3056, 3036,
2936, 2914,1725, 1687, 1600, 1505, 1480, 1365, 1248, 1108, 930, 830 cm-1. 1H NMR (CDCl3) δ=7.62
(1H, , J=7.6), 7.38 (2H, d, J=7.6), 6.82 (4H, ABq, J=8.0 Hz), 6.65 (4H, ABq, J=8.0
Hz), 4.67 (4H, s), 4.21 (4H, m), 4.00(4H, t, J=4.8), 3.89 (2H, m), 3.81 (4H, t, J=2.4), 3.73 (8H, m),
2.42 (4H, m). ESI-MS m/z 519 (M+). Anal. Calcd for C31H37NO6: C, 71.65; H, 7.18; N, 2.70,
Found: C, 71.82; H, 7.13; N, 2.63. 4c (38% yield). Pale yellow viscous liquid. IR (neat) 3056,
3028, 2916, 2876,1732, 1687, 1601, 1598, 1507, 1482, 1357, 1252, 1103, 940, 825 cm-1. 1H NMR
(CDCl3) δ=7.62 (1H, t, J=7.6), 7.39 (2H, d, J=7.6), 6.81 (4H, ABq, J=8.5 Hz), 6.65(4H, ABq, J=8.5
Hz), 4.67 (4H, s), 3.99 (4H, t, J=4.9), 3.88 (2H, m), 3.82 (4H, t, J=4.7), 3.70 (12H, m), 2.40 (2H, m),
2.33 (2H, m). ESI-MS m/z 607 ([M+). Anal. Calcd for C35H45NO8: C, 69.17; H, 7.46; N, 2.30,
Found: C, 69.02; H, 7.42; N, 2.48. 4d (49% yield). Pale yellow viscous liquid. IR (neat) 3056, 3028,
2914, 2874, 1732, 1687, 1602, 1505, 1480, 1355, 1248, 1103, 950, 830 cm-1. 1H NMR (CDCl3)
δ=7.77 (1H, t, J=7.6), 7.45 (2H, d, J=7.6), 6.81 (4H, ABq, J=8.5 Hz), 6.64 (4H, ABq, J=8.5 Hz), 4.75
(4H, s), 3.99 (4H, t, J=4.7), 3.90 (2H, m), 3.78 (4H, t, J=4.9), 3.64 (24H, m), 2.41 (2H, m), 2.33 (2H, m).
ESI-MS m/z 695 (M+). Anal. Calcd for C39H53O10: C, 67.32; H, 7.68; N, 2.01, Found: C, 67.26; H, 7.58;
N, 2.08.
Solvent extraction of heavy metal nitrates. A CH2Cl2 solution of pyridinocrownophane (1 x 10-4
mol dm-3, 5.0 mL) and an aqueous metal nitrate solution (0.1 mol dm-3, 5.0 mL), whose pH value was
adjusted as high as possible not to precipitate the hydroxides, were shaken in a 20-mL test tube with a
o
ground-glass stopper at an ambient temperature (18-20 C) for 2 h. Two liquid phases were separated
and evaporated in vacuo. The residue was dissolved in 0.1 mol dm-3 HNO3 for analysis by atomic absorption
spectrometry. Then the extracted cation into the organic phase was measured by the same manner as
described above.
13C NMR titration of crownophane (4b) with silver perchlorate or lead perchlorate. An
acetonitrile–d3 solution of 4b (2.5 x 10-2 mol dm-3) was prepared, and its 500 µL portions was placed in an
NMR tube, and the solvent level was marked. A second solution was made in acetonitrile–d3 with AgClO4.
An initial spectrum was recorded, then an appropriate volume of the salt solution was added to the NMR
tube and the solvent level was reduced by evaporation to the mark. The spectrum was then recorded again.
This procedure was repeated until the salt concentration is reached three equivalent of that of the
crownophane.
Continuous variation method by using the liquid-liquid extraction of Ag+. To clarify the
stoichiometry of 4b-Ag+ complex, Job’s method was employed at the liquid-liquid extraction under the
conditions shown in Figure 1.
ESI-MS measurement of pyridinocrownophanes (4a-d) in the presence of AgNO3 or
Pb(NO3)2. The sample solution was 1:1 (v/v) MeCN-H O containing of the same concentration of
2
crownophane and the salt (1 x 10-4 mol dm-3 in each).
RESULTS AND DISCUSSION
Synthesis of pyridinocrownophanes. Photocycloaddition of 3a-d was carried out by using a 400-
W high-pressure mercury lamp through Pyrex filter in MeCN. The yields of pyridinocrownophanes (4a-
d) were 23-49% after chromatographic separation. All pyridinocrownophanes were of cis-configuration
which was proved by the specific methine proton signals at δ=3.86-3.90.12
Complexing behavior of pyridinocrownophanes. Pyridinocrownophanes obtained were used as
extractants for heavy metal cations in a liquid-liquid system. Results are summarized in Table 1 with
reference dibenzopyridino-18-crown-6 (5) and paracrownophane (6). Paracrownophane (6) without soft
heteroatom hardly extracted any heavy metal cation examined. Pyridinocrownophane (4a) exclusively
extracted Ag+, however, the extraction efficiency was not so high most likely due to formation of a perching
complex, which is less stable than nesting complex.13 From the frame work investigation using space-
filling model, the cavity of the crownophane is a little small to incorporate the cation. The low

extractability can be improved by increasing lipophilicity of the complex. In fact, the extractability was
increased to 48% by addition of 3 x 10-4 mol dm-3 picric acid in the aqueous phase. This increment is
thought to result from a ternary complex formed from the crownophane, Ag+, and picrate anion, which is
more lipophilic than that formed from the crownophane, Ag+, and nitrate anion. Compound (4b) showed
high affinity toward Ag+, which is closed to that of dibenzopyridino-18-crown-6 (5). Although the cavity
size of compound (4c-d) seemed too large to fit the cation, they showed high affinity toward Ag+. In
these cases, the host compounds formed special kind of complexesdue to their conformational change, just
like a three- dimensional tennis-ball-seam fashion observed for the complexation between valinomycin and
K+.14
Br
Br
c)
a)
b)
d)
O
O
O
O
O
O
O
O
O
O
O
O
OH
O
O
n
n
n
n
n
n
OH
O
O
OH
N
N
Yield (%)
Yield (%)
2a n=0
50
31
48
67
1a n=0
96
95
94
95
b
c
d
n=1
n=2
n=3
b
c
d
n=1
n=2
n=3
Yield (%)
Yield (%)
3a n=0
n=0
n=1
n=2
n=3
86
65
67
63
4a
23
38
38
49
b
c
d
n=1
n=2
n=3
b
c
d
a) n=0: ClC2H4OH/aq. NaOH. n=1-3: TsO(C2H4O)n+1H, K2CO3/DMF. b) CH2=CHSn(n-Bu)3,
Pd(PPh3)4, 2,6-di-tert-butyl-4-methylphenol/toluene. c) 2,6-bis[(tosyloxy)methyl]pyridine, NaH/THF.
d) hν (>280 nm)/MeCN.
Scheme 1.
Preparation of pyridinocrownophanes.
Table 1. Extraction of heavy metal cations with ligands
_________________________________________________________________________________
a
Extractability (%)
____________________________________________________________________
Ligand
+
2+
2+
2+
2+
2+
2+
3+
Ag
Pb
Cu
Mn
Zn
Ni
Co
Fe
_________________________________________________________________________________
4a
4b
4c
4d
5
10(6.2) 0(5.1) 0(4.7) 0(6.5) 0(6.5) 0(4.2) 0(6.4) 0(2.0)
42(5.4) 14(5.4) 0(5.0) 0(6.3) 0(6.4) 0(6.6) 0(7.3) 0(2.0)
53(5.6) 18(5.3) 0(4.9) 0(6.4) 2(5.8) 0(4.4) 0(6.9) 0(1.9)
58(5.5) 16(4.6) 0(4.2) 0(6.3) 2(5.9) 0(6.3) 0(7.0) 0(1.5)
59(5.5) 10(5.6) 0(4.1) 0(6.3) 2(6.2) 0(6.7) 0(6.9) 0(1.6)
6
2(4.1) 0(5.0) 0(4.3)
0(6.2) 0(5.5) 0(6.9) 0(7.0) 0(1.7)
_________________________________________________________________________________
-1
-3
a) Extraction conditions: Aq. phase (5 mL), [metal nitrate]= 1.0 x 10 mol dm ; Org. phase, CH Cl (5 mL),
2 2
o
-4
-4
[ligand]= 1.0 x 10 mol dm ; ca. 20 C, shaken for 1 h. The values were based on the concentration of the
crown compounds. Values in parentheses were equilibrium pH of aqueous phase. Reproducibility was not
more than ±15% which was the average value obtained from three independent runs.
O
O
O
O
O
O
O
O
N
O
5
6
O

8.0
6.0
4.0
2.0
0.0
●
●
●
●
●
●
●
●
0.2
1.0
0.0
0.8
0.4
0.6
Mol fraction of [Metal]/([Metal] + [4b])
-3
-3
-3
pH 5.3 (0.1 mol dm acetate buffer), [Metal] + [4b] = 0.1 x 10 mol dm
Figure 1. Job’s plots of the extraction of Ag+ by pyrinocrownophane (4b).
The binding behavior of Ag+ ion to 4b was studied by the continuous variation method (Figure 1) in a
similar manner as described previously.10 The clear maximum is not seen at any molar fraction.
Consequently, the ratios are not determined by this method.
124.00
●
●
123.00
122.00
●
●
O
O
O
O
O
O
●
●
N
observed carbon
●
121.00
4b
0.0 1.0 2.0 3.0
Guest/Host (mol/mol)
Figure 2. Ag+-induced changes of an aromatic carbon of pyridinocrownophane (4b) in 13C NMR
chemical shifts in CD3CN.
In order to make the complexing behavior of 4b to Ag+ in homogeneous system, we spectroscopically
13
investigated the interaction in CH3CN by using C NMR titration method. As shown in Figure 2, the
chemical shift of its β-carbon of pyridine moiety considerably changed with increasing the amount of
AgClO4 added to the host solution, but the titration curve was not reached to a plateau within the
observation, indicating a variety of complexes were produced.

a)
100
[M + Ag]+ (m/z=626)
[M + H]+ (m/z=520)
80
60
40
[M2 + Ag]+ (m/z=1146)
20
0
400 500 600 700 800 900 1000 1100 1200 1300 1400
m/z
b)
100
[M + H]+ (m/z=520)
80
60
40
[M + Pb]2+ (m/z=364)
[M + Pb(NO3)]+ (m/z=789)
Figure
ESI-MS
of
20
0
3.
spectra
pyridinocrowno
phane (4b) in
1:1
(v/v)
400 500 600 700 800 900 1000 1100 1200 1300 1400
m/z
CH3CN-H2O
containing
AgNO3 (a) and Pb(NO3) 2.
Furthermore, to make the behavior of complex formation between 4 and Ag+ ion more clear and to solve a
question of why the complexing ability is considerably different between silver and lead in spiteof almost
the same ionic diameter to each other, we investigated the interaction between 4a-d and Ag+ or Pb2+ ion in
CH3CN-H2O (1:1) by employing ESI-MS. The behavior of representative 4b-Ag+ complex was first
disclosed as shown in Figure 3. It was clarified that 4b formed large amount of 1:1 and 2:1 (host/guest)
complexes with Ag+. This is the reason why the stoichiometry was not simply determined by both
continuous variation method and 13C NMR titration method as mentioned above. Host (4b) was formed
two kinds of 1:1 complexes with Pb2+ in contrast with Ag+ complexation (Figure 3b). As shown in Table

2, the extraction efficiency of 4a for Ag+ was not so high, while large amount of 4a existed in Ag+-
complex with 1:1 stoichiometry. Although Pb2+ was not extracted by 4a, similar spectrum of Pb2+-
complexes to that of Ag+-complexes was obtained in the system. Host (4c) behaved similarly to 4b at the
complexation with the both cations. In the case of complex formation of Ag+ with 4d, over 90% of the
host molecule was converted to the 1:1 complex. On the Ag+ extraction, the high hydrophilicity of 4d,
which possess ten ethereal oxygens, is thought to be compensated by extraordinarily high complexing
ability of 4d toward silver. Very high complexing ability of 4d toward Pb2+ was observed in this method,
however, the extraction percent of the metal by 4d was low as mentioned above. This low extractability is
most likely due to the high hydrophilicity of the complex formed from high hydrophilic host (4d), the
cation, and two nitrate anions.15
Thus, different equilibrium complexing abilities were observed for these metals due to different polarity of
solvents and different phase systems, and the compositions and the stoichiometry of the complexes in
CH3CN-H2O phase were detailedly clarified.
Table 2 Peak intensity data for ESI-MS analysis for complexation of pyridinocrownophanes (4a-d) with
Ag+ or Pb2+.
____________________________________________________________________________________
Compound
Salt added
Species (relative intensity/%)
____________________________________________________________________________________
4a
4b
4c
AgNO3
AgNO3
AgNO3
[M + H]+ (13, m/z=432), [M + Ag]+ (100, m/z=538), [M2 + Ag]+ (14,
m/z=970)
[M + H]+ (27, m/z=520), [M + Ag]+ (100, m/z=626), [M2 + Ag]+ (6,
m/z=1146)
[M + H] + (34, m/z=608), [M + Ag]+ (100, m/z=714), [M2 + Ag] + (20,
m/z=1322)
4d
4a
AgNO3
Pb(NO3)2
[M + H]+ (8, m/z=696), [M + Ag]+ (100, m/z=802)
[M + Pb]2+ (34, m/z=320), [M + H]+ (100, m/z=432), [M +Pb(NO3)]+ (80,
m/z=701)
4b
4c
4d
Pb(NO3)2
Pb(NO3)2
Pb(NO3)2
[M + Pb]2+ (22, m/z=364), [M + H]+ (100, m/z=520), [M + Pb(NO3)]+ (27,
m/z=789)
[M + Pb]2+ (71, m/z=408), [M + H]+ (100, m/z=608), [M + Pb(NO3)]+ (68,
m/z=878)
[M + Pb]2+ (100, m/z=452), [M + H]+ (26, m/z=696), [M + Pb(NO3)]+ (64,
m/z=965)
____________________________________________________________________________________
50
●
●
●
●
●
●
40
●
●
30
20
10
▲
▲
▲
▲
▲
▲
▲
▲
0
0
1
2
3
4
5
Equilibrium pH of aqueous phase
Figure 4. Effect of pH on the extraction of Ag+ and Pb2+ ions by pyridinocrownophane (4b).

Table 1 showed the extractability observed in the single system at the equilibrium pH of the aqueous
solution which was adjusted as high as possible without precipitating the hydroxide. In a practical point of
view, the extraction ability of crownophane (4b) was evaluated in the various pH region by the competitive
extraction experiments as shown in Figure 4. The complexing ability and high Ag+-selectivity over Pb2+
were maintained in all pH region examined. This high complexing ability toward Ag+ in acidic region is
required to recovery of the cation from the waste stream16 since the stream is generally shows low pH
values.
REFERENCES
1. R. M. Izatt, G. C. LindH, R. L. Bruening, P. Hunszthy, C. W. McDaniel, J. S. Bradshaw, and J. J.
Christensen, Anal. Chem., 1988, 60, 1694.
2. H. Tsukube, H. Minatogawa, M. Munakata, M. Toda, and K. Matsumoto, J. Org. Chem., 1992, 57,
542.
3. P. R. Westmark, S. J. Gardiner, and B. D. Smith., J. Am. Chem. Soc., 1996, 118, 11093.
4. B. Hansenknopf, J. M. Lehn, B. O. Kneisel, G, Baum, and D. Fenske, Angew. Chem., Int. Ed.
Engl., 1996, 35, 1838.
5. Y. Habata, J. S. Bradshaw, X. X. Zhang, and R. M. Izatt., J. Am. Chem. Soc., 1997, 119, 7145.
6. M. Takeuchi, M. Yamamoto, and S. Shinkai, Chem. Commun., 1997, 1731.
7. H. Tsukube, S. Shinoda, J. Uenishi, T. Hiraoka, T. Imakoga, and O. Yonemitsu, J. Org. Chem.,
1998, 63, 3884.
8. S. Inokuma, T. Yamamoto, and J. Nishimura, Tetrahedron Lett., 1990, 31, 97.
9. S. Inokuma, T. Yasuda, S. Araki, S. Sakai, and J. Nishimura, Chem. Lett., 1994, 201.
10. S. Inokuma, S. Sakai, R. Katoh, and J. Nishimura, Bull. Chem. Soc. Jpn., 1994, 67, 1462.
11. J. S. Bradshaw, P. Huszthy, C. W. McDaniel, C. Y. Zhu, N. K. Dalley, and R. M. Izatt., 1990, 55,
3129.
12. J. Nishimura, A. Ohbayashi, H. Doi, K. Nishimura, and A. Oku, Chem. Ber., 1988, 121, 2019.
13. A. Ohki, S. Maeda, J. P. Lu, and R. A. Bartsch, Anal. Chem., 1994, 66, 1743.
14. M. Pinkerton, L. K. Steinruaf, and P. Dawkins, Biochem. Biophy. Rev. Commun., 1969, 35, 512.
15. S. Inokuma, A. Kobayashi, R. Katoh, T. Yasuda, and J. Nishimura, Heterocycles, 1995, 40, 401.
16. W. J. McDowell, G. N. Case, J. A. McDonough, and R. A. Bartsch, Anal. Chem., 1992, 64, 3013.