New macrocycles derived from biphenyl for pH-switched solvent extraction

Article abstract of DOI:10.1016/j.tet.2005.12.029

Four new fluorescent macrocyclic ligands derived from biphenyl are described. The new compounds have been used in liquid-liquid extraction experiments and the influence of pH has been studied in those ligands containing carboxylic groups. The results obta

Full text of DOI:10.1016/j.tet.2005.12.029

Tetrahedron 62 (2006) 2671–2676
New macrocycles derived from biphenyl for pH-switched
solvent extraction
a
b
Ana M. Costero,a, Sergio Peransi and Karsten Gloe
*
a
´
´
`
Departamento de Quımica Organica, Universitat de Valencia, Dr. Moliner 50, 46100-Bujassot, Valencia, Spain
bInstitut fuer Anorganische Chemie, TU Dresden, 01062 Dresden, Germany
Received 20 October 2005; revised 2 December 2005; accepted 14 December 2005
Available online 9 January 2006
Abstract—Four new fluorescent macrocyclic ligands derived from biphenyl are described. The new compounds have been used in liquid–
liquid extraction experiments and the influence of pH has been studied in those ligands containing carboxylic groups. The results obtained for
the latter ligands have been compared with those observed in the presence of an external acid.
q 2005 Elsevier Ltd. All rights reserved.
1. Introduction
For several years our research group has been interested in
the preparation of crown ethers derived from biphenyl for
use, not only in cation sensing, but also in solvent extraction
as well as for use as ionophores for transport experiments
across organic membranes.6 We now report the preparation
of five new functionalized ligands of the above type in order
to study their efficiency in extraction experiments under
different pH conditions (Chart 1).
Solvent extraction belongs to one of the most important
processes in water treatment and hydrometallurgical metal
winning. The design of the complexing agents plays an
important role in such processes. In the solvent extraction of
metal ions it is now well established that a variety of ligand
types can be employed as the extracting agent and, for
example, can form chelate or solvated complexes with metal
ions.1 In particular, macrocyclic ligands, such as certain
crown compounds, complex cations selectively and have
played an important role in the separation and recovery of
toxic metals from waste water.2 For macrocyclic polyethers,
the strong influence of the ligand topology on the extraction
efficiency has been well established.3 On the other hand,
the presence of additional functional groups sensitive to the
medium pH have been used to regulate complexation and to
improve extraction under chosen conditions.4 In particular,
crowns with pendant acidic arms can bind and extract metal
ions in the form of their neutral complexes.5
2. Discussion and results
Ligand 1 has been previously reported. Ligands 3 and 4
were easily prepared by direct reaction of 2-chlorocarbonyl-
20-methoxycarbonyl-4,40-dinitrobiphenyl with 2-hydroxy-
methyl-18-crown-6 and 4,13-diaza-18-crown-6, respec-
tively. Hydrolysis of ligands 1 and 4 gave rise to
compounds 2 and 5, respectively, in high yield (Scheme 1).
NO2
O
NO2
O
NO2
NO2
O
O
O
O
O
O
O
O
O
O
N
N
O
N
O
O
O
O
O
O
O
O
O
O
OR
O
RO
MeO
RO
3
4 R=Me
5 R=H
1 R=Me
2 R=H
NO2
NO2
NO2
NO2
Chart 1.
Keywords: Extraction; pH-switched ligands; Biphenyl; Cations.
*
Corresponding author. Tel.: C34 963544410; fax: C34 963543152; e-mail: ana.costero@uv.es
0040–4020/$ - see front matter q 2005 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2005.12.029

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A. M. Costero et al. / Tetrahedron 62 (2006) 2671–2676
O
O
O
O
KOH/EtOH
2
1
NH
O
O
O
CH2Cl2/Et3N
NO2
O
O
O
O
HO
Cl
O
NH
O
O
O
O
3
Me
HN
CH2Cl2/Et3N
O
NO2
CH3CN/K2CO3
KOH/EtOH
5
4
Scheme 1.
2.1. Liquid–liquid extraction studies
conditions. Thus, data for extraction of ZnCl2 with ligands
1–5, at pHZ8.6–8.7, are presented in Figure 1. Under basic
conditions, extractabilities using 2 and 5 were strongly
enhanced when compared with the behaviour of 1 and 4,
respectively (from 0.7% for 1 to 75.5% for 2 and from 5.4%
for 4 to 90.3% for 5).
In order to evaluate the potential of the newly prepared
compounds as extracting agents and also the influence of
pH on the extraction efficiency, liquid–liquid extraction of
several metal cations (NaC, CsC, AgC, Zn2C, Eu3C) were
conducted using the extraction system metal salt/acid–
buffer–H2O/ligand–chloroform. It is well established that
the efficiency of extraction by a lipophilic ligand is
influenced by the nature of counter anions, which
accompany the cation–ligand complex.7 To compare the
efficiency of the ionophores, experimental conditions need
to be carefully controlled as does the nature of the
companion anions. The experiments were carried out
under different pH conditions in order to determine the
influence of the free carboxylic groups on extraction
efficiency. Preliminary extraction experiments showed a
very poor efficiency for all ligands towards the alkali cations
NaC and CsC. The influence of pH was studied between
pHZ2.7 and 7.6 and also the effect of different counter
anions (picrate, NO3K, ClOK4 and ClK) was investigated but
no substantial change in extraction were observed. Only
ligand 3 was found to extract cesium picrate with an
efficiency that was independent of the pH. However, the
extraction with this ligand 3 was more than seven times
lower than for 18-C-6. The loss of efficiency observed with
ligand 3 can be related to the presence of the biphenyl unit
that tends to inhibit complexation. The stoichiometry of the
complexes formed with both ligands (18-C-6 and 3) and
cesium picrate was in each case 1:1 and the extraction
constants were log KexZ4.5 and 3.6, respectively. Experi-
ments carried out with sodium salts demonstrated that
the extraction was always negligible even though a range of
experimental conditions were used. In addition, experiments
for AgC also showed most efficient extraction occurs
for 3 to form a 1:1 complexes with silver picrate with a
log KexZ3.8.
100
80
60
40
20
0
1
2
3
4
5
1+1 equiv
4+1 equiv
tBuPhCOOH tBuPhCOOH
Ligands
Figure 1. Extraction of Zn2C from aqueous AMP buffer solutions
(pHZ8.6–8.7) with ligands 1–5 in chloroform. [ZnCl2]Z2.10K4 M,
[L]Z10K3 M.
To confirm that the presence of additional carboxylic groups
in the ligands is responsible of the observed strong
extraction increments, additional experiments for 1 and 4
in the presence of external acid were carried out.8 The
results obtained (shown in Fig. 1) demonstrate that the effect
of the carboxylic groups is only important when they are
included as part of the ligand structure and complex through
intramolecular interactions.
Similar studies were carried out with Eu(ClO4)3 under
different pH conditions and the results obtained are
illustrated in Figure 2.
As was expected, the influence of the pH on extraction with
ligands 1 and 4 is essentially negligible, with only a small
increment being observed at higher pH. In contrast, the
ligands incorporating carboxylic groups in their structures
are more sensitive to pH. Thus, 2 leads to a clear increase in
The results obtained in the experiments involving Zn2C and
Eu3C were more interesting. Thus, the extractability
showed by ligands 1–5 at pHZ2.4 (HPic) was negligible;
however, clearly different results were observed under basic

A. M. Costero et al. / Tetrahedron 62 (2006) 2671–2676
2673
In the case of 4, more interesting behaviour was observed
since the stoichiometry appears to be a function of pH. Thus,
a 2:1 stoichiometry was assigned at pHZ4.6, changing to
1:1 at pHZ5.3.
100
80
60
40
20
0
1
2
4
5
2.2. Spectroscopic studies
In order to obtain additional information about the structure
of these ligands a number of spectroscopic measurements
were carried out. 1H NMR spectra in CD3CN were obtained
for the complexes formed by 2 and 5 with Eu(ClO4)3.
Figure 4 shows the 1H NMR spectra of free 5 and this ligand
after addition of 0.5 equiv of Eu3C in CD3CN. Significant
upfield shifts were observed for the protons on the crown
moiety suggesting that the complexation involves the crown
cavity. In addition, a broadening on the signals correspond-
ing to one of the aromatic rings in the biphenyl systems was
also observed. The other aromatic protons are less affected
(Table 2). Similar proton NMR shifts and line broadening
have been reported for the complexation of Eu3C with a
crown ether.10
5.7
6.9
7.5
8.9
pH
Figure 2. Extraction of Eu(ClO4)3 from aqueous solution with ligands 1,
2, 4 and 5 in chloroform at different pH values. [Eu(ClO4)3]Z10K4 M,
[L]Z10K3 M.
extraction when the pH was higher than 7. Similar
behaviour was observed with ligand 5; this gives rise to
high extraction values even at pHZ5.7. This behaviour is in
accord with pKa values for 2 (pKaZ5.28G0.3) and 5
(pKa1Z4.76G0.2 and pKa2Z6.06G0.3) determined by
potentiometry in dioxane/water 70:30.
The IR absorption spectral data of the free ligands 2 and 5
and their Eu3C complexes are summarized in Table 3. The
shift of the CC–O stretching frequencies arising from the
polyether ring, 1115 cmK1 in 2 and 1110 cmK1 in 5 to 1096
and 1098 cmK1, respectively, for their corresponding
complexes, is in keeping with complexation of Eu3C with
the cavity oxygens. On the other hand, the amide band I in
the 2:1 complexes compared to the bands for the free
ligands shows a displacement to lower frequencies,
suggesting some coordination by the carbonyl oxygen
atom.11 In comparison, almost no change was observed in
the frequency of the acid carbonyl group under the above
conditions.
Additional experiments were carried out to investigate the
type of complexes formed by 2 and 5 under different
conditions and the results are summarised in Table 1.9 Thus,
it was determined that the complex formed by 2 had a L2M
stoichiometry with log KexZ8.7 when the buffer was
HEPES (Fig. 3). By contrast, when the buffer was AMP
no extraction was observed even though the pH of the
solution was the same.
Table 1. Eu(ClO4)3 extraction studies with ligands 2 and 4
Ligand Acid
Buffer
pH Extraction Stoichiometry Log Kex
(%)
Finally, a clearly different situation was observed for the 1:1
complex formed between 5 and Eu(ClO4)3. In this complex,
the most affected carbonyl frequency is that of the acid
group (1728 cmK1 in the free ligand and 1714 cmK1 in the
complex). Also clear shifts were observed in the amide II
band; this appears to be related more to a conformational
change of the ligand rather than arising from a contribution
of the amide nitrogen atom to complex formation.
2
2
4
4
HClO4 AMP
HClO4 HEPES 5.2
HClO4 AMP 4.6
5.3
0
—
—
3.96
8.99
2:1
2:1
1:1
8.7
4.7
11.2
HClO4 HEPES 5.3 99.34
Complex stoichiometry and log K determinations under different experi-
mental conditions.
3
2
1
3. Conclusions
The extraction experiments carried out with ligands 1–5
clearly demonstrate that these systems are not useful for
alkali cation extraction. In contrast, high extraction was
observed for 2 and 5 towards Zn2C and Eu3C. In addition,
the presence of carboxylic groups in these systems allows
pH control of extraction. This effect is undoubtedly
influenced by the pKa value for the carboxylic groups. On
the other hand, ligand 5 forms two types of complexes
depending on the pH. Thus, when only one carboxylic group
is deprotonated a L2M complex is formed but at higher
pH values deprotonation of both acid groups occurs to yield
a LM complex.
0
D
–1
2 + HEPES
5 + HEPES
–2
5 + AMP
–3
–4
–4
–3
–2
–1
0
log C
Structural modelling suggests interactions between the
crown cavity and the different carbonyl groups present in
Figure 3. Plot of log D versus log cL for Eu(ClO4)3 extraction for ligands 2
and 4 at different pH values.

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A. M. Costero et al. / Tetrahedron 62 (2006) 2671–2676
Figure 4. 1H NMR spectra in CD3CN (a) aromatic region for free 5, (b) aromatic region for 5 plus 0.5 equiv of Eu(ClO4)3, (c) crown ether region for free 5,
(d) crown ether region for 5 plus 0.5 equiv of Eu(ClO4)3.
Table 2. 1H NMR shifts for 2 and 5 and their complexes with Eu(ClO4)3 in CD3CN
0
0
0
0
Hd/Hd
Ha/Ha
Hb/Hb
Hc/Hc
Crown
2
8.62/8.34
—/—
8.63/8.28
8.29/—
8.29/—
8.28/8.37
—/—
8.38/8.30
8.39/—
8.40/—
7.57/7.53
7.53/—
7.54/7.51
7.47/—
7.47/7.41
3.51
3.40
3.41
2.94
3.24
3.24/3.30
3.07/3.29
3.27/3.26
3.45
2$Eu(ClO4)3 1:1
5
5$Eu(ClO4)3 2:1
5$Eu(ClO4)3 1:1
3.42
Table 3. Assignments in the IR absorptions for the free ligands 2 and 5 and their Eu(ClO4)3 complexes
Acid (C]O)
Amide I
Amide II
NO2 as
NO2 si
CC–O
d (C]C)
2
1723
1633
1610
1635
1610
1644
1606
1606
1604
1606
1598
1523
1524
1524
1524
1518
1348
1349
1349
1349
1348
1115
1096
1110
1098
1084
658
652
652
627
626
2$Eu(ClO4)3 2:1 1724
1728
5
5$Eu(ClO4)3 2:1 1724
5$Eu(ClO4)3 1:1 1714
ligands 2 and 5. This fact is in agreement with the
information obtained by 1H NMR and IR spectroscopic
measurements.
4.1.1. Synthesis of 2. To a stirred suspension of KOH/EtOH
(10%) heated at 60 8C was added a solution of 13 (0.423 g,
0.715 mmol) in absolute EtOH (10 ml). When the addition
was finished, the heating was continued until the completion
of the reaction (TLC, 25 min). Then the reaction was
quenched with a solution of HCl (10%) until pHZ1. A
white powder appeared in the solution and it was removed
by filtration. After that, the solution was concentrated under
reduced pressure and redissolved in a CH2Cl2/H2O mixture.
The organic phase was washed with three portions of
H2O (3!25 ml) and dried over anhydrous Na2SO4. The
organic solvent was distilled to give a yellow solid.
4. Experimental
4.1. General methods
All commercially available reagents were used without
further purification. Water sensitive reactions were per-
formed under argon. Column chromatography was carried
out on SDS activated neutral aluminium oxide (0.05–
0.2 mm; activity degree 1). IR spectra were recorded on a
Perkin-Elmer 1750 FT-IR and a Bruker Equinox 55 FT-IR.
NMR spectra were recorded with Bruker Avance 300/400/
500 spectrometers. Chemical shifts are reported in parts per
million downfield from TMS. Spectra were referenced to
residual undeuterated solvent. High-resolution mass spectra
were taken with a Fisons VG-AUTOSPEC.
1
(0.396 g, 0.686 mmol). (96% yield). H NMR (300 MHz,
CD3COCD3) dH 8.77 (1H, s, Ar-H), 8.49 (1H, dd, J1Z
2.3 Hz, J2Z8.5 Hz, Ar-H), 8.40 (1H, d, JZ2.3 Hz, Ar-H),
8.33 (1H, dd, J1Z2.3 Hz, J2Z8.5 Hz, Ar-H), 7.74 (1H, d,
JZ8.5 Hz, Ar-H), 7.66 (1H, d, JZ8.5 Hz, Ar-H), 3.65–3.45
(20H, m, –CH2O–), 3.41 (2H, m, –NCH2–), 3.34 (2H, m,
–NCH2–). 13C NMR (75 MHz, CD3COCD3) dC 169.15
(–CON(CH2)2–), 166.53 (–COOCH3–), 149.09 (CAr),

A. M. Costero et al. / Tetrahedron 62 (2006) 2671–2676
2675
148.64 (CAr), 146.11 (CAr), 145.05 (CAr), 138.43 (CAr),
133.98 (2CAr), 132.42 (CAr), 127.03 (CAr), 126.21 (CAr),
124.24 (CAr), 123.49 (CAr), 73.76 (–OCH2–), 72.12
(–OCH2–), 71.79 (–OCH2–), 71.70 (–OCH2–), 71.68
(–OCH2–), 71.62 (–OCH2–), 71.31 (–OCH2–), 71.28
(–OCH2–), 69.80 (–OCH2–), 69.72 (–OCH2–), 50.78
(–NCH2–), 45.92 (–NCH2–). IR nmax (KBr) 3088 (Ar-H),
2871 (–(C]O)–OH), 1724 (–(C]O)–OH), 1633 (amide I),
1606 (amide II), 1523 (–NO2asym), 1349 (–NO2sym). EM
(EIC): MC found 577.19077. C26H31N3O12 required
577.19077. Mp: 65–678.
washed with three portions of HCl (10%) (3!15 ml) and
dried over anhydrous Na2SO4. Then the organic phase was
concentrated under reduced pressure and the crude reaction
product was purified by chromatography using an alumina
neutral column and CH2Cl2–AcOEt (8/2) as eluent to give
the desired compound as a white solid. (0.445 g,
0.484 mmol). (67% yield). 1H NMR (300 MHz, CDCl3)
dH 8.85 (1H, d, JZ2.3 Hz, Ar-H), 8.84 (1H, d, JZ2.3 Hz,
Ar-H), 8.39 (1H, dd, J1Z2.3 Hz, J2Z8.0 Hz, Ar-H), 8.37
(1H, dd, J1Z2.3 Hz, J2Z8.0 Hz, Ar-H), 8.31–8.26 (4H, m,
Ar-H), 7.62 (2H, d, JZ8.0 Hz, Ar-H), 7.40 (2H, d, JZ
8.0 Hz, Ar-H), 3.80 (3H, s, –COOCH3), 3.79 (3H, s,
–COOCH3), 3.51–3.36 (24H, m, crown). 13C NMR
(75 MHz, CDCl3) dC 168.24 (2-CON(CH2)2–), 165.25
(2-COOCH3–), 148.13 (2CAr), 147.72 (CAr), 145.38 (CAr),
145.33 (CAr), 143.54 (CAr), 137.16 (CAr), 130.99 (CAr),
126.42 (CAr), 125.96 (CAr), 123.72 (CAr), 122.75 (CAr),
70.92 (2-OCH2CH2O–), 69.86 (4-NCH2CH2O–), 53.33 (2-
COOCH3), 49.96 (2-NCH2CH2O–), 46.05 (2-NCH2CH2O–).
IR nmax (KBr) 3090 (Ar-H), 1731 (–(C]O)–OCH3), 1635
(amide I), 1608 (amide II), 1524 (–NO2asym), 1349
(–NO2sym), 1123 cmK1 (–(O]C)–OCH3). EM (FABC):
MC1 found 919.263384. C42H43N6O18 required
919.26338. Mp: 179–180 8C.
4.1.2. Synthesis of 3. 2-Chlorocarbonyl-20-methoxy-
carbonyl-4,40-dinitrobiphenyl (0.307 g, 0.886 mmol) was
added to an excess of thionyl chloride (30 ml). The
suspension was refluxed with magnetic stirring until a
clear solution had formed (2 h). Then the excess of thionyl
chloride was distilled, dry benzene was added and the
solution was redistilled. The solid obtained was dissolved in
dry CH2Cl2 (25 ml) and added dropwise to a stirred mixture
of 2-(hydroxymethyl)-18-crown-6 (0.261 g, 0.886 mmol)
and dry triethylamine (99%) (0.0897 g, 0.886 mmol) in dry
CH2Cl2 (20 ml) at 0 8C, under an inert atmosphere of Ar.
When the addition was finished, the stirring was continued
at room temperature. After completion of the reaction (TLC,
12 h), the solution was washed with three portions of HCl
(10%) (3!15 ml) and dried over anhydrous Na2SO4. Then
the organic phase was concentrated under reduced pressure
and the crude reaction product was purified by chromato-
graphy through an alumina neutral column using CH2Cl2–
AcOEt (7/3) as eluent to give the desired compound as a
4.1.4. Synthesis of 5. This product was prepared following
the same method used to obtain 2, but in this case starting
from 4 (0.384 g, 0.379 mmol). The compound was isolated
1
as a yellow solid (0.360 g, 0.405 mmol). (97% yield). H
NMR (300 MHz, CDCl3) dH 8.91 (2H, d, JZ2.3 Hz, Ar-H),
8.45 (2H, dd, J1Z2.3 Hz, J2Z8.5 Hz, Ar-H), 8.35 (2H, dd,
J1Z2.3 Hz, J2Z8.5 Hz, Ar-H), 8.21 (2H, d, JZ2.3 Hz, Ar-
H), 7.66 (2H, d, JZ8.5 Hz, Ar-H), 7.49 (2H, d, JZ8.5 Hz,
Ar-H), 3.59–3.23 (24H, m, crown). 13C NMR (75 MHz,
CDCl3) dC 176.11 (–COOH), 171.71 (–COOH), 169.92
(–CON(CH2)2–), 168.08 (–CON(CH2)2–), 148.18 (CAr),
147.69 (CAr), 146.23 (CAr), 144.26 (CAr), 136.73 (CAr),
134.37 (CAr), 131.26 (CAr), 127.47 (CAr), 126.52 (CAr),
126.10 (CAr), 124.04 (CAr), 121.81 (CAr), 70.71 (2-OCH2-
CH2O–), 70.22 (2-OCH2CH2O–), 67.64 (4-NCH2CH2O–),
48.46 (4-NCH2CH2O–). IR nmax (KBr) 3089 (Ar-H), 2870
(–(C]O)–OH), 1728 (–(C]O)–OH), 1636 (amide I), 1605
(amide II), 1524 (–NO2asym), 1349 (–NO2sym). EM (FABC):
MC1 found 891.232084. C40H39N6O18 required
891.23207. Mp: 142–143 8C.
1
yellow oil. (0.358 g, 0.575 mmol). (65% yield). H NMR
(300 MHz, CDCl3) dH 8.94 (2H, d, JZ2.5 Hz, Ar-H), 8.43
(2H, dd, J1Z2.5 Hz, J2Z8.5 Hz, Ar-H), 7.38 (1H, d, JZ
8.5 Hz, Ar-H), 7.37 (1H, d, JZ8.5 Hz, Ar-H), 4.31 (1H, m,
–CH2–), 4.17 (1H, m, –CH2–), 3.75 (3H, s, –COOCH3),
3.68–3.57 (23H, m, crown). 13C NMR (75 MHz, CDCl3) dC
164.96 (–COOCH3), 164.48 (–COOCH2–), 148.45 (2CAr),
147.83 (2CAr), 131.18 (2CAr), 130.76 (CAr), 130.66 (CAr),
126.81 (2CAr), 125.86 (2CAr), 71.39 (–(OCH2)2–CH–
OCH2–), 71.27 (–OCH2–), 71.22 (–OCH2–), 71.09
(–OCH2–), 71.05 (–OCH2–), 71.01 (–OCH2–), 70.19
(–OCH2–), 69.00 (–OCH2–), 67.06 (–OCH2–), 65.82
(–OCH2–), 65.77 (–COOCH2–), 65.27 (–OCH2–), 62.30
(–OCH2–), 53.09 (–COOCH3). IR nmax (KBr) 3401 (Ar-H),
1731 (–(C]O)–OCH3), 1524 (–NO2asym), 1349 (–NO2sym),
1106 (–(O]C)–OCH3). EM (FABC): MC1 found
623.208829. C28H35N2O14 required 623.20882.
4.2. Potentiometric titrations
4.1.3. Synthesis of 4. 2-Chlorocarbonyl-20-methoxy-
carbonyl-4,40-dinitrobiphenyl (0.504 g, 1.45 mmol) was
added to an excess of thionyl chloride (30 ml). The
suspension was refluxed under magnetic stirring until it
became a clear solution (2 h). The excess of thionyl chloride
was removed by distillation, dry benzene was added and the
solution was redistilled. The solid obtained was dissolved in
dry CH2Cl2 (25 ml) and this solution was added dropwise to
a stirred mixture of 4,13-diaza-18-crown-6 (0.190 g,
0.725 mmol) and dry triethylamine (99%) (0.147 g,
1.45 mmol) in dry CH2Cl2 (20 ml) at 0 8C under an inert
atmosphere of Ar. When the addition was finished, the
stirring was continued at a room temperature. After
completion of the reaction (TLC, 12 h) the solution was
They were carried out under nitrogen in dioxane–water (70/30
v/v) using a reaction vessel water-thermostatted at 25.0G
0.1 8C (0.1 mol dmK3 tetrabutylammonium perchlorate). The
titrant was added by means of a Crison microburete 2031.
The potentiometric measurements were made using a Crison
2002 pH-meter and a combined glass electrode. The titration
systemwas automatically controlled bya PC computer using a
program that monitors the e.m.f. values and the volume of
titrant added. The electrode was dipped in dioxane–water (70/
30 v/v) for half an hour before use. It was calibrated for
hydrogenconcentrationbytitration ofa known amountof HCl
with CO2 free LiOH solution and determining the equivalent
point by the Gran’s method; this gives the standard potential
E08 and the ionic product of water (K0wZ[HC][OH–], pKZ

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A. M. Costero et al. / Tetrahedron 62 (2006) 2671–2676
15.9G0.1).12 The computer program SUPERQUAD13 was
used to calculate the protonation constants.
the equipment employed. One of us (S.P.) acknowledges the
Spanish Government for a PhD grant. The authors are grateful
to Dr. Juan Soto and Dra Teresa Pardo, from Universidad
Politecnica de Valencia, for their assistance with the
4.3. Liquid–liquid extraction experiments
¨
potentiometric measurements and Ms. Ursula Stockgen, TU
Dresden for her assistance during the radiotracer studies.
The liquid–liquid extraction experiments were carried out at
22G2 8C in polypropylene microcentrifuge tubes (2 ml)
with a phase ratio V(w):V(org) of 1:1 (each phase 0.5 ml). The
aqueous phase contained the metal ion (at 10K4 M), a
supporting anion, HPic, HNO3, HClO4 or HCl, at different
concentrations and a selected buffer (HEPES or AMP, used
to maintain the chosen pH). The organic phase contained a
References and notes
known concentration of ligand in CHCl3 (normally 10K3
M
1. Solvent Extraction Principles and Practice; Rydberg, J., Cox, M.,
Musikas, C., Choppin, G. R., Eds.; Marcel Dekker: New York,
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except variable concentration experiments were employed).
All experiments involved mechanical shaking of the vials
for 30 min. At the end of these periods, the phases were
separated, centrifuged (to ensure full phase separation) and
then duplicate 100 ml samples of both phases were removed
for analysis.
2. Moyer, B. A. In Comprehensive Supramolecular Chemistry;
¨
Atwood, J. L., Davies, J. E., MacNicol, D. D., Vogtle, F., Eds.;
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The metal concentration in both phase was determined
radiometrically by means of g-counting using a NaI(Tl)
scintillation counter (Cobra II, Canberra-Packard). The
following radioisotopes were employed: 22Na, 137Cs, 65Zn,
110mAg and 152Eu.
4. (a) Bartsch, R. A.; Ivy, S. N.; Lu, J.; Huber, V. J.;
Talanov, V. S.; Walkowiak, W.; Park, C.; Amiri-Eliasi, B.
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Ramirez de Arellano, M. C. Supramol. Chem. 2003, 15,
403–408.
The distribution ratio DM for each metal was calculated by
the following equation:
½MnC
Š
ðorgÞ
DM
Z
½MnC
Š
ðwÞ
With this parameter it was possible to calculate the
extractability E using the equation:
5. Brown, P. R.; Bartsch, R. A. In Inclusion Aspects of Membrane
Chemistry; Osa, T., Atwood, J. L., Eds.; Kluwer Academic:
Dordrecht, 1991; pp 1–57.
DM
Eð%Þ Z
100
DM C1
6. Costero, A. M.; Sanchis, J.; Peransi, S.; Gil, S.; Sanz, V.;
Domenech, A. Tetrahedron 2004, 60, 4683–4691.
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(b) Talanova, G. G.; Elkarim, N. S. A.; Talanov, V. S.;
Hanes, R. E., Jr.; Hwang, H.-S.; Bartsch, R. A.; Rogers, R. D.
J. Am. Chem. Soc. 1999, 121, 11281–11290.
All the extraction reactions are described by the following
two equilibria:
Kex
MnCðwÞ CnAKðwÞ CsLðorgÞ#MLsAnðwÞ;ðorgÞ
nC
8. Georgiev, G.; Zakharieva, M. Solvent Extr. Ion Exch. 2003, 21,
735–749.
M
CsHnLðorgÞ %MLsðorgÞ CnsHCðwÞ
ðwÞ
9. Gloe, K.; Graubaum, H.; Wu¨st, M.; Rambusch, T.;
Seichter, W. Coord. Chem. Rev. 2001, 222, 105–126.
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Harada, M.; Tomiyasu, H.; Nakamura, Y. Inorg. Chim. Acta
2001, 320, 75–82.
½MLsAnŠðorgÞ
Kex
Z
s
½MnC
Š
½AKŠn ½LŠ
ðwÞ
ðwÞ
ðorgÞ
log DM Z log Kex Cn log½AKŠðwÞ Cs log½LŠ
ðorgÞ
´
11. Teotonio, E. E. S.; Espınola, J. G. P.; Brito, H. F.; Malta, O. L.;
Acknowledgements
Oliveira, S. F.; de Faria, D. L. A.; Izumi, C. M. S. Polyhedron
2002, 21, 1837–1844.
The present research has been financed by DGCYT
(PPQ2002-00986), Generallitat Valenciana Grupos 03/206
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Rossotti, H. J. Chem. Educ. 1965, 42, 375–378.
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´
and Acciones Integradas Hispano-Alemanas 2004/2005
(MECD, Spain and DAAD, Germany). We acknowledge the
Universitat de Valencia (S.C.I.E.) and TU Dresden for most of