Tripodal diglycolamides as highly efficient extractants for f-elements

Article abstract of DOI:10.1039/b715671e

A series of new ligands bearing three diglycolamide functions preorganized at the C-pivot and trialkylphenyl platforms was synthesized. They are very efficient extractants for Am³⁺ and Eu³⁺ with an up to five times relative extractio

Full text of DOI:10.1039/b715671e

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Tripodal diglycolamides as highly efficient extractants for f-elements
ab
d
Dominik Janczewski, David N. Reinhoudt,a Willem Verboom,*ac Clement Hill,
´
Cecile Allignol and Marie-Therese Duchesne
´
d
d
´
´
Received (in Montpellier, France) 11th October 2007, Accepted 5th November 2007
First published as an Advance Article on the web 22nd November 2007
DOI: 10.1039/b715671e
A series of new ligands bearing three diglycolamide functions preorganized at the C-pivot and
trialkylphenyl platforms was synthesized. They are very efficient extractants for Am3+ and Eu3+
with an up to five times relative extraction ability for Eu3+. The distribution coefficients are up to
1000 times increased upon alkylation or arylation of the N-position of the diglycolamide moieties.
The tripodal diglycolamides show a 1 : 1 metal to ligand stoichiometry as proven with three
independent methods for the complexation of the 3-pentyl N-substituted diglycolamide ligand
with Eu3+ (K = 2.5 Â 105 MÀ1 in acetonitrile–water). A cage-like cryptand, containing three
diglycolamide units, was prepared using a Eu3+ templated synthesis. However, it does not exhibit
improved extraction properties.
lanthanides12 compared to other diamides. Except for the
Introduction
work of Scott and co-workers13,14 related to the trityl plat-
form, to the best of our knowledge there are no reports on
preorganized diglycolamides containing more than one
ligating group in a single ionophore.
Despite political, financial, and scientific efforts to explore new
renewable energy sources, nuclear electricity remains the main
sustainable replacement for that generated from fossil fuels. A
current topic of ongoing research is the reprocessing of the
spent nuclear fuel produced by atomic power plants world-
wide. Presently, plutonium and uranium are effectively re-
moved from waste streams by the PUREX (Plutonium
Uranium Extraction) process.1 The most commonly used
TRUEX (TransUranium EXtraction)2 process for the recov-
ery of the remaining highly radiotoxic trivalent trans-pluto-
nium actinides cannot properly differentiate between the
actinides and the much more abundant lanthanides. Isolation
of the long-living radiotoxic actinides (103–105 years) is neces-
sary to differentiate the radioactive wastes, and consequently
to reduce the cost affecting handling, treatment, and storage.3
There are a few types of extracting ionophores, compatible
with highly acidic conditions, studied as potential ligands for
the liquid/liquid–actinide/lanthanide separation. They contain
both different ligating groups such as phosphorus–oxygen,4
amide–oxygen,5 or nitrogen6 type donors and different
arrangements of these functions at various platforms such as
for example: tripodal type,7 calixarenes8 or cavitands.9
In this paper we report on the synthesis and extraction
behavior of two new classes of efficient actinide and lanthanide
ligands, having diglycolamide functions, build upon the
tripodal C-pivot and trialkylbenzene platforms.
Results and discussion
Synthesis
The tripodal amines 1a,15 1b,c16 1d17 and 4a,b,16 acting as
platform for the construction of ligands, were synthesized by
previously described reduction strategies. Reaction of digly-
colic anhydride with N-methyl-N-butylamine gave glycolamic
acid 2 in 78%. Subsequent attachment of 2 to the C-pivot
(1a–d) and trialkylphenyl amines 4a,b using peptide (DCC)
coupling conditions afforded ligands 3a–d (Scheme 1) and 5a,b
(Scheme 2), respectively.
1
All compounds show in the H NMR spectra a character-
istic series of signals for the C(O)CH2O protons in the 4.0–4.3
ppm region, namely three singlets when three secondary amide
groups are present (3a and 5a,b) and more complex multiplets
for compounds with six tertiary amide groups (3b–d).
Diglycolamides have drawn attention as very effective
ionophores for the complexation of f-elements.10 They act as
tridentate binding groups11 thanks to the presence of an
additional oxygen atom between the carbonyl groups and
therefore display a very high affinity toward actinides and
To study the influence of more shielding on the extraction
behavior, cryptand 7 was prepared, consisting of a combina-
tion of a tripodal secondary amide derivative of 1a and a
tripodal tertiary amide derivative of 1c (Scheme 3). Diglycolic
anhydride was reacted with tripodal amine 1c to give the
corresponding tricarboxylic acid, that for purification reasons
was esterified with methanol to give the tripodal ester 6 in 52%
yield. Saponification of 6 and subsequent reaction of the
resulting tricarboxylic acid with tripodal amine 1a in the
presence of DCC and Eu(NO3)3 gave cryptand 7 in 9% yield.18
In this reaction the presence of Eu(NO3)3 is essential, the Eu3+
acting as a template cation, since it strongly coordinates to the
a Laboratory of Supramolecular Chemistry and Technology, Mesa+
Research Institute for Nanotechnology, University of Twente, P. O.
Box 217, 7500 AE Enschede, The Netherlands. E-mail:
w.verboom@utwente.nl; Fax: +31489 4645; Tel: +31 53489 2977
b Institute of Materials Research and Engineering, 3 Research Link,
Singapore, 117602, Singapore
c Laboratory of Molecular Nanofabrication, Mesa+ Research Institute
for Nanotechnology, University of Twente, P. O. Box 217, 7500 AE
Enschede, The Netherlands
d
`
Commissariat a l’ Energie Atomique, CEA-Valrho, DRCP/SCPS/
LCSE, baˆt. 399, Bp 17171, 30207 Bagnols-sur-Ceze, France
`
ꢀc
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490 | New J. Chem., 2008, 32, 490–495

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Scheme 1
C-pivot tripodal glycolamide arms. Cryptand 7 has a rather
complicated 1H NMR spectrum, but its formation was clearly
evidenced by its high resolution FAB mass spectrum showing
a distinct signal at m/z 1153.7220 (M + K). Despite many
efforts using different coupling strategies, the synthesis of a
corresponding cryptand, containing tertiary amide moieties
(like e.g. 1c) at both sites, was not successful.
Scheme 3
extractants and reach much higher D values at comparable
conditions. The D-values for ligands 3b–d, with N-alkyl or aryl
substituted amide groups, are 20 to 1000 times larger than that
of unsubstituted ligand 3a. The highest extraction perfor-
mance is comparable to that reported by Scott and co-workers
for tripodal diglycolamides constructed upon the trityl plat-
form.13,14 In general, the C-pivot diglycolamides 3a–d show a
pronounced relative extraction ability toward Eu3+ extracting
it up to five times more efficient than Am3+ (3b). The trialk-
ylbenzene platform derived ligands 5a,b, using the preorgani-
zation concept proposed by Anslyn and co-workers,19 extract
better than 3a, however, not as well as the N-substituted
ligands 3b–d. They also display a lower relative extraction
ability.20
Extraction
To investigate the ability of the tripodal glycolamide ligands
3a–d, 5a,b and 7 to extract Am3+ and Eu3+ from acidic
aqueous solutions to an organic phase, trace level extraction
tests were carried out using 1,1,2,2-tetrachloroethane (TCE)
and n-octanol as the organic diluents. The results are summar-
ized in Table 1.
Compared to the previously investigated CMP(O)s and
malonamides,16 similar in structure but armed with different
ligating groups, the diglycolamides are much more effective
Closing a tripodal structure into a preorganized cage is less
beneficial than one would expect. The extraction efficiency of
cryptand 7, having features of both ligands 3a and 3c, lies
between these two. Unfortunately, we were not able to obtain
a cryptand closed at both sides with N-substituted amides,
which probably would be more efficient. All investigated
ligands extract better at the higher nitric acid concentration,
which is prerequisite for back extraction of the ligand and
potential applications.
Complexation stoichiometry
To investigate the ligand/metal stoichiometry, a fluorescence
spectroscopy titration of Eu(NO3)3 with ligand 3c in
CH3CN–H2O solution was performed (Fig. 1). The initial,
very low luminescence of Eu3+ in the presence of water is
strongly increased already upon addition of the first portion of
Scheme 2
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Table 1 Distribution and separation coefficients for ligands 3a–d, 5a,b and 7
Solvent/HNO3 initial conc.
TCE
1 M
n-Octanol
Ligand
Conc./M
3 M
0.74
3.2
4.3
143
797
1 M
3 M
4.8 Â 10À2
DAm
DEu
2.9 Â 10À2
DAm
DEu
SEu/Am
DAm
DEu
SEu/Am
DAm
DEu
SEu/Am
DAm
DEu
SEu/Am
DAm
DEu
SEu/Am
DAm
DEu
SEu/Am
DAm
DEu
2.5
3.5
1.4
6.8
8.9
1.3
a
3a
8.3 Â 10À2
2.9
8.9
33
b
SEu/Am
DAm
DEu
SEu/Am
DAm
DEu
SEu/Am
DAm
DEu
SEu/Am
DAm
DEu
SEu/Am
DAm
DEu
SEu/Am
DAm
DEu
3b
3c
3d
5a
5b
7
3.6 Â 10À2
7 Â 10À2
100
125
1.25
1380
780
0.6
311
884
2.8
3.1
3.0
1.0
10.2
8.9
0.9
2.0
184
219
1.2
3.7
43
130
3.0
12
11
0.9
14
5.6
c
c
c
4103
4103
—
7.7 Â 10À2
4.2 Â 10À2
3.9 Â 10À2
5.3 Â 10À2
141
344
2.4
55
49
0.9
100
102
1.0
2.6
3.6
1.4
346
1164
3.4
9.1
9.9
1.1
31
2.2
26
23
26
84
3.2
0.19
0.15
0.8
1.1
9.2
5.0
2.5
25
SEu/Am
SEu/Am
2.7
a
b
Ligand efficiency D: distribution of a metal ion between the organic and water phase after extraction. Ligand selectivity S: ratio
c
. Not determined.
DEu/DAm
the ligand. Fig. 1(b) clearly shows the 1 : 1 stoichiometry of
the complex; fitting of the data gave a binding constant
K = 2.5 Â 105 MÀ1
.
Fig. 2 (a) Molecular ion of the [3cÁEu(NO3)2]+ complex in the mass
spectrum; (b) Distribution as function of the concentration of ligand
3c in n-octanol.
The same stoichiometry was also confirmed by MS soft
ionization. The mass spectrum of a 1 : 1 mixture of ligand 3c
with Eu(NO3)3 shows a stable complex in the gas phase with a
molecular ion formed by dissociation of one nitrate anion
(Fig. 2(a)). The stoichiometry of the extraction with ligand 3c
in n-octanol was also determined from the slope of the curve of
the logarithm of the distribution coefficient vs. the logarithm
of the concentration of 3c. In this way values for Am3+ and
Eu3+ of 1.05 and 1.09, respectively, were obtained, which in
the case of Eu3+ is in good agreement with the stoichiometries
determined with the other methods (Fig. 2(b)).
Conclusions
Fig. 1 (a) Fluorescence spectroscopy titration of Eu(NO3)3 with
ligand 3c in CH3CN–H2O = 5 : 1; excitation at 230 nm. (b) Integra-
tion of the signal at 603–635 nm, fitting data with a model.
New tripodal diglycolamide ligands, based on the C-pivot and
trialkylphenyl platforms, were synthesized and their extraction
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492 | New J. Chem., 2008, 32, 490–495

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behavior investigated. They completely fill the metal coordi-
nation sphere and form 1 : 1 complexes as proven for the
complexation of Eu3+ by ligand 3c. The different tripodal
ligands display very high distribution coefficients for Am3+
and Eu3+ extraction, particularly upon substitution of the
amide NH with an alkyl or aryl groups (3b–d). They are up to
five times more selective toward Eu3+ than Am3+. The high
complexation ability was successfully used for the synthesis of
tripodal cryptand receptor 7, however its extraction perfor-
mance was less than expected.
(1.05 g, 3.42 mmol) gave product 3a (0.74 g, 25%). dH (300
MHz; CDCl3) 7.48 (br, 3 H, CH2NHCO), 4.25 (s, 2.7 H,
C(O)CH2O), 4.22 (s, 3.3 H, C(O)CH2O), 4.05 (s, 6 H,
C(O)CH2O), 3.33–3.46 (m, 15 H, OCH2CH2CH2N, NC-
H2C2H4CH3), 3.27 (s, 6 H, CCH2O), 3.16 (t, 3 H, J 7.5,
NCH2C2H4CH3), 2.93 (s, 4.2 H, NCH3), 2.90 (s, 4.8 H,
NCH3), 1.72–1.84 (m, 6 H, OCH2CH2CH2N), 1.27–1.61 (m,
14 H, NCH2C2H4CH3, CH3CH2C), 0.91–0.98 (m, 9 H,
NCH2C2H4CH3), 0.83 (t, 3 H, J 7.5, CH2CH3); dC (100
MHz; CDCl3) 169.3, 168.3, 168.2, 71.6, 71.5, 71.3, 69.6,
69.4, 48.5, 47.7, 43.0, 36.6, 33.7, 33.3, 30.3, 29.5, 29.1, 22.9,
19.9, 19.8, 13.8, 13.7, 7.7; m/z (FAB) 899.5466 ([M + K]+.
C42H80N6O12K requires 899.5471).
Experimental
1H and 13C NMR spectra were recorded on a Varian Unity
INOVA 300 MHz or a Varian Unity 400 WB NMR spectro-
meter. Fast atom bombardment (FAB) mass spectra were
C-Pivot ligand 3b. Reaction of glycolamic acid 2 (1.41 g,
6.92 mmol) with DCC (1.49 g, 7.23 mmol) and amine 1b (0.47
g, 0.99 mmol) gave product 3b (0.36 g, 35%). dH (300 MHz;
CDCl3) 4.25–4.31 (m, 12 H, COCH2O), 3.15–3.45 (m, 30 H,
CH2OCH2CH2CH2N, NCH2C2H4CH3), 2.97 (s, 4.7 H,
NCH3), 2.91 (s, 4.3 H, NCH3), 1.70–1.85 (m, 6 H, OCH2C-
H2CH2N), 1.26–1.52 (m, 26 H, NCH2C2H4CH3, CH3CH2C),
0.91–0.95 (m, 18 H, NCH2C2H4CH3), 0.84 (t, 3 H, J 7.5,
CCH2CH3); dC (100 MHz; CDCl3) 168.9–168.7, 71.7, 71.5,
69.8, 69.7, 69.3, 69.2, 69.1, 48.9, 47.7, 47.3, 45.7, 44.0, 43.6,
43.2, 36.4, 34.3, 33.3, 31.2, 30.6, 29.8, 29.3, 28.1, 23.4, 20.3,
20.1, 20.0, 14.0, 8.0; m/z (FAB) 1067.7097 ([M + K]+.
C54H104N6O12K requires 1067.7349).
measured on
a Finnigan MAT 90 spectrometer using
m-nitrobenzyl alcohol (NBA) as a matrix. Low fragmentation
spectra of the 3cÁEu(NO3)3 complex were taken with a Micro-
mass LCT-electro spray time of flight spectrometer with a
cone-voltage of 75 V. All solvents were purified by standard
procedures. All other chemicals were analytically pure and
were used without further purification.
Glycolamic acid 2
To a cold solution (0 1C) of diglycolic anhydride (19.1 g, 148
mmol) in dry THF (200 mL), N-methyl-N-butylamine was
added (18.2 mL, 147 mmol). The reaction mixture was allowed
to warm up to room temperature and stirred for 48 h.
Subsequently, the solvent was evaporated and the remaining
oil was dissolved in AcOEt (200 mL). The resulting solution
was washed with 1 M HCl (20 mL) and H2O (2 Â 20 mL).
Evaporation of the solvent afforded product 2 as an oil (23.6 g,
78%). dH (300 MHz; CDCl3) 4.40 (s, 0.9 H, C(O)CH2O), 4.37
(s, 1.1 H, C(O)CH2O), 4.20 (s, 2 H, C(O)CH2O), 3.43 (t, 1.1 H,
J 7.2, NCH2), 3.13 (t, 0.9 H, J 7.5, NCH2), 3.00 (s, 1.4 H
NCH3), 2.90 (s, 1.6 H NCH3), 1.48–1.62, 1.24–1.40 (m, 4 H,
NCH2C2H4CH3), 0.97, (t, 3 H, J 7.2, NCH2C2H4CH3), 0.95 (t,
3 H, J 7.2, NCH2C2H4CH3); dH (75 MHz; CDCl3) 172.1,
172.0, 171.0, 73.0, 71.5, 71.2, 48.8, 34.1, 39.9, 30.3, 29.2, 20.2,
20.1, 14.0; m/z (FAB) 204.1301 ([M + H]+. C9H18NO4
requires 204.1236).
C-Pivot ligand 3c. Reaction of glycolamic acid 2 (4.50 g, 22.2
mmol) with DCC (4.58 g, 22.2 mmol) and amine 1c (2.95 g,
5.71 mmol) gave product 3c (1.39 g, 23%). dH (300 MHz;
CDCl3) 4.30–4.36 (m, 12 H, C(O)CH2O), 3.15–3.45 (m, 27 H,
CH2O, CH2N, CHN), 2.95–2.98 (m, 5 H, NCH3), 2.91 (s, 4 H,
NCH3), 1.72–1.90 (m, 6 H, OCH2CH2CH3), 1.22–1.57 (m, 26
H, CH2CH3, C2H4CH3), 0.82–0.95 (m, 30 H, CH2CH3); dC (75
MHz; CDCl3) 170.3, 170.2, 169.9, 169.8, 169.0, 168.8, 71.7,
69.8, 69.4, 69.3, 68.9, 60.3, 58.8, 49.0, 47.8, 43.4, 40.7, 39.0,
34.4, 33.4, 31.4, 30.6, 29.3, 29.2, 26.5, 25.8, 23.6, 20.2, 20.1,
14.0, 11.4, 11.3, 8.1; m/z (FAB) 1109.7562 ([M + K]+.
C57H110N6O12K requires 1109.7819).
C-Pivot ligand 3d. Reaction of glycolamic acid 2 (1.25 g,
6.13 mmol) with DCC (0.85 g, 4.12 mmol) and amine 1d (0.52
g, 0.90 mmol) gave product 3d (0.52 g, 51%). dH (300 MHz;
CDCl3) 7.17 (d, 6 H, J 8.1, Ph), 7.00 (d, 6 H, J 8.1, Ph),
4.24–4.27 (m, 6 H, OCH2C(O)), 3.91 (s, 6 H, OCH2C(O)), 3.67
(t, 6 H, J 7.8, OCH2, NCH2), 3.22–3.32 (m, 12 H OCH2,
NCH2), 3.05 (s, 6 H, CCH2O, NCH3), 2.96 (s, 5 H, CCH2O,
NCH3), 2.85 (s, 4 H, CCH2O, NCH3), 2.35 (s, 9 H, PhCH3),
1.72 (m, 6 H, OCH2CH2CH2N), 1.40–1.58, 1.13–1.32 (m, 14
H, CH2CH3, C2H4CH3), 0.86–0.94 (m, 9 H, C2H4CH3), 0.66
(t, 3 H, J 7.5 Hz, CH2CH3); dC (75 MHz; CDCl3) 169.2, 169.0,
138.6, 138.2, 130.8, 128.0, 71.5, 70.2, 69.8, 69.0, 68.9, 49.1,
47.8, 47.3, 43.2, 34.6, 33.4, 30.6, 29.3, 28.2, 23.2, 21.3, 20.2,
General procedure for the synthesis of diglycolamide ligands
3a–d and 5a,b
A mixture of glycolamic acid 2 and DCC in dry THF (100 mL)
was stirred for 1 h at room temperature. After addition of the
appropriate tripodal amine (1a–d and 4a,b) stirring was con-
tinued for an additional 16 h at 30 1C. After filtration of the
precipitate and evaporation of the solvent gave an oil that
subsequently was purified with column chromatography
(SiO2, CH2Cl2–MeOH–AcOH = 20 : 1 : 0 - 10 : 3 : 1).
The salts containing products were dissolved in CHCl3
(50 mL). The resulting solutions were washed with 1 M HCl
(20 mL) and H2O (3 Â 20 mL) to give, after solvent evapora-
tion, the pure diglycolamic ligands.
20.1, 14.0, 7.9; m/z (FAB) 1169.6860 ([M
+
K]+.
C63H98N6O12K requires 1169.6880).
Trialkylphenyl ligand 5a. Reaction of glycolamic acid 2
(2.06 g, 10.1 mmol) with DCC (2.14 g, 10.4 mmol) and amine
4a (0.58 g, 2.31 mmol) gave product 5a (0.52 g, 28%). dH
C-Pivot ligand 3a. Reaction of glycolamic acid 2 (3.19 g,
15.7 mmol) with DCC (3.49 g, 16.9 mmol) and amine 1a
ꢀc
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(300 MHz; CDCl3) 7.65 (br s, 3 H, CH2NHCO), 4.26 (s, 3 H,
diisopropylethylamine were added to this solution at À18
1C. The mixture was slowly warmed to room temperature
for 12 h and than stirred for 20 h at 40 1C. After solvent
evaporation the resulting solid was purified with triple column
chromatography (SiO2, CH2Cl2–MeOH–AcOH = 50 : 2 : 0
- 10 : 4 : 1). The salts containing product was dissolved in
CHCl3 (50 mL). The resulting solution was washed with 1 M
HCl (20 mL) and H2O (3 Â 20 mL) to give, after solvent
evaporation, cryptand 7 (0.30 g, 9%). dH (300 MHz; CDCl3)
8.25–8.39, 7.18–7.32 (m, 3 H, NH), 4.18–4.35, 3.96–4.12 (m, 12
H, OCH2C(O)), 3.03–3.55 (m, 39 H, NCH2, NCH, OCH2),
1.62–1.94, 1.13–1.62 (m, 28 H, OCH2CH2CH2N, CH2CH3),
0.79–0.89 (m, 24 H, CH2CH3); dC (75 MHz; CDCl3)
169.3–169.9, 72.7–68.6, 60.4, 59.2, 43.4, 43.3, 40.6, 39.0,
36.6, 33.9, 31.7, 29.9, 29.6, 29.3, 26.6, 25.9, 25.1, 23.7, 23.2,
11.5, 11.4, 8.1, 8.0; m/z (FAB) 1153.7220 ([M + K]+.
C57H106N6O15K requires 1153.7353).
C(O)CH2O), 4.24 (s, 3 H, C(O)CH2O), 4.08 (s, 6 H,
C(O)CH2O), 3.32–3.42 (m,
H2C2H4CH3), 3.16 (t,
9
H, PhCH2CH2N, NC-
3
H, J 7.5, NCH2C2H4CH3),
2.90–2.97 (m, 15 H, PhCH2CH2N, NCH3), 2.40 (s, 9 H,
PhCH3), 1.43–1.57, 1.25–1.38 (m, 12 H, NCH2C2H4CH3),
0.91–0.98 (m, 9 H, NCH2C2H4CH3); dC (100 MHz; CDCl3)
169.4, 168.4, 168.3, 133.8, 133.6, 71.83, 71.77, 69.7, 69.4, 48.5,
47.8, 38.2, 33.7, 33.7, 33.3, 30.7, 30.3, 29.1, 19.95, 19.88, 16.0,
13.8; m/z (FAB) 843.4746 ([M + K]+. C42H72N6O9K requires
843.4998).
Trialkylphenyl ligand 5b. Reaction of glycolamic acid 2
(2.98 g, 14.6 mmol) with DCC (2.27 g, 11.0 mmol) and amine
4b (0.81 g, 2.76 mmol) gave product 5b (1.27 g, 54%). dH (300
MHz; CDCl3) 7.78 (br s, 3 H, CH2NHCO), 4.28 (s, 3 H,
C(O)CH2O), 4.26 (s, 3 H, C(O)CH2O), 4.11 (s, 6 H,
C(O)CH2O), 3.37–3.41 (m,
9 H, PhCH2CH2N, NC-
H2C2H4CH3), 3.16 (t, 3 H, J 7.5, NCH2C2H4CH3) 2.72–2.96
(m, 21 H, PhCH2CH2N, PhCH2CH3, NCH3), 1.47–1.60,
1.26–1.38 (m, 12 H, NCH2C2H4CH3), 1.17 (t, 9 H, J 7.0,
PhCH2CH3), 0.91–0.98 (m, 9 H, NCH2C2H4CH3); dC (100
MHz; CDCl3) 169.7, 168.6, 140.7, 132.6, 72.04, 71.98, 69.9,
69.7, 48.7, 48.1, 40.3, 34.0, 33.6, 30.6, 29.51, 29.48, 29.4, 22.7,
20.20, 20.17, 16.0, 14.0; m/z (FAB) 885.5600 ([M + K]+.
C45H78N6O9K requires 885.5467).
Titration
The photoluminescence titration experiment was carried on a
Edinburgh XE-900 spectrofluorometer. The experiment was
directly carried out in the spectrophotometric cell by addition
of a solution of 3c (12.9 mM) and Eu(NO3)3Á6H2O (0.325
mM) in CH3CN–H2O = 5 : 1 to a solution of Eu(NO3)3Á6H2O
(0.325 mM) in CH3CN–H2O = 5 : 1, maintaining in this way a
constant Eu3+ concentration during the experiment. A spec-
trum was recorded 5 min upon addition of the ligand. A
binding model was constructed assuming the formation of
LM, LM2 and LM3 complexes. However, data analysis re-
vealed that LM2 and LM3 complexes only exist in a very low
concentration and therefore can be omitted.
Tripodal ester 6. To a cold (0 1C) solution of amine 1c (8.7 g,
16.9 mmol) in THF (200 mL) were added diglycolic anhydride
(22.6 g, 194.9 mmol) followed by triethylamine (20 mL, 143
mmol). The mixture was warmed up to room temperature and
stirred for 16 h. After neutralisation with 3 M HCl to pH 1–2
the solvent was evaporated. A solution of the remaining oil
and a catalytic amount of H2SO4 in MeOH (250 mL) was
refluxed for 16 h using a Soxhlet apparatus containing 3 A
molecular sieves to absorb the formed H2O. After addition of
NaHCO3 (2 g) and evaporation of the MeOH, the resulting
residue was separated with column chromatography (SiO2;
CH2Cl2–MeOH = 100 : 6) to give pure ester 6 as an oil (8.0 g,
52%). dH (300 MHz; CDCl3) 4.27 (s, 1.7 H, C(O)CH2OCH2-
C(O)), 4.21–4.24, (m, 5.7 H, C(O)CH2OCH2C(O)), 4.17 (s, 4.6
Extraction experiments
Liquid–liquid extraction experiments were performed using
either 1 or 3 M nitric acid solutions, spiked with 152Eu(III) and
241Am(III), as the aqueous solutions, and solutions of com-
pounds 3a–d, 5a,b or 7, dissolved at various concentrations in
1,1,2,2-tetrachloroethane (TCE) or n-octanol, as the organic
solutions.
Organic and aqueous phases (Vorg = Vaq = 200 mL) were
mixed in 2 mL Eppendorf micro-tubes, thermostated at 25 Æ
0.5 1C and shaken for 60 min with a vortex (Vibrax VXR) IKA
device. Tubes were centrifuged and 40 mL of each phase were
diluted either in 560 mL of TCE or n-octanol (organic sam-
ples), or in 560 mL of molar nitric acid (aqueous samples).
500 mL of these samples were used for radiometric analyses on
a Canberra Eurisys highly pure Ge gamma detector.
The acid contents of the initial and final aqueous solutions
were determined by potentiometric titration of 100 mL sam-
ples, using a METROHM 751 GPD Titrino device and a
0.1 M NaOH solution.
H, C(O)CH2OCH2C(O)), 3.67–3.70 (m,
9 H, OCH3),
3.26–3.38, 3.09–3.20 (m, 21 H, CH2O, CH2NCH), 1.68–1.84,
1.28–1.54 (m, 20 H, CH2CH3, CH2CH2CH2), 0.75–0.84 (m, 21
H, CH2CH3); dC (75 MHz; CDCl3) 170.7, 170.6, 169.5, 169.2,
71.9, 71.6, 70.0, 69.8, 69.4, 68.8, 68.2, 60.4, 58.8, 52.0, 43.4,
52.0, 43.4, 40.7, 38.9, 31.5, 29.2, 26.5, 25.8, 23.5, 11.4, 11.3, 8.0;
m/z (FAB) 944.5371 ([M + K]+. C45H83N3O15K requires
944.5461).
Cryptand 7. A solution of ester 7 (2.84 g, 3.14 mmol) and
LiOH (0.68 g, 28.2 mmol) in a mixture of MeOH (50 mL) and
H2O (20 mL) was stirred for 4 h at room temperature.
Subsequently, it was acidified with conc. HCl to pH 1. After
evaporation of the solvent the residue was dissolved in AcOEt
(50 mL) and the solution washed with H2O (2 Â 5 mL).
Solvent evaporation and long vacuum drying gave an oil,
which was subsequently dissolved in dry THF (500 mL). DCC
(3.8 g, 18.4 mmol) followed by Eu(NO3)3 (1.40 g, 3.14 mmol),
amine 1a (0.96 g, 3.14 mmol) and a catalytic amount of
Acknowledgements
We are thankful to Prof. J. Huskens for helpful discussions
about titration methodology and model fitting. This work was
financially supported by the EEC (contract FIKW-CCT-
200-00088).
ꢀc
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New J. Chem., 2008, 32, 490–495 | 495