Separation of Am (III) by solvent extraction using water-soluble H4tpaen derivatives

Article abstract of DOI:10.1016/j.tet.2015.06.015

The water-soluble ligand N,N,N′,N′-tetrakis[(6-carboxypyridin-2-yl)methyl]ethylenediamine (H₄tpaen) and its derivatives were synthesized and evaluated for Am/Cm separation by solvent extraction. In this context, different ligands were studied for their possible use as selective back-extraction agents of actinides, especially americium, from an organic TPH phase. The solvent consisted of different extractants mixtures (DMDOHEMA/HDEHP or TODGA/TBP systems) and was preliminarily loaded with trivalent lanthanide and actinide cations. The aim of these new water-soluble agents was to strip americium or curium in an aqueous acidic phase in order to perform their mutual separation while maintaining other cations in the organic phase. A specific ligand bearing n-alkoxy groups connected to the pyridyl rings of H₄tpaen showed water solubility slightly enhanced associated with efficient back-extraction properties with the possibility to perform simultaneously inter-group separation of Am (III) from Eu (III), and intra-group separation of Am(III) from Cm(III).

Full text of DOI:10.1016/j.tet.2015.06.015

Accepted Manuscript
Separation of Am (III) by solvent extraction using water soluble H tpaen derivatives
4
Stéphanie Gracia, Guilhem Arrachart, Cécile Marie, Simon Chapron, Manuel
Miguirditchian, Stéphane Pellet-Rostaing
PII:
S0040-4020(15)00870-4
10.1016/j.tet.2015.06.015
TET 26850
DOI:
Reference:
To appear in: Tetrahedron
Received Date: 14 April 2015
Revised Date: 1 June 2015
Accepted Date: 3 June 2015
Please cite this article as: Gracia S, Arrachart G, Marie C, Chapron S, Miguirditchian M, Pellet-Rostaing
S, Separation of Am (III) by solvent extraction using water soluble H tpaen derivatives, Tetrahedron
4
(2015), doi: 10.1016/j.tet.2015.06.015.
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ACCEPTED MANUSCRIPT
Separation of Am (III) by solvent extraction using water soluble
H4tpaen derivatives
Stéphanie Graciaa, Guilhem Arracharta,*, Cécile Marieb,*, Simon Chaprona,b, Manuel
Miguirditchianb, Stéphane Pellet-Rostainga,*
a Institut de Chimie Séparative de Marcoule, CNRS/CEA/UM/ENSCM, UMR 5257, LTSM, Site de Marcoule, Bagnols-sur-Cèze, France
b CEA, Nuclear Energy Division, RadioChemistry & Processes Department, SMCS/LCPE, Site de Marcoule, Bagnols-sur-Cèze, France
* Corresponding author. e-mail address: guilhem.arrachart@cea.fr ; cecile.marie@cea.fr ; stephane.pellet-rostaing@cea.fr
Abstract:
The water soluble ligand N,N,N’N’-tetrakis[(6-carboxypyridin-2-yl)methyl]ethylenediamine
(H4tpaen) and its derivatives were synthesized and evaluated for Am/Cm separation by
solvent extraction. In this context, different ligands were studied for their possible use as
selective back-extraction agents of actinides, especially americium, from an organic TPH
phase. The solvent consisted of different extractants mixtures (DMDOHEMA/HDEHP or
TODGA/TBP systems) and was preliminarily loaded with trivalent lanthanide and actinide
cations. The aim of these new water-soluble agents was to strip americium or curium in an
aqueous acidic phase in order to perform their mutual separation while maintaining other
cations in the organic phase. A specific ligand bearing n-alkoxy groups connected to the
pyridyl rings of H4tpaen showed water solubility slightly enhanced associated with efficient
back-extraction properties with the possibility to perform simultaneously inter-group
separation of Am (III) from Eu (III), and intra-group separation of Am (III) from Cm (III).
Keywords:
H4tpaen ligand / Solvent extraction / Actinides (III) / Lanthanides (III) / inter or intra group
separation.
1

ACCEPTED MANUSCRIPT
1. Introduction
Partitioning and Transmutation of long-lived radionuclides have been widely studied in order
to reduce the long-term radiotoxicity of final nuclear waste. For this purpose, the recycling of
minor actinides (MAs) which are the main contributors to the long term heat power and
radiotoxic inventory of nuclear waste has emerged as a significant issue.1
Partitioning of MAs is a challenging task since it requires the separation of very similar
chemical elements: the 4f lanthanides (Ln) and 5f actinides (An).2-4 Nevertheless, the
presence of spatially extended 5f-orbitals in actinides allows a slightly stronger interaction of
An with specific ligands compared to Ln, allowing their differentiation. Separation between
americium and curium is even more challenging since they have almost the same radii and
charge density.5,6
S-donor7-9 or N-donor10,11 ligands have attracted attention because they can exploit the slight
softness difference (Pearson’s HSAB principle12) between actinides and lanthanides resulting
in a slight increase of covalency in the actinide-ligand bond. Polyaromatic N-donor ligands
were investigated for their ability to separate trivalent actinides (An3+) from lanthanides
(Ln3+) by solvent extraction.13,14
An(III) and Ln(III) can be co-extracted through the DIAMEX (DIAMide EXtraction) process,
based on the use of a diamide extractant such as the malonamide DMDOHEMA (N’-
dimethyl-N,N’-dioctylhexylethoxymalonamide)17 or the diglycolamide TODGA (N,N,N’,N’-
tetra-octyldiglycolamide).16
The SANEX (Selective ActiNide EXtraction) process was then developed to perform the
An(III) / Ln(III) separation using N-donor extractants.17,18 In contrast, the TALSPEAK
(Trivalent Actinide-Lanthanide Separation by Phosphorus reagent Extraction from Aqueous
Komplexes) process aims to separate An(III) from Ln(III) by selective back-extraction (or
stripping) of An(III) using selective aminopolycarboxylate complexing agents.19,20
More recently, a focus was put on recycling Am alone, leaving Cm with vitrified fission
products. Indeed, after 100 years, americium is the main contributor to heat emissions in final
spent fuel wastes. Moreover, Cm reprocessing would be difficult to implement due to its very
significant neutron emissions which would require very thick shielding at any step of the fuel
cycle.
Americium can be separated from curium by chemical or electro-chemical oxidation followed
by selective extraction. Several methods were proposed and are still under development, but
these technics are often limited by the difficulty to stabilize higher oxidation states of Am.21-25
2

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The LUCA process was the first liquid-liquid extraction system developed for the specific
Am/Cm separation without redox chemistry starting from a DIAMEX raffinate (already
cleared from major actinides and fission products). With the synergistic extractant mixture
(ClPh)2PSSH and tris(2-ethylhexyl)phosphate (TEHP), Am can be extracted in the organic
phase with selectivity versus Cm (SFAm/Cm = 8) and lanthanides (SFAm/Eu = 2 000).26
At the CEA, a hydrometallurgical process called EXAm (Extraction of Americium), was
developed to separate Am alone from Cm and other fission products starting from a PUREX
raffinate (a nitric acid solution of spent fuel dissolution liquor already cleared from U, Np and
Pu).27
The principle of the EXAm process is based on two main steps:
-
-
Am extraction, at high acidity, along with light lanthanides, allowing the separation of
americium from curium;28
Selective back-extraction of Am by complexation with a polyaminocarboxylic acid at
low acidity in the aqueous phase.27,29
The first step involves the separation of americium from curium using DMDOHEMA in the
organic phase with the help of a water soluble complexing agent N,N,N’,N’’-
tetraethyldiglycolamide (TEDGA) which leads to an increase in the separation factor (SF)
Am/Cm from ~1.6 to 2.5.30 Americium is extracted along with light lanthanides, while curium
and heavy lanthanides remain in the highly acidic aqueous phase.Then in a second step, Am is
selectively back-extracted (stripped) from light lanthanides using a polyaminocarboxylic acid
(HEDTA or DTPA) at low acidity (pH=3). However, the addition of a buffering molecule is
necessary to fix the pH during Am back-extraction.
Recently, several analogs of TEDGA were synthesized with simple structural modifications to
better understand the relationship between physico-chemical properties of this ligand and
Am/Cm selectivity. It was shown that the partitioning of TEDGA species between both
phases plays an important role on selectivity and it was not possible to find a better
diglycolamide analog of TEDGA to separate Am/Cm at high acidity.31 Moreover, TEDGA is
an O-donor and it cannot provide selectivity between An and Ln (only intra-group
separation).
Recently, water soluble ligands based on dipicolinic acid (pyridine-2,6-dicarboxylic acid -
PDCA) derivatives (with N-and O-donor atoms) were tested to complex americium in an
aqueous acidic phase (pH 1) while maintaining other trivalent lanthanide and actinide species
in an organic phase containing TODGA as neutral extractant with SFEu/Am values around 10.32
3

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The efficiency of the back-extraction was enhanced when the picolinic platform was engaged
in a heterocyclic decadentate ligand called N,N,N’N’-tetrakis[(6-carboxypyridin-2-
yl)methyl]ethylenediamine (H4tpaen).33 Beyond the selective inter-group separation of
Am(III) from Eu(III), the water soluble H4tpaen ligand highlights the possibility to perform
the intra-group separation of Am(III) from Cm(III) with a separation factor SF Cm/Am equal to
3.5. These properties allowed considering the H4tpaen ligand as a good complexing agent
candidate for the separation of Am from Cm and Ln in an alternative EXAm process.34
One limitation can be due to the low solubility of the H4tpaen ligand in the acidic aqueous
stripping solution. Hence, it appeared interesting to modify the structure of H4tpaen ligand in
order to improve its solubility without changing the ability of the ligand to selectively
separate Am from other cations.
From this statement, we synthesized new water soluble ligands, based on H4tpaen framework,
and then evaluated their performance to selectively back-extract Am(III) from a loaded
organic phase while maintaining other cations in the solvent.
A structure-selectivity relationship study was investigated through two different approaches
(Figure 1): the modification of the spacer between the two nitrogen atoms of the central
bridge and the introduction of different substituents on para positions of pyridine units.
Figure 1a: H4tpaen ligand and structural modifications considered.
-
Modification of the ethylene diamine spacer:
Different spacers were investigated such as tetraazamacrocycles (L1 & L2), DTPA and
EDTA analogs (L3 & L4) or more rigid units (L7, L8 & L9) (Figure 2).
Tetraazamacrocycles have shown their potential as chelators used for complexation of
different metal ions. Cyclen or cyclam macrocyclic fully N-substituted derivatives with
coordinative pendant arms (H4dota and H4teta) are of particular interest for the complexation
of heavy metals or lanthanide ions.35 With this in mind, we investigated the behavior of
cyclen and cyclam ligands containing four picolinic acid groups (L1 & L2). This series of
4

ACCEPTED MANUSCRIPT
ligands should allow to better evaluate the role of the ethylene bridge in Am complexation by
H4tpaen.
Polyaminocarboxylic acids are well-known reagents used to separate An(III) from Ln(III),
ethylenediamine tetraacetic acid (EDTA) or diethylenetriamine-N,N,N',N",N"-pentaacetic
acid (DTPA) has demonstrated a considerable utility for the selective back-extraction of
trivalent actinides from trivalent fission product lanthanides in solution. Thus the combination
of polyaminocarboxylic acids19 such as EDTA and DTPA and picolinic acids has been studied
(L3 & L4).
The influence of the spacer was finally investigated through more rigid structures having a
cyclohexane or benzyl unit between the two nitrogen atoms (L7, L8 & L9).
-
Introduction of substituents on para positions of the pyridinecarboxylic acid moieties:
One limitation of H4tpaen arises from its low solubility in an acidic aqueous solution. In order
to modify the H4tpaen ligand structure and improve its solubility, we decided to investigate
the behaviour of H4tpaen ligands containing hydrophilic substituents: morpholine and
methoxy (L5 & L6) (Figure 2).
CO2H
CO2H
N
N
HO2C
N
N
N
N
CO2H
L8
HO2C
N
OCH3
L6
CO2H
OCH3
N
HO2C
N
N
N
N
N
N
HO2C
CO2H
N
N
CO2H
CO2H
N
L1
N
N
N
HO2C
N
N
OCH3
HO2C
N
N
N
OCH3
CO2H
N
CO2H
HO2C
H4tpaen
CO2H
CO2H
CO2H
N
N
N
O
L4
HN
O
NH
N
N
N
N
CO2H
N
CO2H
N
CO2H
CO2H
Figure 2: Structure of the ligands synthesized and evaluated in this work.
5

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2. Results and discussion
2.1 Synthetic Chemistry
2.1.1 Spacer modification
The decadentate ligand N,N,N’N’-tetrakis[(6-carboxypyridin-2-yl)methyl]ethylenediamine
(H4tpaen) synthesis was described in five steps from pyridine-2,6-dicarboxylic acid (PDCA)
and ethylenediamine in 21% yield33 (Scheme 1).
Scheme 1: Synthetic route for H4tpaen
After the esterification of carboxylic acid groups of PDCA (90%), a selective reduction36 with
NaBH4 of one methyl ester was performed selectively resulting in the mono-alcohol 2 (82%).
This alcohol group was then chlorinated37 with SOCl2 giving the compound 3 (90%).
Reaction between the chloromethylpyridine 3 and ethylenediamine provided the tetra-
substituted compound 4 (40%). Hydrolysis of methyl ester groups (HCl 6M) gave the desired
H4tpaen compound 5 (80%).
In order to improve the global yield of the synthesis, each reaction was optimized (reaction
time, nature of solvents, reagents …) with a particular effort on the coupling step between
ethylenediamine and methyl-(6-chloromethyl)-picolinate (3) considered as the yield limiting
step of this synthetic route. These optimizations of reaction conditions were then applied to
the synthesis of H4tpaen derivatives. Different ways were tested including the use of various
alcoholate or carboxylate bases in different solvents and a more reactive iodized compound
instead of a chlorinated compound. For the coupling step, the isolated yield was improved
from 40% to 70% by using compound 3 in the presence of K2CO3 with freshly distilled
ethylene diamine and acetonitrile in very dry conditions (H2O< 0.005%). In these conditions,
the formation of the saponification side product that penalizes the yield of the reaction was
reduced.
6

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This procedure was then applied to other amines in order to access to modified H4tpaen
derivatives (Table 1).
Table 1: H4tpaen derivative - Spacer modification with introduction of cage-like chelators (L1 & L2) or rigid
units (L7, L8 & L9).
Global
yield
NH HN
HN
NH
30%
49%
a
cyclen ( )
HN
NH
NH HN
b
cyclam ( )
NH2
H2N
47%
52%
20%
c
( )
NH2
d
( )
NH2
e
( )
NH2
NH2
NH2
f
( )
O
-
NH2
7

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The syntheses of cyclen derivative (1,4,7,10-tetraazacyclododecane, L1) bearing four
picolinate pendant arms, and its cyclam analogue (1,4,8,11-tetraazacyclotetradecane, L2)
were achieved by using cyclen (a) or cyclam (b) as starting amine. The introduction of a more
“rigid” spacer between the two central nitrogen atoms with a cyclohexane was performed
starting from 1,3-cyclohexanediamine (c) and 1,3-bis(aminomethyl)-cyclohexane (d). A
benzyl group was then introduced using 1,3-bis(aminomethyl)-benzene (e) as starting amine.
For all amines, the coupling step yield was about 70 – 80% except for the amine e. In the
latter case, the recrystallization procedure could not be implemented to purify the final
product. Therefore, the necessity of column chromatography purification penalizes the
isolated yield (34 %).
The 5f compound starting from 2-(2-aminoethoxy)-ethylamine (f) could not be synthesized
either under thermal or microwave conditions.
After the hydrolysis of methyl ester groups, five new modified H4tpaen derivatives were
obtained (global yield 20 – 52%) with spacers of different nature. Introduction of a cage-like
chelators spacer (L1 & L2) and modification of the spacer flexibility (L7, L8 & L9) were
investigated.
Another approach was investigated in order to introduce some chelating spacers based
on EDTA or DTPA structures. We firstly synthesized an amine moiety with a structural
framework close to the H4tpaen which was then able to react with the bisanhydride of EDTA
or DTPA.
The amine 9 was synthesized using the similar coupling step involved in the synthesis of the
H4tpaen from N-Boc-ethylenediamine and compound 3, then followed by the amine
deprotection using TFA (Scheme 2).
Scheme 2: Synthetic route for amine 9
38
The reaction with the bisanhydrides of EDTA (n=0) or DTPA (n=1)
followed by the
hydrolysis of the carboxylate groups led to H4tpaen derivatives with EDTA (L3) or DTPA
(L4) spacers with global yields about 65% (Scheme 3).
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Scheme 3: Synthetic route for H4tpaen derivative through EDTA (L3) or DTPA (L4) complexing agents.
2.1.2 Functionalization of H4tpaen pyridine para positions
Considering the separation of Am(III) from Eu(III), it was shown that the selectivity of
pyridine-2,6-dicarboxylic acid (PDCA) remains unchanged and is not affected by the
introduction of different substituents on the para position of the PDCA.32
Taking into consideration these results, we decided to introduce substituents on para positions
of pyridinocarboxylate units of H4tpaen with appropriate organic functions that would make it
more water-soluble. For this purpose, two substituents were considered: a methoxy, or a
morpholine group (Scheme 4).
Scheme 4: Structural modifications considered by introduction of substituents on pyridinecarboxylate units
The first stage was to synthesize the specific chloromethylpyridine 17 and 20 (Scheme 5).
Chelidamic acid (13), obtained from chelidonic acid,39 is one of the precursors able to give
access to such O and N-functionalized dipicolinate derivative through the 4-methoxypyridine-
2,6-dicarboxylate compound. This compound was obtained from the NH deprotonation of the
chelidamic acid using K2CO3, allowing the electron delocalization and the access to the
aromatic mesomeric form which reacts with an excess of methyl iodide through a nucleophilic
substitution. The esterification of carboxyl groups was simultaneously performed to the
methylation reaction.
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The intermediate 17 was obtained in three steps from 4-chloro-pyridine-2,6-
dicarboxylate compound (14). The substitution of the chlorine atom with morpholine was
performed following a procedure inspired from Masciadri study40 using N,N-
Diisopropylethylamine (DIPEA) and DMF in a sealed tube heated at 100°C. The
monoreduction of the morpholine-PDCA derivative (15) was realized with NaBH4 in MeOH
with an adequate amount of CH2Cl2 in order to dissolve the compound. Then the resulting
alcohol group was then chlorinated with SOCl2 giving the desired compound 17. Similar
reactions were conducted with N-methylpiperazine instead of morpholine but unfortunately
the monoreduction step could not be achieved. The H4tpaen derivative with a morpholine
group L5 on para of the pyridine ring was obtained after the coupling step of 17 with
ethylenediamine and ester deprotection (scheme 5).
The intermediate 20 was obtained from the selective reduction and chlorination step
starting from the 4-methoxypyridine-2,6-dicarboxylate compound (18). The coupling steps
with ethylene diamine and the ester deprotection were performed in the similar way as
described for the H4tpaen ligand synthesis giving access to the compound L6 (scheme 5).
From the methodology developed, two new H4tpaen derivatives were obtained
incorporating a hydrophilic substituent, morpholine groups (L5) or methoxy (L6), with
respectively 20% and 9% global yields (Scheme 5).
Scheme 5: Synthetic route for N- and O-functionalized H4tpaen derivative L5and L6.
10

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2.2 Solvent Extraction Results
Preliminary solvent extraction experiments were carried out to determine the ability of
H4tpaen derivatives to selectively back-extract Am(III) with selectivity towards Cm(III) and
Eu(III) from loaded organic phases.
Two
organic
systems
were
studied:
a
mixture
of
N’-dimethyl-N,N’-
dioctylhexylethoxymalonamide (DMDOHEMA, 0.6 M) and di-2-ethyl-hexyl-phosphoric acid
(HDEHP, 0.3 M) in hydrogenated tetrapropylene (TPH) or N,N,N’,N’-tetra-
octyldiglycolamide (TODGA, 0.2 M) and tributylphosphate (TBP, 0.5 M) in TPH.
The choice of the solvent was motivated by the fact that DMDOHEMA has a particular
affinity for Am and light lanthanides41 whereas TODGA exhibits more affinity for Cm and
heavy lanthanides.42 HDEHP and TBP were added respectively to the different extractants in
order to increase the loading capacity of the solvent. They also participate to the extraction
process. By testing each new aqueous H4tpaen derivative with both solvent systems
(DMDOHEMA/HDEHP and TODGA/TBP), the objective was to find an optimal system for
Am/Cm separation.
The aim was also to evaluate possible relationships between the structures of the complexing
agents and their selectivity/affinity towards Am and Cm.
2.2.1 DMDOHEMA/HDEHP system
The back-extraction parameters studied were pH and H4tpaen derivatives
concentrations. The results are reported in Table S1 (supporting information) and illustrated in
figures 3 and 4. Distribution ratios of Am(III), Eu(III) and Cm(III) were determined and
compared to the same experiment without any aqueous complexing agent.
The influence of pH at equilibrium on Am distribution ratio is reported in Figure 3. DAm-
values were measured at pH 0.3, 1 and 1.5 while maintaining total concentrations of cations
and ligand constant. Without any complexing agent in the aqueous phase, the extraction of
Am increases while raising the pH, due to the effect of HDEHP which exchanges its protons
with extracted cations. When adding H4tpaen into the aqueous phase, the inverse tendency is
observed: distribution ratios are significantly decreasing at lower acidity. This is due to the
strong complexation effect of this ligand which is favoured at a higher pH range where the
competition between Am complexation and carboxylic acids protonation is reduced. For all
other molecules except L6, DAm-values decrease when decreasing the pH, and reaches values
close to those obtained with the solvent alone.
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no ligand
L1
L8
100
10
L5
L7
L2
L9
L4
L3
L6
1
1
2
3
4
5
0.1
6
7
8
9
0.01
1E-3
h4tpaen
no ligand
H4tpaen
0.5
1.0
pH
1.5
Figure 3: Distribution ratios for Am (III) as a function of pH;
Organic solution: [DMDOHEMA] = 0.6M, [HDEHP] = 0.3 M in TPH
Aqueous solution: [Eu]=0.1mM with ~ 10 kBq/mL of 152Eu, 241Am and 244Cm
Aqueous stripping solution: [L] = 1mM
10000
1000
100
10
SF Cm/Am
SF Eu/Am
3.0
2.5
2.0
1.5
1.0
0.5
0.0
pH 0.3
pH 1
pH 1.5
pH 0.3
pH 1
pH 1.5
1
0.1
L2
L4
L3
L5
L1
L6
L8
L9
L7
L1
L4 L5
L6
L8 L9
L2 L3
L7
Figure 4: The separating factor for Eu/Am or Cm/Am: pH= 0.3, 1, and 1.5
Organic solution: [DMDOHEMA] = 0.6M, [HDEHP] = 0.3 M in TPH
Aqueous solution: [Eu]=0.1mM with ~ 10 kBq/mL of 152Eu, 241Am and 244Cm
Aqueous stripping solution: [L] = 1mM
Consequently, no effect of the complexing agent was observed at pH 0.3 anymore
because of ligand protonation.
Among all newly synthesised ligands, L6 showed the strongest complexation effect on Am
and significant selectivity for Am(III) versus Eu(III) and Cm(III) at pH 1.5 (SFCm/Am=2.7,
SFEu/Am=188). These results indicate that L6 is able to strip Am(III) selectively towards
Eu(III) and Cm(III). It should be noted that L6 is slightly less selective towards Cm compared
to H4tpaen and SFEu/Am is around 60 times lower (Figure 4).
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Concerning the other ligands, the affinity for americium seems to increase in the following
order: L1, L8 < L5, L7 < L2, L9 < L4 < L3 < L6 < H4tpaen. The data obtained with L1 and
L8 were very close to the system with “no ligand” even at pH 1.5 showing that those two
compounds have no affinity for cations in these conditions. Although not as efficient as ligand
L6 and H4tpaen, L3 and L4 with spacers containing additional amino-carboxylate functions
(EDTA and DTPA derivatives) have a certain affinity for Am. Nevertheless, the Cm/Am
selectivity is lost and Eu/Am selectivity is significantly lower. After L6, the analog L7 with a
cyclohexyl ring on the bridge shows the highest Cm/Am selectivity (SFCm/Am = 1.2 at pH 1.5).
This is indicating that the length of the bridge between the two nitrogen atoms is very
important and optimal with two carbons and that the loss of flexibility induced by the
cyclohexyl ring is not favorable to Am complexation. For all other ligands, the SFCm/Am is
lower than 1.
Considering Eu/Am selectivity, L3 and L4 (DTPA and EDTA analogs) show the highest SF
values showing that the presence of additional nitrogen atoms on the chelate structures is
favorable to An/Ln selectivity as already known.43 Nevertheless, those complexing agents are
33
less selective than H4tpaen showing that the “cage”-like structure of H4tpaen allowing the
four picolinate arms to surround the cation is very well adapted to Am complexation
compared to L3 and L4 where the structure of the coordination site was completely changed
with the addition of new oxygen and nitrogen donor functions.
The pH was then maintained constant and equal to 1.5, and the ligand concentration
was raised to 5 mM. One limitation of the H4tpaen ligand in the acidic aqueous solution is its
limited solubility. Thus, its concentration can not exceed values upper than 1 mM at pH 1.5.
Likewise, the L9 ligand was not soluble enough to be engaged in experiments at 5 mM.
By increasing the concentration of other H4tpaen derivatives (L1 to L8) from 1 mM to 5 mM,
the Am distribution ratio decreases resulting from a better Am(III) complexation in the
aqueous phase (Figure 5 & 6, full sets of data are reported in Table S2 - supporting
information).
The separation factors SF Eu/Am and SF Cm/Am seem to be constant whatever the concentration
of the ligands. This is suggesting that the complex(es) formed in the aqueous phase with
ligands is(are) the same for Am, Cm and Eu, or at least they have the same cation-ligand
stoichiometry.
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1mM
5mM
1000
100
10
1
0.1
0.01
1E-3
*
*
L9
L4
L5
L2
L3
L6
L7
L8
L1
Figure 5: The distribution ratios for Am (III): pH=1.5
Organic solution: [DMDOHEMA] = 0.6M, [HDEHP] = 0.3 M in TPH
Aqueous solution: [Eu]=0.1mM with ~ 10 kBq/mL of 152Eu, 241Am and 244Cm
Aqueous stripping solution: [L] = 1 or 5 mM
*
L9 and H4tpaen not soluble enough for experiments at 5 Mm
SFEu/Am
SFCm/Am
3.0
10000
1000
100
10
1mM
5mM
2.5
1mM
5mM
2.0
1.5
1.0
0.5
1
0.0
* *
* *
L2 L3 L4 L5 L6 L7
L8 L9
L1
L3 L4 L5 L6 L7
L2
L8 L9
L1
Figure 6: The separating factor for Eu/Am or Cm/Am: pH=1.5
Organic solution: [DMDOHEMA] = 0.6M, [HDEHP] = 0.3 M in TPH
Aqueous solution: [Eu]=0.1mM with ~ 10 kBq/mL of 152Eu, 241Am and 244Cm
Aqueous stripping solution: [L] = 1 or 5 Mm
*
L9 and H4tpaen not soluble enough for experiments at 5 mM
L6 is an effective ligand for separating Am(III) from Eu(III) and Am(III) from Cm(III) from
an organic DMDOHEMA / HDEHP phase with a selective recovery of Am(III) into the acidic
aqueous phase. Nevertheless, the introduction of methoxy groups has a certain influence on
properties of the ligand and complexation capacity is slightly weaker compared to non-
functionalized H4tpaen ligand. One of the advantages of the introduction of the methoxy
groups is the possibility to increase the solubility in the acidic aqueous solution up to 5mM in
comparison to the H4tpaen ligand which is limited to 1mM.
14

ACCEPTED MANUSCRIPT
2.2.2 TODGA/TBP system
A second set of data was acquired with the evaluation of the back-extraction properties
as a function of pH and H4tpaen derivatives concentrations from a TODGA/TBP organic
phase (Figure 7 & 8, full sets of data are reported in Tables S3 & S4 - supporting
information). Solvent extraction experiments were carried out at a fixed ionic strength (using
0.25 M NaNO3). Nitrate anions were introduced in order to reach distribution ratios higher
than 1 for Eu and Cm and in the same time keep low acidity conditions to allow Am
complexation by H4tpaen derivatives. The solvent was made of TODGA 0.2M and TBP 0.5M
in TPH.
pH 1
4
pH 1.5
3
2
1
L4 L5 L6 L7 L8 L9
L1
L3
L2
Figure 7: The distribution ratios for Am (III): pH= 1 and 1.5
Organic solution: [TODGA] = 0.2M, [TBP] = 0.5 M in TPH
Aqueous solution: [Eu]=0.1mM with ~ 10 kBq/mL of 152Eu, 241Am and 244Cm
Aqueous stripping solution: [L] = 1 mM
SF Eu/Am
SF Cm/Am
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0.0
pH 1
pH 1.5
pH 1
pH 1.5
1000
100
10
1
L3
L5
L7
L8
L1
L3
L5
L7
L8
L1
L4
L6
L4
L6
L2
L9
L2
L9
Figure 8: The separating factor for Eu/Am or Cm/Am: pH= 1 and 1.5
Organic solution: [TODGA] = 0.2M, [TBP] = 0.5 M in TPH
Aqueous solution: [Eu]=0.1mM with ~ 10 kBq/mL of 152Eu, 241Am and 244Cm
Aqueous stripping solution: [L] = 1 mM
15

ACCEPTED MANUSCRIPT
The influence of pH (1 or 1.5) on Am distribution ratio is illustrated in Figure 7. Among the
different ligands, the results obtained confirm that L3, L4 and L6 have a certain affinity for
Am and therefore a potential application for the back-extraction of Am(III) in the aqueous
phase. The affinity of the H4tpaen analogue for Am at pH 1.5 followed the order: L3 < L4 <
L6 < H4tpaen. Other ligands should have a very low affinity for Am since DAm-values are
even higher than the experiment with no complexing agent in the aqueous phase. It could also
be suggested that the ligands are partially extracted into the organic phase but it was not
verified in those experiments. Again in those conditions, L6 shows the strongest
complexation effect on Am and significant selectivity for Am(III) versus Eu(III) and Cm(III)
at pH 1.5: SFCm/Am value up to 3.1 at pH 1.5 (Figure 8). This selectivity is slightly higher with
the TODGA/TBP than with DMDOHEMA/HDEHP solvent (SFCm/Am = 2.7).
By increasing the concentration of the H4tpaen derivatives (L1 to L8) from 1 mM to
5 mM, the Am distribution ratio slightly decreases resulting from a better Am(III)
complexation in the aqueous phase (Figure 9). The SFCm/Am-value for L6 ligand slightly
increases from 3.1 to 3.3 while maintaining the separation from Eu(III) (Figure 10). This is
showing that with TODGA as the extractant in the organic phase, the use of L6 ligand at
5mM would become interesting since a SFCm/Am close to H4tpaen (1mM) values is reached.
1mM
5mM
100
10
1
0.1
0.01
1E-3
1E-4
* *
L3
L5
L7 L8
L1 L2
L4
L6
L9
Figure 9: The distribution ratios for Am (III): pH=1.5
Organic solution: [TODGA] = 0.2M, [TBP] = 0.5 M in TPH
Aqueous solution: [Eu]=0.1mM with ~ 10 kBq/mL of 152Eu, 241Am and 244Cm
Aqueous stripping solution: [L] = 1 or 5 Mm
*
L9 and H4tpaen not soluble enough for experiments at 5 mM
16

ACCEPTED MANUSCRIPT
SF Cm/Am
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0.0
SF Eu/Am
1mM
5mM
1mM
5mM
1000
100
10
1
* *
L*9 *
L2
L8 L9
L2
L8
L1
L3
L4
L5 L6
L7
L1
L3 L4 L5 L6 L7
Figure 10: The separating factor for Eu/Am or Cm/Am: pH=1.5
Organic solution: [TODGA] = 0.2M, [TBP] = 0.5 M in TPH
Aqueous solution: [Eu]=0.1mM with ~ 10 kBq/mL of 152Eu, 241Am and 244Cm
Aqueous stripping solution: [L] = 1 or 5 mM
*
L9 and H4tpaen not soluble enough for experiments at 5 mM
2.3 Discussion
In general, all the ligands synthesized showed a higher solubility compared to H4tpaen
in acidic medium except L9 with a phenyl group on the spacer. Nevertheless, only L3, L4 and
L6 showed a significant affinity for Am in acidic conditions (pH 1.5) and only methoxy L6
derivative conserved a good selectivity between Am and Cm.
According to observations made through extraction tests, three tendencies have emerged:
•
Flexibility of the spacer seems to be essential. Indeed, ligands L7, L8 and L9 whose
central arms (constituted by benzyl or cyclohexyl moiety) provide rigidity to the ligands,
poorly strip actinides as well as lanthanides. The length appears also as an important
parameter with highest performances obtained with the ethylene diamine bridge (two carbon
atoms).
• The use of chelating spacers such as tetraazamacrocycles (L1 and L2) induces a loss
of affinity in those specific conditions. Nevertheless coordination studies would be necessary
to better understand if this lower affinity is linked to a loss size effect of the chelating site.
The protonation of N-atoms should also be studied and might enter in strong competition with
Am complexation.
•
EDTA and DTPA derivatives (L3 and L4) are less selective than H4tpaen showing
that changing the structure of the coordination site with the addition of new oxygen and
nitrogen donor functions is not favorable to Am/Cm selectivity.
•
Addition of hydrophilic substituents such as methoxy group (L6) in para position of
the pyridine cores does not affect significantly the selectivity but induces a weaker
17

ACCEPTED MANUSCRIPT
complexation. But as observed with L5, introducing bulkier substituents like morpholine
might induce steric effects that strongly penalize the coordination.
3. Conclusion
Water
soluble
ligands
such
as
N,N,N’N’-tetrakis[(6-carboxypyridin-2-
yl)methyl]ethylenediamine (H4tpaen) and their derivatives were synthesized and studied as
potential complexing agents for the separation of minor trivalent actinides from lanthanides
and Am/Cm separation by solvent extraction. Structural modifications like spacer
modification or addition of bulky substituents on para positions of pyridine rings involved a
loss of affinity in acidic conditons. Analogs L3 & L4 with spacers containing additional
amino-carboxylate functions (EDTA and DTPA derivatives) would still show high affinity for
Am but lower Am/Cm selectivity.
A specific ligand with methoxy groups on para positions of pyridines (L6) showed a slightly
higher solubility in water and interesting performances in separation for selective Am
stripping from a TODGA 0.2M / TBP 0.5M (in TPH) organic phase. While the affinity of L6
seems to be slightly lower than H4tpaen, efficient separation between Cm and Am can be
reached using 5 mM of ligand in the acidic stripping phase (pH 1.5) with SFCm/Am close to 3.2.
4. Experimental part
4.1 Synthetic Chemistry
4.1.1. Chemicals and Identification Techniques
Chemicals (analytically pure) were purchased from Sigma-Aldrich or Alfa Aesar and were
used without further purification. Anhydrous solvents were purchased from Acros
(AcroSeal®). Reactions were monitored by Thin Layer Chromatography (Merck TLC Silica
Gel 60 F254) using different revelatory system: phosphomolybdic acid (25 g / 500 ml ethanol),
sulphuric acid (10% in ethanol), or ninhydrine (1% in ethanol) following by heating and
potassium permanganate (10 g K2CO3, 1.5 g KMnO4, 150 mL H2O, 1.5 mL NaOH 10%).
Flash chromatography purifications were performed on a combiflash agilent Intelliflash 971-
FP. NMR analyses were performed on Bruker 400 ultrashield VS spectrometer.
Displacements are reported in ppm using internal reference of the solvent (CDCl3: 7.26 ppm
1H; 77.16 ppm 13C). Elemental analysis was performed using a Flash EA 1112
(ThermoFinnigan 2003) apparatus (C, H, N combustion analysis). HRMS were realized using
a ThermoFisher LTQ-Orbitrap XL spectrometer.
18

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4.1.2. Procedure and characterizations of compounds
Dimethyl pyridine-2,6-dicarboxylate (1)
Dimethyl 2,6-pyridinedicarboxylate was synthesised using an adapted
literature protocol.44
PDCA (5.2 g, 3.1.10-2 mol) and sulphuric acid (0.9 mL) were stirred in
MeO2C
N
CO2Me
refluxing methanol (20 mL) during 16 hours. After reaction completion (followed by TLC),
methanol was concentrated. The residue was diluted in dichloromethane then washed with
saturated NaHCO3 then water. The combined organic layers were dried over Na2SO4 then the
solvent was removed under reduced pressure to afford the desired ester 1 (5.4 g, 90 %) as a
white solid.
1
RMN H (400 MHz, CDCl3) : 4.01 (s, 6H), 8.0 (t,1H, J = 7.6 Hz), 8.30 (d, 2H, J = 7.6 Hz);
RMN 13C (100 MHz, CDCl3) : 52.9 (CH3), 127.9 (CHarom), 138.4 (CHarom), 148.0 (Cq),
164.8 (CO).
Methyl 6-hydroxymethyl-pyridine-2-carboxylate (2)
Methyl (6-hydroxymethyl)-pyridine-2-carboxylate was synthesised using an
adapted literature protocol.45
OH
MeO2C
N
NaBH4 (390 mg, 10.3 mmol) was slowly added, at 0ꢀ°C, to a solution of
dimethyl pyridine-2,6-dicarboxylate (1; 2.00 g, 10.2 mmol) in a dry MeOH (100 mL). The
reaction mixture was stirred for 12 h at room temperature and then neutralized with an
aqueous saturated NH4Cl solution. After extraction with CH2Cl2 (3×50 mL), the combined
organic layers were dried with Na2SO4 and the solvent was removed under reduced pressure.
The resulting crude residue was purified by column chromatography (dichloromethane)
giving the mono-alcohol 3 (1.4 g, 82 %) as a white solid.
RMN 1H (400 MHz, CDCl3) : 3.96 (s, 3H), 4.84 (s, 2H), 7.52 (d,1H, J = 7.6 Hz), 7.82 (t, 1H,
13
J = 7.6 Hz), 8.0 (d, 2H, J = 7.6 Hz); RMN C (100 MHz, CDCl3) : 53.1 (CH2), 64.8 (CH3),
124.0 (CHarom), 124.2 (CHarom), 137.9 (CHarom), 147.2 (Cq), 160.4 (Cq), 165.7 (CO).
Methyl 6-chloromethyl-pyridine-2-carboxylate (3)
Methyl (6-chloromethyl)-pyridine-2-carboxylate was synthesised using an
adapted literature protocol.45
Cl
MeO2C
N
5 ml of thionyl chloride is slowly added to methyl 6-hydroxymethyl-2-
pyridine carboxylate 2 (2.5 g, 14.9 mmol) at 0°C. under nitrogen and stirred for 1 hour. The
reaction mixture is concentrated under vacuum. The obtained residue was diluted in toluene
and washed with saturated sodium bicarbonate solution. The aqueous solution was extracted
three times by toluene. The combined organic layers were dried on Na2SO4, filtered and
concentrated by evaporation in a vacuum. The chloride compound 3 was obtained as a
yellowish solid (2.48 g, 90%) and used without further purification.
RMN 1H (400 MHz, CDCl3) : 3.97 (s, 3H), 4.74 (s, 2H), 7.69 (d,1H, J = 7.6 Hz), 7.86 (td, 1H,
J = 7.6 and 0.8 Hz), 8.25 (d, 2H, J = 7.6 Hz); RMN 13C (100 MHz, CDCl3) : 46.4 (CH2), 53.2
(CH3), 124.6 (CHarom), 126.3 (CHarom), 138.3 (CHarom), 147.6 (Cq), 157.4 (Cq), 165.5
(CO).
N,N,N’,N’-tetrakis[(6-carboxymethylpyridin-2-yl)methyl]ethylene diamine (4)
N,N,N’N’-tetrakis[(6-carboxymethyl
pyridin-2-yl)methyl]-
CO2Me
ethylenediamine was synthesised using an adapted literature
N
CO2Me protocol.27
N
N
N
Methyl 6-chloromethyl-2-pyridine carboxylate 3 (500 mg, 2.7
MeO2C
N
mmol), K2CO3 (391 mg, 2.8 mmol) followed by freshly distilled
N
MeO2C
19

ACCEPTED MANUSCRIPT
acetonitrile (10 mL) were added to a Schlenk flask under argon atmosphere. Ethylene diamine
(45 µL, 0.67 mmol) was then added. The mixture was stirred at 80°C for 12 hours.
Acetonitrile was then removed under vacuum. The obtained residue was diluted with
dichloromethane and washed with water. The organic layers were dried on Na2SO4, filtered
and concentrated under vacuum. The resulting residue was recristallized in iPrOH to afford a
slightly yellow powder (314 mg, 70%).
1
RMN H (400 MHz, CDCl3) : 2.75 (s,4H), 3.66 (s, 8H), 3.95 (s, 12 H), 7.68 (m, 8H), 7.94
(dd, 4H, J = 6.8 and 2 Hz); RMN 13C (100 MHz, CDCl3) : 52.9 (CH2), 53.3 (CH3), 60.9
(CH2), 124.0 (CHarom), 126.3 (CHarom), 137.8 (CHarom), 147.7 (Cq), 160.6 (Cq), 165.1
(CO).
N,N,N’,N’-tetrakis[(6-carboxypyridin-2-yl)methyl]ethylene diamine H4tpaen (5)
CO2H
N,N,N’,N’-tetrakis[(6-carboxymethylpyridin-2-yl)methyl]ethylene
N
diamine 4 (445 mg, 0.678 mmol) was mixed in HCl 6M (2 mL) at
N
CO2H
N
N
100°C for 12 hours. The suspension was filtered and washed with
cold water. H4tpaen was obtained as a white powder (345 mg,
85%)
N
HO2C
N
HO2C
1
RMN H (400 MHz, DMSO) : 3.75 (s,4H), 4.54 (s, 8H), 7.68
(massif, 4H), 7.92 (d, 8H, J = 4 Hz); RMN 13C (100 MHz, DMSO) : 49.8 (CH2), 57.5 (CH2),
124.0 (CHarom), 127.6 (CHarom), 138.4 (CHarom), 147.5 (Cq), 153.6 (Cq), 165.5 (CO).
General procedure for H4tpaen derivatives (6a-e)
Coupling step (5a-e):
Methyl 6-chloromethyl-pyridine-2-carboxylate 3 (500 mg, 2.7 mmol), K2CO3 (391 mg, 2.8
mmol) followed by freshly distilled acetonitrile (10 mL) were added to a Schleck flask under
argon atmosphere. Diamine (0.67 mmol) was then added. The mixture was stirred at 80°C for
12 hours. Acetonitrile was then removed under vacuum. The obtained residue was diluted
with dichloromethane and washed with water. The organic layers were dried on Na2SO4,
filtered and concentrated under vacuum. The resulting residue was recrystallized in iPrOH.
Hydrolysis step (6a-e):
Carboxylate compound (5a-e, 1.26 mmol) was suspended in an aqueous solution of HCl (6M,
4.5 mL). The mixture was refluxed for 14h, the solid was filtered, washed with water (2 x 2
mL) and dried under vacuum at room temperature for 14h to give the H4tpaen derivatives (6a-
e).
tetramethyl6,6',6'',6'''-((1,4,7,10-tetraazacyclododecane-1,4,7,10-tetrayl)-
tetrakis(methylene))tetrapicolinate (5a)
Yield = 70%
1
RMN H (400 MHz, CDCl3) : 2.76 (s,16H), 3.72 (s, 8H), 3.94 (s,
13
12H), 7.50 (t, 4H, J = 8 Hz), 7.92 (massif, 8H); RMN C (100
MHz, CDCl3) : 53.1 (CH3), 53.8 (CH2), 61.7 (CH2), 123.6
(CHarom), 126.0 (CHarom), 137.3 (CHarom), 147.6 (Cq), 161.3
(Cq), 165.9 (CO); Anal. Calcd (%) for C40H48N8O8: C, 62.49;
H, 6.29; N, 14.57; O, 16.65; found: C, 62.36; H, 6.35; N, 14.49.
6,6',6'',6'''-((1,4,7,10-tetraazacyclododecane-1,4,7,10-tetrayl)-
tetrakis(methylene))tetrapicolinic acid (6a – L1)
Yield = 65%
20

ACCEPTED MANUSCRIPT
1
CO2H
N
RMN H (400 MHz, DMSO): 3.44 (s, 16H), 4.32 (s, 8H), 7.69 (t,
8H), 7.97 (d, 4H, J = 3.6 Hz); RMN 13C (100 MHz, D2O) : 49.7
(CH2), 57.1 (CH2), 125.6 (CHarom), 128.8 (CHarom), 140.6
(CHarom), 146.5 (Cq), 146.6 (Cq), 166.5 (CO); Anal. Calcd (%)
for C36H40N8O8: C, 60.66; H, 5.66; N, 15.72; O, 17.96; found: C,
61.02; H, 5.95; N, 16.09.
N
CO2H
N
N
N
N
HO2C
N
N
CO2H
tetramethyl6,6',6'',6'''-((1,4,8,11-tetraazacyclotetradecane-1,4,8,11-tetrayl)-
tetrakis(methylene))tetrapicolinate (5b)
Yield = 76%
1
CO2Me
RMN H (400 MHz, CDCl3) : 1.71 (quint, 4H, J = 6.8 Hz), 2.54
(t,8H, J = 6.8 Hz), 2.63 (s, 8H), 3.67 (s, 8H), 3.90 (s, 12H), 7.62
(massif, 8H), 7.89 (dd, 4H, J = 6 and 1.8 Hz); RMN 13C (100
MHz, CDCl3) : 23.9 (CH2), 51.2 (CH2), 51.9 (CH2), 53.1 (CH3),
61.3 (CH2), 123.7 (CHarom), 126.1 (CHarom), 137.3 (CHarom),
147.4 (Cq), 161.5 (Cq), 166.0 (CO); Anal. Calcd (%) for
C42H52N8O8: C, 63.30; H, 6.58; N, 14.06; O, 16.06; found: C,
63.72; H, 7.71; N, 14.19.
N
N
CO2Me
N
N
N
N
MeO2C
N
N
CO2Me
6,6',6'',6'''-((1,4,8,11-tetraazacyclotetradecane-1,4,8,11-tetrayl)-
tetrakis(methylene))tetrapicolinic acid (6b – L2)
Yield = 97%
1
CO2H
RMN H (400 MHz, DMSO) : 2.25 (m, 4H), 3.44 (m, 8H), 4.34 (s,
8H), 7.72 (d, 4H, J = 7.2 Hz), 8.0 (m, 8H); RMN C (100 MHz,
DMSO) : 23.3 (CH2), 52.5 (CH2), 54.6 (CH2), 59.8 (CH2), 126.9
(CHarom), 129.6 (CHarom), 141.5 (CHarom), 149.0 (Cq), 156.0
(Cq), 168.4 (CO); Anal. Calcd (%) for C38H44N8O8: C, 61.61; H,
5.99; N, 15.13; O, 17.28; found: C, 61.78; H, 6.26; N, 15.27.
13
N
N
CO2H
N
N
N
N
HO2C
N
N
CO2H
tetramethyl-6,6',6'',6'''-(((1R,2R)-cyclohexane-1,2-diylbis(azanetriyl))-
tetrakis(methylene))tetrapicolinate (5c)
Yield = 76%
RMN 1H (400 MHz, CDCl3) : 1.08 (m, 4H), 1.71 (d, 2H, J = 6.8
Hz), 2.18 (d, 2H, J = 10.8 Hz), 2.70 (d, 2H, J = 6.8 Hz), 1.27, m,
1.2H), 3.73 (m, 8H), 3.88 (s, 12H), 7.39 (t, 4H, J = 7.6 Hz), 7.8
(d, 8H, J = 7.6 Hz) ; RMN 13C (100 MHz, CDCl3) : 25.3 (CH2),
25.9 (CH2), 52.8 (CH3), 55.7 (CH2), 60.9 (CH), 123.4
(CHarom), 127.1 (CHarom), 136.8 (CHarom), 147.2 (Cq), 161.0
(Cq), 165.7 (CO).
6,6',6'',6'''-(((1R,2R)-cyclohexane-1,2-diylbis(azanetriyl))-tetrakis(methylene))tetrapicolinic
acid (6c – L7)
Yield = 93%
1
RMN H (400 MHz, D2O) : 1.41 (t, 2H, J = 9.8 Hz), 1.66 (m,
2H), 1.91 (d, 2H, J = 8.8 Hz), 2.39 (d, 2H, J = 12 Hz), 4 (d, 2H,
J = 8 Hz), 4.3 (d, 8H, J = 13.6 Hz), 3.88 (s, 12H), 7.66 (m,
12H); RMN 13C (100 MHz, D2O) : 23.6 (CH2), 23.8 (CH2),
55.2 (CH2), 62.5 (CH), 125.5 (CHarom), 128.6 (CHarom),
137.5 (CHarom), 145.9 (Cq), 149.8 (Cq), 166.7 (CO); HRMS:
HO2C
N
N
N
N
CO2H
N
HO2C
N
HO2C
21

ACCEPTED MANUSCRIPT
[M+H]exp = 655.2507.
tetramethyl6,6',6'',6'''-(((cyclohexane-1,3-diylbis(methylene))bis(azanetriyl))-
tetrakis(methylene))tetrapicolinate (5d)
Yield = 85%
1
RMN H (400 MHz, CDCl3) : 0.19 (q, 0.8H, J = 12 Hz),
CO2Me
N
0.54 (q, 1.2H, J = 12 Hz and 1 Hz), 1.08 (m, 2H), 1.18 (s,
0.8H), 1.27, m, 1.2H), 1.46 ( broad m, 2H), 1.63 (m, 1.6H),
1.84 (m, 2.4H), 3.73 (s, 3.2H), 3.82 (d, 4.8H, J = 4.4 Hz),
3.91 (s, 12H), 7.72 (m, 8H), 7.91 (d, 4 H, J = 6.8 Hz) ;
RMN 13C (100 MHz, CDCl3) : 25.6 (CH2), 31.7 (CH2),
CO2Me
N
MeO2C
N
N
N
N
CO2Me
35.7 (CH), 52.9 (CH3), 59.4 (CH2), 60.7 (CH2), 123.6 (CHarom), 125.8 (CHarom), 137.3
(CHarom), 147.3 (Cq), 160.7 (Cq), 165.8 (CO).
6,6',6'',6'''-(((cyclohexane-1,3-diylbis(methylene))bis(azanetriyl))-
tetrakis(methylene))tetrapicolinic acid (6d – L8)
Yield = 91%
RMN 1H (400 MHz, D2O) : 0.98 (m, 1H), 1.3 (m, 1H), 1.08
CO2H
CO2H
(m, 2H), 1.18 (s, 0.8H), 1.76 (m, 4H), 2.05 (m, 2H), 2.18
N
N
HO2C
(m, 2H), 3.26 (m, 2.4H), 3.37 (m, 2H), 4.62 (s, 8H), 7.44 (d,
4 H, J = 6 Hz), 7.90 (d, 8 H, J = 6 Hz) ; RMN C (100
MHz, , D2O) : 24.1 (CH2), 29.4 (CH2), 33.1 (CH2), 33.2
(CH), 62.2 (CH2), 125.3 (CHarom), 128.2 (CHarom), 139.8
N
13
N
N
N
CO2H
(CHarom), 146.4 (Cq), 149.6 (Cq), 166.7 (CO); HRMS: [M+H]exp = 683.2819.
tetramethyl-6,6',6'',6'''-((1,2-phenylenebis(azanetriyl))-tetrakis(methylene))tetrapicolinate (5e)
Yield = 34%
1
RMN H (400 MHz, CDCl3) : 3.88 (s, 8H), 3.94 (s, 12H),
MeO2C
N
7.25 (m, 4H), 7.76 (m, 8H), 7.93 (dd, 4H, J = 2.8 and 6 Hz) ;
N
N
RMN 13C (100 MHz, CDCl3) : 52.9 (CH3), 59.8 (CH2), 123.6
(CHarom), 125.8 (CHarom), 127.8 (CHarom), 128.5
(CHarom), 137.4 (CHarom), 138.7 (Cq), 147.4 (Cq), 160.3
(Cq), 165.7 (CO).
N
CO2Me
N
MeO2C
N
MeO2C
6,6',6'',6'''-((1,2-phenylenebis(azanetriyl))-tetrakis(methylene))tetrapicolinic acid (6e – L9)
Yield = 87%
1
RMN H (400 MHz, CDCl3) : 3.88 (s, 8H), 3.94 (s, 12H), 7.25
HO2C
(m, 4H), 7.76 (m, 8H), 7.93 (dd, 4H, J = 2.8 and 6 Hz) ; RMN
N
13C (100 MHz, CDCl3) : 52.9 (CH3), 59.8 (CH2), 123.6
CO2H (CHarom), 125.8 (CHarom), 127.8 (CHarom), 128.5 (CHarom),
137.4 (CHarom), 138.7 (Cq), 147.4 (Cq), 160.3 (Cq), 165.7
(CO) ; HRMS: [M+H]exp = 677.2350.
N
N
N
N
HO2C
N
HO2C
N-Boc-ethylene diamine (7)
Di tert-butyl bicarbonate (2.18 g, 10 mmol) dissolved in chloroform (50 mL)
H
N
O
H2N
was added dropwise to a solution of ethylenediamine (6.7 mL, 0.1 mmol) in
chloroform (100 mL) during 3 hours with stirring and cooling in an ice bath.
O
The reaction mixture was stirred for additional 16 hours in an ice bath. The reaction mixture
was stirred for an additional 18 hours at room temperature and was then washed with water.
22

ACCEPTED MANUSCRIPT
Organic layer was dried over Na2SO4, concentrated to dryness and obtained as colourless oil
with 95% yield.
RMN 1H (400 MHz, CDCl3) : 1.37 (s, 9H), 2.72 (t, 2H, J = 6 Hz), 3.09 (t, 2H, J = 6 Hz), 5.02
(bs, 1H, NH); RMN 13C (100 MHz, CDCl3) : 28.6 (CH3), 42.0 (CH2), 43.5 (CH2), 79.3 (Cq),
156.4 (CO).
N-Boc-dimethyl 6,6'-(((2-aminoethyl)azanediyl)bis(methylene))dipicolinate (8)
CO2Me
6-chloromethylpyridine-2-carboxylic acid methyl ester 3 (3.5 g, 18.8
N
mmol), N-Boc ethylenediamine 7 (1.5 g, 9.4 mmol) and K2CO3 (2.85g,
20.7 mmol) are dried under vacuum then put under argon atmosphere.
H
N
O
N
Dry acetonitrile (30 mL) is added. The mixture is stirred at 70°C for 18h.
After concentration of the solvent, the residue is dissolved in NaHCO3
and extracted with dichloromethane. The collected organic layer was
dried over sodium carbonate and concentrated. The residue is purified by
O
N
CO2Me
column chromatography on alumina (eluent: cyclohexane to cyclohexane/ethyl acetate (7/3)
to afford colourless oil with 67% yield.
1
RMN H (400 MHz, CDCl3) : 1.36 (s, 9H), 2.68 (t, 2H, J = 5.2 Hz), 3.20 (m, 2H), 3.91 (s,
4H), 3.94 (s, 6H), 5.26 (bs, 1H, NH), 7.65 (d, 2H, J = 8 Hz), 7.73 (t, 2H, J = 7.6 Hz), 7.94 (dd,
2H, J = 7.6 and 0.4 Hz), ; RMN 13C (100 MHz, CDCl3) : 28.4 (CH3), 38.6 (CH2), 52.7 (CH2),
54.3 (CH2), 60.2 (CH2), 78.9 (Cq), 123.6 (CHarom), 126.1 (CHarom), 137.3 (CHarom), 147.4
(Cq), 156.0 (Cq), 160.1 (CO), 165.7 (CO).
dimethyl 6,6'-(((2-aminoethyl)azanediyl)bis(methylene))dipicolinate (9)
CO2Me
Trifluoroacetic acid (16 mL) was added dropwise to a solution of [2-(bis-
N
N
methyl-6-pyridinylcarboxylate methylamino)ethyl]carbamic acid tert-butyl
ester 8 (820 mg, 1.79 mmol) in dry dichloromethane at 0°C. The mixture was
stirred for 1 hour at 0°C then for 18 hours at room temperature. After
concentration of the solvent, the residue is dissolved in saturated NaHCO3
and extracted with dichloromethane. The collected organic layer was dried
over sodium carbonate and concentrated. The resulting product was purified
NH2
N
CO2Me
on alumina to afford the amine as a yellow solid with 66% yield.
RMN 1H (400 MHz, CDCl3) : 3.1 (t, 2H, J = 5.2 Hz), 3.23 (t, 2H, J = 5.2 Hz), 3.97 (s, 6H),
4.0 (s, 4H), 7.30 (t, 2H, J = 7.6 Hz), 7.61 (t, 2H, J = 7.6 Hz), 7.96 (t, 2H, J = 8 Hz) ; RMN 13C
(100 MHz, CDCl3) : 37.8 (CH2), 53.0 (CH3), 59.5 (CH2), 62.1 (CH2), 123.7 (CHarom), 126.3
(CHarom), 137.7 (CHarom), 147.0 (Cq), 159.4 (Cq), 165.4 (CO).
General procedure for H4tpaen derivatives (11a-b)
Coupling step (10a-b):
A solution of 9 (500 mg, 1.39 mmol) in dry DMF (10 mL) were added to a schlenk flask
under argon atmosphere. The appropriate EDTA or DTPA dianhydride (0.7 mmol) was then
added. The mixture was stirred overnight at room temperature. The mixture was concentrated
then and dried under vacuum at room temperature for 14h to give the derivatives 11a-b.
Hydrolysis step (11a-b):
Carboxylate compound (10a-b, 1.26 mmol) was suspended in an aqueous solution of HCl
(6M, 4.5 mL). The mixture was refluxed for 14h, the solid was filtered, washed with cold
water (2 x 2 mL) and dried under vacuum at room temperature for 14h to give the H4tpaen
derivatives (11a-b).
23

ACCEPTED MANUSCRIPT
11-(2-((2-(bis((6-(methoxycarbonyl)pyridin-2-yl)methyl)amino)ethyl)amino)-2-oxoethyl)-8-
(carboxymethyl)-1-(6-(methoxycarbonyl)pyridin-2-yl)-2-((6-(methoxycarbonyl)pyridin-2-
yl)methyl)-6-oxo-2,5,8,11-tetraazatridecan-13-oic acid (10a)
Yield = 74%
1
CO2Me
RMN H (400 MHz, D2O) : 2.92 (s, 4H), 3.19
N
N
HO2C
CO2H
(s, 4H), 3.55 (s, 4H), 3.66 (m, 4H), 3.77 (m,
4H), 3.86 (12H), 4.66 (s, 8H), 7.47 (d, 4H, J =
7.2 Hz), 7.86 (m, 8H); RMN 13C (100 MHz,
D2O) : 38.5 (CH2), 52.7 (CH2), 53.3 (CH3), 55.2
(CH2), 56.1 (CH2), 58.4 (CH2), 109.2 (Cq),
125.4 (CHarom), 128.3 (CHarom), 139.6
N
N
O
CO2Me
H
N
N
N
N
N
H
O
N
CO2Me
CO2Me
(CHarom), 149.9 (Cq), 165.92 (CO), 176.2 (CO), 177.7 (CO); HRMS: [M+H]exp = 973.4055
6,6'-(8,11-bis(carboxymethyl)-2,17-bis((6-carboxypyridin-2-yl)methyl)-6,13-dioxo-
2,5,8,11,14,17-hexaazaoctadecane-1,18-diyl)dipicolinic acid (11a – L3)
Yield = 95%
RMN 1H (400 MHz, D2O) : 2.45 (s, 4H), 3.36 (m,
CO2H
N
N
HO2C
4H), 3.88 (m, 4H), 3.93 (s, 8H), 4.55 (s, 8H), 7.42
(qd, 4H, J = 5.2 and 4 Hz), 7.78 (m, 8H); RMN
13C (100 MHz, D2O) : 34.8 (CH2), 50.8 (CH2),
53.2 (CH2), 54.9 (CH2), 57.2 (CH2), 58.2 (CH2),
125.5 (CHarom), 128.3 (CHarom), 140.7
N
N
O
CO2H
H
N
N
N
N
N
H
O
CO2H
N
CO2H
CO2H
(CHarom), 145.7 (Cq), 150.2 (Cq), 166.1 (CO),
169.7 (CO), 169.8 (CO); Anal. Calcd (%) for C42H48N10O14: C, 55.02; H, 5.28; N, 15.28;
O, 24.43; found: C, 55.19; H, 5.19; N, 14.98.
14-(2-((2-(bis((6-(methoxycarbonyl)pyridin-2-yl)methyl)amino)ethyl)amino)-2-oxoethyl)-
8,11-bis(carboxymethyl)-1-(6-(methoxycarbonyl)pyridin-2-yl)-2-((6-(methoxy-
carbonyl)pyridin-2-yl)methyl)-6-oxo-2,5,8,11,14-pentaazahexadecan-16-oic acid (10b)
Yield = 70%
1
RMN H (400 MHz, D2O) : 2.92 (s, 4H), 3.26
(s, 8H), 3.66 (m, 4H), 3.5-3.9 (m, 30H), 7.47
(m, 4H), 7.8-7.96 (m, 8H); RMN 13C (100
MHz, D2O) : 51.3 (CH2), 51.8 (CH2), 53.2
(CH3), 55.1 (CH2), 55.3 (CH2), 56.3 (CH2), 56.9
(CH2), 58.4 (CH2), 125.4 (CHarom), 128.2
(CHarom), 139.6 (CHarom), 146.4 (Cq), 149.8 (Cq), 164.8 (CO), 166.6 (CO), 171.5 (CO);
HRMS: [M+H]exp = 1074.4557.
6,6'-(8,11,14-tris(carboxymethyl)-2,20-bis((6-carboxypyridin-2-yl)methyl)-6,16-dioxo-
2,5,8,11,14,17,20-heptaazahenicosane-1,21-diyl)dipicolinic acid (11b – L4)
Yield = 92%
RMN 1H (400 MHz, D2O) : 2.96 (m, 4H), 3.19
CO2H
CO2H
(m, 4H), 3.26 (m, 4H), 3.3 (m, 4H), 3.88 (s, 10H),
4.34 (s, 8H), 7.3 (d, 4H, J = 7.2 Hz), 7.49 (m,
2NH), 7.62 (m, 8H); RMN 13C (100 MHz, D2O) :
34.4 (CH2), 34.8 (CH2), 49.3 (CH2), 52.3 (CH2),
52.4 (CH2), 52.8 (CH2), 53.8 (CH2), 54.9 (CH2),
57.7 (CH2), 125.5 (CHarom), 128.3 (CHarom),
N
N
HO2C
N
H
H
N
N
N
N
N
N
O
O
CO2H HO2C
N
N
CO2H
CO2H
141.3 (CHarom), 144.9 (Cq), 150.2 (Cq), 165.3 (CO), 165.9 (CO), 166.2 (CO), 172.0 (CO);
24

ACCEPTED MANUSCRIPT
Anal. Calcd (%) for C46H55N11O16: C, 54.27; H, 5.45; N, 15.14; O, 25.15; found: C, 54.12;
H, 5.33; N, 15.01.
chelidonic acid (4-oxo-4H-pyran-2,6-dicarboxylic acid) (12)
Chelidonic acid was synthesised using an adapted literature protocol.33
O
In a typical experiment, EtONa (69.4 g, 1.02 mol) was suspended in ethanol
(300 mL). After 45 min at 60°C, a solution of dry acetone (29 g, 38 ml, 0.5
HO2C
O
CO2H
mol) and diethyl oxalate (155 g, 144 ml, 1.06 mol) was added over a period of
1h. After the addition was complete, the solution was maintained at 60°C and stirred for an
additional 14 h. Then 230 mL of HCl (37% aqueous solution) and 100 ml of water were
added and the mixture was stirred for one day. After 24h, about half of aqueous ethanol was
removed under reduced pressure then 300 mL of water and 60 mL of HCl (37% aqueous
solution) were added to this mixture and stirring was continued for 20h at 50°C. The resulting
solid was filtered off, washed first with water then with acetone before recrystallization from
boiling water using charcoal. The filtrate was left at room temperature until formation of
crystals. The white crystals were collected and dried under vacuum to give the desired
compound 12 (42.3 g, 46%).
RMN 1H (400 MHz, D2O): 7.09 (s, 2H); 13C (100 MHz, D2O) : 117.4 (Cq), 157.2 (Cq), 163.5
(CO), 184.1(CO).
chelidamic acid (1,4-dihidro-4-oxo-2,6-pyridinedicarboxylic acid) (13)
Chelidamic acid was synthesised using an adapted literature protocol.33
In a typical experiment, 425 mL of NH3 (30% aqueous solution) was added
dropwise at 0°C to 12 (41.8 g, 0.21 mol) over a period of 1h.. After the
addition was complete, the resulting suspension was stirred at room
temperature for 48h. The excess of aqueous ammonia solution was removed under reduced
pressure and the residue was refluxed for 15 min with 50 ml of water using charcoal. After
filtration, the hot filtrate was collected and after return to room temperature acidified with
HCl (37% aqueous solution) until pH = 1. The resulting white solid was filtered off, washed
several times with cold water and dried under vacuum for 16h. The desired compound 13 was
obtained as a white solid (42 g, 98%).
RMN 1H (400 MHz, D2O) : 6.97 (s, 2H); RMN 13C (100 MHz, D2O) : 116.8 (Cq), 154.5 (Cq),
174.9 (CO), 176.1 (CO).
dimethyl 4-chloropyridine-2,6-dicarboxylate (14)
PCl5 (11.8g, 56.8mmol) was slowly added to chelidamic acid 13 (2.5g,
Cl
13.8mmol) in CHCl3 (30mL). The mixture was refluxed for three days.
After cooling to 0°C, MeOH was added dropwise until the end of the gas
MeO2C
N
CO2Me
evolution. The solution was stirred for 2h at room temperature and then
concentrated. Saturated aqueous NaHCO3 was added until pH = 7. The organic layer was
dried over Na2SO4, filtered and evaporated under vacuum. The residue is purified by column
chromatography (cyclohexane/AcOEt, 8/2) giving the resulting 17 (2.57 g, 93 %) as a white
solid.
1
13
RMN H (400 MHz, CDCl3) : 4.4 (s, 3H), 8.27 (s, 2H); RMN C (100 MHz, CDCl3) : 53.5
(CH3), 128.3 (CHarom), 146.8 (Cq), 149.4 (Cq), 164.1 (CO)
dimethyl 4-morpholinopyridine-2,6-dicarboxylate (15)
O
To a solution of 14 (1.44g, 7.17 mmol) in DMF (2mL) was added
morpholine (750µL, 8.6 mmol) then DIPEA (1.1mL, 8.6 mmol). The mixture
N
was heated at 100°C overnight in a sealed tube. After completion of the
MeO2C
N
CO2Me
25

ACCEPTED MANUSCRIPT
reaction (followed by TLC), the mixture was concentrated. The residue was diluted with
CH2Cl2 then washed with water then brine. The combined organic layers were dried with
Na2SO4 and the solvent was removed under reduced pressure. The resulting crude residue was
purified by column chromatography (cyclohexane/AcOEt, 6/4) giving 15 (1.42 g, 71 %) as a
white powder.
RMN 1H (400 MHz, CDCl3) : 3.39 (t, 4H, J = 5 Hz), 3.72 (s, 3H), 3.77 (t, 4H, J = 5 Hz), 3.89
(s, 3H), 7.11 (d, 1H, J = 2.8 Hz), 7.48 (d, 1H, J = 2.8 Hz); RMN 13C (100 MHz, CDCl3) : 46
(CH2), 52.9 (CH3), 66.2 (CH2), 110.1 (CHarom), 110.5 (CHarom), 147.4 (Cq), 156.5 (Cq),
165.9 (CO), 167.3 (CO); HRMS: [M+H]exp = 281.1133.
methyl 6-(hydroxymethyl)-4-morpholinopicolinate (16)
NaBH4 (662.1 mg, 2.36 mmol) was slowly added, at 0ꢀ°C, to a solution of 15
O
(181 mg, 4.77 mmol) in a dry MeOH (25 mL). The reaction mixture was
N
stirred for 1h at room temperature and then acidified with an aqueous saturated
HCl until pH=2. After concentration, the residue was basified with NaHCO3
OH
MeO2C
N
and extracted with CH2Cl2. The combined organic layers were dried with
Na2SO4 and the solvent was removed under reduced pressure. The resulting crude residue was
purified by column chromatography (AcOEt/MeOH, 95/5) giving the mono-alcohol 16 (398.5
mg, 67 %) as a white solid.
RMN 1H (400 MHz, CDCl3) : 2.79 (t, 4H, J = 5 Hz), 3.22 (t, 4H, J = 5 Hz), 3.32 (s, 3H), 4.05
(d, 2H, J = 5.6 Hz), 4.58 (t, OH, J = 5.6 Hz), 6.52 (d, 1H, J = 2.8 Hz), 6.8 (d, 1H, J = 2.8 Hz);
RMN 13C (100 MHz, CDCl3) : 46.2 (CH2), 52.9 (CH3), 65 (CH2), 66.3 (CH2), 106.8
(CHarom), 108.9 (CHarom), 147.9 (Cq), 156.5 (Cq), 160.9 (Cq), 166.3 (CO); HRMS:
[M+H]exp = 253.1256.
methyl 6-(chloromethyl)-4-morpholinopicolinate (17)
Thionyl chloride (1mL) is slowly added to the mono-alcohol 16 (376.5 mg,
O
1.49 mmol) at 0°C. under nitrogen and stirred for 1 hour. The reaction mixture
is concentrated under vacuum. The obtained residue was diluted in toluene
N
and washed with saturated NaHCO3 solution. The aqueous solution was
extracted three times by toluene. The combined organic layers were dried on
Cl
MeO2C
N
Na2SO4, filtered and concentrated by evaporation in a vacuum. The chlorinated compound 17
was quantitatively obtained as colourless oil which easily crystallised.
1
RMN H (400 MHz, CDCl3) : 3.42 (t, 4H, J = 4.8 Hz), 3.86 (t, 4H, J = 4.8 Hz), 4.0 (s, 3H),
4.69 (s, 2H), 7.04 (d, 1H, J = 2.4 Hz), 7.51 (d, 1H, J = 2.4 Hz); RMN 13C (100 MHz, CDCl3) :
46.1 (CH2), 46.6 (CH2), 53.1 (CH3), 66.1 (CH2), 109.0 (CHarom), 109.2 (CHarom), 148.2
(Cq), 156.7 (Cq), 157.8 (Cq), 166.0 (CO) ); HRMS: [M+H]exp = 271.0914.
dimethyl 4-methoxypyridine-2,6-dicarboxylate (18)
Chelidamic acid 13 (15g, 71.4mmol) was suspended in dry DMF (600mL)
OMe
under nitrogen atmosphere. Solid K2CO3 (65g, 0.47mol) and CH3I (29mL,
0.47mol) were added to the mixture and heated at 35°C. After 24h, the
MeO2C
N
CO2Me
orange mixture was filtered over celite, washed with CH2Cl2 then
concentrated. The residue is diluted with CH2Cl2 then washed with water. The aqueous layer
was extracted twice with CH2Cl2. The combined organic layer were washed with HCl 1M
then brine, and dried over sodium sulphate, filtered and evaporated under vacuum to afford a
yellow powder with 75% yield.
13
RMN 1H (400 MHz, CDCl3) : 3.94 (s, 3H), 3.97 (s, 6H), 7.77 (s, 2H); RMN C (100 MHz,
CDCl3) : 53.4 (CH3), 56.2 (CH3), 114.3 (CHarom), 149.9 (Cq), 165.3 (Cq), 167.8 (CO).
26

ACCEPTED MANUSCRIPT
methyl 6-(hydroxymethyl)-4-methoxypicolinate (19)
OMe
NaBH4 (2.6 mg, 69.6 mmol) was slowly added, at 0ꢀ°C, to a solution of 18
(7.83 g, 34.8 mmol) in a dry MeOH (115 mL). The reaction mixture was
stirred for 1h at room temperature and then acidified with an aqueous
OH
MeO2C
N
saturated HCl until pH=2. After concentration, the residue was basified with NaHCO3 and
extracted with CH2Cl2. The combined organic layers were dried with Na2SO4 and the solvent
was removed under reduced pressure. The resulting crude residue was purified by column
chromatography (AcOEt/MeOH, 95/5) giving the mono-alcohol 17 (4.34 g, 63 %) as a white
solid.
1
63% RMN H (400 MHz, CDCl3) : 3.87 (s, 3H), 3.93 (s, 6H), 4.76 (s, 2H), 7.04 (d, 1H, J =
2.4 Hz), 7.50 (d, 1H, J = 2.4 Hz); RMN 13C (100 MHz, CDCl3) : 53.1 (CH3), 55.8 (CH3), 64.9
(CH2), 109.4 (CHarom), 110.8 (CHarom), 148.7 (Cq), 162.5 (Cq), 165.7 (Cq), 167.4 (CO).
methyl 6-(chloromethyl)-4-methoxypicolinate (20)
OMe
Thionyl chloride (100mL) is slowly added to the mono-alcohol 19 (4.34 g, 22
mmol) at 0°C. under nitrogen and stirred for 1 hour. The reaction mixture is
concentrated under vacuum. The obtained residue was diluted in toluene and
Cl
MeO2C
N
washed with saturated NaHCO3 solution. The aqueous solution was extracted
three times by toluene. The combined organic layers were dried on Na2SO4, filtered and
concentrated by evaporation in a vacuum. The chlorinated compound 20 was quantitatively
obtained as colourless oil which easily crystallised.
1
RMN H (400 MHz, CDCl3) : 3.86 (s, 3H), 3.91 (s, 3H), 4.65 (s, 2H), 7.14 (d, 1H, J = 2.4
13
Hz), 7.53 (d, 1H, J = 2.4 Hz); RMN C (100 MHz, CDCl3) : 46.4 (CH2), 53.2 (CH3), 55.8
(CH3), 110.9 (CHarom), 111.9 (CHarom), 149.2 (Cq), 158.8 (Cq), 165.5 (Cq), 167.6 (CO).
General procedure for H4tpaen derivatives (22a-b)
Coupling step (21a-b):
The appropriate chloromethyl-pyridine-2-carboxylate (17 or 20) (2.7 mmol), K2CO3 (391 mg,
2.8 mmol) followed by freshly distilled acetonitrile (10 mL) were added to a schlenk flask
under argon atmosphere. Ethylene diamine (45 µL, 0.67 mmol) was then added. The mixture
was stirred at 80°C for 12 hours. Acetonitrile was then removed under vacuum. The obtained
residue was diluted with dichloromethane and washed with water. The organic layers were
dried on Na2SO4, filtered and concentrated under vacuum. The resulting residue was
recristallized in iPrOH.
Hydrolysis step (22a-b):
Carboxylate compound (21a-b, 1.26 mmol) was suspended in an aqueous solution of HCl
(6M, 4.5 mL). The mixture was refluxed for 14h, the solid was filtered, washed with cold
water (2 x 2 mL) and dried under vacuum at room temperature for 14h to give the H4tpaen
derivatives (22a-b).
Tetramethyl-6,6',6'',6'''-((ethane-1,2-diylbis(azanetriyl))tetrakis(methylene))-tetrakis(4-
morpholinopicolinate) (21a)
O
Yield = 71%
RMN 1H (400 MHz, CDCl3) : 2.72 (s, 4H), 3.7 (s, 24H), 3.88 (s,
N
N
O
12H), 3.94 (m, 12H), 7.14 (d, 4H, J = 2.8 Hz), 7.43 (d, 4H, J =
2.8 Hz); RMN C (100 MHz, CDCl3) : 29.7 (CH2), 52.6 (CH2),
CO2Me
N
13
N
N
CO2Me
55.5 (CH3), 60.5 (CH2), 109.9 (CHarom), 111.4 (CHarom),
N
MeO2C
N
N
MeO2C
N
27
N
O
O

ACCEPTED MANUSCRIPT
148.9 (Cq), 161.6 (Cq), 165.7 (Cq), 167 (CO); HRMS: [M+H]exp = 997.4768.
tetramethyl-6,6',6'',6'''-((ethane-1,2-diylbis(azanetriyl))-tetrakis(methylene))-tetrakis(4-
methoxypicolinate) (21b)
Yield = 81%
1
OMe
N
RMN H (400 MHz, CDCl3) : 2.81 (s, 4H), 3.84 (s, 12H), 3.86
(s, 8H), 3.98 (s, 12H), 7.24 (s, 4H), 7.52 (s, 4H); RMN 13C (100
MHz, CDCl3) : 52.9 (CH3), 55.4 (CH3), 60.2 (CH2), 60.6 (CH2),
109.9 (CHarom), 111.4 (CHarom), 149 (Cq), 161.9 (Cq), 165.8
(Cq), 167 (CO); HRMS: [M+H]exp = 777.3062
CO2Me
MeO
N
N
CO2Me
N
MeO2C
N
N
MeO2C
OMe
OMe
6,6',6'',6'''-((ethane-1,2-diylbis(azanetriyl))-tetrakis(methylene))-tetrakis(4-
morpholinopicolinic acid) (22a – L5)
Yield = 88%
1
RMN H (400 MHz, D2O) : 2.72 (s, 4H), 3.7 (s, 24H), 3.88 (s,
12H), 3.94 (m, 12H), 7.14 (d, 4H, J = 2.8 Hz), 7.43 (d, 4H, J = 2.8
Hz); RMN 13C (100 MHz, D2O) : 29.7 (CH2), 52.6 (CH2), 55.5
(CH3), 60.5 (CH2), 109.9 (CHarom), 111.4 (CHarom), 148.9 (Cq),
161.6 (Cq), 165.7 (Cq), 167 (CO); Anal. Calcd (%) for
C46H56N10O12: C, 58.71; H, 6.00; N, 14.89; O, 20.40; found: C,
58.89; H, 6.19; N, 14.82.
6,6',6'',6'''-((ethane-1,2-diylbis(azanetriyl))tetrakis(methylene))-tetrakis(4-methoxypicolinic
acid) (22b – L6)
Yield = 88%
1
OMe
RMN H (400 MHz, D2O) : 2.81 (s, 4H), 3.84 (s, 12H), 3.86 (s, 8H),
CO2H
MeO
3.98 (s, 12H), 7.24 (s, 4H), 7.52 (s, 4H); RMN 13C (100 MHz, D2O) :
52.9 (CH3), 55.4 (CH3), 60.2 (CH2), 60.6 (CH2), 109.9 (CHarom),
111.4 (CHarom), 149 (Cq), 161.9 (Cq), 165.8 (Cq), 167 (CO); Anal.
Calcd (%) for C34H36N6O12: C, 56.66; H, 5.04; N, 11.66; O, 26.64;
found: C, 56.81; H, 5.12; N, 11.84.
N
N
N
CO2H
N
N
HO2C
N
HO2C
OMe
OMe
4.2 Solvent Extraction Experiments
4.2.1 Chemicals and Solutions
Two different organic solutions were prepared from a mixture of N’-dimethyl-N,N’-
dioctylhexylethoxymalonamide (DMDOHEMA, 0.6 M) with di-2-ethyl-hexyl-phosphoric
acid (HDEHP, 0.3 M) in hydrogenated tetrapropene (TPH) or N,N,N’,N’-tetra-
octyldiglycolamide (TODGA, 0.2 M) with tributylphosphate (TBP, 0.5 M) in TPH.
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ACCEPTED MANUSCRIPT
Lanthanide-actinide stock solutions were prepared with Eu(NO3)3, 5H2O (0.1 mM) and trace
amounts (18MBq/L) of radionuclides 152Eu, 241Am and 244Cm at the desired acidity.
The aqueous stripping solutions containing the ligands were prepared from mother solutions
of H4tpaen derivatives (5 mM) in deionized water. The concentrations of ligands in the
solutions were measured by TOC (Total Organic Carbon) analysis and the acidity was
adjusted with nitric acid. Concentrations of nitric acid in the aqueous phase at equilibrium
([HNO3]eq) were determined by automatic titration with NaOH 0.1 M.
4.2.2 Pre-equilibrium
Organic phases were pre-equilibrated with an aqueous phase at the same acidity and ionic
strength as the back-extraction step but without Ln and An cations. For this purpose, a volume
of organic solution was contacted with the appropriate sodium nitrate (1 M) aqueous solution
during 15 min at ambient temperature with the aid of a vortex shaker (2000 min-1). The
organic / aqueous solution ratio was fixed to 1 / 3. After the pre-equilibrium of pH, the
resulting mixture was centrifuged at 4000 rpm for 5 min and the organic phase was separated
completely from the aqueous phase. The operation was repeated twice.
4.2.3 Extraction
The pre-equilibrated organic phase was then contacted with an equal volume of an aqueous
stock solution of 241Am, 244Cm and 152Eu for 15 min at ambient temperature. After 5 min of
centrifugation at 4000 rpm, an aliquot was sampled from both phases to evaluate the
concentrations of cations. Activities of 152Eu, 241Am and 244Cm in the aqueous and organic
phases were analyzed by alpha and gamma-spectrometry (respectively Silicon detector and
Hyper pure Ge detector, CANBERRA). The pH of the resulting aqueous phase at equilibrium
was measured and controlled using a pH meter.
4.2.4 Back-extraction
The previous organic phase loaded with cations was contacted with an equal volume of
aqueous solution containing the ligands during 15 min at 25 ± 0.5°C with the aid of a vortex
shaker (2000 min-1). The resulting mixture was centrifuged at 4000 rpm for 5 min and the
organic phase was separated completely from the aqueous phase. The pH value of aqueous
phase at equilibrium was measured and monitored with a pH meter. The activities of 152Eu,
241Am and 244Cm in the aqueous and organic phases were analyzed by alpha and gamma
spectrometry. For all samples, each step and analysis was repeated three times.
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