ISMSC 2007 - Università degli Studi di Pavia

Binding of uranyl and lanthanide cations by azacalix[n]arenes :
thermodynamic and kinetic approach
V. Hubscher-Bruder a , F. Arnaud-Neu a , C. Ambard a , P. Jost b , G. Wipff b
a Laboratoire de Chimie-Physique, Département des Sciences Analytiques, Institut
Pluridisciplinaire Hubert Curien, ULP, CNRS - ECPM, 25 rue Becquerel, 67087 Strasbourg
Cedex 02, France
b Laboratoire de Modélisation et de Simulations Moléculaires, Institut de Chimie, ULP, CNRS -
4 rue Blaise Pascal, 67070 Strasbourg, France
Azacalix[n]arenes are calix[n]arenes derivatives in which at least one methylene bridge is
replaced by a –CH2-N(R)-CH2- group.[1, 2] Compared with calixarenes, they have a larger more
flexible cavity and possess two different kinds of potential binding sites. Previous structural
studies on azacalixarenes showed their ability to complex uranyl and lanthanide cations even
without the presence of a base, by internal transfer of the phenolic protons to the nitrogen
atoms.[3-5]
We present here the thermodynamic and kinetic studies
of the binding of uranyl and some trivalent lanthanides
(La 3+ , Nd 3+ , Eu 3+ and Yb 3+ ) by the two azacalixarenes, pmethyl-N-tetrahomodiazacalix[4]arene
[1] and p-chloro-
N-benzylhexahomotriazacalix[3]arene [2]. These
calixarenes are locked in cone conformation by strong
intramolecular hydrogen bonds.[6]
H3C
H 3C
OH
N
HO
OH HO
N
CH 3
CH3
Cl
N OH N
OH HO
N
Cl Cl
[1] [2]
PSA 75
In the first part, the stoichiometry and the stability constants of the different complexes formed in
acetonitrile determined using UV absorption spectrophotometry will be presented. The results
showed the formation of strong 1:1 complexes in all cases (log in the range 3.8 - 6.4), whose
stability constants were strongly dependent on the ligand and medium (10 -2 M Et4NNO3 as
supporting electrolyte, presence or absence of Et3N as base). They could be explained by
considering the size and protonation state of the ligand, the coordination mode, the nature of
the interactions, in the light of molecular modelling studies using molecular dynamics in
explicitely represented solutions.
In the second part, the stopped-flow spectrophotometric technique was used to study the fast
kinetics of complexation of uranyl (25°C). The rate constants of the complexation reaction were
determined from the exponential variations of the absorbances vs. time according to the
pseudo-first order method. They were observed to depend on the presence or absence of base.
The results could be interpreted on the basis of previous X-ray studies of the complexes
isolated in the solid state [3-5], ESI-MS data and molecular dynamics modelling studies and a
mechanisms were proposed showing the formation in one or more steps of either external or
internal complexes.
[1] Takemura H., J. Inclusion Phenom., 2002, 42, 169.
[2] Niikura K., Anslyn E. V., J. Chem. Soc., Perkin Trans. 2, 1999, 2769.
[3] Thuéry P., Nierlich M., Vicens J., Takemura H., J. Chem. Soc., Dalton Trans., 2000, 279.
[4] Thuéry P., Nierlich M., Vicens J., Takemura H., Polyhedron, 2000, 19, 2673.
[5] Thuéry P., Nierlich M., Vicens J., Masci B., Takemura H., Eur. J. Inorg. Chem., 2001, 637.
[6) Masci B., in “Calixarenes 2001”, Asfari Z., Böhmer V., Harrowfield J., Vicens J., Eds, Kluwer
Academic Publishers, Dordrecht, 2001, p.235.
Anion recognition by triurea based macrocycles
PSA 76
E. Jobin a , V. Hubscher-Bruder a , F. Arnaud-Neu a , S. Michel a , V. Böhmer b , D. Meshcheryakov b ,
M. Bolte c
a Laboratoire de Chimie-Physique, Département des Sciences Analytiques, Institut
Pluridisciplinaire Hubert Curien, ULP, CNRS - ECPM, 25 rue Becquerel, 67087 Strasbourg
Cedex 02, France
b J.-Gutenberg-Universität, 55099 Mainz, Germany
c J.-W.-Goethe Universität, 60439 Frankfurt/Main, Germany
Anion recognition is today an increasingly topical field in supramolecular chemistry due to the
possible applications in ion selective sensors for biological and environmental concerns. The
design of efficient and selective synthetic anion receptors is not an easy task because of
specific anion properties (negative charge, large size, various geometries, high solvation free
energies, pH-dependent forms) which have to be taken into account. [1-4] Urea functions
which are powerful hydrogen bond donors can be used to design neutral macrocyclic
receptors. Some of these receptors have already shown selective recognition of anions.[5-6]
We report here the synthesis and the binding properties of four cyclic trimers in which urea
functions are linked by all combinations of rigid xanthene (X) and flexible diphenylether (D)
subunits.
The complexing abilities of these molecules towards different anions (Cl - , Br - , SCN - , NO3 - ,
H2PO4 - , HSO4 - , ClO4 - and AcO - ) have been assessed by 1 H NMR, UV-absorption
spectrophotometry and microcalorimetry in various solvents. In acetonitrile, complexes with
different stoechiometries are formed depending on the ligand and the anion. Their
thermodynamic parameters (stability constants, complexation enthalpies and entropies) are
discussed in terms of rigidity or flexibility of the ligands and of geometry and basicity of the
anions.
[1] S. Mangani, M. Ferraroni, in “Supramolecular Chemistry of Anions”, A. Bianchi, K. Bowman-
James, E. Garcia-Espana (Editors), Wiley-VCH, New-York, 1997, 63.
[2] P.D. Beer, P.A. Gale, Angew. Chem. Int. Ed., 2001, 40, 486.
[3] P.A. Gale, Coord. Chem. Rev., 2003, 240, 191.
[4] R.S. Dickins, D. Parker, in “Macrocyclic Chemistry: Current Trends and Future
Perspectives”, K. Gloe (Editor), 2005, 121.
[5] C.R. Bondy, P.A. Gale, S.L. Loeb, J. Am. Chem. Soc., 2004, 126, 5030
[6] D. Meshcheryakov, V. Böhmer, M. Bolte, V. Hubscher-Bruder, F. Arnaud-Neu, H.
Herschbach, A. Van Dorsselaer, I. Thondorf, W. Mögelin, Angew. Chem. Int. Ed., 2006, 45,
1648.