ISMSC 2007 - Università degli Studi di Pavia

PSB 17
Metal controlled anion interaction at the thiourea subunit: low-spin iron(II)
2-formylpyridine-thiosemicarbazone complexes
Lorenzo Mosca a , Valeria Amendola a , Massimo Boiocchi b , Luigi Fabbrizzi a , Antonio Poggi a
a Dipartimento di Chimica Generale, Università di Pavia, 27100 Pavia, Italy
b Centro Grandi Strumenti, Laboratorio di Cristallografia, Università di Pavia, 27100 Pavia, Italy
Thiourea is a powerful donor of bifurcate H-bonds and its derivatives are currently used for
anion recognition and sensing in non-aqueous media. However, more basic anions may induce
deprotonation of one of the two NH fragments. [1] For instance, benzylidenethiourea
derivatives of type 1 form stable 1:1 H-bond complexes with CH3COO and H2PO4 in MeCN,
but, in presence of two equiv. of F , undergo deprotonation. [2]
X
N
N
H
S
N
H
H +
X
N
S
N N
H
X
N
S
N N
H
1 X = CH; 2 X = N 3 4
We have now observed that system 2 shows a very low affinity towards anions, even in the
poorly polar solvent CHCl3, probably due to the existence of an intramolecular H-bond
interactions. On the other hand, 2 (= HL) behaves as a terdentate ligand with transition metals.
For instance, a crystalline complex salt of formula [Fe II (HL)2](CF3SO3)2 . H2O was isolated, whose
X-ray structure is shown in the Figure. The low-spin iron(II) complex exhibits a distorted
octahedral geometry, with the ligand adopting a meridional coordination mode (NFeS angle =
165°). Moreover, in a CHCl3 solution, on titration with strong
base, the complex undergoes two stepwise deprotonation
equilibria, according to the scheme:
[Fe II (HL)2] 2+ [Fe II (HL)(L)] + [Fe II (L)2]
It is suggested that deprotonation takes places at the hydrazide
NH fragment (formula 3), followed by electronic rearrangement
to the resonance formula 4. Metal coordination by the thiolate
group has been documented by a number of structures of Fe II
complexes with analogous ligands. The [Fe II (HL)2] 2+ complex
exposes two thiourea subunits towards the outside and could act
as a ditopic receptor for anions. However, on titration with
oxoanions of varying basicity (e.g. CH3COO , NO2 ), two-step
deprotonation takes place. Only the poorly basic anion NO3
forms genuine H-bond complexes with [Fe II (HL)2] 2+ , of 1:1 and
2:1 stoichiometry, whose logK values differ only for the statistical
factor. Present results emphasize the role of metals in polarizing
the NH fragments of the thiourea subunit and open the way to
the design of metal containing anion receptors of novel selectivity.
[1] D. Esteban-Gómez, L. Fabbrizzi, M. Licchelli, E. Monzani, Org. Biomol. Chem., 2005, 3,
1495–1500.
[2] M. Bonizzoni, L. Fabbrizzi, A. Taglietti, F. Tiengo, Eur. J. Org. Chem., 2006, 3567-3574.
PSB 18
Peptides transport through liquid membrane by calix[n]arene derivatives
Lucia Mutihac a , Hans-Jürgen Buschmann b , Radu-Cristian Mutihac b , Eckhard Schollmeyer b
a
University of Bucharest, Department of Analytical Chemistry, 4-12 Regina Elisabeta, 030018,
Bucharest, Romania
b
Deutsches Textilforschungszentrum Nord-West, e.V., Institut an der Universität Duisburg-
Essen, Adlerstrasse 1, D-47798 Krefeld, Germany
The investigation of the nature of interactions involved in ligand-peptide complex formation is of
particular relevance for understanding several specific biomolecular interactions which play a
key role in regulation of cellular processes [1-4]. Along this topics, the study of factors that
contribute to the complex formation are of current interest in peptide chemistry.
In order to outline the possibility of calixarenes acting as an carriers through membrane, we
have investigated some aspects of the transport through chloroform liquid membrane of
peptides, namely: glycyl-glycine, glycyl-L-alanine, glycyl-L-leucine, glycyl-L-phenylalanine, Lleucyl-glycine,
L-leucyl-L-alanine, and glycyl-L-valine with with p-tert-butylcalix[n, n = 4,6,
8]arenes in the presence of tropaeolin 00. The effects of physicochemical parameters involved
in the process transport such as the structure of calixarene, the nature of the anion used as
counterion, and the structure of peptide have been studied. Additionally, the influence of the
composition and the structure of the compounds under study upon the partition processes
occurring in triphasic systems have been reported. A relationship between the transport yields
through liquid membrane of peptides and their structural characteristics has been pointed out.
The results showed that the inclusion abilities of the investigated hosts were correlated with
their conformational properties.
[1] M. W. Peczuh, A. D. Hamilton, Chem. Rev. 100, 2479 (2000). [2] C.D. Gutsche, Calixarenes
Revisited, The Royal Society of Chemistry, Cambridge, UK, 1998. [3]. J. Vicens, V. Böhmer,
Calixarenes- A Versatile Class of Macrocyclic Compounds, Kluwer Academic Publishers,
Dordrecht, 1991. [4] L. Mutihac, H.-J. Buschmann, R.-C. Mutihac, E. Schollmeyer, J. Incl.
Phenom. Macrocyclic Chem. 51, 1, 2005.