ISMSC 2007 - Università degli Studi di Pavia

Lead(II) complexation by calix[4]-hydroxamates.
Synthesis, X-ray structure and potentiometric studies in ion selective
electrodes
Maria Bocheska and Urszula Lesiska
Department of Chemical Technology, Chemical Faculty, Gdask University of Technology, 80-
952 Gdask, Poland, marboch@chem.pg.gda.pl
Hydroxamic acid moiety is found in naturally occurring metal complexing compounds,
known as siderophores, which are especially strong iron(III) chelators. [1]. These natural
compounds of rather low molecular weight are produced by bacteria and fungi and play crucial
role in the iron uptake and transport into the cell. But it was also found that compounds with
hydroxamic units are able to complex other metal cations, such as for example Cu(II), Al(III),
Pb(II) or uranyl ions. Such ability of siderophores generate many important biological activities
(antibacterial, antifungal, anticancer or specific enzyme inhibition) which makes them worth to
be considered as a potential pharmaceutics. Also synthetic ligands are planned based on the
structure of natural siderophores and on coordination geometry of the metal ion to be complex.
The determination of heavy metals in variety of samples (drinking or waste waters) is of
urgent need. Naturally occurring siderophores seem to be very effective chelators, active in
metal recovery and waste remediation. However, majority of these compounds known in nature
are water soluble and such property disqualify them from the use as active materials for
chemical sensors. To use them for such purpose in chemical sensors (ion-selective electrodes
(ISEs) they should of higher lipophilicity.
We use t-butylcalix[4]arene as a scaffold for building synthetic siderophores. We present
here synthesized hydroxamate derivatives of p-tert-butylcalix[4]arene and their ionophoric
properties when applied in the membrane of ion selective electrodes (ISEs). The electrodes are
lead (II) selective with nernstian slope in a wide linear range (10 -6 – 10 -1 M). Crystal structures of
the complex of ligand 1 with Pb(ClO4)2 was obtained and will be presented. The interaction with
lead(II) cations was also studied by 1 H NMR [2,3].
[1] J.B. Neilands, Science, 156, 1967, 1443
[2] U. Lesiska, PhD Thesis, Gdansk, Poland 2007-04-20
[3] U. Lesiska, M. Bocheska, publication in preparation
Acknowledgement
FINANCIAL SUPPORT FROM GDASK UNIVERSITY OF TECHNOLOGY (DS 014668/003) ARE GRATEFULLY
ACKNOWLEDGED
.
PSA 21
Anion receptors based on the cooperation of metal coordination and
hydrogen bonding
Renato Bonomi, Fabrizio Mancin and Umberto Tonellato
Università di Padova, Dipartimento di Scienze Chimiche, via Marzolo 1, 35131 Padova, Italy
Anions are the most important species in the natural world and are critically involved in
many of known chemical processes. They are at the center of energy transduction (ATP),
biological information processing (DNA and RNA) or as a cofactors in many chemical
reactions.[1] The synthesis and study of synthetic receptors for the purpose of anion recognition
continues, therefore, to attact increasing attention within the supramulecular community.
Since the beginning of anion coordination chemistry the main strategies in the design
of synthetic anion complexing reagents have focused on cationic polyammonium, guanidinium
system and a variety of Lewis acidic containing metals ions receptors.[2] In this systems the
Coulombic forces largely dominate the long-range noncovalent communication between
molecules. Neutral organic receptors which bind anions solely via favourable hydrogen bond
interactions, instead, have also been recently exploited. The spherical anion is then bind by an
array of hydrogen bonds within a cavity formed in a molecular framework. A better selectivity is
achievable with this strategy, but low affinity is expected in competitive protic solvents.
In this
communication we
describe a strategy to
obtain new anion
receptors with high
binding constats and
selectivity in acquoses
solvents. This strategy is
based on the
introduction of groups
capable to donor
hydrogen in the
structure of suitable
metal ion complexes. In
H
N N
N
Mn+ A- H
H
H H
H
N
N
1
N
this way, the metal ion provides high affinity for the substrate either by coordination and
electrostatic interactions while hydrogen bond donor groups cooperate to increase the substrate
affinity and provide a size selective cleft for the anion itself.
In the case of ligands 1 and 2, reported in Figure 1, three or two amino groups have been
introduced in the in such position to allows the formations of intracomplex hydrogens bonds with
the metal bound substrate. Preparation of the ligands and their Cu(II) and Zn(II) complexes and
anion recognition resuts are reported.
[1] Schrader, T.; D.Hamilton, A. Functional Synthetic Receptors, Wiley-VCH, 2005.
[2] Beer, P.D.; Cadman, J. Coord. Chem. Rev. 2000, 205, 131.
N
H
Figure 1
H
A
H
N N
-
N
N
M n+
N
N N
2
PSA 22
H