ISMSC 2007 - Università degli Studi di Pavia

PSA 35
Molecular design of macrocyclic receptors containing two phenanthroline
units and evaluation of their binding ability
Carla Cruz a , Rita Delgado b,c , Michael G. B. Drew d , Vítor Félix a
a Departamento Química, CICECO, Universidade de Aveiro, 3810-193 Aveiro, Portugal
b Instituto de Tecnologia Química e Biológica, UNL, Apartado 127, 2781-901 Oeiras, Portugal
c Instituto Superior Técnico, Av. Rovisco Pais, 1049-001 Lisboa, Portugal
d School of Chemistry, University of Reading, Whiteknights, Reading RG6 6AD, UK
Carboxylate substrates participate in many chemical, biological and environmental processes.
A wide number of these compounds is used in several industrial (e.g. toys) and agricultural
applications (e.g pesticides). 1 Searching for suitable synthetic sensors for these substrates, the
molecular design of macrocyclic receptors incorporating two
phen moieties was undertaken. 3 The (Hi[26]phen2N4O2) i+ ,
(Hi[26]phen2N6) i+ and (HiMe2[30]phen2N6) i+ receptors, were
synthesized and their acid-base behaviour evaluated by
potentiometric and 1 H NMR methods. 3 For [26]phen2N4O2, five
protonation constants were determined, the fifth proton is
located in one of the phen nitrogen atoms. This assignment,
was confirmed by the crystal structures of the receptor as
bromide and chloride salts. In the solid state, the
(H5[26]phen2N4O2) 5+ cation adopts a “horseshoe” topology with
{(H5[26]phen2N4O2)Br4(H2O)} +
enough room to accommodate three or four halogen anions
through the N–H···X (Cl - or Br - ) hydrogen bonding interactions
(left). This structural result prompted us to envisage these
receptors as good candidates to promote the selective uptake of carboxylate substrates through
the establishment of multiple and cooperative electrostatic interactions and hydrogen bonds.
The binding interaction of the three receptors with several carboxylates (bzc - , naphc - , anthc - ,
pyrc - , ph 2- , iph 2- , tph 2- and btc 3- ) and herbicides (PMG, ATCP and
2,4-D) was investigated in water. The binding data available now
show that the Hi[26]phen2N4O2 i+ uptakes selectively charged or
extended aromatic carboxylate anions, such as btc 3- (4.0–8.5 pH
range) and pyrc - (pH < 4.0) from an aqueous solution containing
the remaining aliphatic and aromatic anions as pollutants or
contaminants. A further insight on the molecular recognition
process was obtained by molecular dynamics simulations in water
solution. For example, the binding of btc 3- to the
(H5[26]phen2N4O2) 5+ occurs with insertion of the anion between
the two phen units showing that the molecular recognition
involves N–H···O multiple hydrogen bonds complemented by -
stacking interactions (right).
[1] V. Amendola, M. Bonizzoni, D. Esteban-Gómez, L. Fabbrizzi, M. Licchelli, F. Sancenón and
A. Taglietti, Coord. Chem. Rev. 2006, 250, 1451–1470.
[2] K. E. Krakowiak, J. S. Bradshaw, W. Jiang, N. K. Dalley, G. Wu and R. M. Izatt,
J. Org. Chem. 1991, 56, 2675–2680.
[3] C. Cruz, R. Delgado, M. G. B. Drew and V. Félix, J. Org. Chem. 2007, in press.
The authors acknowledge the financial support from Fundação para a Ciência e Tecnologia
(FCT) and POCI, with coparticipation of the European Community fund FEDER (Project n.
POCI/QUI/56569/2004). C. C. acknowledges the PhD grant from FCT (SFRH/BD/19266/2004)
and ITQB for the access to the potentiometric and NMR facilities.
Controlled uptake-release of the citrate anion in a system capable of
pH-driven triple Cu 2+ translocation
Giacomo Dacarro, Piersandro Pallavicini, Angelo Taglietti
Dipartimento di Chimica Generale, Università di Pavia, v.le Taramelli, 12 – 27100 Pavia
The pH-controlled translocation of one or two metal cations plays an important role for the
change in shape and in the secondary coordinative properties of the molecular system inside
which the process takes place.[1] As an example, we have recently demonstrated that in a
macrocyclic system capable of double Cu 2+ translocation, the pH-controlled movement of the
cations may be exploited for the uptake-release of a bridging imidazolate anion.[2] We have
now sinthesized non-cyclic ligands capable of simultaneous double and triple pH-controlled
Cu 2+ translocation. The movement of the cations from sites in which they are coordinatively
saturated to sites in which they are coordinatively unsaturated candidates these system for the
controlled uptake-release of multidentate anionic species, thanks also to the particular geometry
of the multicomponent ligands. In particular, we have found that in a system capable to
simultaneously move three Cu 2+ cations, the citrate anion is selectively bound at pH 6, when the
Cu 2+ cations are inside binding sites in which only four donors are coordinating them, giving a
complex with an overall + 6 charge. A jump to pH values higher than 8 makes the three Cu 2+
cations to move inside deprotonated amino-amido binding sites, forming a coordinatively
saturated and neutral complex. As a consequence, the citrate anion is released.
N N
N
N
O
NH
HN
O O
HO N NHO
NHNH
N
N
HNO NH
O
NH
HN
O
O
O
HN NH
O
O
O
- 6H +
+ 6H +
N N
N
N
HN NH
N
N
HN NH
HN
NH
N N
- - N
N O
N
N
-
- O
O -
- O
O
O
+
O
O
O
O
PSA 36
[1] a) P. Pallavicini, G. Dacarro, C. Mangano, S. Patroni, A. Taglietti and R. Zanoni, Eur. J.
Inorg. Chem., 2006, 4649-4657; b) A. Aurora, M. Boiocchi, G. Dacarro, F. Foti, C. Mangano, P.
Pallavicini, S. Patroni, A. Taglietti and R. Zanoni, Chem. Eur. J., 2006, 12, 5535; c) V.
Amendola, L.Fabbrizzi, C. Mangano, H. Miller, P. Pallavicini, A. Perotti and A. Taglietti, Angew.
Chem. Int. Ed., 2002, 41, 2553; d) V. Amendola, L. Fabbrizzi, C. Mangano and P. Pallavicini,
Acc. Chem. Res., 2001, 34, 488
[2] L. Fabbrizzi, F. Foti, S. Patroni, P. Pallavicini and A. Taglietti, Angew. Chem. Int. Ed., 2004,
43, 5073
O
O
O