ISMSC 2007 - Università degli Studi di Pavia

PSB 53
New chromogenic sensors using hybrid organic-inorganic nanomaterials
Elena Aznar a , Pilar Calero a , Carmen. Coll a , Maria Dolores Marcos a , Ramón Martínez-Máñez a ,
Félix Sancenón a , Juan Soto a , Pedro Amorós b , Jose Manuel Lloris c , Celia Silvestre c
a) Instituto de Química Molecular Aplicada (IQMA), Universidad Politécnica de Valencia,
Camino de Vera s/n, 46022, Valencia, Spain
b) Institut de Ciència dels Materials (ICMUV), Universitat de Vàlencia, 46071, Vàlencia, Spain.
c) Instituto Tecnológico de la Construcción (AIDICO), Avenida Benjamín Franklin 17, 46980,
Paterna (Valencia), Spain.
The blending of supramolecular chemistry with material science is in recent times leading to the
preparation of hybrid organic-inorganic materials that opens new and exciting possibilities of
applications in the field of molecular sensing. Some advanced examples have recently been
reported based on the use of biomimetic concepts and gated supramolecular chemistry in
nanomaterials. [1] Some examples developed in our research group were based on the
formation of nanometer-sized binding pockets by anchoring suitable binding sites to the surface
of preorganised solids in order to create sensing ensembles for the chromo-fluorogenic sensing
of target species. Also recently we have reported for the first time the design of a colorimetric
probe by using nanoscopic gate-like scaffoldings. [2,3] Inspired by these findings we report
herein some novel hetero-supramolecular sensing systems based on nanoscopic scaffoldings
for the selective and sensitive colorimetric signalling in water of borate and fatty acids.
Borate sensing is based on the use of molecular nanoscopic gate-like ensembles as advanced
chromo-fluorogenic sensory materials. The concept involves the development of molecular
gate-like systems (on a MCM41 mesoporous support containing a polyalcohol anchored to the
pore outlets) that is selectively closed in the presence of borate. Borate coordination inhibits the
delivery of a dye (Ru(bipy)3 2+ ) in the inner pores of the mesoporous scaffolding therefore
signalling its presence. Also inhibition of dye delivery and colorimetric recognition has been
achieved using a polarity-controlled gate-like structure on mesoporous materials for the
signalling of fatty acids in aqueous environments.
A carboxylate sensing system in water has also been prepared by the grafting of
spirobenzopyrane derivatives as signalling subunit and ureas and thioureas as binding site into
silica nanoparticles (20 nm of diameter). The coordination of long-chain carboxylates with the
urea/thiourea binding sites leads to the formation of a highly hydrophobic monolayer that
stabilized the neutral form of the spirobenzopyran and induced a colour change from violet
(cationic form of the spirobenzopyran) to light pink (neutral form of the spirobenzopyran).
[1] A. B. Descalzo, R. Martínez-Máñez, F. Sancenón, K. Hoffman, K. Rurack, Angew. Chem.
Int. Ed., 2006, 45, 5924-5948.
[2] See for instance: M. Comes, G. Rodríguez-López, M. D. Marcos, R. Martínez-Máñez, F.
Sancenón, J. Soto, L. A. Villaescusa, P. Amorós, D. Beltrán, Angew. Chem. Int. Ed., 2005, 44,
2918-2922. A.B. Descalzo, K. Rurack, H. Weibhoff, R. Martínez-Máñez, M.D. Marcos, P.
Amorós, K. Hoffmann, J. Soto, J. Am. Chem. Soc., 2005, 127, 184-200
[3] R. Casasús, E. Aznar, M. D. Marcos, R. Martínez-Máñez, F. Sancenón, J. Soto, P. Amorós,
Angew. Chem. Int. Ed., 2006, 45, 6661-6664.
PSB 54
Computational Studies on the Cooperative AND Ion-Pair recognition by
Heteroditopic Calix[4] diquinone Receptors.
Sérgio Santos a , Michael D. Lankshear b , Paul D. Beer b and Vítor Félix a
a
Departamento Química, CICECO, Universidade de Aveiro, 3810-193 Aveiro, Portugal.
b
Inorganic Chemistry Laboratory, Department of Chemistry, University of Oxford, South Parks
Road, Oxford, OX1 3QR, U.K.
A computational study on the recognition of MX alkali
halide ion-pairs (M = Li + , Na + , K + , Rb + , Cs + and NH4 + and
X=Cl - , Br - and I - ) by five novel heteroditopic
calix[4]diquinone receptors (see right) is hereby
reported. 1 These synthetic receptors allow cooperative
binding to the associated ion-pairs, revealing an
unprecedented AND recognition phenomena, in which
the receptors display no affinity towards the free ions, but
bind strongly the ion-pairs. A first insight into the binding
interaction was obtained through gas-phase
conformational analyses of both free and complexed
receptors, and conventional solution molecular dynamics.
Succinctly results showed that all receptors have enough
flexibility to accommodate different sized ion-pairs; however larger macrocycles prefer larger
ion-pairs. Subsequently, the relative binding free energies (G) were obtained by means of
thermodynamic integration calculations. Generally, the theoretical G values are in excellent
agreement with those derived from the experimental binding constants, thus validating our
calculations. The insertion mechanism of the ion-pairs into the receptors was investigated by
means of Potentials of Mean Force. It was shown that the contact ion-pair interaction occurs
through a cone conformation of the calix entity of the receptor, so as to allow - stacking
interactions between one
diquinone unit and the
isophthalamide fragment, which
is adopted after folding both
diquinone rings from a 1,3
alternate into a cone
MX
conformation (see left). In this
binding arrangement, the anion
and cation binding sites are
arranged in close proximity
allowing the AND gate
recognition process. The
enhanced affinity revealed by -NO2 containing receptors 2 and 4, relative to corresponding 1
and 3, investigated by DFT NBO calculations, was attributed to the delocalization of the charge
distribution due to the presence of that additional electron withdrawing group, leading to an
increased acidity of the hydrogens of the amide clefts.
[1] Lankshear, M. D.; Cowley, A. R.; Beer, P. D., Chem. Commun. 2006, 612-614.
Acknowledgements: Sérgio M. Santos thanks FCT – Fundação para a Ciência e Técnologia –
for the financial support under the PhD scholarship SFRH/BD/29596/2006.