ISMSC 2007 - Università degli Studi di Pavia

Chiral chemosensors for enantiomeric recognition of aspartate
Ana M. Costero a , Manuel Colera a , Pablo Gaviña a , Margarita Parra a , Miklós Kubinyi b , Krisztina
Pál b , Mihály Kállay b
a. Department of Organic Chemistry. Universidad de Valencia. Valencia. Spain. b Department of
Physical Chemistry, University of Technology and Economics. Budapest. Hungary
Over the last years, the development of chemosensors capable of recognizing anionic species
have aroused great interest.[1] However, enantioselective recognition and sensing of
biologically relevant molecules remains a major challenge for host-guest chemists.[2] Although
several receptors have been developed for chiral dicarboxylates[3] less examples of
enantioselective chemosensors have been described.[4] In our efforts to develop fluorescent
chemosensors for dicarboxylates, now we would like to report the preparation of the
cyclohexane based chiral ligands (+)-1, and (-)-1 and their utility in selective recognition of
aspartate (2) versus glutamate (3) anions and what is more interesting the enantiomeric sensing
of L-aspartate versus D-aspartate (Chart1).
The relative configuration of the
stereocentres in (+)-1 and (-)-1 was perfectly
established by NMR techniques and the
absolute configurations were determined
from the CD spectra with help of the exciton
chirality rule.[5]
In the complexation experiments in DMSO
the reactions with L-aspartate (L-2), D-
EtOOC
NHCS NHR
NHCS NHR
aspartate (D-2), L-glutamate (L-3) and D-glutamate (D-3), all as their tetramethylammonium
(TMA) salts were studied. The stoichometries and equilibrium constants were determined by
fitting of the UV spectra of equilbrium mixtures. The fluorescence spectrum of (-)-1 substantially
changes upon the addition of D-2. The band of the pure ligand shifts from 410 nm to longer
wavelengths and a new band emerge at 495 nm. The latter feature does not appear when L-2 is
added to the solution. As can be expected, the opposite behaviour can be observed with ligand
(+)-1. The appearance of the new band may be related to the fomation of an excimer species.
[1] L. Fabbrizzi, M. Licchelli and G. Labaioli, Coord. Chem. Rev. 2000, 205, 85-108. (b) K.
Nikura and E.V. Anslyn, J. Am. Chem. Soc. 1998, 120, 8533-8534. (c) P. Anzenbacher, Jr.,
K. Jursíková and J.L. Sessler. J. Am. Chem. Soc. 2000, 122, 9350-9351.
[2] C.S. Wilcox, Chem. Soc. Rev. 1993, 22, 383-395.
[3] See for example. (a) A. Ragusa, S. Rossi, J.M. Hayes, M. Stein and J.D. Kilburn, Chem. Eur.
J. 2005, 11, 5674-5688. (b) S.Rossi, G.M. Kyne, D.L. Turner, N.J. Wells, and J.D. Kilburn,
Angew. Chem., Int. Ed. 2002, 41, 4233-4236. (c) C.-S. Lee, P.-F. Teng, W.-L. Wong, H.-L.
Kwong and A.S.C. Chan, Tetrahedron 2005, 61, 7924-7930.
[4] (a) A.J. Folmer, L. Frantz; M. Vincent and E.V. Anslyn, J. Am. Chem. Soc. 2005, 127, 7986-
7987. (b) K. Tsubaki, D. Tanima, M. Nuruzzaman, T. Kusumoto, K. Fuji and T. Kawabata, J.
Org. Chem. 2005, 70, 4609-4616.(c) S. Pagliari, R. Corradini, G. Galaverna, S. Sforza, A.
Dossena, M. Montalti,L. Prodi, N. Zaccheroni and R.Marchelli, Chem.Eur.J. 2004, 10, 2749-
2758. (d) W.-L.Wong, K.-H. Huang, P.-F.Teng, C.-S.; Lee, and H.-L. Kwong, Chem.
Commun. 2004, 384-385.
[5] N. Berova, N. Nakanishi, in Circular dichroism: principles and applications, Ed. N. Berova, N.
Nakanishi and R. W. Woody, Wiley-VCH, New York, 2000, 2nd edn., pp. 337-382.
EtOOC
EtOOC
EtOOC
(+)-1
(-)-1
NHCSNHR
NHCSNHR
R=
Chart 1
- O2C
- O2C
H
H
NH2
CO2 -
(R)-2 L-aspartate
CO 2 -
H2N H
-
O 2C
(S)-2 D-aspartate
NH2
CO 2 -
(R)-3 L-glutamate
PSB 35
Residual and exploitable fluorescence in micellar self-assembled ON-OFF
sensors for Copper(II)
Piersandro Pallavicini, Carlo Mangano, Luca Pasotti and Stefano Patroni
Dipartimento di Chimica Generale, Università di Pavia, v.le Taramelli, 12 – 27100 Pavia
PSB 36
ON-OFF fluorescent sensors are said to display full emission (ON state) in the absence of the
target species, while the emission is nihil (OFF state) when the target species is added.
However, this is often an oversimplified view. As a matter of fact, when all the receptors
available in the sensing medium are binding the species to be sensed (e.g. in large excess of
the target), the read fluorescence may be not zero. Calling I0 the full fluorescence of the system
(ON state) and IRES the residual fluorescence intensity in the presence of excess target species,
IRES may be as high as 5-20% of I0. Moreover, in the conditions in which the receptor can
effectively interact with the target species, the emission of the fluorophore could be not full even
before that the target species is added (e.g. when the receptor is an amino ligand and the
working pH is basic). Accordingly, it should be remembered that the ON state displays an
“exploitable” fluorescence intensity, IEXP, that could be lower than I0. When the sensing system
is a micellar self-assembly of the Receptor and of the Fluorophore, IRES and IEXP may depend on
many factors such as R and F shape, R lipophilicity, reciprocal positioning of R and S inside
micelles, acid/base properties of R, redox properties of its complex with the target.[1] In this
work we have examined IEXP and IRES for a series of micellar sensors for Cu 2+ , made of pyrene
(F) plus a R featuring the same amino-amido binding site and different lipophilizing groups.
IRES is found to depend on the R lipophilicity, that may be quantitatively evaluated by measuring
the difference between the protonation constants of a model ligand not included in micelle
(L0H2) and the protonation constants of the micellized lipophilic receptors.
[1] a) Y. Díaz-Fernandez, A. Perez-Gramatges, S. Rodríguez-Calvo, C. Mangano and P.
Pallavicini, Chem. Phys. Lett., 2004, 398, 245; b) Y. Diaz-Fernandez, F. Foti, C. Mangano, P.
Pallavicini, S. Patroni, A. Perez-Gramatges and S. Rodriguez-Calvo, Chem. Eur. J., 2006, 12,
921-930