ISMSC 2007 - Università degli Studi di Pavia

PSA 33
Ratiometric Ion Sensors by Rational Design: Modulated Resonance Energy
Transfer in Fluorescence Sensing of Cations
Ali Coskun, Ruslan Guliyev and Engin U. Akkaya*
Middle East Technical University, Department of Chemistry, 06531 Ankara, Turkey.
Fluorescent chemosensor design is an active field of supramolecular chemistry, not only
because of potential practical benefits in cell physiology, analytical and environmental
chemistry, but also as a proving ground for manipulation and/or engineering of various
photophysical processes towards an ultimate goal of selective and sensitive signaling of
targeted molecular or ionic species. Recently, boradiazaindacenes have become the
fluorophore of choice in many chemosensor designs, not only because of their exceptional
properties as fluorophores, but also as a result of their remarkably rich chemistry. Previously,
we reported[1] a dimeric boradiazaindacene, which can be converted into an energy transfer
cassette and furthermore, into a ratiometric ICT (internal charge transfer) based cation sensor,
selective for silver ions, all through simple structural modifications. In that design the two
fluorophores were kept very close to each other, so that the through-space EET was nearly
100% efficient, thus creating a large pseudo-Stokes’ shift chemosensor. ICT based
chemosensors typically, have an advantage of two distinct emissive states, (analyte-free and
analyte-bound) which makes these chemosensors potentially wavelength-ratiometric i.e.,
internal referencing of the signal is possible, eliminating potential artifacts.[2]
We now demonstrate that the EET modulation can be either on the energy donor or
energy acceptor site.
EET
D A R
Larger EET
D A R
[1] Coskun, A.; Akkaya, E. U. J. Am. Chem. Soc. 2005, 127, 10464.
[2] Coskun, A.; Akkaya, E.U. J. Am. Chem. Soc. 2006, 128, 14474.
D
EET
Smaller EET
A
D A
Artificial transmembrane ion channels from commercial surfactants
Khayzuran S. J. Iqbal, Marcus C. Allen, Flavia Fucassi and Peter J. Cragg
PSA 34
School of Pharmacy and Biomolecular Sciences, University of Brighton, Brighton BN2 4GJ, UK
As part of our ongoing interest in artificial transmembrane ion channels 1 we wished to harness
the membrane penetrating qualities of these surfactants to the ion specific filtering abilities of
rigid macrocycles. Thus far the examples in the literature relate predominantly to modified
calixarenes 2 and derivatives that pair up within a bilayer to effect transport in a manner
reminiscent of the gramicidin class of antibiotics. 3 Here we report preliminary results for Na +
transport across a phospholipid bilayer by a new class of transmembrane ion channel mimetic
compounds where the filtering effect of a calixarene has been coupled to the membrane
piercing qualities of a commercial surfactant. Compound 1 was prepared through tosylation of
commercially available Triton X-100 ® . Reaction of 1 with 4-t-butylcalix[4]arene in a 2:1 ratio,
according to literature procedures for 1,3-dialkylation of calixarenes, 4 yielded compound 2. We
then prepared a trisubstituted derivative with no free phenolic groups, 3, from the larger
homologue, 4-t-butylcalix[6]arene trimethylether. Electrophysiology data show that at low
concentrations 3 forms single channels (Na + flux: 7 x 10 6 ions s -1 ) but at higher concentrations
multiple insertions occur without compromising membrane integrity.
Synthesis of Tritonylcalixarenes Bilayer conduction of Na + : a) 4 µM and b) 64 µM
[1] K. S. J. Iqbal and P. J. Cragg, Dalton Trans., 2007, 26.
[2] J. de Mendoza, F. Cuevas, P. Prados, E. S. Medows and G. Gokel, Angew. Chem. Int. Ed.,
1998, 37, 1534; V. Siderov, F. W. Kotch, J. L. Keubler, Y.-F. Lam and J. T. Davis, J. Am. Chem.
Soc., 2003, 125, 2840.
[3] Y. Tanaka, Y. Kobuke and M. Sokabe, Angew. Chem. Int. Ed. Engl., 1995, 34, 693.
[4] M. D. Lankshear, A. R. Cowley and P. D. Beer, Chem. Commun., 2006, 612.