ISMSC 2007 - Università degli Studi di Pavia

PSB 29
Control of Translation of the Cyclic Component onto the Rotaxane bearing
2-Pyridinium Moieties
Tomoya Oshikiri, Hiroyasu Yamaguchi, Yoshinori Takashima, Yasushi Okumura, Akira Harada.
Department of Macromolecular Science, Graduate School of Science,
Osaka University, Toyonaka, Osaka 560-0043, Japan Email: oshikiri@chem.sci.osaka-u.ac.jp
In recent years, designing and constructing “molecular machines” and “molecular
devices” have received much attention. Interlocked
molecules such as rotaxanes and catenanes have
been extensively used as models for “molecular
machines” and “molecular devices” due to the
relative mobility of each component. Cyclodextrin
(CD) has a rigid, well-defined "non-symmetric" ring
structure.
Previously, we reported kinetic control of the
face direction of cyclodextrin in the construction of
Figure 1. Structures of axle molecules.
pseudo-rotaxane with the alkyl chain bearing pyridyl
end caps. 1,2 faster
We report here the face-direction
control of CD in the threading and the sliding
process of pseudo-rotaxane with the alkyl chain
bearing the bulky and the non-symmetric linker
moiety. Figure 1 shows axle molecules prepared by
the reaction of α, ω-dihalodecane with pyridine
derivatives.
slower
After the addition of α-CD to the aqueous
solution of axle 1, the NMR spectra showed obvious changes. First, the protons of the
decamethylene moiety bound to the 4-position of 2methylpyridinium
were splitted. And then, the
protons of decamethelene moiety in the vicinity of
3,5-dimethylpyridinium were separated into the free
guest and the complex. These results mean α-CD
threads on the first station rapidly, and then slides
to the station close to the stopper gradually.
Furthermore, the 2D ROESY spectrum revealed
that α-CD formed an inclusion complex at the
station close to the stopper moiety in a unique
direction where the secondary side in the α-CD
faces to the 3,5-dimethylpyridine moiety. The
kinetic analysis revealed that the rate constant of
the translation from the first station to second station
by the wider side is 10 times larger than that by the
Figure 2. Schematic representation of
shuttling process of α-CD with 1.
Figure 3. Degree of complex formation
of 1 with α-CD as a function of time..
narrow side. In the case of 2, the 2-methylpyridinium linker also could control the rate of the
translation of CDs.
These results indicate that the 2-methylpyridinium linker bearing axle molecules could
control the face direction of α-CD in the sliding process.
[1] Oshikiri, T.; Takashima, Y.; Yamagushi, H.; Harada, A J. Am. Chem. Soc. 2005, 127(35),
12186-12187.
[2] Yamaguchi, H.; Oshikiri, T.; Harada, A.J. Phys. Condens. Matter 2006, 18(33), S1809-
S1816.
A fluorescent micellar lipophilicity-meter for carboxylates
PSB 30
Giacomo Dacarro, a Franck Denat, b Yuri Diaz Fernandez, a Piersandro Pallavicini, a Luca Pasotti a ,
Stefano Patroni, a and Yoann Rousselin b
a:Dipartimento di Chimica Generale, Università di Pavia, v.le Taramelli, 12 – 27100 Pavia, Italy;
b: Institut de Chimie Moléculaire de l'Université de Bourgogne, UMR CNRS 5260, 9 avenue
Alain Savary - BP 47870 - 21078 DIJON cedex - France
Sensing processes signalled by the variation of fluorescence may take advantage of the use of
micelles, exploiting their ability to self-assembling in water and to host a huge number of
different lipophilic species.[1] The sparingly water-soluble Pyrenecarboxylic acid, PyrCOOH,
can be dissolved easily in TritonX-100 micelles. The fluorescence of PyrCOOH is intense, while
deprotonation (pKa = 5.22 in micelles) leads to the poorly fluorescent PyrCOO - species. Working
at pH > 6.5, addition of the lipophilic Zn 2+ complex of the N-dodecyl-N’,N’’,N’’’-trimethylcyclen
ligand, [Zn(C12-Me3-CYC)] 2+ , results in an intense fluorescence reviving, due to the
coordination of PyrCOO - to the apical position of the Zn 2+ complex. The process takes place
exclusively inside micelles (no reviving is observed in water), and it is promoted both by local
overconcentration of [Zn(C12-Me3-CYC)] 2+ and PyrCOO - , and by the poorly efficient
competition of water, that inside micelles is less concentrated with respect to the bulk solution.
[Zn(C12-Me3-CYC)(PyrCOO)] + may be considered as the ON state of an ON-OFF fluorescent
meter for the lipophilicity of carboxylates.
Addition of carboxylates results in a decrease of the system IF that is proportional to the quantity
(and nature) of their carbon content. Fluorescence decrease is due to an intra-micellar
competition for coordination to the Zn 2+ centre that is efficient only if the R group appended to
R-COO - is lipophilic enough to result in a significant micellar inclusion of R-COO - . As an
example, the acetate anion does not influence IF at all, while dodecanoate gives a dramatic
fluorescence decrease. A correlation between the measurable IF and the observed micellar
pKa of a series of carboxylic acids may also be put forward.
[1] a) Y. Diaz Fernandez, A. Perez Gramatges, V. Amendola, F. Foti, C. Mangano, P. Pallavicini
and S. Patroni, Chem. Commun., 2004, 1650; 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; c) P. Pallavicini, Y. A. Diaz-Fernandez, F. Foti, C. Mangano and S. Patroni, Chem. Eur. J.,
2007, 13, 178