ISMSC 2007 - Università degli Studi di Pavia

High Order Bistable [n]Rotaxane Architectures
Ivan Aprahamian, William Dichtel, Travis Gasa, John-Carl Olsen, J. Fraser Stoddart
California NanoSystems Institute and Department of Chemistry and Biochemistry, University of
California Los Angeles, 405 Hilgard Avenue, Los Angeles, CA 90095, USA
(jcolsen@chem.ucla.edu)
The efficient preparation of high order interlocked structures will facilitate the development of
sophisticated molecular machinery. For example, three-fold symmetric bistable [4]rotaxanes
might form the basis of electrochemically switchable elevators 1 , artificial muscles 2 , or stimuliresponsive
nanovalves. 3 We recently found that the kinetically controlled synthesis of [2]-, [3]-,
and [4]rotaxanes 4 and catenanes 5 proceeds with excellent yield from relatively simple
precursors. This success has recently been extended to bistable rotaxanes. 6 The synthesis
and characterization of a variety of bistable [4]rotaxane architectures including tripods (Figure
1), capsules, and elevators will be presented.
Figure 1. A fully-synthesized, bistable, tripodal [4]rotaxane incorporating tetrathiafulvalene (TTF), 1,5-dioxynaphthalene
(DNP), and cyclobi s(paraquat-p-phenylene) (CBPQT 4+ ) components.
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[1] Badjic, J. D.; Balzani, V. Credi, A.; Silvi, S.; Stoddart. J. F. Science, 2004, 303, 1845
[2] Liu, Y.; Flood, A. H.; Bonvallet, P. A.; Vignon, S. A.; Northrop, B. H.; Tseng, H.-R.;
Jeppesen, J. O.; Huang, T. J.; Brough, B.; Baller, M.; Magonov, S.; Solares, S. D.;
Goddard, W. A.; Ho, C.-M.; Stoddart, J. F. J. Am. Chem. Soc. 2005, 127, 9745
[3] Hernandez, R.; Tseng, H.-R.; Wong, J. W.; Stoddart, J. F.; Zink, J. I. J. Am. Chem. Soc.
2004, 126, 3370
[4] Dichtel, W. R.; Miljanic, O. S.; Spruell, J. M.; Heath, J. R.; Stoddart, J. F. J. Am. Chem.
Soc. 2006, 128, 10388
[5] Miljanic, O. S.; Dichtel, W. R.; Mortezaei, S.; Stoddart, J. F. Org. Lett. 2006, 8, 4835.
[6] [6] Aprahamian, I.; Dichtel, W. R.; Ikeda, T.; Heath, J. R.; Stoddart, J. F. Org. Lett. 2007,
9, 1287
12PF 6
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O
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PSB 27
PSB 28
Polymerization of Lactones and Lactides Initiated by Cyclodextrins in Bulk:
Effects of Cyclodextrins on the Initiation and Propagation
Motofumi Osaki, Yoshinori Takashima, Hiroyasu Yamaguchi, Akira Harada
Department of Macromolecular Science, Graduate School of Science, Osaka University,
Toyonaka, Osaka 560-0043, Japan. e-mail: harada@chem.sci.osaka-u.ac.jp
Cyclodextrins (CDs) have attracted
much attention of many researchers as
enzyme models. Previously, cyclodextrins
(CDs) were found to accelerate the hydrolysis
of some lactones in aqueous solutions. 1 Here,
the authors found that CDs initiate the
polymerization of lactones in bulk at 100 o C to
give CD-tethered polyesters. 2
The order of the polymerization activity
for δ-valerolactone (δ-VL) with CDs was β-CD
> γ-CD >> α-CD (no CD), depending on the
cavity size of CDs (Figure 1). Polymerizations
of DL-lactide (DL-LA) were also initiated by CDs.
The order of the activity for DL-LA was γ-CD >
β-CD > α-CD > (no CD). These results indicate
that the formation of the inclusion complexes
between CD and monomer plays an important
role in the polymerizations.
The details of the polymerization of
lactones by CDs were investigated to propose
the mechanism (Scheme 1). 3 The included
lactone in the CD cavity is activated by the
formation of a hydrogen bond between the
carbonyl oxygen of the lactone and the
hydroxyl group of CD. A secondary hydroxyl
group attacks the activated carbonyl carbon of
the lactone in the CD cavity, cleaving the CO
bond of δ-VL to give the monomer-attached CD
in the initial step. In the propagation step, the
monomer recognition, the activation of the
monomer and the insertion of monomers are
serially repeated to give CD-tethered poly(δ-
VL).
In the presentation, the authors would
talk about the detail of the polymerization
mechanism.
Figure 1. Yields of the poly(δ-VL) as a
function of time. δ-VL was initiated by
various CDs in bulk at 100 o C.
Scheme 1. Proposed mechanism for the
polymerization of δ-VL initiated by CD.
[1] Takashima, Y.; Kawaguchi, Y.; Nakagawa, S.; Harada, A. Chem. Lett. 2003, 32, 1122-1123.
[2] Takashima, Y.; Osaki, M.; Harada, A. J. Am. Chem. Soc. 2004, 126, 13588-13589.
[3] Osaki, M.; Takashima, Y; Yamaguchi, H.; Harada, A. Macromolecules 2007, in press.