ISMSC 2007 - Università degli Studi di Pavia

pH-Responsive Molecular Shuttles Containing Palladium
James D. Crowley, David A. Leigh, Paul J. Lusby, Roy T. McBurney, Laure-Emmanuelle Perret-
Aebi, Christiane Petzold and Mark D. Symes
School of Chemistry, University of Edinburgh, The King’s Buildings, West Mains Road,
Edinburgh, EH9 3JJ, United Kingdom (m.d.symes@sms.ed.ac.uk)
Following the synthesis of Pd(II)-containing rotaxanes [1] and catenanes [2] , we report the
synthesis of two Pd(II)-based molecular shuttles, in which the position of a macrocycle in a
[2]rotaxane can be controlled with high precision by altering the pH of the environment. A
macrocycle with a tridentate carboxamide binding motif shows an equilibrium distribution in
favour of a substituted dimethylaminopyridine (DMAP) station over a substituted pyridine
station in a ratio of 9:1 at neutral pH in deuterated DMF. Under acidic conditions, this
equilibrium shifts so that the macrocycle prefers the pyridine over DMAP in a 9:1 ratio
(Scheme 1).
O
O
DMAP Station Pyridine Station
O
N
O
N
N PdN
N
O O
N
N +
H X- O
N
-H + 1 equiv. H +
N
O
N PdN
O
N
O
Scheme 1: A Pd(II)-based pH shuttle
Subtle alteration of the structure of the macrocycle allows improved discrimination for DMAP
over pyridine in the neutral form and pyridine over DMAP in the protonated form. Furthermore,
the reaction time is greatly reduced and milder conditions (room temperature as opposed to
110 °C) are found sufficient to bring about the shuttling.
[1] A.-M. Fuller, D. A. Leigh, P. J. Lusby, I. D. H. Oswald, S. Parsons and D. B. Walker,
Angew. Chem. Int. Ed., 2004, 43, 3914-3918.
[2] A.-M. L. Fuller, D. A. Leigh, P. J. Lusby, A. M. Z. Slawin and D. B. Walker, J. Am. Chem.
Soc, 2005, 127, 12612-12619.
O
O
PSB 63
Contraction of Supramolecular Double-Threaded Dimer Formed by α-
Cyclodextrin with Long Alkyl Chain
Yoshinori Takashima, Shouichi Tsukagoshi, Atsuhisa Miyawaki, Hiroyasu Yamaguchi, and Akira
Harada*
Department of Macromolecular Science, Graduate School of Science, Osaka University,
Toyonaka, Osaka 560-0043, Japan; e-mail: takasima@chem.sci.osaka-u.ac.jp
PSB 64
Molecular motors and machines in
biological systems, such as dynein,
flagellar, myosin and kinesin, have highlyprecise
structures and achieve controlled
movements by external stimuli. Recently,
the subject of nanoscale artificial
molecular muscles and motors has
attracted much interest from researchers.
We previously reported that 6cinnamamide-α-CD
and 6aminocinnamate-α-CD
formed a doublethreaded
dimer, however, substituent
groups on α-CDs are too short to mimic
the contraction and extension of skeletal
muscle. 6 Scheme
In this paper, we have prepared
a modified 6-aminocinnamamide-α-CD
and investigated the formation of the double-threaded dimer. We discuss the conformational
change of the double-threaded dimer by increased solvent polarity.
To estimate the size of the double-threaded dimer 3 in DMSO-d6 and H2O/DMSO-d6
(1:1), the pulse field gradient spin-echo (PFGSE) NMR technique was used and the diffusion
coefficients (D) and hydrodynamic radii (RH) of the supramolecular complexes were determined.
The apparent RH of the double-threaded dimer 3 in DMSO-d6 and H2O/DMSO-d6 (1:1) showed
1.63 nm and 2.08 nm in diluted solution (5 mM), respectively. The change of length of the
double threaded dimer (3) is estimated to be about 0.66 nm calculated by the molecular
modeling. These results are conconsistent with the hydrodynamic radii, and indicate that
double-threaded dimer 3 forms the complex with larger size or the stretched state in
H2O/DMSO-d6.
We are currently expanding these studies to the synthesis of supramolecular polymers
based on double threaded dimer units.
[1] Tsukagoshi, S.; Miyawaki, A.; Takashima, Y.; Yamaguchi, H.; Harada, A.
Org. Lett. 2007, 6, 1053-1059.