Fig. 1 Partial 1H NMR spectra (left) in CDCl3 at 5 °C of (a) macrocycle 6 (2 mM); (b) macrocycle 6 (2 mM) + trans-1 (4 mM); (c) after irradiation for 3
h with UV light (365 nm) 8; (d) after heating (50–55 °C) for 12 h, and 1H NMR titration curves (right) plotting NH chemical shift of macrocycle 6 against
equivalent of 1 (trans-1 and cis-1).
2 (a) P. R. Ashton, V. Balzani, O. Kocian, L. Prodi, N. Spencer and J. F.
heating the solution that causes the isomerisation of cis-1 into
Stoddart, J. Am. Chem. Soc., 1998, 120, 11190; (b) M. Asakawa, P. R.
trans-1 (Fig. 1d). This cycle can be repeated by continuously
Ashton, V. Balzani, C. L. Brown, A. Credi, O. A. Matthews, S. P.
alternating irradiation and heating, which results in reversible
Newton, F. M. Raymo, A. N. Shipway, N. Spencer, A. Quick, J. F.
switching between assembly and disassembly modes.
Stoddart, A. J. P. White and D. J. Williams, Chem. Eur. J., 1999, 5, 860;
(c) E. Ishow, A. Credi, V. Balzani, F. Spadola and L. Mandolini, Chem.
Eur. J., 1999, 5, 984; (d) J. W. Lee, K. Kim and K. Kim, Chem.
Commun., 2001, 1042; (e) V. Balzani, A. Credi, F. Marchioni and J. F.
The association constants between the thread 1 (cis-1 and
trans-1) and the macrocycle 6 were determined and compared
by 1H NMR titration experiments. The experiments were
performed in CDCl3 at a low temperature, 5 °C, to prevent
possible thermal isomerisation of the thread 1. Under these
titration conditions, time-averaged resonances for the free and
the complexed species were always observed. As demonstrated
in Fig. 1 (right), the NH chemical shift changes of 6 induced by
trans-1 are very small compared to those induced by cis-1. Even
these small changes may be attributed to a small amount ( ~
6%) of cis-1 existing in the stock solution of trans-1. The
association constants (Ka) were calculated by nonlinear least
squares fitting methods9 and found to be 5 1 M21 for trans-1
and 5200 ± 100 M21 for cis-1,10 respectively. The difference in
binding affinities is nearly four orders of magnitude, one of the
highest exhibited by light-driven molecular machines devel-
oped to date.
In conclusion, we have described a new molecular machine
based on a pseudorotaxane whose assembly occurs only with
the cis isomer of the threading molecule. On the other hand, the
pseudorotaxane is completely disassembled into its molecular
components on isomerisation to the trans isomer caused by an
external stimulus.
Stoddart, Chem. Commun., 2001, 1860; (f) R. Ballardini, V. Balzani, M.
Clemente-León, A. Credi, M. T. Gandolfi, E. Ishow, J. Perkins, J. F.
Stoddart, H.-R. Tseng and S. Wenger, J. Am. Chem. Soc., 2002, 124,
12786.
3 For some examples of azobenzene-containing molecular machines, see:
(a) H. Murakami, A. Kawabuchi, K. Kotoo, M. Kunitake and N.
Nakashima, J. Am. Chem. Soc., 1997, 119, 7605; (b) C. A. Stanier, S. J.
Alderman, T. D. W. Claridge and H. L. Anderson, Angew. Chem., Int.
Ed., 2002, 41, 1769 and see also the references 2c and 2e.
4 J. S. Nowick, P. Ballester, F. Ebmeyer and J. Rebek, Jr., J. Am. Chem.
Soc., 1990, 112, 8902.
5 (a) W. Shuangxi and C. A. Rigiberto, Org. Lett., 2001, 3, 3831; (b) M.
H. Davey, V. Y. Lee, R. D. Miller and T. J. Marks, J. Org. Chem., 1999,
64, 4976.
6 For studies of binding between terephthalamides and tetralactam
metallomacrocycles, see: (a) C. A. Hunter and L. D. Sarson, Angew.
Chem., Int. Ed. Engl., 1994, 33, 2313; (b) K.-S. Jeong, Y. L. Cho, J. U.
Song, H.-Y. Chang and M. G. Choi, J. Am. Chem. Soc., 1998, 120,
10982; (c) K.-S. Jeong, J. W. Lee, T.-Y. Park and S.-Y. Chang, Chem.
Commun., 1999, 2069. For synthesis and spectroscopic properties of 6,
see Electronic Supplementary Information†.
7 H. S. Kim and K.-S. Jeong, unpublished results. For metallomacrocycles
showing similar substituent effects, see: K.-S. Jeong, Y. L. Cho, S.-Y.
Chang, T.-Y. Park and J. U. Song, J. Org. Chem., 1999, 64, 9459.
8 A common UV lamp for TLC spot detection was used as the UV light
source (365 nm, long-wave). The 1H NMR spectral change was
negligible after 3 h irradiation.
This work was financially supported by the Korea Science
and Engineering Foundation (R02-2002-000-00115-0).
9 R. S. Macomber, J. Chem. Educ., 1992, 69, 375; L. Fielding,
Tetrahedron, 2000, 56, 6151.
Notes and references
1 For reviews, see: (a) V. Balzani, M. Gómez-López and J. F. Stoddart,
Acc. Chem. Res., 1998, 31, 405; (b) V. Balzani, A. Credi, F. M. Raymo
and J. F. Stoddart, Angew. Chem., Int. Ed., 2000, 39, 3348; (c) Acc.
Chem. Res., 2001, 34, (6)) (Special Issue on Molecular Machines).
10 In the titration of 6 with cis-1, the stock solution of cis-1 contained 30%
of trans-1 based on the 1H NMR integrations. Therefore, the
concentrations of cis-1 have been corrected for the calculation of the
association constants (Ka).
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