C O M M U N I C A T I O N S
A
A
Scheme 2. Operation of trans-6 -Deoxy-6 -(N-methylcinnamido)-
â-cyclodextrin 2 and the Cis Isomer 3 as a Molecular Machine
Having a Photochemical On/Off Switch
different conformations and ratios of the amide isomers in DMSO
and water without 1-adamantol, that changing the solvent in this
way, and vice versa, drives these molecular machines in a similar
manner to the addition and removal of 1-adamantanol to aqueous
solutions.
In summary, the apparatus illustrated in Figure 1 and exemplified
by the cyclodextrin derivatives 1-3 constitutes a molecular machine
where the output energy of molecular recognition is harnessed to
do work and constrain the geometry of an amide bond. In the case
of the cinnamides 2 and 3, their photoisomerization provides the
machine’s on/off switch. The apparent work performed on the amide
-
1
bond is 1.4, 2.1, and -0.2 kcal mol , with the propionamide 1,
and the cinnamides 2 and 3, respectively. This demonstration that
work output can be harnessed and quantified in such molecular
devices takes us one step closer to their practical application.
Acknowledgment. The authors gratefully acknowledge the
support of this work by the Australian Research Council.
Supporting Information Available: Details for the synthesis of
1
-3 and their operation as molecular machines. This material is
available free of charge via the Internet at http://pubs.acs.org.
References
(
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2) For some recent examples of molecular machines, see (a) Morin, J.-F.;
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5
.6:1, found when 1-adamantanol is present in the mixture, is very
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the competitive guest. This is consistent with the NMR spectra
recorded for this system, which show little interaction of the phenyl
group with the cyclodextrin cavity, irrespective of the presence of
(
f) Onagi, H.; Blake, C. J.; Easton, C. J.; Lincoln, S. F. Chem.sEur. J.
2
003, 9, 5978-5988.
(3) For detailed discussions of such processes in the context of supramolecular
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1
-adamantanol. The small difference between the ∆G values for
-
1
the isomers 3Z and 3E (1.0 kcal mol ), and 3Z′ and 3E′ (0.8 kcal
-
1
mol ), shows a corresponding lack of work on the amide bond
1
(
δ∆G ) -0.2 kcal mol- ). Thus the cis double bond prevents the
(4) (a) Anelli, P. L.; Spencer, N.; Stoddart, J. F. J. Am. Chem. Soc. 1991,
1
13, 5131-5133. (b) Murakami, H.; Kawabuchi, A.; Kotoo, K.; Kunitake,
host-guest interaction and in that mode the machine is turned off.
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5) (a) Onagi, H.; Easton, C. J.; Lincoln, S. F. Org. Lett. 2001, 3, 1041-
(
attributable to removal of 1-adamantanol causing complexation of
the aryl substituent by the cyclodextrin, as observed in NMR
spectra. In this case the energy harnessed by the amide bond, as
calculated from the difference between the ∆G values for the
1
044. (b) Miyauchi, M.; Takashima, Y.; Yamaguchi, H.; Harada, A. J.
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(
6) Thomas, K. M.; Naduthambi, D.; Zondlo, N. J. J. Am. Chem. Soc. 2006,
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-
1
isomers in the presence of 1-adamantanol (0.6 kcal mol ) and in
(
7) The work performed to stabilize the amide (Z)-isomer is the inverse of
the apparent stability and increase in proportion of that isomer. Therefore
the ∆G and δ∆G values are calculated from the inverse of the amide
its absence (2.7 kcal mol ), is δ∆G ) 2.1 kcal mol-1. It follows
that the trans alkene moiety allows complexation, and in this mode
the machine is turned on.
-1
(Z)-/(E)-isomer ratios.
(
8) Irradiation of the trans alkene 2 at 300 nm affords a 1:9 mixture of 2 and
3 in the photostationary state, from which the cis isomer 3 was isolated
using HPLC. Irradiation of the cis isomer at 254 nm affords a 1:1 mixture
of 2 and 3. The efficiency of the photoreversion is limited by the
overlapping absorptions of 2 and 3 at this wavelength. Sources of lower
wavelength light that might be more effective are not readily available.
9) Easton, C. J.; Lincoln S. F. Modified Cyclodextrins: Scaffolds and
Templates for Supramolecular Chemistry; Imperial College Press: London,
The conformations of the cyclodextrin derivatives 1-3 were also
examined in d -DMSO. The NMR spectra show that in this solvent
6
there is little interaction of the aryl substituent with the cyclodextrin
cavity, consistent with there being no driving force for the
(
9
inclusion. As expected on this basis, the ratios of the (Z)- and
1999.
(E)-amide isomers in DMSO were found to be remarkably similar
to those in water containing 1-adamantanol. It follows from the
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