2 (a) D. W. Griffiths and M. L. Bender, Adv. Catalysis, 1973, 23, 209;
probe reactions, because the probe reactions were incompletely
inhibited or not inhibited at all by added alcohols.15 In retro-
spect, this finding is not so surprising because it has been found
that even with β-CD, which has a smaller cavity, there may be
binding of a molecule of a simple alcohol and an aromatic
probe.23 Clearly, the assessment of alcohol binding to γ-CD
alone is not straightforward and requires further careful study.24
(b) J. H. Fendler and E. J. Fendler, Catalysis in Micellar and
Macromolecular Systems, Academic Press, New York, 1975; (c)
M. Komiyama and M. L. Bender, in The Chemistry of Enzyme
Action, ed. M. I. Page, Elsevier, Amsterdam, 1984, ch. 14.
3 O. S. Tee, Carbohydr. Res., 1989, 192, 181; Adv. Phys. Org. Chem.,
1994, 29, 1.
4 (a) O. S. Tee and J. M. Bennett, J. Am. Chem. Soc., 1988, 110,
269; (b) O. S. Tee and B. C. Javed, J. Chem. Soc., Perkin Trans. 2,
1994, 23.
5 (a) E. H. Cordes and H. G. Bull, Chem. Rev., 1974, 74, 581; (b)
B. Capon and K. Nimmo, J. Chem. Soc., Perkin Trans. 2, 1975, 1113;
(c) J. L. Jensen and P. A. Lenz, J. Am. Chem. Soc., 1978, 100, 1291;
(d) J. L. Jensen, L. R. Herold, P. A. Lenz, S. Trusty, V. Sergi, K. Bell
and P. Rogers, J. Am. Chem. Soc., 1979, 101, 4672; (e) R. L. Finley,
D. G. Kubler and R. A. McClelland, J. Org. Chem., 1980, 45,
644.
6 (a) B. Capon, K. Nimmo and G. L. Reid, J. Chem. Soc., Chem.
Commun., 1976, 871; (b) J. L. Jensen, A. B. Martinez and C. L.
Shimazu, J. Org. Chem., 1983, 48, 4175; (c) C. J. Brown and A. J.
Kirby, J. Chem. Soc., Perkin Trans. 2, 1997, 1081; (d) cf. R. A.
McClelland and P. E. Sorensen, Acta Chem. Scand., 1990, 44, 1082.
7 (a) R. L. VanEtten, J. F. Sebastian, G. A. Clowes and M. L. Bender,
J. Am. Chem. Soc., 1967, 89, 3242; (b) R. L. VanEtten, G. A. Clowes,
J. F. Sebastian and M. L. Bender, J. Am. Chem. Soc., 1967, 89, 3253.
8 O. S. Tee, M. Bozzi, J. J. Hoeven and T. A. Gadosy, J. Am. Chem.
Soc., 1993, 115, 8990.
9 (a) O. S. Tee, T. A. Gadosy and J. B. Giorgi, J. Chem. Soc., Perkin
Trans. 2, 1993, 1705; (b) O. S. Tee, T. A. Gadosy and J. B. Giorgi,
Can. J. Chem., 1996, 74, 736; (c) O. S. Tee, A. A. Fedortchenko,
P. G. Loncke and T. A. Gadosy, J. Chem. Soc., Perkin Trans. 2, 1996,
1243. (d) O. S. Tee and J. B. Giorgi, J. Chem. Soc., Perkin Trans. 2,
1997, 1013.
10 (a) K. J. Laidler, Chemical Kinetics, 3rd edn., Harper and Row,
New York, 1987, pp. 279–282; (b) B. G. Cox, Modern Liquid Phase
Kinetics, Oxford University Press, Oxford, 1994, pp. 27–29.
11 (a) Y. Matsui and K. Mochida, Bull. Chem. Soc. Jpn., 1979, 52,
2808; (b) Y. Matsui, T. Nishioka and T. Fujita, Top. Curr. Chem.,
1985, 128, 61.
12 (a) I. Tabushi, K. Shimokawa, N. Shimizu, H. Shirakata and
K. Fujita, J. Am. Chem. Soc., 1976, 98, 7855; (b) I. Tabushi,
N. Shimizu, T. Sugimoto, M. Shiozuka and K. Yamamura, J. Am.
Chem. Soc., 1977, 99, 7100; (c) Y. Matsui, K. Ogawa, S. Mikami,
M. Yoshimoto and K. Mochida, Bull. Chem. Soc. Jpn., 1987, 60,
1219; (d) Y. Aoyama, Y. Nagai, J. Otsuki, K. Kobayashi and H. Toi,
Angew. Chem., Int. Ed. Engl., 1992, 31, 745; (e) Y. Aoyama, J. Otsuki,
Y. Nagai, K. Kobayashi and H. Toi, Tetrahedron Lett., 1992, 33,
3775.
Experimental
The cyclodextrins were purchased from the Aldrich Chemical
Company or Wacker-Chemie (Munich, Germany) and used
as supplied. Hydroxypropyl-β-cyclodextrin is available with
different degrees of substitution: we used the Wacker product
(Beta W 7 HP 0.9), with an average molecular weight of 1500,
corresponding to alkylation of six of the seven primary
hydroxyl groups of β-CD by 2-hydroxypropyl groups. Benz-
aldehyde dimethyl acetal, alcohols and ketones were of the best
grade available from Aldrich. Hydrochloric acid solutions were
made by dilution of standard 1.00 solutions obtained from
American Chemicals Ltd (Montreal).
Reactions were initiated by 1:1 mixing in a stopped-flow
spectrophotometer. Since the acetal hydrolyses slowly but
appreciably in water, the substrate solutions were made fresh for
each set of kinetic runs. These solutions were made up by 1000-
fold dilution of a 0.10 stock solution of the acetal in spectral
grade acetonitrile, so as to give [acetal]o = 50 µ, after 1:1 mix-
ing. For experiments with varying [CD] (Fig. 1), one syringe of
the stopped-flow apparatus contained 0.20 aqueous HCl and
the other had the substrate and the CD at twice the concen-
trations desired in the reaction. For the competition experi-
ments, with fixed [CD]o and varying [guest]o, one syringe con-
tained 2 × [CD]o and 0.20 aqueous HCl, and the other had
the acetal (100 µ) and 2 × [guest]o. The values of [CD]o (in
m) were: α-CD, 20.0 or 30.0; β-CD, 5.00; hp-β-CD, 5.00; γ-
CD, 20.0. The concentrations of the guests were varied between
zero and the following maximum values (in m): propan-1-ol,
200; butan-1-ol, 200; pentan-1-ol, 50; hexan-1-ol, 15; heptan-1-
ol, 2.2; propan-2-ol, 200; hexan-3-ol, 20; 2-methylpropan-1-ol
(tert-butyl alcohol), 100; cyclohexanol, 50; hexan-3-one, 20;
cyclohexanone, 50 (e.g. Fig. 2).
Hydrolysis of the acetal was followed by the appearance of
the benzaldehyde chromophore at λ 252 nm, using an Applied
Photophysics SX17MV Stopped-flow Apparatus. Normally,
400 absorbance values, spanning 7–12 half-lives, were collected,
and the first 10–20 points were ignored to allow for the induc-
tion period (see Results). A first-order rate constant was esti-
mated from non-linear least squares fitting of an exponential
increase, using computer software supplied with the apparatus.
The recorded rate constants (kobs) were taken as the averages of
5–10 determinations differing by less than 5%. The observation
cell of the apparatus was kept at 25.0 0.1 ЊC.
Non-linear fitting of eqn. (4) to kobs vs. [CD] data was carried
out with commercial or in-house software based on the
Marquardt Algorithm.26 The determination of dissociation
constants using inhibition (competition) kinetics has been
described in detail in previous publications.8,9
13 O. S. Tee and R. A. Donga, J. Chem. Soc., Perkin Trans. 2, 1996,
2763.
14 O. S. Tee and M. J. Boyd, J. Chem. Soc., Perkin Trans. 2, 1995, 1237.
15 O. S. Tee and S. Collins, unpublished results.
16 In Fig. 4, we have depicted the binding of PhCH(OMe)2 as being
with the hydrophobic phenyl ring more or less in the CD cavity and
the two hydrophilic methoxyl groups directed towards the bulk,
aqueous medium. We think that binding of the acetal in the reverse
orientation is much less likely.
17 R. J. Bergeron, in Inclusion Compounds, eds. J. L. Atwood, J. D.
Davies and D. D. McNicol, Academic Press, London, 1984, vol. 3,
ch. 12.
18 (a) T. Okubo, H. Kitano and N. Ise, J. Phys. Chem., 1976, 80, 2661;
(b) S. Hashimoto and J. K. Thomas, J. Am. Chem. Soc., 1985, 107,
4655; (c) I. Satake, T. Ikenoue, T. Takeshita, K. Hayakawa and
T. Meda, Bull. Chem. Soc. Jpn., 1985, 58, 2746; (d) I. Satake,
S. Yoshida, K. Hayakawa, T. Meda and Y. Kusumoto, Bull. Chem.
Soc. Jpn., 1986, 59, 3991; (e) R. Palepu and V. C. Reinsborough,
Can. J. Chem., 1988, 66, 325.
19 (a) J. F. Stoddart and R. Zarzycki, Recl. Trav. Chim. Pays-Bas, 1988,
107, 515; (b) M. D. Johnson, V. C. Reinsborough and S. Ward, Inorg.
Chem., 1992, 31, 1087; (c) M. D. Johnson and V. C. Reinsborough,
J. Solution Chem., 1994, 23, 185.
20 (a) A. Buvari and L. Barcza, J. Chem. Soc., Perkin Trans. 2, 1988,
543; (b) E. A. Lewis and L. D. Hansen, J. Chem. Soc., Perkin Trans.
2, 1973, 2081.
21 J. L. Jensen and K. S. Yamaguchi, J. Org. Chem., 1984, 49, 2613.
22 (a) O. S. Tee and J. J. Hoeven, J. Am. Chem. Soc. 1989, 111, 8318;
(b) O. S. Tee and M. Bozzi, J. Am. Chem. Soc., 1990, 112, 7815;
O. S. Tee, M. Bozzi, N. Clement and T. A. Gadosy, J. Org. Chem.,
1995, 60, 3509; (c) T. A. Gadosy and O. S. Tee, Can J. Chem., 1996,
74, 745.
Acknowledgements
This work was made possible by an operating grant and an
equipment grant from the Natural Sciences and Engineering
and Research Council of Canada. We also thank Professor A. J.
Kirby (Cambridge) for helpful correspondence and Dr T. A.
Gadosy for technical advice.
References
1 (a) M. Bender and M. Komiyama, Cyclodextrin Chemistry,
Springer, New York, 1978; (b) J. Szejtli, Cyclodextrins and their
Inclusion Complexes, Akademiai Kiado, Budapest, 1982.
23 E.g. S. Hamai, J. Am. Chem. Soc., 1989, 111, 3954; J. Phys. Chem.,
1990, 94, 2595; references cited therein.
J. Chem. Soc., Perkin Trans. 2, 1998
127