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the current system may be interfered by the background
fluorescence, for example from enzymes. These problems
could be solved by modifying the structural backbone and side
chains of the molecular tube. We are currently working along
this direction.
DOI: 10.1039/C9CC00762H
rate-
determining
step
O
O
R'
R'
O
R
O
R
O
OH
HO
O
O
HO
H
R
O
R'
R
O
R'
+
+
This research was financially supported by the National
Natural Science Foundation of China (Nos. 21772083 and
21822104), and the SZSTI (JCYJ20170307105848463 and
KQJSCX 20170728162528382). We are grateful to SUSTech-
MCPC for instrumental support.
Scheme 2 The commonly-accepted hydrolysis mechanism of esters under basic
condition.
A series of structurally similar esters (Scheme 1b) were
selected to test how would the steric alkyl groups around the
ester group affect the hydrolysis kinetics under basic condition.
These esters have similar binding affinities (Figs. S3-S12) to
molecular tube 1 as ethyl acetate (Table 2). Therefore,
[esters]:[1] = 100 was selected to keep consistency for the
following experiments. The binding constants of 1 to the
corresponding alcohols were also determined (Figs. S13-S20).
The apparent rate constants were obtained (Figs. S27-S36)
with good R2 and are listed in Table 2. The hydrolysis rates of
the esters are obviously different. With increasing the length
of the linear alkyl groups on both the acids and the alcohols,
the observed rate constants gradually decrease. Branching
makes the reaction kinetics slower. When the branching
groups are located closer to the ester group, the kinetics
becomes even slower. This is both true when the bulky group
is near the acid or the alcohol. The most serious one is t-butyl
acetate, and very slow hydrolysis was observed. This
observation is consistent with Taft parameters determined
from the hydrolysis of methyl esters.15
The underlying reason is easy to understand. As shown in
Scheme 2, the rate-determining step for the hydrolysis of
esters under basic condition is the attack of hydroxide at the
carbonyl group to form the tetrahedron intermediate.16 Any
bulky group, which hinder this step, would slow down the
overall hydrolysis kinetics. Closer are the branching groups
located to the ester group, slower are the reaction kinetics.
In summary, a fluorescent method for monitoring the
hydrolysis of nonfluorescent esters in situ is proposed by using
a fluorescent endo-functionalized molecular tube and its ability
to form host-guest complexes with esters. Ester groups of the
guests can be encapsulated in the cavity of the molecular tube,
leading to significant enhancement of the fluorescent intensity
and quantum yields (from 1.4% to 5.0%). Hydrolysis of esters
disturbs the equilibrium and thus the fluorescent intensity.
This can be used to monitor the hydrolysis kinetics of esters.
The current method provide an alternative in addition to
indicator displacement assays3,4,5 and cucurbit[8]uril-dye
method7. It has the advantage in monitoring the reaction
kinetics of nonaromatic and charge-neutral molecules in
water. However, the reaction types with the current method
are still limited. The basic condition and the carboxylate
groups, which are necessary to render the molecular tube
water-soluble, are not compatible with many reactions.
Conflicts of interest
There are no conflicts to declare.
Notes and references
1
R. A. Bissell, A. P. D. Silva, H. Q. N. Gunaratne, P. L. M. Lynch, G. E. M.
Maguire and K. R. A. S. Sandanayake, Chem. Soc. Rev., 1992, 21, 187.
J.-L. Reymond, V. S. Fluxà and N. Maillard, Chem. Commun., 2009, 41, 34.
(a) S. L. Wiskur, H. Ait-Haddou, J. J. Lavigne and E. V. Anslyn, Acc. Chem.
Res., 2001, 34, 963; (b) B. T. Nguyen and E. V. Anslyn, Coord. Chem.
Rev., 2006, 250, 3118.
2
3
4
5
6
(a) G. Ghale and W. M. Nau, Acc. Chem. Res., 2014, 47, 2150; (b) R. N.
Dsouza, A. Hennig and W. M. Nau, Chem. Eur. J., 2012, 18, 3444.
M. Inouye, K. Hashimoto and K. Isagawa, J. Am. Chem. Soc., 1994, 116,
5517.
(a) A. Hennig, H. Bakirci and W. M. Nau, Nat. Methods, 2007, 4, 629; (b)
G. Ghale, V. Ramalingam, A. R. Urbach and W. M. Nau, J. Am. Chem. Soc.,
2011, 133, 7528; (c) M. Florea and W. M. Nau, Org. Biomol. Chem., 2010,
8, 1033; (d) W. M. Nau, G. Ghale, A. Hennig, H. Bakirci and D. M. Bailey, J.
Am. Chem. Soc., 2009, 131, 11558; (e) D.-S. Guo, V. D. Uzunova, X. Su, Y.
Liu and W. M. Nau, Chem. Sci., 2011, 2, 1722.
7
8
(a) F. Biedermann, D. Hathazi and W. M. Nau, Chem. Commun., 2015, 51,
4977; (b) F. Biedermann and W. M. Nau, Angew. Chem., Int. Ed., 2014,
53, 5694.
(a) G.-B. Huang, Z. He, C.-X. Cai, F. Pan, D. Yang, K. Rissanen and W.
Jiang, Chem. Commun. 2015, 51, 15490; (b) G.-B. Huang, A. Valkonen, K.
Rissanen and W. Jiang, Chem. Commun. 2016, 52, 9078; (c) G.-B. Huang,
S.-H. Wang, H. Ke, L.-P. Yang and W. Jiang, J. Am. Chem. Soc., 2016, 138,
14550; (d) H. Yao, H. Ke, X. Zhang, S.-J. Pan, M.-S. Li, L.-P. Yang, G.
Schreckenbach and W. Jiang, J. Am. Chem. Soc., 2018, 140, 13466; (e) L.-
M. Bai, H. Yao, L.-P. Yang, W. Zhang and W. Jiang, Chin. Chem. Lett.,
9
L.-L. Wang, Z. Chen, W.-E. Liu, H. Ke, S.-H. Wang and W. Jiang, J. Am.
Chem. Soc., 2017, 139, 8436.
10 J. F. Cacho, V. Ferreira, I. M. Vicario and F. J. Heredia, Food. Chem., 2007,
100, 1464.
11 S. E. Ebeler, Food. Rev. Int., 2001, 17, 45.
12 B. J. Shorthill, C. T. Avetta and T. E. Glass, J. Am. Chem. Soc., 2004, 126,
12732.
13 F. Daniels, Experiment Physical Chemistry, 6th ed., McGraw Hill Book Co
Inc: New York, 1962; pp 135- 139.
14 A. Ahmad, M. I. Ahmad, M. Younas, H. Khan, Iran. J. Chem. Chem. Eng.,
2013, 32, 33.
15 E. V. Anslyn and D. A. Dougherty, Modern Physical Organic Chemistry,
University Science Books: Sausalito, 2006; pp 454 – 455.
16 (a) M. L. Bender, J. Am. Chem. Soc., 1951, 73, 1626; (b) M. H. O. Leary,
and J. F. Marlier, J. Am. Chem. Soc., 1979, 101, 3300.
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