DOI: 10.1039/C5CC01626F
Page 3 of 4
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Scheme 2 Proposed mechanism for CN–-triggered transformation of PTZ-AL into PTZ.
To further evaluate the selectivity of PTZ-AL towards CN, we
also measured fluorescence intensity changes upon addition of a
The authors are thankful to National Tsing Hua University
(103N1807E1 and 104N1807E1) and the Ministry of Science and
5
variety of anions. Specifically, 5 equiv. of each anion were added 55 Technology (NSC101-2113-M-007-006-MY3, NSC 102-2621-M-
to an acetonitrile solution of PTZ-AL (5.0 10-5 M) and incubated
for 10 min at room temperature, before being subjected to spectral
analysis. The fluorescence emission intensity of PTZ-AL
007-001) of Taiwan for financial assistance.
Notes and references
a Department of Chemistry, National Tsing Hua University, 101, Section
2, Kuang-Fu Road, Hsinchu, 30013, Taiwan.
Fax: +886 35727774; Tel: +886 35715131 xt.33394
† Electronic Supplementary Information (ESI) available: [Synthesis and
characterization data of PTZ-AL, spectra of 1H NMR, 13C NMR, and
HRMS, 1H NMR titrations and single crystal X-ray data for PTZ-AL.
65 CCDC 1049885]. See DOI: 10.1039/b000000x/
10 enhanced remarkably only after the addition of CN. The other
studied anions (AcO, F, Cl, Br, I, HSO4 , NO3 , and H2PO4 ),
inorganic sulphide, and (bio)thiols did not cause any remarkable
changes in the fluorescence emission intensity (Fig. 3a, S10-17†).
The fact that PTZ exhibits blue fluorescence also allowed the CN-
15 driven transformation of PTZ-AL to be followed visually by
making the use of a short UV hand lamp (UV-GL 25; UV-254/365
nm) (Fig. 3b).
1
(a) S. I. Baskin and T. G. Brewer, in Medical Aspects of Chemical and
Biological Warfare, ed. F. Sidell, E. T. Takafuji and D. R. Franz, TMM
Publication, Washington DC, 1997, ch. 10, pp. 271; (b) K. W. Kulig,
Cyanide Toxicity, U. S. Department of Health and Human Services,
Atlanta, 1991.
The mechanism of interaction of CN with PTZ-AL is proposed
in Scheme 2, which involves initial nucleophilic attack of CN on
20 -position of the aldehyde group (C3’) resulting in the formation
of intermediate A. Under experimental conditions, intermediate A
seems to be unstable and readily undergoes rearrangement,
releasing 4-oxobut-2-enenitrile to produce PTZ.
70
2
3
G. C. Miller and C. A. Pritsos, Cyanide: Soc., Ind., Econ. Aspects,
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J. D Johnson, T. L. Meisenheimer and G. E. Isom, Toxicol. Appl.
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In order to get an unequivocal proof that CN signalling is via
25 selective CN-induced deprotection of PTZ-AL (Scheme 2), the
chemical reaction between PTZ-AL and TBACN (1.2 equiv.) was
performed in acetonitrile solution under ambient conditions (see
ESI†). The progress of the reaction could be easily followed by
TLC. After completing the reaction, the solvent was evaporated
30 and crude was column chromatographed. As expected, the isolated
75 4 (a) M. E. Moragues, R. Martínez-Máñez and F. Sancenόn, Chem. Soc.
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5
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80
1
product turned out to be PTZ as confirmed by H NMR and 13C
NMR spectroscopy.
85
In summary, a PTZ scaffold having an ,-unsaturated aldehyde
group (PTZ-AL) as a putative reacting subunit towards CN– was
35 synthesized. In the presence of CN–, PTZ-AL revealed a highly
selective ‘turn-on’ type fluorogenic signalling behaviour based on
the selective and efficient cleavage of N-C bond (CN–-triggered
deprotection), which was established by 1H NMR titrations as well
as the isolated product from a chemical reaction between PTZ-AL
40 and TBACN. Effective as it is, however, it must be stressed that
PTZ-AL does not serve as a typical signalling probe but can be
classified as a chemodosimeter due to the irreversible nature of as-
proposed chemical reaction to produce fluorescence response.
Although several chemodosimetric probes for CN detection have
45 been reported over the years, to the best of our knowledge, this is
the first example enabling the use of a protection/deprotection
mechanism for selective CN detection. The present approach
holds great promises in organic synthesis and may be further
developed as NH protection/deprotection strategy. Further
50 exploration of this approach, as is a search for other heterocyclic
systems that might allow an exceptional CN recognition, are
currently underway in our laboratory.
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