N-Acyl Triazenes as SelectiVe Chemodosimeters
SCHEME 1. Synthesis of Triazenes 1 and Reference
Compound 2
FIGURE 1. A schematic diagram for the displacement approach to
new chemodosimeters.
4
that recognizes anions through reversible adduct formation. The
new binding motif has a strong affinity toward cyanide, because
of the analyte’s strong affinity toward the trifluoroacetyl
carbonyl carbon. The strong affinity of cyanide toward the
carbonyl carbon suggests that an acylated chromophore may
be developed as a chemodosimeter that is selective toward the
highly toxic anion. Several other unique probes for cyanide are
known, which are mostly based on cyanide addition reactions
scenario, we need a chromophore that is latent in the acylated
form but active in the deacylated state. A number of chro-
mophores may satisfy this condition if the deacylated state
maintains its anionic state, in which state usually a significant
change in the absorption wavelength from its neutral form is
expected. Compounds belonging to this category may be found
5
6
to boronic acid complexes, squaraine derivatives, pyrylium
derivatives,7 and benzooxazine derivatives.8 These sensing
methods are based on reversible covalent bond formation. Also,
a few examples are known for an irreversible approach, that is,
cyanide detection by chemodosimeters, which are based on the
1
1
9
among indicator dyes of phenol derivatives. We have briefly
examined an azophenol compound as the chromophore. Al-
though the result was positive, the absorption change was not
satisfactory to our expectation. Thus, we converted our attention
to the N-acylated triazene system 1, which can be readily
coordination of cyanide to metal complexes. Herein, we wish
to report a simple and tunable chemodosimeter system for
cyanide, which is based on an organic displacement reaction,
rather than the addition reactions. This displacement approach
is based on the strong affinity of cyanide toward an N-acyl
1
2
carbonyl carbon.4a Recently, chemosensors based on intramo-
prepared from the corresponding triazene 4, which, in turn,
was prepared from p-nitroaniline through a diazonium coupling
reaction (Scheme 1). Such acylated triazenes have been used
as acylating agents for amines in the literature.
lecular displacement reactions have been developed for the
detection of chemical warfare agents such as phosphonic acid
1
0
halides.
Detection Studies. We have evaluated the reaction-dependent
absorption change of the acetylated triazene 1a toward cyanide.
A solution of triazene 1a itself in organic solvents such as
acetonitrile and ethyl acetate is almost colorless under a dilute
concentration (0.017 mM), exhibiting an absorption band at λmax
Results and Discussion
Design and Synthesis. Our approach to a new type of cyanide
chemodosimeters is depicted in Figure 1.
A “latent” chromogenic moiety with an acyl group (-COR)
may comprise a new type of chemodosimeters for cyanide,
because cyanide has strong affinity toward the acyl group and
thus the attack of cyanide to the acyl group may trigger the
latent chromogenic moiety into an “active” state. To realize this
)
306 and a very weak one at λmax ) 407 nm in CH3CN. When
triazene 1a in acetonitrile was treated with cyanide as its
tetrabutylammonium salt at room temperature, the intensity of
both of the absorption bands increased with an appearance of a
new band at λmax ) 565 nm, which showed a large change,
giving a deep purple solution. The color change occurred within
minutes and became saturated upon addition of an equimolar
amount of cyanide, which indicates that the color change is due
(4) (a) Kim, Y. K.; Lee, Y.-H.; Lee, H.-Y.; Kim, M. K.; Cha, G. S.;
Ahn, K. H. Org. Lett. 2003, 5, 4003. (b) Chung, Y. M.; Balamurali, R.;
Kim, D. S.; Ahn, K. H. Chem. Commun. 2006, 186. (c) Kim, D. S.; Miyaji,
H.; Chang, B.-Y.; Park, S.-M.; Ahn, K. H. Chem. Commun. 2006, 3314.
-
-
to the displacement reaction. Other anions such as F , Cl ,
(
5) (a) Badugu, R.; Lakowicz, J. R.; Geddes, C. D. J. Am. Chem. Soc.
-
-
-
-
-
SCN, AcO , H2PO4 , ClO4 , and HSO4 were also examined,
2
005, 127, 3645. (b) Badugu, R.; Lakowicz, J. R.; Geddes, C. D. Dyes
-
-
-
and only F , AcO , and H2PO4 showed color changes. A
strong color similar to the case of CN was observed in the
case of F , while a weak color was observed in other cases.
Pigm. 2005, 64, 49. (c) Badugu, R.; Lakowicz, J. R.; Geddes, C. D. Anal.
Biochem. 2004, 327, 82. (d) Badugu, R.; Lakowicz, J. R.; Geddes, C. D.
Anal. Chim. Acta 2004, 522, 9.
-
-
(
6) (a) Ros-Lis, J. V.; Mart ´ı nez-M a´ n˜ ez, R.; Soto, J. Chem. Commun.
The absorption spectra collected for each of the anions are
2
002, 2248. (b) Ros-Lis, J. V.; Garc ´ı a, B.; Jim e´ nez, D.; Mart ´ı nez-M a´ n˜ ez,
1
3
shown in Figure 2, which is clearly in accordance with the
color changes.
R.; Sancen o´ n, F.; Soto, J.; Gonzolvo, F.; Valldecabres, M. C. J. Am. Chem.
Soc. 2004, 126, 4064.
(7) (a) Garc ´ı a, F.; Garc ´ı a, J. M.; Garc ´ı a-Acosta, B.; Mart ´ı nez-M a´ n˜ ez,
R.; Sancen o´ n, F.; Soto, J. Chem. Commun. 2005, 2790. (b) Jimenez, D.;
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Am. Chem. Soc. 2003, 125, 9000. (c) Sancen o´ n, F.; Descalzo, A. B.;
Mart ´ı nez-M a´ n˜ ez, R.; Miranda, M. A.; Soto, J. Angew. Chem., Int. Ed. 2001,
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0, 2640.
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Chem. 2006, 71, 744. (b) Tomasulo, M.; Sortino, S.; White, A. J. P.; Raymo,
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(13) The UV-vis titrations do not show clear isobestic points, indicating
different absorption species are involved other than the two species
(compound 1a and its deacylated anionic species) from the displacement
process. A minor peak (λmax ) 407 nm) appeared in addition to the major
absorption peaks (1a, λmax ) 306 nm; its deacylated species/anionic form
of 4, λmax ) 565 nm). The minor peak is assigned to the absorption from
triazene 4 (Figure S6). The appearance of triazene 4 during the titration is
likely due to the water residue present in the solvent and compounds.
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Am. Chem. Soc. 2003, 125, 7802. (b) Chow, C.-F.; Lam, M. H. W.; Wong,
W.-Y. Inorg. Chem. 2004, 43, 8387.
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J. Org. Chem, Vol. 71, No. 25, 2006 9471