yield of an important insecticide, ethiofencarb, was determined
by measuring the released methylamine. The results showed
that 59 ^ 6% (n \ 3) of the ethiofencarb can be hydrolyzed
under the given conditions (pH 11, temperature 80 ¡C, hydro-
lysis time 40 min), which was obtained by comparing the Ñuo-
rescence signal of the labeled released methylamine with that
of a standard labeled methylamine solution. This Ðnding was
also conÐrmed by analyzing the ethiofencarb remaining in the
hydrolytic solution by HPLC (Kromasil KR100-5 C18,
250 ] 4.6 mm), which showed 64% hydrolysis of ethiofencarb.
These results demonstrate that the present method can be
applied to the in situ monitoring of highly volatile methyl-
amine.
In conclusion, although a variety of Ñuorescent ion sensing
molecules have been designed based on the perturbation of
photophysical processes, less attention has been paid to in situ
Ñuorescent labeling probes for organic molecules. In this study
we have demonstrated the Ðrst in situ Ñuorescent labeling of
highly volatile methylamine with the donorÈacceptor molecule
1. The probe labels spectroscopically inert methylamine
causing a signiÐcant change in the Ñuorescence properties
through suppression of the internal charge transfer, and can
thereby serve as an in situ labeling probe, overcoming the
problem of the ready escape of methylamine from solution
during hydrolysis of N-methylcarbamates such as ethio-
fencarb. Further work in this area may be beneÐcial to the
development of a new generation of di†erent in situ labeling
probes for other organic targets.
Fig. 1 Fluorescence spectra of the probe 1 and methylamine solu-
tions (pH 11). Excitation spectra of (A) the reaction solution of 1
(3.4 ] 10~4 mmol) with methylamine (3.4 ] 10~4 mmol), (B) the solu-
tion of 1 alone (3.4 ] 10~4 mmol) and (C) the solution of methyl-
amine alone (3.4 ] 10~4 mmol). Emission spectra (A@, B@, C@)
corresponding to the above solutions are also shown. Bandpass of 2
nm at the entrance slit and 4 nm at the exit slit.
enhancement and the shift to a longer wavelength may result
from the introduction of the methylamino substituent, which
behaves as a strong electron donor.20 As is well known, when
a Ñuorescent molecule contains an electron-donating group
conjugated to an electron-withdrawing group, it undergoes
internal charge transfer from the donor to the acceptor upon
excitation by light. The consequent change in dipole moment
results in a Stokes shift that is sensitive to environmental
stimuli.17 Also, it is generally accepted that when the internal
charge transfer is perturbed by some factor (e.g. by chemical
reactions), the photophysical properties of the Ñuorescent mol-
ecule are often altered. The probe 1 is a donorÈacceptor mol-
ecule, and the internal charge transfer occurs from the
donating oxyquinoline8 to the electron accepting 1,3,5-tri-
azinyl group. Upon replacement of the second chlorine atom
of the probe by the strong electron-donating group
Acknowledgements
Financial support from the Alexander von Humboldt Foun-
dation of Germany, the NNSF of China and the CMS fund of
CAS is gratefully acknowledged.
ÈNHCH ,20 which reduces the electron acceptor character of
3
the triazinyl ring system,15 the internal charge transfer is sup-
pressed, thus resulting in photophysical changes. As expected,
the probe 1 labels methylamine resulting in signiÐcant changes
to its Ñuorescence properties, and the labeled methylamine,
representing a new compound, exhibits an excitation peak at
340 nm and emission peak at 405 nm (Fig. 1), respectively.
This new compound can be obtained nearly quantitatively by
reacting equimolar portions of the probe 1 and methylamine
at 30È50 ¡C in the presence of NaOH and was identiÐed as
8-(4-chloro-6-methylamino-1,3,5-triazinoxy)quinoline 2 by MS
analysis M300 (18.5) [M ] H ] 2]`, 288 (52.6) [M ] H]`, 252
(12.6) [M [ Cl]`N. Furthermore, the Ñuorescence spectrum of
2 is consistent with that of the in situ labeling solution of
methylamine in Fig. 1.
For a sensitive assay of methylamine with low background
Ñuorescence, 340 and 405 nm were employed as excitation and
emission wavelengths in this system, respectively. With the
present labeling procedure, the linear correlation between the
Ñuorescence intensity (F) and the methylamine concentration
(C) in the range 3.2È34 lM was found to be
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(r \ 0.9804) may be attributed to the fact that, besides the
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probe might follow their basicity [e.g. (CH ) NH [
3 2
CH NH [ NH ]. Nevertheless, this property would enable
3
2
3
the probe to Ðnd a use in pre- or post-column derivatization
of chromatographically separable compounds such as mixed
amines, and perhaps also phenols.
In order to test the applicability of the probe to the in situ
Ñuorescent labeling of volatile methylamine, the hydrolytic
874
New J. Chem., 2001, 25, 872È874