Organic Letters
Letter
of fluorescence of Sn2+-Rhod-Azo(0.25)@Si was determined
to be 55 au. As the loading extent in NHS-Azo(X)@Si used to
generate Rhod-Azo(X)@Si is gradually increased up to 1.13,
the intensity of fluorescence emission from Sn2+-Rhod-Azo(X)
@Si also increases to 634 au in a linear manner (Figure 5c).
A study was carried out to determine if Rhod-Azo@Si can be
used as a selective sensor for Sn2+. For this purpose, various
metal ions, including Sn2+, Zn2+, Hg2+, Cu2+, Ni2+, Mn2+, Ca2+,
and Na+, were added to solutions of Rhod-Azo(0.33)@Si in
methanol while recording fluorescence emission intensities
(Figure 5d). Among various metal ions, Sn2+ promotes the
strongest enhancement in the emission intensity associated
with its promotion of ring opening of rhodamine B. When the
same amount of Sn2+ is added to solutions of Rhod-Azo(0.63)
@Si and Rhod-Azo(1.13)@Si, the intensities of fluorescence
emission dramatically increase. In contrast, other metal ions do
not promote this change. This result shows that the Rhod-
Azo(1.13)@Si can be used as a selective sensor for Sn2+.
Moreover, the sensitivity of Rhod-Azo@Si for Sn2+ can be
controlled by experimentally adjusting the amount of
immobilized NHS-ester groups.
In the investigation described above, we developed a new
methallylsilane coupling reagent that contains an NHS-ester
group and a UV/vis absorbing azobenzene linker. This reagent
enables facile quantitative analysis of the extent of immobiliza-
tion of organic functional groups on the silica surface by simply
measuring the intensity of the azobenzene derived UV/vis
absorption band. We also showed that a linear correlation exists
between the UV/vis absorbance of the immobilized linker and
both the enzymatic activity of GOx and the metal cation
detection efficiency of rhodamine immobilized on silica. The
sensitivity of rhodamine-immobilized silica for detecting Sn2+
can be adjusted by simply controlling the loading extent of
NHS-ester groups, which can be monitored by using UV/vis
absorption spectroscopy.
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ASSOCIATED CONTENT
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* Supporting Information
The Supporting Information is available free of charge on the
Compound characterization data, 1H and 13C NMR
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AUTHOR INFORMATION
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Corresponding Author
ORCID
Author Contributions
§R.-Y.C. and C.-H.L. contributed equally.
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
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This work was supported by a grant from the National
Research Foundation of Korea (NRF) (Grant 2016-R-1-
A2b4009460).
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