C O M M U N I C A T I O N S
Scheme 2. Synthesis and Activation of Enzyme-Responsive
Snap-Top System
used one snap-top precursor to prepare two different snap-top
systems, one with an ester-linked stopper and the other with an
amide-linked stopper. Using luminescence spectroscopy, we have
demonstrated the ability of PLE to selectively activate the ester-
linked snap-top system while the amide-linked system is left intact.
The result of this work is a biocompatible controlled release system
that exploits enzymatic specificity. Because of the wide range of
stoppering units that could be attached to the SCSN precursor, a
multitude of snap-top systems with differentiated modes of activa-
tion could be prepared with relative ease. In the future, the divergent
synthetic approach that we have described will allow the snap-top
motif to be very easily adapted to accommodate many different
applications.
the amide CdO group at 1650 and 1600 cm-1. The ester-
functionalized snap-top system shows instead the expected ester
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1
Acknowledgment. The collaboration was supported by the NSF
CdO stretch at 1731 cm with pronounced C-H absorptions
(Grants CHE 0507929 and DMR 0346601) and the University of
arising from the adamantyl group. In the spectra of the nanoparticles
-1
California Toxic Substances Research and Teaching Program.
after guest release, the region around 3000 cm is broad, a feature
which is characteristic of the new carboxylic acid functionality while
Supporting Information Available: Experimental details, spectral
characterization data of all new compounds. This material is available
free of charge via the Internet at http://pubs.acs.org.
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1
the CdO peak is still evident at 1731 cm indicating some
remaining ester functionalities on the surface of the nanoparticles.
The enzyme-triggered release of cargo molecules was monitored
using luminescence spectroscopy. The dye-loaded, stoppered
particles (15 mg) were placed in the corner of a cuvette before
carefully adding HEPES buffer (50 mM, 12 mL, pH ) 7.5). To
open the snap-tops, a solution of PLE [0.12 mL, 10 mg/mL in 3.2
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Figure 1. Controlled release of rhodamine B from ester (green) or amide
blue) stoppered snap-tops. The response of the ester-stoppered system to
the deactivated enzyme (red) is also shown.
(
(
Prior to the addition of PLE, the emission intensity of rhodamine
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emission intensity asymptotically approaches its maximum value
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(
(
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Described herein is a versatile system that is capable of
entrapment and controlled release of cargo molecules. We have
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J. AM. CHEM. SOC.
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