C O M M U N I C A T I O N S
or all at once. (iii) The release observed in these cases was only
∼45%. This could be due to the ability of the hydrophobic chains
of our monomeric state of the dendrimer to withhold some amount
of pyrene.
Finally, it was important to determine whether the guest release
was really due to micellar disassembly. In order to address this,
we used dynamic light scattering (DLS) to investigate the trans-
formation in the size of these micellar assemblies upon addition of
protein. The initial size of the G1 assembly was found to be ∼300
nm. Upon addition of 10 µM extravidin, the size decreased to 10
nm, corresponding to size of the protein itself (Figure 2d), while
no such decrease in size was observed for other proteins.7 This
dramatic decrease in size supports our hypothesis that the protein
binding indeed caused the micellar disassembly, which then resulted
in the guest release. A similar size decrease was also observed with
G2, which further strengthens our disassembly hypothesis.7
In summary, we have demonstrated that dendrimer-based am-
phiphilic nanocontainers can be disassembled in response to an
engineered ligand-receptor interaction. Our working hypothesis
for the disassembly is based on the alteration in the HLB caused
by the binding event. We have shown that such a disassembly event
is selective to the protein for which the dendrimer is engineered.
We have also demonstrated that these disassembly events can cause
a concurrent release of guest molecules. The supramolecular
disassembly based on ligand binding outlined here could provide
a basis for the design of novel protein-responsive drug delivery
and biosensing systems.
Figure 2. Studies of the disassembly of G1 (25 µM) and G2 (5 µM)
assemblies. (a, b) Concentration-dependent dye release from (a) G1 and
(b) G2. (c) Direct addition of proteins (10 µM) to G1; (d) Size variation
upon exposure to proteins (10 µM), as determined by DLS.
due to the protein-ligand interaction.7 Furthermore, to determine
whether the guest release was selective to extravidin, we exposed
G1 to proteins with varying pI values, namely, thrombin, pepsin,
and chymotrypsin (ChT), and observed only a small percentage of
guest release (Figure 2a), probably due to nonspecific interactions.
This lack of significant guest release provided further evidence that
protein-ligand binding was the most likely reason for the guest
release in the extravidin case.7 Next, we tested whether a similar
guest release and disassembly could also be effected in the G2
dendron. Exposure of 25 µM G2 to extravidin resulted in only 30%
release, as compared with 42% release with G1.7 This is presumably
because the higher-generation dendron provides a more tightly
packed assembly. In addition, the lower CAC of G2 allowed us to
decrease the starting concentration. Indeed, when 5 µM G2 was
used, a release of ∼45% was obtained. Here too, the guest release
was found to be selective to extravidin (Figure 2b).7
Three features are noteworthy. (i) The guest release was entirely
concentration-dependent. For example, in the case of G1, addition
of 2 µM extravidin caused only 18% release, and no further release
was observed. Further release was observed only upon subsequent
addition of extravidin (Figure 2a), indicating the concentration-
dependent release characteristics. (ii) When we exposed G1 and
G2 solutions straightaway to 10 µM extravidin, we observed
immediate releases of ∼30 and 40% in 1 h for G1 and G2,
respectively, and an additional 10% release in 5 h (Figure 2c).
However, the direct addition of proteins other than extravidin did
not result in any significant release of pyrene.7 These results once
again imply that the guest release was controlled by the concentra-
tion of protein and eventually afforded almost the same amount of
release, regardless of whether protein was added in small portions
Acknowledgment. We thank the NIGMS of the National
Institutes of Health for support.
Supporting Information Available: Experimental details and NMR,
DLS, and fluorescence data. This material is available free of charge
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