Chemistry Reference
In-Depth Information
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SCHEME 11.6
General structure of lactosyl groups functionalized oligorotaxane. (Adapted
from ref. 22.)
was effectively conjugated with polyrotaxane. The resulting ligand-density-controlled
PRs were then evaluated for a variety of biological applications.
Similar to this approach, Chwalek et al. developed low-molecular-weight oligoro-
taxanes with adjustable ligand densities as potential multivalent lectin inhibitors [22].
The oligorotaxane has five
-CDs and seven lactosyl groups “clicked” on as pendent
functionalities. In testing its binding ability to Arachis hypogaea peanut lectin, the
oligorotaxane exhibited a threefold increase per lactose unit (Scheme 11.6).
11.3.2.2 Hydrogels
Hydrogels are highly hydrated cross-linked polymer net-
works that have been used extensively in biomedical applications [23]. As a critical
element for the network formation, cross-linking agents with multiple functional-
ities would join the linear polymers together to form the network. As a biocom-
patible multifunctional molecule, CDs are natural selection for the cross-linking
agents. As an example for this design, Xu et al. recently developed a porous
“click” hydrogel using
-CD as the cross-linking structure [24]. They first pre-
pared 2-(2-bromoisobutyl-oxy) ethyl methacrylate (BIEMA) to copolymerize with
N-isopropylacrylamide (NIPAAm) at different ratios; after azidation, it produced a
copolymer with pendent azide groups distributed along the backbones. The seven
primary hydroxy groups of
-CD reacted with alkynecarboxylic acid catalyzed by
N,N
-dicyclohexylcarbodiimide (DCC) to introduce seven alkynyl groups for cross-
linking with azide groups. After mixing the copolymer, the functionalized
-CD and
the catalyst, the “click” hydrogel formation was completed within several minutes
(Scheme 11.7). It is notable that PNIPAAm is a thermosensitive polymer, which can
be employed as on-off switches for drug release purpose. Below the lower critical
solution temperature (LCST), the hydrogel exhibits a swollen state, while above
LCST, the phase separation takes place. To explore the therapeutic potential of the
“click” CD hydrogel, fish DNA was selected as the prototypic drug in the drug release
study and the DNA-loaded hydrogel demonstrated good thermosensitivity and drug
releasing profile.
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