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(CH
2
OH)
6
(OH)
14
N
N
N
O
O
O
O
Si O
2
O
O
Si
Br
m
O
n
O
HO
OH
inner layer
external layer
SCHEME 11.5
The structure of “click” RAM (restricted-access material). (Adapted from
ref. 15.)
the chiral selector. The chiral separation of flavanone enantiomers was achieved in
both capillary electrochromatography and nano-liquid chromatography with good
resolution.
11.3.2 Functional Biomaterials
Due to the presence of multiple reactive hydroxyl groups and their inclusion ability,
CDs have also been used extensively in the development of various biomaterials, such
as polyrotaxane (PR), hydrogel, and functionalized polymers. As a novel chemical
tool, “click” reactions were used to replace the conventional methodologies in the
design and development of these biomaterials, motivated by their high efficiency,
functional tolerance, and mild reaction conditions.
11.3.2.1 Polyrotaxanes
Polyrotaxanes (PRs) are supramolecular assemblies in
which cyclic molecules (CD, calixarene, cucurbituril, or crown ether) are threaded
onto a linear polymer chain capped with bulky end groups. Among all PRs inves-
tigated, the PR consisting of CDs and poly(ethylene glycol) (PEG) were the most
widely investigated. Since first discovered by Harada et al. [17, 18], their applications
in biomaterials and drug delivery have been extensively explored.
The spontaneous supramolecular assembly of CDs onto PEG chain is an enthalpy-
driven process. Such threading is not a thermodynamically stable construct, which
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