capable of attaching gold nanoparticles, but tryptophan units can also capture C 60
[75]. Even more amazing is that the polypseudorotaxanes showed an ability to
cleave DNA under light irradiation. At the same time, we also found that the selfassembly of the polypseudorotaxane containing thiol-modified β-CD and gold
nanoparticles are effective DNA cleavage agents [76].
19.3 Network CD Polymers
Network CD polymers (we can also call them crosslinked CD polymers) were the
first type of CD polymers crosslinked with epichlorohydrin by Solms and Egli in
1965 [77]. Compared with linear CD polymers, the network CD polymers may have
more stable structure, good thermal stability, easier preparation, porous structure,
and a higher CD content. Since there is a plurality of hydroxyl groups in the CDs,
there may be multiple branching points in the polymerization process to form
network structures. When the degree of polymerization is not high, network CD
polymers are water-soluble. As the degree of crosslinking and the molecular weight
increases, the network CD polymers which only can swell and not dissolve will be
formed.
In addition to epichlorohydrin, diacids, dicarboxylic acid dihalides, diesters,
diisocyanates, dihalohydrocarbon, and diepoxides were also used to crosslink CDs
to obtain network CD polymers. Different CDs, crosslinkers, and reaction conditions
result in network CD polymers obtained having different properties (molecular
weight, thermal stability, specific surface area, biocompatibility, solubility, and so
on), so that they can be used as biomaterials in medical biology. So far, epichlorohydrin-crosslinked network CD polymers are most studied. Dating back to about
40 years ago, some researchers have these materials which were crosslinked by
epichlorohydrin for drug delivery [78, 79]. Komiyama et al. have constructed
molecularly imprinted network CD polymers crosslinked by toluene 2,4diisocyanate in the presence of various steroids, which are removed after completion
of the polymerization reaction, in DMSO (Fig. 10) [80]. These CD polymers can
specifically bind the steroid in the mixtures of H 2 O and THF. This type of imprinted
molecule based on network CD polymers is used for chromatography, which can
greatly improve the separation ability of the chromatogram and increase the number
of theoretical plates. The method in this work may be useful for the preparation of
natural products and biomedical molecules.
Nanosponges, as insoluble materials, which are constructed by either inorganic or
organic compounds have nanometric porosity, so these materials may have outstanding absorption or complexation properties. Among these nanosponges, a wellknown example is CD-based nanosponges (CD-NSs) based on network CD polymers. Although the development history of network CD polymers is more than
60 years, CD-NSs only develop for nearly two decades. However, since Li and Ma
constructed first CD-NSs by reacting β-CD with toluene-2,4-diisocyanate and hexamethylene diisocyanate used for purification of sewage [81, 82], the nanosponges
based on network CD polymers have achieved rapid development [83]. Nowadays,
19 Construction and Applications of Cyclodextrin Polymers in Biology
547
[75]. Even more amazing is that the polypseudorotaxanes showed an ability to
cleave DNA under light irradiation. At the same time, we also found that the selfassembly of the polypseudorotaxane containing thiol-modified β-CD and gold
nanoparticles are effective DNA cleavage agents [76].
19.3 Network CD Polymers
Network CD polymers (we can also call them crosslinked CD polymers) were the
first type of CD polymers crosslinked with epichlorohydrin by Solms and Egli in
1965 [77]. Compared with linear CD polymers, the network CD polymers may have
more stable structure, good thermal stability, easier preparation, porous structure,
and a higher CD content. Since there is a plurality of hydroxyl groups in the CDs,
there may be multiple branching points in the polymerization process to form
network structures. When the degree of polymerization is not high, network CD
polymers are water-soluble. As the degree of crosslinking and the molecular weight
increases, the network CD polymers which only can swell and not dissolve will be
formed.
In addition to epichlorohydrin, diacids, dicarboxylic acid dihalides, diesters,
diisocyanates, dihalohydrocarbon, and diepoxides were also used to crosslink CDs
to obtain network CD polymers. Different CDs, crosslinkers, and reaction conditions
result in network CD polymers obtained having different properties (molecular
weight, thermal stability, specific surface area, biocompatibility, solubility, and so
on), so that they can be used as biomaterials in medical biology. So far, epichlorohydrin-crosslinked network CD polymers are most studied. Dating back to about
40 years ago, some researchers have these materials which were crosslinked by
epichlorohydrin for drug delivery [78, 79]. Komiyama et al. have constructed
molecularly imprinted network CD polymers crosslinked by toluene 2,4diisocyanate in the presence of various steroids, which are removed after completion
of the polymerization reaction, in DMSO (Fig. 10) [80]. These CD polymers can
specifically bind the steroid in the mixtures of H 2 O and THF. This type of imprinted
molecule based on network CD polymers is used for chromatography, which can
greatly improve the separation ability of the chromatogram and increase the number
of theoretical plates. The method in this work may be useful for the preparation of
natural products and biomedical molecules.
Nanosponges, as insoluble materials, which are constructed by either inorganic or
organic compounds have nanometric porosity, so these materials may have outstanding absorption or complexation properties. Among these nanosponges, a wellknown example is CD-based nanosponges (CD-NSs) based on network CD polymers. Although the development history of network CD polymers is more than
60 years, CD-NSs only develop for nearly two decades. However, since Li and Ma
constructed first CD-NSs by reacting β-CD with toluene-2,4-diisocyanate and hexamethylene diisocyanate used for purification of sewage [81, 82], the nanosponges
based on network CD polymers have achieved rapid development [83]. Nowadays,
19 Construction and Applications of Cyclodextrin Polymers in Biology
547