can be regarded as a simple model for proteins. Both α-helix and β-sheet
conformations are basic secondary structures of proteins. The studies on ordered
structures of the polypeptides, especially in hierarchical structures, can contribute
to the prediction of the tertiary structures of proteins. Third, due to their biocompatibility and biodegradability, polypeptides and their assemblies are promising
candidates as biorelated materials for use in, for example, drug delivery and tissue
engineering scaffolds. Overall, the research on polypeptides and their ordered
structures can enrich our knowledge of polymer science and also provide useful
information for preparing advanced materials for medical and biotechnological
applications.
In this review, we summarize the features of polypeptide ordered structures in
LCs, gels and micelles and outline recent advances in this field. The article is
divided into four main parts. The first part reviews the ordering of polypeptide
homopolymers in LC structures. Polypeptides with rigid α-helix conformation can
form LCs in concentrated organic solutions. Common aspects of the LC structures
are briefly described. Recent advances, such as the conformation-induced cholesteric LC chirality transitions, the discovery of smectic phase, and the reentrant
isotropic transitions, are the main content of the section. In the second part, ordering
of polypeptide chains in gels is discussed. The structure of homopolymer gels is
compared with homopolymer LCs and studies on copolymer gels are featured in
detail. Samples formed in both organic and aqueous solutions are referred to. The
ordering of polypeptides in self-assembled micelles in dilute solution is
summarized in the third section. The ordering structures can be found in selfassemblies of cylinders and vesicles. The ordered packing tendency makes polypeptide copolymers an important candidate for producing hierarchical aggregates.
Lastly, conclusions and outlook are presented.
2 LC Structures of Polypeptide Homopolymers
Polypeptides adopt α-helix conformation when they are dissolved in organic
solvents such as N,N
0 -dimethylformamide (DMF), CHCl 3 , and benzene. When
the concentration is relatively high, LC structures are usually formed by the sideby-side ordered packing of rigid polypeptide chains. The ordering characteristics of
polypeptides was first observed from the LC structure [39, 49, 64–72]. The formation of polypeptide LCs requires two crucial characteristics, rigidity of the polymer
chain and ordering of the rod chains. Thus, only the α-helix polypeptide supports
the LC structures. The helix-to-coil transition of polypeptide chains can destroy the
LC ordering. In this section, typical LC structures and the arrangement of polypeptide chains in the LCs are discussed.
Ordering of Polypeptides in Liquid Crystals, Gels and Micelles
163
conformations are basic secondary structures of proteins. The studies on ordered
structures of the polypeptides, especially in hierarchical structures, can contribute
to the prediction of the tertiary structures of proteins. Third, due to their biocompatibility and biodegradability, polypeptides and their assemblies are promising
candidates as biorelated materials for use in, for example, drug delivery and tissue
engineering scaffolds. Overall, the research on polypeptides and their ordered
structures can enrich our knowledge of polymer science and also provide useful
information for preparing advanced materials for medical and biotechnological
applications.
In this review, we summarize the features of polypeptide ordered structures in
LCs, gels and micelles and outline recent advances in this field. The article is
divided into four main parts. The first part reviews the ordering of polypeptide
homopolymers in LC structures. Polypeptides with rigid α-helix conformation can
form LCs in concentrated organic solutions. Common aspects of the LC structures
are briefly described. Recent advances, such as the conformation-induced cholesteric LC chirality transitions, the discovery of smectic phase, and the reentrant
isotropic transitions, are the main content of the section. In the second part, ordering
of polypeptide chains in gels is discussed. The structure of homopolymer gels is
compared with homopolymer LCs and studies on copolymer gels are featured in
detail. Samples formed in both organic and aqueous solutions are referred to. The
ordering of polypeptides in self-assembled micelles in dilute solution is
summarized in the third section. The ordering structures can be found in selfassemblies of cylinders and vesicles. The ordered packing tendency makes polypeptide copolymers an important candidate for producing hierarchical aggregates.
Lastly, conclusions and outlook are presented.
2 LC Structures of Polypeptide Homopolymers
Polypeptides adopt α-helix conformation when they are dissolved in organic
solvents such as N,N
0 -dimethylformamide (DMF), CHCl 3 , and benzene. When
the concentration is relatively high, LC structures are usually formed by the sideby-side ordered packing of rigid polypeptide chains. The ordering characteristics of
polypeptides was first observed from the LC structure [39, 49, 64–72]. The formation of polypeptide LCs requires two crucial characteristics, rigidity of the polymer
chain and ordering of the rod chains. Thus, only the α-helix polypeptide supports
the LC structures. The helix-to-coil transition of polypeptide chains can destroy the
LC ordering. In this section, typical LC structures and the arrangement of polypeptide chains in the LCs are discussed.
Ordering of Polypeptides in Liquid Crystals, Gels and Micelles
163