縮氨酸高分子與其團聯共聚合物之自組裝行為探討

Supramolecular Organization in Self-assembly of Polypeptides and Peptide-based Diblock Copolymers

李婉榕(Wan-Jung Lee)

指導教授 ： 何榮銘

國立清華大學/工學院/化學工程學系/碩士(2006年)

摘要

A series of polypeptides, poly(ε-benzyloxycarbonyl-L-lysine) (PZLys), has been synthesized. The self-assembly of the PZLys was studied by using differential scanning calorimetry (DSC), Fourier transform infrared radiation spectroscopy (FTIR), small-angle X-ray scattering (SAXS) and polarizing optical microscopy (POM). The structural variations can be manipulated not only via the change of chain length but also various thermal treatments. The transformation of secondary structures from α-helix to β-sheet and the reversibility of supramolecular organization were examined. The conformational transformation between α-helix and β-sheet is expected to be strongly affected by the intra- and inter-molecular hydrogen bonding of polypeptide chains. The transformation of the secondary structures was found to be thermally irreversible by temperature-dependent FTIR. For high-molecular-weight polypeptides, the β-sheet conformation is destabilized in favor of the α-helical conformation, because the intra-molecular hydrogen bonds stabilize the α-helical conformations. As successively cooling and heating process, the structural evolution from secondary structures to tertiary structures revealed a reversible route and as a function of temperature which was investigated by temperature-dependent SAXS. In the tertiary textures, the dimension of the hexagonally packed α-helical structures exhibit thermally reversible behavior. With a decrease of molecular weight of polypeptides, β-sheet lamellae structures can be found in addition to hexagonal packing of α-helical organization and reveal similar thermal reversibility. The size of the β-sheet lamellar structures that is calculated from half-height width of Bragg peaks by Scherrer formula also changes with temperature. At high temperature, β-sheet conformation is stabilized by inter-molecular hydrogen bonding and contributes to the lamellar assembly of β-sheets, thus the size of β-sheet lamellar structures is thickened. In addition, shear-induced oriented samples were obtained and exhibited similar thermal reversibility in the tertiary structure. Only β-sheet lamellar structure is identified for oriented low-molecular-weight polypeptides, because the minor unstably hexagonal packing of α-helical organization is easily broken by external stress. Subsequently, specific textures are examined in quaternary structures by POM while β-sheet lamellar structures are formed from low-molecular-weight polypeptides. Results show that the textures start to develop at the transition temperature, i.e., from α-helix to β-sheet, and remain unchanged up to the thermal decomposition temperature.
Furthermore, novel nanostructures from self-assembly through secondary forces such as hydrogen bonding in the peptide-based diblock copolymer, poly(ε-benzyloxycarbonyl-L-lysine)-poly(L-Lactide acid) (PZLys-PLLA), were investigated. The secondary structures of PZLys-PLLA also possessed both of α-helical and β-sheet conformations. The lamellar-like structures have been observed by TEM. However, no Bragg peaks are observed in SAXS pattern because of the only slight difference of electron density between PZLys and PLLA blocks. The currently observed structural characteristics in PZLys-PLLA may serve as a basis for future studies.

關鍵字

自組裝 ； 縮氨酸高分子 ； 團聯共聚合物 ； 氫鍵

並列摘要

無資料

並列關鍵字

Self-assembly ； Polypeptides ； Diblock Copolymer ； Hydrogen Bonding

參考文獻

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