Tailoring of amino acid residues is a feasible strategy to design the structure of peptide for special application. We selected poly(ethylene glycol) and α-amino acids with hydrophobic alkyl side group (L-alanine，L-valine and L-leucine) to synthesize di-block co-polypeptide. The copolymers with methyl side group self-assembled into random coil in majority and aggregated further into stable spherical nanoarchitectures with a little filament owing to the small size, less flexibility and less hydrophobicity of methyl group. By lengthening peptide block, the copolymer self-organized into overwhelming β-sheet and ordered nanorods or nanofibers due to the strengthening hydrophobicity as the copolymers with isopropyl side group did. The copolymers with isobutyl side groups showed cloudy solutions and irregular morphology because the flexibility and large size of isobutyl groups hampered the regular stacking of β-plated sheets and agglomerated into micro-sized precipitates despite of the most hydrophobicity. As temperature rising, both the transition of random coil to β-sheet and PEG dehydration contributed to the sol-gel transition for the copolymers with methyl side group, while PEG dehydration was the primary reason of sol-gel transition for the copolymers with isopropyl side group. In this article, we first disclosed the self-organization process of mPEG-b-polypeptide, which would lay the foundation for the designing of polypeptide-related materials with well-defined properties.

氨基酸残基的剪裁是设计特殊应用肽结构的可行策略。我们选择了聚乙二醇和具有疏水烷基侧基的α-氨基酸（L-丙氨酸、L-缬氨酸和L-亮氨酸）来合成双嵌段共聚多肽。由于甲基的尺寸小、柔韧性差和甲基的疏水性差，带有甲基侧基的共聚物大部分自组装成无规卷曲，并进一步聚集成稳定的球形纳米结构，带有少量细丝。通过加长肽段，共聚物由于增强了疏水性而自组织成压倒性的 β-折叠和有序的纳米棒或纳米纤维，就像带有异丙基侧基的共聚物一样。具有异丁基侧基的共聚物显示出浑浊的溶液和不规则的形态，因为异丁基的柔韧性和大尺寸阻碍了 β 镀层的规则堆叠，尽管疏水性最强，但仍会聚集成微米尺寸的沉淀物。随着温度升高，无规卷曲向β-折叠的转变和PEG脱水都有助于甲基侧基共聚物的溶胶-凝胶转变，而PEG脱水是异丙基共聚物溶胶-凝胶转变的主要原因团体。在这篇文章中，我们首先揭示了mPEG-b-多肽的自组织过程，这将为设计具有明确特性的多肽相关材料奠定基础。