Control of association and gelation behavior of ABA triblock copolymers by means of conformational transition of B block

在聚[N^5-(2-羟乙基)L-谷氨酰胺](PHEG)的链两端连接了疏水的正十二基(C12)基团，制备了两端疏水修饰的水溶性多肽。研究了该缔合多肽在水/乙二醇(EG)混合溶剂中的螺旋卷曲转变和缔合行为。1.在稀水溶液中，PHEG中间链处于无规卷曲状态，疏水C12基团缔合形成孤立的小尺寸胶束。随着混合溶剂中EG含量的增加，胶束尺寸急剧增大。这些结果表明，PHEG螺旋含量的增加导致连接不同C12缔合核的桥式构象比例增加，导致结构从孤立的缔合物转变为由PHEG链连接的多个缔合核组成的大缔合物。2.上述缔合模式可以解释稀溶液中样品制备过程对缔合的依赖性以及半浓溶液的凝胶行为。3.考察了单端疏水修饰PHEGs的缔合行为。随着端烷基链疏水性的增加，缔合强度增加。聚乙二醇链的构象转变引起了胶束结构的变化，即当聚乙二醇处于无规卷曲状态时呈球形，当呈α-螺旋构象时呈蠕虫状圆柱体。4.制备了聚乙二醇嵌段共聚物，并研究了其在聚乙二醇选择性溶剂中的缔合作用。当聚乙二醇处于α螺旋状态时，由于聚乙二醇链的刚性堆积，缔合物呈中空圆柱形。当PHEG倾向于无规卷曲构象时，建议形成一个正常的核心-冠状蠕虫状圆柱体。

Both-ends hydrophobically-modified water-soluble polypeptide, in which hydrophobic n-dodecyl (C12) groups are bonded at the both chain ends of poly[N^5-(2-hydroxyethyl) L-glutamine] (PHEG), has been prepared. Helix-coil transition and association behavior of this associative polypeptide in water/ethylene glycol (EG) mixed solvent, which is selective for PHEG block, have been investigated.1.In dilute aqueous solution, the middle PHEG chain is in random coil state, and isolated small-size micelles were formed by association of hydrophobic C12 groups. The micellar size increased drastically with the increase of EG content in the mixed solvent. These results suggest that the increase of the helix content of PHEG induces the increase of fraction of bridge conformation connecting different C12 associated cores, which results in the change of structure from an isolated associate to a large associate including multiple associated cores connected by PHEG chains.2.The above association scheme can explain process dependencies of sample preparation on the association in dilute solutions as well as gelation behavior of semi-concentrated solutions.3.Association behavior of one-end hydrophobically-modified PHEGs was also investigated. Association strength was increased with the increase of hydrophobicity of the terminal alkyl chain. Conformational transition of PHEG chain induced a change in micellar structure, i.e., spherical shape when PHEG is in random coil state and worm-like cylinder when PHEG in α-helix conformation.4.Block copolymer of PHEG and poly(ethylene glycol) was prepared, and its association in a selective solvent for poly(ethylene glycol) was investigated. When PHEG is in α-helical state, the associate is in hollow cylindrical shape because of a packing of rigid PHEG chain. When PHEG prefer to take random-coil conformation, formation of a normal core-corona type wormlike cylinder was suggested.