Yu Beihang, Danielsen Scott P O, Yang Kai-Chieh, Ho Rong-Ming, Walker Lynn M, Segalman Rachel A
Department of Chemical Engineering, National Tsing Hua University, Hsinchu 30010, Taiwan.
Department of Chemical Engineering, Center for Complex Fluids Engineering, Carnegie Mellon University, Pittsburgh, Pennsylvania 15213, United States.
ACS Macro Lett. 2020 Jun 16;9(6):849-854. doi: 10.1021/acsmacrolett.0c00293. Epub 2020 May 26.
The interplay between polymer-polymer and polymer-solvent interactions as well as interactions that impose secondary structures determines the conformation of polymer chains in dilute solution. Polypeptoids-poly(-substituted glycines) have been shown to form helical secondary structures primarily driven by steric interactions from chiral, bulky side chains, while polypeptoids with a racemic mixture of the same side chains lead to unstructured coil chains with a shorter Kuhn length. Small-angle neutron scattering (SANS) of the polypeptoids in dilute solution reveals that the helical polypeptoids are only locally stiffer than the coil chains formed from the racemic analogue, but exhibit overall flexibility. We show that chain conformations of both helical and coil polypeptoids (in terms of radius of gyration, ) are insensitive to solvent quality (parametrized by the second virial coefficient, ). Potential effects from the bulky, chiral/racemic side chains dominating chain conformations are excluded by comparison with an achiral polypeptoid lacking side chain chirality. The specific interactions between polypeptoid segments are likely dominating the chain conformations in this type of polypeptoids as opposed to polymer-solvent interactions or energetic contributions from the helical secondary structure.
聚合物-聚合物和聚合物-溶剂相互作用以及形成二级结构的相互作用之间的相互影响，决定了稀溶液中聚合物链的构象。聚肽类——聚（取代甘氨酸）已被证明主要由手性、庞大侧链的空间相互作用驱动形成螺旋二级结构，而具有相同侧链外消旋混合物的聚肽类则导致具有较短库恩长度的无规卷曲链。稀溶液中聚肽类的小角中子散射（SANS）表明，螺旋聚肽类比由外消旋类似物形成的卷曲链仅在局部更刚硬，但整体表现出柔韧性。我们表明，螺旋和卷曲聚肽类的链构象（以回转半径表示）对溶剂性质（由第二维里系数参数化）不敏感。与缺乏侧链手性的非手性聚肽类相比，排除了主导链构象的庞大、手性/外消旋侧链的潜在影响。与聚合物-溶剂相互作用或螺旋二级结构的能量贡献相反，聚肽类片段之间的特定相互作用可能主导了这类聚肽类的链构象。
