Universal Relationship between Molecular Structure and Crystal Structure in Peptoid Polymers and Prevalence of the &ITcis&IT Backbone Conformation
Universal Relationship between Molecular Structure and Crystal Structure in Peptoid Polymers and Prevalence of the &ITcis&IT Backbone Conformation
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DOI：
10.1021/jacs.7b11891
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发表时间：
2018-01-17
影响因子：
15
通讯作者：
Zuckermann, Ronald N.
中科院分区：
文献类型：
--
作者：
Greer, Douglas R.;Stolberg, Michael A.;Zuckermann, Ronald N.
通过X射线散射检测，类肽聚合物在固态时通常是结晶的，但到目前为止，还没有人试图确定它们之间的共同结构主题。为了探索分子结构和晶体结构之间的关系，我们合成并分析了一系列结晶型类肽共聚物，系统地改变了类肽侧链长度(S)和主链长度(N)。我们还检查了18种先前报道的类肽聚合物的X射线散射数据。在所有的类肽中，我们发现晶胞尺寸a，b和c是S和N的简单函数：a(埃)=4.55，b(埃)=[2.98]N+0.35，c(埃)=[1.86]S+5.5。这些关系既适用于大块晶体，也适用于水中自组装的纳米片，表明分子采用延伸的平面构象。此外，我们对类肽聚合物晶格进行了分子动力学模拟，结果表明所有主链酰胺都采用顺式构象。这是一个令人惊讶的结论，因为之前对分离分子的研究表明，反式构象具有能量偏好。这项研究表明，当被填充到超分子晶格或晶体中时，类肽聚合物更倾向于采用规则的、扩展的、全顺式二级结构。
Peptoid polymers are often crystalline in the solid-state as examined by X-ray scattering, but thus far, there has been no attempt to identify a common structural motif among them. In order to probe the relationship between molecular structure and crystal structure, we synthesized and analyzed a series of crystalline peptoid copolymers, systematically varying peptoid side-chain length (S) and main-chainlength (N). We also examined X-ray scattering data from 18 previously reported peptoid polymers. In all peptoids, we found that the unit cell dimensions, a, b, and c, are simple functions of S and N: a (angstrom) = 4.55, b (angstrom) = [2.98]N + 0.35, and c (angstrom) = [1.86]S + 5.5. These relationships,which apply to both bulk crystals and self-assembled nanosheets in water, indicate that the molecules adopt extended, planar conformations. Furthermore, we performed molecular dynamics simulations (MD) of peptoid polymer lattices, which indicate that all backbone amides adopt the cis conformation. This is a surprising conclusion, because previous studies on isolated molecules indicated an energetic preference for the trans conformer. This study demonstrates that when packed into supramolecular lattices or crystals, peptoid polymers prefer to adopt a regular, extended, all-cis secondary structure.