Universal Relationship between Molecular Structure and Crystal Structure in Peptoid Polymers and Prevalence of the cis Backbone Conformation,Journal of the American Chemical Society

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Universal Relationship between Molecular Structure and Crystal Structure in Peptoid Polymers and Prevalence of the cis Backbone Conformation
Journal of the American Chemical Society ( IF 14.4 ) Pub Date : 2018-01-08 , DOI: 10.1021/jacs.7b11891
Douglas R. Greer _{1,

2} , Michael A. Stolberg ₁ , Joyjit Kundu ₃ , Ryan K. Spencer ₄ , Tod Pascal ₃ , David Prendergast ₃ , Nitash P. Balsara _{1,

2} , Ronald N. Zuckermann ₃

Affiliation

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-chain length (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 (Å) = 4.55, b (Å) = [2.98]N + 0.35, and c (Å) = [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.

中文翻译：

类肽聚合物中分子结构和晶体结构的普遍关系与顺式骨架构象的普遍性

通过 X 射线散射检查，拟肽聚合物通常是固态结晶，但到目前为止，还没有尝试确定它们之间的共同结构基序。为了探究分子结构与晶体结构之间的关系，我们合成并分析了一系列结晶类肽共聚物，系统地改变了类肽的侧链长度（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。在所有拟肽中，我们发现晶胞尺寸 a、b 和 c 是 S 和 N 的简单函数：a (Å) = 4.55，b (Å) = [2.98]N + 0.35，c (Å) ) = [1.86]S + 5.5。这些关系适用于大块晶体和水中的自组装纳米片，表明分子采用扩展的平面构象。此外，我们对拟肽聚合物晶格进行了分子动力学模拟 (MD)，这表明所有骨架酰胺都采用顺式构象。这是一个令人惊讶的结论，因为先前对分离分子的研究表明对反式构象异构体的能量偏好。这项研究表明，当装入超分子晶格或晶体时，类肽聚合物更喜欢采用规则的、延伸的、全顺式二级结构。

更新日期：2018-01-08

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