Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, United States.
Department of Chemical and Biomolecular Engineering, University of California, Berkeley, Berkeley, California 94720, United States.
ACS Macro Lett. 2023 May 16;12(5):632-638. doi: 10.1021/acsmacrolett.3c00101. Epub 2023 Apr 26.
Amphiphilic molecules that can crystallize often form molecularly thin nanosheets in aqueous solutions. The possibility of atomic-scale corrugations in these structures has not yet been recognized. We have studied the self-assembly of amphiphilic polypeptoids, a family of bio-inspired polymers that can self-assemble into various crystalline nanostructures. Atomic-scale structure of the crystals in these systems has been inferred using both X-ray diffraction and electron microscopy. Here we use cryogenic electron microscopy to determine the in-plane and out-of-plane structures of a crystalline nanosheet. Data were collected as a function of tilt angle and analyzed using a hybrid single-particle crystallographic approach. The analysis reveals that adjacent rows of peptoid chains, which are separated by 4.5 Å in the plane of the nanosheet, are offset by 6 Å in the direction perpendicular to the plane of the nanosheet. These atomic-scale corrugations lead to a doubling of the unit cell dimension from 4.5 to 9 Å. Our work provides an alternative interpretation for the observed Å X-ray diffraction peak often reported in polypeptoid crystals.
能够结晶的两亲性分子在水溶液中通常会形成分子级薄的纳米片。这些结构中原子级起伏的可能性尚未被认识到。我们研究了两亲性多肽的自组装，这是一类受生物启发的聚合物，可以自组装成各种结晶纳米结构。使用 X 射线衍射和电子显微镜推断了这些系统中晶体的原子级结构。在这里，我们使用低温电子显微镜来确定结晶纳米片的面内和面外结构。数据是作为倾斜角的函数收集的，并使用混合单颗粒晶体学方法进行分析。分析表明，纳米片平面内相隔 4.5 Å 的肽链相邻行在垂直于纳米片平面的方向上偏移 6 Å。这些原子级起伏导致单元胞尺寸从 4.5 增加到 9 Å。我们的工作为在多肽晶体中经常报道的观察到的 Å X 射线衍射峰提供了另一种解释。
