Zong Zhaohui, Hao Aiyou, Xing Pengyao, Zhao Yanli
Key Laboratory of Colloid and Interface Chemistry of Ministry of Education, School of Chemistry and Chemical Engineering, Shandong University Jinan 250100 People's Republic of China
Division of Chemistry and Biological Chemistry, School of Physical and Mathematical Sciences, Nanyang Technological University 21 Nanyang Link Singapore 637371 Singapore
Chem Sci. 2022 Mar 14;13(14):4029-4040. doi: 10.1039/d2sc00793b. eCollection 2022 Apr 6.
Molecular nanoparticles including polyoxometalates, proteins, fullerenes and polyhedral oligosiloxane (POSS) are nanosized objects with atomic precision, among which POSS derivatives are the smallest nanosilicas. Incorporation of molecular nanoparticles into chiral aggregates either by chiral matrices or self-assembly allows for the transfer of supramolecular chirality, yet the construction of intrinsic chirality with atomic precision in discrete molecules remains a great challenge. In this work, we present a molecular folding strategy to construct giant POSS molecules with inherent chirality. Ferrocenyl diamino acids are conjugated by two or four POSS segments. Hydrogen bonding-driven folding of diamino acid arms into parallel β-sheets facilitates the chirality transfer from amino acids to ferrocene and POSS respectively, disregarding the flexible alkyl spacers. Single crystal X-ray structures, density functional theory (DFT) calculations, circular dichroism and vibrational circular dichroism spectroscopy clearly verify the preferential formation of one enantiomer containing chiral molecular nanosilicas. The chiral orientation and chiroptical properties of POSS show pronounced dependence on the substituents of α-amino acids, affording an alternative way to control the folding behavior and POSS chirality in addition to the absolute configuration of amino acids. Through the kinetic nanoprecipitation protocol, one-dimensional aggregation enables chirality transfer from the molecular scale to the micrometer scale, self-assembling into helices in accordance with the packing propensity of POSS in a crystal phase. This work, by illustrating the construction of chiral molecular nanosilicas, paves a new way to obtain discrete chiral molecular nanoparticles for potential chiroptical applications.
包括多金属氧酸盐、蛋白质、富勒烯和多面体低聚倍半硅氧烷（POSS）在内的分子纳米粒子是具有原子精度的纳米级物体，其中POSS衍生物是最小的纳米二氧化硅。通过手性基质或自组装将分子纳米粒子掺入手性聚集体中，可以实现超分子手性的转移，然而在离散分子中以原子精度构建固有手性仍然是一个巨大的挑战。在这项工作中，我们提出了一种分子折叠策略来构建具有固有手性的巨型POSS分子。二茂铁基二氨基酸通过两个或四个POSS片段共轭。二氨基酸臂通过氢键驱动折叠成平行的β-折叠片，促进了手性分别从氨基酸转移到二茂铁和POSS，而忽略了柔性烷基间隔基。单晶X射线结构、密度泛函理论（DFT）计算、圆二色性和振动圆二色光谱清楚地证实了一种含有手性分子纳米二氧化硅的对映体的优先形成。POSS的手性取向和手性光学性质对α-氨基酸的取代基表现出明显的依赖性，除了氨基酸的绝对构型外，还提供了一种控制折叠行为和POSS手性的替代方法。通过动力学纳米沉淀方法，一维聚集能够使手性从分子尺度转移到微米尺度，根据POSS在晶相中的堆积倾向自组装成螺旋结构。这项工作通过说明手性分子纳米二氧化硅的构建，为获得用于潜在手性光学应用的离散手性分子纳米粒子开辟了一条新途径。
