Pierri Giovanni, Corno Marta, Macedi Eleonora, Voccia Maria, Tedesco Consiglia
Department of Chemistry and Biology "A. Zambelli", University of Salerno, Via Giovanni Paolo II, 84084 Fisciano, SA, Italy.
Department of Chemistry and NIS (Nanostructured Interfaces and Surfaces) Center, University of Turin, Via P. Giuria 7, 10125 Turin, Italy.
Cryst Growth Des. 2021 Feb 3;21(2):897-907. doi: 10.1021/acs.cgd.0c01244. Epub 2021 Jan 20.
We describe the energetic landscape beyond the solid-state dynamic behavior of a cyclic hexapeptoid decorated with four propargyl and two methoxyethyl side chains, namely, cyclo(Nme-Npa), Nme = -(methoxyethyl)glycine, Npa = -(propargyl)glycine. By increasing the temperature above 40 °C, the acetonitrile solvate form starts to release acetonitrile molecules and undergoes a reversible single crystal-to-single crystal transformation into crystal form with a remarkable conformational change in the macrocycle: two propargyl side chains move by 113° to form an unprecedented "CH-π zipper". Then, upon acetonitrile adsorption, the "CH-π zipper" opens and the crystal form transforms back to . By conformational energy and lattice energy calculations, we demonstrate that the dramatic side-chain movement is a peculiar feature of the solid-state assembly and is determined by a backbone conformational change that leads to stabilizing CH···OC backbone-to-backbone interactions tightening the framework upon acetonitrile release. Weak interactions as CH···OC and CH-π bonds with the guest molecules are able to reverse the transformation, providing the energy contribution to unzip the framework. We believe that the underlined mechanism could be used as a model system to understand how external stimuli (as temperature, humidity, or volatile compounds) could determine conformational changes in the solid state.
我们描述了一种带有四个炔丙基和两个甲氧基乙基侧链的环状六肽拟聚物（即环（Nme-Npa），其中Nme = -（甲氧基乙基）甘氨酸，Npa = -（炔丙基）甘氨酸）在固态动态行为之外的能量景观。当温度升高到40°C以上时，乙腈溶剂化物形式开始释放乙腈分子，并经历可逆的单晶到单晶转变，形成晶型 ，大环结构发生显著的构象变化：两个炔丙基侧链移动113°，形成前所未有的“CH-π拉链”。然后，在吸附乙腈时，“CH-π拉链”打开，晶型 转变回 。通过构象能和晶格能计算，我们证明这种显著的侧链移动是固态组装的一个独特特征，并且由主链构象变化决定，这种变化导致在乙腈释放时形成稳定的CH···OC主链到主链相互作用，从而收紧框架。与客体分子的CH···OC和CH-π键等弱相互作用能够逆转这种转变，为解开框架提供能量贡献。我们认为，下划线部分的机制可以作为一个模型系统，来理解外部刺激（如温度、湿度或挥发性化合物）如何决定固态中的构象变化。
