School of Chemistry, Indian Institute of Science Education and Research, Thiruvananthapuram, 695551 Kerala, India.
School of Chemistry, Indian Institute of Science Education and Research, Thiruvananthapuram, 695551 Kerala, India
Proc Natl Acad Sci U S A. 2018 Mar 20;115(12):2896-2901. doi: 10.1073/pnas.1718965115. Epub 2018 Mar 5.
Crystals that show mechanical response against various stimuli are of great interest. These stimuli induce polymorphic transitions, isomerizations, or chemical reactions in the crystal and the strain generated between the daughter and parent domains is transcribed into mechanical response. We observed that the crystals of modified dipeptide LL (N-l-Ala-l-Val-NHCHC≡CH) undergo spontaneous twisting to form right-handed twisted crystals not only at room temperature but also at 0 °C over time. Using various spectroscopic techniques, we have established that the twisting is due to the spontaneous topochemical azide-alkyne cycloaddition (TAAC) reaction at room temperature or lower temperatures. The rate of twisting can be increased by heating, exploiting the faster kinetics of the TAAC reaction at higher temperatures. To address the role of molecular chirality in the direction of twisting the enantiomer of dipeptide LL, N-d-Ala-d-Val-NHCHC≡CH (DD), was synthesized and topochemical reactivity and mechanoresponse of its crystals were studied. We have found that dipeptide DD not only underwent TAAC reaction, giving 1,4-triazole-linked pseudopolypeptides of d-amino acids, but also underwent twisting with opposite handedness (left-handed twisting), establishing the role of molecular chirality in controlling the direction of mechanoresponse. This paper reports () a mechanical response due to a thermal reaction and () a spontaneous mechanical response in crystals and () explains the role of molecular chirality in the handedness of the macroscopic mechanical response.
对能对各种刺激产生机械响应的晶体很感兴趣。这些刺激会在晶体中诱导多晶型转变、异构化或化学反应，而在子域和母域之间产生的应变被转录为机械响应。我们观察到，改性二肽 LL（N-l-丙氨酸-l-缬氨酸-NHCHC≡CH）的晶体不仅在室温下，而且在 0°C 下随着时间的推移自发扭曲，形成右手扭曲晶体。使用各种光谱技术，我们已经确定扭曲是由于室温下或较低温度下自发的叠氮化物-炔烃环加成（TAAC）反应。通过加热可以增加扭曲的速率，利用 TAAC 反应在较高温度下更快的动力学。为了解决分子手性在扭曲方向中的作用，我们合成了二肽 LL 的对映体 N-d-丙氨酸-d-缬氨酸-NHCHC≡CH（DD），并研究了其晶体的拓扑化学反应性和机械响应。我们发现二肽 DD 不仅经历了 TAAC 反应，生成了 d-氨基酸的 1,4-三唑键合假多肽，而且还发生了相反手性的扭曲（左手扭曲），这确立了分子手性在手性机械响应控制中的作用。本文报道了 () 热反应引起的机械响应和 () 晶体中的自发机械响应，以及 () 解释了分子手性在宏观机械响应手性中的作用。
