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Grafted Dipolar Chains: Dipoles and Restricted Freedom Lead to Unexpected Hairpins
Macromolecules ( IF 5.1 ) Pub Date : 2020-01-02 , DOI: 10.1021/acs.macromol.9b02288 Artyom D. Glova 1 , Sergey V. Larin 1 , Victor M. Nazarychev 1 , Mikko Karttunen 1 , Sergey V. Lyulin 1
Macromolecules ( IF 5.1 ) Pub Date : 2020-01-02 , DOI: 10.1021/acs.macromol.9b02288 Artyom D. Glova 1 , Sergey V. Larin 1 , Victor M. Nazarychev 1 , Mikko Karttunen 1 , Sergey V. Lyulin 1
Affiliation
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We use atomistic molecular dynamics simulations to investigate the structure of oligohydroxybutyrate (OHB) and oligolactide (OLA) chains grafted onto cellulose nanocrystals (CNCs) in melts of polyhydroxybutyrate and polylactide chains, respectively. We observed that, contrary to the established theory for neutral chains, the more flexible OHB grafts extend further from the CNC surface, whereas the stiffer OLA ones tend to fold back toward the surface by forming hairpin-like structures. Both OHB and OLA grafts have dipoles but are charge-neutral. To resolve this apparent contradiction, interactions between the grafts’ monomers as well as their flexibilities were evaluated. The interaction analysis, however, showed insignificant differences. We examined this further by systematically switching off the dipolar interactions and dihedrals from the OLA grafts. The observed counterintuitive behavior is due to a subtle combination of the dipole–dipole interactions and the additional methylene group in OHB that is critical in allowing the OHB grafts to sample more conformations than the more restricted OLA chains: the steric restrictions are critical and lead to hairpin-like structures and enable dipole–dipole interactions to effectively form a zipper that maintains the hairpin-like conformations.
中文翻译：
嫁接的偶极链：偶极子和有限的自由导致意外的发夹
我们使用原子分子动力学模拟来研究分别接枝到聚羟基丁酸酯和聚丙交酯链的熔体中的纤维素纳米晶体（CNC）上的寡羟基丁酸酯（OHB）和低聚丙交酯（OLA）链的结构。我们观察到，与已建立的中性链理论相反，更具柔性的OHB接枝从CNC表面延伸得更远，而较硬的OLA接枝则倾向于通过形成发夹状结构向表面折回。OHB和OLA移植物均具有偶极子，但电荷中性。为了解决这个明显的矛盾，评估了接枝单体之间的相互作用以及它们的柔韧性。但是，相互作用分析显示出不明显的差异。我们通过系统地关闭OLA移植物的偶极相互作用和二面体，进一步研究了这一点。观察到的违反直觉的行为是由于偶极-偶极相互作用与OHB中额外的亚甲基的微妙结合，与允许更严格的OLA链相比，这对于允许OHB移植物采样更多构象至关重要：位阻是至关重要的，并导致发夹状结构，使偶极子间相互作用能够有效形成维持发夹状构象的拉链。
更新日期：2020-01-04
中文翻译：
嫁接的偶极链：偶极子和有限的自由导致意外的发夹
我们使用原子分子动力学模拟来研究分别接枝到聚羟基丁酸酯和聚丙交酯链的熔体中的纤维素纳米晶体（CNC）上的寡羟基丁酸酯（OHB）和低聚丙交酯（OLA）链的结构。我们观察到，与已建立的中性链理论相反，更具柔性的OHB接枝从CNC表面延伸得更远，而较硬的OLA接枝则倾向于通过形成发夹状结构向表面折回。OHB和OLA移植物均具有偶极子，但电荷中性。为了解决这个明显的矛盾，评估了接枝单体之间的相互作用以及它们的柔韧性。但是，相互作用分析显示出不明显的差异。我们通过系统地关闭OLA移植物的偶极相互作用和二面体，进一步研究了这一点。观察到的违反直觉的行为是由于偶极-偶极相互作用与OHB中额外的亚甲基的微妙结合，与允许更严格的OLA链相比，这对于允许OHB移植物采样更多构象至关重要：位阻是至关重要的，并导致发夹状结构，使偶极子间相互作用能够有效形成维持发夹状构象的拉链。
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