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Temperature and Viscosity Tune the Intermediates during the Collapse of a Polymer 温度和粘度调节聚合物崩解过程中的中间产物
IF 5.5 1区 化学 Q1 POLYMER SCIENCE Pub Date : 2024-11-04 DOI: 10.1021/acs.macromol.4c01042
Suman Majumder, Henrik Christiansen, Wolfhard Janke
Dynamics of a polymer chain in solution gets significantly affected by the temperature and frictional forces arising due to viscosity of the solvent. Here, using an explicit solvent framework for polymer simulation with the liberty to tune the viscous drag of the system, we study the nonequilibrium dynamics of a flexible homopolymer when it is suddenly quenched from an extended random-coil state in good solvent to poor solvent conditions. Results from our extensive simulations reveal that depending on the temperature T and viscous drag, one encounters long-lived sausage-like intermediates following the usual pearl-necklace intermediates. Using shape factors of the polymer we disentangle these two distinct stages of the overall collapse process. This allows us to extract the corresponding relaxation times and their respective scaling behaviors as a function of the length of the polymer. The relaxation time τs of the sausage stage, which is the rate-limiting stage of the overall collapse process, follows an anti-Arrhenius behavior in the high-T limit, and the Arrhenius behavior in the low-T limit. Furthermore, the variation of τs with the viscous drag provides evidence of internal friction of the polymer, that modulates the overall collapse significantly, analogous to what is observed for relaxation rates of proteins during their folding. This suggests that the origin of internal friction in proteins is plausibly intrinsic to its polymeric backbone rather than other specifications.
溶液中聚合物链的动力学会受到温度和溶剂粘度产生的摩擦力的显著影响。在此,我们利用可自由调节系统粘滞阻力的聚合物模拟显式溶剂框架,研究了柔性均聚物从良好溶剂条件下的延伸无规卷绕状态突然淬火到不良溶剂条件下的非平衡动力学。大量模拟结果表明,根据温度 T 和粘滞阻力的不同,在通常的珍珠项链中间体之后,会出现长寿命的香肠状中间体。利用聚合物的形状因子,我们将整个塌缩过程的这两个不同阶段区分开来。这样,我们就可以提取出相应的弛豫时间以及它们各自作为聚合物长度函数的缩放行为。香肠阶段是整个塌缩过程的限速阶段,其弛豫时间 τs 在高 T 极限遵循反阿伦尼斯行为,而在低 T 极限遵循阿伦尼斯行为。此外,τs 随粘滞阻力的变化提供了聚合物内摩擦的证据,这种内摩擦会显著调节整体塌缩,这与蛋白质在折叠过程中的弛豫速率类似。这表明,蛋白质中内摩擦力的来源可能是其聚合物骨架的固有特性,而非其他规格。
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引用次数: 0
Impact of Ionene Architecture on Ion Mobility 离子烯结构对离子迁移率的影响
IF 5.5 1区 化学 Q1 POLYMER SCIENCE Pub Date : 2024-11-02 DOI: 10.1021/acs.macromol.4c01217
Eric M. Schibli, Colton Lohn, Adrian Yeung, Steven Holdcroft, Barbara J. Frisken
We have investigated the nanostructure of five ionenes based on three different benzimidazolium- and imidizolium-based backbones as a function of hydration using atomistic molecular dynamics simulations supplemented with X-ray scattering. All five samples reveal sponge-like nanostructures with near-complete percolation, even at low degrees of hydration, and no evidence of long-range phase separation. Analysis of the structure and ion dynamics shows that, while connectivity is highest among the samples functionalized with methyl alkylating units, the ionic pathways in the imidizolium-based backbones functionalized with butyl alkylating units are less tortuous, leading to faster ion diffusion at low water content.
我们利用原子分子动力学模拟并辅以 X 射线散射,研究了基于三种不同苯并咪唑和咪唑骨架的五种离子烯的纳米结构与水合作用的关系。所有五个样品都显示出海绵状的纳米结构,即使在水合度较低的情况下也具有近乎完全的渗透性,而且没有长程相分离的迹象。对结构和离子动力学的分析表明,虽然甲基烷基化单元官能化的样品的连通性最高,但丁基烷基化单元官能化的咪唑基骨架的离子通道不那么曲折,因此在低含水量时离子扩散速度更快。
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引用次数: 0
Solutions of Diblock Copolymer Micelles with Bottlebrush Blocks. Scaling Model 二嵌段共聚物胶束与底嵌段的溶液。缩放模型
IF 5.5 1区 化学 Q1 POLYMER SCIENCE Pub Date : 2024-11-01 DOI: 10.1021/acs.macromol.4c02000
Ekaterina B. Zhulina, Oleg V. Borisov
We present a scaling theory describing equilibrium properties of starlike micelles formed by a diblock copolymer with bottlebrush (bb) blocks in solutions. In dilute and semidilute solutions, the blocks are envisioned as linear chains of impermeable superblobs with sizes DA and DB. Depending on the ratio of block “thicknesses”, DA/DB, micelles can exhibit different power law dependences on solution concentration. We demonstrate that bb branching of blocks increases the number of different regimes in the diagram of states compared with diblock copolymers with linear blocks. In particular, in concentrated solution, thickness DA of soluble block A decreases and micelles rearrange similarly to spherical domains in melts of diblock copolymer with the concentration-dependent size of the monomer unit in the corona block. In both the semidilute and concentrated solutions, starlike micelles remain essentially impermeable and exhibit quasi-globular regimes. The theoretical predictions are contrasted to experiments.
我们提出了一种缩放理论,它描述了在溶液中由带有底丛(bottlebrush)嵌段的二嵌段共聚物形成的星形胶束的平衡特性。在稀释和半稀释溶液中,嵌段被设想为尺寸为 DA 和 DB 的防渗超级球状线性链。根据块体 "厚度 "的比率(DA/DB),胶束会表现出与溶液浓度不同的幂律关系。我们证明,与线性嵌段的二嵌段共聚物相比,嵌段的分枝增加了状态图中不同状态的数量。特别是,在浓溶液中,可溶性嵌段 A 的厚度 DA 会减小,胶束的重排类似于二嵌段共聚物熔体中的球形畴,电晕嵌段中单体单元的大小与浓度有关。在半稀释溶液和浓缩溶液中,星形胶束基本上保持不渗透状态,并呈现准球形状态。理论预测与实验结果进行了对比。
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引用次数: 0
Understanding and Tuning the Effects of H2O on Catalytic CO and CO2 Hydrogenation 了解和调整 H2O 对催化 CO 和 CO2 加氢的影响
IF 51.4 1区 化学 Q1 POLYMER SCIENCE Pub Date : 2024-10-31 DOI: 10.1021/acs.chemrev.4c0028210.1021/acs.chemrev.4c00282
Mingrui Wang, Guanghui Zhang*, Hao Wang, Zhiqun Wang, Yu Zhou, Xiaowa Nie, Ben Hang Yin, Chunshan Song* and Xinwen Guo*, 

Catalytic COx (CO and CO2) hydrogenation to valued chemicals is one of the promising approaches to address challenges in energy, environment, and climate change. H2O is an inevitable side product in these reactions, where its existence and effect are often ignored. In fact, H2O significantly influences the catalytic active centers, reaction mechanism, and catalytic performance, preventing us from a definitive and deep understanding on the structure-performance relationship of the authentic catalysts. It is necessary, although challenging, to clarify its effect and provide practical strategies to tune the concentration and distribution of H2O to optimize its influence. In this review, we focus on how H2O in COx hydrogenation induces the structural evolution of catalysts and assists in the catalytic processes, as well as efforts to understand the underlying mechanism. We summarize and discuss some representative tuning strategies for realizing the rapid removal or local enrichment of H2O around the catalysts, along with brief techno-economic analysis and life cycle assessment. These fundamental understandings and strategies are further extended to the reactions of CO and CO2 reduction under an external field (light, electricity, and plasma). We also present suggestions and prospects for deciphering and controlling the effect of H2O in practical applications.

催化 COx(CO 和 CO2)加氢制备有价值的化学品是应对能源、环境和气候变化挑战的有效方法之一。H2O 是这些反应中不可避免的副产物,其存在和影响往往被忽视。事实上,H2O 会对催化活性中心、反应机理和催化性能产生重大影响,使我们无法对真实催化剂的结构-性能关系有明确而深入的了解。有必要澄清其影响,并提供实用的策略来调整 H2O 的浓度和分布,以优化其影响,尽管这很有挑战性。在本综述中,我们将重点讨论 COx 加氢过程中的 H2O 如何诱导催化剂的结构演变并协助催化过程,以及为了解其潜在机理所做的努力。我们总结并讨论了一些具有代表性的调整策略,以实现催化剂周围 H2O 的快速去除或局部富集,并进行了简要的技术经济分析和生命周期评估。这些基本认识和策略将进一步扩展到外部场(光、电和等离子体)条件下的 CO 和 CO2 还原反应。我们还提出了在实际应用中破解和控制 H2O 影响的建议和前景。
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引用次数: 0
Computational Tools for Hydrogen–Deuterium Exchange Mass Spectrometry Data Analysis 氢氘交换质谱数据分析计算工具
IF 51.4 1区 化学 Q1 POLYMER SCIENCE Pub Date : 2024-10-31 DOI: 10.1021/acs.chemrev.4c0043810.1021/acs.chemrev.4c00438
Michele Stofella, Antonio Grimaldi, Jochem H. Smit, Jürgen Claesen, Emanuele Paci* and Frank Sobott*, 

Hydrogen–deuterium exchange (HDX) has become a pivotal method for investigating the structural and dynamic properties of proteins. The versatility and sensitivity of mass spectrometry (MS) made the technique the ideal companion for HDX, and today HDX-MS is addressing a growing number of applications in both academic research and industrial settings. The prolific generation of experimental data has spurred the concurrent development of numerous computational tools, designed to automate parts of the workflow while employing different strategies to achieve common objectives. Various computational methods are available to perform automated peptide searches and identification; different statistical tests have been implemented to quantify differences in the exchange pattern between two or more experimental conditions; alternative strategies have been developed to deconvolve and analyze peptides showing multimodal behavior; and different algorithms have been proposed to computationally increase the resolution of HDX-MS data, with the ultimate aim to provide information at the level of the single residue. This review delves into a comprehensive examination of the merits and drawbacks associated with the diverse strategies implemented by software tools for the analysis of HDX-MS data.

氢氘交换(HDX)已成为研究蛋白质结构和动态特性的重要方法。质谱(MS)的多功能性和灵敏度使其成为 HDX 的理想伴侣,如今,HDX-MS 在学术研究和工业领域的应用日益增多。大量实验数据的产生促进了众多计算工具的同步发展,这些工具旨在自动化部分工作流程,同时采用不同的策略来实现共同的目标。目前有多种计算方法可用于肽的自动搜索和鉴定;不同的统计检验方法可用于量化两种或多种实验条件下交换模式的差异;另有多种策略可用于对表现出多模式行为的肽进行解卷积和分析;还有不同的算法可用于通过计算提高 HDX-MS 数据的分辨率,最终目的是提供单个残基水平的信息。这篇综述全面探讨了用于分析 HDX-MS 数据的软件工具所采用的各种策略的优缺点。
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引用次数: 0
Electrochemical and Non-Electrochemical Pathways in the Electrocatalytic Oxidation of Monosaccharides and Related Sugar Alcohols into Valuable Products 将单糖和相关糖醇电催化氧化成有价值产品的电化学和非电化学途径
IF 51.4 1区 化学 Q1 POLYMER SCIENCE Pub Date : 2024-10-31 DOI: 10.1021/acs.chemrev.4c0026110.1021/acs.chemrev.4c00261
Matthijs P. J. M. van der Ham, Jordi Creus, Johannes H. Bitter, Marc T. M. Koper and Paolo P. Pescarmona*, 

In this contribution, we review the electrochemical upgrading of saccharides (e.g., glucose) and sugar alcohols (e.g., glycerol) on metal and metal-oxide electrodes by drawing conclusions on common trends and differences between these two important classes of biobased compounds. For this purpose, we critically review the literature on the electrocatalytic oxidation of saccharides and sugar alcohols, seeking trends in the effect of reaction conditions and electrocatalyst design on the selectivity for the oxidation of specific functional groups toward value-added compounds. Importantly, we highlight and discuss the competition between electrochemical and non-electrochemical pathways. This is a crucial and yet often neglected aspect that should be taken into account and optimized for achieving the efficient electrocatalytic conversion of monosaccharides and related sugar alcohols into valuable products, which is a target of growing interest in the context of the electrification of the chemical industry combined with the utilization of renewable feedstock.

在这篇论文中,我们回顾了糖类(如葡萄糖)和糖醇(如甘油)在金属和金属氧化物电极上的电化学升级,总结了这两类重要生物基化合物之间的共同趋势和差异。为此,我们对有关糖类和糖醇电催化氧化的文献进行了批判性回顾,寻找反应条件和电催化剂设计对特定官能团氧化为高附加值化合物的选择性的影响趋势。重要的是,我们强调并讨论了电化学和非电化学途径之间的竞争。在化学工业电气化与可再生原料利用相结合的背景下,这是一个日益受到关注的目标。
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引用次数: 0
Nucleation Site Memory in the Spherulite Films of Polydisperse Poly(l-lactic acid) 多分散聚(l-乳酸)球形薄膜中的成核点记忆
IF 5.5 1区 化学 Q1 POLYMER SCIENCE Pub Date : 2024-10-31 DOI: 10.1021/acs.macromol.4c01669
Songyan Lu, Min Chen, Hanying Li
Molecular weight distribution (MWD) is a unique feature of polymers, which endows various properties of polymer materials with broadly regulatable scopes. The various chain dynamics and crystallization behaviors of different molecular-weight polymers coexisting within the same polydisperse system would lead to unique crystallization phenomena and aggregating structures. Recently, an MWD-induced polymorphism texture of poly(l-lactic acid) (PLLA) is reported, called nested PLLA spherulites, where one crystal form is embedded inside the other. Here, an interesting nucleation site memory phenomenon is reported for the PLLA thin films, where the nucleation sites of spherulites recover around the initial positions, even after multiple melting–crystallizing cycles. The nucleation site memory strongly associates with solution processing and the nested spherulites. After the impact of heterogeneous nucleation is excluded, it is demonstrated that the nucleation site memory originates from MWD. The insights provided in this work deepen the fundamental understanding of the influence of MWD on the structure evolution during polymer processing.
分子量分布(MWD)是聚合物的一个独特特征,它使聚合物材料的各种特性具有广泛的可调范围。不同分子量的聚合物共存于同一多分散体系中,其不同的链动力学和结晶行为会导致独特的结晶现象和聚集结构。最近,有报道称聚(l-乳酸)(PLLA)具有一种由 MWD 诱导的多晶质结构,即嵌套聚乳酸(PLLA)球粒,其中一种晶体形式嵌入另一种晶体形式之中。此处报告了聚乳酸薄膜的一种有趣的成核点记忆现象,即即使经过多次熔融-结晶循环,球晶的成核点也会恢复到初始位置附近。成核点记忆与溶液加工和嵌套球晶密切相关。在排除异质成核的影响后,证明了成核点记忆源于 MWD。这项工作提供的见解加深了人们对聚合物加工过程中 MWD 对结构演变影响的基本认识。
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引用次数: 0
Additions and Corrections to Cleavage of Si–H, B–H and C–H Bonds by Metal–Ligand Cooperation 金属配体合作对 Si-H、B-H 和 C-H 键裂解的补充和修正
IF 51.4 1区 化学 Q1 POLYMER SCIENCE Pub Date : 2024-10-31 DOI: 10.1021/acs.chemrev.4c0056310.1021/acs.chemrev.4c00563
Takuya Higashi, Shuhei Kusumoto and Kyoko Nozaki*, 
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引用次数: 0
Role of Entanglement in Polymer Crystal Growth and Melting: Molecular Dynamics Simulations 纠缠在聚合物晶体生长和熔化中的作用:分子动力学模拟
IF 5.5 1区 化学 Q1 POLYMER SCIENCE Pub Date : 2024-10-31 DOI: 10.1021/acs.macromol.4c01877
Fan Peng, Renkuan Cao, Hao Sun, Ziwei Liu, Yunhan Zhang, Tingyu Xu, Liangbin Li
The influence of entanglement on the growth and melting of polymer crystals is investigated by using molecular dynamics simulations across systems with different entanglement densities. Reducing entanglement density leads to a slight decrease of crystal thickness L but an increase of melting temperature Tm. To elucidate the entanglement-related inverse relation between Tm and L, we introduce the fold surface free energy σf predominantly governed by the conformational entropy loss of amorphous segments. Reducing the entanglement density results in a decrease of σf. Combining the contributions of σf and L, a linear relation between Tm and σf/L is obtained, which is consistent with the prediction of the Gibbs–Thompson equation. Crystallization commonly accompanies with disentanglement, while crystal melting precedes before entanglement reconstruction. Considering the thermodynamic contribution of entanglement, polymer crystallization and melting are not two mutually reversible phase transitions, not only kinetically but also thermodynamically.
通过对不同纠缠密度的系统进行分子动力学模拟,研究了纠缠对聚合物晶体生长和熔化的影响。降低纠缠密度会导致晶体厚度 L 略微减小,但熔化温度 Tm 会升高。为了阐明 Tm 与 L 之间与纠缠相关的反比关系,我们引入了主要受非晶段构象熵损失支配的折叠表面自由能 σf。降低纠缠密度会导致 σf 下降。结合 σf 和 L 的贡献,可以得到 Tm 与 σf/L 之间的线性关系,这与吉布斯-汤普森方程的预测一致。结晶通常伴随着解纠缠,而晶体熔化则先于纠缠重建。考虑到纠缠的热力学贡献,聚合物结晶和熔化不仅在动力学上而且在热力学上都不是两个相互可逆的相变。
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引用次数: 0
Modeling of Diels–Alder Reversible Network Formation in Diffusion-Controlled Conditions 扩散控制条件下的 Diels-Alder 可逆网络形成模型
IF 5.5 1区 化学 Q1 POLYMER SCIENCE Pub Date : 2024-10-30 DOI: 10.1021/acs.macromol.4c01616
Jessica Mangialetto, Robrecht Verhelle, Guy Van Assche, Niko Van den Brande
A novel mechanistic model is developed for a vitrifying covalent adaptable polymer network based on the thermoreversible furan-maleimide Diels–Alder (DA) cycloaddition. To account for the effect of diffusion limitations on the reaction rates, a diffusion-controlled encounter pair formation mechanism is introduced, with the related rates of formation and separation calculated using the Williams–Landel–Ferry equation. The kinetic, thermodynamic, and diffusion parameters are optimized using calorimetric data and the variation of the glass transition temperature (Tg) with time and/or temperature, leading to a set of parameters that can describe a specific thermosetting system in vitrifying conditions. These parameters are shown to be also valid for a second, chemically similar, reversible network having a comparable Tg. Lastly, the parameters obtained are used to simulate time–temperature-transformation (TTT) and continuous-heating-transformation (CHT) diagrams of these systems, including also the vitrified sections. With these results, this model proves to be a versatile tool suitable for the prediction of the effect of diffusion limitations for any time–temperature cure program, aiding in the accurate interpretation of analytical results related to these reversible networks. This is of particular interest for the design and processing of these self-healing and reprocessable materials.
在热可逆呋喃-马来酰亚胺 Diels-Alder (DA) 环加成法的基础上,为玻璃化共价适应性聚合物网络建立了一个新的机理模型。为了考虑扩散限制对反应速率的影响,引入了扩散控制的遇对形成机制,并使用 Williams-Landel-Ferry 方程计算了相关的形成和分离速率。利用量热数据和玻璃化转变温度(Tg)随时间和/或温度的变化,对动力学、热力学和扩散参数进行了优化,从而得出了一组可以描述玻璃化条件下特定热固性体系的参数。这些参数也适用于第二种化学性质相似、具有可比 Tg 的可逆网络。最后,获得的参数被用于模拟这些体系的时间-温度-转变(TTT)和连续-加热-转变(CHT)图,包括玻璃化部分。这些结果证明,该模型是一种多功能工具,适用于预测任何时间-温度固化程序的扩散限制效应,有助于准确解释与这些可逆网络有关的分析结果。这对于这些自愈合和可再加工材料的设计和加工具有特别重要的意义。
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引用次数: 0
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