NSF-DFG Confine: MolPEC – Molecular Theory of Weak Polyelectrolytes in Confined Space

在这个由化学系化学理论、模型和计算方法项目（CTMC）支持的项目中，加州大学河滨分校的吴建忠教授正在开发描述一类被称为弱聚电解质（WPEs）的聚合物的理论模型。这是一个与德国Georg-August-Universität Göttingen研究人员合作的项目。wpe是一大类大分子，可以根据环境条件（如pH和盐浓度）发生质子化或去质子化。它们的刺激响应行为已广泛应用于功能“智能”材料，如靶向药物输送或水下粘附。尽管实际应用通常需要在空间限制下进行化学和物理过程，但由于单体和聚合物尺度上反应和聚合物介导的相关性的强耦合，wpe的结构和动力学仍然不完全清楚。WPE体系的合理设计需要在理论和计算方法上取得进展，以便能够准确地描述约束对局部溶液环境的影响、质子化/去质子化平衡以及聚合物与可电离表面反应的动力学。本研究旨在建立一个理论框架来描述wpe在密闭空间中的性质及其对环境条件的响应，包括溶液pH、电解质组成和约束化学。我们将利用这些技术来研究离子大小、价态、电离、表面反应和聚合物结合动力学之间的相互作用，这些是传统方法无法可靠地解决的。理论和计算的进步将有助于弱聚电解质体系的合理设计，以广泛的技术应用。基于聚合物密度泛函理论（PDFT）和分子模拟的互补进展，美德团队将研究表面和表面之间的弱聚电解质的结构、热力学和动力学。其思想是结合和扩展伊辛密度泛函理论（iDFT）和单链平均场（SCMF）模拟。iDFT考虑单链构型和同等基础上的片段电离状态，并通过分子密度捕获液体样包装和静电相关性。整个大分子的构型和电离态的联合概率分布是由单链势决定的，而单链势又是分子密度的函数。利用iDFT单链势，在并行、gpu加速的超级计算机上进行SCMF模拟，有效地评估了高维分子密度。该团队将扩展模拟代码SOft粗粒度蒙特卡罗加速（SOMA），以结合静电相互作用和沿分子轮廓的非局部相互作用。基于粒子的模拟，动态idft (D-iDFT)，考虑了长期波动，使我们能够研究结构动力学。此外，我们将推导出基于段的动态iDFT (SD-iDFT)，用于描述响应环境变化的局部聚合物质量和电荷密度。在这项工作中提出的理论技术的一般性质确保了广泛应用于聚合物和生物系统中的各种现象。该项目将为早期职业科学家提供培训机会，以获得跨学科的研究经验，培养他们在计算分子工程方面的职业兴趣。除了支持研究生，它还为现役本科生、退伍军人和大学荣誉项目（UHP）的学生提供基于研究的论文项目。该项目是通过“密闭空间中的化学和传输（NSF-DFG）”机会获得的，这是一项由美国国家科学基金会和德国科学研究协会（DFG）共同发起的合作征集。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

In this project supported by the Chemical Theory, Models and Computational Methods Program (CTMC) of the Division of Chemistry, Professor Jianzhong Wu of the University of California-Riverside is developing theoretical models that describe a class of polymers known as weak polyelectrolytes (WPEs). This is a collaborative project with researchers from the Georg-August-Universität Göttingen, Germany. WPEs are a large class of macromolecules that may either protonate or deprotonate depending upon the environmental conditions such as pH and salt concentration. Their stimuli-responsive behavior has been broadly utilized in functional “smart” materials for applications such as targeted drug delivery or underwater adhesion. Whereas practical applications often entail chemical and physical processes under spatial confinement, the structure and dynamics of WPEs remain incompletely understood due to the strong coupling of reaction and polymer-mediated correlations at both monomer and polymer scales. The rational design of WPE systems is calling for advances in theoretical and computational methods that are able to accurately describe confinement effects on local solution environment, protonation/deprotonation equilibrium, and the dynamics of polymers reacting with ionizable surfaces. This research aims to develop a theoretical framework for describing the properties of WPEs in confined space and their responses to environmental conditions including solution pH, electrolyte composition, and the chemistry of confinement. We will utilize these techniques to investigate the interplay between ionic size, valence, ionization, surface reactions and the dynamics of polymer binding that cannot be reliably addressed with conventional methods. The theoretical and computational advances will contribute to a rational design of weak polyelectrolyte systems for a wide spectrum of technological applications. Building on complementary advances in polymer density functional theory (PDFT) and molecular simulation, the US-German team will study the structure, thermodynamics, and dynamics of weak polyelectrolytes at and between surfaces. The idea is to combine and extend Ising Density Functional Theory (iDFT) and Single-Chain-in-Mean-Field (SCMF) simulation. iDFT considers single-chain configurations and ionization states of segments on equal footing and captures liquid-like packing and electrostatic correlations via the molecular density. The joint probability distribution of configurations and ionization states of an entire macromolecule is dictated by a single-chain potential, which, in turn, is a functional of the molecular density. The high-dimensional molecular density will be efficiently evaluated via SCMF simulation on parallel, GPU-accelerated supercomputers, employing the iDFT single-chain potential. The team will extend the simulation code, SOft coarse-grained Monte-carlo Acceleration (SOMA), to incorporate electrostatic interactions and nonlocal interactions along the molecular contour. The particle-based simulation, Dynamic-iDFT (D-iDFT), accounts for long-range fluctuations and allows us to study the configuration dynamics. Additionally, we will derive a segment-based dynamic iDFT (SD-iDFT) for describing the local polymer mass and charge density in response to environmental changes. The generic nature of the theoretical techniques proposed in this work ensures broad applications to diverse phenomena in polymeric and biological systems. This project will provide training opportunities for early career scientists to gain interdisciplinary research experience and cultivate their career interests in computational molecular engineering. In addition to supporting graduate students, it offers research-based thesis projects for undergrads in active military service, veterans, and students from the University Honors Program (UHP). This project is being awarded through the “Chemistry and Transport in Confined Spaces (NSF-DFG Confine)" opportunity, a collaborative solicitation that involves the National Science Foundation and Deutsche Forschungsgemeinschaft (DFG).This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.