Fundamental Principles of Multivalency in Nanoscale and Macromolecular Systems

在化学系大分子、超分子和纳米化学项目的支持下，马萨诸塞州学院（MIT）的Robert Macfarlane教授将研究一个重要的知识缺口，将多价性原理扩展到涉及聚合物和纳米颗粒组装的更复杂的材料系统。与弱的单价结合相反，多价相互作用提供了在分子尺度上多重并因此显著增强的结合的优点。多价结构在许多系统中起作用，在两个物体之间产生强烈但可逆的相互作用，并且是一种关键的设计工具，可以用于以传统有机合成无法获得的方式精确编程材料特性。多价性的基本原理已经在很大程度上用分子模型进行了研究，然而这些模型具有局限性，并且不允许充分解释多价性如何在聚合物或纳米颗粒基材料中发生。该提案将允许通过“逐步”方法来解决这一挑战，以增加多价系统的复杂性。通过首先测量单个分子的超分子行为，然后测量具有逐渐增加的修饰的附加系统，可以单独检查可能影响超分子多价性的每个复杂因素。因此，拟议的工作旨在允许合理的审查大规模多价系统组成的100或1000个个别的超分子基团。从这项研究中获得的设计原则，然后被翻译为基础研究，解释如何纳米级系统的大规模多价粘合剂可以用来控制宏观系统的行为，在可回收和易于加工的聚合物，以及自组装的纳米粒子超晶格的上下文中。该提案还将被用作当地社区学院代表性不足群体学生的外展计划的基础，为他们提供技术专业知识和研究经验，以追求更高的STEM（科学、技术、工程和数学）教育目标或STEM领域的职业。为了实现更好地理解如何使用系统级方法来控制多价性的目标，已建立的实验技术将首先用于测量模型单价超分子粘合剂（SMBs）的热力学参数。随后的实验将引入复杂性的“逐步”增加（例如，对SMB的分子修饰、将SMB接枝到聚合物链、将多个聚合物束缚的SMB结合到纳米颗粒支架），并且将重新测量这些相同的热力学参数以确定系统复杂性的每次逐步增加如何影响SMB相互作用。使用从这些实验中获得的单价结合热力学的信息，多价作为纳米级支架设计的函数的趋势将被检查。将测量大分子和用沉积在表达互补SMB的基底上的SMB修饰的刷接枝纳米颗粒的多价数（以测量单个多价结合事件的热力学），以及测量表达互补SMB的颗粒和聚合物支架的二元组装体的多价数。然后将研究调整多价解离的宽度和起始温度的能力，以允许使用超分子化学来改变聚合物的加工性。短链聚合物之间的可定制的多价结合将被检查作为一种方法来生产聚合物，易于加工，回收，或重新配置，但仍然机械强度。另外，改变超分子多价性对纳米粒子自组装的影响将被用来作为一种手段，以了解集体超分子相互作用如何决定超晶格架构内纳米粒子的层次结构。该奖项反映了NSF的法定使命，并已被认为是值得通过使用基金会的智力价值和更广泛的影响审查标准进行评估的支持。

With the support of the Macromolecular, Supramolecular, and Nanochemistry Program in the Division of Chemistry, Professor Robert Macfarlane at the Massachusetts Institute of Technology (MIT) will investigate an important gap in knowledge for extending principles of multivalency to more complex materials systems involving polymers and nanoparticle assemblies. In contrast to weak monovalent binding, multivalent interactions offer the advantage of a multiple and thus dramatically enhanced binding on a molecular scale. Multivalent structures function in a number of systems to generate a strong but reversible interaction between two objects and is a key design tool that can be used to precisely program material properties in a manner that is unobtainable through traditional organic synthesis. The fundamentals of multivalency have largely been examined with molecular models, however these models have limitations and do not permit full explanation of how multivalency occurs in polymer- or nanoparticle-based materials. This proposal will permit this challenge to be addressed via a “stepwise” approach to increasing complexity in multivalent systems. By first measuring the supramolecular behaviors of individual molecules, then measuring additional systems with gradually increasing modifications, each of the complicated factors that may influence supramolecular multivalency can be individually examined. As a result, the proposed work seeks to permit rational examination of massively multivalent systems consisting of 100s or 1000s of individual supramolecular groups. The design principles gained from this research are then to be translated to fundamental studies explaining how nanoscale systems of massively multivalent binders can be used to control the behaviors of macroscopic systems in the context of both recyclable and easily processed polymers, and the self-assembly of nanoparticle superlattices. This proposal will also be used as the basis of an outreach program for students from underrepresented groups in local community colleges, providing them with the technical expertise and research experience to pursue either higher STEM (science, technology, engineering and mathematics) education goals or careers in STEM fields.To achieve the goal of better understanding how to use a systems-level approach to control multivalency, established experimental techniques will first be used to measure the thermodynamic parameters of model monovalent supramolecular binders (SMBs). Subsequent experiments will introduce “step-wise” increases in complexity (e.g. molecular modification to the SMB, grafting the SMB to a polymer chain, binding multiple polymer-tethered SMBs to nanoparticle scaffolds), and these same thermodynamic parameters will be re-measured to determine how each step-wise increase in system complexity affects SMB interactions. Using the information on monovalent binding thermodynamics obtained from these experiments, trends in multivalency as a function of nanoscale scaffold design will be examined. Multivalency numbers will be measured for both macromolecules and brush-grafted nanoparticles modified with SMBs deposited onto substrates expressing complementary SMBs (to measure the thermodynamics of a single multivalent binding event), and for binary assemblies of particle- and polymer-scaffolds that express complementary SMBs. The ability to tune the breadth and onset temperature of multivalent dissociation will then be investigated to allow the use of supramolecular chemistry to alter polymer processability. Tailorable multivalent binding between short-chain polymers will be examined as an approach to produce polymers that are easily processed, recycled, or reconfigured but still mechanically strong. Separately, the effects of altering supramolecular multivalency on nanoparticle self-assembly will be used as a means to understand how collective supramolecular interactions dictate the hierarchical organization of nanoparticles within superlattice architectures.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.