Fundamental Principles of Multivalency in Nanoscale and Macromolecular Systems

在化学系大分子、超分子和纳米化学计划的支持下，麻省理工学院(MIT)的罗伯特·麦克法兰教授将研究在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体系方面的一个重要知识缺口。与弱的单价结合相比，多价相互作用提供了多价结合的优势，从而显著增强了分子尺度上的结合。多价结构在许多系统中发挥作用，在两个对象之间产生强烈但可逆的相互作用，是一种关键的设计工具，可以用来以传统有机合成无法获得的方式精确地编程材料性质。多价性的基本原理在很大程度上已经用分子模型进行了研究，然而这些模型有局限性，不能完全解释聚合物或纳米颗粒材料中如何发生多价性。这项提议将允许通过“循序渐进”的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，然后通过逐渐增加修改来测量额外的系统，可以单独地检查可能影响超分子多价性的每一个复杂因素。因此，拟议的工作试图允许对由100个或1000个单独的超分子基团组成的大规模多价体系进行理性检查。从这项研究中获得的设计原则随后将被转化为基础研究，解释如何使用大规模多价粘结剂的纳米系统来控制宏观系统在可回收和易于加工的聚合物以及纳米颗粒超晶格的自组装的背景下的行为。这项建议还将被用作当地社区大学中代表不足群体的学生扩展计划的基础，为他们提供技术专长和研究经验，以追求更高的STEM(科学、技术、工程和数学)教育目标或STEM领域的职业生涯。为了实现更好地了解如何使用系统水平的方法来控制多价性的目标，将首先使用现有的实验技术来测量模型单价超分子结合体(SMB)的热力学参数。随后的实验将“逐步”增加SMB的复杂性(例如，对SMB进行分子修饰，将SMB嫁接到聚合物链上，将多个聚合物系留的SMB结合到纳米颗粒支架上)，这些相同的热力学参数将被重新测量，以确定系统复杂性的每一步增加如何影响SMB相互作用。利用从这些实验中获得的关于单价结合热力学的信息，将考察作为纳米级支架设计的函数的多价性的趋势。将测量沉积在表达互补SMB(以测量单个多价结合事件的热力学)上的SMB修饰的大分子和刷子接枝纳米颗粒的多价数，以及表达互补SMB的颗粒和聚合物支架的二元组件的多价数。然后将研究调节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。短链聚合物之间可定制的多价结合将被视为一种生产易于加工、回收或重新配置但仍具有机械强度的聚合物的方法。另外，改变超分子多价性对纳米粒子自组装的影响将被用作一种手段，以了解集体超分子相互作用如何决定超晶格结构中纳米粒子的分级组织。这一奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

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.