Spin-Polarized Local Probes of Soft Matter and Free Radical Chemistry

我的研究涉及使用自旋极化的局域探针(Muons和8Li+)以及相应的磁共振技术(分别是Muon自旋共振(MuSR)和β-检测核磁共振(beta-NMR))来研究软物质中的动力学以及自由基的结构和动力学。注入的放射性同位素作为一种低密度、高信噪比的局部环境和动力学原位探测器，在化学和材料科学中有着广泛的应用。通过结合高极化和贝塔衰减各向异性，MUSR和贝塔-核磁共振提供了比传统磁共振技术高10个数量级的灵敏度改进。这些技术的敏感性使我能够研究不适用于更传统研究工具的系统。我将使用注入的8Li+和β-核磁共振来研究聚合物中随深度变化的性质。我将确定(1)聚甲基丙烯酸甲酯自由表面附近增强动力学的长度-尺度；(2)由低分子聚苯乙烯(PS)和高相对分子质量聚苯乙烯(PS)混合物组成的薄膜中熵驱动分离的长度-尺度；以及(3)PS中埋入界面附近的苯环在焊接接头制造过程中如何变化。我还将使用β-核磁共振来研究锂离子在聚合物电解质聚氧乙烷(PEO)薄膜中扩散的微观过程。我将确定8Li+跃迁参数如何依赖于盐锂双(三氟甲烷)磺酰亚胺(LiTFSI)的浓度和薄膜厚度。将介子植入材料中可以产生离化自由基，我将其用作软物质系统中100%自旋极化的标记。我建议用MUSR研究由1，2-二棕榈酰-sn-甘油-3-磷胆碱和胆固醇组成的模型双层中胆固醇的动力学和局部环境，以及由DPPC和1-palmitoyl-2-oleoyl-sn-glycero-3-phospho-choline(POPC)组成的双层中含有一个C=C键的酰链的动力学。在这两个系统中，我将确定自旋探针的动力学如何随双层的组成和温度而变化。抗氧化剂是与自由基发生反应的分子，自由基会导致细胞损伤。一个重要的问题是，分子的哪些部分负责抗氧化行为。我将通过确定生成的自由基的结构来确定氢的一种轻同位素Mu(Mu)在哪里与抗氧化剂反应。我将研究Mu与表没食子儿茶素没食子酸酯(EGCG)的反应，表没食子儿茶素没食子酸酯(EGCG)是一种在绿茶中发现的高浓度抗氧化剂，并确定EGCG的结构修饰，如改变立体化学，如何影响抗氧化性能。

My research involves using spin-polarized, local probes (muons and 8Li+) and the corresponding magnetic resonance techniques (muon spin resonance (muSR) and beta-detected NMR (beta-NMR), respectively) to study dynamics in soft matter and the structure and dynamics of free radicals. Implanted radioisotopes have broad applications in chemistry and materials science as a low-density, very-high-signal-to-noise in situ detectors of local environments and dynamics. muSR and beta-NMR offer as much as 10-orders-of-magnitude improvement in sensitivity over conventional magnetic resonance techniques through the combination of high polarization and beta-decay anisotropy. The sensitivity of these techniques allows me to study systems not amenable to more conventional research tools. I will use implanted 8Li+ and beta-NMR to study depth-dependent properties in polymers. I will determine (1) the length-scale of enhanced dynamics near the free surface in poly(methyl methacrylate); (2) the length-scale of entropy-driven segregation in thin films made up of mixtures of low and high molecular-weight polystyrene (PS) and (3) how the dynamics of phenyl rings near a buried interface in PS change during the process of making a welded joint. I will also use beta-NMR to study the microscopic process of Li+ diffusion in thin films of the polymer electrolyte poly(ethylene oxide) (PEO). I will determine how the 8Li+ hopping parameters depend on the concentration of the salt lithium bis(trifluoromethane)sulfonimide (LiTFSI) and on the film thickness. Implanting muons into materials can produce muoniated radicals, which I use as 100% spin-polarized labels in soft matter systems. I propose to use muSR to study the dynamics and local environment of cholesterol within model bilayers composed of phospholipids such as 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) and cholesterol and the dynamics of the acyl chains in bilayers composed of DPPC and 1-palmitoyl-2-oleoyl-sn-glycero-3-phospho-choline (POPC), which contains a C=C bond in one chain. In both systems I will determine how the dynamics of the spin probe varies with composition of the bilayer and temperature. Antioxidants are molecules that react with free radicals, which can cause cellular damage. An important question is what parts of a molecule are responsible for the antioxidant behaviour. I will determine where muonium (Mu), a light isotope of hydrogen, reacts with an antioxidant by determining the structures of the resulting radicals. I will study the reaction of Mu with epigallocatechin gallate (EGCG), an antioxidant that is found in high concentrations in green tea, and determine how structural modifications of EGCG, such as altering the stereochemistry, affect the antioxidant properties.