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

我的研究涉及使用自旋极化，局部探针（μ子和8Li+）和相应的磁共振技术（μ子自旋共振（muSR）和β -探测核磁共振（β -NMR）分别）来研究软物质中的动力学和自由基的结构和动力学。植入放射性同位素作为一种低密度、高信噪比的局部环境和动态原位探测器，在化学和材料科学中有着广泛的应用。通过结合高极化和β衰变各向异性，muSR和β - nmr在灵敏度上比传统磁共振技术提高了10个数量级。这些技术的敏感性使我能够研究传统研究工具无法适应的系统。***我将使用注入的8Li+和β - nmr来研究聚合物的深度依赖性质。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)由低分子量和高分子量聚苯乙烯（PS）组成的薄膜中熵驱动偏析的长度尺度；(3)聚苯乙烯中埋藏界面附近的苯环在焊接接头过程中的动力学变化。我还将使用β - nmr来研究Li+在聚合物电解质聚环氧乙烷（PEO）薄膜中的微观扩散过程。我将确定8Li+跳跃参数如何取决于盐锂二（三氟甲烷）磺酰亚胺（LiTFSI）的浓度和薄膜厚度。***将μ子植入材料中可以产生静音自由基，我将其作为软物质系统中100%自旋极化的标签。我建议使用muSR来研究由1,2-二棕榈酰-sn-甘油-3-磷脂胆碱（DPPC）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DPPC和1-棕榈酰-2-油基-sn-甘油-3-磷脂胆碱（POPC）组成的双层中酰基链的动力学，其中一条链上含有C=C键。在这两个系统中，我将确定自旋探针的动力学如何随双分子层的组成和温度而变化。***抗氧化剂是与自由基反应的分子，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。我将通过测定生成自由基的结构来确定氢的轻同位素——介子元素（Mu）与抗氧化剂发生反应的位置。我将研究Mu与表没食子儿茶素没食子酸酯（EGCG）的反应，EGCG是一种在绿茶中高浓度存在的抗氧化剂，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.