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检测NMR（β-NMR），分别）研究软物质的动力学和自由基的结构和动力学。注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力学原位探测器，在化学和材料科学中有着广泛的应用。muSR和β-NMR通过高极化和β-衰减各向异性的组合，在灵敏度方面比传统磁共振技术提高了多达10个数量级。这些技术的敏感性使我能够研究不适合更传统的研究工具的系统。* 我将使用植入的8Li+和β-NMR来研究聚合物的深度依赖性。我将确定（1）在聚（甲基丙烯酸甲酯）的自由表面附近的增强动力学的长度尺度;（2）在由低分子量和高分子量聚苯乙烯（PS）的混合物组成的薄膜中的熵驱动的偏析的长度尺度和（3）如何在PS中的埋界面附近的苯环的动态变化过程中，使焊接接头。我还将使用β-NMR研究锂离子在聚合物电解质聚（环氧乙烷）（PEO）薄膜中扩散的微观过程。我将确定8Li+跳跃参数如何取决于盐锂双（三氟甲烷）磺酰亚胺（LiTFSI）的浓度和膜厚度。* 将μ子植入材料可以产生μ子化的自由基，我将其用作软物质系统中的100%自旋极化标签。我建议使用muSR来研究模型双层内的胆固醇的动力学和局部环境的磷脂，如1，2-二棕榈酰-sn-甘油-3-磷酸胆碱（DPPC）和胆固醇和DPPC和1-棕榈酰-2-油酰-sn-甘油-3-磷酸胆碱（POPC），其中包含一个C = C键在一个链组成的双层中的酰基链的动力学。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反应的分子，自由基可导致细胞损伤。一个重要的问题是分子的哪些部分负责抗氧化行为。我将通过确定产生的自由基的结构来确定氢的轻同位素μ 鎓（Mu）与抗氧化剂反应的位置。我将研究Mu与表没食子儿茶素没食子酸酯（EGCG）的反应，表没食子儿茶素没食子酸酯是一种在绿色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.