Rational Design of Atomically Precise Catalysts for Parahydrogen Enhanced Nuclear Magnetic Resonance Imaging and Spectroscopy

核磁共振（NMR）是一种强大的化学和生物分析方法，通过探测原子核对强磁场的响应来提供有关分子中原子排列的信息。提高NMR的灵敏度将使生物医学中的新成像模式能够用于药物发现、蛋白质相互作用、磁共振血管造影、用于肿瘤检测的代谢功能障碍的识别/监测以及脑灌注。当分子含有来自相同氢源分子的两个氢原子时，可以优先检测在这些和其他应用中使用的NMR信号。然而，当在金属表面上进行氢加成时，反应倾向于从不同的氢分子转移氢原子，因此没有NMR信号增强的结果。研究人员建议合成催化剂，通过系统地改变催化剂粒度和反应位点组成，驱动从同一氢源分子中选择性添加两个氢原子的反应。使用这些新催化剂合成的分子，具有改进的磁共振信号，可用作各种诊断技术中的生物标志物。这一进展将代表生物医学成像领域的变革性发展和对催化剂结构-活性关系的新理解。该研究项目基于这样的假设，即通过限制氢原子在金属表面上的扩散，可以提高烯烃和炔烃加氢的成对选择性。预测选择性地阻断表面位点以减少由氢化反应的解离-重组过程导致的对位-邻位反转化。这些假设将通过合理的设计和使用原子层沉积（ALD）的催化剂的原子精确合成进行测试。通过将活性金属仔细沉积到具有特定表面刻面的纳米氧化物形状上，将合成定义明确的催化剂。通过这种方法，连同仔细的催化剂表征，在丙烯和丙炔的加氢，作为模型系统的活性和成对选择性的颗粒尺寸的影响，将确定使用从原子分散的物种的金属纳米粒子的颗粒。现有技术的催化剂合成（区域选择性ALD）还将允许封闭特定的金属位点，即平台位点或配位不饱和的角和边缘位点。在拟议的研究中的系统方法可以揭示不同的活性金属位点的相对重要性，并促进结构-活性关系。使用纳米氧化物形状与适当的催化剂表征方法一起将导致电子金属载体相互作用的新的理解，以及它们如何影响探针reactions.This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。

Nuclear magnetic resonance (NMR) is a powerful chemical and biological analytical method that provides information about the arrangement of atoms in molecules by probing responses of atomic nuclei to strong magnetic fields. Improving the sensitivity of NMR will enable new imaging modalities in biomedicine for drug-discovery, protein interactions, magnetic resonance angiography, identification/monitoring of metabolic dysfunction for tumor detection, and brain perfusion. NMR signals used in these and other applications can be preferentially detected when a molecule contains two hydrogen atoms from the same hydrogen source molecule. However, when hydrogen addition is performed on metal surfaces the reaction is prone to transfer of hydrogen atoms from different hydrogen molecules, and therefore no NMR signal enhancement results. The investigators propose to synthesize catalysts that drive reactions which selectively add two hydrogen atoms from the same hydrogen source molecule by systematically varying the catalyst particle size and reaction site composition. Molecules synthesized using these new catalysts, with improved magnetic resonance signals, can be used as biomarkers in various diagnostic techniques. This advance will represent a transformative development in the field of biomedical imaging and new understanding of catalyst structure-activity relationships. This research project is based upon the hypothesis that pair-wise selectivity in alkene and alkyne hydrogenation can be increased by restricting hydrogen ad-atom diffusion on the metal surface. Selectively blocking surface sites is predicted to reduce para-ortho back-conversion that results from the hydrogenation reaction's dissociation-recombination process. The hypotheses will be tested through rational design and atomically precise synthesis of catalysts using atomic layer deposition (ALD). Well-defined catalysts will be synthesized through careful deposition of active metal onto nanoparticle oxide shapes with specific surface facets. Through this approach, together with careful catalyst characterizations, the effects of particle size on the activity and pairwise selectivity in the hydrogenation of propene and propyne, as model systems, will be determined using particles ranging from atomically dispersed species to metal nanoparticles. State-of-the-art catalyst synthesis (area-selective ALD) will also allow blocking of specific metal sites, i.e. terrace sites or coordinatively unsaturated corner and edge sites. The systematic approach in the proposed research can reveal the relative importance of different active metal sites and facilitate structure-activity relationships. The use of nanoparticle oxide shapes together with appropriate catalyst characterization methods will lead to a new understanding of electronic metal-support interactions and how they affect the probe reactions.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.