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.
