The International Research Fellowship Program enables U.S. scientists and engineers to conduct nine to twenty-four months of research abroad. The program's awards provide opportunities for joint research, and the use of unique or complementary facilities, expertise and experimental conditions abroad.
This award will support a twenty-four-month research fellowship by Dr. Leah B. Casabianca to work with Dr. Lucio Frydman at the Weizman Institute in Israel.
Nuclear Magnetic Resonance (NMR) spectroscopy is undoubtedly one of the most versatile and useful tools for the determination of structure and dynamics in chemical systems and materials. No other technique compares in the wealth of atomistic detail that can become available from this kind of spectroscopy. The greatest disadvantage of NMR spectroscopy, however, is its low sensitivity. NMR would be ideally suited for structural studies of catalytic organic systems, functionalized surfaces, or inorganic nanotubes ? should only its sensitivity problems be surmounted. This goal of this work is the development of new NMR techniques exploiting cryogenic dynamic nuclear polarization (DNP) to characterize hyperpolarized nuclei in static solids. The application of DNP to metal nuclei in solids will be validated, optimized and understood through the development of pulse sequences, optimal hyperpolarization conditions for polarization transfer specifically to metal nuclei, and hardware for use in cryogenic environments. These approaches will then be used to examine metal nuclei in catalysts and inorganic nanotubes. A concomitant goal of this project is to examine the feasibility of using endogenous paramagnetic impurities present in single-walled carbon nanotubes (SWNTs) and nanodiamonds as polarizing agents for DNP, enhancing the signal of 13C nuclei in these carbon nanomaterials. Catalysts are ubiquitous in synthetic and industrial chemistry as well as in everyday life, inorganic nanotubes have unique potential applications due to their non-toxic nature, and carbon nanomaterials have applications ranging from membranes and sensors to batteries and nanoelectronics. Whereas structural characterization in these fields has traditionally been dominated by low-resolution techniques, sensitivity-enhanced NMR has the potential to allow atomic-level characterization of these and other emerging advanced materials.
The proposed work will lead to advances in the field of hyperpolarized solid-state NMR, and will also have a positive impact on other fields including catalysis and materials science. The techniques being developed will allow the characterization of systems that have traditionally been difficult to study by NMR due to the inherent sensitivity limitations of this method, thus advancing the field of NMR by increasing the applicability of this technique. In addition, this project will contribute to the understanding of hyperpolarization processes in general. This work will benefit society through the potential applications of metal-containing catalysts, inorganic nanotubes, SWNTs, and other carbon-based nanomaterials. Atomic-level structural characterization of these materials will allow applications of these systems in the biomedical, electronics, automotive, and aerospace industries to be realized.
Nuclear magnetic resonance (NMR) is a valuable tool for structural characterization used in fields from organic chemistry to medicine, yet one of the main disadvantages of NMR is its low signal-to-noise. A method to improve the signal-to-noise ratio in NMR involves transferring polarization from a nearby electron to the nucleus of interest, and is known as dynamic nuclear polarization (DNP). In this project, we used the DNP technique to hyperpolarize various nuclei using well-established radicals and glassing solvents. In addition, we explored using the intrinsic radicals in diamond samples as polarization agents in order to hyperpolarize the 13C nuclei in diamonds. We observed that as the size of the diamond sample approaches the nanoscale regime, the DNP enhancement factor decreases. This was attributed to a decrease in electron and nuclear relaxation times as the length scale of the diamond samples decreases. As the electron relaxation time decreases, saturation of the electrons (the essential first step in the DNP process) becomes more difficult, and as nuclear relaxation time decreases, spin diffusion from nuclei near the paramagnetic center to the bulk becomes less effective. Both of these factors lead to a decrease in DNP efficiency. The postdoctoral mentoring goals of this project were met, as the PI received training in an international setting, which will be beneficial to her students in both a classroom setting as well as training of graduate student researchers.
