580 California St., Suite 400
San Francisco, CA, 94104
Key research themes
1. How can hyperpolarized nuclear spins in solids be coherently manipulated and protected to improve magnetic resonance sensitivity and resolution?
This theme investigates advanced quantum control techniques and pulse sequences that convert and maintain hyperpolarized spin order in solids, enabling enhanced NMR signal detection and imaging contrast. It focuses on overcoming the intrinsic low polarization and rapid signal decay associated with nuclear spins by exploiting multiplet-to-net polarization conversion, coherent spin manipulation, and long-lived singlet states in specially designed molecules or solids. Such approaches are crucial for increasing the sensitivity of magnetic resonance methods and extending their applicability in chemical and biomedical studies.
Key finding: Introduced a simple NMR pulse sequence based on an out-of-phase echo that converts para-hydrogen induced multiplet spin order into net polarization, enabling background-free detection by effectively filtering out thermally... Read more
Key finding: Demonstrated proton nuclear singlet states in hyperpolarized organic molecules (dimethyl fumarate) exhibiting lifetimes approaching six minutes, achieved via para-hydrogen induced polarization. Using chemical desymmetrization... Read more
Key finding: Showed that optical nuclear polarization (ONP) in hyperpolarized triplet states undergoes coherent spin order transfer involving well-defined oscillations (precessions and nutations) which are consistent across molecular... Read more
2. What advances enable hyperpolarization and sensitive detection of heteronuclei (e.g., 31P, 15N, 13C) using reversible exchange and dynamic nuclear polarization methods at high magnetic fields?
This theme focuses on chemical and instrumental strategies to hyperpolarize low-sensitivity heteronuclei via parahydrogen-induced polarization (PHIP) and dynamic nuclear polarization (DNP), with special emphasis on signal amplification by reversible exchange (SABRE) methods. It covers synthetic design of molecular scaffolds for improved hyperpolarization transfer, pulse sequences enabling high-field SABRE experiments without field cycling, and cross-polarization approaches that yield high heteronuclear polarization and long relaxation times. These improvements broaden the scope of nuclei accessible to hyperpolarization and increase the practicality of hyperpolarized NMR and MRI applications.
Key finding: Designed a series of regioisomeric phosphonate esters and demonstrated that incorporation of heteroaromatic motifs facilitated parahydrogen-induced hyperpolarization of 31P nuclei with signal enhancements up to 3588-fold... Read more
Key finding: Developed RF-SABRE, employing radiofrequency irradiation to create level anti-crossings (LACs) at high magnetic fields (~Tesla), enabling efficient polarization transfer from parahydrogen to substrate nuclei without field... Read more
Key finding: Achieved 15N nuclear spin hyperpolarization levels up to 25% at 1.2 K via cross polarization from proton spins polarized by DNP of nitroxide radicals, dramatically reducing polarization build-up times to ~10-15 minutes... Read more
Key finding: Showed that spin mixing at level anti-crossings allows efficient transfer of hyperpolarization from parahydrogen-derived hydrides to spin-1/2 heteronuclei via SABRE at low and high magnetic fields. The study experimentally... Read more
3. How does many-body localization and spin dynamics impact the creation and sustainability of dynamic nuclear polarization in driven quantum systems?
This theme explores the role of electron spin interactions, disorder, and localization phenomena in governing the thermalization and hyperpolarization efficiency of nuclear spins in systems under dynamic nuclear polarization (DNP). It addresses theoretical and experimental analyses of ergodicity breaking, such as many-body localization transitions, and their effects on spin temperature formation, polarization transfer mechanisms, and steady-state hyperpolarization levels. Understanding these effects is critical to optimizing DNP protocols in solid-state and disordered systems for enhanced nuclear spin polarization.
Key finding: Identified that achieving significant nuclear hyperpolarization via DNP requires electron spin interactions to be strong enough to avoid many-body localization (MBL) and establish a spin temperature. The study numerically and... Read more
Key finding: Developed a theoretical framework solving the Liouville-von Neumann equation to model MAS-DNP, explicitly including spin interaction modulation due to sample spinning. Results revealed that MAS alters DNP mechanisms by... Read more
Key finding: Utilized a Monte Carlo approach to simulate solid effect DNP in large spin systems with an electron surrounded by many nuclei, validating against exact quantum master equation solutions. Demonstrated that nuclear bulk... Read more
Key finding: Introduced an experimental approach to identify the predominance of thermal mixing (TM) DNP mechanism by monitoring hyperpolarization time dynamics involving multiple nuclear species. Found TM dominates at high radical... Read more