Physical Chemistry Seminar: Metal-Ion Dynamic Nuclear Polarization for Probing Host-Guest Interactions in MOFs: the role of mobility and spin diffusion

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Abstract:

Dynamic Nuclear Polarization (DNP) is a powerful technique that increases the sensitivity of solid-state Nuclear Magnetic Resonance (NMR) spectroscopy by 1-4 orders of magnitude by transferring high electron spin polarization from a polarizing agent (PA) to nuclear spins with the assistance of microwave irradiation.1 We and others have recently demonstrated that paramagnetic metal ions introduced as dopants into inorganic and molecular solids can play the role of the PAs, an approach referred to as metal-ion DNP (MIDNP).2 It has successfully been applied to a broad range of technologically relevant materials used in batteries, catalysis and fuel cells.3

In this talk, I will introduce MIDNP approach, show how it can be expanded to porous solids such as metal organic frameworks (MOFs) to enhance their NMR signals and discuss the potential of this approach for polarizing molecular guests present in the MOF pores.4 The effect of PA concentration, molecular oxygen trapped in the pores, and the MOF/guest mobility on the MIDNP performance will be covered. The second part of my talk will be devoted to the role of spin diffusion in MIDNP – a phenomenon of polarization exchange between nuclear spins. I will demonstrate how spin diffusion affects polarization buildup time and the steady-state enhancement, based on DNP experiments and corroborated by simulations on a large ensemble of spins.5

1. Hu, Yu, Swager, and Griffin, J. Am. Chem. Soc., 2004, 126, 10844

2. Jardón-Álvarez and Leskes, Prog. Nucl. Magn. Reson. Spectrosc., 2023, 138, 70-104

3. Moroz and Leskes, Annu. Rev. Mater. Res., 2022, 52, 25-55

4. Moroz, Feldman, Carmieli, Liu, and Leskes, Chem. Sci., 2024, 15, 336-348

5. Moroz, Jardón-Álvarez, and Leskes, J. Chem. Phys., 2025, 162, 024201

Seminar Organizer: Prof. Ilia Kaminker