Sorbitol-Based Glass Matrices Enable Dynamic Nuclear Polarization beyond 200 K

Area of Science:

• Solid-state Nuclear Magnetic Resonance (NMR) Spectroscopy
• Dynamic Nuclear Polarization (DNP)
• Materials Science

Background:

• Magic Angle Spinning Dynamic Nuclear Polarization (MAS-DNP) relies on rigid glass-forming matrices, often glycerol/water mixtures.
• The low glass-transition temperature (T_g) of glycerol/water limits MAS-DNP to lower temperatures, restricting its applications.
• Developing new matrices and understanding DNP mechanisms are crucial for expanding high-temperature MAS-DNP capabilities.

Purpose of the Study:

• To introduce sorbitol as a superior matrix for high-temperature MAS-DNP experiments.
• To develop a physical model explaining the temperature dependence and efficiency of MAS-DNP.
• To demonstrate the utility of the new DNP formulation on a challenging biological sample.

Main Methods:

• Magic Angle Spinning Dynamic Nuclear Polarization (MAS-DNP) experiments were conducted using sorbitol/DMSO and glycerol/water matrices.
• Comparison of DNP enhancement and spectral quality at various temperatures (up to 230 K) and magnetic fields (600 MHz/395 GHz).
• Development and application of a simple analytical model to explain DNP behavior, including biradical concentration and temperature effects.

Main Results:

• Sorbitol (T_g ≈ 267 K) advantageously replaces glycerol (T_g ≈ 190 K), enabling higher temperature MAS-DNP.
• Significant DNP enhancement was achieved at 230 K in sorbitol/DMSO, compared to glycerol/water which becomes ineffective around 180 K.
• The proposed analytical model accurately explains temperature dependence, biradical effects, and signal enhancement, identifying electron spin relaxation as a limiting factor for specific biradicals.

Conclusions:

• Sorbitol is an effective matrix for high-temperature MAS-DNP, expanding the operational temperature range.
• The developed analytical model provides valuable physical insights into MAS-DNP mechanisms.
• The new DNP formulation enabled rapid heteronuclear correlation spectra acquisition on chitin from cicada exoskeleton at elevated temperatures (100 K and 225 K).