Polarization Amplification in Dynamic Nuclear Polarization Magic-Angle Spinning Solid-State Nuclear Magnetic...

Area of Science:

• Nuclear Magnetic Resonance Spectroscopy
• Solid-State NMR
• Dynamic Nuclear Polarization (DNP)

Background:

• Dynamic nuclear polarization (DNP) significantly enhances solid-state NMR sensitivity.
• Aqueous DNP typically uses a glycerol-d8/D2O/H2O mixture (DNP juice) as a cryoprotectant to prevent phase separation of polarizing agents.
• This cryoprotectant ensures efficient electron spin polarization transfer for DNP.

Purpose of the Study:

• To investigate alternative methods for achieving high DNP enhancements in aqueous media without cryoprotectants.
• To explore the role of electrolytes in mitigating phase separation of polarizing agents at cryogenic temperatures.
• To demonstrate the feasibility of glycerol-free DNP in water for solid-state NMR applications.

Main Methods:

• Investigating DNP performance in aqueous solutions with high electrolyte concentrations (NaCl, LiCl).
• Analyzing the effect of electrolytes on ice crystallization and phase separation of paramagnetic polarizing agents upon cooling.
• Measuring 1H DNP enhancements using magic-angle spinning solid-state NMR.

Main Results:

• High 1H DNP enhancements (approximately 60) were obtained in aqueous solutions without glycerol.
• Electrolytes (NaCl, LiCl) were shown to perturb ice crystallization, reducing polarizing agent phase separation.
• This perturbation maintained DNP efficiency in the absence of traditional cryoprotectants.

Conclusions:

• Glycerol-free aqueous DNP is feasible for enhancing solid-state NMR sensitivity.
• Electrolytes offer a viable strategy to prevent polarizing agent phase separation in aqueous DNP.
• This finding provides a simpler and potentially more versatile approach for aqueous DNP experiments.