Using low-E resonators to reduce RF heating in biological samples for static solid-state NMR up to 900 MHz

Area of Science:

• Biophysical Chemistry
• Magnetic Resonance Spectroscopy
• Structural Biology

Background:

• Radiofrequency (RF) heating destabilizes solid-state biological samples during high-field Nuclear Magnetic Resonance (NMR) experiments.
• Sample dehydration and shortened lifetime result from high-power cross-polarization and decoupling pulses.
• Studying membrane proteins in native lipid bilayers is challenging due to dielectric losses and RF heating.

Purpose of the Study:

• To develop and characterize novel, large-volume, low-electric field (low-E) 15N-1H solid-state NMR probes.
• To enable high-field (600 and 900 MHz) Parallel Imaging with Enhanced Matrix (PISEMA) studies of membrane proteins.
• To reduce radiofrequency-induced sample heating in lossy biological samples.

Main Methods:

• Designed and implemented orthogonal coil probes with separate resonators for 15N and 1H frequencies.
• Utilized a loop-gap resonator to minimize electric field (E) and ensure a homogeneous magnetic field (B1).
• Employed a multi-turn solenoid as an efficient observe coil within the loop-gap resonator.
• Quantified RF power dissipation by measuring changes in 1H 360-degree pulse lengths.

Main Results:

• The new low-E probe demonstrated an order of magnitude reduction in sample heating compared to a conventional probe.
• Minimized RF loss was achieved for a typical dielectrically lossy bilayer sample.
• Effective B1 homogeneity and efficient observation were confirmed.

Conclusions:

• The developed low-E solid-state NMR probes significantly mitigate RF heating issues in high-field NMR.
• These probes facilitate high-quality PISEMA studies of membrane proteins in hydrated lipid bilayers at 600 and 900 MHz.
• The design offers improved sample stability and extended experimental possibilities for structural biology.