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

• Published in: Journal of magnetic resonance (1997) Vol. 185; no. 1; pp. 77 - 93
• Main Authors: Gor’kov, Peter L., Chekmenev, Eduard Y., Li, Conggang, Cotten, Myriam, Buffy, Jarrod J., Traaseth, Nathaniel J., Veglia, Gianluigi, Brey, William W.
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 01-03-2007
• Subjects: Biopolymers - chemistry; Biopolymers - radiation effects; Computer-Aided Design; Dielectric loss; Equipment Design; Equipment Failure Analysis; Field in solenoid; Flat-coil probe; Heating - instrumentation; Hot Temperature; LGR; Lipid bilayers; Lipid Bilayers - chemistry; Lipid Bilayers - radiation effects; Loop-gap resonator; Low-E; Magnetic Resonance Spectroscopy - instrumentation; Magnetic Resonance Spectroscopy - methods; Magnetics - instrumentation; Membrane protein; Powders; Radio Waves; RF sample heating; Solid-state NMR probe; Specimen Handling - instrumentation; Specimen Handling - methods; Temperature; Transducers; Dielectric loss; Flat-coil probe; Membrane protein; Loop-gap resonator; Solid-state NMR probe; LGR; Field in solenoid; RF sample heating; Lipid bilayers; Low-E
• ISSN: 1090-7807; 1096-0856
• DOI: 10.1016/j.jmr.2006.11.008

RF heating of solid-state biological samples is known to be a destabilizing factor in high-field NMR experiments that shortens the sample lifetime by continuous dehydration during the high-power cross-polarization and decoupling pulses. In this work, we describe specially designed, large volume,
low-E
15N–
1H solid-state NMR probes developed for 600 and 900
MHz PISEMA studies of dilute membrane proteins oriented in hydrated and dielectrically lossy lipid bilayers. The probes use an orthogonal coil design in which separate resonators pursue their own aims at the respective frequencies, resulting in a simplified and more efficient matching network. Sample heating at the
1H frequency is minimized by a loop-gap resonator which produces a homogeneous magnetic field
B
1 with low electric field
E. Within the loop-gap resonator, a multi-turn solenoid closely matching the shape of the sample serves as an efficient observe coil. We compare power dissipation in a typical lossy bilayer sample in the new low-E probe and in a previously reported
15N–
1H probe which uses a double-tuned 4-turn solenoid. RF loss in the sample is measured in each probe by observing changes in the
1H 360° pulse lengths. For the same values of
1H
B
1 field, sample heating in the new probe was found to be smaller by an order of magnitude. Applications of the low-E design to the PISEMA study of membrane proteins in their native hydrated bilayer environment are demonstrated at 600 and 900
MHz.