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 B1 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 B1 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.
|Original language||English (US)|
|Number of pages||17|
|Journal||Journal of Magnetic Resonance|
|State||Published - Mar 2007|
Bibliographical noteFunding Information:
This work was supported by NSF Cooperative agreement (DMR 00884173) and the State of Florida. The spectroscopy was supported by NSF MCB-0235774 to T.A.C. (FSU). E.Y.C’s. position was supported by NIH GM-64676. M.C. acknowledges support from the Research Corporation (CC6128) and Dreyfus Foundation (SU-02-061). The SLN and PLN work was supported by National Institutes of Health Grants GM64742 and K02HL080081 to GV. J.J.B. was supported by the Minnesota Craniofacial Research Training Program (MinnCResT), the NIH National Institute of Dental and Craniofacial Research (NIDCR 5T32-DE007288-10); and N.J.T. is supported by an American Heart Association Greater Midwest Affiliate pre-doctoral fellowship (0515491Z). We particularly want to thank Prof. Timothy A. Cross for many helpful suggestions during preparation of this manuscript. We also wish to acknowledge Richard Desilets for fabrication of the parts used in the probes, Brenna S. Vollmar for help with sample preparation, Dr. Raiker Witter and Kiran K. Shetty for help with probe testing, Dr. Riqiang Fu for help with PISEMA setup, Dr. Yit A. Lim, Dr. Werner Maas, and Dr. F. David Doty for helpful discussions.
- Dielectric loss
- Field in solenoid
- Flat-coil probe
- Lipid bilayers
- Loop-gap resonator
- Membrane protein
- RF sample heating
- Solid-state NMR probe