DNP Probe -- translucent horizontal (Autodesk Inventor)

This movie shows a DNP/NMR probe equipped with a sample ejection system described A.B. Barnes et al., Cryogenic sample exchange NMR probe for magic angle spinning dynamic nuclear polarization, J. Magn. Reson. (2009), doi:10.1016/j.jmr.2009.03.003 Please site this paper if this video is used in any presentation or research, and please feel free to read the paper (available through Elsevier and Journal of Magnetic Resonance) if you have further interest.

The video shows a cryogenic sample exchange system that dramatically improves the efficiency of magic angle spinning (MAS) dynamic nuclear polarization (DNP) experiments by reducing the time required to change samples and by improving long-term instrument stability. Changing samples in conventional cryogenic MAS DNP/NMR experiments involves warming the probe to room temperature, detaching all cryogenic, RF, and microwave connections, removing the probe from the magnet, replacing the sample, and reversing all the previous steps, with the entire cycle requiring a few hours. The sample exchange system shown here — which relies on an eject pipe attached to the front of the MAS stator and a vacuum jacketed dewar with a bellowed hole — circumvents these procedures. To demonstrate the excellent sensitivity, resolution, and stability achieved with this quadruple resonance sample exchange probe, we have performed high precision distance measurements on the active site of the membrane protein bacteriorhodopsin. In the publication, we also include a spectrum of the tripeptide N-f-MLF-OH at 100 K which shows 30 Hz linewidths.

Dynamic nuclear polarization (DNP) increases the sensitivity of NMR by transferring the large spin polarization from stable paramagnetic centers to the nuclear spin reservoir. In recent applications to biological solids, the enhanced polarization is generated by millimeter wave irradiation of the EPR transitions of biradical polarizing agents and is uniformly dispersed to the system of interest via proton spin diffusion. During the polarization process, spin-lattice relaxation mechanisms compete with the polarization growth in the proton bath and hinder the saturation of the EPR transition. These T1 processes are slower at lower temperatures and cryogenic operation (presently around 85 K) permits the polarization from the electrons to effectively complete a relayed transfer to such systems as membrane or amyloid proteins and peptide nanocrystals. In addition, in the temperature regime discussed here, the spin polarization is proportional to the inverse of the sample temperature; thus, at 85 K the polarization is another factor of approximately three larger than at room temperature.

Category:

Science & Technology

Tags:

• DNP
• NMR Instrumentation
• SSNMR