2D R1ρ relaxation experiment

This is the original experiment to measure rotating frame relaxation rate. It is sensitive to carrier frequency offset, particularly in the case of a large CSA, coil based rf-inhomogeneity and imprefections in RF pulses. This is a pseudo 2D experiment with 1H-X (X=13C/15N) cross polarization pulse followed by a refocusing composite pulse spin locking.

Citation

Magic-Angle 13C NMR Analysis of Motion in Solid Glassy Polymers, J. Schaefer, E. O. Stejskal, R. Buchdahl, , Macromolecules 10, 384–405 (1977). https://pubs.acs.org/doi/abs/10.1021/ma60056a031 Carbon-13 (T1p) Experiments on Solid Glassy Polymers, . Schaefer, E. O. Stejskal, T. R. Steger, M. D. Sefcik, R. A. McKay, Macromolecules 13, pp 1121–1126 (1980). https://pubs.acs.org/doi/abs/10.1021/ma60077a018

Sample heating

To minimized heating of conductive samples, we recommend using an Efree/lowE probe. However, a combination of frictional heating from spinning and RF heating on long pulses on both channel may cause substantial sample heating and temperature gradient across the sample even in an Efree probe. The heating may damage the sample. The heating and temperature gradient across the rotor may substantially compromise the precision of measurements and data fitting.

Citation

[https://www.ncbi.nlm.nih.gov/pubmed/10868566?dopt=Abstract] Heating of samples induced by fast magic-angle spinning, Brus, J., Solid State Nucl. Magn. Reson. 16, 151–160 (2000).

[https://onlinelibrary.wiley.com/doi/abs/10.1002/mrc.4450] Heating and temperature gradients of lipid bilayer samples induced by RF irradiation in MAS solid-state NMR experiments, Wang, J., Zhang, Z., Zhao, W., Wang, L. & Yang, J., Magn. Reson. Chem. 54, 753–759 (2016).

[https://www.biorxiv.org/content/10.1101/566729v1.full] TmDOTP : An NMR- based Thermometer for Magic Angle Spinning NMR Experiments Dongyu Zhang, Boris Itin, Ann E. McDermott; preprinted

Probe and power limitations

R1ρ experiments require long simultaneous medium to high power pulses on 1H and X channels. Make sure that you don't exceed the maximum allowed powers/lengths and damage the probe. When in doubt, contact the manufacturer.

Protocol

The experimental setup of RECRR experiments is very similar to the experimental setup of CP and basic CP R1ρ experiments. Make sure you measure and calculate X fields/pulses as precisely as possible. The experiment is rotor synchronized. Make sure you enter correct rotor frequency in the parameter set.

Samples

The experiments were performed with crystallized u-15N,13C-labeled-N-acetyl-valine and u-15N,13C membrane protein in hydrated lipids.

Processing and analysis

Fourier transform a pseudo-2D experiment in the direct dimension, measure the peak intensities as a function of length of the spin locking pulse and use a monoexponential function to obtain R1ρ values.

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Pulse Sequence and Parameter Set