TROSY
From NMR Wiki
TROSY Transverse relaxation optimized spectroscopy
Are a class of experiment that use the cancellation between dipolar coupling and chemical shift anisotropy ( CSA ), or between different dipolar coupling. They allow to record signal with sharp peaks on big complex. They are mostly useful for big proteins, or dna/proteins complexes.
The concept and the first experiment of this class was introduced in 1997 by K. Pervushin and K. Wüthrich. It use the cancellation between N chemical shift anisotropy and the NH dipole. It work on selecting some coherence on which this cancellation occurs, in order to get a long lasting signal, and so after Fourier transform sharp peaks. As the chemical shift ( in Hz ) depend on the strength of the magnetic field, it's required to have the right value of magnetic field in order that the chemical shift could cancel with the dipolar coupling. In this case the experiment is optimal around frequency close to 1 Ghz.
More recently a new kind of experiment was introduced : canceling the different dipolar coupling of the methyl, this is done using a HMQC experiment. In this case their is no dependence on the strength of the magnetic field.
Limitation
This kind of experiment could only cancel a limited set of this kind of interactions, and in the case of NH TROSY their is a signal loose by a factor 2. This could partially be compensated by doing the quick TROSY experiment that is able to recover the magnetization that was not used to build the signal, and use it again, allowing in this way to have an extra spectra within the same experiment accumulation rate. It may also require special condition like high magnetic field.
Longer range dipolar relaxation could still occure, to avoid this different labeling strategies exists :
- Partial labeling
- Position specific labeling
Variation
- qTROSY : get back the lost component
- Double TROSY : TROSY in direct and indirect dimension
- TROSY effect when decoupling in solid state NMR : avoid relaxation during decoupling
