Relaxation interference

Tjandra N, Szabo A and Bax A 1996 Protein backbone dynamics and N-15 chemical shift anisotropy from quantitative measurement of relaxation interference effected. Am. Chem. Soc. 118 6986-91... 

Tessari, M., Vis, H., Boelens, R., Kaptein, R., Vuister, G. W. Quantitative measurement of relaxation interference effects between Hn CSA and H- N dipolar interaction correlation with secondary structure. J. Am. Chem. Soc. 1997, 119, 8985-8990. 

When both effects are present, the transverse relaxation interferes with the 2-mixing because the relaxation makes the off-diagonal elements decay. The expression for this case is... 

FIGURE 40 Dantrolene, a skeletal muscle relaxant, interferes with the release of calcium ion from the sarcoplasmic reticulum, resulting in decreased muscle contraction. 

TjandraN, Gizesiek S, Bax A (1996) Magnetic field dependence of nitrogen-proton J splittings in N-enriched human ubiquitin resulting from relaxation interference and residual dipolar coupling. J Am Chem Soc 118(26) 6264—6272... 

Kroenke CD, Loria JP, Lee LK, Ranee M, Palmer AG (1998) Longitudinal and transverse H-l-N-15 dipolar N-15 chemical shift anisotropy relaxation interference unambiguous determination of rotational diffusion tensors and chemical exchange effects in biological macromolecules. J Am Chem Soc 120 7905-7915... 

Lee D, Hilty C, Wider G, Wiithrich K (2006) Effective rotational correlation times of proteins from NMR relaxation interference. J Magn Reson 178 72-76... 

The relaxation interference between the H- N dipolar interaction and the nitrogen-15 CSA is the basis of the transverse relaxation optimized spectroscopy (TROSY), nowadays a standard tool in NMR of larger proteins. Zuiderweg and Rousaki reviewed the field of gradient-enhanced TROSY and described the experiments of this kind in terms of the cartesian product operators. Other midifications of TROSY have also been reported, but are judged to be beyond the scope of this review. 

The eigenvalues of this eigenvalue problem are found by diagonalizing the matrix M. The situation is more complicated if collisional relaxation is not fast compared to chemical reaction. In that case, the solution will yield more than one small negative eigenvalues and the overall reaction will proceed on a non-exponential time scale. In other words, if collisional relaxation interferes with unimolecular reaction, the reaction process cannot be described by a time-independent rate constant A uni-We now take a look at the corresponding chemically activated reaction,... 

Werbelow L G 1996 Relaxation processes cross correlation and interference terms Encyclopedia of Nuclear Magnetic Resonance ed D M Grant and R K Harris (Chichester Wiley) pp 4072-8... 

Snap-Fit and Press-FitJoints. Snap-fit joints offer the advantage that the strength of the joint does not diminish with time because of creep. Press-fit joints are simple and inexpensive, but lose hoi ding power. Creep and stress relaxation reduce the effective interference, as do temperature variations, particularly with materials with different thermal expansions. 

The major relaxing transmitters are those that elevate the cAMP or cGMP concentration (Fig. 3). Adenosine stimulates the activity of cAMP kinase. The next step is not clear, but evidence has been accumulated that cAMP kinase decreases the calcium sensitivity of the contractile machinery. In vitro, cAMP kinase phosphorylated MLCK and decreased thereby the affinity of MLCK for calcium-calmodulin. However, this regulation does not occur in intact smooth muscle. Possible other substrate candidates for cAMP kinase are the heat stable protein HSP 20, (A heat stable protein of 20 kDa that is phosphorylated by cGMP kinase. It has been postulated that phospho-HSP 20 interferes with the interaction between actin and myosin allowing thereby smooth muscle relaxation without dephosphorylation of the rMLC.) Rho A and MLCP that are phosphorylated also by cGMP kinase I (Fig. 3). 

Interference in the Q-branch and population relaxation are ruled by the operator... 

The transverse magnetization and the applied radiofrequency field will therefore periodically come in phase with one another, and then go out of phase. This causes a continuous variation of the magnetic field, which induces an alternating current in the receiver. Furthermore, the intensity of the signals does not remain constant but diminishes due to T and T2 relaxation effects. The detector therefore records both the exponential decay of the signal with time and the interference effects as the magnetization vectors and the applied radiofrequency alternately dephase and re-... 

ISOMORPHISMS AND INTERFERENCES BETWEEN ELECTRONIC AND NUCLEAR RELAXATIONS... 

If we add a known amount of a compound to our solution, we can use it to quantify the material of interest. This is great except that we may not want to contaminate our material with some other compound. A number of people have looked at using standards that are volatile so that they can be got rid of later (TMS is an example that we have seen published). The problem with this approach is that if the sample is volatile then you need to run it quickly before it disappears. TMS disappears really quickly from DMSO so it is probably not a good idea in this case. TMS also suffers from the fact that it has a long relaxation time so you have to be very careful with your experiment to ensure that you do not saturate the signal. The last major problem with TMS is that it comes at the same part of the spectrum as silicon grease which can be present in samples. Choosing a standard so that it has a short relaxation time, is volatile and comes in a part of the spectrum free of interference is really tricky. In fact, we wouldn t recommend it at all. 

Of course, we still have the problem of selecting a compound that doesn t interfere with the spectrum and that has a suitable relaxation time but we don t need to worry about its volatility. What would be really good is a standard that doesn t interfere with the sample at all. Something that has no relaxation... 

Figure 1 Schematic representation of the 13C (or 15N) spin-lattice relaxation times (7"i), spin-spin relaxation (T2), and H spin-lattice relaxation time in the rotating frame (Tlp) for the liquid-like and solid-like domains, as a function of the correlation times of local motions. 13C (or 15N) NMR signals from the solid-like domains undergoing incoherent fluctuation motions with the correlation times of 10 4-10 5 s (indicated by the grey colour) could be lost due to failure of attempted peak-narrowing due to interference of frequency with proton decoupling or magic angle spinning.

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