Timescales motion

There are also tremendous possibilities for using RDCs as a direct probe of conformational dynamics. Recalcitrant problems such as the characterization of intermediate timescale motions (microsecond-nanosecond), both for... 

Ishima R, et al. Carbonyl carbon transverse relaxation dispersion measurements and ms-micros timescale motion in a protein hydrogen bond network. J. Biomol. NMR 2004 29 187-198. Ishima R, Torchia DA. Extending the range of amide proton relaxation dispersion experiments in proteins using a constant-time relaxation-compensated CPMG approach. J. Biomol. NMR 2003 25 243-248. 

Experiments [6,11,12] and simulations [6,16] have recently established that a large part of the relaxation of the nonequilibrium solvation around a solute immediately after its photoexcitation is due to the shortest timescale motions of the first shell solvent molecules. This result is in accord with the theoretical notions we have been developing since 1979 [20a], which after refinement [22] has led to our use of the Gaussian friction model as the basis of our molecular friction methods [19,24],... 

We ask what relation exists between and td. Assuming that long-timescale motions of a chain occur dominantly in the reptation mode, Dol and Edwards [65] formulated an elegant theory of viscoelasticity of entangled polymer systems and showed that is related to td by... 

Fast ccMT >onents in the anisotn y decays are characteristic of many proteins and pq>rides and have been reported in many publications. Picosecond-timescale motions were also reported for tyrosine residues in pro-teins in these studies, a streak camera was used to obtain adequate time resolution. The short correlation rime observed in protons is variable and ranges from 50 to 5(X) ps, with the values being detemuned in part by the rime resolution of the instrument. The shorty correlation time is )proximately equal to that observed for NAIA in w er or fcorrelation times are typically insensitive to protein folding and are not greatly affected ly the viscosity of the solution. 

It should be noted that the two-step rotational dynamics of the long axis in a semidilute solution qualitatively resembles the jS- and a-processes in the solid state of flexible polymers the short-timescale motion in the cage may be compared to the jS-process, the long-timescale fluctuations in the environment with the a-process. 

The principal dilTerence from liquid-state NMR is that the interactions which are averaged by molecular motion on the NMR timescale in liquids lead, because of their anisotropic nature, to much wider lines in solids. Extra infonnation is, in principle, available but is often masked by the lower resolution. Thus, many of the teclmiques developed for liquid-state NMR are not currently feasible in the solid state. Furthemiore, the increased linewidth and the methods used to achieve high resolution put more demands on the spectrometer. Nevertheless, the field of solid-state NMR is advancing rapidly, with a steady stream of new experiments forthcoming. 

If the molecular motion is faster than the NMR timescale, the distance pre-... 

Pulsed deuteron NMR is described, which has recently been developed to become a powerftd tool for studying molectdar order and dynamics in solid polymers. In drawn fibres the complete orientational distribution function for the polymer chains can be determined from the analysis of deuteron NMR line shapes. By analyzing the line shapes of 2H absorption spectra and spectra obtained via solid echo and spin alignment, respectively, both type and timescale of rotational motions can be determined over an extraordinary wide range of characteristic frequencies, approximately 10 MHz to 1 Hz. In addition, motional heterogeneities can be detected and the resulting distribution of correlation times can directly be determined. 

In presence of molecular motion the NMR line shape will change. A particularly simple situation arises, if the motion is rapid on timescale defined by the inverse width of the spectrum in absence of motion 6 1. In this fast exchange limit, which in 2H NMR is reached for correlation times tc < 1CT7 s, the motion leads to a partially averaged quadrupole coupling and valuable information about the type of motion can directly be obtained from analysis of the resulting line shapes. The NMR frequency is then given by... 

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