Intermediate exchange regime

At temperatures around 50-60°C the three-site jump model is not a good approximation to the multi-site jump model, because the motion is not sufficiently rapid to be in the fast motion limit. However, the calculated spectra are fairly fitted with the observed ones. This is because the calculated spectrum is a superposition of constituent spectra whose rates are spread over several orders, so that the resultant spectrum is governed by the constituent spectra in the fast and slow motion limits having greater intensity than that in the intermediate exchange regime. 

It is clear that this approach does not deliver information about the binding process at atomic resolution. Rather, it focuses on the binding affinities of ligands to the virus. Careful data analysis allows discrimination of residues that actively participate in the binding from those that contribute less to the interaction. Ligands in the intermediate exchange regime on the chemical... 

Temperature dependence of the relaxation rate is a precious tool to exploit if dealing with the intermediate exchanging regime. In fact, x is expected to have a temperature dependence described by an Eyring relationship ... 

Figure 21 H resonances ofheme methyl groups ofHydrogenobac-ter thermophilus ferricytochrome C552 at (a) 26, (b), 11 (c) 1, (d) —6 °C. The chemical shifts observed are an average of shifts for two different axial methionine orientations in fast exchange on the NMR timescale. Upon lowering the temperature, the exchange process is slowed so that resonance broadening is evident as the process approaches the intermediate exchange regime. Samples for (b)-(d) are in 20% methanol...

Fast exchange (average signal observed) Intermediate exchange regime (broad lines)... 

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