Excess relaxation rate

Addition of bovine serum albumin (BSA) to a solution of LaCl3 results in a linear increase of the relaxation rate, the slope of the thus obtained straight lines being frequency-dependent. This is illustrated in Fig. 20 where the excess relaxation rate, 1/Tip = l/Tj — /T , is plotted against BSA concentration. For the former quantity... 

The excess relaxation rate or the excess broadening will thus be very small and will increase approximately linearly with the chemical exchange rate. The relative chemical shift displacement, in... 

In this case the excess relaxation rate has become appreciable - having reached about half its limiting value (P3/T23) t very rapid chemical exchange ( >> 1) as we shall see below. 

This is the limiting excess relaxation rate at very fast exchange. Under the same conditions we have... 

When n - C the excess relaxation rate will depend on n and may now exceed the limiting value Pg/T2g The shift change will also depend on n but may never exceed its limiting value... 

Fig. 5.14. Graph showing the excess relaxation rate of the dominant NMR sig-...

We can infer from Eq. (8,42) that the excess relaxation rates... 

Useful biological information can sometimes be obtained from studies of the competition between halide ions and other ions or small molecules for the same macromolecular binding sites. Formally, the halide NMR excess relaxation rate in a system of two classes of sites upon addition of a second ion or molecule Y competing for the X binding sites may be described by the equation ... 

As has already been mentioned earlier in this section the excess transverse and longitudinal relaxation rates may become unequal for halide ions undergoing rapid exchange with macromolecular binding sites characterized by large values of Tj. The quotient between the apparent T2 and T values is in reverse a convenient experimental parameter which may be employed for the determination of For the simple case of very rapid chemical exchange the following expression holds approximately for the ratio of the two excess relaxation rates in a two-site case ... 

A(1/T2) is the excess relaxation rate, which also defines the excess line broadening Av = A(1/T2)/tt. Let us now consider a few special cases. 

Figure 2. Graph showing the excess relaxation rate (I/T2) of the dominant NMR signal in a system where the observed nucleus is undergoing chemical exchange between two sites, A and B. The mole fraction of nuclei in site B, pg, is much less than that of site A, p. The definitions of n and are given by eqs. 5 and 6 (from Ref. 1). (with permission from Springer Verlag)...

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