Evaluation of Rotational Correlation Times

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  

The use of Eq. (8,50) is however very limited in the range of parameters which may be encountered. Therefore we have made detailed cal-culations of the ratio A(T2/T ) as a function of the halide NMR frequency making use of the full expressions in Eqs. (8.23) to (8.27). Some results are shown in Figs. 8.6, A, B and C. At observing frequencies approaching zero the quotient A(T2/T ) tends of course to unity for any value of t (B). It is also evident that t (B)-values less than 

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