Curie-spin relaxation

The Curie spin relaxation is also called magnetic susceptibility relaxation. Vega and Fiat (52) have also considered the Curie spin relaxation originating from anisotropic magnetic susceptibility, rather than an isotropic one as assumed in Eqs. (21-23). 

Fig. 3.13. Field dependence of the Curie spin relaxation contributions to R u and R2M (arbitrary scale) zr = 2 x 10 9 s.

No explicit temperature dependence is included in the equations for R m and Rim, except for cases where Curie spin relaxation is the dominant term (Section 3.6). In the latter case, Curie paramagnetism has a T x dependence and therefore relaxation depends on T 2. The effect of temperature on linewidths determined by Curie relaxation is dramatic also because of the xr dependence on temperature, as shown in Eq. (3.8). All the correlation times modulating the electron-nucleus coupling, either contact or dipolar, are generally temperature dependent, although in different ways, and their variation will therefore be reflected in the values of Rim and Rim-... 

One important source of distance constraints for paramagnetic proteins are cross correlations between Curie spin relaxation and H-X dipolar relaxation (X = H, C, or N). These cross correlations can in principle be detected by the same pulse sequences as are commonly used in diamagnetic systems to detect cross correlation between chemical shift anisotropy and H- N dipolar relaxation. However, in paramagnetic systems, rapid transverse self-relaxation tends to quench the build-up of relaxation allowed coherence transfer. To overcome this problem, Kateb and Piccioli have proposed a modified HSQC experiment to observe and quantify relaxation-allowed coherence transfer before it is quenched by a short T2. 

PAMAM dendrimers of generation 5 have also been functionalized with DOTA metal-binding domains and dysprosium complexes investigated as T2 contrast agents. Relaxivity measurements on the dysprosium complexes were interpreted in terms of an inner sphere Curie spin relaxation model with the large temperature dependence suggesting relaxation by a contact interaction effect, with the proton residence time as the primary time constant. The authors beheve that it will be possible to create a new class of T2-selective contrast agents with systems of this type. ... 

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