Curie nuclear spin relaxation

The enhancement of the longitudinal contact relaxation rate, after extension to the general case S V2, is given by the Bloembergen equation [29,36] 

The term S(S + )(A/h)2 is proportional to the square of the coupling energy between an electron spin vector S and the nuclear spin vector /. The same equations hold for lanthanides. 

As in the case of dipolar relaxation, the presence of a field-independent term in the equation for R.2M causes the two nuclear relaxation values to diverge for 

The occurrence of this particular relaxation mechanism can be recognized through the field and temperature dependence of the linewidths. In the absence of other effects, the line broadening is proportional to the square of the magnetic field 

In principle, there may also be a Curie relaxation contribution of the contact-type whenever there is chemical exchange or intramolecular rotation to modulate the coupling. The contribution to R2M would then be 

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A COMPARISON OF DIPOLAR, CONTACT, AND CURIE NUCLEAR SPIN RELAXATION... 

A comparison of dipolar, contact, and Curie nuclear spin relaxation... 

Relaxation in the Rotating Frame. The magnetization (Mq) established when an ensemble of nuclear spins, I, are allowed to reach equilibrium with the lattice in a d.c. field, Hq, is given by Curie s law ... 

A development in the theory of nuclear relaxation in macromolecules by paramagnetic ions has been suggested by Gueron. (675) In the case of heme proteins there is a net polarization of the iron electronic spin magnetic moment which is oriented along the direction of the magnetic field. Modulation of this dipolar field due to the spin polarization (Curie spin) by rotational diffusion introduces an additional term into the expression for transverse relaxation [equation (18)] giving ... 

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