Paramagnetic relaxation, nuclear

III. The Many-Spin Problem in Nuclear Paramagnetic Relaxation. 295... 

In this article, we study some aspects of irreversible processes in spins systems. We essentially treat nuclear paramagnetic relaxation the case of ferromagnetism is not discussed. 

III. THE MANY-SPIN PROBLEM IN NUCLEAR PARAMAGNETIC RELAXATION... 

Wang XT, Goff HM. A nuclear paramagnetic relaxation study of the interaction of the cyclopentanedione substrate with chloroperoxidase. Biochim. Biophys. Acta 1997 1339 88-96. 

Kowalewski J 1996 Paramagnetic relaxation in solution Encyclopedia of Nuclear Magnetic Resonance ed D M Grant and R K Harris (Chichester Wiley) pp 3456-62... 

Specific Molecular Interactions (Jardetzky) Nuclear Paramagnetic (Spin-Spin) Relaxation in Solids 7 499... 

On the other hand, if the chemical entity under consideration has a contribution of triplet or higher-spin configurations, its nmr signals are expected to suffer from contact shifts and broaden readily due to paramagnetic relaxation of the observing nuclear spins. It could be extremely difficult to observe nmr signals for such species under the above experimental conditions. 

In this connection, attention should be paid to an unusual NMR technique called nuclear magnetic relaxation dispersion (NMRD). In contrast with NMR spectroscopy, the NMRD signal arises from the nuclei of the abundant solvent molecules and not from the dissolved substances. The relaxation properties of the solvent molecules are profoundly modified if the solvent contains paramagnetic particles (see a review by Desreux 2005). A solvent molecule sails in the vicinity of an ion-radical and finds itself in the local magnetic field of this paramagnetic particle. Then, induced magnetism of the solvent molecule dissipates in the solvent bulk. This kind of relaxation seems to be registered by NMR. NMRD is applicable to studies on ion-radical solvation/desolvation, ion-pair dynamics, kinetics of ion-radical accumulation/consumption, and so on. 

Fig. 7. NMRD profiles calculated for slightly asymmetric, weakly deformable complexes with different electron spin quantum numbers (a) cylindrically-symmetric ZFS, E = 0 (b) maximum rhombicity E = DjS. Reprinted from J. Magn. Reson. vol. 146, Nilsson, T. Kowalewski, J., Slow-motion theory of nuclear spin relaxation in paramagnetic low-symmetry complexes A generalization to high electron spin , pp. 345-358, Copyright 2000, with permission from Elsevier.

Fig. 12. Experimental and calculated NMRD profiles for GdEDTA in aqueous solution in the presence (upper curve) and absence (lower curve) of bovine serum albumin. Reprinted from J. Magn. Reson. vol. 162, Kruk, D. Kowalewski, J., Nuclear Spin Relaxation in Paramagnetic Systems (S > 1) under Fast Rotation Conditions , pp. 229-240, Copyright 2003, with permission from Elsevier.

Theoretical models for outer-sphere nuclear spin relaxation in paramagnetic systems, including an improved description of the electron spin relaxation, have been developed intensively for the last couple of years. They can be treated as counterparts of the models of inner-sphere PRE, described in the Section V.B and V.C. 

A more general theory for outer-sphere paramagnetic relaxation enhancement, valid for an arbitrary relation between the Zeeman coupling and the axial static ZFS, has been developed by Kruk and co-workers (96 in the same paper which dealt with the inner-sphere case. The static ZFS was included, along with the Zeeman interaction in the unperturbed Hamiltonian. The general expression for the nuclear spin-lattice relaxation rate of the outer-sphere nuclei was written in terms of electron spin spectral densities, as ... 

Fig. 3. Illustration of the origin of proton nuclear magnetic relaxation induced by a super-paramagnetic crystal. The water molecule (symbolized by a bee) experiences a magnetic field which fluctuates because of the translational diffusion and because of Neel relaxation. The bottom curve represents a typical time evolution of this field.

---