Ions, paramagnetic

In a second attempt to obtain more insight into the binding location of the dienophile and now also the diene, we have made use of the influence of paramagnetic ions on the spin-lattice relaxation rates of species in their proximity. Qose to these ions the spin-lattice relaxation rate is dramatically enhanced. This effect is highly distance-dependent as is expressed by Equation 5.7, describing the spin-lattice... 

Here Ti is the spin-lattice relaxation time due to the paramagnetic ion d is the ion-nucleus distance Z) is a constant related to the magnetic moments, i is the Larmor frequency of the observed nucleus and sis the Larmor frequency of the paramagnetic elechon and s its spin relaxation time. Paramagnetic relaxation techniques have been employed in investigations of the hydrocarbon chain... 

Figure 5.8. Paramagnetic ion-induced spin-lattice relaxation rates (rp) of the protons of 5.1c and 5.1 f in CTAB solution and of CTAB in the presence of 5.1c or 5.1 f, normalised to rpfor the surfactant -CH-j. The solutions contained 50 mM of CTAB, 8 mM of 5.1c or 5.1f and 0 or 0.4 mM of [Cu (EDTA) f ...

The high sensitivity and selectivity of the EPR response enables diamagnetic systems to be doped with very low concentrations of paramagnetic ions, the fate of which can be followed during the progress of a reaction. The criteria [347] for the use of such tracer ions are that they should give a distinct EPR spectrum, occupy a single coordination site and have the same valency as, and a similar diffusion coefficient to, the host matrix ion. Kinetic data are usually obtained by comparison with standard materials. 

Giauque s technique still is used in contemporary low-temperature research. A sample containing paramagnetic ions (Fe, for example) is bathed in liquid helium under reduced pressure to chill it to a temperature below 4.2 K. The sample is held in a strong magnetic field, which aligns the magnetic... 

For a reUable extraction of distances, it is important that dipolar relaxation is strongly dominating other relaxation processes. Hence, it is important to avoid paramagnetic ions or molecules such as transition metals or (paramagnetic) oxygen. Especially solution of small molecules therefore have to be carefully degased. 

In paramagnetic materials, the relaxation frequency is in general determined by contributions from both spin-lattice relaxation and spin-spin relaxation. Spin-lattice relaxation processes can conveniently be studied in samples with low concentrations of paramagnetic ions because this results in slow spin-spin relaxation. Spin-spin relaxation processes can be investigated at low temperatures where the spin-lattice relaxation is negligible. Paramagnetic relaxation processes have... 

As discussed in Sect. 6.2, the electronic states of a paramagnetic ion are determined by the spin Hamiltonian, (6.1). At finite temperamres, the crystal field is modulated because of thermal oscillations of the ligands. This results in spin-lattice relaxation, i.e. transitions between the electronic eigenstates induced by interactions between the ionic spin and the phonons [10, 11, 31, 32]. The spin-lattice relaxation frequency increases with increasing temperature because of the temperature dependence of the population of the phonon states. For high-spin Fe ", the coupling between the spin and the lattice is weak because of the spherical symmetry of the ground state. This... 

Spin-spin relaxation is primarily induced by magnetic dipole interactions between paramagnetic ions. Usually, the most important spin-spin relaxation process is the so-called cross-relaxation process in which a transition of an ion / from the state K) to toe state is accompanied by a transition of another ion j from the... 

Xiang, T.-X. Anderson, B. D., Development of a combined NMR paramagnetic ion-induced line-broadening dynamic light scattering method for permeability measurements across lipid bilayer membranes, J. Pharm. Sci. 84, 1308-1315 (1995). 

Spin-Spin Interaction within Paramagnetic Ions. Physic. Rev. 80,1107 (1950). 

O- species. Similarly, Che, Naccache, and Imelik (91) proposed that the electron donor centers are associated with OH- groups which are present on the surface following activation at temperatures below 350°. Again, it is difficult to devise a mechanism in which one obtains a single paramagnetic ion from two relatively immobile diamagnetic species. Obviously, the details for the formation of the radical cations and anions are not well understood. 

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