Nuclear and electronic relaxation in lanthanide solutions: (CH3)4N+/Gd3+ repulsive ion pair in D2O

19F and 1H Magnetic Relaxation Dispersion Determination of the Translational Encounter between Ionic Salts and Nitroxide Free Radicals in Aqueous Solution

“…The quantum mechanical formulation connecting ensemble spin relaxation to the more fundamental power spectral densities is well established , and there exists a number of recent experimental reports relating the NMR relaxation phenomena of, for example, microporous materials, biological interfaces, and mesophases , to models of molecular motion. Notably, the electrostatically repulsive translational encounter between ( 1 H 3 C) 4 N + and Gd(III) ( S = 7 / 2 ) has been described in terms of the relative diffusion of ions in an exponentially decaying isotropic potential . With a priori knowledge of the relative diffusion constant and distance of closest approach for the system, Vigouroux et al found good agreement between the observed proton relaxation rates and the standard treatment of spin relaxation in the Redfield limit incorporating ion−ion Coulombic potentials that radially oscillate with successive hydration shells.…”

Mechanisms of the Intermolecular Nuclear Magnetic Relaxation Dispersion of the (CH3)4N+ Protons in Gd3+ Heavy-Water Solutions. Interest for the Theory of Magnetic Resonance Imaging

“…On the other hand, at 200 MHz and above, , the measurements were performed on high-resolution Bruker spectrometers, where the (CH 3 ) 4 N + protons display a NMR signal well separated from that of the HOD molecules and have a spin−lattice relaxation time T 1 that can be recorded straightforwardly. In these cases, the temperature was well calibrated at 25 °C.…”

“…As the field decreases, ω I τ decreases, whereas τ/ T 1e increases, so that τ/ T 1e cannot be neglected with respect to ω I τ . Thus, the NMRD of protons requires a detailed knowledge of the electronic relaxation of the Gd 3+ ion.…”

Molecular Dynamics of Gd(III) Complexes in Aqueous Solution by HF EPR

“…The low field part of a given NMRD profile was calculated using one single average point at 0.14 MHz proton frequency with the electron spin relaxation rates obtained through a Monte Carlo simulation. The initial parameters in the fitting procedure were those of Powell (Powell et al, 1996) (see Table 1) except for the following: the Gd-H relative diffusion constant was fixed to the sum of the water (22.36 × 10 10 m 2 /s (1986)) and aqua ion (3.9 × 10 10 m 2 /s (Vigouroux et al, 1998)) self-diffusion coefficients, and the electronic parameters a 2 , a 4 , a 6 , a 2T , τ v and g of Rast et al (Rast et al, 2001b) were used for the electronic part. The rotational correlation time τ R was the one of Powell (41 ps), while its activation energy was restrained to reasonable values (16-19 kJ/mol) as discussed by Rast based on the temperature dependence of water viscosity.…”