Field-Dependent Proton NMR Relaxation in Aqueous Solutions of Ni(II) Ions. A New Interpretation

Extensive NMRD studies of Ni(II) salt solutions in water and water–glycerol mixtures

“…Such features were noticed and explained in the early theoretical paper on the pseudorotation model by Westlund et al [9]. We assume, in analogy with the earlier studies [8,10] that the static ZFS can be set to zero, because of the octahedral coordination (averaged on the time scale of molecular reorientation). In the earlier studies, the data at each temperature were fitted separately.…”

“…In late eighties, we reported an investigation of low-pH aqueous solution of Ni(II) at a series of magnetic field up to 11.7 T [8] and interpreted the experimental data using a theoretical model of Westlund et al [9]. The same data sets were re-interpreted by Svoboda et al [10], using a slightly more sophisticated version of the theory. The experiments show that the PRE increases with increasing magnetic field in the high-field range.…”

Zero-field splitting in nickel(II) complexes: A comparison of DFT and multi-configurational wavefunction calculations

“…Measurements of the paramagnetic relaxation enhancement for aqueous proton NMR signal over a broad range of magnetic fields allow a model-dependent estimation of the fluctuations of the ZFS in solution. [70][71][72][73] Simple non-empirical quantum chemical calculations of the ZFS for the hexaaqua-nickel(II) ion were reported long time ago. 13 Also in the 1990s, these calculations were combined with molecular dynamics simulations to generate the timecorrelation function for ZFS fluctuations in aqueous solution of nickel(II) and their consequences for proton relaxation.…”

“…This observation was also employed in building simple models for NMR relaxation in aqueous nickel(II) solutions with a certain success. 72 Next, we also want to compare again the ab initio methods with DFT. For that purpose, we choose to decrease the high symmetry of the optimized structure in a more systematic way.…”

Four complementary theoretical approaches for the analysis of NMR paramagnetic relaxation

“…Systematic studies of this relationship have also been published by the laboratories of Kowalewski and Westlund in Sweden [14][15][16] and Kruk in Germany [17]. Experimental information concerning the physical mechanism of NMR-PRE is derived primarily from the analysis of magnetic relaxation dispersion (MRD) profiles, in which the NMR relaxation rate of solvent protons in paramagnetic solutions is measured as a function of laboratory magnetic field strength across a broad range (several orders of magnitude) of field variation.…”