Metal nuclei

Dechter J J, Henriksson U, Kowalewski J and Nilsson A-C 1982 Metal nucleus quadrupole coupling constants in aluminum, gallium and indium acetylacetonates J. Magn. Reson. 48 503-11... 

Dhir H, Sharma A, Talukler G. 1985. Alteration of cytotoxic effects of lead through interaction with other heavy metals. Nucleus 28 68-89. 

For a nucleus sharing all the molecular symmetry elements (e.g., the metal nucleus in a mononuclear complex), the hyperfine matrix is subject to the same... 

Figures 4.2 L5 show accurate perspective ball-and-stick diagrams of the idealized structures in (4.45)-(4.49), in order to aid visualization of the rather unfamiliar shapes associated with equivalent sdM hybrids. Note that a surprising proportion of these hypothetical sdM geometries corresponds to placing all ligands on one side of a plane through the metal nucleus (see, e.g., Figs. 4.3(b) and (c) and 4.4(b) and (d)), and will thus be disfavored on steric or electrostatic grounds. Hence, the most reasonable structures are those shown in Figs. 4.3(a), 4.4(a) and (b), and 4.5(a) and (c), which have fewer cramped aacute angles and fill space more equitably.

Information concerning the symmetry of the electric field at the metal nucleus can be found from this latter parameter, AEq, which can also be measured directly by nuclear quadrupole resonance techniques. Additional information concerning the symmetry of the ligand around the metal can be deduced from x-ray, infrared, and nuclear magnetic resonance data. 

The Florence NMRD program (8) (available at www.postgenomicnmr.net) has been developed to calculate the paramagnetic enhancement to the NMRD profiles due to contact and dipolar nuclear relaxation rate in the slow rotation limit (see Section V.B of Chapter 2). It includes the hyperfine coupling of any rhombicity between electron-spin and metal nuclear-spin, for any metal-nucleus spin quantum number, any electron-spin quantum number and any g tensor anisotropy. In case measurements are available at several temperatures, it includes the possibility to consider an Arrhenius relationship for the electron relaxation time, if the latter is field independent. 

Fig. 4. Effect of (A) axial zero field splitting for the spin systems S = 1,3/2,2, and 5/2 (with Bo applied along the z direction of the ZFS tensor), and (B) isotropic hyperfine coupling with the metal nucleus for systems with I = 1/2, S = 1/2 and I = 3/2, S = 1/2.

Complexes in which the spin rbit coupling gives rise to anisotropy in the hyperfine coupling to the metal nucleus and in the g tensors. 

As an example on the relationship between proton relaxivity, electron relaxation and coordination environment, we report the case of azurin and its mutants. The relaxivity of wild type azurin is very low (Fig. 6) due to a solvent-protected copper site, the closest water being found at a distance of more than 5 A from the copper ion. The fit, performed with the Florence NMRD program, able to take into account the presence of hyperfine coupling with the metal nucleus (Ay = 62 x 0 cm , see Section II.B) indicates Tie values of 8 X 10 s. Although the metal site in azurin is relatively inaccessible, several mutations of the copper ligands open it up to the solvent. The H NMRD profiles indicate the presence of water coordination for the... 

Fig. 5. Water NMRD profiles for solutions of superoxide dismutase at various temperatures (124). The solid lines are best-fit curves obtained with the inclusion of the effect of hyperfine coupling with the metal nucleus (27).

C) A = 0.016 cm , A = 0.005 cm and different angles (0 = 0, 30, 45, 60, 90°). The profile in bold shows the relaxation rate values calculated without including hyperfine coupling with the metal nucleus effects (Solomon profile). 

The isotropic shift. The isotropic shift is the sum of two contributions the contact and the dipolar contributions. The former is due to the presence of unpaired electron density on the resonating nucleus. The latter arises from the anisotropy of the magnetic susceptibility tensor, modulated by the distance between the unpaired electron and the resonating nucleus, and is also dependent on the orientation of the metal nucleus vector with respect to the principal axes of the magnetic susceptibility tensor. Some problems arise when the spin delocalization is taken into account in calculating the dipolar coupling, but we will not address this problem except when strictly necessary. 

In addition, one must consider the possibility of interaction between adjacent groups. This is of particular importance when dealing with the beryllium derivatives in which the metal nucleus is very small and may also be of significance in other systems such as the lithium aggregates. Unfortunately, little quantitative information has appeared with regard to this feature other than statements of distance observed in a few systems. 

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