Residual hyperfine coupling

The copper-binding sites in copper-containing proteins are characterized by three distinct classes. In Type-1, or blue copper centers, the copper is coordinated to at least two imidazole nitrogens from two histidyl residues and one sulfur from a cysteinyl residue. Type-1 coppers have small copper hyperfine couplings and a strong visible absorption in the Cu(ll) state. Type-2 or non-blue copper... 

Another remarkable feature of these results (Hirota and Weissman, 1960) is that hyperfine coupling to the /3-proton in the isopropyl group was only about 2-4 G. This is very small compared with the results for /3-protons in comparable alcohol radicals (Table 2), and is thought to arise because of restricted rotation about the C—C bond (Symons, 1962). Indeed, molecular models show that only the conformation of this ketyl in which the /3-proton lies in the radical plane is not severely strained. Under these conditions hyper conjugation is at a minimum, and the splitting detected may be a measure of residual coupling in the absence of hyperconjugation (Symons, 1962). 

Bertini et report a detailed study of the magnetic properties of myglobin, in which they determined the axial and orthorhombic terms of the paramagnetic susceptibility tensor using a combination of hyperfine chemical shift measurements and static suscetibility measurements (Evans Method). The determination of the magnetic anisotropy provided a measurement of the residual dipolar couplings and also permitted a separation of the contact and pseudocontact chemical shift contributions of resonances of the Fe(III) ligands. 

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