| Abstract
| - Solution 1H NMR has been used to elucidate the magnetic properties and electronic structure ofthe prosthetic group in high-spin, ferrous deoxy myoglobin from the sea hare Aplysialimacina. A sufficientnumber of dipolar shifted residue signals were assigned to allow the robust determination of the orientationand anisotropy of the paramagnetic susceptibility tensor, χ. The resulting quantitative description of dipolarshifts allows a determination of the contact shifts for the heme. χ was found to be axial, with Δχax = −2.07× 10-8 m3/mol, with the major axis tilted (∼76°) almost into the heme plane and in the general direction ofthe orientation of the axial HisF8 imidazole plane which coincides approximately with the β-,δ-meso axis.The factored contact shifts for the heme are shown to be consistent with the transfer of positive π spindensity into one of the two components of the highest filled π molecular orbital, 3eπ, and the transfer ofnegative π-spin density, via spin−spin correlation, into the orthogonal excited-state component of the 3eπmolecular orbital. The thermal population of the excited state leads to strong deviation from the Curie lawfor the heme substituents experiencing primarily the negative π-spin density. The much larger transfer ofnegative spin density via the spin-paired dπ orbital into the excited state 3eπ in high-spin iron(II) than inlow-spin iron(III) hemoproteins is attributed to the much stronger correlation exerted by the four unpairedspin on the iron in the former, as compared to the single unpaired spins on iron in the latter.
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