Magnetic and hyperfine properties of deoxymyoglobin and nitrosyl-myoglobin

Abstract

Density functional spin-polarized calculations for model molecules representing the heme moiety of deoxymyoglobin and nitrosylmyoglobin were performed with the self-consistent numerical discrete variational method (DVM). Charges and electron-spin magnetic moments were obtained with a Mulliken population analysis of the orbitals. The 57Fe Mössbauer quadrupole splitting was calculated for deoxymyoglobin and shows good agreement with experiment. The isotropic and anisotropic components of the magnetic hyperfine interaction were calculated for several small radicals containing N, and the values compared to reported experimental measurements to assess the precision of the calculations. The method was then applied to calculate the magnetic hyperfine interactions of N atoms in deoxymyoglobin and nitrosylmyoglobin, in the latter for several values of the Fe–N(NO) distance and Fe–N–O angle; the values obtained were compared with reported experimental values from EPR and ENDOR spectroscopies, when available. The present results contribute to the understanding of the chemical bonding of the N atoms in these biological molecules.