Electronic Structure and the Magnetic Hyperfine Interactions in Heme Unit of Metmyoglobin

The $^{14}$N and $^{57m}$Fe hyperfine interactions in the heme unit of metmyoglobin are available experimentally by electron-nuclear double resonance (ENDOR) and Mossbauer spectroscopic techniques. We have carried out electronic structure investigations on the heme system including the H$_{2}$O and proximal imidazole ligands by the first-principles Hartree-Fock procedure and studied the magnetic hyperfine and nuclear quadrupole coupling constants for the $^{57m}$Fe nucleus and all the six $^{14}$N nuclei on the four pyrrole and imidazole ligands as well as the $^{17}$O nucleus on the H$_{2}$O ligand. Comparison will be made with available experimental data [1, 2] and earlier theoretical investigations [3] by the approximate self-consistent charge Extended Huckel procedure. Results will also be presented for the optical frequencies and intensities from transitions between ligand-like and iron d-like states and the Fe-N$_{\varepsilon }$ vibrational frequency [1] G. Lang, Q. Rev. Biophys. \underline {3}, 1 (1970) [2] C.P. Scholes, R.A. Isaacson and G Feher, Biochim. Biophys. Acta \underline {263},448(1972) [3] S.K. Mun, Jane C. Chang and T.P. Das J. Am. Chem. Soc. \underline {101}, 5562(1979)