Electronic structure of the active site of truncated hemoglobin $\mathrm N$ in MCSCF approach

The MCSCF approach with the geometry optimization is applied to the calculation of electronic properties of active site of heme $\mathrm{trHbN}$ including ($\mathrm{ONOO}$) functional group and two water molecules. The localized molecular orbitals are employed as a starting set. Two subspaces of full interaction (CAS) have been used by the construction of MCSCF wavefunction, the first one includes 3d orbitals of iron atom and the second contains bonding and antibonding molecular orbitals (MOs) of peroxynitrite with one unshared electronic pair of the $\mathrm O_2$ fragment. The geometry of the anionic $\mathrm{(ONOO)}^-$ structures arising due to the charge transfer from $\mathrm{Fe(II)}$ are close to that of nitrate anion and peroxynitrite in gas phase. The peroxynitrite is considered in its turn in two different forms corresponding to singlet and triplet states of this anion in the gas phase. The possible role of peroxynitrite structure is discussed in a connection with the defense reaction of M. tuberculosis.