Estudo químico quântico dos estados de Spin do Cátion Meso-Tetra-Fenil-Ferro III Porfirinato domplexado com a dimetilnitrosamina

Abstract

A research of nitrosamines has attracted attention, because its complexation with the heme group of cytochrome P450 may be associated with its carcinogenic potential. To characterize this problem is realized quantum-chemical treatment of some molecules from the class of metalloporphyrins, more specifically porphyrins Iron III, similar to the heme group mentioned above, with two nitrosamines ligand in axial positions. In literature it is reported that, experimentally these ferroporfirinas containing nitrosamines ligand, have been synthesized and structurally characterized and properly paramagneticamente (sextet spin state). As the Fe (III), this complex presents three possible spin state (doublet, quartet and sextet) the motivation of this dissertation is to know theoretically what spin state most likely to be the ground state, with the goal of describing the relative energy difference between these spin states of Fe (III), as well as characterize the order of energy d orbitals belonging to unpaired electrons alpha iron, these three electronic states. Thus, we performed single-point calculations analyzing guess in control from the beginning of SCF calculation using the program Gaussian09, using ab initio methods at the Hartree-Fock version restricted and unrestricted layer to open with charges calculations NBO, with a set base 6-31 + g *, 6-311 + g * and cc-pVDZ. The method UHF / cc-pVDZ, with Harris and guess Rdscale, showed the best results, providing the lowest energies and contamination in spin states. For the method using the ROHF wave function generated by calculating the spin state in the method sextet UHF wave function as initial results showed parallel to the UHF method. The Mulliken population analysis and NBO, the shape of the spin density and the electrostatic potential map show the location of the positive charge on the iron. The d orbitals, the unpaired electrons, show no overlap with the orbitals of dimetilnitrosaminas. The main contribution of the theoretical results are in agreement with the experimental results available in the literature about the spin state of Fe (III) heme group in the interaction with the dimetilnitrosaminas.