Um estudo de estrutura eletrônica de algumas mn(ii/iii)-n-alquilpiridilporfirinas de alto spin: avaliação do efeito de crescente carga positiva ao redor do centro metálico

• Autor(a) principal: Cavalcanti, Higo de Lima Bezerra
• Data de Publicação: 2011
• Tipo de documento: Dissertação
• Idioma: por
• Título da fonte: Biblioteca Digital de Teses e Dissertações da UFPB
• Texto Completo: https://repositorio.ufpb.br/jspui/handle/tede/7039
• topic: Química; Metaloporfirinas; Química computacional; CIENCIAS EXATAS E DA TERRA::QUIMICA

Synthetic manganese porphyrins comprise the most potent mimics of Superoxide Dismutases (SOD) and redox modulators in vivo. Superoxide (O2 ) and its reactive oxygen/nitrogen species progenies are associated to numerous human pathologies, such as stoke, cardiovascular conditions among others. The effectiveness of ortho Mn N-tetrapyridylporphyrin derivatives (MnT-2-PyP) as SOD mimics has been achieved by appropriate choice of the substituent on the pyridyl moieties to control lipophilicity, charge distribution, and electrostatic facilitation to O2 approach. Hereon we evaluate the semiempirical method PM6 on the treatment of manganese porphyrins based on a comparison over the structural features obtained theoretically and experimentally. Our evaluation on PM6 method showed us that it would not be an appropriate choice on the treatment of our interest complexes and then we decided to carry out a DFT level of theory treatment of MnXM-2-PyP (X = B, Tr, T), where each X indicates the sequencial methylation of the pyridyl groups, entailing an increase of positive charges. We investigate the effect of this increasing charge on some geometrical and electronic properties of aqua high-spin complexes. Geometry optimizations were performed with NWchem6.0 package, applying UDFT/B3LYP method (for a quintet or sextet spin state) with a 6-311G(d,p) basis set for all atoms except Mn where LANL2DZ ECP was used. Vibrational analysis was carried out, followed by an NBO analysis on the optimized structures with Gaussian 2009 package. For the Mn(II)P(H2O) systems studied, the NBO charge in the Mn atom increases with methylation and overall positive charge of the compound. The presence of a single water molecule as axial ligand drives Mn out of the porphyrin plan. An increase in positive charge is accompanied by an increase in Mn-N bond length, while Mn-O bond is shortened. We also point out the fact that the HOMO orbital of these complexes are primarily constituted of d orbitals basis functions from the metal center, and the addition of positive charges contribute to stabilize these orbitals. For the Mn(III)P(H2O)2 systems, the extra coordination water renders Mn nearly within the porphyrin plane. The HOMO orbital is now related to a double-occupied orbital while the LUMO orbital is given by about 55% of d orbitals and resembles the HOMO of Mn(II) species. These results may shed some light on the electronic and structural features underlying the catalytic activity of these compounds.