EPR and semi-empirical studies as tools to assign the geometric structures of FeIII isomer models for transferrins

Journal of the Brazilian Chemical Society

Mangrich, Antonio S.¹  Casellato, Annelise¹  Universidade Federal do Rio de Janeiro, Rio de Janeiro, Brazil¹  Bortoluzzi, Adailton J.¹  Scarpellini, Marciela¹  Universidade Federal de Goiás, Goiânia, Brazil¹  Universidade Federal de Santa Catarina, Florianópolis, Brazil¹  Machado, Sérgio P.¹  Universidade Federal do Paraná, Curitiba, Brazil¹  Vencato, Ivo¹  Neves, Ademir¹ 

关键词: FeIII complex;    geometric isomers;    EPR;    transferrins;    semi-empirical studies;   

DOI  :  10.1590/S0103-50532006000800020

学科分类：化学（综合）

来源: SciELO

【 摘 要 】

The reaction of Fe(ClO4)3.nH2O with N,N'-bis[(2-hydroxybenzyl)-N,N' -bis(1-methylimidazole-2-yl-methyl)]ethylenediamine (H2bbimen) affords two geometric isomers, A and B, of the complex cation [Fe(bbimen)]+, which were fully characterized by IR and UV-visible spectroscopies, ESI mass spectrometry, molar conductivity measurements, cyclic voltammetry, spectroelectrochemistry and EPR spectroscopy. The geometry of one of these isomers has been clearly demonstrated through X-ray crystallographic analysis. It crystallizes in the monoclinic system, space group P21/c, a = 14.104 (3), b = 15.626 (3), c = 13.291 (3) Å, b = 98.07 (3)º, Z = 4, R1 = 6.35% and wR2 = 20.57%. The electrochemical properties of [Fe(bbimen)]+ (-0.58 V versus NHE) are quite similar to those of transferrins (-0.52 V versus NHE) and indicate that it is a good model for the redox potential of these metalloenzymes. EPR spectroscopy was the only spectroscopic technique able to differentiate the isolated isomers A and B. EPR studies revealed that isomer A is better described as a rhombically distorted (E/D @ 0.33) high-spin FeIII complex (g1  @ 4.1 with a shoulder at g2  @ 9.0), while the spectrum of B has a set of lines at g1  @ 3.0, g2  @ 3.6 and g3  @ 5.1, in addition to the line at g1  @ 4.2 and a shoulder at g2 @ 9.0, which have been ascribed to FeIII complexes in axial symmetry (E/D @ 0.22). Semi-empirical theoretical studies, combined with EPR data, were essential to the proposition of the geometric structures of A and B.

【 授权许可】

Unknown