Acta Phys. -Chim. Sin. ›› 2013, Vol. 29 ›› Issue (08): 1673-1680.doi: 10.3866/PKU.WHXB201306041


Spin-Orbit Coupling and Zero-Field Splitting in Dioxygen Activation by Non-Heme Iron(III)

LV Ling-Ling1, WANG Xiao-Fang1, ZHU Yuan-Cheng1, LIU Xin-Wen1, YUAN Kun1, WANG Yong-Cheng2   

  1. 1 College of Life science and Chemistry, Tianshui Normal University, Tianshui 741001, Gansu Province, P. R. China;
    2 College of Chemistry and Chemical Engineering, Northwest Normal University, LanZhou 730070, P. R. China
  • Received:2013-02-27 Revised:2013-06-03 Published:2013-07-09
  • Contact: LV Ling-Ling
  • Supported by:

    The project was supported by the National Natural Science Foundation of China (21263022) and University Research Fund of Gansu Province Financial Department, China.


The mechanism of the O2 activation by the protocatechuate 3,4-dioxygenase was investigated using density functional calculations. In the initial complex, the ultrafast formation of the sextet 61 was probably the result of electron-exchange-induced intersystem crossing, and Fe dz:O2 π*(z) was the dominant exchange pathway, with an overlap of dz: O2π*(z) was dominant exchange pathway with the overlap of Sijdz α|π*(z) β>=0.3758 at an Fe―O bond length of 0.2487 nm. Two coexisting effects, electron spin exchange coupling and spin-orbit coupling (SOC) in the sextet 61, are responsible for formation of the quartet state 41 from the sextet 61. The exchange interaction competes with the SOC interaction as a driving force for spin conversion. The calculated results show that the latter is the dominant factor, because of the larger SOC constant (353.16 cm-1). In cleavage of the O― O bond, electron transfer from the protocatechuate (PCA) highest occupied molecular orbital (HOMO) plays a vital role. The Fe center of the non-heme enzyme is a buffer to transfer an electron pair from the PCA HOMO to O2.222

Key words: Protocatechuate 3,4-dioxygenase, Spin-orbit coupling, Zero-field splitting, Reaction mechanism