Probing ligand effects on the redox energies of [4Fe-4S] clusters using broken-symmetry density functional theory.-猫眼课题宝

使用破缺对称密度泛函理论探测配体对 [4Fe-4S] 簇氧化还原能的影响。

DOI：

10.1021/jp809446q

发表时间：

2009

期刊：

The journal of physical chemistry. A

影响因子：

通讯作者：

中科院分区：

文献类型：

作者：

Niu,Shuqiang;Ichiye,Toshiko

A central issue in understanding redox properties of iron−sulfur proteins is determining the factors that tune the reduction potentials of the Fe−S clusters. Recently, Solomon and coworkers have shown that the Fe−S bond covalency of protein analogs measured by %L, the percent ligand character of the Fe 3d orbitals, from ligand K-edge X-ray absorption spectroscopy (XAS) correlates with the electrochemical redox potentials. Also, Wang and coworkers have measured electron detachment energies for iron−sulfur clusters without environmental perturbations by gas-phase photoelectron spectroscopy (PES). Here the correlations of the ligand character with redox energy and %L character are examined in [Fe4S4L4]2−clusters with different ligands by broken symmetry density functional theory (BS-DFT) calculations using the B3LYP functional together with PES and XAS experimental results. These gas-phase studies assess ligand effects independently of environmental perturbations and thus provide essential information for computational studies of iron−sulfur proteins. The B3LYP oxidation energies agree well with PES data, and the %L character obtained from natural bond orbital analysis correlates with XAS values, although it systematically underestimates them because of basis set effects. The results show that stronger electron-donating terminal ligands increase %Lt, the percent ligand character from terminal ligands, but decrease %Sb, the percent ligand character from the bridging sulfurs. Because the oxidized orbital has significant Fe−Ltantibonding character, the oxidation energy correlates well with %Lt. However, because the reduced orbital has varying contributions of both Fe−Ltand Fe−Sbantibonding character, the reduction energy does not correlate with either %Ltor %Sb. Overall, BS-DFT calculations together with XAS and PES experiments can unravel the complex underlying factors in the redox energy and chemical bonding of the [4Fe−4S] clusters in iron−sulfur proteins.