Multistate CASPT2 study of native iron(III)-dependent catechol dioxygenase and its functional models: electronic structure and ligand-to-metal charge-transfer excitation.
Multistate CASPT2 study of native iron(III)-dependent catechol dioxygenase and its functional models: electronic structure and ligand-to-metal charge-transfer excitation.
复制标题
DOI：
10.1021/jp110045f
复制
发表时间：
2011-04
期刊：
影响因子：
--
通讯作者：
N. Nakatani;Y. Hitomi;S. Sakaki
中科院分区：
文献类型：
--
作者：
N. Nakatani;Y. Hitomi;S. Sakaki
我们从理论上研究了配体-金属电荷转移（LMCT）激发的天然铁（III）依赖性儿茶酚双加氧酶及其功能模型复合物与多态完全活性空间二阶微扰理论（MS-CASPT 2），因为LMCT（儿茶酚-铁（III）电荷转移）激发能被认为与天然酶及其功能模型复合物的反应性。当活性中心存在于蛋白质环境中而模型复合物存在于溶液中时，MS-CASPT 2方法计算的酶活性中心和模型复合物的基态主要由铁（III）-邻苯二酚电子构型组成，适量的铁（II）-半醌电子构型。然而，基态波函数主要由铁（II）-semiquinonate电子配置的酶活性位点没有蛋白质的环境和模型复合物在真空中。这些结果清楚地表明，蛋白质环境和溶剂在决定邻苯二酚铁（III）复合物的电子结构方面发挥着重要作用。LMCT激发能明显与基态铁（III）-儿茶酚盐构型的重量有关。反应性和LMCT激发能直接与模型复合物中儿茶酚盐（IP（CAT））的电离势相关。这是因为从儿茶酚酯部分到分子氧分子的电荷转移对活化分子氧分子起关键作用。然而，天然儿茶酚双加氧酶的反应性是远远大于那些模型复合物，尽管类似的IP（CAT）值，这表明其他因素，如配位不饱和铁（III）中心的天然酶的反应性发挥了至关重要的作用。
We theoretically investigated the ligand-to-metal charge-transfer (LMCT) excitation of the native iron(III)-dependent catechol dioxygenase and its functional model complexes with multistate complete active space second-order perturbation theory (MS-CASPT2) because the LMCT (catecholate-to-iron(III) charge-transfer) excitation energy is believed to relate to the reactivity of the native enzyme and its functional model complexes. The ground state calculated by the MS-CASPT2 method mainly consists of the iron(III)-catecholate electron configuration and moderately of the iron(II)-semiquinonate electron configuration for both of the enzyme active centers and the model complexes when the active center exists in the protein environment and the model complexes exist in the solution. However, the ground-state wave function mainly consists of the iron(II)-semiquinonate electron configuration for both the enzyme active site without a protein environment and the model complexes in vacuo. These results clearly show that the protein environment and solvent play important roles to determine the electronic structure of the catecholatoiron(III) complex. The LMCT excitation energy clearly relates to the weight of the iron(III)-catecholate configuration in the ground state. The reactivity and the LMCT excitation energy directly relate to the ionization potential of the catecholate (IP(CAT)) in the model complex. This is because the charge transfer from the catecholate moiety to the dioxygen molecule plays a key role to activate the dioxygen molecule. However, the reactivity of the native catechol dioxygenase is much larger than those of the model complexes, despite the similar IP(CAT) values, suggesting that other factors such as the coordinatively unsaturated iron(III) center of the native enzyme play a crucial role in the reactivity.