TPPFe(II)、L-Thr-TPPFe(II)的电子结构特征及其载氧功能模拟

Theoretical studies on the Electronic structures and oxygen carrying functions of TPPFe(II) and L-Thr-TPPFe(II)

摘要:

采用密度泛函理论B3LYP方法和混合基组（Fe(II)采用赝式基组Lan2dz；C、H原子采用6-31G(d)；N、O采用6-311++G(2d, p)）对卟啉亚铁（TPPFe(II)）、L-苏氨酸卟啉亚铁（L-Thr-TPPFe(II)）的电子结构特征进行了研究；为了模拟真实的体内环境和实验条件，理论计算采用了极化连续介质模型（PCM）模拟CHCl3和H2O的溶剂效应. 在优化获得稳定构型的基础上，采用Multiwfn软件对获得的波函数进行了拓扑分析和静电势研究，获得了键鞍点电荷密度和分子表观静电势数据. 利用VMD软件绘制得到了表观静电势分布图. 研究发现：（1）苏氨酸残基中的羰基O原子与Fe(II)原子形成配位键，H(7)与N(1)之间存在分子内氢键；以上作用使得卟吩环扭曲变形. （2）苏氨酸残基与Fe(II)配位后可减弱O2和Fe(II)的配位作用，有利于O2的离去. （3）溶剂效应主要使分子内氢键作用减弱，卟吩环扭曲程度增加；减弱苏氨酸残基与Fe(II)的配位作用，增强O2与Fe(II)的配位作用. （4）L-Thr-TPPFe(II)的表观静电势的负值区域主要集中在O原子、N原子附近和苯环的轴面，分别体现了孤对电子和π电子的贡献；正值区域主要集中在苯环H原子和Fe(II)附近区域；中心Fe(II)处存在具有较大的表观静电势，容易与O2配位.

Abstract:

The geometry of TPPFe(II) and L-Thr-TPPFe(II) were optimized using density functional theory (DFT) at the B3LYP level with the mixed basis sets: Lan2dz for Fe(II), 6-31G(d) for C and H atoms, and 6-311++G(2d, p) for N and O atoms. To simulate real conditions, the solvent effects of CHCl3 and H2O were studied using the polarized continuum model (PCM). The electron density at the bond critical point was calculated using the topology analysis of the Multiwfn software. Based on the calculated data of electrostatic potential obtained by quantitative analysis of molecular surface using the Multiwfn software, the molecular electrostatic potential maps were illustrated using VMD software. The bond length and electron density at the bond critical point indicate the coordination bond between the Fe(II) atom and the O atom of carbonyl group in L-threonine and the intramolecular hydrogen bond between H(7) atom and N(1) atom. The porphin ring is warped by the effect of the coordination bond and the intramolecular hydrogen bond. The coordination effect between the Fe(II) atom and carbonyl group may weaken the bond strength between Fe(II) atom and O2, but it is beneficial for the reversible oxygen carrying functions. The solvent effects of CHCl3 and H2O may attenuate the intramolecular hydrogen bond and the coordination effect between the Fe(II) atom and carbonyl group, and enhance the warping of porphin ring and the coordination effect between Fe(II) atom and O2. The computation of molecular electrostatic potential show that the more negative value outside the O atom, N atom and benzene ring are contributed by lone-pair electrons and π-electrons, respectively. The electrostatic potential outside the H atom of the benzene ring and the Fe(II) atom is positive. The most positive value is outside the Fe(II) atom which is the most probable active sites in coordination reactions between the Fe(II) atom and O2.