Radical abstraction reactions by the cytochrome P450 compound I are investigated on the basis of the one quartet two doublet model consisted of three configurations; ⁴{²[↑• ⁺Por]–[↑• ³Fe(IV)=O •↑]} (⁴CpdI; S = 3/2), ²{²[↓• ⁺Por]–[↑• ³Fe(IV)=O •↑]} (²CpdI_a; S = 1/2) and ²{¹[Por(↑↓)]–²[↑• Fe(V)=O]} (²CpdI_b; S = 1/2) where Por denotes porphyrin and axial cysteine anion (–SR) is neglected. The dπ-pπ bond of ²CpdI_b was highly spin-polarized in the transition-state region of hydrogen abstraction reactions, providing the doublet configuration; ²{¹[Por(↑↓)]–²[↑↑•• Fe(IV)–O •↓]} (²CpdI_b,oxyl). The oxyl-radical character of ²CpdI_b,oxyl plays an important role for hydrogen radical abstraction from alkanes. The spin populations on the iron atom at the transition structures by available density functional theory (DFT) results were about 2.0 for ²CpdI_b,oxyl, whereas they were about 1.0 for ⁴CpdI and ²CpdI_a. On the other hand, the spin density population on the carbon atom of alkyl radical were negative and positive in sign for ²CpdI_b,oxyl and ⁴CpdI, respectively, in consistent with their spin structures. In order to elucidate possible reaction pathways by the cytochrome P450 compound I, relative stabilities between ⁴CpdI and ²CpdI_b were examined on the basis of available DFT and beyond DFT results. The refined DFT results obtained by the beyond DFT elucidated one of the possible reaction pathways for hydrogen abstractions; ²CpdI_a → ²Cpd_b → ²CpdI_b,oxyl → ²(TS) → (rebound). Implications of the computational results are also discussed in relation to water oxidation in artificial catalysts.

在一个由四个构型组成的四重二重峰模型的基础上，研究了细胞色素P450化合物I的自由基提取反应。⁴ { ² [↑• ⁺ Por] – [↑• ³ Fe（IV）= O•↑]}（⁴ CpdI; S  = 3/2），² { ² [↓• ⁺ Por] – [↑• ³ Fe （IV）= O•↑]}（² CpdI _a ; S  = 1/2）和² { ¹ [Por（↑↓）] – ² [↑•Fe（V）= O]}（² CpdI _b ; S = 1/2），其中Por表示卟啉，而轴向半胱氨酸阴离子（–SR）被忽略。² CpdI _b的dπ-pπ键在夺氢反应的过渡态区域内高度自旋极化，提供了双峰构型。² { ¹ [Por（↑↓）] – ² [↑↑••Fe（IV）–O•↓]}（² CpdI _b， oxyl ）。² CpdI _b， oxy的氧自由基特性对于从烷烃中提取氢自由基起着重要作用。根据可用的密度泛函理论（DFT）结果，在过渡结构上，铁原子上的自旋种群为^2个CpdI _b， oxy，而对于⁴ CpdI和² CpdI _a，它们约为1.0 。另一方面，烷基的碳原子上的自旋密度总体在² CpdI _b，氧基和⁴ CpdI的符号上分别为负和正，与其自旋结构一致。为了阐明细胞色素P450化合物I可能的反应途径，根据可用的DFT和超出DFT结果的结果，研究了⁴ CpdI和² CpdI _b之间的相对稳定性。通过超越DFT获得的精确DFT结果阐明了提取氢的可能反应途径之一；² CpdI_a → ² Cpd _b → ² CpdI _b，氧基→ ²（TS）→（回弹）。还讨论了与人工催化剂中水氧化有关的计算结果的含义。