Shaik Sason, de Visser Samuël P, Ogliaro François, Schwarz Helmut, Schröder Detlef
Department of Organic Chemistry and The Lise Meitner-Minerva Center for Computational Quantum Chemistry, Hebrew University, 91904 Jerusalem, Israel.
Curr Opin Chem Biol. 2002 Oct;6(5):556-67. doi: 10.1016/s1367-5931(02)00363-0.
Recent computational studies of alkane hydroxylation and alkene epoxidation by a model active species of the enzyme cytochrome P-450 reveal a two-state reactivity (TSR) scenario in which the information content of the product distribution is determined jointly by two states. TSR is used to reconcile the dilemma of the consensus 'rebound mechanism' of alkane hydroxylation, which emerged from experimental studies of ultra-fast radical clocks. The dilemma, stated succinctly as 'radicals are both present and absent and the rebound mechanism is both right and wrong', is simply understood once one is cognizant that the mechanism operates by two states, one low-spin (LS) the other high-spin (HS). In both states, bond activation proceeds in a manner akin to the rebound mechanism, but the LS mechanism is effectively concerted, whereas the HS is stepwise with incursion of radical intermediates.
最近，通过细胞色素P-450酶的模型活性物种对烷烃羟基化和烯烃环氧化进行的计算研究揭示了一种双态反应性（TSR）情景，其中产物分布的信息含量由两种状态共同决定。TSR用于调和烷烃羟基化的共识“反弹机制”的困境，该困境源于超快自由基时钟的实验研究。简而言之，“自由基既存在又不存在，反弹机制既正确又错误”这一困境，一旦认识到该机制由两种状态运行，一种是低自旋（LS），另一种是高自旋（HS），就很容易理解。在这两种状态下，键活化均以类似于反弹机制的方式进行，但LS机制实际上是协同的，而HS机制是逐步的，有自由基中间体的介入。
