Decomposition Reaction of Dioxetanone in Firefly Bioluminescence by Computer Experiment
Decomposition Reaction of Dioxetanone in Firefly Bioluminescence by Computer Experiment
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DOI：
10.1007/s10867-005-0172-1
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发表时间：
2005-12
影响因子：
1.8
通讯作者：
N. Wada;H. Sakai
中科院分区：
文献类型：
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作者：
N. Wada;H. Sakai
萤火虫荧光素（Ln）在荧光素酶（E）、Mg+2离子和ATP存在下与分子氧反应生成四元环过氧化物，称为二氧杂环丁烷酮，目前还没有用分光光度法观察到。随后，二氧杂环丁烷酮分解成二氧化碳（CO2）和电子激发的荧光素（Oxyln− β），发出黄绿光。为了阐明从二氧杂环戊酮到Oxyln-* 基元反应路径的特征，通过使用AM 1 Hamilton的内禀反应坐标（IRC）计算，获得了单重态基态（S 0-PEC）沿着反应坐标的势能曲线。此外，计算了单重激发态（S1-PEC）的势能曲线，因为二氧杂环丁烷酮沿着反应坐标沿着分解为Oxyln− ε。使用INDO/S在反应坐标的每个点处估计S1-PEC相对于S 0-PEC，其中仅考虑由20个占据和20个未占据分子轨道（MO）构建的单激发构型相互作用（CI）。计算结果表明：（1）萤火虫二氧杂环丁烷酮可能不是中间体，而是处于不稳定的过渡态，（2）S 0-PEC生成二氧杂环丁烷酮的活化能垒为37.5 kcal/mol，反应是沿着S 0-PEC放热的;（3）S1-PEC以凹进方式接近S 0-PEC，其中二氧杂环丁烷酮分解以有效地产生Oxyln− 1;和（4）二氧杂环戊酮中O-O键的断裂可以触发电子在朝向Oxyln-* 的化学激发步骤中以S 0-和S1-佩奇介导的“摇篮”运动进出。
Firefly luciferin (Ln) reacts with molecular oxygen in the presence of the enzyme luciferase (E), the Mg+2ion and ATP to form a four-membered cyclic peroxide, so-called dioxetanone, which has not yet been observed by spectrophotometric techniques. Subsequently, dioxetanone decomposes into carbon dioxide (CO2) and electronically excited oxyluciferin (Oxyln−∗), emitting yellow-green light. In order to clarify the characteristics of the elementary reaction path from dioxetanone to Oxyln−∗, the potential energy curve of the singlet ground-state (S0-PEC) along the reaction coordinate was obtained by the intrinsic reaction coordinate (IRC) calculations using the AM1 Hamiltonian. Furthermore, the potential energy curve of the singlet excited-state (S1-PEC) was calculated, because dioxetanone decomposes to Oxyln−∗along the reaction coordinate. The S1-PEC relative to S0-PEC was estimated at each point of the reaction coordinate using the INDO/S, where only the singly-excited configuration interactions (CI) constructed from 20 occupied and 20 unoccupied molecular orbitals (MOs) were considered. As a result of these calculations, it was concluded that (1) firefly dioxetanone might not be an intermediate but rather be in an unstable transition state; (2) the S0-PEC has an activation barrier of 37.5 kcal/mol for dioxetanone formation and the reaction is exothermic along the S0-PEC; (3) the S1-PEC approaches the S0-PEC in a concave manner where dioxetanone decomposes to efficiently produce Oxyln−∗; and (4) rupturing of an O–O bond in dioxetanone can trigger the coming and going of electrons in a “cradle" motion mediated by S0- and S1-PECs in the chemiexcitation step toward Oxyln−∗.