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YUE Ling 《高等学校化学研究》2018,34(5):758-766
The bioluminescent mechanism of colenterazine dioxetanone(CZD) in the photoprotein of Obelia(obelin) was investigated by the combined quantum and molecular mechanics(QM/MM) method at TD-DFT level, which involved the real protein environment in decomposition of 1,2-dioxetanones. The anionic decomposition of CZD in (CZD+H2O)- model can go through a charge transfer(CT) catalyzed asynchronous-concerted process, which can be elucidated by the gradual reversible CT initiated luminescence(GRCTIL) mechanism. The neutral CZD in (CZDH+H2O) decomposes through an uncatalyzed non-CT biradical process. The anionic decomposition catalyzed by CT, in which the S0/S1 surface "double crossing" hence has ability to provide high quantum yield of singlet chemiexcitation is thus more possible in bioluminescence of photoprotein. 相似文献
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Fluorescence of the phenolate anion (3(O)−) and the amide anion (5(N)−) of coelenteramide analogues in ion pairs with various counter cations was systematically investigated to elucidate the ionic structure of the light emitter in the bioluminescence of the calcium-activated photoproteins aequorin and obelin. The fluorescent properties of 3(O)− in an ion pair with a conjugate acid of an organic base (BASE-H+) were varied depending on the structural variation of the ion pair and the solvent polarity. In particular, the fluorescence of 3(O)− in the ion pair with the conjugate acid of n-butylamine (NBA-H+) indicates that the singlet-excited state of 3(O)− (13(O)−∗) and NBA-H+ make a contact ion pair in which the fluorescence emission maxima of 3(O)− is sensitive to the solvent polarity and the fluorescence quantum yields of 3(O)− increase in a less polar solvent. The results also confirm that 13(O)−∗ is a twisted intramolecular charge transfer state. By contrast, the fluorescence of 5(N)− in an ion pair depends little on the BASE-H+ or the solvent polarity. Based on these results, we conclude that the light emitter in aequorin and obelin bioluminescences is the singlet-excited state of coelenteramide phenolate anion 2(O)− (12(O)−∗) in a contact ion pair with an imidazolium side chain of a histidine residue, which is located at the less polar active sites of the photoproteins. We also propose a mechanism for the bioluminescence reaction, including the chemiexcitation process to give 12(O)−∗. 相似文献
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