QM/MM Investigations on the Bioluminescent Decomposition of Coelenterazine Dioxetanone in Obelin

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+H 2 O) – 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+H 2 O) decomposes through an uncatalyzed non-CT biradical process. The anionic decomposition catalyzed by CT, in which the S 0 /S 1 surface “double crossing” hence has ability to provide high quantum yield of singlet chemiexcitation is thus more possible in bioluminescence of photoprotein.