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Ab initio calculation for D-(-)-luciferin and its intermediates in dimethyl sulfoxide Naohisa Wada*1; N Samezima2 (1) 1-1-1 Izumino, Itakura-machi, Gunma 374, Japan; (2) 1-9-3Nakase, Mihama-ku, Chiba-shi,Chiba,261,Japan      *(bhwada@itakura.toyo.ac.jp) It has been well known that chemiluminescence of D-(-)-luciferin (Ln) is produced in dimethyl sulfoxide (DMSO) on dissolving potassium tert-butoxide(t-BuOK). Ln has an absorption maximum at 335nm in DMSO. If DMSO is previously deoxygenated and mixed with t-BuOK, new absorption bands of Ln are observed at about 440nm (M440) and 420nm (M420), respectively. Furthermore, chemiluminescence is initiated on reacting M420 with O2 in the solution. We report the electronic properties of Ln and its related intermediates to study the primary chemiexcitation process of Ln, especially concerning the dioxetane formation in view of quantum chemistry. We first look for the energy-optimized structure of Ln by the AM1 semiempirical method, and then by using this structure as an initial conformation for the Gaussian98 program, we obtain the electronic characteristics of Ln. We also reproduce absorption spectra of Ln, M440 and M420, by the INDO semiempirical method, including the interaction of these molecules with solvent DMSO. Thus, the change of electronic structures from Ln to M420 through M440 can be related to each other to clarify the molecular mechanism of dioxetane formation in firefly chemiluminescence. [Poster: wada.naohisa.12062]

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