x-RAY PHOTOELECTRON VALENCE BAND STUDIES ON FIREFLY D-(-)-LUCIFERIN

Abstract— The valence band spectrum of firefly D-(-)-luciferin (Ln) was measured for the first time by x-ray photoelectron spectroscopy (XPS). Since the conversion of Ln to decarboxydehydroluciferin (dcrL) by x-ray irradiation occurred even within ∼30 min, the effect of the irradiation on the valence band spectrum of Ln was investigated quantitatively. We found that the XPS valence band spectrum of Ln during irradiation for 3 h corresponds to the state density of Ln calculated by the LCAO-ASMO-SCF-CI method for π-electrons. Moreover, the weak coupling model for π-electron transfer between Ln and oxygen was proposed for the primary electronic process in Ln chemiluminescence, assuming that the calculated π-electron state densities of Ln in acidic and basic solutions reflect the characteristics of their XPS valence band spectra.