SPECTROSCOPIC PROPERTIES OF FIREFLY LUCIFERIN AND RELATED COMPOUNDS . AN APPROACH TO PRODUCT EMISSION

The spectroscopic properties of firefly luciferin, its adenylate, and several analogs were investigated in an effort to understand the excited state formed in firefly bioluminescence. It was found that in aqueous solutions, the 6′-hydroxyl group of firefly luciferin (phenol form) dissociates its proton in the excited state. Fluorescence is from the corresponding phenolate anion, the phenol form being relatively nonfluorescent in aqueous solutions. In addition, the fluorescence emission peak of the phenolate anion of luciferin is red-shifted by more than 3200 cm-1 in going from nonpolar solvents to water. In aqueous solutions, Zn2+ and Cd2+ ions produce a further red shift of the fluorescence emission peak. The spectra of the adenylates of luciferin and dehydroluciferin showed effects which could be interpreted in terms of an intramolecular interaction between the benzothiazole and adenine chromophores. All these perturbations of the luciferin chromophore result in significant shifts of the peaks but only small changes in the band width of luciferin emission. Finally, the relevance of these results to the bioluminescence is discussed. © 1969, American Chemical Society. All rights reserved.