Theoretical analysis of the color tuning mechanism of oxyluciferin and 5-hydroxyoxyluciferin

Firefly luciferase exhibits a multicolor bioluminescence, which is caused by the modulation of the emission of oxyluciferin by intermolecular interactions. One of the objectives of the present paper was analyze the possible effect of the charge density of the emitter in the color tuning. Theoretical calculations on oxyluciferin, and its respective moieties, demonstrated that no correlation between charge density and light emission can be found once solvent effects are considered. Further computational calculations demonstrate that intermolecular interactions modulate the emission by affecting the geometry of oxyluciferin, which controls the energy gap between the excited and ground state. Direct intermolecular interactions and polarity also affect the color of emission of oxyluciferin, by the same mechanism. Also, the effect of charge density modulation of Keto-(−1). A novel emitter, 5-hydroxyoxyluciferin, was considered and demonstrated to be more red-shifted that oxyluciferin.