dioxetanone and oxyluciferin

To elucidate the emission process of firefly d-luciferin oxidation across the pH range of 7-9, we identified the emission process by comparison of the potential and free-energy profiles for the formation of the firefly substrate and emitter, including intermediate molecules such as d-luciferyl adenylate, 4-membered dioxetanone, and their deprotonated chemical species. From these relative free energies, it is observed that the oxidation pathway changes from d-luciferin → deprotonated d-luciferyl adenylate → deprotonated 4-membered dioxetanone → oxyluciferin to deprotonated d-luciferin → deprotonated d-luciferyl adenylate → deprotonated 4-membered dioxetanone → oxyluciferin with increasing pH value. This indicates that deprotonation on 6'OH occurs during the formation of dioxetanone at pH 7-8, whereas luciferin in the reactant has a 6'OH-deprotonated form at pH 9.

Topics: Animals; Fireflies; Firefly Luciferin; Heterocyclic Compounds, 1-Ring; Hydrogen-Ion Concentration; Indoles; Luminescent Agents; Oxidation-Reduction; Pyrazines

The chemiluminescence properties of firefly luciferin were studied, in a variety of chemical systems different from those in which it is usually studied. It was found that luciferin is a multifunctional chemiluminescence molecule, as it can behave as a chemiluminescence sensitizer, an emitter and a substrate. The first two roles are here reported for the first time, while we have found a novel way of obtaining excited state oxyluciferin from luciferin. Evidence was also found that does not support the newly proposed radical-mechanism of the formation of firefly dioxetanone. With this study we hope to open the way for novel chemiluminescence applications for firefly luciferin.

Topics: Firefly Luciferin; Heterocyclic Compounds, 1-Ring; Indoles; Luminescent Agents; Luminescent Measurements; Pyrazines

Both experimental and theoretical methodologies were employed in order to study the possibility of excited state oxyluciferin being formed as the result of the decomposition of a neutral dioxetanone. Excitation measurements in water (at different pH values) and in methanol, along with computational calculations, demonstrated that the hydroxyl-benzothiazole group of firefly dioxetanone and six oxyluciferin analogues is only deprotonated in conditions not in line with the firefly bioluminescence reaction. Thus, a new mechanism involving a neutral firefly dioxetanone must be presented in order to explain the chemiexcitation of oxyluciferin. It was also studied for the first time the interaction between a molecule involved in the bioluminescence reaction (neutral firefly dioxetanone) and the real second conformation of firefly luciferase.

Topics: Firefly Luciferin; Heterocyclic Compounds, 1-Ring; Hydrogen-Ion Concentration; Indoles; Luciferases, Firefly; Luminescent Agents; Luminescent Measurements; Molecular Structure; Pyrazines; Thermodynamics

We demonstrate that the emission energy of the cypridinid oxyluciferin depends strongly on the polarity and, to a lesser extent, on the basicity of the medium. The emission color can be tuned by environment effects from violet to green. We also provide firm evidence that the natural system utilizes the neutral form of the emitter.

Topics: Amides; Animals; Color; Crustacea; Heterocyclic Compounds, 1-Ring; Indoles; Luminescent Measurements; Molecular Conformation; Pyrazines