Excited-state proton transfer of firefly dehydroluciferin.
Steady-state and time-resolved emission techniques were used to study the protolytic processes in the excited state of dehydroluciferin, a nonbioluminescent product of the firefly enzyme luciferase. We found that the ESPT rate coefficient is only 1.1 × 10(10) s(-1), whereas those of d-luciferin and oxyluciferin are 3.7 × 10(10) and 2.1 × 10(10) s(-1), respectively. We measured the ESPT rate in water-methanol mixtures, and we found that the rate decreases nonlinearly as the methanol content in the mixture increases. The deprotonated form of dehydroluciferin has a bimodal decay with short- and long-time decay components, as was previously found for both D-luciferin and oxyluciferin. In weakly acidic aqueous solutions, the deprotonated form's emission is efficiently quenched. We attribute this observation to the ground-state protonation of the thiazole nitrogen, whose pK(a) value is ~3.
Raymond and Beverly Sackler Faculty of Exact Sciences, School of Chemistry, Tel Aviv University, Tel Aviv 69978, Israel.
Itay
I
Presiado
Yuval
Y
Erez
Ron
R
Simkovitch
Shay
S
Shomer
Rinat
R
Gepshtein
Luís
L
Pinto da Silva
Joaquim C G
JC
Esteves da Silva
Dan
D
Huppert
D000818:Animals; D048888:Fireflies; D049454:Firefly Luciferin / Q000737:chemistry*; D015394:Molecular Structure; D011522:Protons; D011789:Quantum Theory; D013050:Spectrometry, Fluorescence
D011522:Protons; C107793:dehydroluciferin; D049454:Firefly Luciferin