Excited-state intermolecular proton transfer of firefly luciferin III. Proton transfer to a mild base.
Steady-state and time-resolved techniques were employed to study the excited-state proton transfer (ESPT) from d-luciferin, the natural substrate of the firefly luciferase, to the mild acetate base in aqueous solutions. We found that in 1 M aqueous solutions of acetate or higher, a proton transfer (PT) process to the acetate takes place within 30 ps in both H(2)O and D(2)O solutions. The time-resolved emission signal is composed of three components. We found that the short-time component decay time is 300 and 600 fs in H(2)O and D(2)O, respectively. This component is attributed either to a PT process via the shortest water bridged complex available, ROH··H(2)O··Ac(-), or to PT taking place within a contact ion pair. The second time component of 2000 and 3000 fs for H(2)O and D(2)O, respectively, is attributed to ROH* acetate complex, whose proton wire is longer by one water molecule. The decay rate of the third, long-time component is proportional to the acetate concentration. We attribute it to the diffusion-assisted reaction as well as to PT process to the solvent.
Raymond and Beverly Sackler Faculty of Exact Sciences, School of Chemistry, Tel Aviv University, Tel Aviv 69978, Israel.
Itay
I
Presiado
Yuval
Y
Erez
Dan
D
Huppert
D000818:Animals; D017666:Deuterium Oxide / Q000737:chemistry; D004058:Diffusion; D048888:Fireflies / Q000737:chemistry; D049454:Firefly Luciferin / Q000737:chemistry*; D006863:Hydrogen-Ion Concentration; D049408:Luminescent Agents / Q000737:chemistry*; D011522:Protons; D019346:Sodium Acetate / Q000737:chemistry; D012996:Solutions / Q000737:chemistry; D013050:Spectrometry, Fluorescence; D013997:Time Factors; D014867:Water / Q000737:chemistry
D049408:Luminescent Agents; D011522:Protons; D012996:Solutions; D014867:Water; D019346:Sodium Acetate; D049454:Firefly Luciferin; D017666:Deuterium Oxide