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Excited-state intermolecular proton transfer of the firefly's chromophore D-luciferin. 2. Water-methanol mixtures
Itay Presiado1, Yuval Erez, Dan Huppert
1Raymond and Beverly Sackler Faculty of Exact Sciences, School of Chemistry, Tel Aviv University, Tel Aviv 69978, Israel.
Abstract:
Steady-state emission and time-resolved techniques were employed to study the photoprotolytic processes d-luciferin undergoes in water-methanol mixtures over a wide range of molar fractions (chi(MeOH)) of methanol. We found that in the concentration range of 0 < chi(MeOH) < 0.8 the rate constant of the excited-state proton transfer (ESPT) to the solvent decreases nearly exponentially with increasing chi(MeOH). At chi(MeOH) > 0.8 the proton transfer rate constant decreases with an even steeper slope. The kinetic isotope effect (KIE) maintains a constant value of 2.4 +/- 0.2 at all the mixture's compositions.
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