1. Emission Properties of Oxyluciferin and Its Derivativesin Water: Revealing the Nature of the Emissive Species in FireflyBioluminescence.
- Author
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Ghose, Avisek, Rebarz, Mateusz, Maltsev, Oleg V., Hintermann, Lukas, Ruckebusch, Cyril, Fron, Eduard, Hofkens, Johan, Mély, Yves, Naumov, Panče, Sliwa, Michel, and Didier, Pascal
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BIOLUMINESCENCE , *CHEMICAL derivatives , *WATER , *TIME-resolved spectroscopy , *AQUEOUS solutions , *HYDROGEN bonding - Abstract
Thefirst systematic steady-state and time-resolved emission studyof firefly oxyluciferin (emitter in firefly bioluminescence) and itsanalogues in aqueous buffers provided the individual emission spectraof all chemical forms of the emitter and the excited-state equilibriumconstants in strongly polar environment with strong hydrogen bondingpotential. The results confirmed the earlier hypothesis that excited-stateproton transfer from the enol group is favored over proton transferfrom the phenol group. In water, the phenol-keto form is the strongestphotoacid among the isomers and its conjugate base (phenolate-keto)has the lowest emission energy (634 nm). Furthermore, for the firsttime we observed green emission (525 nm) from a neutral phenol-ketoisomer constrained to the keto form by cyclopropyl substitution. Theorder of emission energies indicates that in aqueous solution a seconddeprotonation at the phenol group after the enol group had dissociated(that is, deprotonation of the phenol-enolate) does not occur in thefirst excited state. The pH-dependent emission spectra and the time-resolvedfluorescence parameters revealed that the keto-enol tautomerism reaction,which can occur in a nonpolar environment (toluene) in the presenceof a base, is not favored in water. [ABSTRACT FROM AUTHOR]
- Published
- 2015
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