Photoinduced Dynamics of Oxyluciferin Analogues: Unusual Enol “Super”photoacidity and Evidence for Keto–Enol Isomerization
Citations Over TimeTop 10% of 2012 papers
Abstract
The first systematic pico-nanosecond time-resolved spectroscopic study of the firefly emitter oxyluciferin and two of its chemically modified analogues revealed that in the excited state the enol group is more acidic than the phenol group. The 6'-dehydroxylated derivative, in which only the 4-enolic hydroxyl proton is acidic, has an experimentally determined pK(a)* of 0.9 in dimethyl sulfoxide and an estimated pK(a)* of -0.3 in water. Moreover, this compound provided direct evidence that in a nonpolar, basic environment the keto form in the excited state can tautomerize into the enol, which subsequently undergoes excited-state proton transfer (ESPT) to produce enolate ion. This observation presents the first experimental evidence of excited-state keto-enol tautomerization of a firefly fluorophore, and it could be important in resolving the enol-keto conundrum related to the color-tuning mechanism of firefly bioluminescence. The 6'-dehydroxylated form of oxyluciferin adds a very rare case of a stable enol to the family of "super"photoacids.
Related Papers
- → Enol-keto tautomerism of aromatic photochromic Schiff base N,N′-bis(salicylidene)-p-phenylenediamine: Ground state equilibrium and excited state deactivation studied by solvatochromic measurements on ultrafast time scale(2006)116 cited
- → Enolisation of Simple Carbonyl Compounds and Related Reactions(1982)103 cited
- → Intrahydrogen Bonding and Transition States Between Enol and Enethiol Tautomers in À-Thioxoketones(2011)9 cited
- → The Mills-Nixon effect on enol-enol tautomerism in β-dicarbonyl compounds and on annular tautomerism in NH-pyrazoles: A semi-empirical study(1997)28 cited
- → The 2-Oxocyclohexanecarboxylic Acid Keto−Enol System in Aqueous Solution(2003)11 cited