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Fungal Light Emitter: Understanding Its Chemical Nature and pH-Dependent Emission in Water Solution
journal contribution
posted on 2020-04-01, 16:04 authored by Cristina García-Iriepa, Raúl Losantos, Diana Fernández-Martínez, Diego Sampedro, Isabelle NavizetFungal bioluminescence
is a fascinating natural process, standing
out for the continuous conversion of chemical energy into light. The
structure of fungal oxyluciferin (light emitter) was proposed in 2017,
being different and more complex than other oxyluciferins. The complexity
of fungal oxyluciferin arises from diverse equilibria such as keto/enol
tautomerization or deprotonation equilibria of four titratable groups.
For this reason, still some crucial details of its structure remain
unexplored. To obtain further structural information, a combined experimental
and computational study of natural and three synthetic fungal oxyluciferin
analogues has been performed. Here, we state the most stable chemical
form of fungal oxyluciferin regarding its keto and enol tautomers,
in the ground and excited states. We propose the (3Z,5E)-6-(3,4-dihydroxyphenyl)-4-hydroxy-2-oxohexa-3,5-dienoic
acid form as the light emitter (fluorescent state) in water solution.
Moreover, we show that chemical modifications on fungal oxyluciferin
can affect the relative stability of the conformers. Furthermore,
we show the clear effect of pH on emission. General conclusions about
the role of these titratable groups in emission modulation have been
drawn, such as the key role of dihydroxyphenyl deprotonation. This
study is key to further analyze the properties of fungal bioluminescence
and propose novel synthetic analogues.