A photochemical and theoretical study of the triplet reactivity of furano- and pyrano-1,4-naphthoquionones towards tyrosine and tryptophan derivatives

The photochemical reactivity of the triplet state of pyrano- and furano-1,4-naphthoquinone derivatives (1 and 2) has been examined employing nanosecond laser flash photolysis. The quinone triplets were efficiently quenched by l-tryptophan methyl ester hydrochloride, l-tyrosine methyl ester hydrochlo...

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Bibliographic Details
Published in:RSC advances 2019-04, Vol.9 (24), p.13386-13397
Main Authors: Teixeira, Rodolfo I, Goulart, Juliana S, Corrêa, Rodrigo J, Garden, Simon J, Ferreira, Sabrina B, Netto-Ferreira, José Carlos, Ferreira, Vitor F, Miro, Paula, Marin, M Luisa, Miranda, Miguel A, de Lucas, Nanci C
Format: Article
Language:English
Subjects:
Absorption spectra
Amino acids
Atomic energy levels
Chemistry
Derivatives
Electron transfer
Electrons
Esters
Flash photolysis
Mathematical analysis
Phenols
Protons
Quenching
Rate constants
Substrates
Tryptophan
Tyrosine
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Summary:The photochemical reactivity of the triplet state of pyrano- and furano-1,4-naphthoquinone derivatives (1 and 2) has been examined employing nanosecond laser flash photolysis. The quinone triplets were efficiently quenched by l-tryptophan methyl ester hydrochloride, l-tyrosine methyl ester hydrochloride, -acetyl-l-tryptophan methyl ester and -acetyl-l-tyrosine methyl ester, substituted phenols and indole ( ∼10 L mol s ). For all these quenchers new transients were formed in the quenching process. These were assigned to the corresponding radical pairs that resulted from a coupled electron/proton transfer from the phenols, indole, amino acids, or their esters, to the excited state of the quinone. The proton coupled electron transfer (PCET) mechanism is supported by experimental rate constants, isotopic effects and theoretical calculations. The calculations revealed differences between the hydrogen abstraction reactions of phenol and indole substrates. For the latter, the calculations indicate that electron transfer and proton transfer occur as discrete steps.
ISSN:2046-2069
2046-2069
DOI:10.1039/c9ra01939a