Photoreactions of p-benzo-, p-naphtho- and p-anthraquinones with ascorbic acid.
Photochem Photobiol Sci
; 3(10): 933-8, 2004 Oct.
Article
em En
| MEDLINE
| ID: mdl-15480484
ABSTRACT
The photoreduction of 1,4-benzoquinone (BQ), 1,4-naphthoquinone (NQ), 9,10-anthraquinone (AQ) and several derivatives, e.g. dimethylBQ, trimethylBQ, duroquinone, bromoNQ, methoxyNQ, methylAQ and dimethylAQ in acetonitrile-water by ascorbate was studied by time-resolved UV-vis spectroscopy using 20 ns laser pulses at 308 nm and continuous 254 nm irradiation. The semiquinone radical (*QH/Q*(-)) is formed after H-atom transfer from ascorbate to the quinone triplet state. The rate constant for quenching is k(q)=(2-9) x 10(9) M(-1) s(-1). Termination of the radicals takes place in the micros-ms range. The results are compared with those initiated by electron transfer from DABCO under similar conditions, where the k(q) values are similar, but the termination of Q*(-) takes place by electron back transfer not yielding hydroquinones. Specific properties of the quinone triplet state, e.g. self-quenching, nucleophilic water addition and the effects of structure are discussed.
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Coleções:
01-internacional
Base de dados:
MEDLINE
Assunto principal:
Ácido Ascórbico
/
Benzoquinonas
/
Antraquinonas
/
Naftoquinonas
Idioma:
En
Revista:
Photochem Photobiol Sci
Assunto da revista:
BIOLOGIA
/
QUIMICA
Ano de publicação:
2004
Tipo de documento:
Article
País de afiliação:
Alemanha