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QUENCHING OF CHEMIEXCITED TRIPLET ACETONE BY BIOLOGICALLY IMPORTANT COMPOUNDS IN AQUEOUS MEDIUM
Author(s) -
Catalani Luiz H.,
Bechara Etelvino J. H.
Publication year - 1984
Publication title -
photochemistry and photobiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.818
H-Index - 131
eISSN - 1751-1097
pISSN - 0031-8655
DOI - 10.1111/j.1751-1097.1984.tb08866.x
Subject(s) - chemistry , xanthene , photochemistry , quenching (fluorescence) , acetone , aqueous solution , triplet state , singlet oxygen , fluorescence , oxygen , organic chemistry , molecule , physics , quantum mechanics
— Thermolysis of tetramethyl‐l,2‐dioxetane is a convenient source of triplet acetone, which can be monitored in aerated solutions by the sensitized fluorescence of 9,10‐dibromoanthracene. We have investigated the quenching of chemiexcited triplet acetone in air‐equilibrated aqueous solutions containing the 9,10‐dibromoanthracene‐2‐sulfonate ion by five classes of compounds: indoles, tyrosine derivatives, quinones, riboflavin, and xanthene dyes. Quenching rates for indoles, tyrosine and its 3,5‐dihalogenoderivatives, and xanthene dyes (k q = 10 8 ‐10 9 M ‐1 s ‐1 ) are considerably smaller than the diffusion controlled rate, whereas those for quenchers with high electroaffinities, such as quinones (IP = 10–11 eV), approach the diffusion controlled rate (k q = 10 10 M ‐1 s ‐1 ). Energy transfer for riboflavin probably occurs by a triplet‐singlet Förster type process. A comparison of the present data with previous studies of quenching of enzymically generated triplet acetone (isobutanal/O 2 /horseradish peroxidase) by the same classes of quenchers (except riboflavin) reveals that, independent of the nature of the quencher and the deactivation mechanism, the Stern‐Volmer quenching constants ( k q t 0 ) are systematically about one order of magnitude higher in the enzymatic system. The difference is attributed to a longer lifetime of triplet acetone in the latter case, “protected” in an enzyme cavity against collisions with dissolved oxygen.