Lifetimes of Triplet Dissolved Natural Organic Matter (DOM) and the Effect of NaBH4 Reduction on Singlet Oxygen Quantum Yields: Implications for DOM Photophysics

The natural lifetimes of triplet dissolved organic matter (3DOM*) were determined by an O2 saturation kinetics study of singlet oxygen quantum yields (Φ1O2) in buffered D2O. At least two distinct 3DOM* pools are present, and the observed lifetime range (∼20 to 80 μs) leads to a dependence of Φ1O2 on...

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Bibliographic Details
Published in:Environmental science & technology 2012-04, Vol.46 (8), p.4466-4473
Main Author: Sharpless, Charles M
Format: Article
Language:English
Subjects:
Benzopyrans - chemistry
Borohydrides - chemistry
Deuterium Oxide - chemistry
Earth sciences
Earth, ocean, space
Exact sciences and technology
Geochemistry
Humic Substances
Marine and continental quaternary
Mineralogy
Oxidation-Reduction
Photochemical Processes
Silicates
Singlet Oxygen - chemistry
Surficial geology
Water - chemistry
Water geochemistry
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Summary:The natural lifetimes of triplet dissolved organic matter (3DOM*) were determined by an O2 saturation kinetics study of singlet oxygen quantum yields (Φ1O2) in buffered D2O. At least two distinct 3DOM* pools are present, and the observed lifetime range (∼20 to 80 μs) leads to a dependence of Φ1O2 on O2 concentrations between 29 and 290 μM. Thus, steady-state 1O2 concentrations will depend on [O2] in natural waters. The lifetimes are essentially identical for DOM samples of different origins and do not vary with excitation wavelength. However, Φ1O2 varies greatly between samples and decreases with excitation wavelength. These data strongly suggest that 3DOM* quantum yields decrease with excitation wavelength, which gives rise to the Φ1O2 variation. Borohydride reduction of several samples in both D2O and H2O lowers the absorbance and 1O2 production rates, but it does not alter Φ1O2. This is consistent with a model in which 1O2 sensitizing chromophores are borohydride reducible groups in DOM, such as aromatic ketones. Interpreted in the framework of a charge transfer (CT) model for DOM optical properties, the collective data suggest a model in which electron acceptor moieties are important 1O2 sensitizers and where CT interactions of these moieties disrupt their ability to produce 1O2.
ISSN:0013-936X
1520-5851
DOI:10.1021/es300217h