skip to main content
US FlagAn official website of the United States government
dot gov icon
Official websites use .gov
A .gov website belongs to an official government organization in the United States.
https lock icon
Secure .gov websites use HTTPS
A lock ( lock ) or https:// means you've safely connected to the .gov website. Share sensitive information only on official, secure websites.

Explore Research Products in the PAR
It may take a few hours for recently added research products to appear in PAR search results.


  • NSF Public Access
  • Search Results
  • Photoproduction Rates of One-Electron Reductants by Chromophoric Dissolved Organic Matter via Fluorescence Spectroscopy: Comparison with Superoxide and Hydrogen Peroxide Rates
Title: Photoproduction Rates of One-Electron Reductants by Chromophoric Dissolved Organic Matter via Fluorescence Spectroscopy: Comparison with Superoxide and Hydrogen Peroxide Rates
One-electron reductants (OER) photoproduced by chromophoric dissolved organic matter (CDOM) have been shown to be likely precursors for the formation of superoxide and subsequently hydrogen peroxide. An improved method that employs a nitroxide radical probe (3AP) has been developed and utilized to determine the photoproduction rates of OER from a diverse set of CDOM samples. 3AP reacts with OER to produce the hydroxyl- amine, which is then derivatized with fluorescamine and quantified spectrofluorometrically. Although less sensitive than traditional methods for measuring RO2•−, measuring RH provides a simpler and faster method of estimating RO2•− and is amenable to continuous measurement via flow injection analysis. Production rates of OER (RH), superoxide (RO2•−), and hydrogen peroxide (RH2O2) have a similar wavelength dependence, indicating a common origin. If all the OER react with molecular oxygen to produce superoxide, then the simplest mechanism predicts that RH /RH2O2 and RO2•−/RH2O2 should be equal to 2. However, our measurements reveal RH /RH2O2 values as high as 16 (5.7−16), consistent with prior results, and RO2•−/RH2O2 values as high as 8 (5.4−8.2). These results indicate that a substantial fraction of superoxide (65−88%) is not undergoing dismutation. A reasonable oxidative sink for superoxide is reaction with photoproduced phenoxy radicals within CDOM.  more » « less
Award ID(s):
1924595
PAR ID:
10319355
Author(s) / Creator(s):
; ;
Date Published:
Journal Name:
Environmental science and technology
Volume:
55
Issue:
17
ISSN:
0194-0287
Format(s):
Medium: X
Sponsoring Org:
National Science Foundation
More Like this
  1. ; ; (, Environmental Science & Technology)
    Superoxide (O2• –) is produced photochemically in natural waters by chromophoric dissolved organic matter (CDOM) via the reaction of molecular oxygen with photoproduced one-electron reductants (OERs) within CDOM. In the absence of other sinks (metals or organic radicals), O2• – is believed to undergo primarily dismutation to produce hydrogen peroxide (H2O2). However, past studies have implicated the presence of an additional light-dependent sink of O2• – that does not lead to H2O2 production. Here, we provide direct evidence of this sink through O2• – injection experiments. During irradiations, spikes of O2• – are consumed to a greater extent (∼85–30% loss) and are lost much faster (up to ∼0.09 s–1) than spikes introduced post-irradiation (∼50–0% loss and ∼0.03 s–1 rate constant). The magnitude of the loss during irradiation and the rate constant are wavelength-dependent. Analysis of the H2O2 concentration post-spike indicates that this light-dependent sink does not produce H2O2 at low spike concentrations. This work further demonstrates that simply assuming that the O2• – production is twice the H2O2 production is not accurate, as previously believed. 
    more » « less
  2. ; ; (, Limnology and Oceanography)
    Abstract Superoxide () is a reactive oxygen species (ROS) that is primarily produced by the one‐electron transfer of photooxidized chromophoric dissolved organic matter (CDOM) to O2in sunlit natural waters. Here we examine the environmental and chemical parameters (pH, ionic strength, buffer, and halides) that may influence photochemical production rates and decay pathways in natural water. Using the enzyme superoxide dismutase and H2O2measurements, we present results from an irradiated freshwater CDOM source indicating that reductive decay pathways (P/PSOD) dominate with increased pH and NaCl additions and maximal photoproduction rates () increase with carbonate compared to borate buffer. Over 2 h of irradiation, a significant decline in was seen for all samples along with a minor increase in oxidative pathways. These results imply shifts in decay pathways and production rates that seem to vary across natural waters and as a function of irradiation history. 
    more » « less
  3. ; ; (, Environmental Science: Processes & Impacts)
    In Lake Erie, toxin-forming harmful algal blooms (HABs) occur following high concentrations of hydrogen peroxide (H 2 O 2 ). Correlation between H 2 O 2 concentrations and HABs revealed knowledge gaps on the controls of H 2 O 2 production in Lake Erie. One way H 2 O 2 is produced is upon absorption of sunlight by the chromophoric fraction of dissolved organic matter (CDOM). Rates of this photochemical production of H 2 O 2 may increase in proportion to the apparent quantum yield of H 2 O 2 ( Φ H 2 O 2 ,λ ) from CDOM. However, the Φ H 2 O 2 ,λ for H 2 O 2 production from CDOM remains too poorly constrained to predict the magnitude and range of photochemically produced H 2 O 2 , particularly in freshwaters like Lake Erie. To address this knowledge gap, the Φ H 2 O 2 ,λ was measured approximately biweekly from June–September 2019 in the western basin of Lake Erie along with supporting analyses ( e.g. , CDOM concentration and composition). The average Φ H 2 O 2 ,λ in Lake Erie was within previously reported ranges. However, the Φ H 2 O 2 ,λ varied 5-fold in space and time. The highest Φ H 2 O 2 ,λ was observed in the Maumee River, a tributary of Lake Erie. In nearshore waters of Lake Erie, the Φ H 2 O 2 ,λ decreased about five-fold from June through September. Integration of the controls of photochemical production of H 2 O 2 in Lake Erie show that the variability in rates of photochemical H 2 O 2 production was predominantly due to the Φ H 2 O 2 ,λ . In offshore waters, CDOM concentration also strongly influenced photochemical H 2 O 2 production. Together, the results confirm prior work suggesting that photochemical production of H 2 O 2 contributes but likely cannot account for all the H 2 O 2 associated with HABs in Lake Erie. 
    more » « less
  4. ; ; ; ; ; ; ; ; ; ; et al (, International Journal of Molecular Sciences)
    1,4-Napththoquinones (NQs) are clinically relevant therapeutics that affect cell function through production of reactive oxygen species (ROS) and formation of adducts with regulatory protein thiols. Reactive sulfur species (RSS) are chemically and biologically similar to ROS and here we examine RSS production by NQ oxidation of hydrogen sulfide (H2S) using RSS-specific fluorophores, liquid chromatography-mass spectrometry, UV-Vis absorption spectrometry, oxygen-sensitive optodes, thiosulfate-specific nanoparticles, HPLC-monobromobimane derivatization, and ion chromatographic assays. We show that NQs, catalytically oxidize H2S to per- and polysulfides (H2Sn, n = 2–6), thiosulfate, sulfite and sulfate in reactions that consume oxygen and are accelerated by superoxide dismutase (SOD) and inhibited by catalase. The approximate efficacy of NQs (in decreasing order) is, 1,4-NQ ≈ juglone ≈ plumbagin > 2-methoxy-1,4-NQ ≈ menadione >> phylloquinone ≈ anthraquinone ≈ menaquinone ≈ lawsone. We propose that the most probable reactions are an initial two-electron oxidation of H2S to S0 and reduction of NQ to NQH2. S0 may react with H2S or elongate H2Sn in variety of reactions. Reoxidation of NQH2 likely involves a semiquinone radical (NQ·−) intermediate via several mechanisms involving oxygen and comproportionation to produce NQ and superoxide. Dismutation of the latter forms hydrogen peroxide which then further oxidizes RSS to sulfoxides. These findings provide the chemical background for novel sulfur-based approaches to naphthoquinone-directed therapies. 
    more » « less
  5. ; (, Organic & Biomolecular Chemistry)
    This work reports a new ATP-independent bioluminescent probe (bor-DTZ) for detecting hydrogen peroxide that is compatible with the Nanoluciferase enzyme. The probe is designed with an arylboronate ester protecting group appended to a diphenylterazine core via a self-immolative phenolate linker. Reaction with hydrogen peroxide reveals diphenylterazine, which can then react with Nanoluciferase to produce a detectable bioluminescent signal. Bor-DTZ shows a dose-dependent response to hydrogen peroxide and selectivity over other biologically relevant reactive oxygen species and can be applied to detect either intra- or extracellular species. We further demonstrate the ability of this platform to monitor fluxes in extracellular hydrogen peroxide in a breast cancer cell line in response to the anticancer treatment, cisplatin. 
    more » « less
  • Citation Formats
  • MLA
  • APA
  • Chicago
  • BibTeX
  • Save / Share this Record
  • Send to Email