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The role of dissolved organic matter as an antioxidant in triplet-induced oxidation reactions

English title The role of dissolved organic matter as an antioxidant in triplet-induced oxidation reactions
Applicant Canonica Silvio
Number 134801
Funding scheme Project funding (Div. I-III)
Research institution Eawag
Institution of higher education Swiss Federal Institute of Aquatic Science and Technology - EAWAG
Main discipline Other disciplines of Environmental Sciences
Start/End 01.04.2011 - 31.01.2012
Approved amount 51'228.00
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All Disciplines (3)

Discipline
Other disciplines of Environmental Sciences
Physical Chemistry
Organic Chemistry

Keywords (7)

organic contaminants; oxidation; NOM; DOM; excited triplet states; antioxidants; carbonate radical

Lay Summary (English)

Lead
Lay summary

Dissolved organic matter (DOM), ubiquitous in natural waters, can both accelerate and inhibit the transformation of organic contaminants under the action of sunlight. In this project we relate the inhibition effect of DOM to its antioxidant capacity.

 

Background

Triplet-induced oxidation of several organic contaminants is likely to play a significant role for their fate in the aquatic environment. DOM carries not only photosensitizer moieties, able to form excited triplet states with oxidizing character, but also moieties that may be considered as antioxidants. Thus, DOM can act as a light-activated oxidant as well as a reductant. In a preceding project, we employed model aromatic ketones as the photosensitizers to disentangle this dual chemical nature and study the possible inhibition of triplet-induced oxidation. We could show that DOM is able to inhibit (or, in other words; slow down the rate of) triplet-induced oxidation of several organic contaminants, but especially those containing aniline functionalities. Various phenolic compounds, used as model antioxidants to mimic the corresponding moieties of DOM, were also shown to inhibit triplet-induced oxidation. The basic hypothesis, still valid at the present state of knowledge, is that oxidation intermediates of the target contaminant interact with model antioxidants or antioxidant moieties of the DOM, leading to reduction of the oxidation intermediates with consequent regeneration of the parent compound. However, the reason why certain contaminants undergo inhibition while others don’t is still open.

 

Objectives and methods

We now intend to improve our understanding of the mechanisms that govern triplet-induced oxidation of contaminants and its inhibition by DOM. The two main objectives and the corresponding experimental methods are:

1.  Detection, by nanosecond laser flash photolysis, of the oxidation intermediates of a few selected aniline derivatives and investigation of their decay kinetics in the presence of DOM and model antioxidants.  

2.  Study of the relationships between extent of inhibition of triplet-induced oxidation and electron donating capacity of different types of DOM to narrow down the suite of possible antioxidant moieties in DOM responsible for the observed inhibition of oxidation. Electrochemical measurements and selective oxidation of DOM by various chemical oxidants (ozone, chlorine, chlorine dioxide) will be used as additional experimental tools.

 

Significance

The results are anticipated to provide quantitative methods to assess the photoinduced degradation of a wide class of organic contaminants containing aniline moieties, including sulfonamide antibiotics, in natural waters.

Direct link to Lay Summary Last update: 21.02.2013

Responsible applicant and co-applicants

Employees

Publications

Publication
Photosensitizing and Inhibitory Effects of Ozonated Dissolved Organic Matter on Triplet-Induced Contaminant Transformation.
Wenk Jannis, Aeschbacher Michael, Sander Michael, von Gunten Urs, Canonica Silvio (2015), Photosensitizing and Inhibitory Effects of Ozonated Dissolved Organic Matter on Triplet-Induced Contaminant Transformation., in Environmental science & technology, 49(14), 8541-8549.
Chemical Oxidation of Dissolved Organic Matter by Chlorine Dioxide, Chlorine, And Ozone: Effects on Its Optical and Antioxidant Properties
Wenk Jannis, Aeschbacher Michael, Salhi Elisabeth, Canonica Silvio, von Gunten Urs, Sander Michael (2013), Chemical Oxidation of Dissolved Organic Matter by Chlorine Dioxide, Chlorine, And Ozone: Effects on Its Optical and Antioxidant Properties, in ENVIRONMENTAL SCIENCE & TECHNOLOGY, 47(19), 11147-11156.

Scientific events

Active participation

Title Type of contribution Title of article or contribution Date Place Persons involved
Symposium: Reaction mechanisms in environmental organic chemistry, 242nd ACS National Meeting Talk given at a conference Triplet-induced oxidation of organic contaminants: Inhibition by dissolved organic matter and model antioxidants 28.08.2011 Denver, Colorado, United States of America Wenk Jannis Henrik;


Associated projects

Number Title Start Funding scheme
140815 Antioxidant effect of dissolved organic matter (DOM) on indirect photochemical transformation of contaminants in surface waters ("Oxindom 3") 01.09.2012 Project funding (Div. I-III)
117911 Aqueous oxidation of organic contaminants: Inhibition by dissolved natural organic matter 01.02.2008 Project funding (Div. I-III)
142015 Advanced oxidation processes for removal of micropollutrants from wastewater 01.05.2012 International short research visits
126893 Using quantum chemistry to assess reactivity of contaminants in surface waters 01.01.2010 Project funding (Div. I-III)
125856 Riverbank filtration under climate change scenarios (RIBACLIM) 01.01.2010 NRP 61 Sustainable Water Management

Abstract

Triplet-induced oxidation of several organic contaminants is likely to play a significant role for their fate in the aquatic environment. Dissolved organic matter (DOM) carries not only photosensitizer moieties, able to form excited triplet states with oxidizing character, but also moieties that may be considered as antioxidants. Thus, DOM can act as a light-activated oxidant as well as a reductant. In the preceding project, we employed model aromatic ketones as the photosensitizers to be able to disentangle this dual chemical nature and study the possible inhibition of triplet-induced oxidation by DOM. We could show that DOM is able to inhibit (or, in other words; slow down the rate of) triplet-induced oxidation of several organic contaminants, but especially those containing aniline moieties. The basic hypothesis, still valid at the present state of knowledge, is that oxidation intermediates formed upon oxidation of the target contaminant interact with antioxidant moieties of the DOM, leading to reduction of the oxidation intermediate with consequent regeneration of the parent compound.In the preceding, still ongoing project we have succeeded in a phenomenological characterization of the inhibition effect and we have proven that model antioxidants are also capable, as DOM, of inhibition of triplet-induced oxidation. However, the reason why certain contaminants undergo inhibition while others don’t is still open.In this follow-on proposal we intend to improve our understanding of the mechanisms that govern triplet-induced oxidation of contaminants and its inhibition by DOM. Further experimental methods will be used, which focus on the one hand on the detection of oxidation intermediates and on the other hand on the characterization of the moieties in DOM that are responsible for the inhibition of oxidation. Therefore the two main objectives of the current proposal are: (i)Detection, by nanosecond laser flash photolysis, of the oxidation intermediates of a few selected aniline derivatives resulting from triplet-induced oxidation and investigation of their decay kinetics in the presence of DOM and model antioxidants.(ii)Study of the relationships between extent of inhibition of triplet-induced oxidation and electron donating capacity of different types of DOM to narrow down the suite of possible (probably antioxidant) moieties in DOM responsible for the observed inhibition of oxidation. Electrochemical measurements and selective oxidation of DOM by various chemical oxidants (ozone, chlorine, chlorine dioxide) will be used as additional experimental tools.
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