Project

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Humic substance redox properties and redox reactions with oxygen

Applicant Sander Michael
Number 135515
Funding scheme Project funding (Div. I-III)
Research institution Institut für Biogeochemie und Schadstoffdynamik ETH Zürich
Institution of higher education ETH Zurich - ETHZ
Main discipline Other disciplines of Environmental Sciences
Start/End 01.01.2012 - 31.12.2015
Approved amount 260'528.00
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All Disciplines (2)

Discipline
Other disciplines of Environmental Sciences
Organic Chemistry

Keywords (7)

Natural organic matter; Humic substances; char; electron transfer reactions; electrochemistry; reactive oxygen species; reduction and oxidation

Lay Summary (English)

Lead
Lay summary

Humic substances (HS) are large and complex organic molecules that are ubiquitous in the terrestrial and aquatic environment, including soils, sediments, and lakes and rivers. HS play an important role in many environmental processes. Among these processes are chemical reactions in which HS either accept or donate electrons from/to living (e.g., microbial) or non-living (e.g., mineral or chemical) reaction partners. These reactions are also referred to as redox reactions. There are many different redox reactions in which HS are involved. For instance, HS may transfer electrons to minerals, which may dissolve as a consequence. HS may also accept or donate electrons from/to organic and inorganic pollutants, which may affect their stability, mobility, and persistence in the environment. HS in fens and bogs may store electrons that otherwise, in the absence of HS, would end up in methane, an unwanted greenhouse gas. Understanding these important reactions requires that the redox properties of HS are known.

The major goal of this research project is to characterize the redox properties of HS. The following aspects will be studied: (i) What are the maximum numbers of electrons that HS can accept or donate? And how are these numbers affected by the origin and composition of the HS? (ii) How easy is it to withdraw an electron from or give an electron to HS? (ii) Once an electron has been withdrawn from or given to HS, can this step be reversed? For instance, can electrons stored in HS be retrieved, for instance by molecular oxygen? These questions have been raised in the past by numerous researchers in the field. However, it was previously difficult to answer these questions because suitable experimental methods were missing. In this project, we will use a novel experimental approach based on analytical electrochemistry that helps overcome limitations of previous methods. In analytical electrochemistry, the numbers of electrons transferred to or withdrawn from HS are directly counted (i.e., the electron flow). Furthermore, electrochemical techniques allow for an accurate control of the reduction potential, which defines whether there is an excess or limitation of electrons in the system.

The results from this project will lead to a better understanding of HS redox properties, which will help bio-geochemists and environmental chemists in assessing the role of HS in electron transfer reactions. This information may help predicting the environmental fate of organic and inorganic pollutants and the emission of the greenhouse gas methane from fens and bogs.

Direct link to Lay Summary Last update: 21.02.2013

Responsible applicant and co-applicants

Employees

Publications

Publication
Redox properties of plant biomass-derived black carbon (biochar)
Klüpfel Laura E., Keiluweit Marco, Kleber Markus, Sander Michael (2014), Redox properties of plant biomass-derived black carbon (biochar), in Environmental Science and Technology, 48(10), 5601-5611.
Redox properties of structural Fe in clay minerals: 3. Relationships between smectite redox and structural properties
Gorski Christopher, Klüpfle Laura, Voegelin Andreas, Sander Michael, Hofstetter Thomas (2013), Redox properties of structural Fe in clay minerals: 3. Relationships between smectite redox and structural properties, in Environmental Science and Technology, submitted(47), 11147-1115.
Humic substances as fully regenerable terminal electron acceptors in recurrently anoxic environments
Klüpfel Laura, Piepenbrock Annette, Kappler Andreas, Sander Michael, Humic substances as fully regenerable terminal electron acceptors in recurrently anoxic environments, in Nature Geoscience, accepted.
Redox Properties and Dynamics of Natural Organic Matter as Assessed by Mediated Electrochemical Analysis
Kluepfel Laura, Redox Properties and Dynamics of Natural Organic Matter as Assessed by Mediated Electrochemical Analysis.
Solid phases as important electron acceptors in freshwater organic sediments
Lau Maximilian, Sander Michael, Gelbrecht Joerg, Hupfer Michael, Solid phases as important electron acceptors in freshwater organic sediments, in Biogeochemistry.

Collaboration

Group / person Country
Types of collaboration
Dr. Jörg Gelbrecht / IGB Berlin Germany (Europe)
- in-depth/constructive exchanges on approaches, methods or results
- Exchange of personnel
Dr. Andrea Paul / Bundesanstalt für Materialforschung und -Prüfung Germany (Europe)
- in-depth/constructive exchanges on approaches, methods or results
Prof. Dr. Aron Stubbins / Skidaway Institute of Oceanography United States of America (North America)
- in-depth/constructive exchanges on approaches, methods or results
Prof. Andreas Kappler / Universität Tübingen Germany (Europe)
- in-depth/constructive exchanges on approaches, methods or results
- Publication
- Research Infrastructure
- Exchange of personnel
Prof. Dr. Kristopher McNeill / ETH Zurich Switzerland (Europe)
- in-depth/constructive exchanges on approaches, methods or results
- Exchange of personnel
- Industry/business/other use-inspired collaboration
Dr. Beat Müller Switzerland (Europe)
- in-depth/constructive exchanges on approaches, methods or results
- Publication
- Research Infrastructure
- Exchange of personnel
Dr. Klaus-Holger Knorr / Universität Münster Germany (Europe)
- in-depth/constructive exchanges on approaches, methods or results
- Research Infrastructure
- Exchange of personnel
Prof. Scott Bridgham United States of America (North America)
- in-depth/constructive exchanges on approaches, methods or results
- Exchange of personnel
Prof. Martin Schroth Switzerland (Europe)
- in-depth/constructive exchanges on approaches, methods or results
- Research Infrastructure
- Exchange of personnel
Prof. Dr. Christian Blodau / University of Guelph Canada (North America)
- in-depth/constructive exchanges on approaches, methods or results
Prof. Dr. Markus Kleber / University of Oregon United States of America (North America)
- in-depth/constructive exchanges on approaches, methods or results
- Publication
- Research Infrastructure
Prof. Dr. George Aiken / U.S. Geological Survey United States of America (North America)
- in-depth/constructive exchanges on approaches, methods or results

Scientific events

Active participation

Title Type of contribution Title of article or contribution Date Place Persons involved
SOM conference 2015 Talk given at a conference Electron transfer to and from dissolved and particulate organic matter: from electrochemical interrogation to redox dynamics in peatlands. 20.09.2015 Göttingen, Germany Klüpfel Laura Elisabeth; Sander Michael;
Goldschmidt 2015 conference Talk given at a conference Enzymatic Oxidation of Phenolic Moieties in Dissolved Organic Matter 16.08.2015 Prague, Czech Republic Sander Michael; Klüpfel Laura Elisabeth;
Goldschmidt 2015 Conference Talk given at a conference Particulate Organic Matter in Northern Peatlands as a Terminal Electron Acceptor 16.08.2015 Prague, Czech Republic Klüpfel Laura Elisabeth; Sander Michael;
Goldschmidt 2015 Conference Talk given at a conference From Lab to Field: Multi-Scale Spatiotemporal Redox Dynamics of Geochemical Phases 16.08.2015 Prague, Czech Republic Sander Michael; Klüpfel Laura Elisabeth;
Stanford School of Earth Sciences - Invited Seminar Talk Individual talk Redox properties and reactivities of natural organic matter: from molecular level insights towards understanding carbon cycling in wetlands. 15.08.2014 Stanford, United States of America Sander Michael; Klüpfel Laura Elisabeth;
248th ACS National Meeting Talk given at a conference Humic Substances Redox Redux: From molecular scale electron transfer to global biogeochemical cycles 10.08.2014 San Francisco, United States of America Klüpfel Laura Elisabeth; Sander Michael;
Conference IAP 2014: Interfaces in Water and Environmental Science Talk given at a conference Should I stay or should I go now: Assessing electron transfer properties of organic and mineral phases using analytical electrochemistry. Invited plenary conference lecture 26.05.2014 Leeuwarden, Netherlands Sander Michael; Klüpfel Laura Elisabeth;
Invited Seminar talk, Institute of Earth Surface Dynamics; University of Lausanne Individual talk Redox properties and reactivities of organic and mineral phases: from electrochemical interrogation to biogeochemical implications 27.02.2014 Lausanne, Switzerland Sander Michael; Klüpfel Laura Elisabeth;
'Dycap' Seminar Talk given at a conference Redox dynamics of natural organic matter in temporarily anoxic systems 23.02.2014 Karlsruhe, Germany Sander Michael; Klüpfel Laura Elisabeth;
IGB colloquium Individual talk Redox Redux: New and 'electrifying' insights into the redox properties and reactivities of organic and mineral phases using mediated electrochemical analysis 06.02.2014 Berlin, Leibniz-Institute of Freshwater Ecology and Inland Fisheries, Germany Sander Michael;
Swiss Geoscience Meeting 2013 Talk given at a conference Natural organic matter as a fully regenerable terminal electron acceptor for anaerobic microbial respiration in temporarily anoxic systems 15.11.2013 Lausanne, Schweiz, Switzerland Klüpfel Laura Elisabeth;
Goldschmidt 2013, Florence, Session: Biogeochemical and Geochemical Processes and Cycles in Wetlands Talk given at a conference Quantification of organic matter redox states by mediated electrochemical analysis … applied to redox processes in wetlands 28.08.2013 Florence, Italy Sander Michael;
EGU General Assembly 2013 Talk given at a conference Redox buffering by natural organic matter in microbial reduction and O2 re-oxidation cycles: Assessment of reversibility and sustainability, and implications for carbon cycling in temporarily anoxic environments 07.04.2013 Vienna, Austria Klüpfel Laura Elisabeth;


Awards

Title Year
SCNAT/SCS 2014 Chemistry Travel Award 2014
Bernd Rendel Preis der Deutschen Forschingsgemeinschaft (DFG) für Laura Klüpfel http://www.dfg.de/gefoerderte_projekte/wissenschaftliche_preise/rendel-preis/2013/index.html 2013

Associated projects

Number Title Start Funding scheme
159692 Dissolved phenols in ombrotrophic bogs: occurrence and enzymatic transformations 01.01.2016 Project funding (Div. I-III)
129476 Redox Reactivity of Iron-Bearing Clay Minerals 01.06.2010 Project funding (Div. I-III)
159692 Dissolved phenols in ombrotrophic bogs: occurrence and enzymatic transformations 01.01.2016 Project funding (Div. I-III)
149283 Characterization of the redox properties of iron minerals by combined electrochemical and spectroscopic analyses 01.01.2015 Project funding (Div. I-III)

Abstract

1. Summary of the research planHumic substances (HS) play a key role in important biogeochemical redox reactions and in the reductive and oxidative transformation of organic and inorganic contaminants. Despite the importance of HS, a thorough characterization of their redox properties and redox reactivities is yet missing. This proposal aims at overcoming the resulting knowledge gaps through a research plan directed towards improving our understanding of the fundamental redox properties of HS (Part A) and their redox reactions with oxygen (O2) (Part B). The proposed work, which is to be completed by one doctoral student, has the following specific objectives:Part A. Characterization of the fundamental redox properties of HS•Determination of the electron accepting capacities (EAC) and electron donating capacities (EDC) of representative HS as a function of HS origin and solution pH•Identification of the oxidizable and reducible moieties in HS •Determination and parameterization of the dependencies of HS reduction potentials on HS redox state and on solution chemistryPart B. Characterization of the reactivity of reduced HS with O2•Determination of kinetics and extent of the reaction between reduced HS and O2 •Identification and quantification of hydrogen peroxide, H2O2, formed by O2-reoxidation of reduced HSThese objectives will be accomplished through a combination of approaches, including analytical electrochemistry, spectroscopic techniques (electron paramagnetic resonance (EPR), UV-visible spectroscopy), stopped-flow kinetic investigations, and molecular probe methods for selective detection and quantification of H2O2. The proposed work follows a tiered approach in which the EACs and EDCs will be determined in a fast screening step for a large and diverse set of HS, followed by a more time-demanding, in-depth redox characterization of selected HS. The latter will include terrestrial, mixed terrestrial-aquatic, and aquatic HS, whose chemical properties are well characterized and which are commercially available. This will ensure that other research groups working on related questions may study the same HS in the future, which facilitates the advancement of science by allowing for knowledge transfer and discussion between groups. The key anticipated outcomes of the project include (i) the identification and quantification of HS redox properties as a function of the origin, chemical properties, and structural features of HS, and on the solution pH, (ii) establishing the applicability of analytical electrochemistry for the redox quantification of environmental HS samples, and (iii) an improved understanding of electron transfer dynamics at oxic-anoxic interfaces and in intermittently anoxic environments by studying the reactivity of reduced HS with O2. This project will advance our mechanistic understanding of HS redox reactions, and will ultimately improve our ability to unravel the role of HS in biogeochemical and contaminant redox reactions in different environmental systems.The proposed project is designed for the education of one PhD student. In addition, two related master thesis projects are anticipated.
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