Thomas Hofstetter


Last Name

Hofstetter

First Name

Thomas

ORCID

0000-0003-1906-367X

Organisational unit

01709 - Lehre Umweltsystemwissenschaften

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2018 - 201912020 - 20252
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Publications 1 - 3 of 3
  • Characterization of O₂ uncoupling in biodegradation reactions of nitroaromatic contaminants catalyzed by rieske oxygenases
    Item type: Book Chapter
    Bopp, Charlotte E.; Bernet, Nora M.; Pati, Sarah G.; et al. (2024)
    Methods in Enzymology ~ Mononuclear Non-heme Iron Dependent Enzymes Part A
    Rieske oxygenases are known as catalysts that enable the cleavage of aromatic and aliphatic C–H bonds in structurally diverse biomolecules and recalcitrant organic environmental pollutants through substrate oxygenations and oxidative heteroatom dealkylations. Yet, the unproductive O2 activation, which is concomitant with the release of reactive oxygen species (ROS), is typically not taken into account when characterizing Rieske oxygenase function. Even if considered an undesired side reaction, this O2 uncoupling allows for studying active site perturbations, enzyme mechanisms, and how enzymes evolve as environmental microorganisms adapt their substrates to alternative carbon and energy sources. Here, we report on complementary methods for quantifying O2 uncoupling based on mass balance or kinetic approaches that relate successful oxygenations to total O2 activation and ROS formation. These approaches are exemplified with data for two nitroarene dioxygenases (nitrobenzene and 2-nitrotoluene dioxygenase) which have been shown to mono- and dioxygenate substituted nitroaromatic compounds to substituted nitrobenzylalcohols and catechols, respectively.
  • Linking Thermodynamics to Pollutant Reduction Kinetics by Fe2+ Bound to Iron Oxides
    Item type: Journal Article
    Stewart, Sydney M.; Hofstetter, Thomas; Joshi, Prachi; et al. (2018)
    Environmental Science & Technology
    Numerous studies have reported that pollutant reduction rates by ferrous iron (Fe2+) are substantially enhanced in the presence of an iron (oxyhydr)oxide mineral. Developing a thermodynamic framework to explain this phenomenon has been historically difficult due to challenges in quantifying reduction potential (EH) values for oxide-bound Fe2+ species. Recently, our group demonstrated that EH values for hematite- and goethite-bound Fe2+ can be accurately calculated using Gibbs free energy of formation values. Here, we tested if calculated EH values for oxide-bound Fe2+ could be used to develop a free energy relationship capable of describing variations in reduction rate constants of substituted nitrobenzenes, a class of model pollutants that contain reducible aromatic nitro groups, using data collected here and compiled from the literature. All the data could be described by a single linear relationship between the logarithms of the surface-area-normalized rate constant (kSA) values and EH and pH values [log(kSA) = −EH/0.059 V – pH + 3.42]. This framework provides mechanistic insights into how the thermodynamic favorability of electron transfer from oxide-bound Fe2+ relates to redox reaction kinetics.
  • Determining Contributions of Three Different Pathways to Total Degradation of a Contaminant Using Data From Triple-Element Isotope Analysis
    Item type: Journal Article
    Thullner , Martin; Hofstetter, Thomas (2025)
    Water, Air, & Soil Pollution
    The analysis of multi-elemental compound-specific stable isotope analysis (CSIA) has been established for the determination of contaminant degradation pathways. For systems with two pathways taking place simultaneously also a quantitative analysis of each pathway’s contribution to total degradation has been introduced using the combined information from the stable isotope fractionation of two elements. Recent experimental approaches also allow for the assessment of stable isotope fractionation of three different elements of a degraded compound, which would provide the opportunity to analyze systems with three simultaneously occurring degradation pathways using stable isotope data. Yet, approaches for a quantitative analysis of such systems are missing. Here we mathematically derive and present an approach to determine the contribution of three different degradation pathways to total degradation of a contaminant compound using the stable isotope fractionation of three different elements in the remaining compound. To verify the accuracy of the computational approach numerical simulations of virtual batch experiments were performed considering the degradation of a compound via three degradation pathways each leading to a stable isotope fractionation of three different elements. Applying the computational approach to the simulated concentration and stable isotope data allowed an exact determination of the contribution of the individual degradation pathways to total contaminant degradation regardless of the considered degradation rates. As application example we apply our approach to experimental data from the literature on the in-situ degradation of 2,4-DNT and the associated stable isotope fractionation of C, H and N. Calculated results of deoxygenation contributing 92%, partial reduction contributing 7% and CH3-group oxidation contributing 1% to total degradation are in agreement with estimates presented in the literature. The new computational approach provides a novel tool for an improved analysis of multi-element CSIA data and for the quantitative assessment of contaminant degradation processes.
Publications 1 - 3 of 3