News Archive

Nicola's third PhD research paper (shared first authorship with Linda Oennby from eawag) just was accepted in Water Reseach. Congratulations Nicolas and Linda! The paper compares two analytical methods to monitor changes in the redox state of dissolved organic matter (DOM) during chemical oxidation. Both methods have in common that they quantifying the number of electrons that DOM donates to a chemical oxidant (ABTS°⁺). The first method is a flow injection analysis system coupled to electrochemical detection. The second method coupled size exclusion chromatography to UV-vis absorbance detection. Both methods yield comparable results.

We just got word that a paper from Meret was accepted for publication in ES&T. Congratulations, Meret! In her work, Meret demonstrates that mediated electrochemical analysis can be used to systematically study rates and extents of iron (oxyhydr-)oxide reduction (shown for goethite, hematite and ferrihydrite) as a function of the thermodynamic boundary conditions for oxide reduction. The latter were systematically altered by varying the reduction potential applied to the electrochemical cell, the solution pH and the dissolved Fe²⁺ concentration in the cell. At intermediate negative free energies for oxide reduction, the natural logarithm of the reaction rate constant linearly correlated with the free energy, strongly suggesting that thermodynamics controlled the rate of reductive oxide dissolution. Meret further showed that the approach can be used to monitor decreases in the reducibility of oxides during transformation of amorphous to more crystalline phases, as shown for the Fe²⁺-catalyzed transformation of ferrihydrite to goethite.

Michael (S.) gave an oral presentation in a symposium on biodegradable mulch films at Novamont in Novara, Italy. The title of the presentation was 'Biodegradation of polyesters in Agricultural Soils.'
The talk provided an overview of our current research efforts to advance a mechanistic understanding of polymer biodegradation in natural environments, including soils. Recent findings were presented addressing the three key steps in polyester biodegradation: microbial colonization of the polyester surfaces, extracellular enzymatic hydrolysis of polyester, and microbial uptale and utilization of low-molecular weight hydrolysis products.

We currenty are on a two week field trip to Värmland, Sweden, to study redox processes in Northern Peatlands. We are conducting experiments in selected ombrotrophic bogs and also collect peat samples to take back to ETH for further analysis.

While the science is exciting, the weather isn't this year. Rain from above, peat water from below. Pick your poison !

Michi Zumstein's paper on the enzymatic hydrolysis of aliphatic and aliphatic-aromatic polyesters was just accepted in Environ Sci Technol. Congratulations, Michi! In this work, Michi systematically studied the hydrolysis of a set of aliphatic polyesters -varying in the length of the dicarboxylic acid component- and a set of aliphatic-aromatic polyesters -varying in the content of the aromatic diacid component- by a total of eight carboxylesterases using quartz crystal microbalance with dissipation monitoringmeasurements.

The results show that enzymatic hydrolyzability decreases with increasing microcrystallinity of the polyester and with decreasing accessibility of the active site of the carboxylesterase by virtue of their negative effects on the formation of enzyme-substrate complexes. This work successfully links polyester and enzyme structures to hydrolyzability, thereby providing a basis to design polyesters and/or engineer esterases with enhanced hydrolyzability. This information is critical to advance next-generation biodegradable polymers to replace persistent, non-degradable polymers that accumulate in the environment.

A paper on the electron donating capacities of dissolved sulfide and dissolved organic matter in sediment pore waters of external pageprarie potholescall_made was just accepted in ESPI. This work was let by Grant Wallace and external pageBill Arnoldcall_made at the University of Minnessota. Congratulations! In this paper, we compared two experimental approaches to quantify the electron donating capacities of dissolved reduced porewater constituents: (i) the reductive transformation of nitroaromatic compounds with different ring substituents and (ii) the reduction of the radical cation of 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulphonic acid) (i.e., ABTS°+) in mediated electrochemical oxidation. Similar capacities were obtained by both approaches. Furthermore, sulfide was identified as the major reductant in these systems. 

Wallace, G., M. Sander, Y.-P. Chin, and W.A. Arnold. Quantifying the electron donating capacities of sulfide and dissolved organic matter in sediment pore waters of wetlands. Environmental Sciences: Processes & Impacts. 2017, DOI: external page10.1039/C7EM00060Jcall_made

Michi Zumstein's paper on enzymatic polyester hydrolysis made it on the cover of ES&T. In this paper, Michael introduces a sensitive and high-throughput method to study enzymatic polyester hydrolysis. The method is based on monitoring the co-hydrolysis of a fluorogenic ester probe embedded into the polyester matrix. The cover shows an artists' view on this hydrolysis process depicting the polyester strands (grey ribbons), carboxylesterase molecules (larger blue spheres), the fluorogenic probe fluorescein dilaurate (dark green spheres with two grey bars), and the fluorescent product, fluorescein (green sphere) (external pageElla Maru Studiocall_made). In the paper, the novel method was validated by monitoring the rates and extents of hydrolysis of a set of aliphatic polyesters by two enzymes, Rhizopus oryzae lipase and Fusarium solani cutinase.

M.T. Zumstein, H.-P. E. Kohler, K. McNeill, and M. Sander. High-throughput analysis of enzymatic hydrolysis of biodegradable polyesters by monitoring co-hydrolysis of a polyester-embedded fluorogenic probe. Environ Sci Technol. 2017. asap, DOI: external page10.1021/acs.est.6b06060call_made

By invitation of the group of Prof. external pageThilo Hofmanncall_made, I visited the Department of Environmental Geosciences at the University of Vienna and gave a seminar talk entitled Environmental Chemistry of (Bio-) Macromolecules: Joys and Tribulations!

I had a very good time in Vienna and enjoyed the meetings and discussions with the members of Thilo Hofmann's group, Stefan Krämer's group and other groups and collaborators at the Univeristy of Vienna and at the BOKU. Thanks for the invitation!

Christine (Poggenburg) just got note that her external pagepapercall_made on microbial and electrochemical reduction of Fe-organic matter (OM) coprecipitates got accepted in Chemical Geology. Christine's work, conducted at the Insitute of Soil Science at the Leipniz University of Hanover under the lead of external pageRobert Mikuttacall_made and external pageGeorg Guggenbergercall_made, assessed the rates and extents of microbial reduction of different Fe-OM coprecipitates. Both Shewanella putrefaciens and Geobacter metallireducens were used as model iron reducing bacteria. This work was complemented by mediated electrochemical reduction of the Fe-OM specimen that Christine conducted in our group here at ETH Zurich. The work shows that OM may affect the reduction dynamics of Fe-OM coprecipitates in various ways: besides affecting reduction by providing electron shuttling moieties, OM may also alter reduction dynamics by impacting the aggregate sizes of Fe-OM coprecipitates. Both chemical and physical effects thus need to be taken into account in in future work directed towards understanding the reduction dynamcis of Fe-OM coprecipitates. Congratulations Christine!

I visited the Helmholtz Centre for Environmental Research - UFZ in Leipzig, Germany, for the first time (somewhat unbelievable, after more than 10 years of working in the environmental sciences)! Besides giving a seminar talk on the fate and reactivity of (bio)macromolecules in natural and engineered systems, I had the opportunity to catch up with former colleagues (Kai-Uwe Goss and Martin Krauss) as well as to personally meet and discuss science with a number of researchers at UFZ. I had a very good and interesting time, thanks for the invitation!

The photo shows the mosaic "Kernspaltung" (1959; Bert Heller) that can be found in the entrance of the former building of the Institute of Applied Radiology, now part of the overall building complex of the UFZ.

Michael Zumstein has attended and presented at the international conference "Enzymes in the Environment: Ecology, Activity & Applications" in Bangor, Wales. Michael presented part of his PhD research on the enzymatic hydrolysis of polyester thin films. For his contribution Enzymatic Hydrolysis of Polyester Films Investigated by Novel Approaches, Michael was awarded with one of the PhD travel grants by the conference organizers.

Michael Zumstein was awarded a PhD travel stipend to attend the conference "Enzymes in the Environment: Activity, Ecology & Applications" to be held in Bangor, Wales, 14-18th July, 2016. Michael's contribution will focus on the enzymatic hydrolysis of snythetic polyester polymers in soils and water. More information on the conference can be found external pageherecall_made. Congratulations, Michi!  

Tony's second paper on virus adsorption to solid-water interfaces has been accepted in  Environ Sci Technol. Congratulations, Tony! In this paper, Tony systematically assessed competitive co-adsorption dynamics of dissolved organic matter and one of four bacteriophages (MS2, fr, GA, and Qb) or negatively charged nanospheres to positively charged sorbent surfaces. While all viruses directly competed with the DOM for adsorption sites, the effects of competition on overall virus adsorption strongly depended on the interactions of viruses with DOM adlayers that formed on the sorbent surface: DOM competitively suppressed adsorption of MS2 and fr because these two viruses did not adsorb to DOM adlayers. Similar results were obtained for the negatively charged nanospheres. Conversely, adsorption of GA and Qb was only modulated in the presence of DOM because these two viruses adsorbed to DOM adlayers. The experimental data of MS2-DOM competition was complemented by calculations using a random sequential adsorption model. This model accurately described the experimental data when accounting for unfolding of DOM on the surface of the adsorbent. Overall, this paper provides a more fundamental understanding of competitive coadsorption of DOM and negatively charged biomacromolecules and nanoparticles. This paper is the result of a collaborative  external pageSinergiacall_made project with external pageTamar Kohncall_made at EPFL. 

Michi Z's first paper just got accepted in Environmental Science and Technology! This paper focusses on the enzymatic hydrolysis of polyester thin films as assessed by quartz crystal microbalance with dissipation monitoring (QCM-D) measurements. This novel analytical approach allows monitoring film mass changes and dissipation dynamics in real-time and label-free at a very high sensitivity (i.e., mass changes in the ng/cm² range are detectable). In this paper, Michi systematically studied the effects of solution pH and temperature on the hydrolysis of poly(butylene succinate) -a commercially important biodegradable polyester- by the lipase of Rhizopus oryzae (RoL), a fungus found in soils. The versatility of the QCM-D based approach was demonstrated by analyzing the hydrolysis of additional polyesters by RoL. This work is part of a larger effort in our group to understand the factors that govern the fate of biodegradable polyesters in soils (as well as other natural systems).

Chiheng's second paper was just accepted in ES&T. In his paper, which is a continuation of an earlier study, Chiheng investigated the indirect photolysis of histidine-containing dissolved combined amino acids. More specifically, Chiheng systematically studied the effect of neighbouring photostable amino acids, including aliphatic, cationic, anionic and aromatic residues) on the reactivity of the histidine residue with singlet oxygen. The study shows that the reactivity of histidine is modulated by the neighbouring amino acids. In systems containing chromophoric dissolved organic matter (cDOM), association of the oligopeptides with cDOM resulted in enhanced indirect photolysis of the histidine residues, due to elevated concentrations of singlet oxygen in and around the cDOM associations. This work shows that photostable amino acids in oligopeptides can largely modulate the indirect photochemistry of photolabile amino acids, particularly in systems in which the oligopeptides associate with natural photosensitizers.

Laura has successfully defended her PhD work! Congratulations!

The title of her thesis is "Redox properties and dynamics of natural organic matter as assessed by mediated electrochemical analysis". The external committee member was external pageProf. Thorsten Dittmarcall_made (Carl von Ossietzky Universität Oldenburg and MPI Bremen)

The picture on the left shows Laura in July 2014 on the road to Värmland, Sweden (field trip).

This paper focusses on the effect of ozonation on the photosensitizing and inhibitory effects of DOM on the phototransformation of organic contaminants. The research project was conceptualized and conducted by our colleagues at Eawag. Michael Aeschbacher and I contributed to the work by quantifying changes in the redox states of DOM upon ozonation using mediated electrochemical analysis.

This paper is a sequel to an earlier publication in ES&T in 2013 in which we assessed the changes in the optical and electrochemical properties of DOM upon treatment with different chemical oxidants (Wenk et al. Environ Sci Technol, 2013, 47, 11147-11156. DOI: external page10.1021/es402516bcall_made).

While the direct phototransformation of amino acids in sunlit waters is well studied, the indirect photochemistry of amino acids in the presence of chromophoric dissolved organic matter (cDOM) is poorly studied and understood. In this paper, Chiheng reports the results of a systematic assessment of the transformation of histidine by single oxygen formed by photoirradiation of cDOM. The work shows that association of His with cDOM enhanced its phototransformation by exposure to elevated singlet oxygen concentrations in the cDOM microenvironment. Sorption-enhanced phototransformation of His was supported by loss of the enhancement upon adding a co-sorbate that competitively suppressed sorption of His. This work highlights that the association of amino acids (and likely larger oligopeptides as well as biomacromolecules) with cDOM may result in enhanced phototransformation of these molecules in natural systems. 

In this paper, Max Lau systematically analyzed the microbial reduction of freshwater sediments, including particulate organic matter (POM) and of Fe(III) (oxyhydr-)oxides, during anoxic incubations. This study is the first to use mediated electrochemical analyses to analyze complex natural samples that contain more than one redox-active constituent. The work provides evidence that particulate organic matter is an important terminal electron acceptor in anaerobic microbial respiration in freshwater sediments. The work was conceptualized and led by Max Lau and his advisors Michael Hupfer and Jörg Gelbrecht.

On the left you can see how Max reacted when he heard that the paper was accepted ... no ... it shows Max in a peat bog in July 2014 when he participated on a field sampling campaign in Central Sweden.

In this paper, Tony reports on the nanoscalar properties and dynamics of DOM adlayers formed from a diverse set of eight humic and fulvic acids, used as DOM models, on model surfaces that vary in charge and polarity. Tony found that, on positively charged surfaces, DOM formed water-rich adlayers with nanometer thicknesses that were relatively rigid, irreversibly adsorbed, and collapsed upon air drying. The DOM adlayer thicknesses varied only slightly with solution pH from 5 to 8 but increased markedly with increasing ionic strength. The surfaces of the adlayers are relatively polar. Finally, using laccase adsorption to the DOM adlayers as an example, Tony demonstrated the applicability of the presented experimental approach to study the interactions of (bio)macromolecules and (nano)particles with DOM.