Ammann, Erik
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Ammann, Erik
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- PublikationLeaching of dissolved organic carbon from commercial reverse osmosis membranes exacerbates interferences in organic solute rejection during bench-scale filtration(Elsevier, 15.03.2023) Li, Zhao; Orlando, Adriano; Müller, Sarah I.; Ammann, Erik; Ding, An; Desmond, Peter [in: Desalination]01A - Beitrag in wissenschaftlicher Zeitschrift
- PublikationLow-Temperature Reactive Aerosol Processing for Large-Scale Synthesis of Selenium Nanoparticles(American Chemical Society, 22.08.2020) Viacava, Karen; Ammann, Erik; Lenz, Markus [in: Industrial & Engineering Chemistry Research]Selenium nanoparticles (SeNPs) have been suggested for various applications such as food, animal feed, and biomedicine. However, thus far, wet chemical synthesis cannot produce sufficient quantities of SeNPs at the required quality. In this study, reactive aerosol processing is employed to produce SeNPs as powder concentrates of 2.2 to 4.0% (dry weight basis) on the scale of hundreds of kilograms. Citric acid is the most efficient organic precursor (92.5% SeNPs), but polydisperse particles are obtained, and some unknown dissolved Se species are present in the final product. Glycine is less efficient (82.2% SeNPs); however, monodisperse nanoparticles (153 nm; D90 = 215 nm) are obtained, with selenite being the only residue in the final product. The obtained particles consisted of X-ray amorphous (i.e., not diffracting) Se, since no elemental Se allotrope or other solid Se phases were indicated in X-ray diffraction. Reactive aerosol processing involves a limited number of preparation steps (i.e., dissolution and atomization), uses only food-/feed-approved ingredients (selenite, citric acid, glycine) and allows continuous operation and zero waste generation. This makes reactive aerosol processing ideal for the large-scale production of SeNPs.01A - Beitrag in wissenschaftlicher Zeitschrift
- PublikationProduction of superparamagnetic nanobiocatalysts for green chemistry applications(Springer, 23.04.2016) Gasser, Christoph; Ammann, Erik; Schäffer, Andreas; Shahgaldian, Patrick; Corvini, Philippe [in: Applied Microbiology and Biotechnology]Immobilization of enzymes on solid supports is a convenient method for increasing enzymatic stability and enabling enzyme reuse. In the present work, a sorption-assisted surface conjugation method was developed and optimized to immobilize enzymes on the surface of superparamagnetic nanoparticles. An oxidative enzyme, i.e., laccase from Trametes versicolor was used as model enzyme. The immobilization method consists of the production of superparamagnetic nanoparticles by co-precipitation of FeCl2 and FeCl3. Subsequently, the particle surface is modified with an organosilane containing an amino group. Next, the enzymes are adsorbed on the particle surface before a cross-linking agent, i.e., glutaraldehyde is added which links the amino groups on the particle surface with the amino groups of the enzymes and leads to internal cross-linking of the enzymes as well. The method was optimized using response surface methodology regarding optimal enzyme and glutaraldehyde amounts, pH, and reaction times. Results allowed formulation of biocatalysts having high specific enzymatic activity and improved stability. The biocatalysts showed considerably higher stability compared with the dissolved enzymes over a pH range from 3 to 9 and in the presence of several chemical denaturants. To demonstrate the reusability of the immobilized enzymes, they were applied as catalysts for the production of a phenoxazinone dye. Virtually, 100 % of the precursor was transformed to the dye in each of the ten conducted reaction cycles while on average 84.5 % of the enzymatic activity present at the beginning of a reaction cycle was retained after each cycle highlighting the considerable potential of superparamagnetic biocatalysts for application in industrial processes.01A - Beitrag in wissenschaftlicher Zeitschrift
- PublikationEnzyme Shielding in an Enzyme-thin and Soft Organosilica Layer(Wiley, 2016) Correro, Maria Rita; Moridi, Negar; Schützinger, Hansjörg; Sykora, Sabine; Ammann, Erik; Peters, E. Henrik; Dudal, Yves; Corvini, Philippe; Shahgaldian, Patrick [in: Angewandte Chemie: International Edition]The fragile nature of most enzymes is a major hindrance to their use in industrial processes. Herein, we describe a synthetic chem. strategy to produce hybrid org./inorg. nanobiocatalysts; it exploits the self-assembly of silane building blocks at the surface of enzymes to grow an organosilica layer, of controlled thickness, that fully shields the enzyme. Remarkably, the enzyme triggers a rearrangement of this organosilica layer into a significantly soft structure. We demonstrate that this change in stiffness correlates with the biocatalytic turnover rate, and that the organosilica layer shields the enzyme in a soft environment with a markedly enhanced resistance to denaturing stresses.01A - Beitrag in wissenschaftlicher Zeitschrift
- PublikationArsenic Mobilization from Historically Contaminated Mining Soils in a Continuously Operated Bioreactor: Implications for Risk Assessment(Taylor & Francis, 2016) Rajpert, Liwia; Kolvenbach, Boris; Ammann, Erik; Hockmann, Kerstin; Nachtegaal, Maarten; Eiche, Elisabeth; Schäffer, Andreas; Corvini, Philippe; Sklodowska, Aleksandra; Lenz, Markus [in: Environmental Science & Technology]Concentrations of soil arsenic (As) in the vicinity of the former Złoty Stok gold mine (Lower Silesia, southwest Poland) exceed 1000 μg g–1 in the area, posing an inherent threat to neighboring bodies of water. This study investigated continuous As mobilization under reducing conditions for more than 3 months. In particular, the capacity of autochthonic microflora that live on natural organic matter as the sole carbon/electron source for mobilizing As was assessed. A biphasic mobilization of As was observed. In the first two months, As mobilization was mainly conferred by Mn dissolution despite the prevalence of Fe (0.1 wt % vs 5.4 for Mn and Fe, respectively) as indicated by multiple regression analysis. Thereafter, the sudden increase in aqueous As[III] (up to 2400 μg L–1) was attributed to an almost quintupling of the autochthonic dissimilatory As-reducing community (quantitative polymerase chain reaction). The aqueous speciation influenced by microbial activity led to a reduction of solid phase As species (X-ray absorption fine structure spectroscopy) and a change in the elemental composition of As hotspots (micro X-ray fluorescence mapping). The depletion of most natural dissolved organic matter and the fact that an extensive mobilization of As[III] occurred after two months raises concerns about the long-term stability of historically As-contaminated sites.01A - Beitrag in wissenschaftlicher Zeitschrift