Stephan Küppers

Electrochemistry-mass spectrometry for mechanistic studies and simulation of oxidation processes in the environment.

Electrochemistry (EC) coupled to mass spectrometry (MS) has already been successfully applied to metabolism research for pharmaceutical applications, especially for the oxidation behaviour of drug substances. Xenobiotics (chemicals in the environment) also undergo various conversions; some of which are oxidative reactions. Therefore, EC-MS might be a suitable tool for the investigation of oxidative behaviour of xenobiotics. A further evaluation of this approach to environmental research is presented in the present paper using sulfonamide antibiotics. The results with sulfadiazine showed that EC-MS is a powerful tool for the elucidation of the oxidative degradation mechanism within a short time period. In addition, it was demonstrated that EC-MS can be used as a fast and easy method to model the chemical binding of xenobiotics to soil. The reaction of sulfadiazine with catechol, as a model substance for organic matter in soil, led to the expected chemical structure. Finally, by using EC-MS a first indication was obtained of the persistence of a component under chemical oxidation conditions for the comparison of the oxidative stability of different classes of xenobiotics. Overall, using just a few examples, the study demonstrates that EC-MS can be applied as a versatile tool for mechanistic studies of oxidative degradation pathways of xenobiotics and their possible interaction with soil organic matter as well as their oxidative stability in the environment. Further studies are needed to evaluate the full range of possibilities of the application of EC-MS in environmental research.

Fenton-Like Catalysis and Oxidation/Adsorption Performances of Acetaminophen and Arsenic Pollutants in Water on a Multimetal Cu–Zn–Fe-LDH

Acetaminophen can increase the risk of arsenic-mediated hepatic oxidative damage; therefore, the decontamination of water polluted with coexisting acetaminophen and arsenic gives rise to new challenges for the purification of drinking water. In this work, a three-metal layered double hydroxide, namely, Cu-Zn-Fe-LDH, was synthesized and applied as a heterogeneous Fenton-like oxidation catalyst and adsorbent to simultaneously remove acetaminophen (Paracetamol, PR) and arsenic. The results showed that the degradation of acetaminophen was accelerated with decreasing pH or increasing H2O2 concentrations. Under the conditions of a catalyst dosage of 0.5 g·L(-1) and a H2O2 concentration of 30 mmol·L(-1), the acetaminophen in a water sample was completely degraded within 24 h by a Fenton-like reaction. The synthesized Cu-Zn-Fe-LDH also exhibited a high efficiency for arsenate removal from aqueous solutions, with a calculated maximum adsorption capacity of 126.13 mg·g(-1). In the presence of hydrogen peroxide, the more toxic arsenite can be gradually oxidized into arsenate and adsorbed at the same time by Cu-Zn-Fe-LDH. For simulated water samples with coexisting arsenic and acetaminophen pollutants, after treatment with Cu-Zn-Fe-LDH and H2O2, the residual arsenic concentration in water was less than 10 μg·L(-1), and acetaminophen was not detected in the solution. These results indicate that the obtained Cu-Zn-Fe-LDH is an efficient material for the decontamination of combined acetaminophen and arsenic pollution.

Enhanced photocatalytic activity of Ce-doped Zn-Al multi-metal oxide composites derived from layered double hydroxide precursors.

In this work, a series of novel Zn-Al-Ce multi-metal oxide (Zn-Al-Ce-MMO) photocatalysts with different Ce doping contents were prepared by calcination of Ce-doped Zn-Al layered double hydroxide (Zn-Al-Ce-LDH) precursors at various temperatures in air atmosphere. The synthesized Zn-Al-Ce-MMO materials were characterized by XRD, FTIR, TGA, BET, SEM, TEM, XPS and UV-vis DRS. The photocatalytic activities of the Zn-Al-Ce-MMO materials were evaluated by the photodegradation of rhodamine B (RhB) dye and paracetamol in aqueous solution under simulated solar light irradiation. The result of photodegradation of RhB showed that the Zn-Al-Ce-MMO samples exhibit much higher photocatalytic activity than that of Zn-Al-MMO, and the optimal Ce doping content is 5% of mole ratio (nCe/n(Zn+Al+Ce)). The enhanced photocatalytic activity of the Zn-Al-Ce-MMO was mainly attributed to the increasing in the separation efficiency of electrons and holes. The effect of calcination temperature was also studied. The photocatalytic activity of Zn-Al-Ce-MMO increased with increasing calcination temperature up to 750°C, which can be ascribed to the formation of well-crystallized metal oxides during calcination. Under experimental conditions, 97.8% degradation efficiency of RhB and 98.9% degradation efficiency of paracetamol were achieved after 240min. Active species trapping and EPR experiments suggested that hole (h(+)), superoxide radical (O2(-)) and hydroxyl radical (OH) played important roles during the RhB photocatalytic process. Moreover, the results indicated that the synthesized Zn-Al-Ce-MMO materials had good stability and reusability.

An efficient laboratory workflow for environmental risk assessment of organic chemicals

In this study, we demonstrate a fast and efficient workflow to investigate the transformation mechanism of organic chemicals and evaluate the toxicity of their transformation products (TPs) in laboratory scale. The transformation process of organic chemicals was first simulated by electrochemistry coupled online to mass spectrometry (EC-MS). The simulated reactions were scaled up in a batch EC reactor to receive larger amounts of a reaction mixture. The mixture sample was purified and concentrated by solid phase extraction (SPE) for the further ecotoxicological testing. The combined toxicity of the reaction mixture was evaluated in fish egg test (FET) (Danio rerio) compared to the parent compound. The workflow was verified with carbamazepine (CBZ). By using EC-MS seven primary TPs of CBZ were identified; the degradation mechanism was elucidated and confirmed by comparison to literature. The reaction mixture and one primary product (acridine) showed higher ecotoxicity in fish egg assay with 96 h EC50 values of 1.6 and 1.0 mg L(-1) than CBZ with the value of 60.8 mg L(-1). The results highlight the importance of transformation mechanism study and toxicological effect evaluation for organic chemicals brought into the environment since transformation of them may increase the toxicity. The developed process contributes a fast and efficient laboratory method for the risk assessment of organic chemicals and their TPs.

Online electro-Fenton-mass spectrometry reveals 2,4′,5-trichlorobiphenyl oxidation products and binding to organic matter

Electrochemistry–mass spectrometry is used to simulate redox reactions in many research disciplines because this technique is fast and provides information on compound metabolites. However, the analysis of the degradation of refractory organic pollutants by reactive oxygen species is difficult to achieve by the electrochemistry step. Therefore, here we use online electro-Fenton-mass spectrometry to study for the first time the oxidation of 2,4′,5-trichlorobiphenyl [polychlorinated biphenyl (PCB) 31] by reactive oxygen species and the binding reactions of PCB degradation products with model substances of natural organic matter. The degradation products were identified by coupled Q Trap mass spectrometry. We observed a binding of a degradation product with γ-l-glutamyl-l-cysteinyl-glycine. We propose a transformation pathway. We conclude that online electro-Fenton-mass spectrometry is a promising technique to study the oxidation of refractory organic pollutants and further binding of degradation products with natural organic matter.

Supply Chain Event Management in the Pharmaceutical Industry — Status and Outlook

Supply chain event management combines the real-time modelling of relevant business processes with early warning systems. This means that SCEM attempts to help the sequences of internal and external processes run even smoother throughout the supply chain. Before focusing on establishing individual SCEM tools for use in the pharmaceutical supply chain, we should take a look at the supply chain as a whole and the potential for optimising it. The supply chains in the pharmaceutical industry are often highly integrated and are characterised by long processing times.

Electrochemical simulation of triclosan metabolism and toxicological evaluation

Tricolsan (TCS), an antimicrobial agent, is considered as emerging pollutant due to its wide dispersive use in personal care products and high aquatic toxicity. In the present study, phase I metabolism of triclosan was investigated through laboratory electrochemical simulation studies. The products formed in the electrochemical (EC) cell were identified by online and offline coupling with QTRAP and high-resolution FTICR mass spectrometers, respectively. The sequential formation and disappearance of each product, with the continuous increase of voltage from 0 to 3500 mV, was observed to reveal the transformation pathways of TCS. The toxic potential of TCS and the identified products was estimated using Quantitative structure-activity relationship (QSAR) modeling on 16 target proteins. The toxicity change of TCS during simulated metabolism and toxicological effects of reaction mixture were assessed by Fish embryo toxicity (FET) test (Danio rerio) and quantitative real-time polymerase chain reaction (qPCR). Eight metabolites formed during the simulated metabolism of TCS mainly via the mechanisms of hydroxylation, ether-bond cleavage and cyclization. In FET test, the reaction mixture (LC50, 48h=1.28 mg/L) after electrochemical reactions showed high acute toxicity on zebrafish embryos, which was comparable to that of triclosan (LC50, 48h=1.34 mg/L). According to the modeling data, less toxic products formed only via ether-bond cleavage of TCS while the products formed through other mechanisms showed high toxicity. AhR-mediated dioxin-like effects on zebrafish embryos, such as developmental retardation in skeleyton and malformations in cardiovascular system, were also observed after exposure to the TCS reaction mixture in FET test. Activation of the AhR by the reaction mixture in zebrafish embryos was further proved in cyp1a gene expression analysis.