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Start date: 2020 × DDC: 540 × DDC: 660 × Has files: Yes × WGL Institute: INP ×

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Now showing 1 - 5 of 5
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    Supercritical fluid extraction-supercritical fluid chromatography of saliva: Single-quadrupole mass spectrometry monitoring of caffeine for gastric emptying studies†
    (Weinheim : Wiley-VCH, 2021) Hofstetter, Robert K.; Schulig, Lukas; Bethmann, Jonas; Grimm, Michael; Sager, Maximilian; Aude, Philipp; Keßler, Rebecca; Kim, Simon; Weitschies, Werner; Link, Andreas
    Saliva is an attractive sampling matrix for measuring various endogenous and exogeneous substances but requires sample treatment prior to chromatographic analysis. Exploiting supercritical CO2 for both extraction and chromatography simplifies sample preparation, reduces organic solvent consumption, and minimizes exposure to potentially infectious samples, but has not yet been applied to oral fluid. Here, we demonstrate the feasibility and benefits of online supercritical fluid extraction coupled to supercritical fluid chromatography and single-quadrupole mass spectrometry for monitoring the model salivary tracer caffeine. A comparison of 13C- and 32S-labeled internal standards with external standard calibration confirmed the superiority of stable isotope-labeled caffeine over nonanalogous internal standards. As proof of concept, the validated method was applied to saliva from a magnetic resonance imaging study of gastric emptying. After administration of 35 mg caffeine via ice capsule, salivary levels correlated with magnetic resonance imaging data, corroborating caffeine's usefulness as tracer of gastric emptying (R2 = 0.945). In contrast to off-line methods, online quantification required only minute amounts of organic solvents and a single manual operation prior to online bioanalysis of saliva, thus demonstrating the usefulness of CO2-based extraction and separation techniques for potentially infective biomatrices.
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    Ring-Closure Mechanisms Mediated by Laccase to Synthesize Phenothiazines, Phenoxazines, and Phenazines
    (Washington, DC : ACS Publications, 2020) Hahn, Veronika; Mikolasch, Annett; Weitemeyer, Josephine; Petters, Sebastian; Davids, Timo; Lalk, Michael; Lackmann, Jan-Wilm; Schauer, Frieder
    The green and environmentally friendly synthesis of highly valuable organic substances is one possibility for the utilization of laccases (EC 1.10.3.2). As reactants for the herein described syntheses, different o-substituted arylamines or arylthiols and 2,5-dihydroxybenzoic acid and its derivatives were used. In this way, the formation of phenothiazines, phenoxazines, and phenazines was achieved in aqueous solution mediated by the laccase of Pycnoporus cinnabarinus in the presence of oxygen. Two types of phenothiazines (3-hydroxy- and 3-oxo-phenothiazines) formed in one reaction assay were described for the first time. The cyclization reactions yielded C–N, C–S, or C–O bonds. The syntheses were investigated with regard to the substitution pattern of the reaction partners. Differences in C–S and C–N bond formations without cyclization are discussed.
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    Application of scanning electrochemical microscopy for topography imaging of supported lipid bilayers
    (Cambridge : RSC Publ., 2022) Nasri, Zahra; Memari, Seyedali; Striesow, Johanna; Weltmann, Klaus-Dieter; von Woedtke, Thomas; Wende, Kristian
    Oxidative stress in cellular environments may cause lipid oxidation and membrane degradation. Therefore, studying the degree of lipid membrane morphological changes by reactive oxygen and nitrogen species will be informative in oxidative stress-based therapies. This study introduces the possibility of using scanning electrochemical microscopy as a powerful imaging technique to follow the topographical changes of a solid-supported lipid bilayer model induced by reactive species produced from gas plasma. The introduced strategy is not limited to investigating the effect of reactive species on the lipid bilayer but could be extended to understand the morphological changes of the lipid bilayer due to the action of membrane proteins or antimicrobial peptides.
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    Singlet-Oxygen-Induced Phospholipase A2 Inhibition: A Major Role for Interfacial Tryptophan Dioxidation
    (Weinheim : Wiley-VCH, 2021) Nasri, Zahra; Memari, Seyedali; Wenske, Sebastian; Clemen, Ramona; Martens, Ulrike; Delcea, Mihaela; Bekeschus, Sander; Weltmann, Klaus-Dieter; von Woedtke, Thomas; Wende, Kristian
    Several studies have revealed that various diseases such as cancer have been associated with elevated phospholipase A2 (PLA2) activity. Therefore, the regulation of PLA2 catalytic activity is undoubtedly vital. In this study, effective inactivation of PLA2 due to reactive species produced from cold physical plasma as a source to model oxidative stress is reported. We found singlet oxygen to be the most relevant active agent in PLA2 inhibition. A more detailed analysis of the plasma-treated PLA2 identified tryptophan 128 as a hot spot, rich in double oxidation. The significant dioxidation of this interfacial tryptophan resulted in an N-formylkynurenine product via the oxidative opening of the tryptophan indole ring. Molecular dynamics simulation indicated that the efficient interactions between the tryptophan residue and phospholipids are eliminated following tryptophan dioxidation. As interfacial tryptophan residues are predominantly involved in the attaching of membrane enzymes to the bilayers, tryptophan dioxidation and indole ring opening leads to the loss of essential interactions for enzyme binding and, consequently, enzyme inactivation. © 2021 The Authors. Chemistry - A European Journal published by Wiley-VCH GmbH
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    D-Glucose Oxidation by Cold Atmospheric Plasma-Induced Reactive Species
    (Washington, DC : ACS Publications, 2022) Ahmadi, Mohsen; Nasri, Zahra; von Woedtke, Thomas; Wende, Kristian
    The glucose oxidation cascade is fascinating; although oxidation products have high economic value, they can manipulate the biological activity through posttranslational modification such as glycosylation of proteins, lipids, and nucleic acids. The concept of this work is based on the ability of reactive species induced by cold atmospheric plasma (CAP) in aqueous liquids and the corresponding gas-liquid interface to oxidize biomolecules under ambient conditions. Here, we report the oxidation of glucose by an argon-based dielectric barrier discharge plasma jet (kINPen) with a special emphasis on examining the reaction pathway to pinpoint the most prominent reactive species engaged in the observed oxidative transformation. Employing d-glucose and d-glucose-13C6solutions and high-resolution mass spectrometry and ESI-tandem MS/MS spectrometry techniques, the occurrence of glucose oxidation products, for example, aldonic acids and aldaric acids, glucono- and glucaro-lactones, as well as less abundant sugar acids including ribonic acid, arabinuronic acid, oxoadipic acid, 3-deoxy-ribose, glutaconic acid, and glucic acid were surveyed. The findings provide deep insights into CAP chemistry, reflecting a switch of reactive species generation with the feed gas modulation (Ar or Ar/O2with N2curtain gas). Depending on the gas phase composition, a combination of oxygen-derived short-lived hydroxyl (•OH)/atomic oxygen [O(3P)] radicals was found responsible for the glucose oxidation cascade. The results further illustrate that the presence of carbohydrates in cell culture media, gel formulations (agar), or other liquid targets (juices) modulate the availability of CAP-generated species in vitro. In addition, a glycocalyx is attached to many mammalian proteins, which is essential for the respective physiologic role. It might be questioned if its oxidation plays a role in CAP activity.