Prof. Dr. Christian Mayer

Physical Chemistry
University of Duisburg-Essen

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  • Capsules from synthetic diblock-peptides as potential artificial oxygen carriers
    Feng, H. and Linders, J. and Myszkowska, S. and Mayer, C.
    Journal of Microencapsulation 38 (2021)
    The design of an encapsulation system consisting of a synthetic peptide which is fully biodegradable into non-toxic constituents. This system should be capable of encapsulating perfluorinated hydrocarbons and should be a promising basis for oxygen carriers to be used as artificial blood replacement. A diblock-peptide is synthesised following a phosgene-free method and characterised by 1H-NMR. Subsequently, this diblock-peptide is self-assembled with perfluorodecalin (PFD) to form PFD-filled capsules as potential artificial oxygen carriers allowing for rapid oxygen uptake and release. The diblock-peptide Bu-PAsp10-PPhe10 is successfully synthesised and used to encapsulate PFD. The capsules have a spherical shape with an average diameter of 360 nm in stable aqueous dispersion. NMR measurements prove their physical capability for reversible uptake and release of oxygen. The resulting capsules are expected to be fully biodegradable and possibly could act as oxygen carriers for artificial blood replacement. © 2021 Informa UK Limited, trading as Taylor & Francis Group.
    view abstract10.1080/02652048.2021.1903594
  • Durchstarten mit Peptiden
    Mayer, C.
    Nachrichten aus der Chemie 68 (2020)
    view abstract10.1002/nadc.20204102086
  • Preparation and characterization of inclusion complexes of β-cyclodextrin and phenolics from wheat bran by combination of experimental and computational techniques
    Simsek, T. and Rasulev, B. and Mayer, C. and Simsek, S.
    Molecules 25 (2020)
    Bitterness often associated with whole wheat products may be related to phenolics in the bran. Cyclodextrins (CDs) are known to form inclusion complexes. The objective was to form inclusion complexes between β-CD and wheat phenolics. Pure phenolic acids (trans-ferulic acid (FA), caffeic acid (CA), and p-coumaric acid (CO)) and phenolic acids from wheat bran were used to investigate complex formation potential. Complexes were characterized by spectroscopy techniques, and a computational and molecular modeling study was carried out. The relative amount of complex formation between β-CD and wheat bran extract was CA > CO > FA. The phenolic compounds formed inclusion complexes with β-CDs by non-covalent bonds. The quantum-mechanical calculations supported the experimental results. The most stable complex was CO/β-CD complex. The ∆H value for CO/β-CD complex was −11.72 kcal/mol and was about 3 kcal/mol more stable than the other complexes. The QSPR model showed good correlation between binding energy and 1H NMR shift for the H5 signal. This research shows that phenolics and β-CD inclusion complexes could be utilized to improve the perception of whole meal food products since inclusion complexes have the potential to mask the bitter flavor and enhance the stability of the phenolics in wheat bran. © 2020 by the authors. Licensee MDPI, Basel, Switzerland.
    view abstract10.3390/molecules25184275
  • Prevention of Decompression Sickness by Novel Artificial Oxygen Carriers
    Mayer, D. and Guerrero, F. and Goanvec, C. and Hetzel, L. and Linders, J. and Ljubkovic, M. and Kreczy, A. and Mayer, C. and Kirsch, M. and Ferenz, K.B.
    Medicine and Science in Sports and Exercise 52 (2020)
    For three decades, studies have demonstrated the therapeutic efficacy of perfluorocarbon (PFC) in reducing the onset of decompression trauma. However, none of these emulsion-based preparations are accepted for therapeutic use in the western world, mainly because of severe side effects and a long organ retention time. A new development to guarantee a stable dispersion without these disadvantages is the encapsulation of PFC in nanocapsules with an albumin shell. Purpose Newly designed albumin-derived perfluorocarbon-based artificial oxygen carriers (A-AOC) are used in a rodent in vivo model as a preventive therapy for decompression sickness (DCS). Methods Thirty-seven rats were treated with A-AOC (n = 12), albumin nanocapsules filled with neutral oil (A-O-N, n = 12), or 5% human serum albumin solution (A-0-0, n = 13) before a simulated dive. Eleven rats, injected with A-AOC, stayed at normal pressure (A-AOC surface). Clinical, laboratory, and histological evaluations were performed. Results The occurrence of DCS depended on the treatment group. A-AOC significantly reduced DCS appearance and mortality. Furthermore, a significant improvement of survival time was found (A-AOC compared with A-0-0). Histological assessment of A-AOC-dive compared with A-0-0-dive animals revealed significantly higher accumulation of macrophages, but less blood congestion in the spleen and significantly less hepatic circulatory disturbance, vacuolization, and cell damage. Compared with nondiving controls, lactate and myoglobin showed a significant increase in the A-0-0-but not in the A-AOC-dive group. Conclusion Intravenous application of A-AOC was well tolerated and effective in reducing the occurrence of DCS, and animals showed significantly higher survival rates and less symptoms compared with the albumin group (A-0-0). Analysis of histological results and fast reacting plasma parameters confirmed the preventive properties of A-AOC. © 2020 Lippincott Williams &Wilkins.
    view abstract10.1249/MSS.0000000000002354
  • Singlet-Oxygen Generation by Peroxidases and Peroxygenases for Chemoenzymatic Synthesis
    Ingenbosch, K.N. and Quint, S. and Dyllick-Brenzinger, M. and Wunschik, D.S. and Kiebist, J. and Süss, P. and Liebelt, U. and Zuhse, R. and Menyes, U. and Scheibner, K. and Mayer, C. and Opwis, K. and Gutmann, J.S. and Hoffmann-Jacobsen, K.
    ChemBioChem (2020)
    Singlet oxygen is a reactive oxygen species undesired in living cells but a rare and valuable reagent in chemical synthesis. We present a fluorescence spectroscopic analysis of the singlet-oxygen formation activity of commercial peroxidases and novel peroxygenases. Singlet-oxygen sensor green (SOSG) is used as fluorogenic singlet oxygen trap. Establishing a kinetic model for the reaction cascade to the fluorescent SOSG endoperoxide permits a kinetic analysis of enzymatic singlet-oxygen formation. All peroxidases and peroxygenases show singlet-oxygen formation. No singlet oxygen activity could be found for any catalase under investigation. Substrate inhibition is observed for all reactive enzymes. The commercial dye-decolorizing peroxidase industrially used for dairy bleaching shows the highest singlet-oxygen activity and the lowest inhibition. This enzyme was immobilized on a textile carrier and successfully applied for a chemical synthesis. Here, ascaridole was synthesized via enzymatically produced singlet oxygen. © 2020 Wiley-VCH GmbH
    view abstract10.1002/cbic.202000326
  • Chiral hydrogen-bonded supramolecular capsules: Synthesis, characterization and complexation of C70
    Kohlhaas, M. and Zähres, M. and Mayer, C. and Engeser, M. and Merten, C. and Niemeyer, J.
    Chemical Communications 55 (2019)
    Two supramolecular nanocapsules were generated by multi-component self-assembly of the novel bisphosphoric acid (R,R)-6 with suitable bis- and trisamidines. The resulting chiral, hydrogen-bonded capsules are stable even in polar media and at low concentrations and can be employed for the binding of C70-fullerene in solution. © 2019 The Royal Society of Chemistry.
    view abstract10.1039/c8cc10152c
  • Combined computational and experimental study on the inclusion complexes of β-cyclodextrin with selected food phenolic compounds
    Simsek, T. and Simsek, S. and Mayer, C. and Rasulev, B.
    Structural Chemistry 30 (2019)
    Phenolic compounds, such as caffeic acid, trans-ferulic, acid and p-coumaric acid that are commonly found in food products, are beneficial for human health. Cyclodextrins can form inclusion complexes with various organic compounds in which the physiochemical properties of the included organic molecules are changed. In this study, inclusion complexes of three phenolic compounds with β-cyclodextrin were investigated. The complexes were characterized by various analytical methods, including nuclear magnetic resonance (NMR) spectroscopy, Fourier IR (FT-IR) spectroscopy, mass spectrometry, differential scanning calorimetry, and scanning electron microscopy. Results showed that the phenolic compounds used in this study were able to form inclusion complexes in the hydrophobic cavity of β-cyclodextrin by non-covalent bonds. Their physicochemical properties were changed due to the complex formation. In addition, a computational study was performed to find factors that were responsible for binding forces between flavors and β-cyclodextrin. The quantum-mechanical calculations supported the results obtained from experimental studies. Thus, ΔHf for the complex of p-coumaric acid and β-cyclodextrin has been found as − 11.72 kcal/mol, which was about 3 kcal/mol more stable than for inclusion complexes of other flavors. Energies of frontier orbitals (higher occupied molecular orbital (HOMO) and lower unoccupied molecular orbital (LUMO)) were analyzed, and it was found that H-L gap for the complex of p-coumaric acid and β-cyclodextrin had the largest value (8.19 eV) in comparison to other complexes, which confirmed the experimental findings of the most stabile complex. © 2019, Springer Science+Business Media, LLC, part of Springer Nature.
    view abstract10.1007/s11224-019-01347-4
  • Glancing angle deposition of Zn-doped calcium phosphate coatings by RF magnetron sputtering
    Prosolov, K.A. and Belyavskaya, O.A. and Linders, J. and Loza, K. and Prymak, O. and Mayer, C. and Rau, J.V. and Epple, M. and Sharkeev, Y.P.
    Coatings 9 (2019)
    Zn-substituted hydroxyapatite with antibacterial effect was used in radiofrequency (RF) magnetron deposition of calcium phosphate coating onto Ti- and Si-inclined substrates. The development of surface nanopatterns for direct bacteria killing is a growing area of research. Here, we combined two approaches for possible synergetic antibacterial effect by manufacturing a patterned surface of Zn-doped calcium phosphate using glancing angle deposition (GLAD) technique. A significant change in the coating morphology was revealed with a substrate tilt angle of 80°. It was shown that an increase in the coating crystallinity for samples deposited at a tilt angle of 80° corresponds to the formation of crystallites in the bulk structure of the thin film. The variation in the coating thickness, uniformity, and influence of sputtered species energy on Si substrates was analyzed. Coatings deposited on tilted samples exhibit higher scratch resistance. The coating microand nano-roughness and overall morphology depended on the tilt angle and differently affected the rough Ti and smooth Si surfaces. GLAD of complex calcium phosphate material can lead to the growth of thin films with significantly changed morphological features and can be utilized to create self-organized nanostructures on various types of surfaces. © 2019 by the authors.
    view abstract10.3390/coatings9040220
  • Lipopolysaccharide-Induced Hemolysis Is Abolished by Inhibition of Thrombin Generation but Not Inhibition of Platelet Aggregation
    Brauckmann, S. and Effenberger-Neidnicht, K. and Nagel, M. and Mayer, C. and Peters, J. and Hartmann, M.
    Inflammation 42 (2019)
    In human sepsis, hemolysis is an independent predictor of mortality, but the mechanisms evoking hemolysis have not been fully elucidated. Therefore, we tested the hypotheses that (1) lipopolysaccharide (LPS)-induced hemolysis is dependent on thrombin generation or platelet aggregation and (2) red cell membranes are weakened by LPS. Anesthetized male Wistar rats were subjected to LPS or vehicle for 240 min. The effects of hemostasis inhibition on LPS-induced hemolysis were investigated by use of the thrombin inhibitor argatroban or the platelet function inhibitor eptifibatide. Free hemoglobin concentration, red cell membrane stiffness and red cell morphological changes were determined by spectrophotometry, atomic force microscopy, and light microscopy. Efficacy of argatroban and eptifibatide was assessed by rotational thrombelastometry and impedance aggregometry, respectively. LPS markedly increased free hemoglobin concentration (20.8 μmol/l ± 3.6 vs. 3.5 ± 0.3, n = 6, p < 0.0001) and schistocytes, reduced red cell membrane stiffness, and induced disseminated intravascular coagulation. Inhibition of thrombin formation with argatroban abolished the increase in free hemoglobin concentration, schistocyte formation, and disseminated intravascular coagulation in LPS-treated animals. Eptifibatide had no inhibitory effect. The LPS evoked decrease of red cell stiffness that was not affected by argatroban or eptifibatide. LPS causes hemolysis, schistocyte formation, and red cell membrane weakening in rats. The thrombin inhibitor argatroban but not the platelet inhibitor eptifibatide abolished hemolysis and schistocyte formation. Thus, LPS-induced hemolysis depends on disseminated intravascular coagulation, possibly enhanced by red cell membrane weakening. Clinical studies are necessary to investigate whether thrombin antagonists can decrease hemolysis and mortality in sepsis. © 2019, Springer Science+Business Media, LLC, part of Springer Nature.
    view abstract10.1007/s10753-019-01038-6
  • Solution NMR Spectroscopy with Isotope-Labeled Cysteine ( 13 C and 15 N) Reveals the Surface Structure of l -Cysteine-Coated Ultrasmall Gold Nanoparticles (1.8 nm)
    Ruks, T. and Beuck, C. and Schaller, T. and Niemeyer, F. and Zähres, M. and Loza, K. and Heggen, M. and Hagemann, U. and Mayer, C. and Bayer, P. and Epple, M.
    Langmuir 35 (2019)
    Ultrasmall gold nanoparticles with a diameter of 1.8 nm were synthesized by reduction of tetrachloroauric acid with sodium borohydride in the presence of l-cysteine, with natural isotope abundance as well as 13 C-labeled and 15 N-labeled. The particle diameter was determined by high-resolution transmission electron microscopy and differential centrifugal sedimentation. X-ray photoelectron spectroscopy confirmed the presence of metallic gold with only a few percent of oxidized Au(+I) species. The surface structure and the coordination environment of the cysteine ligands on the ultrasmall gold nanoparticles were studied by a variety of homo- and heteronuclear NMR spectroscopic techniques including 1 H- 13 C-heteronuclear single-quantum coherence and 13 C- 13 C-INADEQUATE. Further information on the binding situation (including the absence of residual or detached l-cysteine in the solution) and on the nanoparticle diameter (indicating the well-dispersed state) was obtained by diffusion-ordered spectroscopy ( 1 H-, 13 C-, and 1 H- 13 C-DOSY). Three coordination environments of l-cysteine on the gold surface were identified that were ascribed to different crystallographic sites, supported by geometric considerations of the nanoparticle ultrastructure. The particle size data and the NMR-spectroscopic analysis gave a particle composition of about Au 174 (cysteine) 67 . © 2018 American Chemical Society.
    view abstract10.1021/acs.langmuir.8b03840
  • Solution NMR Spectroscopy with Isotope-Labeled Cysteine (13C and 15N) Reveals the Surface Structure of l -Cysteine-Coated Ultrasmall Gold Nanoparticles (1.8 nm)
    Ruks, T. and Beuck, C. and Schaller, T. and Niemeyer, F. and Zähres, M. and Loza, K. and Heggen, M. and Hagemann, U. and Mayer, C. and Bayer, P. and Epple, M.
    Langmuir 35 (2019)
    Ultrasmall gold nanoparticles with a diameter of 1.8 nm were synthesized by reduction of tetrachloroauric acid with sodium borohydride in the presence of l-cysteine, with natural isotope abundance as well as 13C-labeled and 15N-labeled. The particle diameter was determined by high-resolution transmission electron microscopy and differential centrifugal sedimentation. X-ray photoelectron spectroscopy confirmed the presence of metallic gold with only a few percent of oxidized Au(+I) species. The surface structure and the coordination environment of the cysteine ligands on the ultrasmall gold nanoparticles were studied by a variety of homo- and heteronuclear NMR spectroscopic techniques including 1H-13C-heteronuclear single-quantum coherence and 13C-13C-INADEQUATE. Further information on the binding situation (including the absence of residual or detached l-cysteine in the solution) and on the nanoparticle diameter (indicating the well-dispersed state) was obtained by diffusion-ordered spectroscopy (1H-, 13C-, and 1H-13C-DOSY). Three coordination environments of l-cysteine on the gold surface were identified that were ascribed to different crystallographic sites, supported by geometric considerations of the nanoparticle ultrastructure. The particle size data and the NMR-spectroscopic analysis gave a particle composition of about Au174(cysteine)67. © 2018 American Chemical Society.
    view abstract10.1021/acs.langmuir.8b03840
  • ADWISE: Adaptive window-based streaming edge partitioning for high-speed graph processing
    Mayer, C. and Mayer, R. and Tariq, M.A. and Geppert, H. and Laich, L. and Rieger, L. and Rothermel, K.
    Proceedings - International Conference on Distributed Computing Systems 2018-July (2018)
    In recent years, the graph partitioning problem gained importance as a mandatory preprocessing step for distributed graph processing on very large graphs. Existing graph partitioning algorithms minimize partitioning latency by assigning individual graph edges to partitions in a streaming manner - at the cost of reduced partitioning quality. However, we argue that the mere minimization of partitioning latency is not the optimal design choice in terms of minimizing total graph analysis latency, i.e., the sum of partitioning and processing latency. Instead, for complex and long-running graph processing algorithms that run on very large graphs, it is beneficial to invest more time into graph partitioning to reach a higher partitioning quality - which drastically reduces graph processing latency. In this paper, we propose ADWISE, a novel window-based streaming partitioning algorithm that increases the partitioning quality by always choosing the best edge from a set of edges for assignment to a partition. In doing so, ADWISE controls the partitioning latency by adapting the window size dynamically at run-time. Our evaluations show that ADWISE can reach the sweet spot between graph partitioning latency and graph processing latency, reducing the total latency of partitioning plus processing by up to 23-47 percent compared to the state-of-the-art. © 2018 IEEE.
    view abstract10.1109/ICDCS.2018.00072
  • Biocatalytic and solvent-free synthesis of a bio-based biscyclocarbonate
    Wunschik, D.S. and Ingenbosch, K.N. and Zähres, M. and Horst, J. and Mayer, C. and Jäger, M. and Strehmel, V. and Dornbusch, M. and Hoffmann-Jacobsen, K.
    Green Chemistry 20 (2018)
    A biocatalytic synthesis of sebacic biscyclocarbonate has been developed. Sebacic biscyclocarbonate is a monomer for non-isocyanate polyurethane (NIPU) synthesis. The synthesis was performed in neat glycerol carbonate in the presence of lipase B from Candida antarctica (CalB immo Plus). The bifunctional molecule was synthesized directly from the bio-based reactants sebacic acid and glycerol carbonate, a product of glycerol. The optimization of reaction conditions in terms of reaction time and temperature revealed a temperature optimum at room temperature in contrast to the activity optimum of the lipase. NMR analysis was used to investigate the dominant competing reactions and the mechanism of selectivity at the optimized reaction parameters. 1H- and 13C-NMR as well as mass spectrometry confirm that sebacic biscyclocarbonate can be synthesized in the highest purity by the optimized process. © The Royal Society of Chemistry 2018.
    view abstract10.1039/c8gc02267d
  • Coil-coated steel sheets measured by DMA using an immersion testing cell
    Haakmann, F. and Mayer, C. and Raulf, M.
    Journal of Thermal Analysis and Calorimetry (2018)
    The effect of humidity on the glass transition temperature of coatings is well known and analyzed. In this study, an analysis method is introduced for analyzing coil-coated metal sheets submerged in water and water/methyl ethyl ketone (MEK) by using an immersion cell coupled to a DMA. For this purpose, a model polyurethane acrylate coating was applied to zinc/magnesium-coated steel plates and measured before and after immersion in water and water/MEK by DMA and immersion cell. The results show a shift of glass transition temperature from 138 to 13 °C of the coating by storing the coated steel plates under water and immersion testing. A time-dependent diffusion of water from the cell into the coating until saturation can be observed. An increasing concentration of MEK within the immersion cell results in a greater shift of the glass transition temperature. Overall, the immersion cell seems to be a useful tool for in situ characterization of the behavior of coil coating varnishes in liquid environment (Foster et al. in Prog Organ Coat 51:244–249, 2004, van der Wel et al. in Prog Organ Coat 37:1–14, 1999). © 2018, Akadémiai Kiadó, Budapest, Hungary.
    view abstract10.1007/s10973-018-7944-x
  • GrapH: Traffic-Aware Graph Processing
    Mayer, C. and Tariq, M.A. and Mayer, R. and Rothermel, K.
    IEEE Transactions on Parallel and Distributed Systems 29 (2018)
    Distributed graph processing systems such as Pregel, PowerGraph, or GraphX gained popularity due to their superior performance of data analytics on graph-structured data. These systems employ partitioning algorithms to parallelize graph analytics while minimizing inter-partition communication. Recent partitioning algorithms, however, unrealistically assume a uniform and constant amount of data exchanged between graph vertices (i.e., uniform vertex traffic) and homogeneous network costs between workers hosting the graph partitions. This leads to suboptimal partitioning decisions and inefficient graph processing. To this end, we developed GrapH, the first graph processing system using vertex-cut graph partitioning that considers both, diverse vertex traffic and heterogeneous network costs. The main idea is to avoid frequent communication over expensive network links using an adaptive edge migration strategy. Our evaluations show an improvement of 10 percent in graph processing latency and 60 percent in communication costs compared to state-of-the-art partitioning approaches. © 1990-2012 IEEE.
    view abstract10.1109/TPDS.2018.2794989
  • Investigation of the network structure of new bisphenol A non-intent interior food can coatings using high-resolution solid-state 13C-NMR spectroscopy
    Weber, K. and Wegmann, V. and Mayer, C. and Hilt, M.
    Progress in Organic Coatings 122 (2018)
    Facing recent controversial debates about commonly used epoxy resins in food contact applications, an understanding of newly developed polyester-based BPA-non-intent (BPA-NI) interior food can coatings is necessary. So far, little is known about the polymer structure of the polyester-based blends which have been brought to the European market. We report a detailed study on a polyester-phenol blend model system suitable for interior can coating in terms of its mechanical properties such as high flexibility, very good adhesion and hardness. We employ vibrational spectroscopy (FTIR), thermoanalysis (DSC) and an in-depth high-resolution solid-state 13C-NMR analysis to reveal that an overall homogeneity on molecular scale of the two main components in the blend is sustained in the solid state. This is remarkable, taking into account the overall different characteristics of polyesters and phenolic resins and explains the exceptional material properties of this coating. © 2018 Elsevier B.V.
    view abstract10.1016/j.porgcoat.2018.05.015
  • Local Structure of Nanocrystalline Aluminum Nitride
    Ognjanović, S.M. and Zähres, M. and Mayer, C. and Winterer, M.
    Journal of Physical Chemistry C 122 (2018)
    The local structure of chemical-vapor-synthesized (CVS) crystalline AlN nanoparticles is investigated by combining magic angle spinning nuclear magnetic resonance and X-ray absorption spectroscopies. Extended X-ray absorption fine structure data are analyzed by reverse Monte Carlo method, and X-ray absorption near edge structure is interpreted by first principles FEFF calculations. The measurements show behavior characteristic of partially disordered systems. Nevertheless, combined analysis of the data, supported by Rietveld refinement of X-ray diffraction patterns, leads to the conclusion that the observed behavior is due to the small size (large surface to volume ratios) of the nanoparticles (dXRD &lt; 6 nm) and that highly crystalline wurtzite AlN is formed during the CVS process. © 2018 American Chemical Society.
    view abstract10.1021/acs.jpcc.8b06610
  • Molecular evolution in a peptide-vesicle system
    Mayer, C. and Schreiber, U. and Dávila, M.J. and Schmitz, O.J. and Bronja, A. and Meyer, M. and Klein, J. and Meckelmann, S.W.
    Life 8 (2018)
    Based on a new model of a possible origin of life, we propose an efficient and stable system undergoing structural reproduction, self-optimization, and molecular evolution. This system is being formed under realistic conditions by the interaction of two cyclic processes, one of which offers vesicles as the structural environment, with the other supplying peptides from a variety of amino acids as versatile building blocks. We demonstrate that structures growing in a combination of both cycles have the potential to support their own existence, to undergo chemical and structural evolution, and to develop unpredicted functional properties. The key mechanism is the mutual stabilization of the peptides by the vesicles and of the vesicles by the peptides together with a constant production and selection of both. The development of the proposed system over time would not only represent one of the principles of life, but could also be a model for the formation of self-evolving structures ultimately leading to the first living cell. The experiment yields clear evidence for a vesicle-induced accumulation of membrane-interacting peptide which could be identified by liquid chromatography combined with high-resolution mass spectroscopy. We found that the selected peptide has an immediate effect on the vesicles, leading to (i) reduced vesicle size; (ii) increased vesicle membrane permeability; and (iii) improved thermal vesicle stability. © 2018 by the authors. Licensee MDPI, Basel, Switzerland.
    view abstract10.3390/life8020016
  • Q-graph: Preserving query locality in multi-query graph processing
    Mayer, C. and Mayer, R. and Grunert, J. and Rothermel, K. and Tariq, M.A.
    Proceedings of the 1st ACM SIGMOD Joint International Workshop on Graph Data Management Experiences and Systems (GRADES) and Network Data Analytics (NDA), GRADES-NDA 2018 (2018)
    Arising user-centric graph applications such as route planning and personalized social network analysis have initiated a shift of paradigms in modern graph processing systems towards multiquery analysis, i.e., processing multiple graph queries in parallel on a shared graph. These applications generate a dynamic number of localized queries around query hotspots such as popular urban areas. However, existing graph processing systems are not yet tailored towards these properties: The employed methods for graph partitioning and synchronization management disregard query locality and dynamism which leads to high query latency. To this end, we propose the system Q-Graph for multi-query graph analysis that considers query locality on three levels. (i) The query-aware graph partitioning algorithm Q-cut maximizes query locality to reduce communication overhead. (ii) The method for synchronization management, called hybrid barrier synchronization, allows for full exploitation of local queries spanning only a subset of partitions. (iii) Both methods adapt at runtime to changing query workloads in order to maintain and exploit locality. Our experiments show that Q-cut reduces average query latency by up to 57 percent compared to static query-agnostic partitioning algorithms. © 2018 Copyright held by the owner/author(s).
    view abstract10.1145/3210259.3210265
  • Albumin-derived perfluorocarbon-based artificial oxygen carriers: A physico-chemical characterization and first in vivo evaluation of biocompatibility
    Wrobeln, A. and Laudien, J. and Groß-Heitfeld, C. and Linders, J. and Mayer, C. and Wilde, B. and Knoll, T. and Naglav, D. and Kirsch, M. and Ferenz, K.B.
    European Journal of Pharmaceutics and Biopharmaceutics 115 (2017)
    Until today, artificial oxygen carriers have not been reached satisfactory quality for routine clinical treatments. To bridge this gap, we designed albumin-derived perfluorocarbon-based nanoparticles as novel artificial oxygen carriers and evaluated their physico-chemical and pharmacological performance. Our albumin-derived perfluorocarbon-based nanoparticles (capsules), composed of an albumin shell and a perfluorodecalin core, were synthesized using ultrasonics. Their subsequent analysis by physico-chemical methods such as scanning electron-, laser scanning- and dark field microscopy as well as dynamic light scattering revealed spherically-shaped, nano-sized particles, that were colloidally stable when dispersed in 5% human serum albumin solution. Furthermore, they provided a remarkable maximum oxygen capacity, determined with a respirometer, reflecting a higher oxygen transport capacity than the competitor Perftoran®. Intravenous administration to healthy rats was well tolerated. Undesirable effects on either mean arterial blood pressure, hepatic microcirculation (determined by in vivo microscopy) or any deposit of capsules in organs, except the spleen, were not observed. Some minor, dose-dependent effects on tissue damage (release of cellular enzymes, alterations of spleen's micro-architecture) were detected. As our promising albumin-derived perfluorocarbon-based nanoparticles fulfilled decisive physico-chemical demands of an artificial oxygen carrier while lacking severe side-effects after in vivo administration they should be advanced to functionally focused in vivo testing conditions. © 2017 Elsevier B.V.
    view abstract10.1016/j.ejpb.2017.02.015
  • An inverted supramolecular amphiphile and its step-wise self-assembly into vesicular networks
    Samanta, K. and Zellermann, E. and Zähres, M. and Mayer, C. and Schmuck, C.
    Soft Matter 13 (2017)
    A host-guest interaction between a multi-cationic dendrimer 1 functionalized with 16 guanidiniocarbonyl pyrrole (GCP) groups on its surface and naphthalene diimide dicarboxylic acid (NDIDC) in a 1:8 ratio leads to the formation of a new type of inverted amphiphile. This amphiphile further self-assembles in a step-wise manner first into reverse micelles and then into reverse vesicles, which adhere to form an extensive 3D network several micrometers in length. Self-assembly is based on the aromatic stacking interactions of the surface-bound NDIDC. Furthermore, these aggregates only form at neutral pH but not in acidic or basic solutions in which no ion pairing between 1 and NDIDC is possible. The step-wise self-assembly process of the inverted amphiphile which follows a theoretical prediction recently proposed for hyperbranched polymers was studied and visualized in detail using atomic force microscopy (AFM) and transmission electron microscopy (TEM). © 2017 The Royal Society of Chemistry.
    view abstract10.1039/c7sm01641g
  • Functionality of albumin-derived perfluorocarbon-based artificial oxygen carriers in the Langendorff-heart
    Wrobeln, A. and Schlüter, K.D. and Linders, J. and Zähres, M. and Mayer, C. and Kirsch, M. and Ferenz, K.B.
    Artificial Cells, Nanomedicine and Biotechnology 45 (2017)
    The aim of this study was to prove whether albumin-derived perfluorocarbon-based nanoparticles (capsules) can operate as a novel artificial oxygen carrier in a rat Langendorff-heart perfusion model. Hearts perfused with capsules showed increased left ventricular pressure and rate pressure product compared to hearts perfused with pure Krebs–Henseleit (KH)-buffer. The capsules prevented the myocardium from functional fail when in their absence a noxious ischemia was observed. Capsules did not change rheological properties of KH-buffer and could repeatedly reload with oxygen. This albumin-derived perfluorocarbon-based artificial oxygen carrier preserved the function of rat hearts due to the transport of oxygen in a satisfactory manner. Because of these positive results, the functionality of the applied capsules should be verified in living animals. © 2017 Informa UK Limited, trading as Taylor & Francis Group
    view abstract10.1080/21691401.2017.1284858
  • Organic compounds in fluid inclusions of Archean quartz - Analogues of prebiotic chemistry on early Earth
    Schreiber, U. and Mayer, C. and Schmitz, O.J. and Rosendahl, P. and Bronja, A. and Greule, M. and Keppler, F. and Mulder, I. and Sattler, T. and Schöler, H.F.
    PLoS ONE 12 (2017)
    The origin of life is still an unsolved mystery in science. Hypothetically, prebiotic chemistry and the formation of protocells may have evolved in the hydrothermal environment of tectonic fault zones in the upper continental crust, an environment where sensitive molecules are protected against degradation induced e.g. by UV radiation. The composition of fluid inclusions in minerals such as quartz crystals which have grown in this environment during the Archean period might provide important information about the first organic molecules formed by hydrothermal synthesis. Here we present evidence for organic compounds which were preserved in fluid inclusions of Archean quartz minerals from Western Australia. We found a variety of organic compounds such as alkanes, halocarbons, alcohols and aldehydes which unambiguously show that simple and even more complex prebiotic organic molecules have been formed by hydrothermal processes. Stable-isotope analysis confirms that the methane found in the inclusions has most likely been formed from abiotic sources by hydrothermal chemistry. Obviously, the liquid phase in the continental Archean crust provided an interesting choice of functional organic molecules. We conclude that organic substances such as these could have made an important contribution to prebiotic chemistry which might eventually have led to the formation of living cells. © 2017 Schreiber et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
    view abstract10.1371/journal.pone.0177570
  • Polyol synthesized aluminum doped zinc oxide nanoparticles - Influence of the hydration ratio on crystal growth, dopant incorporation and electrical properties
    Straube, T. and Linders, J. and Mayer-Gall, T. and Textor, T. and Mayer, C. and Gutmann, J.S.
    Materials Today: Proceedings 4 (2017)
    The wet chemical deposition of solution processed transparent conducting oxides (TCO) provides an alternative low cost and economical deposition technique to realize large-areas of conducting films. Since the price for the most common TCO Indium Tin Oxide rises enormously, Aluminum Zinc Oxide (AZO) as alternative TCO reaches more and more interest. The optoelectronical properties of nanoparticle coatings strongly depend beneath the porosity of the coating on the shape and size of the used particles. By using bigger or rod-shaped particles it is possible to minimize the amount of grain boundaries resulting in an improvement of the electrical properties, whereas particles bigger than 100 nm should not be used if highly transparent coatings are necessary as these big particles scatter the visible light and lower the transmittance of the coatings. In this work we present a simple method to synthesize AZO particles with different shape and size, but comparable electronical properties. We use a simple, well reproducible polyol method for synthesis and influence the shape and size of the particles by adding different amounts of water to the precursor solution. We can show that the addition of aluminum as dopant strongly hinders the crystal growth but the addition of water counteracts this, so that both, spherical and rod-shaped particles can be obtained. © 2017 Elsevier Ltd.
    view abstract10.1016/j.matpr.2017.09.196
  • Selection of prebiotic molecules in amphiphilic environments
    Mayer, C. and Schreiber, U. and Dávila, M.J.
    Life 7 (2017)
    A basic problem in all postulated pathways of prebiotic chemistry is the low concentration which generally is expected for interesting reactants in fluid environments. Even though compounds, like nucleobases, sugars or peptides, principally may form spontaneously under environmental conditions, they will always be rapidly diluted in an aqueous environment. In addition, any such reaction leads to side products which often exceed the desired compound and generally hamper the first steps of a subsequent molecular evolution. Therefore, a mechanism of selection and accumulation of relevant prebiotic compounds seems to be crucial for molecular evolution. A very efficient environment for selection and accumulation can be found in the fluid continuum circulating in tectonic fault zones. Vesicles which form spontaneously at a depth of approximately 1 km present a selective trap for amphiphilic molecules, especially for peptides composed of hydrophilic and hydrophobic amino acids in a suitable sequence. The accumulation effect is shown in a numeric simulation on a simplified model. Further, possible mechanisms of a molecular evolution in vesicle membranes are discussed. Altogether, the proposed scenario can be seen as an ideal environment for constant, undisturbed molecular evolution in and on cell-like compartments. © 2017 by the authors; licensee MDPI, Basel, Switzerland.
    view abstract10.3390/life7010003
  • Conjugation of thiol-terminated molecules to ultrasmall 2 nm-gold nanoparticles leads to remarkably complex 1H-NMR spectra
    Schuetze, B. and Mayer, C. and Loza, K. and Gocyla, M. and Heggen, M. and Epple, M.
    Journal of Materials Chemistry B 4 (2016)
    Gold nanoparticles, functionalized by aliphatic and aromatic mercapto-functionalized carboxylic acids and by two small peptides (CG and CGGRGD), respectively, were synthesized by the reduction of HAuCl4 with NaBH4 in the presence of the above ligands. After purification by centrifugation or filtration and redispersion, the dispersed nanoparticles were analysed by differential centrifugal sedimentation (DCS), high-resolution transmission electron microscopy (HRTEM), and a variety of NMR spectroscopic techniques: 1H-NMR, 1H,1H-COSY and 1H-DOSY. The hydrodynamic diameter of the particles was between 1.8 and 4.4 nm, as determined by DOSY, in good agreement with the DCS and HRTEM results. Diffusion ordered spectroscopy (DOSY) turned out to be a valuable and non-destructive tool to determine the hydrodynamic diameter of dispersed nanoparticles and to control the purity of the final particles. The coordination of the organic molecules to the gold nanoparticles resulted in distinct and complex changes in the 1H-NMR spectra. These were only partially explainable but clearly caused by the vicinity of the molecules to the gold nanoparticle. © The Royal Society of Chemistry 2016.
    view abstract10.1039/c5tb02443a
  • Insertion stability of poly(ethylene glycol)-cholesteryl-based lipid anchors in liposome membranes
    Molnar, D. and Linders, J. and Mayer, C. and Schubert, R.
    European Journal of Pharmaceutics and Biopharmaceutics 103 (2016)
    Liposomes consist of a hydrophilic core surrounded by a phospholipid (PL) bilayer. In human blood, the half-life of such artificial vesicles is limited. To prolong their stability in the circulation, liposomal bilayers can be modified by inserting poly(ethylene glycol) (PEG) molecules using either PL or sterols as membrane anchors. This establishes a hydrophilic steric barrier, reducing the adsorption of serum proteins, recognition and elimination by cells of the immune system. In addition, targeting ligands (such as antibodies) are frequently coupled to the distal end of the PEG chains to direct the vesicles (then called 'immuno-liposomes') to specific cell types, such as tumor cells. To our knowledge, experiments on the stability of ligand anchoring have so far only been conducted with PL-based PEGs and not with sterol-based PEGs after insertion via the sterol-based post-insertion technique (SPIT). Therefore, our study examines the insertion stability of PEG-cholesteryl ester (Chol-PEG) molecules with PEG chains of 1000, 1500 and 2000 Da molecular mass which have been inserted into the membranes of liposomes using SPIT. For this study we used different acceptor media and multiple analytical techniques, including pulsed-field-gradient nuclear magnetic resonance (PFG-NMR), free-flow electrophoresis, size exclusion chromatography and ultracentrifugation. The obtained data consistently showed that a higher molar mass of PEG chains positively correlates with higher release from the liposome membranes. Furthermore, we could detect and quantify the migration of Chol-PEG molecules from radioactively double-labeled surface-modified liposomes to negatively charged acceptor liposomes via free-flow electrophoresis. Insertion of Chol-PEG molecules into the membrane of preformed liposomes using SPIT is an essential step for the functionalization of liposomes with the aim of specific targeting. For the first time, we present a kinetic analysis of this insertion process using PFG-NMR, showing that insertion into the liposomal membranes takes place within 90 s for Chol-PEG1000 molecules. © 2016 Published by Elsevier B.V.
    view abstract10.1016/j.ejpb.2016.03.023
  • Lipopolysaccharide-induced hemolysis: Evidence for direct membrane interactions
    Brauckmann, S. and Effenberger-Neidnicht, K. and De Groot, H. and Nagel, M. and Mayer, C. and Peters, J. and Hartmann, M.
    Scientific Reports 6 (2016)
    While hemolysis in patients with sepsis is associated with increased mortality its mechanisms are unknown and Toll-like receptor (TLR)-4 mediated effects, complement-mediated hemolysis, or direct cell membrane effects are all conceivable mechanisms. In this study, we tested the hypotheses that toxic lipopolysaccharide (LPS) as well as non-toxic RS-LPS evokes hemolysis (1) by direct membrane effects, and (2) independent of the complement system and TLR-4 activation. We found, that incubation with LPS resulted in a marked time and concentration dependent increase of free hemoglobin concentration and LDH activity in whole blood and washed red cells. Red cell integrity was diminished as shown by decreased osmotic resistance, formation of schistocytes and rolls, and a decrease in red cell membrane stiffness. Non-toxic RS-LPS inhibited the LPS-evoked increase in TNF-α concentration demonstrating its TLR-4 antagonism, but augmented LPS-induced increase in supernatant hemoglobin concentration and membrane disturbances. Removal of plasma components in washed red cell assays failed to attenuate hemolysis. In summary, this study demonstrates direct physicochemical interactions of LPS with red cell membranes resulting in hemolysis under in vitro conditions. It might thus be hypothesized, that not all effects of LPS are mediated by TLR and may explain LPS toxicity in cells missing TLR. © 2016 The Author(s).
    view abstract10.1038/srep35508
  • Permeability profile of poly(alkyl cyanoacrylate) nanocapsules
    Erdmann, C. and Mayer, C.
    Journal of Colloid and Interface Science 478 (2016)
    The permeability profile of poly(alkyl cyanoacrylate) nanocapsules is studied using pulsed-field gradient NMR on a variety of tracer molecules of different size and polarity. In addition, the influence of the surfactant layer and of organic tracer molecules on the capsule membrane permeability for water is examined. The aim of the study is a detailed understanding of the dependencies between molecular properties of a given tracer and its capability to permeate the polymer membrane. As expected, the results clearly show that the capsule membrane permeability depends on the size of the tracer molecule: the exchange rate of polyethylene glycols continuously decreases with increasing chain length. However, the permeation rate also varies with the polarity of the tracer molecule: molecules of lower polarity exchange faster than more polar ones. In turn, the capsule membrane permeability is influenced by added organic compounds. Focusing on water as a characteristic permeate and depending on the type of the additive, the permeability can be varied by almost an order of magnitude, offering an opportunity to reversibly switch the uptake and release properties of the capsules. © 2016 Elsevier Inc.
    view abstract10.1016/j.jcis.2016.06.034
  • Silver nanoparticles with different size and shape: Equal cytotoxicity, but different antibacterial effects
    Helmlinger, J. and Sengstock, C. and Groß-Heitfeld, C. and Mayer, C. and Schildhauer, T.A. and Köller, M. and Epple, M.
    RSC Advances 6 (2016)
    The influence of silver nanoparticle morphology on the dissolution kinetics in ultrapure water as well as the biological effect on eukaryotic and prokaryotic cells was examined. Silver nanoparticles with different shapes but comparable size and identical surface functionalisation were prepared, i.e. spheres (diameter 40-80 and 120-180 nm; two different samples), platelets (20-60 nm), cubes (140-180 nm), and rods (diameter 80-120 nm, length &gt; 1000 nm). All particles were purified by ultracentrifugation and colloidally stabilized with poly(N-vinyl pyrrolidone) (PVP). Their colloidal dispersion in ultrapure water and cell culture medium was demonstrated by dynamic light scattering. Size, shape, and colloidal stability were analysed by scanning electron microscopy, atomic force microscopy, dynamic light scattering, and differential centrifugal sedimentation. The dissolution in ultrapure water was proportional to the specific surface area of the silver nanoparticles. The averaged release rate for all particle morphologies was 30 ± 13 ng s-1 m-2 in ultrapure water (T = 25 ± 1°C; pH 4.8; oxygen saturation 93%), i.e. about 10-20 times larger than the release of silver from a macroscopic silver bar (1 oz), possibly due to the presence of surface defects in the nanoparticulate state. All particles were taken up by human mesenchymal stem cells and were cytotoxic in concentrations of &gt;12.5 μg mL-1, but there was no significant influence of the particle shape on the cytotoxicity towards the cells. Contrary to that, the toxicity towards bacteria increased with a higher dissolution rate, suggesting that the toxic species against bacteria are dissolved silver ions. © The Royal Society of Chemistry 2016.
    view abstract10.1039/c5ra27836h
  • Surface investigation and tribological mechanism of a sulfate-based lubricant deposited on zinc-coated steel sheets
    Timma, C. and Lostak, T. and Janssen, S. and Flock, J. and Mayer, C.
    Applied Surface Science 390 (2016)
    Phosphatation is a well-known technique to improve friction and wear behaviour of zinc coated steel, but has a variety of economic and ecologic limitations. In this study an alternative coating based on ammonium sulfate ((NH4)2SO4) is applied on skin-passed hot-dip galvanized steel sheets in order to investigate its surface chemical and tribological behaviour in a Pin-on-Disk Tribometer. Raman- and X-ray photoelectron spectroscopic results revealed a formation of ammonium zinc sulfate ((NH4)2Zn(SO4)2 * xH2O) on the surface, which is primarily located in the skin-passed areas of the steel material. Sulfate coated samples exhibited a superior friction behaviour in Pin-on-Disk Tests using squalane as a model substance for oil-like lubricated conditions and a formation of a thin lubrication film is obtained in the wear track. Squalane acts as a carrier substance for ammonium zinc sulfate, leading to an effective lubrication film in the wear track. © 2016 Elsevier B.V.
    view abstract10.1016/j.apsusc.2016.09.002
  • Core-Shell Hybrid Particles by Alternating Copolymerization of Ionic Liquid Monomers from Silica as Sorbent for Solid Phase Microextraction
    Rahman, M. M. and Barajas, X. L. O. and Lujan, J. L. H. and Jochmann, M. A. and Mayer, C. and Schmidt, T. C.
    Macromolecular Materials and Engineering 300 (2015)
    Multifunctional ionic liquid monomer (1) was synthesized from 1-vinylimidazole and 2-acrylamido-2-methylpropane sulphonic acid (AMPS) and alternately copolymerized from 3-mercaptopropyltrimethoxysilane grafted silica core (2) to obtain hybrid core-shell particles Sil-PIL.1. Elemental analysis and C-13 CP/MAS results confirmed that the ionic monomers retained the alternation after grafting on silica surface, which make it a promising candidate as sorbent for trapping analytes from aqueous and other samples for solventless microextraction processes. The material demonstrated excellent extraction efficiency for low molecular weight polar compounds and the peak areas for derivatized aldehydes can be increased up to 200 times in comparison with a commercial polydimethylsiloxane (PDMS) sorbent.
    view abstract10.1002/mame.201500097
  • Impact of bacterial endotoxin on the structure of DMPC membranes
    Nagel, M. and Brauckmann, S. and Moegle-Hofacker, F. and Effenberger-Neidnicht, K. and Hartmann, M. and De Groot, H. and Mayer, C.
    Biochimica et Biophysica Acta - Biomembranes 1848 (2015)
    Abstract Bacterial lipopolysaccharides are believed to have a toxic effect on human cell membranes. In this study, the influence of a lipopolysaccharide (LPS) from Escherichia coli on the structure, the dynamics and the mechanical strength of phospholipid membranes are monitored by nuclear magnetic resonance spectroscopy (NMR) and by atomic force microscopy (AFM). Model membranes are formed from 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) and are either prepared as multilamellar bulk samples or multilamellar vesicles. Field gradient NMR data directly prove the rapid integration of LPS into DMPC membranes. Solid state NMR experiments primarily detect decreasing molecular order parameters with increasing LPS content. This is accompanied by a mechanical softening of the membrane bilayers as is shown by AFM indentation measurements. Altogether, the data prove that lipopolysaccharide molecules quickly insert into phospholipid bilayers, increase membrane fluctuation amplitudes and significantly weaken their mechanical stiffness. © 2015 Published by Elsevier B.V.
    view abstract10.1016/j.bbamem.2015.06.008
  • Perfluorodecalin-filled Poly(n-butyl-cyanoacrylate) nanocapsules as potential artificial oxygen carriers: Preclinical safety and biocompatibility
    Laudien, J. and Groß-Heitfeld, C. and Mayer, C. and De Groot, H. and Kirsch, M. and Ferenz, K.B.
    Journal of Nanoscience and Nanotechnology 15 (2015)
    With regard to the development of artificial blood substitutes, perfluorodecalin-filled poly(n-butyl-cyanoacrylate) nanocapsules are already discussed for the use as artificial oxygen carriers. The aim of the present study was to thoroughly investigate the preclinical safety and biocompatibility of the perfluorodecalin-filled poly(n-butyl-cyanoacrylate) nanocapsules prepared by interfacial polymerization. Nanocapsules were assessed for physical and microbial stability. Subsequent to intravenous infusion to anesthetized rats, effects on systemic parameters, microcirculation, circulatory in vivo half-life, acid base/metabolic status, organ damage and biodistribution were evaluated using inter alia 19F-NMR spectroscopy and in vivo microscopy. Perfluorodecalin-filled poly (n-butyl-cyanoacrylate) nanocapsules displayed physical and microbianl stability over a period of 4 weeks and the circulatory in vivo half-life was t1/2 = 30 min. In general, all animals tolerated intravenous infusion of the prepared nanocapsules, even though several side-effects occurred. As a consequence of nanocapsule infusion, a transient decrease in mean arterial blood pressure, impairment of hepatic microcirculation, organ/tissue damage of liver, spleen and small intestine, as well as an elevation of plasma enzyme activities such as lactate dehydrogenase, creatine kinase and aspartate aminotransferase could be observed. The assessment of the distribution pattern revealed nanocapsule accumulation in spleen, kidney and small intestine. Perfluorodecalin-filled poly(n-butyl-cyanoacrylate) nanocapsules conformed to basic requirements of drugs under preclinical development but further improvement is needed to establish these nanocapsules as novel artificial oxygen carriers. Copyright © 2015 American Scientific Publishers All rights reserved.
    view abstract10.1166/jnn.2015.10044
  • Periodic Vesicle Formation in Tectonic Fault Zones—an Ideal Scenario for Molecular Evolution
    Mayer, C. and Schreiber, U. and Dávila, M.J.
    Origins of Life and Evolution of Biospheres 45 (2015)
    Tectonic fault systems in the continental crust offer huge networks of interconnected channels and cavities. Filled mainly with water and carbon dioxide (CO<inf>2</inf>), containing a wide variety of hydrothermal chemistry and numerous catalytic surfaces, they may offer ideal reaction conditions for prebiotic chemistry. In these systems, an accumulation zone for organic compounds will develop at a depth of approximately 1 km where CO<inf>2</inf> turns sub-critical and dissolved components precipitate. At this point, periodic pressure changes caused for example by tidal influences or geyser activity may generate a cyclic process involving repeated phase transitions of carbon dioxide. In the presence of amphiphilic compounds, this will necessarily lead to the transient formation of coated water droplets in the gas phase and corresponding vesicular structures in the aqueous environment. During this process, the concentration of organic components inside the droplets and vesicles would be drastically increased, allowing for favorable reaction conditions and, in case of the vesicles generated, large trans-membrane concentration gradients. Altogether, the process of periodic formation and destruction of vesicles could offer a perfect environment for molecular evolution in small compartments and for the generation of protocells. The basic process of vesicle formation is reproduced experimentally with a lipid in a water/CO<inf>2</inf> system. © 2015, The Author(s).
    view abstract10.1007/s11084-015-9411-z
  • Aluminum-doped ZnO nanoparticles: Gas-phase synthesis and dopant location
    Schilling, C. and Zähres, M. and Mayer, C. and Winterer, M.
    Journal of Nanoparticle Research 16 (2014)
    Aluminum-doped ZnO (AZO) nanoparticles are studied widely as transparent conducting alternatives for indium tin oxide. However, the properties of AZO vary in different investigations not only with the amount of dopant and the particle size, but also with other parameters such as synthesis method and conditions. Hence, AZO nanoparticles, synthesized in the gas phase, were investigated to study the influence of the synthesis parameters dopant level, reactor temperature and residence time in the reaction zone on the particle characteristics. The local structure of the dopant in semiconductors determines whether the doping is functional, i.e., whether mobile charge carriers are generated. Therefore, information obtained from 27Al solid-state NMR spectroscopy, X-ray diffraction, photoluminescence and UV-Vis spectroscopy was used to understand how the local structure influences particles characteristics and how the local structure itself can be influenced by the synthesis parameters. In addition to AZO particles of different Al content, pure ZnO, Al2O3, ZnAl2O4 and core-shell particles of ZnO and Al2O3 were synthesized for comparison and aid to a deeper understanding of the formation of AZO nanoparticles in the gas phase. © 2014 Springer Science+Business Media.
    view abstract10.1007/s11051-014-2506-z
  • Artificial oxygen carriers based on perfluorodecalin-filled poly(n-butyl-cyanoacrylate) nanocapsules
    Stephan, C. and Schlawne, C. and Grass, S. and Waack, I.N. and Ferenz, K.B. and Bachmann, M. and Barnert, S. and Schubert, R. and Bastmeyer, M. and De Groot, H. and Mayer, C.
    Journal of Microencapsulation 31 (2014)
    Poly(n-butyl-cyanoacrylate)-nanocapsules filled by perfluorodecalin (PFD) are proposed as potential oxygen carriers for blood substitute. The capsule dispersion is prepared via interfacial polymerisation from a PFD emulsion in water which in turn is generated by spontaneous phase separation. The resulting dispersion is capable of carrying approximately 10% of its own volume of gaseous oxygen, which is approximately half of the capacity of human blood. The volumes of the organic solvents and water are varied within a wide range, connected to a change of the capsule radius between 200 and 400-nm. The principal suitability of the capsule dispersion for intravenous application is proven in first physiological experiments. A total amount of 10-ml/kg body weight has been infused into rats, with the dispersion supernatant and a normal saline solution as controls. After the infusion of nanocapsules, the blood pressure as well as the heart rate remains constant on a normal level. © 2014 Informa UK Ltd. All rights reserved: reproduction in whole or part not permitted.
    view abstract10.3109/02652048.2013.843600
  • Hydrogels from phospholipid vesicles
    Gräbner, D. and Hoffmann, H. and Förster, S. and Rosenfeldt, S. and Linders, J. and Mayer, C. and Talmon, Y. and Schmidt, J.
    Advances in Colloid and Interface Science 208 (2014)
    It is shown that phospholipid dispersions with a few percent of diacylphosphocholine PC in water can be swollen to single-phase lyotropic liquid crystalline Lα-phases by the addition of co-solvents like glycerol, 1,3-butyleneglycol BG or 1,2-propyleneglycol PG. The birefringent Lα-phases contain small unilamellar and multilamellar vesicles if the temperature of the samples is above the Krafft-Temperature Tm of the phospholipid. When such transparent birefringent viscous samples are cooled down below Tm the samples are transformed into birefringent gels. Cryo-TEM and FF-TEM measurements show that the bilayers of the vesicles are transformed from the liquid to the crystalline state during the transformation while the vesicle structure remains. The bilayers of the crystalline vesicles form adhesive contacts in the gel. Pulsed-field gradient NMR measurements show that two different kinds of water or co-solvent can be distinguished in the gels. One type of solvent molecules can diffuse like normal solvent in a continuous bulk phase. A second type of water diffuses much more slowly. This type of solvent is obviously trapped in the vesicles. The permeability of the crystalline vesicles for water and solvent molecules is much lower in the crystalline state than in the fluid state. Maximum swelling of the diacylphosphocholin dispersions occurs when the refractive index of the solvent is matched to the refractive index of the bilayers. The attraction between the bilayers is at a minimum in this state and the liquid crystalline L α-phase's undulation forces between the bilayers push the bilayers apart. On transformation to the gel state the crystalline bilayers assume a high elastic bending rigidity. Undulations of the bilayers are now suppressed, and the bilayers can form adhesive contacts. Oscillating rheological measurements show that the gels with only 1% of phospholipids can have a storage modulus of 1000 Pa. The gels are very brittle. They break when they are deformed by a few percent. © 2014 Elsevier B.V.
    view abstract10.1016/j.cis.2014.02.011
  • Nanocapsules of a cationic polyelectrolyte and nucleic acid for efficient cellular uptake and gene transfer
    Ruesing, J. and Rotan, O. and Gross-Heitfeld, C. and Mayer, C. and Epple, M.
    Journal of Materials Chemistry B 2 (2014)
    Polyelectrolyte nanocapsules, consisting of poly(allylamine hydrochloride) (PAH) and a nucleic acid, i.e. either DNA or siRNA, were prepared with calcium phosphate nanoparticles as template. This inorganic core was removed by a combination of acid treatment and dialysis, leading to capsules with a diameter of about 140 nm. These capsules were well taken up by HeLa cells and led to an efficient gene transfer, i.e. transfection by DNA and gene silencing by siRNA. They behaved clearly different from unstructured aggregates of DNA and PAH, i.e. polyplexes, underscoring the effect of their internal structure. © 2014 the Partner Organisations.
    view abstract10.1039/c4tb00392f
  • Perfluorodecalin-soluble fluorescent dyes for the monitoring of circulating nanocapsules with intravital fluorescence microscopy
    Laudien, J. and Naglav, D. and Groß-Heitfeld, C. and Ferenz, K.B. and De Groot, H. and Mayer, C. and Schulz, S. and Schnepf, A. and Kirsch, M.
    Journal of Microencapsulation 31 (2014)
    Perfluorodecalin (PFD) is an established artificial oxygen carrier due to its physical capability to solve the respiratory gases oxygen and carbon dioxide. PFD-filled poly(n-butyl-cyanoacrylate) (PACA) nanocapsules are already discussed as effective artificial oxygen carriers, and their principal suitability for intravenous administration had been shown. To further elucidate their action in vivo, it is imperative to characterise their preclinical safety and particularly their biodistribution. For these purposes, intravital fluorescence microscopy would display an attractive technique in order to monitor the PACA nanocapsules in vivo, but unfortunately, it is impossible to stain the PACA nanocapsules with a fluorescent dye fulfilling special criteria required for in vivo microscopy. In order to develop such a dye, a long-chained fluorinated thiol was used to modify a BODIPY derivative that is a highly fluorescent organic compound belonging to the difluoro-boraindacene family, as well as to functionalise mesoscopic systems, such as CdSe/ZnS-quantum dots and gold nanoparticles. Furthermore, a functionalisation of porphyrin derivatives was investigated by placing divalent ions in the centre of these systems. Due to the high solubility of all synthesised dyes in PFD, it should be possible to stain PFD-filled particles in general. However, only the functionalised BODIPY derivative was suitable for in vivo monitoring of the PFD-filled PACA nanocapsules. © 2014 Informa UK Ltd.
    view abstract10.3109/02652048.2014.918668
  • Polyalkylcyanoacrylate nanocapsules: Variation of membrane permeability by chemical cross-linking
    Gross-Heitfeld, C. and Linders, J. and Appel, R. and Selbach, F. and Mayer, C.
    Journal of Physical Chemistry B 118 (2014)
    The permeability of the polymer walls of polyalkylcyanoacrylate nanocapsules varies by different degrees of chemical cross-linking. For this reason, different amounts of bivalent alkylcyanoacrylates are added to the monovalent alkylcyanoacrylate prior to an interfacial polymerization step in order to generate capsules with various cross-linking densities. The obtained nanocapsules are characterized by observing the water molecules via pulsed field-gradient nuclear magnetic resonance using a stimulated echo sequence. The resulting echo decay plots reveal the exchange rate of the water molecules between the free and encapsulated states. The observed dwell times of water molecules in the encapsulated state are characteristic parameters for the permeability of the given capsule membranes. They show a clear dependence on the degree of cross-linking, proving the potential of this approach for a controlled variation of the capsule permeability. Also, the cross-linked nanocapsules exhibit a significantly decreased solubility in tetrahydrofuran which may lead to new applications for polyalkylcyanoacrylate nanocapsules in organic solvents. © 2014 American Chemical Society.
    view abstract10.1021/jp5003098
  • Safety of poly (ethylene glycol)-coated perfluorodecalin-filled poly (lactide-co-glycolide) microcapsules following intravenous administration of high amounts in rats
    Ferenz, K.B. and Waack, I.N. and Laudien, J. and Mayer, C. and Broecker-Preuss, M. and Groot, H.D. and Kirsch, M.
    Results in Pharma Sciences 4 (2014)
    The host response against foreign materials designates the biocompatibility of intravenously administered microcapsules and thus, widely affects their potential for subsequent clinical use as artificial oxygen/drug carriers. Therefore, body distribution and systemic parameters, as well as markers of inflammation and indicators of organ damage were carefully evaluated after administration of short-chained poly (vinyl alcohol, (PVA)) solution or poly (ethylene glycol (PEG))-shielded perfluorodecalin-filled poly ( d,. l-lactide-co-glycolide, PFD-filled PLGA) microcapsules into Wistar rats. Whereas PVA infusion was well tolerated, all animals survived the selected dose of 1247mg microcapsules/kg body weight but showed marked toxicity (increased enzyme activities, rising pro-inflammatory cytokines and complement factors) and developed a mild metabolic acidosis. The observed hypotension emerging immediately after start of capsule infusion was transient and mean arterial blood pressure restored to baseline within 70min. Microcapsules accumulated in spleen and liver (but not in other organs) and partly occluded hepatic microcirculation reducing sinusoidal perfusion rate by about 20%.Intravenous infusion of high amounts of PFD-filled PLGA microcapsules was tolerated temporarily but associated with severe side effects such as hypotension and organ damage. Short-chained PVA displays excellent biocompatibility and thus, can be utilized as emulsifier for the preparation of drug carriers designed for intravenous use. © 2014.
    view abstract10.1016/j.rinphs.2014.04.001
  • Acid-base and electrolyte status during normovolemic hemodilution with succinylated gelatin or HES-containing volume replacement solutions in rats
    Teloh, J.K. and Ferenz, K.B. and Petrat, F. and Mayer, C. and De Groot, H.
    PLoS ONE 8 (2013)
    Background: In the past, several studies have compared different colloidal replacement solutions, whereby the focus was usually on the respective colloid. We therefore systematically studied the influence of the carrier solution's composition of five approved colloidal volume replacement solutions (Gelafundin, Gelafusal, Geloplasma, Voluven and Volulyte) on acid-base as well as electrolyte status during and following acute severe normovolemic hemodilution. The solutions differed in the colloid used (succinylated gelatin vs. HES) and in the presence and concentration of metabolizable anions as well as in their electrolyte composition. Methods: Anesthetized Wistar rats were subjected to a stepwise normovolemic hemodilution with one of the solutions until a final hematocrit of 10%. Subsequent to dilution (162 min), animals were observed for an additional period (150 min). During dilution and observation time blood gas analyses were performed eight times in total. Additionally, in the Voluven and Volulyte groups as well as in 6 Gelafundin animals, electrolyte concentrations, glucose, pH and succinylated gelatin were measured in urine and histopathological evaluation of the kidney was performed. Results: All animals survived without any indications of injury. Although the employed solutions differed in their respective composition, comparable results in all plasma acid-base and electrolyte parameters studied were obtained. Plasma pH increased from approximately 7.28 to 7.39, the plasma K+ concentration decreased from circa 5.20 mM to 4.80-3.90 mM and the plasma Cl- concentration rose from approximately 105 mM to 111-120 mM. Urinary analysis revealed increased excretion of K+, H+ and Cl-. Conclusions: The present data suggest that the carrier solution's composition with regard to metabolizable anions as well as K+, Ca2+ only has a minor impact on acid-base and electrolyte status after application of succinylated gelatin or HES-containing colloidal volume replacement solutions. © 2013 Teloh et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
    view abstract10.1371/journal.pone.0072848
  • Cation induced conformation changes in hyaluronate solution
    Zellermann, A.-M. and Bergmann, D. and Mayer, C.
    European Polymer Journal 49 (2013)
    The influence of barium as a bivalent metal cation on the molecular conformation of partially deprotonated hyaluronic acid is studied by viscosimetry and atomic force microscopy (AFM). The resulting data are compared with corresponding observations on dextran as an uncharged representative of the group of polysaccharides. Titrations monitored by rotational viscosimetry and conductometry are carried out using diluted aqueous solutions of hyaluronate and dextran, stepwise adding small amounts of a Ba2+ solution. The AFM measurements are performed on single molecules of hyaluronate and dextran in absence and presence of Ba2+ ions. The cation induced conformational changes lead to a decrease of the solution viscosity in case of the hyaluronate. The corresponding AFM micrographs reveal that Ba2+ ions induce a transformation from extended and slightly curved chains to internally linked molecules exhibiting sharp bends and significantly smaller hydrodynamic radii. In contrast, the solution viscosity and the conformation of dextran remain largely unchanged in presence of barium.© 2012 Elsevier Ltd. All rights reserved.
    view abstract10.1016/j.eurpolymj.2012.09.025
  • Long-circulating poly(ethylene glycol)-coated poly(lactid-co-glycolid) microcapsules as potential carriers for intravenously administered drugs
    Ferenz, K.B. and Waack, I.N. and Mayer, C. and De Groot, H. and Kirsch, M.
    Journal of Microencapsulation 30 (2013)
    The intrinsic advantages of microcapsules with regard to nanocapsules as intravenous drug carrier systems are still not fully exploited. Especially, in clinical situations where a long-term drug release within the vascular system is desired, if large amounts of drug have to be administered or if capillary leakage occurs, long-circulating microparticles may display a superior alternative to nanoparticles. Here, microcapsules were synthesised and parameters such as in vitro tendency of agglomeration, protein adsorption and in vivo performance were investigated. Biocompatible poly(ethylene glycol) (PEG)-coated poly(DL-lactide-co-glycolide) (PLGA) as wall material, solid and perfluorodecalin (PFD)-filled PEG-PLGA microcapsules (1.5 μm diameter) were manufactured by using a modified solvent evaporation method with either 1% poly(vinyl alcohol) (PVA) or 1.5% cholate as emulsifying agents. Compared to microcapsules manufactured with cholate, the protein adsorption (albumin and IgG) was clearly decreased and agglomeration of capsules was prevented, when PVA was used. The intravenous administration of these microcapsules, both solid and PFD-filled, in rats was successful and exhibited a circulatory half-life of about 1 h. Our data clearly demonstrate that PEG-PLGA microcapsules, manufactured by using PVA, are suitable biocompatible, long-circulating drug carriers, applicable for intravenous administration. © 2013 Informa UK Ltd. All rights reserved.
    view abstract10.3109/02652048.2013.770098
  • Synthesis and characterization of poly(ethylene glycol) methacrylate based hydrogel networks for anti-biofouling applications
    Lei, J. and Mayer, C. and Freger, V. and Ulbricht, M.
    Macromolecular Materials and Engineering 298 (2013)
    A series of hydrogels based on poly(ethylenglycol) methyl ether methacrylate (PEGMEMA) is synthesized using macromonomers of three different molecular weights, in combination with varied degrees of chemical crosslinking. The effects of PEGMEMA, initiator, and crosslinker concentrations on gel yield and swelling properties are studied. In addition, the chemical structure of the gels is characterized by FTIR and solid-state NMR spectra. The swelling and rheological behaviors of hydrogels as well as protein partitioning into the gels are discussed in terms of the network mesh size. Low protein sorption and bacteria deposition tendencies indicate that PEGMEMA-based hydrogels could be highly beneficial for uses as fouling-resistant materials, for instance, as protective coatings for desalination membranes. The storage modulus correlates well with the swelling ratio for different hydrogels prepared from a variety of PEG monomers with different degrees of crosslinking, and these properties show a profound influence on protein uptake and bacterial adhesion. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    view abstract10.1002/mame.201200297
  • Chemical vapor functionalization: A continuous production process for functionalized ZnO nanoparticles
    Ali, M. and Donakowski, M.D. and Mayer, C. and Winterer, M.
    Journal of Nanoparticle Research 14 (2012)
    The continuous functionalization of nanoparticles in the gas-phase directly after their generation, chemical vapor functionalization, is studied with ZnO and 1-hexanol as a model system using two reactors in series. In the first reactor ZnO nanoparticles are synthesized in the gas-phase from diethylzinc and oxygen at 1,073 K with grain sizes of 13 nm as determined by Rietveld refinement of X-ray diffractograms. The second reactor, connected at the exit of the first reactor and kept at lower temperatures (573, 673, and 773 K), is used as a functionalization chamber. At the connection point of the two reactors, the vapor of 1-hexanol is injected to react with the surface of ZnO nanoparticles in the gas phase. The process has been analyzed by quadrupole mass spectrometry to obtain information about optimal conditions for functionalization. Dynamic light scattering data show that the functionalized particles have substantially improved colloidal dispersibility with hydrodynamic diameters of 60 nm. Diffuse reflectance fourier transform infrared spectra and 1H nuclear magnetic resonance spectra are consistent with 1-hexanol adsorbed at the particle surface acting as a functionalizing agent. The agglomerate size is substantially reduced owing to chemical vapor functionalization. © Springer Science+Business Media B.V. 2012.
    view abstract10.1007/s11051-011-0689-0
  • Hypothesis: Origin of Life in Deep-Reaching Tectonic Faults
    Schreiber, U. and Locker-Grütjen, O. and Mayer, C.
    Origins of Life and Evolution of Biospheres 42 (2012)
    The worldwide discussion on the origin of life encounters difficulties when it comes to estimate the conditions of the early earth and to define plausible environments for the development of the first complex organic molecules. Until now, the role of the earth's crust has been more or less ignored. In our opinion, deep-reaching open, interconnected tectonic fault systems may provide possible reaction habitats ranging from nano- to centimetre and even larger dimensions for the formation of prebiotic molecules. In addition to the presence of all necessary raw materials including phosphate, as well as variable pressure and temperature conditions, we suggest that supercritical CO 2 as a nonpolar solvent could have played an important role. A hypothetical model for the origin of life is proposed which will be used to design crucial experiments for the model's verification. Because all proposed processes could still occur in tectonic faults at the present time, it may be possible to detect and analyse the formation of prebiotic molecules in order to assess the validity of the proposed hypothesis. © 2012 Springer Science+Business Media B.V.
    view abstract10.1007/s11084-012-9267-4
  • PFG-NMR self-diffusion measurements in the single phase channels of a microemulsion system with an anionic-nonionic surfactant mixture
    Wolf, L. and Hoffmann, H. and Linders, J. and Mayer, C.
    Soft Matter 8 (2012)
    The single phase channels of a presently reported microemulsion system were investigated by electrical conductivity and pulsed-field gradient nuclear magnetic resonance (PFG-NMR) spectroscopy. The system consists of a mixed anionic-non-ionic surfactant mixture, water and decane. At constant surfactant concentration and temperature, the phase diagram exhibits two single phase microemulsion channels, separated by an anisotropic lamellar channel. The lower microemulsion channel starts from the water side of the phase diagram with a micellar L1 phase and reaches the middle of the phase diagram with increasing mass fraction of decane in the solvent mixture and increasing mass fraction of lipophilic co-surfactant in the surfactant mixture. The upper microemulsion channel passes from the aqueous side with an L3 phase to the oil side of the diagram. Conductivity data and self-diffusion coefficients, obtained by PFG-NMR, support the previously made conclusion that the nanostructure in the upper channel undergoes an abrupt transition from a bicontinuous structure to a water-in-oil High Internal Phase Microemulsion (HIPME) with already less than 10% of oil in the solvent mixture, while the structures in the lower microemulsion channel are oil-in-water droplets. The HIPME structure is a feature of the surfactant mixture and probably formed due to a high interfacial tension between the aqueous diluted surfactant phase and the oil. By the addition of salt, the HIPME structures are obviously disturbed, resulting in an increased conductivity and self-diffusion rate for the water fraction. © 2012 The Royal Society of Chemistry.
    view abstract10.1039/c2sm07301c
  • Pulsed-field gradient NMR measurements on hydrogels from phosphocholine
    Linders, J. and Mayer, C. and Sekine, T. and Hoffmann, H.
    Journal of Physical Chemistry B 116 (2012)
    Gels from diacylphosphatidylcholine in glycerol/butylene glycol mixtures were investigated by pulsed-field gradient NMR measurements. Previous measurements had shown that the gels are formed by networks from crystalline multilamellar vesicles (MLV). The obtained self-diffusion coefficients for water and butylene glycol molecules indicate that both molecules occur in two different environments, even at temperatures above the phase transition T m where the system is still in a liquid crystalline state. While the larger fraction of the molecules shows a free self-diffusion process like in a homogeneous phase, the smaller fraction seems to be encapsulated in closed domains and undergoes only hindered self-diffusion. It is concluded that the hindered diffusions are due to the solvent molecules trapped between the bilayers of the multilamellar vesicles, while the free diffusion is assigned to the solvent molecules outside of the MLV. Since the fraction of the entrapped molecules does not change during phase transition, we assume that the structure of the network in the samples remains the same when gelation occurs. The gelation process is simply due to the transformation of the vesicle bilayers from the liquid crystalline to the crystalline state. The permeability of the bilayer for the solvent molecules is drastically changed by this transition. The exchange of water molecules through the bilayers slows down significantly below Tm: while the average residence time of water molecules inside the vesicles is smaller than 50 ms in the liquid crystalline state, this value increases to more than 1 s for the gel state. In the case of pure butylene glycol, no vesicles are present, and it is likely that these gels are formed from crystalline fibers. © 2012 American Chemical Society.
    view abstract10.1021/jp3046565
  • Solution behavior of double-hydrophilic block copolymers in dilute aqueous solution
    Casse, O. and Shkilnyy, A. and Linders, J. and Mayer, C. and Häussinger, D. and Völkel, A. and Thünemann, A.F. and Dimova, R. and Cölfen, H. and Meier, W. and Schlaad, H. and Taubert, A.
    Macromolecules 45 (2012)
    The self-assembly of double-hydrophilic poly(ethylene oxide)-poly(2-methyl- 2-oxazoline) diblock copolymers in water has been studied. Isothermal titration calorimetry, small-angle X-ray scattering, and analytical ultracentrifugation suggest that only single polymer chains are present in solution. In contrast, light scattering and transmission electron microscopy detect aggregates with radii of ca. 100 nm. Pulsed field gradient NMR spectroscopy confirms the presence of aggregates, although only 2% of the polymer chains undergo aggregation. Water uptake experiments indicate differences in the hydrophilicity of the two blocks, which is believed to be the origin of the unexpected aggregation behavior (in accordance with an earlier study by Ke et al. [Macromolecules2009, 42, 5339-5344]). The data therefore suggest that even in double-hydrophilic block copolymers, differences in hydrophilicity are sufficient to drive polymer aggregation, a phenomenon that has largely been overlooked or ignored so far. © 2012 American Chemical Society.
    view abstract10.1021/ma300621g
  • The necessity for the coating of perfluorodecalin-filled poly(lactide-co-glycolide) microcapsules in the presence of physiological cholate concentrations: Tetronic-908 as an exemplary polymeric surfactant
    Kirsch, M. and Bramey, T. and Waack, I.N. and Petrat, F. and Mayer, C. and De Groot, H.
    Journal of Microencapsulation 29 (2012)
    Recently, we demonstrated that biodegradable poly(lactide-co-glycolide) (PLGA) micro- and nanocapsules with a liquid content of perfluorodecalin are principally useful for the development of artificial oxygen carriers. In order to solve a decisive and well-known problem with PLGA microcapsules, i.e. the spontaneous agglomeration of the capsules after depletion of the emulsifying agent (i.e. cholate), coating with the ABA block copolymer, Tetronic-908 was studied. After Tetronic-908 treatment at concentrations that were harmless to cultured cells, the clustering of the microcapsules was prevented, the adsorption of opsonins was decreased and the attachment to cells was inhibited, but the oxygen transport capacity of PLGA microcapsules was even increased. The present data clearly show that perfluorodecalin-filled PLGA microcapsules must be coated before decreasing the emulsifying agent cholate to physiological concentrations, in order to develop a solution that has the capabilities to function as a potential artificial oxygen carrier suspension. © 2012 Informa UK Ltd All rights reserved.
    view abstract10.3109/02652048.2011.629743
  • Self-assembly of calcium phosphate nanoparticles into hollow spheres induced by dissolved amino acids
    Hagmeyer, D. and Ganesan, K. and Ruesing, J. and Schunk, D. and Mayer, C. and Dey, A. and Sommerdijk, N.A.J.M. and Epple, M.
    Journal of Materials Chemistry 21 (2011)
    Nanoparticles of calcium phosphate assemble spontaneously within a few seconds into hollow spheres with a diameter around 200-300 nm in the presence of dissolved amino acids and dipeptides. The process of formation was followed by cryo-transmission electron microscopy (cryoTEM), proving their hollow nature which was also confirmed by nano-indentation by atomic force microscopy (AFM). The hollow spheres were analyzed by scanning electron microscopy (SEM), dynamic light scattering (DLS), nanoparticle tracking analysis (NTA) and elemental analysis. The hollow spheres were moderately stable against heating and ultrasonication. A self-assembly of the primarily formed calcium phosphate nanoparticles around amino acid-rich domains in water is proposed. As this process was observed with different amino acids, it appears to be a more general phenomenon. © 2011 The Royal Society of Chemistry.
    view abstract10.1039/c1jm11316j
  • Stepwise deposition of metal organic frameworks on flexible synthetic polymer surfaces
    Meilikhov, M. and Yusenko, K. and Schollmeyer, E. and Mayer, C. and Buschmann, H.-J. and Fischer, R.A.
    Dalton Transactions 40 (2011)
    Thin films of [Cu3(btc)2]n (btc = 1,3,5-benzenetricarboxylate) metal organic framework were deposited in a stepwise manner on surfaces of flexible organic polymers. The thickness of films can be precisely controlled. The deposition of the first cycles was monitored by UV-vis spectroscopy. The porosity was proven by the adsorption of pyrazine, which was monitored by FT-IR and thermogravimetric analysis. The deposition of MOF thin films on flexible polymer surfaces might be a new path for the fabrication of functional materials for different applications, such as protection layers for working clothes and gas separation materials in the textile industry. © 2011 The Royal Society of Chemistry.
    view abstract10.1039/c0dt01820a
  • Biocompatibility evaluation of nano-rod hydroxyapatite/gelatin coated with nano-HAp as a novel scaffold using mesenchymal stem cells
    Zandi, M. and Mirzadeh, H. and Mayer, C. and Urch, H. and Eslaminejad, M.B. and Bagheri, F. and Mivehchi, H.
    Journal of Biomedical Materials Research - Part A 92 (2010)
    This study is devoted to fabricate a novel hydroxyapatite(HAp)/gelatin scaffold coated with nano-HAp in nano-rod configuration to evaluate its biocompatibility potential. The nano-HAp particles are needle and rod-like with widths ranging between 30 to 60 nm and lengths from 100 to 300 nm, respectively. Because of their higher surface area and higher reactivity, the nano-rod particles were distributed in gelatin much better than spherical and mixed shapes particles. The compressive modulus of the nano-HAp/gelatin scaffolds coated with nano-HAp was comparable with the compressive modulus of a human cancellous bone. The potential performance of the fabricated scaffolds as seeding media was assayed using mesenchymal stem cells (MSCs). MTT (3-(4,5-dimethylthiazol-2-yl)-1,5-diphenyl tetrazulium bromide) assays were performed on days 4 and 7 and the number of the cells per scaffold was determined. On the basis of this assay, all the studied scaffolds exhibited an appropriate environment in which the loaded cells appeared to be proliferated during the cultivation periods. In all fabricated composite scaffolds, marrow-derived MSCs appeared to occupy the scaffolds internal spaces and attach on their surfaces. According to the cell culture experiments, the incorporation of rod-like nano-HAp and coating of scaffolds with nano-HAp particles enabled the prepared scaffolds to possess desirable biocompatibility, high bioactivity, and sufficient mechanical strength in comparison with noncoated HAp samples. This research suggests that the newly developed scaffold has a potential as a suitable scaffold for bone tissue engineering. © 2009 Wiley Periodicals, Inc.
    view abstract10.1002/jbm.a.32452
  • Perfluorocarbon-filled poly(lactide-co-gylcolide) nano- and microcapsules as artificial oxygen carriers for blood substitutes: A physico-chemical assessment
    Bauer, J. and Zähres, M. and Zellermann, A. and Kirsch, M. and Petrat, F. and De Groot, H. and Mayer, C.
    Journal of Microencapsulation 27 (2010)
    The physico-chemical suitability of perfluorocarbon-filled capsules as artificial oxygen carriers for blood substitutes is assessed on the example of biodegradable poly(lactide-co-gylcolide) micro- and nanocapsules with a liquid content of perfluorodecalin. The morphology of the capsules is studied by confocal laser scanning microscopy using Nile red as a fluorescent marker. The mechanical stability and the wall flexibility of the capsules are examined by atomic force microscopy. The permeability of the capsule walls in connection with the oxygen uptake is detected by nuclear magnetic resonance. It is shown that the preparation in fact leads to nanocapsules with a mechanical stability which compares well with the one of red blood cells. The capsule walls exhibit sufficient permeability to allow for the exchange of oxygen in aqueous environment. In the fully saturated state, the amount of oxygen dissolved within the encapsulated perfluorodecalin in aqueous dispersion is as large as for bulk perfluorodecalin. Simple kinetic studies are presently restricted to the time scale of minutes, but so far indicate that the permeability of the capsule walls could be sufficient to allow for rapid gas exchange.
    view abstract10.3109/02652040903052002
  • PH-Switchable vesicles from a serine-derived guanidiniocarbonyl pyrrole carboxylate zwitterion in DMSO
    Rodler, F. and Linders, J. and Fenske, T. and Rehm, T. and Mayer, C. and Schmuck, C.
    Angewandte Chemie - International Edition 49 (2010)
    Tightly closed: Zwitterion 1 forms vesicles that have an approximate size of 50nm in DMSO solution. The vesicles can be opened and closed by the addition of either acid or base, as vesicle formation depends on the protonation state of zwitterion 1 (see picture). The membrane permeability of the vesicles is surprisingly low: the encapsulated solvent does not exchange with the surrounding solution, even on a time scale of a few hundred milliseconds. © 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    view abstract10.1002/anie.201003405
  • Temporal stability of photothermally fabricated micropatterns in supported phospholipid multilayers
    Mathieu, M. and Schunk, D. and Franzka, S. and Mayer, C. and Hartmann, N.
    Journal of Vacuum Science and Technology A: Vacuum, Surfaces and Films 28 (2010)
    The temporal stability of photothermally fabricated micropatterns in multilayered films of 1,2-dioleoyl-sn-glycero-3-phosphate on surface-oxidized silicon substrates is investigated. Multilayered films are fabricated via spin coating of diluted phospholipid solutions. A focused beam of an Ar+ laser at λ=514 nm and a 1/ e2 spot diameter of 2.5 μm is used to locally remove the coating and fabricate micropatterns. Subsequently, the temporal stability of such patterns at ambient conditions in air and in water is examined using optical microscopy. Generally, these patterns are stable on a time scale of several hours to days, both in air and in water, and hence provide sufficient time for most follow-on experiments. The spin-coated phospholipid films, though, are intrinsically unstable in water. In particular, some hours after immersion in water, dewetting of the film starts to set in. The implications of these results for potential applications are discussed. © 2010 American Vacuum Society.
    view abstract10.1116/1.3271156
  • biocompatibility

  • nanocapsules

  • nanoparticles

  • nuclear magnetic resonance

  • polymers

  • solid state NMR

  • synthesis

  • vesicles

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