Karl Fischer

Johannes Gutenberg-Universität Mainz, Mainz, Rhineland-Palatinate, Germany

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Publications (53)233.74 Total impact

  • [show abstract] [hide abstract]
    ABSTRACT: For systemic siRNA delivery applications, well-defined drug carriers are required that guarantee stability for both carrier and cargo. Among various concepts progressing in market or final development, cationic nanohydrogel particles may serve as novel transport media especially designed for siRNA-in vivo experiments. In this work, the interaction of nanohydrogel particles with proteins and serum components was studied via dynamic light scattering in human blood serum as novel screening method prior to applications in vivo. The formation of larger aggregates mostly caused by charge interaction with albumin could be suppressed by nanogel loading with siRNA affording a neutral zeta potential for the complex. Preliminary in vivo studies confirmed the results inside the light-scattering cuvette. Although both carrier and cargo may have limited stability on their own under physiological relevant conditions, they can form safe and stable complexes at a charge neutralized ratio and thus making them applicable to systemic siRNA delivery.
    Biomacromolecules 04/2014; · 5.37 Impact Factor
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    ABSTRACT: Monodisperse multifunctional and non-toxic Au@MnO nano-hetero-particles with different sizes and morphologies were prepared by a seed-mediated nucleation and growth technique with precise control over domain sizes, surface functionalization, and dye labeling. The metal oxide domain could be coated selectively with a thin silica layer leaving the metal domain untouched. In particular, size and morphology of the individual (metal and metal oxide) domains could be controlled by adjustment of the synthetic parameters. The SiO2 coating of the oxide domain allows biomolecule conjugation (e.g. antibodies, proteins) in a single step for converting the photoluminescent and magnetic Janus nanoparticles into multifunctional efficient vehicles for theranostics. The Au@MnO@SiO2 heterodimers were characterized using high-resolution transmission electron microscopy (HR-) TEM, powder x-ray diffraction (PXRD), optical (UV-VIS) spectroscopy, confocal laser fluorescence scanning microscopy (CLSM) and dynamic light scattering (DLS). The functionalized nanoparticles were stable in buffer solution or serum showing no indication of aggregation. Biocompatibility and potential biomedical applications of the Au@MnO@SiO2 Janus particles were assayed by a cell viability analysis by co-incubating the Au@MnO@SiO2 Janus particles with Caki 1 and HeLa cells. Time-resolved fluorescence spectroscopy in combination with CLSM revealed the silica-coated Au@MnO@SiO2 heterodimers to be highly two-photon active; no indication for an electronic interaction between the dye molecules incorporated in the silica shell surrounding the MnO domains and the attached Au domains was found; fluorescence quenching was observed when dye molecules were bound directly to the Au domains.
    Journal of the American Chemical Society 01/2014; · 10.68 Impact Factor
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    ABSTRACT: Poly(ε-N-methacryloyl-l-lysine) (PMALys) was synthesized by free radical polymerization yielding a zwitterionic polymer with Mw = 721 000 g mol–1. The polymer dissolves in pure water as well as in aqueous salt solution up to 5 M NaClO4 and over wide range of pH values (1.3 ≤ pH ≤ 12.7) as single chains without any sign for aggregate formation. The zwitterionic polymer shows an expanded random coil structure at and close to isoelectric conditions and further expands upon addition of acid and base, respectively. The polymer fulfills four major prerequisites for a promising nano carrier in potential biomedical applications: (1) It is biocompatible, indicated by a low cytotoxicity. (2) It does not aggregate in concentrated human blood serum solution. (3) The amino groups in the polyzwitterion may be utilized for conjugations as demonstrated by labeling reactions with AlexaFluor488. (4) Cell uptake experiments revealed little uptake in bone marrow dendritic cells, i.e., little unspecific uptake, which is mandatory for a successful specific targeting of cells. Finally, upon addition of Zn2+ ions the polyzwitterions may be converted into polycations which are demonstrated to form complexes with DNA. Such complexes may be advantageous for application in gene transfection studies.
    Macromolecules 10/2013; 46(21):8519-8527. · 5.52 Impact Factor
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    ABSTRACT: Herein, a new method for the realization of a thin and homogenous carbonaceous particle coating, made by carbonizing RAFT polymerization derived block copolymers anchored on anatase TiO2 nanorods, is presented. These block copolymers consist of a short anchor block (based on dopamine) and a long, easily graphitizable block of polyacrylonitrile. The grafting of such block copolymers to TiO2 nanorods creates a polymer shell, which can be visualized by atomic force microscopy (AFM). Thermal treatment at 700 °C converts the polyacrylonitrile block to partially graphitic structures (as determined by Raman spectroscopy), establishing a thin carbon coating (as determined by transmission electron microscopy, TEM, analysis). The carbon-coated TiO2 nanorods show improved electrochemical performance in terms of achievable specific capacity and, particularly, long-term cycling stability by reducing the average capacity fading per cycle from 0.252 mAh g(-1) to only 0.075 mAh g(-1) .
    Macromolecular Rapid Communications 10/2013; · 4.93 Impact Factor
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    ABSTRACT: Supramolecular assembly: Spherical and stable hybrid assemblies based on a cationic polymer with spermine side chains and an anionic Gd(3+) -containing polyoxometalate cluster (GdW) are prepared by electrostatic interaction. The T1 -weighted MRI performance of GdW is enhanced about three times in the assemblies; meanwhile, the assemblies show good biocompatibility, which enables them to be promising candidates for MRI contrast agents.
    Chemistry 09/2013; · 5.93 Impact Factor
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    ABSTRACT: Immediately after administration, polymer therapeutics are exposed to complex biological media like blood which may influence and alter their physicochemical properties due to interactions with proteins or serum components. Among such interactions those leading to larger sized aggregates can be sensitively detected by dynamic light scattering (DLS) as a pre in vivo screening method. Random copolymers from N-(2-hydroxypropyl)methacrylamide and lauryl methacrylate p(HPMA-co-LMA) and copolymers loaded with the model drug domperidone were characterized by DLS in isotonic salt solution and in blood serum. The bare amphiphilic copolymer micelles (Rh = 30 nm in isotonic salt solution) formed large aggregates in serum of over 100 nm radius which were shown to originate from interactions with very low density lipoproteins (VLDLs). Encapsulation of the hydrophobic drug domperidone resulted, at first, in drug-copolymer formulations with larger hydrodynamic radii (39 nm < Rh < 49 nm) which, however, did not induce aggregate formation in human serum. Since p(HPMA-co-LMA) copolymers were demonstrated to have a high potential for drug delivery into the brain, the knowledge of serum-copolymer interactions provides a better understanding of their function in the biological context.
    Molecular Pharmaceutics 09/2013; · 4.57 Impact Factor
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    ABSTRACT: A high-molar-mass cylindrical brush polymer with a main chain degree of polymerization of P(w) = 1047 is synthesized by free-radical polymerization of a poly-2-isopropyloxazoline macromonomer with P(n) = 28. The polymerization is conducted above the lower phase transition temperature of the macromonomer, i.e., in the phase-separated regime, which provides a sufficiently concentrated macromonomer phase mandatory to obtain high-molar-mass cylindrical brushes. Upon heating to the phase transition temperature, the hydrodynamic radius is observed to shrink from 34 to 27 nm. Further increase in temperature resulted in aggregated chains which were observed to coexist with single chains until eventually only aggregates of μm size were detectable.
    Macromolecular Rapid Communications 02/2013; · 4.93 Impact Factor
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    ABSTRACT: Scale formation, the deposition of certain minerals such as CaCO3, MgCO3 and CaSO4 x 2H2O in industrial facilities and household devices, leads to reduced efficiency or severe damages. Therefore, incrustation is a major problem in everyday life. In recent years, double hydrophilic block copolymers (DHBC) have been in the focus of interest in academia with regards to their anti-scaling potential. In this work, we synthesized well-defined block-like PAA-PAMPS copolymers consisting of acrylic acid (AA) and 2-acrylamido-2-methyl-propane sulfonate (AMPS) units in a one-step reaction by RAFT polymerization. The derived copolymers had dispersities of 1.3 and below. The copolymers have then been investigated in detail regarding their impact on the different stages of the crystallization process of CaCO3. Ca2+ complexation, the first step of a precipitation process, and polyelectrolyte stability in aqueous solution have been investigated by potentiometric measurements, isothermal titration calorimetry (ITC) and dynamic light scattering (DLS). A weak Ca2+ induced copolymer aggregation without concomitant precipitation was observed. Nucleation, early particle growth and colloidal stability have been monitored in situ with DLS. The copolymers retard or even completely suppress nucleation, most probably by complexation of solution aggregates. In addition, they stabilize existing CaCO3 particles in the nanometer regime. In situ AFM was used as a tool to verify the coordination of the copolymer to the calcite (104) crystal surface and to estimate its potential as a growth inhibitor in a supersaturated CaCO3 environment. All investigated copolymers instantly stopped further crystal growth. The carboxylate richest copolymer as the most promising anti-scaling candidate proved its enormous potential in scale inhibition as well in an industrial-filming test (Fresenius standard method).
    Langmuir 02/2013; · 4.19 Impact Factor
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    ABSTRACT: Cylindrical brush polymers with poly-L-lysine side chains were prepared by grafting lysine NCA from a macroinitiator via living ring-opening polymerization. The main chain degree of polymerization of the methacrylate main chain was P-w = 870, the side chains consisted of 25 and 55 lysine repeat units, respectively. Upon deprotection, the cylindrical brush polymers in 0.005 M NaBr exhibited an almost rodlike conformation with a Kuhn statistical segment length of several hundred nanometers. Cryo-TEM as well as AFM in aqueous solution clearly demonstrated pronounced undulations along the main chain at low ionic strength which could not be detected at higher salt concentrations. With increasing concentration of NaClO4 the PLL side chains underwent a coil-to-helix transition as revealed by CD measurements. The effect of the side chain coil-to-helix transition on the main chain stiffness could not be followed by light scattering due to intramolecular attraction ("folding") of the cylindrical brushes at high salt concentration, which is somewhat more pronounced for the helical as compared to the coiled PLL side chain conformation. Comparison with linear PLL revealed the coil-to-helix transition to be hardly affected by the high grafting density of the PLL side chains in the cylindrical brush structures.
    Macromolecules 06/2012; 45(12):5167-5175. · 5.52 Impact Factor
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    ABSTRACT: We report herein the unexpected temperature triggered self-assembly of proteins fused to thermally responsive elastin-like polypeptides (ELPs) into spherical micelles. A set of six ELP block copolymers (ELP(BC)) differing in hydrophilic and hydrophobic block lengths were genetically fused to two single domain proteins, thioredoxin (Trx) and a fibronectin type III domain (Fn3) that binds the α(v)β(3) integrin. The self-assembly of these protein-ELP(BC) fusions as a function of temperature was investigated by UV spectroscopy, light scattering, and cryo-TEM. Self-assembly of the ELP(BC) was unexpectedly retained upon fusion to the two proteins, resulting in the formation of spherical micelles with a hydrodynamic radius that ranged from 24 to 37 nm, depending on the protein and ELP(BC). Cryo-TEM images confirmed the formation of spherical particles with a size that was consistent with that measured by light scattering. The bioactivity of Fn3 was retained when presented by the ELP(BC) micelles, as indicated by the enhanced uptake of the Fn3-decorated ELP(BC) micelles in comparison to the unimer by cells that overexpress the α(v)β(3) integrin. The fusion of single domain proteins to ELP(BC)s may provide a ubiquitous platform for the multivalent presentation of proteins.
    Biomacromolecules 04/2012; 13(5):1598-605. · 5.37 Impact Factor
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    ABSTRACT: Oligonucleotides such as short, double-stranded RNA (siRNA) or plasmid DNA (pDNA) promise high potential in gene therapy. For pharmaceutical application, however, adequate drug carriers are required. Among various concepts progressing in the market or final development, nanosized hydrogel particles may serve as novel transport media especially for siRNA. In this work, a new concept of synthesizing polymeric cationic nanohydrogels was developed, which offers a promising strategy to complex and transport siRNA into cells. For this purpose, amphiphilic reactive ester block copolymers were synthesized by RAFT polymerization of pentafluorophenyl methacrylate as reactive ester monomer together with tri(ethylene glycol)methyl ether methacrylate. In polar aprotic solvents, a self-assembly of these polymers could be observed leading to the formation of nanometer-sized polymer aggregates. The resulting superstructures were used to convert the reactive precursor block copolymers with amine-containing cross-linker molecules into covalently stabilized hydrogel particles. Detailed dynamic light scattering studies showed that the structure of the self-assembled aggregates can permanently be locked-in by this process. This method offers a new possibility to synthesize precise nanohydrogels of different size starting from various block copolymers. Moreover, via reactive ester approach, further functionalities could be attached to the nanoparticle, such as fluorescent dyes, which allowed distinct tracing of the hydrogels during complexation with siRNA or cell uptake experiments. In this respect, cellular uptake of the particles themselves as well as with its payload could be detected successfully. Looking ahead, these novel cationic nanohydrogel particles may serve as a new platform for proper siRNA delivery systems.
    ACS Nano 03/2012; 6(3):2198-214. · 12.06 Impact Factor
  • Chemistry 04/2011; 17(20):5503-6. · 5.93 Impact Factor
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    ABSTRACT: Poly(butadiene)-b-poly(ethylene oxide) vesicles were successfully loaded with hydrophilic dye Phloxine B. Dye addition during vesicle formation leads to Phloxine B encapsulated inside the water filled vesicle core as well as to freely diffusing dye molecules. The removal of uncapsulated substrate involves time consuming methods like dialysis or harsher methods like ultra filtration or selective precipitation, posing the risk of irreversible sample manipulation. Here used Phloxine B as pH sensitive fluorescence indicator allows the characterization of hydrophilic loading without separation procedure by adjusting the pH value. Additionally membrane blocking efficiency can be studied by time dependent fluorescence measurements. Cryogenic TEM studies showed that the self-assembled structure remained unchanged when the hydrophilic dye was incorporated within the vesicles. Fluorescence microscopy imaging proved the encapsulation of the hydrophilic dye inside the core volume. The combination of fluorescence correlation spectroscopy (FCS) and dynamic light scattering (DLS) measurements as ensemble methods confirmed those results additionally.
    Polymer, v.52, 1263-1267 (2011). 01/2011;
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    Angewandte Chemie International Edition 01/2011; 50(3):737-40. · 13.73 Impact Factor
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    ABSTRACT: In a certain stage of development, the performance of nanoparticle- or polymer-drug conjugates is tested "in vivo", that is, in mice or rats. Besides pharmaceutical and chemical characterization, the structural characterization of such drug carrier systems in terms of size, size distribution, and shape is typically performed in physiological salt solution prior to animal tests. The present work introduces a simple method based on dynamic light scattering to monitor the particle size in blood serum. Utilizing a model system of pegylated poly-l-lysines (PLL-g-PEO(x)) of various degrees of pegylation, x, it is demonstrated that large aggregates may form in human serum solution that are not observed in isotonic salt solution. Aggregates of a few hundred nanometers in size were found in mixtures of serum solution and PLL-g-PEO(x) with degrees of pegylation <10%, whereas no aggregates are being observed if the degree of pegylation exceeds 20%. The described method may have the potential to become an easy and routine test for drug carrier systems prior to animal applications.
    Biomacromolecules 10/2010; · 5.37 Impact Factor
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    Biomacromolecules 10/2010; · 5.37 Impact Factor
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    ABSTRACT: Two straight monomers were subjected to an AA/BB-type Suzuki polycondensation with a hairpin-shaped 1,8-anthrylene monomer as the counterpart leading to a novel polyarylene which should have the preferred conformation of a folded chain. The molar masses were determined by gel permeation chromatography and dynamic light scattering and found to be M(w) = 14,000 and M(n) = 7,000. MALDI-TOF MS analysis of a fraction provides a fingerprint of the step-growth nature of this polymerization.
    Organic Letters 09/2009; 11(18):4112-5. · 6.14 Impact Factor
  • Frauke Kuehn, Karl Fischer, Manfred Schmidt
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    ABSTRACT: The complex formation of pUC19 DNA and a cylindrical brush polymer with quaternized poly(vinyl pyridinium) side chains is investigated by stopped flow light scattering (LS). In highly dilute solutions up to two kinetic processes are observable, depending on the mole fraction of anionic charges, x(anion) . For x(anion)  < 0.2 and x(anion)  > 0.4-0.5 only one kinetic process was identified leading to the largest complexes at x(anion)  = 0.4 well below charge stoichiometry. For 0.2 < x(anion)  < 0.4 two kinetic growth processes were identified: The initially formed complexes on the time scale of a few hundred milliseconds keep growing by an unusual fractal growth process until after several minutes they become stable. This last fractal process does not follow the classical Smoluchowski coagulation theory as monitored by LS up to 90 s after mixing.
    Macromolecular Rapid Communications 09/2009; 30(17):1470-6. · 4.93 Impact Factor
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    ABSTRACT: In order to better understand the collapse of polyions in poor solvent conditions the effective charge and the solvent quality of the hypothetically uncharged polymer backbone need to be known. In the present work this is achieved by utilizing poly-2-vinylpyridine quaternized to 4.3% with ethylbromide. Conductivity and light scattering measurements were utilized to study the polyion collapse in isorefractive solvent/non-solvent mixtures consisting of 1-propanol and 2-pentanone, respectively, at nearly constant dielectric constant. The solvent quality of the uncharged polyion could be quantified which, for the first time, allowed the experimental investigation of the effect of the electrostatic interaction prior and during polyion collapse, by comparing to a newly developed theory. Although the Manning parameter for the investigated system is as low as $l_B/l = 0.6$ ($l_B$ the Bjerrum length and $l$ the mean contour distance between two charges), i.e. no counterion binding should occur, a qualitative interpretation of the conductivity data revealed that the polyion chain already collects its counter ions when the dimensions start to shrink below the good solvent limit but are still well above the $\theta$-dimension.
    02/2009;

Publication Stats

391 Citations
233.74 Total Impact Points

Institutions

  • 2003–2013
    • Johannes Gutenberg-Universität Mainz
      • • Institute of Physical Chemistry
      • • Institute of Organic Chemistry
      Mainz, Rhineland-Palatinate, Germany
  • 2010
    • Duke University
      • Department of Biomedical Engineering (BME)
      Durham, NC, United States
  • 2004
    • Northeast Institute of Geography and Agroecology
      • State Key Laboratory of Polymer Physics and Chemistry
      Beijing, Beijing Shi, China
  • 1995
    • University of Bayreuth
      • Chair of Macromolecular Chemistry II
      Bayreuth, Bavaria, Germany