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  • 1
    Keywords: CELLS ; IN-VITRO ; CELL ; Germany ; MICROSCOPY ; imaging ; TOOL ; TIME ; MRI ; MAGNETIC-RESONANCE ; magnetic resonance imaging ; PARTICLES ; RELAXATION ; ASSAY ; MASS-SPECTROMETRY ; STEM-CELLS ; PROGENITOR CELLS ; self-assembled monolayers ; surface modification ; CLUSTER ; CHEMISTRY ; RE ; INCREASE ; GELS ; ASSAYS ; INTERNALIZATION ; NANOPARTICLES ; USA ; uptake ; MR CONTRAST AGENTS ; progenitor cell ; PROGENITOR-CELL ; CONJUGATION ; BIOSEPARATIONS ; DISPERSIONS
    Abstract: In this study silica- and alkoxysilane-coated ultrasmall superparamagnetic iron oxide (USPIO) particles were synthesized, and their ability to label immortalized progenitor cells for magnetic resonance imaging (MRI) was compared. USPIO particles were synthesized by coprecipitation of ferric and ferrous salts. Subsequently, the particles were coated with silica, (3-aminopropyl)trimethoxysilane (APTMS), and [N-(2-aminoethyl)-3-aminopropyl]trimethoxysilane (AEAPTMS). The size of the USPIO particles was about 10 nm without a significant increase in diameter after coating. The highest T-2 relaxivity was achieved for silica-coated USPIO particles, 339.80 +/- 0.22 s(-1) mM(-1), as compared with APTMS- and AEAPTMS-coated ones, reaching 134.40 +/- 0.01 and 84.79 +/- 0.02 s(-1) mM(-1), respectively. No toxic effects on the cells could be detected by trypan blue, TUNEL, and MTS assays. Uptake of USPIO particles was evaluated by Prussian blue staining, transmission electron microscopy, T-2-MR relaxometry, and mass spectrometry. It was found that cell uptake of the different USPIO particles increased for longer incubation times and higher doses. Maximum cellular iron concentrations of 42.1 +/- 4.0 pg/cell (silica-coated USPIO particles), 37.1 +/- 3.5 pg/cell (APTMS-coated USPIO particles), and 32.7 +/- 4.0 pg/cell (AEAPTMS-coated USPIO particles) were achieved after incubation of the cells with USPIO particles at a dose of 3 mu mol/mL for 6 h. The decrease of the T-2 relaxation time of the cell pellets was most pronounced for cells incubated with silica-coated USPIO particles followed by APTMS- and AEAPTMS-coated particles, respectively. In gelatin gels even small clusters of labeled cells were detected by 1.5 T MRI, and significant changes in the T-2 relaxation times of the gels were determined for 10000 labeled cells/mL for all particles. In summary, as compared with APTMS- and AEAPTMS-coated particles, silica-coated USPIO particles provide the highest T-2 relaxivity and most effectively reduce the T-2 relaxation time of immortalized progenitor cells after internalization. This suggests silica-coated USPIO particles are most suited for cell labeling approaches in MRI
    Type of Publication: Journal article published
    PubMed ID: 17241069
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  • 2
    Keywords: PEPTIDE ; Germany ; MICROSCOPY ; PROTEIN ; DOMAIN ; SPECTROSCOPY ; resistance ; CELL-ADHESION ; surface modification ; POLY(ETHYLENE GLYCOL) ; CHEMISTRY ; FEATURES ; RE ; USA ; adsorption ; THICKNESS ; X-RAY ; interactions ; POLYMERIZATION ; AMBIENT-TEMPERATURE ; AQUEOUS-MEDIA ; MODIFIED POLY(METHYL METHACRYLATE) ; OLIGO(ETHYLENE GLYCOL) METHACRYLATE ; PEPTIDE ARRAYS ; TRANSFER RADICAL POLYMERIZATION
    Abstract: We synthesized various graft copolymer films of poly(ethylene glycol) methacrylate (PEGMA) and methyl methacrylate (MMA) on silicon to examine the dependency of protein-surface interactions on grafting composition. We optimized atom transfer radical polymerizations to achieve film thicknesses from 25 to 100 nm depending on the monomer mole fractions, and analyzed the resulting surfaces by X-ray photoelectron spectroscopy (XPS), ellipsometry, contact angle measurements, and atomic force microscopy (AFM). As determined by XPS, the stoichiometric ratios of copolymer graftings correlated with the concentrations of provided monomer solutions. However, we found an unexpected and pronounced hydrophobic domain on copolymer films with a molar amount of 10-40% PEGMA, as indicated by advancing contact angles of up to 90 degrees. Nevertheless, a breakdown of the protein-repelling character was only observed for a fraction of 15% PEGMA and lower, far in the hydrophobic domain. Investigation of the structural basis of this exceptional wettability by high-resolution AFM demonstrated the independence of this property from morphological features
    Type of Publication: Journal article published
    PubMed ID: 18605707
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  • 3
    Keywords: MOLECULES ; RESOLUTION ; WATER ; ARRAYS ; CELL-ADHESION ; BACTERIA ; GRADIENTS ; POLY(DIMETHYLSILOXANE) ; STAMPS
    Abstract: Microcontact printing (muCP) of proteins is widely used for biosensors and cell biology but is constrained to printing proteins adsorbed to a low free energy, hydrophobic surface to a high free energy, hydrophilic surface. This strongly limits muCP as harsh chemical treatments are required to form a high energy surface. Here, we introduce humidified muCP (HmuCP) of proteins which enables universal printing of protein on any smooth surface. We found that by flowing water in proximity to proteins adsorbed on a hydrophilized stamp, the water vapor diffusing through the stamp enables the printing of proteins on both low and high energy surfaces. Indeed, when proteins are printed using stamps with increasing spacing between water-filled microchannels, only proteins adjacent to the channels are transferred. The vapor transport through the stamp was modeled, and by comparing the humidity profiles with the protein patterns, 88% relative humidity in the stamp was identified as the threshold for HmuCP. The molecular forces occurring between PDMS, peptides, and glass during printing were modeled ab initio to confirm the critical role water plays in the transfer. Using HmuCP, we introduce straightforward protocols to pattern multiple proteins side-by-side down to nanometer resolution without the need for expensive mask aligners, but instead exploiting self-alignment effects derived from the stamp geometry. Finally, we introduce vascularized HmuCP stamps with embedded microchannels that allow printing proteins as arbitrary, large areas patterns with nanometer resolution. This work introduces the general concept of water-assisted muCP and opens new possibilities for "solvent-assisted" printing of proteins and of other nanoparticles.
    Type of Publication: Journal article published
    PubMed ID: 25222734
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  • 4
    Keywords: ACTIN, assembly, ASSOCIATION, ATOMIC-FORCE, CHEMISTRY, DESMIN, DIFFUSION, EXPRESSION, intermediate f
    Abstract: The salt-induced in vitro assembly of cytoplasmic intermediate Filament (IF) proteins such as vimentin is characterized by a very rapid lateral association of soluble tetrameric subunits into 60-nm-long full-width "unit-length" filaments (ULFs). We have demonstrated for this prototype IF protein that filament elongation occurs by the longitudinal annealing of ULFs into short IFs. These IFs further longitudinally anneal and thus constitute a progressively elongating filament population that over time yields filaments of several mu m in length. Previously, we provided a mathematical model for the kinetics of the assembly process based on the average length distribution of Filaments as determined by time-lapse electron and atomic force microscopy. Thereby, we were able to substantiate the concept that end-to-end-annealing of both ULFs and short filaments is obligatory for the formation of long IFs (Kirmse, R.; Portet, S.; Mucke, N. Aebi, U.; Herrmann, H.; Langowski, J.J. Biol. Client. 2007, 282, 18563-18572). As the next step in understanding the mechanics of IF formation, we have expanded our mathematical model to describe the quantitative aspects of IF assembly by taking into account geometry constraints as well as the diffusion properties of rodlike linear aggregates. Thereby, we have developed it robust model for the time-dependent filament length distribution of IFs under standard conditions
    Type of Publication: Journal article published
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  • 5
    Keywords: Germany ; MICROSCOPY ; IONS ; MOLECULE ; RELAXATION ; PRESSURE ; INTERFACE ; BEHAVIOR ; ORGANIZATION ; DYE ; CHEMISTRY ; PHASE ; SURFACE-TENSION ; AQUEOUS-SOLUTION ; aggregates ; AA ; 2ND-HARMONIC GENERATION ; AIR-WATER-INTERFACE ; AQUEOUS-SOLUTIONS ; COUNTERIONS ; HEMICYANINE DYES ; LANGMUIR-BLODGETT-FILMS ; PHOTOCURRENT GENERATION ; SALT-SOLUTIONS
    Abstract: Amphiphilic 4-(3',4'-dimethoxystyryl)-N-octadecylpyridinium perchlorate and bromide form stable monolayers at the air/water interface. Small differences in the surface pressure-area and Surface potential-area isotherms depending on the anion indicate interactions between the chromophore and the anions on the pure water subphase. The monolayer behavior is considerably modified on 10 mM aqueous solutions of KI, KClO4, KCl, and KF as revealed by isotherm measurements, reflection spectroscopy, and Brewster angle microscopy. The phase transition observed in the isotherms is shifted to higher surface pressure because of variation of the salt according to the Hofmeister series. Upon monolayer compression, the chromophores are increasingly tilted, and a shift of the band to longer wavelengths is attributed to the environment becoming less polar. However, in the case of KCl at small areas per molecule, relaxation is observed at constant area with the appearance of a new band shifted to shorter wavelengths. This band is assigned to small associates of about four chromophores (H aggregates). In the case of KI, a new band shifted to longer wavelengths is found. Theoretical calculations did not yield a transition in the observed range, even for large aggregates (J aggregates). Therefore, other interactions may be responsible for the appearance of this band
    Type of Publication: Journal article published
    PubMed ID: 16460076
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  • 6
    Keywords: X-RAY-DIFFRACTION ; fluorescence correlation spectroscopy ; SUPPORTED LIPID-BILAYERS ; MITOCHONDRIAL INNER MEMBRANE ; POLYMORPHIC PHASE-BEHAVIOR ; INVERTED HEXAGONAL PHASE ; PHOSPHATIDYLCHOLINE BILAYERS ; TETRALINOLEOYL-CARDIOLIPIN ; BARTH-SYNDROME ; LINE TENSION
    Abstract: Cardiolipin (CL) is a lipid with unique properties solely found in membranes generating electrochemical potential. It contains four acyl chains and tends to form nonlamellar structures, which are believed to play a key role in membrane structure and function. Indeed, CL alterations have been linked to disorders such as Barth syndrome and Parkinson's disease. However, the molecular effects of CL on membrane organization remain poorly understood. Here, we investigated the structure and physical properties of CL-containing membranes using confocal microscopy, fluorescence correlation spectroscopy, and atomic force microscopy. We found that the fluidity of the lipid bilayer increased and its mechanical stability decreased with CL concentration, indicating that CL decreases the packing of the membrane. Although the presence of up to 20% CL gave rise to flat, stable bilayers, the inclusion of 5% CL promoted the formation of flowerlike domains that grew with time. Surprisingly, we often observed two membrane-piercing events in atomic force spectroscopy experiments with CL-containing membranes. Similar behavior was observed with a lipid mixture mimicking the mitochondrial outer membrane composition. This suggests that CL promotes the formation of membrane areas with apposed double bilayers or nonlamellar structures, similar to those proposed for mitochondrial contact sites. All together, we show that CL induces membrane alterations that support the role of CL in facilitating bilayer structure remodeling, deformation, and permeabilization.
    Type of Publication: Journal article published
    PubMed ID: 23962277
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  • 7
    Electronic Resource
    Electronic Resource
    s.l. : American Chemical Society
    Langmuir 3 (1987), S. 159-163 
    ISSN: 1520-5827
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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  • 8
    ISSN: 1520-5827
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    s.l. : American Chemical Society
    Langmuir 3 (1987), S. 300-302 
    ISSN: 1520-5827
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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  • 10
    Electronic Resource
    Electronic Resource
    s.l. : American Chemical Society
    Langmuir 3 (1987), S. 309-315 
    ISSN: 1520-5827
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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