49 research outputs found

    Forbidden Chemistry: Two-Photon Pathway in [2+2] Cycloaddition of Maleimides

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    Two-photon excitation provides high spatial resolution in three dimensions of the corresponding chemical or physical processes, allowing submicrometer structuring in stereolithography and three-dimensional (3D) microfabrication. While studying two-photon structuring applications, we observed an undescribed phenomenon in photochemistry that dictates reactivity of maleimide groups in two-photon mode. A low-absorbance transition formerly ignored in classical photochemistry has been found for maleimides. This transition was assigned to symmetry-breaking donor–acceptor complex formation, which revealed a formally forbidden pathway in [2+2] cycloaddition reactions of maleimide moieties. This synthetic pathway allowed for the creation of hydrogel materials under physiological conditions at low laser excitation energy (0.1 J/cm<sup>2</sup> at 800 nm) without the use of photoinitiators, which makes it truly two-photon click chemistry

    Fluidity Modulation of Phospholipid Bilayers by Electrolyte Ions: Insights from Fluorescence Microscopy and Microslit Electrokinetic Experiments

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    Fluidity and charging of supported bilayer lipid membranes (sBLMs) prepared from 1,2-dioleoyl-<i>sn</i>-glycero-3-phosphatidylcholine (DOPC) were studied by fluorescence recovery after photobleaching (FRAP) and microslit electrokinetic measurements at varying pH and ionic composition of the electrolyte. Measurements in neutral electrolytes (KCl, NaCl) revealed a strong correlation between the membrane fluidity and the membrane charging due to unsymmetrical water ion adsorption (OH<sup>–</sup> ≫ H<sub>3</sub>O<sup>+</sup>). The membrane fluidity significantly decreased below the isoelectric point of 3.9, suggesting a phase transition in the bilayer. The interactions of both chaotropic anions and strongly kosmotropic cations with the zwitterionic lipids were found to be related with nearly unhindered lipid mobility in the acidic pH range. While for the chaotropic anions the observed effect correlates with the increased negative net charge at low pH, no correlation was found between the changes in the membrane fluidity and charge in the presence of kosmotropic cations. We discuss the observed phenomena with respect to the interaction of the electrolyte ions with the lipid headgroup and the influence of this process on the headgroup orientation and hydration as well as on the lipid packaging

    Hybrid Hairy Janus Particles as Building Blocks for Antibiofouling Surfaces

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    Herein, we report a new strategy for the design of antifouling surfaces by using hybrid hairy Janus particles. The amphiphilic Janus particles possess either a spherical or a plateletlike shape and have core–shell structures with an inorganic core and hydrophilic/hydrophobic polymeric shells. Subsequently, these bifunctional Janus particles enable the fabrication of surfaces with modularity in chemical composition and final surface topography, which possess antifouling properties. The antifouling and fouling-release capability of the composite Janus particle-based surfaces is investigated using the marine biofilm-forming bacteria <i>Cobetia marina</i>. The Janus particle-based coatings are robust and significantly reduce bacterial retention under both static and dynamic conditions independent of the particle geometry. The plateletlike (kaolinite-based) Janus particles represent a scalable system for the rational design of antifouling coatings as well as their large-scale production and application in the future

    Canine prominin-1-GFP is found in microvilli and the primary cilium at the apical domain of polarized epithelial cells.

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    <p>(<b>A-C</b>) Stably transfected MDCK cells expressing either canine (c) or human (h) prominin-1-GFP (Prom1-GFP, green) were immunolabeled for acetylated α-tubulin (ac Tub, red) and their nuclei were counterstained with DAPI (blue). 3-dimensional reconstruction of 32 optical x-y sections (0.6 μm-slices) (A) and a single x-z section (B) are shown. The three single x-y sections (1–3) displayed in (C) are located as illustrated in the cartoon above. They reveal the presence of prominin-1-GFP at the apical plasma membrane with fluorescent signals characteristic of microvilli (mv) and the primary cilium (pc, arrow; see also <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0164079#pone.0164079.s008" target="_blank">S1 Video</a>) as well as in intracellular structures such as the endoplasmic reticulum (ER, asterisk). Tj, tight junction. Scale bars, 5 μm.</p

    A Positively Charged Surface Triggers Coagulation Activation Through Factor VII Activating Protease (FSAP)

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    Contact between biomedical materials and blood often initiates undesirable pro-coagulant and pro-inflammatory processes. On negatively charged materials, blood coagulation is known to be triggered through autoactivation of Factor XII, while activation on cationic surfaces follows a distinct and so far enigmatic mechanism. Because Factor VII activating protease (FSAP) is known to be activated on positively and on negatively charged macromolecules in plasma, we have investigated its interaction with charged biomaterials and its consequences for coagulation. Several activation processes in blood and plasma were characterized after contact with material surfaces with varied charge. FSAP was found to be exclusively activated by the positively charged surfaces polyethylenimine (PEI) and poly-l-lysine (PLL), not by the negatively charged glass or self-assembled monolayer with carboxyl group termination (SAM-COOH), as well as uncharged (Teflon AF) surfaces. Whole blood incubation on PEI showed that this activation was concomitant with coagulation as determined by thrombin and fibrin formation, which was high for glass (F1+2, 138 nM) and PEI (F1+2, 44 nM) but low for Teflon AF (F1+2, 3.3 nM) and SAM COOH (F1+2, 5.8 nM). Contact phase inhibitor diminished coagulation to background levels for all surfaces except PEI (F1+2: ^PEI 43 to 25 nM; glass, 58 to 1.5 nM) indicating that coagulation activation is not dependent on FXII activation on the PEI surface. A decisive role of endogenous FSAP for coagulation however was confirmed with the use of FSAP inhibitory antibodies which showed no influence on Teflon AF, glass and SAM COOH but diminished F1+2 on PEI to less than 50%. We propose that FSAP activation could be a novel mechanism of surface-driven coagulation. An inhibition of this protease might improve hemocompatibility of cationic surfaces and therefore facilitate the application of polycationic surfaces in blood

    Monoclonal Antibodies 13A4 and AC133 Do Not Recognize the Canine Ortholog of Mouse and Human Stem Cell Antigen Prominin-1 (CD133)

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    <div><p>The pentaspan membrane glycoprotein prominin-1 (CD133) is widely used in medicine as a cell surface marker of stem and cancer stem cells. It has opened new avenues in stem cell-based regenerative therapy and oncology. This molecule is largely used with human samples or the mouse model, and consequently most biological tools including antibodies are directed against human and murine prominin-1. Although the general structure of prominin-1 including its membrane topology is conserved throughout the animal kingdom, its primary sequence is poorly conserved. Thus, it is unclear if anti-human and -mouse prominin-1 antibodies cross-react with their orthologs in other species, especially dog. Answering this issue is imperative in light of the growing number of studies using canine prominin-1 as an antigenic marker. Here, we address this issue by cloning the canine prominin-1 and use its overexpression as a green fluorescent protein fusion protein in Madin-Darby canine kidney cells to determine its immunoreactivity with antibodies against human or mouse prominin-1. We used immunocytochemistry, flow cytometry and immunoblotting techniques and surprisingly found no cross-species immunoreactivity. These results raise some caution in data interpretation when anti-prominin-1 antibodies are used in interspecies studies.</p></div

    Supplement figures 1 - 4 from Impact of the springtail's cuticle nanotopography on bioadhesion and biofilm formation <i>in vitro</i> and in the oral cavity

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    Fig. S1: SEM: bacterial colonization in vitro (replicates and springtail); Fig. S2: TEM: pellicle formation and bacterial colonization on dental enamel; Fig. S3: DAPI-staining, springtails and enamel; Fig. S4: DAPI-staining, replicates

    Homemade mouse monoclonal antibody 80B258 and rabbit antiserum αhE2 fail to detect canine prominin-1.

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    <p>(<b>A, B</b>) MDCK cells stably transfected with human or mouse prominin-1, canine prominin-1-GFP as well as wild type cells (MDCK) were analyzed either by immunocytochemistry (A) or immunoblotting under reducing conditions (B) using mouse mAb 80B258 or rabbit antiserum αhE2. As a negative control, only the secondary antibody (as indicated) was used (A, B). For immunocytochemistry, cells were counterstained with DAPI (A). For immunoblotting, β-actin was used as loading control (black arrowhead). The arrow indicates the plasma membrane-associated form of prominin-1, and the open arrowhead indicates its endoplasmic reticulum-associated form. The original and uncropped blots are presented in in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0164079#pone.0164079.s005" target="_blank">S5 Fig</a>. Scale bar, 30 μm.</p