109 research outputs found
Synthesis and Bioactivity of PolymerâBased Synthetic Mimics of Antimicrobial Peptides (SMAMPs) Made from Asymmetrically Disubstituted Itaconates
A series of asymmetrically disubstituted diitaconate monomers is presented. Starting from itaconic anhydride, functional groups could be placed selectively at the two nonequivalent carbonyl groups. By using 2D NMR spectroscopy, it was shown that the first functionalization step occurred at the carbonyl group in the ÎČ position to the double bond. These monomers were copolymerized with N,Nâdimethylacrylamide (DMAA) to yield polymerâbased synthetic mimics of antimicrobial peptides (SMAMPs). They were obtained by free radical polymerization, a metalâfree process, and still maintained facial amphiphilicity at the repeat unit level. This eliminates the need for laborious metal removal and is advantageous from a regulatory and product safety perspective. The poly(diitaconateâcoâDMAA) copolymers obtained were statistical to alternating, and the monomer feed ratio roughly matched that of the repeat unit content of the copolymers. Investigations of varied R group hydrophobicity, repeat unit ratio, and molecular mass on antimicrobial activity against Escherichia coli and on compatibility with human keratinocytes showed that the polymers with the longest R groups and lowest DMAA content were the most antimicrobial and hemolytic. This is in agreement with the biological activity of previously reported SMAMPs. Thus, the design concept of facial amphiphilicity has successfully been transferred, but the selectivity of these polymers for bacteria over mammalian cells still needs to be optimized
Nitrogen mineralization and gaseous nitrogen losses from waterlogged and drained organic soils in a black alder (<i>Alnus glutinosa</i> (L.) Gaertn.) forest
Black alder (<i>Alnus glutinosa</i> (L.) Gaertn.) forests on peat soils
have been reported to be hotspots for high nitrous oxide (N<sub>2</sub>O) losses.
High emissions may be attributed to alternating water tables of peatlands and
to the incorporation of high amounts of easily decomposable nitrogen (N) into
the ecosystem by symbiotic dinitrogen (N<sub>2</sub>)-fixation of alder trees. Our
study addressed the question to what extent drainage enhances the emissions
of N<sub>2</sub>O from black alder forests and how N turnover processes and
physical factors influence the production of N<sub>2</sub>O and total
denitrification. The study was conducted in a drained black alder forest with
variable groundwater tables at a southern German fen peatland. Fluxes of
N<sub>2</sub>O were measured using the closed chamber method at two drained sites
(D-1 and D-2) and one undrained site (U). Inorganic N contents and net N
mineralization rates (NNM) were determined. Additionally a laboratory
incubation experiment was carried out to investigate greenhouse gas and
N<sub>2</sub> fluxes at different temperature and soil moisture conditions.
Significantly different inorganic N contents and NNM rates were observed,
which however did not result in significantly different N<sub>2</sub>O fluxes in the
field but did in the laboratory experiment. N<sub>2</sub>O fluxes measured were low
for all sites, with total annual emissions of 0.51 ± 0.07 (U),
0.97 ± 0.13 (D-1) and
0.93 ± 0.08 kg N<sub>2</sub>OâN ha<sup>â1</sup> yr<sup>−1</sup> (D-2). Only 37%
of the spatiotemporal variation in field N<sub>2</sub>O fluxes could be explained
by peat temperature and groundwater level, demonstrating the complex
interlinking of the controlling factors for N<sub>2</sub>O emissions. However,
temperature was one of the key variables of N<sub>2</sub>O fluxes in the incubation
experiment conducted. Increasing soil moisture content was found to enhance
total denitrification losses during the incubation experiment, whereas
N<sub>2</sub>O fluxes remained constant. At the undrained site, permanently high
groundwater level was found to prevent net nitrification, resulting in a
limitation of available nitrate (NO<sub>3</sub><sup>−</sup>) and negligible gaseous N
losses. N<sub>2</sub>O flux rates that were up to four times higher were measured
in the incubation experiment. They reveal the potential of high N<sub>2</sub>O
losses under changing soil physical conditions at the drained alder sites.
The high net nitrification rates observed and high NO<sub>3</sub><sup>−</sup> contents bear
the risk of considerable NO<sub>3</sub><sup>−</sup> leaching at the drained sites
Stimulus-Responsive Polyelectrolyte Surfaces: Switching Surface Properties from Polycationic/Antimicrobial to Polyzwitterionic/Protein-Repellent
Surfaces coated with polyzwitterions are most well-known for their ability to resist protein adsorption. In this article, a surface-attached hydrophobically modified poly(carboxybetaine) is presented. When protonated by changes of the pH of the surrounding medium, this protein-repellent polyzwitterion switches to a polycationic state in which it is antimicrobially active and protein-adhesive. The pH range in which these two states exist are recorded by zeta potential measurements. Adsorption studies at different pH values (monitored by surface plasmon resonance spectroscopy) confirm that the adhesion of protein is pH dependent and reversible, that is, protein can be released upon a pH change from pH 3 to pH 7.4. At physiological pH, the poly(carboxyzwitterion) is antimicrobially active, presumably because it becomes protonated by bacterial metabolites during the antimicrobial activity assay. Stability studies confirm that the here presented material is storage-stable, yet hydrolyses after longer incubation in aqueous media
Poly(oxanorbornene)âBased Polyzwitterions with Systematically Increasing Hydrophobicity : Synthesis, Physical Characterization, and Biological Properties
Surfaces coated with polyzwitterions are known to resist protein adhesion and
to be generally bio-inert. In recent reports, several polyzwitterionic coatings
with carboxylate groups and intrinsic antimicrobial activity due to the
pH-responsivity of that group are described, but the design rules to obtain
such activity remain unclear. Therefore, in this work, a set of surface-attached
polyzwitterions with carboxylate groups and varying alkyl residues is studied.
The gradually increasing hydrophobicity of these surfaces (verified by contact
angle and swellability measurements) has an impact on their biological
properties. Hydrophilic surfaces (polyzwitterions bearing short alkyl residues)
behave like âclassicalâ polyzwitterions: they repel proteins and human cells
and are non-toxic to bacteria. The more hydrophobic polyzwitterionic surfaces
are protein-adhesive, cell-toxic, and can kill bacteria. This indicates that the
hydrophobicity of polyzwitterionic surfaces needs to be balanced precisely to
combine protein-repellency and antimicrobial activity in a single material
3D-Printed Hermetic Alumina Housings
Ceramics are repeatedly investigated as packaging materials because of their gas tightness,
e.g., as hermetic implantable housing. Recent advances also make it possible to print the established
aluminum oxide in a Fused Filament Fabrication process, creating new possibilities for manufacturing
personalized devices with complex shapes. This study was able to achieve integration of channels
with a diameter of 500 m (pre-sintered) with a nozzle size of 250 m (layer thickness 100 m) and
even closed hemispheres were printed without support structures. During sintering, the weightbearing
feedstock shrinks by 16.7%, resulting in a relative material density of 96.6%. The well-known
challenges of the technology such as surface roughness (Ra = 15â20 m) and integrated cavities
remain. However, it could be shown that the hollow structures in bulk do not represent a mechanical
weak point and that the material can be gas-tight (<1012 mbar s1). For verification, a volume-free
helium leak test device was developed and validated. Finally, platinum coatings with high adhesion
examined the functionalization of the ceramic. All the prerequisites for hermetic housings with
integrated metal structures are given, with a new level of complexity of ceramic shapes available
Identifying firing mammalian neurons in networks with high-resolution multi-transistor array (MTA)
Effect of Poly(Oxanorbonene)- and Poly(Methacrylate)-Based Polyzwitterionic Surface Coatings on Cell Adhesion and Gene Expression of Human Keratinocytes
Polyzwitterions are generally known for their anti-adhesive properties,
including resistance to protein and cell adhesion, and overall high
bio-inertness. Yet there are a few polyzwitterions to which mammalian cells
do adhere. To understand the structural features of this behavior, a panel of
polyzwitterions with different functional groups and overall degrees of
hydrophobicity is analyzed here, and their physical and biological properties
are correlated to these structural differences. Cell adhesion is focused on,
which is the basic requirement for cell viability, proliferation, and growth. With
the here presented polyzwitterion panel, three different types of cell-surface
interactions are observed: adhesion, slight attachment, and cell repellency.
Using immunofluorescence methods, it is found that human keratinocytes
(HaCaT) form focal adhesions on the cell-adhesive polyzwitterions, but not on
the sample that has only slight cell attachment. Gene expression analysis
indicates that HaCaT cells cultivated in the presence of a non-adhesive
polyzwitterion have up-regulated inflammatory and apoptosis-related cell
signaling pathways, while the gene expression of HaCaT cells grown on a
cell-adhesive polyzwitterion does not differ from the gene expression of the
growth control, and thus can be defined as fully cell-compatible
SÀchsischer Waldbodenbericht: Aktueller Waldbodenzustand und dessen VerÀnderung
Im Rahmen der zweiten bundesweiten Bodenzustandserhebung (BZE) wurden der aktuelle Zustand und die VerÀnderung von Waldböden, Vegetation, Kronenzustand, Schwermetallen und der WaldernÀhrung an einem systematischen Stichprobenraster untersucht.
Redaktionsschluss: 30.10.201
CO2 fluxes and ecosystem dynamics at five European treeless peatlands â merging data and process oriented modeling
The carbon dioxide (CO2) exchange of five different peatland systems across Europe with a wide gradient in land use intensity, water table depth, soil fertility and climate was simulated with the process oriented CoupModel. The aim of the study was to find out whether CO2 fluxes, measured at different sites, can be explained by common processes and parameters or to what extend a site specific configuration is needed. The model was calibrated to fit measured CO2 fluxes, soil temperature, snow depth and leaf area index (LAI) and resulting differences in model parameters were analyzed. Finding site independent model parameters would mean that differences in the measured fluxes could be explained solely by model input data: water table, meteorological data, management and soil inventory data.
Seasonal variability in the major fluxes was well captured, when a site independent configuration was utilized for most of the parameters. Parameters that differed between sites included the rate of soil organic decomposition, photosynthetic efficiency, and regulation of the mobile carbon (C) pool from senescence to shooting in the next year.
The largest difference between sites was the rate coefficient for heterotrophic respiration. Setting it to a common value would lead to underestimation of mean total respiration by a factor of 2.8 up to an overestimation by a factor of 4. Despite testing a wide range of different responses to soil water and temperature, rate coefficients for heterotrophic respiration were consistently the lowest on formerly drained sites and the highest on the managed sites. Substrate decomposability, pH and vegetation characteristics are possible explanations for the differences in decomposition rates.
Specific parameter values for the timing of plant shooting and senescence, the photosynthesis response to temperature, litter fall and plant respiration rates, leaf morphology and allocation fractions of new assimilates, were not needed, even though the gradient in site latitude ranged from 48° N (southern Germany) to 68° N (northern Finland) differed largely in their vegetation. This was also true for common parameters defining the moisture and temperature response for decomposition, leading to the conclusion that a site specific interpretation of these processes is not necessary. In contrast, the rate of soil organic decomposition, photosynthetic efficiency, and the regulation of the mobile carbon pool need to be estimated from available information on specific soil conditions, vegetation and management of the ecosystems, to be able to describe CO2 fluxes under different condition
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