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The properties of polyelectrolyte multilayers are ruled by the process parameters employed during self-assembly. This is the first study in which a design of experiment approach was used to validate and control the production of ultrathin polyelectrolyte multilayer coatings by identifying the ranges of critical process parameters (polyelectrolyte concentration, ionic strength and pH) within which coatings with reproducible properties (thickness, refractive index and hydrophilicity) are created. Mathematical models describing the combined impact of key process parameters on coatings properties were developed demonstrating that only ionic strength and pH affect the coatings thickness, but not polyelectrolyte concentration. While the electrolyte concentration had a linear effect, the pH contribution was described by a quadratic polynomial. A significant contribution of this study is the development of a new approach to estimate the thickness of polyelectrolyte multilayer nanofilms by quantitative rhodamine B staining, which might be useful in all cases when ellipsometry is not feasible due to the shape complexity or small size of the coated substrate. The novel approach proposed here overcomes the limitations of known methods as it offers a low spatial sampling size and the ability to analyse a wide area without restrictions on the chemical composition and shape of the substrate.
Here, we report the continuous peroxide-initiated grafting of vinyltrimethoxysilane (VTMS) onto a standard polyolefin by means of reactive extrusion to produce a functionalized liquid ethylene propylene copolymer (EPM). The effects of the process parameters governing the grafting reaction and their synergistic interactions are identified, quantified and used in a mathematical model of the extrusion process. As process variables the VTMS and peroxide concentrations and the extruder temperature setting were systematically studied for their influence on the grafting and the relative grafting degree using a face-centered central composite design (FCD). The grafting degree was quantified by 1H NMR spectroscopy. Response surface methodology (RSM) was used to calculate the most efficient grafting process in terms of chemical usage and graft yield. With the defined processing window, it was possible to make precise predictions about the grafting degree with at the same time highest possible relative degree of grafting.
The transmembrane Ca2+ − activated Cl− channel - human bestrophin-1 (hBest1) is expressed in retinal pigment epithelium and mutations of BEST1 gene cause ocular degenerative diseases colectivelly referred to as “bestrophinopathies”. A large number of genetical, biochemical, biophysical and molecular biological studies have been performed to understand the relationship between structure and function of the hBest1 protein and its pathophysiological significance. Here, we review the current understanding of hBest1 surface organization, interactions with membrane lipids in model membranes, and its association with microdomains of cellular membranes. These highlights are significant for modulation of channel activity in cells.
High-performance liquid chromatography is one of the most important analytical tools for the identification and separation of substances. The efficiency of this method is largely determined by the stationary phase of the columns. Although monodisperse mesoporous silica microspheres (MPSM) represent a commonly used material as stationary phase their tailored preparation remains challenging. Here we report on the synthesis of four MPSMs via the hard template method. Silica nanoparticles (SNPs) which form the silica network of the final MPSMs were generated in situ from tetraethyl orthosilicate (TEOS) in the presence of (3-aminopropyl) triethoxysilane (APTES) functionalized p(GMA-co-EDMA) as hard template. Methanol, ethanol, 2-propanol, and 1-butanol were applied as solvents to control the size of the SNPs in the hybrid beads (HB). After calcination, MPSMs with different sizes, morphology and pore properties were obtained and characterized by scanning electron microscopy, nitrogen adsorption and desorption measurements, thermogravimetric analysis, solid state NMR and DRIFT IR spectroscopy. Interestingly, the 29Si NMR spectra of the HBs show T and Q group species which suggests that there is no covalent linkage between the SNPs and the template. The MPSMs were functionalized with trimethoxy (octadecyl) silane and used as stationary phases in reversed-phase chromatography to separate a mixture of eleven different amino acids. The separation characteristics of the MPSMs strongly depend on their morphology and pore properties which are controlled by the solvent during the preparation of the MPSMs. Overall, the separation behavior of the best phases is comparable with those of commercially available columns. The phases even achieve faster separation of the amino acids without loss of quality.
The present study investigated the possibilities and limitations of using a low-cost NIR spectrometer for the verification of the presence of the declared active pharmaceutical ingredients (APIs) in tablet formulations, especially for medicine screening studies in low-resource settings. Spectra from 950 to 1650 nm were recorded for 170 pharmaceutical products representing 41 different APIs, API combinations or placebos. Most of the products, including 20 falsified medicines, had been collected in medicine quality studies in African countries. After exploratory principal component analysis, models were built using data-driven soft independent modelling of class analogy (DD-SIMCA), a one-class classifier algorithm, for tablet products of penicillin V, sulfamethoxazole/trimethoprim, ciprofloxacin, furosemide, metronidazole, metformin, hydrochlorothiazide, and doxycycline. Spectra of amoxicillin and amoxicillin/clavulanic acid tablets were combined into a single model. Models were tested using Procrustes cross-validation and by projection of spectra of tablets containing the same or different APIs. Tablets containing no or different APIs could be identified with 100 % specificity in all models. A separation of the spectra of amoxicillin and amoxicillin/clavulanic acid tablets was achieved by partial least squares discriminant analysis. 15 out of 19 external validation products (79 %) representing different brands of the same APIs were correctly identified as members of the target class; three of the four rejected samples showed an API mass percentage of the total tablet weight that was out of the range covered in the respective calibration set. Therefore, in future investigations larger and more representative spectral libraries are required for model building. Falsified medicines containing no API, incorrect APIs, or grossly incorrect amounts of the declared APIs could be readily identified. Variation between different NIR-S-G1 spectroscopic devices led to a loss of accuracy if spectra recorded with different devices were pooled. Therefore, piecewise direct standardization was applied for calibration transfer. The investigated method is a promising tool for medicine screening studies in low-resource settings.
Polyethylene glycol (PEG) is a widely used modification for drug delivery systems. It reduces undesired interaction with biological components, aggregation of complexes and serves as a hydrophilic linker of ligands for targeted drug delivery. However, PEGylation can also lead to undesired changes in physicochemical characteristics of chitosan/siRNA nanoplexes and hamper gene silencing.
To address this conflicting issue, PEG-chitosan copolymers were synthesized with stepwise increasing degrees of PEG substitution (1.5% to 8.0%). Subsequently formed PEG-chitosan/siRNA nanoplexes were characterized physicochemically and biologically. The results showed that small ratios of chitosan PEGylation did not affect nanoplex stability and density. However, higher PEGylation ratios reduced nanoplex size and charge, as well as cell uptake and final siRNA knockdown efficiency.
Therefore, we recommend fine-tuning of PEGylation ratios to generate PEG-chitosan/siRNA delivery systems with maximum bioactivity. The degree of PEGylation for chitosan/siRNA nanoplexes should be kept low in order to maintain optimal nanoplex efficiency.
Hypothesis
The origin of negative surface charge at water/air interface is still not clear. The most probable origin is specific adsorption of OH− ions. From diffuse layer potential, we can evaluate the surface density of ions in the Stern layer which can be a measure for the specific adsorption of ions and determines whether the surface charge is solely due to the specific adsorption of OH− ions.
Experiments
Equilibrium thickness of foam films of pure water and aqueous solutions of NaCl, HCl, and NaOH was measured as a function of disjoining pressure for water and as a function of concentration for the aqueous solutions at 298.15 K. Quartz-glass cells thoroughly cleaned and immersed in pure water before use were used for the measurement.
Findings
Application of a modified Poisson-Boltzmann equation to the equilibrium film thickness gave the diffuse layer potential and the surface density of ions in the Stern layer. From the concentration dependence of the surface density, it was concluded that not only OH− ions but also Cl− ions and HCO3− and/or CO32− ions adsorb specifically at the water/air interface.
The sol-gel approach offers a new class of flame retardants with a high potential for textile applications. Pure inorganic sol-gel systems do, however, typically not provide an effect sufficient for a sel-fextinguishing behavior on its own. We therefore employed compounds with nitrogen and phosphorous containing groups. Especially the combination of compounds with both elements, using the synergism, is promising for the aim to find well-applicable, environmental friendly, halogen-free flame retardants. In our approach, the sol-gel network ensured on the one hand the link to the textile as nonflammable binder. On the other hand, the sol-gel-based networks modified with functional groups containing nitrogen groups provided flame retardancy. In this way, a flame retardant finishing for textiles could be obtained by simple finishing techniques as, e.g., padding. Besides a characterization with various flame tests (e.g., according to EN ISO 15025 e protective clothing), we used a combination of cone calorimetry, thermogravimetry coupled with infrared spectroscopy analysis and scanning electron microscopy to analyze the mechanism of flame retardancy. Thus, we could show that the main mechanism is based on the formation of a protection layer. This work provides a model system for sol-gel-based flame retardants and has the potential to show the principle feasibility of the sol-gel approach in flame retardancy of textiles. It therefore lays the groundwork for tailoring sol-gel layers from newly synthesized sol-gel precursors containing nitrogen and phosphorous groups.
Human bestrophin-1 (hBest1) is a transmembrane Ca2+- dependent anion channel, associated with the transport of Cl−, HCO3- ions, γ-aminobutiric acid (GABA), glutamate (Glu), and regulation of retinal homeostasis. Its mutant forms cause retinal degenerative diseases, defined as Bestrophinopathies. Using both physicochemical - surface pressure/mean molecular area (π/A) isotherms, hysteresis, compressibility moduli of hBest1/sphingomyelin (SM) monolayers, Brewster angle microscopy (BAM) studies, and biological approaches - detergent membrane fractionation, Laurdan (6-dodecanoyl-N,N-dimethyl-2-naphthylamine) and immunofluorescence staining of stably transfected MDCK-hBest1 and MDCK II cells, we report:
1) Ca2+, Glu and GABA interact with binary hBest1/SM monolayers at 35 °C, resulting in changes in hBest1 surface conformation, structure, self-organization and surface dynamics. The process of mixing in hBest1/SM monolayers is spontaneous and the effect of protein on binary films was defined as “fluidizing”, hindering the phase-transition of monolayer from liquid-expanded to intermediate (LE-M) state;
2) in stably transfected MDCK-hBest1 cells, bestrophin-1 was distributed between detergent resistant (DRM) and detergent-soluble membranes (DSM) - up to 30 % and 70 %, respectively; in alive cells, hBest1 was visualized in both liquid-ordered (Lo) and liquid-disordered (Ld) fractions, quantifying protein association up to 35 % and 65 % with Lo and Ld. Our results indicate that the spontaneous miscibility of hBest1 and SM is a prerequisite to diverse protein interactions with membrane domains, different structural conformations and biological functions.
In vitro cultured cells produce a complex extracellular matrix (ECM) that remains intact after decellularization. The biological complexity derived from the variety of distinct ECM molecules makes these matrices ideal candidates for biomaterials. Biomaterials with the ability to guide cell function are a topic of high interest in biomaterial development. However, these matrices lack specific addressable functional groups, which are often required for their use as a biomaterial. Due to the biological complexity of the cell-derived ECM, it is a challenge to incorporate such functional groups without affecting the integrity of the biomolecules within the ECM. The azide-alkyne cycloaddition (click reaction, Huisgen-reaction) is an efficient and specific ligation reaction that is known to be biocompatible when strained alkynes are used to avoid the use of copper (I) as a catalyst. In our work, the ubiquitous modification of a fibroblast cell-derived ECM with azides was achieved through metabolic oligosaccharide engineering by adding the azide-modified monosaccharide Ac4GalNAz (1,3,4,6 tetra-O-acetyl-N-azidoacetylgalactosamine) to the cell culture medium. The resulting azide-modified network remained intact after removing the cells by lysis and the molecular structure of the ECM proteins was unimpaired after a gentle homogenization process. The biological composition was characterized in order to show that the functionalization does not impair the complexity and integrity of the ECM. The azides within this ‘‘clickECM” could be accessed by small molecules (such as an alkyne modified fluorophore) or by surface-bound cyclooctynes to achieve a covalent coating with clickECM.