Polystyrene-block-poly(1,4-isoprene)-block-poly(dimethyl siloxane)-block-poly(tert-butyl methacrylate)-block-poly(2-vinyl pyridine), PS-b-PI-b-PDMS-b-PtBMA-b-P2VP, self-assembles in acetone into ...polymersomes with asymmetric (directional) PI-b-PDMS membranes. The polymersomes, in turn, self-assemble into superstructures. Analogically to supravesicular structures at a smaller length scale, we refer to them as suprapolymersome structures. Electron tomograms are shown to be invaluable in the structural assessment of such complex self-assemblies.
New main chain azopolymers comprising dibenzo-18-crown-6-ether units joined by azo-bridges have been prepared and fractionated. UV-vis studies show that the polymers are solvatochromic and ...pH-sensitive. Upon irradiation with specific wavelengths they undergo reversible
trans
-to-
cis
photo-isomerisation. Owing to the nature of the crown ether moiety, the polymers can furthermore interact with low molar mass pyridinium guests and Ba
2+
metal ions, resulting in complex-induced phase separation in solvents of lower polarity. In alcohols, the upper critical solution temperature (UCST) type transitions are observed, which are strongly dependent on the polymer concentration and the degree of polymerization. Irradiation of the polymers leads to reversible photo-tuning of the demixing temperature, which decreases proportionally to the decrease in the
trans
content of the sample. The UCST-type transitions in alcohols are also influenced by the water content in the mixtures and addition of barium ions results in an increase of the demixing temperature. Irradiation of the polymer–barium complexes induces the photo-isomerisation but does not change the demixing temperature.
High pressure and rotor/stator homogenisation are widely used techniques in modifying rheologically interesting polysaccharides such as cereal β-glucan for food purposes. However, the influence of ...the homogenisation-induced mechanical stress on β-glucan has not been reported. The influence of three different homogenisers (two high-pressure homogenisers and a rotor/stator homogeniser) was examined in terms of the change in flow and molecular properties of oat β-glucan in semi-dilute and concentrated solutions. A clear and irreversible decrease in viscosity and change in flow behaviour were observed after each homogenisation treatment of the semi-dilute solution. The viscosity had a linear relationship with molar mass in the high-pressure homogenised samples and they both decreased in parallel with the mechanical energy input. With the molar mass decrease, the shape of β-glucan became more spherical and dense. In addition, the molecular weight distribution narrowed and storage-related viscosity stabilized. No considerable differences between the influences of the two high-pressure techniques were observed inconsistently with previous studies. Both molecular and technical characteristics were concluded to affect the fragmentation of β-glucan in high-pressure homogenisation. Since homogenisation enhanced the structural stability of the solution and the fragmentation was dependent on the energy input, the techniques were concluded to be relevant methods for controlled fragmentation of β-glucan.
Confocal scanning laser micrographs of oat β-glucan assemblies in 2 weeks stored aqueous solutions.
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The rheological modeling of a polymer melt in the course of its extrusion through a circular cylindrical channel inside a shaping die equipped with a rotating mandrel and a rotating or stationary ...nozzle is investigated. This paper attempts to provide a detailed rheological description of the physical processes of a polymer melt based on Leonov model inside the channel of an extruder under its kinematic deformation upon two-dimensional shear flow. Based on the obtained rheological equations of state, the flow process can be described in a form of dependencies reflecting kinematics of complex polymer deformation in the die channel. These expressions allow estimation of the velocity distribution for the flow elements within the channel as well as of the flow-pressure characteristics of the process. A quantitative relation between flow characteristics, rheological properties of polymer, and technical parameters of the channel of an extruder was determined. Comparison of this theoretical model with experimental results validates the suggested model.
Two neutral star-shaped polymers with calix8arene core and eight amphiphilic alkyloligoethyleneoxide arms have been synthesised using the arm-first approach. One of them has arms with oligoethylene ...oxide block attached to the calix8arene core, whereas the other one has arms where the oligoethylene oxide is the outer block. Both polymers are soluble in most common organic solvents and form true, i.e., molecularly dispersed solutions. In highly dilute aqueous solutions these polymers form loose multimolecular clusters, which do not disintegrate upon further dilution but break in a shear flow. Aggregation of these star polymers in water is investigated using light scattering and the structure of the aggregates is discussed. The ability of the stars to bind a series of metal ions and the effectiveness of these polymers as phase-transfer agents were investigated in respect to their molecular architecture. The performance of the star-shaped polymers was also compared to that of crown ethers.
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Human β-defensin-2 (HBD-2) is a member of the defensin family of antimicrobial peptides. HBD-2 was first isolated from inflamed skin where it is posited to participate in the killing of invasive ...bacteria and in the recruitment of cells of the adaptive immune response. Static light scattering and two-dimensional proton nuclear magnetic resonance spectroscopy have been used to assess the physical state and structure of HBD-2 in solution. At concentrations of ≤2.4 mM, HBD-2 is monomeric. The structure is amphiphilic with a nonuniform surface distribution of positive charge and contains several key structural elements, including a triple-stranded, antiparallel β-sheet with strands 2 and 3 in a β-hairpin conformation. A β-bulge in the second strand occurs at Gly28, a position conserved in the entire defensin family. In solution, HBD-2 exhibits an α-helical segment near the N-terminus that has not been previously ascribed to solution structures of α-defensins or to the β-defensin BNBD-12. This novel structural element may be a factor contributing to the specific microbicidal or chemokine-like properties of HBD-2.
The article presents a comparison of the traditional methods to investigate the fractional composition of nanosized powders, namely atomic force microscopy (AFM), scanning electron microscopy (SEM), ...dynamic light scatterin, (DLS) and a new one – analysis of the aerosol products of submillimeter pulse laser ablation (SLA). As has previously been proven, biological macromolecules retain activity after ablation under submillimeter wavelengths, molecules become separated in the aerosol phase and each sort of molecules forms its own fraction of the aerosol particles. We suggest that this process is made possible as the result of influence on the hydrogen and van der Waals’ bonds, with the energies within the submillimeter range. Results of investigations on SiO2 and artificial diamond clusters using the above methods in both powder and colloid states are discussed. SLA with subsequent detection of aerosol products with the help of convenient aerosol equipment is found to be simple, fast and informative, and can act as a competitor to mass spectrometry, X-ray scattering and other methods.
The effect of the solvent composition on the conformation of a super high molar mass polyelectrolyte,
M
w=22–25×10
6, dissolved in a water–acetone mixture was investigated using static and dynamic ...light scattering. When increasing the concentration of acetone above 80 mass percent, a reversible conformational change of macromolecules occurs, which causes a sharp decrease in the viscosity, a rise in the light scattering intensity, and also a decrease in the radius of gyration,
R
g, the hydrodynamic radius,
R
h, as well as in the second virial coefficient
A
2. The correlation function measured by dynamic light scattering changes from bimodal to unimodal indicating the formation of compact globular structures.
Polystyrene-
block
-poly(1,4-isoprene)-
block
-poly(dimethyl siloxane)-
block
-poly(
tert
-butyl methacrylate)-
block
-poly(2-vinyl pyridine), PS-
b
-PI-
b
-PDMS-
b
-PtBMA-
b
-P2VP, self-assembles in ...acetone into polymersomes with asymmetric (directional) PI-
b
-PDMS membranes. The polymersomes, in turn, self-assemble into superstructures. Analogically to supravesicular structures at a smaller length scale, we refer to them as suprapolymersome structures. Electron tomograms are shown to be invaluable in the structural assessment of such complex self-assemblies.
Polystyrene-
block
-poly(1,4-isoprene)-
block
-poly(dimethyl siloxane)-
block
-poly(
tert
-butyl methacrylate)-
block
-poly(2-vinyl pyridine), PS-
b
-PI-
b
-PDMS-
b
-PtBMA-
b
-P2VP, self-assembles in acetone into polymersomes with asymmetric (directional) PI-
b
-PDMS membranes.
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