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.
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.
Complex formation between a natural polysaccharide – gellan and an antimicrobial drug – ofloxacin was studied in aqueous solution. Conductimetric and potentiometric titration curves revealed that ...gellan and ofloxacin forms a water-soluble complex of composition 2:1 mol/mol stabilized by ionic and hydrogen bonds. The formation of the gellan-ofloxacin complex was confirmed by FTIR spectroscopy, dynamic light scattering, zeta-potential and thermogravimetric analysis. The average hydrodynamic size of the complex was found 307±5 nm and its zeta-potential was negative and equal to -15 mV. Thin films of the gellan-ofloxacin complex, gelled in 0.3 wt.% of CaCl2, were used to study the release kinetics of ofloxacin in distilled water and phosphate buffer. The drug release kinetics evaluated by UV-Vis spectroscopy at λmax = 289 nm and calculated by the Ritger-Peppas model correspond to non-Fickian diffusion in distilled water and Case II transport (zero-order kinetics) in phosphate buffer. The cumulative release of ofloxacin from the gellan-ofloxacin films was equal to 96±2% and 36±2% in phosphate buffer and distilled water, respectively. It is expected that the gellan-ofloxacin complex is able to form in situ gel on the surface of the eye and to prolong the drug residence time in the tear fluid.
The three human β-defensins, HBD1–3, are 33–47-residue, cationic antimicrobial proteins expressed by epithelial cells. All three proteins have broad spectrum antimicrobial activity, with HBD3 ...consistently being the most potent. Additionally, HBD3 has significant bactericidal activity against Gram-positive Staphylococcus aureus at physiological salt concentrations. We have compared the multimeric state of the three β-defensins using NMR diffusion spectroscopy, dynamic and static light scattering, and analysis of the migration of the three β-defensins on a native gel. All three techniques are in agreement, suggesting that HBD-3 is a dimer, while HBD-1 and HBD-2 are monomeric. Subsequently, the NMR solution structures of HBD1 and HBD3 were determined using standard homonuclear techniques and compared with the previously determined solution structure of HBD2. Both HBD1 and HBD3 form well defined structures with backbone root mean square deviations of 0.451 and 0.616 Å, respectively. The tertiary structures of all three β-defensins are similar, with a short helical segment preceding a three-stranded antiparallel β-sheet. The surface charge density of each of the defensins is markedly different, with the surface of HBD3 significantly more basic. Analysis of the NMR data and structures led us to suggest that HBD3 forms a symmetrical dimer through strand β2 of the β-sheet. The increased anti-Staphylococcalactivity of HBD3 may be explained by the capacity of the protein to form dimers in solution at low concentrations, an amphipathic dimer structure, and the increased positive surface charge compared with HBD1 and HBD2.
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